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Biology Class 11 WBCHSE Plant Growth And Development Some Important Questions And Answers

Question 1. Which plant hormone is known as stress hormone?
Answer: Abscisic acid is known as a stress hormone as it helps the plant tolerate adverse conditions like drought, extreme cold, etc.

Question 2. Which growth control hormone is used for the rapid ripening of fruits?
Answer: Ethylene hormone is used for rapid ripening of fruits.

“plant growth and development questions and answers pdf”

Question 3. What will happen if cytokinin is not used in the culture medium?
Answer: Cytokinin hormone is important for cell division. If cytokinin is not used in the culture medium then cells will not divide properly. As a result, callus formation will be affected.

Question 4. What will happen if GA3 is applied to the seedlings of paddy?
Answer: GA3 increases the length of the internodes which results in better yield of the crops. If GA3 is applied to the paddy seedlings, they will grow in height.

Question 5. What will happen if the differentiation of dividing cells stops?
Answer: The part of the plant where differentiation of dividing cells stops remains a deformed mass of cells and the plant organs like leaves and stems would not form well. This deformed mass of cells is known as a callus.

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Question 6. Write the direction of growth of the vascular bundle.
Answer: Vascular bundles grow along the length of the stem. HIS What is senescence?

Question 7. What is an inflection point?
Answer: The slow deterioration of structural and functional characteristics in a mature plant due to aging is known as senescence.

“important questions on plant growth and development”

Question 8. What is seed dormancy? Mention the types of seed on the basis of seed dormancy.
Answer: The point at which the log phase ends and the lag phase starts during growth is known as an inflection point.

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Question 9. What is seed dormancy? Mention the types of seed on the basis of seed dormancy.
Answer:

Seed dormancy: The failure of an intact, viable seed to complete germination under favorable conditions is known as seed dormancy.

Types of seed on the basis of dormancy:

There are three types of seeds—

1. Macrobiotic,
2. Mesobiotic,
3. Macrobiotic.

Question 10. Which is the primary site of perception of photoperiodic induction?
Answer: Leaves are the primary site of perception of photoperiodic induction. Mature leaves are more sensitive to photoperiodic induction than any young and old leaves.

Question 11. Name a plant growth regulator that is not a phytohormone.
Answer: Polyamine is a plant growth regulator which is not a phytohormone.

Question 12. Which hormone is applied to plants for rapid closure of stomata?
Answer: Abscisic acid is applied to plants for rapid closure of stomata.

Question 13. What will happen if a fully ripe fruit is placed in a basket of unripe fruits?
Answer: The ethylene present in the fully ripe fruit will be released soon and induce early ripening in all the unripe fruits.

Question 14. What is the determining factor for the growth of dicot leaves?
Answer: The determining factor for the growth of dicot leaves is the upper surface area of the leaves.

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Question 15. If an apple merchant wants to wait for the rise of the market price of the apples while increasing the size of the fruits, then which plant growth regulator will he apply?
Answer: He will use gibberellin, as this plant growth regulator helps to increase the size of the fruit and also delay the abscission. Thus he can wait till the rise of market price and he would get an increase in yield as well.

Biology Class 11 WBCHSE

Question 16. Will a leafless plant respond to photoperiodic induction? Explain with reason.
Answer: The leaves of the plant contain a covalently bound chromatophore-containing protein system called phytochrome. Phytochrome perceives the photoperiodic induction. Hence a leafless plant will not show any response to photoperiodic induction.

Question 17. How will you prove that leaves are receptors of photoperiodic induction?
Answer: If a plant with only a leaf is kept under appropriate photoperiodic conditions, then it will bloom. But if a leafless plant is kept under suitable photoperiodic conditions then it will not bloom. This proves that leaves are the site of perception of photoperiodic induction.

Question 18. What do you mean by apical dominance?
Answer: Apical dominance is the condition where the growth of the lateral buds is inhibited by the apical buds. In this case, auxin remains more active and the plant increases in height without profuse branching. Decapitation or the removal of the apical bud can deactivate the power of auxin. Thus lateral buds resume their growth to produce branches.

Question 19. What is the sigmoid growth curve?
Answer: The sigmoid growth curve is an ‘S’-shaped curve representing the average growth of all organisms, where young ones experience an initial slow growth followed by rapid accelerating growth. This is followed by continuous steady growth and as organisms reach maturity, the growth rate slows down and finally comes to a stop.

“MCQ on plant growth and development with answers”

Question 20. What is parthenocarpy?
Answer: Parthenocarpy refers to the production of fruits without fertilization. This process produces seedless fruits. Auxins are used to produce such fruits.

Biology Class 11 WBCHSE Plant Growth And Development Very Short Answer Type Questions

Question 1. What does the stationary phase of the sigmoid curve indicate?
Answer: The maturation phase or slow growth rate is indicated by the steady phase or stationary phase in a sigmoid growth curve.

Question 2. Name the growth regulator which was isolated from the endosperm of maize.
Answer: Zeatin—a cytokinin was isolated from corn kernel by Letham et al (1963).

Question 3. What is vernalisation?
Answer: Vernalisation is the promotion of flowering by treating the plant at low temperatures (1°C-2°C) in its primary growth phase.

Question 4. What would happen if soaked, light-sensitive lettuce seeds were exposed to far-red light followed by red light?
Answer: When soaked lettuce seeds are exposed to far-red light followed by exposure to red light, then the seeds will germinate. This phenomenon is known as photomorphogenesis.

Question 5. Name any two synthetic auxins used in agriculture.
Answer: 2,4-dichlorophenoxyacetic acid (2,4-D) and ff-naphthylacetic acid or 1 naphthaleneacetic acid (NAA).

“previous year questions on plant growth and development”

Question 6. What induces parthenocarpy in grapes?
Answer: Gibberellin induces parthenocarpy in grapes

Question 7. What can induce bolting in cabbage plants?
Answer: Boltingin cabbage is triggered mainly by gibberellin. Also, bolting can occur as a result of other factors such as cold spells or changes in day length (long day).

Question 8. What are quiescent seeds?
Answer: The seeds which fail to germinate due to unfavorable, external environmental conditions are called quiescent seeds.

Question 9. Name the hormone that makes the plant more tolerant to various stresses.
Answer: Abscisic acid (ABA) makes the plant tolerant to various stresses.

Question 10. Name the plant hormone that inhibits the growth of plants.
Answer: Abscisic acid (ABA) inhibits the growth of plants.

Question 11. What are the full forms of IAA, NAA, and IBA?
Answer: IAA—Indoleacetic acid, NAA—Naphthaleneacetic acid, IBA—Indole-3-butyric acid.

Question 12. What does an overripe apple release, that affects other apples in the basket?
Answer: An overripe apple releases ethylene—a gaseous hormone, that affects other applesin the basket.

Question 13. What is the growth curve?
Answer: A growth curve is constructed by plotting the increase in cell number versus time of incubation and can be used to delineate stages of the growth cycle.

Question 14. What would develop first, shoot bud or the root, from the callus of tobacco pith, grown in a sterile minimal nutrient medium, when cytokinin added is more than auxins?
Answer: Shoot bud will develop.

Question 15. Define growth regulators.
Answer: A plant growth regulator is an organic compound, either natural or synthetic, that modifies or controls one or more specific physiological processes within a plant to accelerate or inhibit growth in plants.

Question 16. Which part of the plant perceives light for flowering?
Answer: the mature leaf perceives the light stimulus for flowering. It is the organ for the perception of light.

Question 17. Name the phytohormone that stimulates the production of the enzymes that mobilize nutrients in the cotyledon in some germinating seeds.
Answer: Gibberellic acid.

Question 18. A farmer grows cucumber plants in his field. He wants to increase the number of female flowers in them. Which plant growth regulatory hormone (PGR) can be used to achieve this?
Answer: Auxin can Increase the number of female flowers in a cucumber plant. It is responsible for changes in sex expression.

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Question 19. In botanical gardens and tea gardens, gardeners trim the plants regularly so that they remain bushy. Does this practice have any scientific explanation?
Answer: Yes. This practice can be related to a phenomenon called apical dominance. The apical buds suppress the growth of lateral buds and prevent branch formation. If it is removed by trimming, the lateral buds start to grow to give the plant a bushy look.

Question 20. A gardener finds some broad-leaf dicot weeds growing in his lawns. What can be done to get rid of the weeds efficiently?
Answer: If the synthetic auxin 2, 4-D (2,4-dichloro phenoxy acetic acid) is sprayed over the lawns, in a particular concentration, the broad leaf dicot weeds will die, leaving the grasses alive. This is due to the selective herbicidal action of the synthetic auxin 2, 4-D.

Question 21. Name a plant hormone that can delay senescence.
Answer: Cytokinin is the plant hormone that delays senescence.

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Question 22. Which plant hormone is called anti-aging hormone?
Answer: Cytokinin is known as an anti-aging hormone as it delays senescence.

Question 23. What is meant by apparent growth?
Answer: Apparent growth is an increase in the size, volume, and weight of the plants, which can be observed from outside.

Question 24. What is real growth?
Answer: Real growth is the formation of new cytoplasm and the accumulation of other cellular materials in the cell.

“long answer questions on plant growth and development”

Question 25. Which plant hormone is known as anti-auxin?
Answer: Abscisic acid

Question 26. While eating watermelons, all of us wish—it was seedless. As a plant physiologist can you suggest any method by which this can be achieved?
Answer: Watermelon plants can be treated with artificial auxin which will induce parthenocarpic fruit production. These fruits will be seedless.

Plant Growth And Development Multiple Choice Questions

Question 1. Fruit and leaf drop at early stages can be prevented by the application of

1. Ethylene
2. Auxins
3. Gibberellic acid
4. Cytokinins

Answer: 2. Auxins

Question 2. Asymptote in a logistic growth curve is obtained when—

1. K = N
2. K> N
3. K< N
4. The value of ‘r’ approaches zero

Answer: 1. K = N

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Question 3. The Avena curvature is used for bioassay of—

1. GA₃
2. IAA
3. Ethylene
4. ABA

Answer: 2. IAA

“plant growth and development MCQ with answers”

Question 4. You are given a tissue with its potential for differentiation in an artificial culture. Which of the following pairs of hormones would you add to the medium to secure shoots as well as roots?

1. IAA and gibberellin
2. Auxin and cytokinin
3. Auxin and abscisic acid
4. Gibberellin and abscisic acid

Answer: 2. Auxin and cytokinin

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Question 5. Phytochrome is a—

1. Flavoprotein
2. Rotein
3. Lipoprotein
4. Chromoprotein

Answer: 4. Chromoprotein

Question 6. Auxin can be bioassayed by—

1. Lettuce hypocotyl elongation
2. Avena coleoptile curvature
3. Hydroponics
4. Potometer

Answer: 2. Avena coleoptile curvature

“multiple choice questions on plant growth and development”

Question 7. Which one of the following fruits is parthenocarpic?

1. Banana
2. Brinjal
3. Apple
4. Jackfruit

Answer: 1. Banana

Question 8. Dr. F. Went noted that if coleoptile tips were removed and placed on agar for one hour, the agar would produce a bending when placed on one side of freshly cut coleoptile stumps. Of what significance is this experiment?

1. It made possible the isolation and exact identification of auxin
2. It is the basis for the quantitative determination of small amounts of growth-promoting substances
3. It supports the hypothesis that IAA is auxin
4. It demonstrated the polar movement of auxins

Answer: 4. It demonstrated the polar movement of auxins

Question 9. Which one of the following growth regulators is known as the ‘stress hormone’?

1. Abscisic acid
2. Ethylene
3. GA₃
4. Indole acetic acid

Answer: 1. Abscisic acid

Question 10. Match the following columns

1. 1-2, 2-4, 3-3, 4-1
2. 1-3, 2-1, 3-4, 4-2
3. 1-1, 2-2, 3-4, 4-3
4. 1-2, 2-4, 3-1, 4-3

Answer: 2. 1-3, 2-1, 3-4, 4-2

Question 11. Which one of the following is a growth regulator produced by plants?

1. Naphthalene acetic acid
2. Zeatin
3. 2, 4-dichloro phenoxy acetic acid
4. Benzyl aminopurine

Answer: 2. Zeatin

“plant growth and development quiz with answers”

Question 12. Which of the following plant growth hormones increases the yields of sugar by increasing the length of the stem in sugarcane?

1. Cytokinin
2. Auxin
3. Abscisic acid
4. Ethylene
5. Gibberellic acid

Answer: 5. Gibberellic acid

Question 13. One hormone hastens the maturity period in juvenile conifers, a second hormone controls xylem differentiation while, the third increases the tolerance of plants to various stresses and they are respectively—

1. Auxin, gibberellin, and cytokinin
2. Gibberellin, auxin, and cytokinin
3. Gibberellin, auxin, and ethylene
4. Gibberellin, auxin, and ABA
5. Auxin, gibberellin, and ABA

Answer: 4. Auxin, gibberellin, and ABA

Question 14. Which of the following is not an effect of ethylene?

1. Promotes senescence and abscission of plant organs
2. Breaks seed and bud dormancy
3. Brings about horizontal growth of seedlings
4. Hastens fruit ripening
5. Helps to overcome apical dominance

Answer: 5. Helps to overcome apical dominance

“MCQ on plant growth and development for NEET”

Question 15. Auxin was first isolated from—

1. Fungus
2. Apple
3. Sperm DNA
4. Human urine

Answer: 4. Human urine

Question 16. Apical dominance in plants means—

1. Growth of lateral buds
2. Inhibition of the growth of lateral buds
3. Both A and B
4. None of the above

Answer: 2. Inhibition of the growth of lateral buds

Question 17. Vernalization is dependent on exposure to—

1. Low temperature
2. High temperature
3. Both A and BNOA
4. None of these

Answer: 1. Low temperature

Question 18. In flowering plants, the site of perception of light/dark duration is—

1. Stem
2. Leaves
3. Shoot apex
4. Floral meristem

Answer: 2. Leaves

Question 19. Study the following columns

1. 1-3, 2-1, 3-5, 4-2
2. 1-2, 2-5, 3-4, 4-3
3. 1-2, 2-1, 3-5, 4-4
4. 1-4, 2-3, 3-2, 4-1

Answer: 2. 1-2, 2-5, 3-4, 4-3

“important MCQs on plant growth and development”

Question 20. Senescence in plants leads to cells.

1. Increase in number
2. Increase in size
3. Death
4. Differentiation

Answer: 3. Death

“objective questions on plant growth and development”

Question 21. If a plant produces flowers when exposed only to alternating periods of 5 hours of light and 3 hours of dark in a 24-hour cycle, then the plant should be.

1. Short-Question day plant
2. Long-day plant
3. Short-long day plant
4. Day-neutral plant

Answer: 2. Long-day plant

Question 22. Hormone replacing the requirement of vernalization is

1. Ethylene
2. Gibberellins
3. Auxin
4. Cytokinin

Answer: 3. Auxin

Question 23. Monocarpic plants are those in which—

1. Flowering and fruiting occur only once
2. Flowering and fruiting occur regularly
3. Produce fruits with a single-seed
4. Fruits are produced without fertilization

Answer: 1. Flowering and fruiting occur only once

“plant growth and development class 11 MCQ”

Question 24. During seed germination, its stored food is mobilized

1. Ethylene
2. Cytokinin
3. ABA
4. Gibberellin

Answer: 4. Gibberellin

Class 11 Biology WBCHSE Respiration In Plants Some Important Questions And Answers

Question 1. Name the main three events that occur during glycolysis.
Answer:

The main three events of glycolysis are—

1. Oxidation of glucose and synthesis of pyruvate.
2. Reduction of NAD and formation of NADH+H⁺
3. Formation of ATP from ADP by substrate-level phosphorylation.

Question 2. Respiration is known as an exothermic process. Why?
Answer: During respiration respiratory substrates are oxidized to convert static energy into kinetic energy. Some percentage of this energy is stored in highly energized ATP compounds as chemical energy. The rest of the kinetic energy is converted into heat energy. Because of this release of heat energy and so, respiration is known as an exothermic process.

“respiration in plants questions and answers for class 11”

Question 3. Why is glucose considered as the ‘starting point of respiration’?
Answer: The substances, oxidised in the cytoplasm during respiration are known as respiratory substrates. Among all the substances, glucose is used as the primary respiratory substrate. Hence, glucose is considered the ‘starting point of respiration’.

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Question 4. What is the pentose phosphate pathway?
Answer: The pentose phosphate pathway is an alternative pathway of glycolysis or EMP pathway. NADPH+H⁺ is produced by this pathway. This pathway also takes part in the synthesis of fats and nucleic acids.

“important questions on respiration in plants with answers”

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Question 5. What happens to the reactions of the TCA cycle in the absence of oxygen?
Answer: In the electron transport chain, NADH+H⁺ and FADH₂ are oxidized in the presence of oxygen to form NAD and FAD respectively. The FAD and NAD are again used in the TCA cycle in the presence of oxygen. These two compounds keep the TCA cycle running. So, reactions of the TCA cycle stop in the absence of oxygen.

Question 6. What is the fate of products, produced during glycolysis?
Answer: Pyruvic acid is produced during glycolysis. Pyruvic acid follows any of the following three processes to produce more energy.

The processes are—

1. lactic acid fermentation,
2. Ethyl alcohol fermentation,
3. Krebs cycle. The fate of pyruvic acid depends on the availability of free oxygen.

Question 7. Name the enzymes present in the mitochondrial matrix.
Answer:

The following enzymes are present in the mitochondrial matrix—

1. Citric acid synthetase
2. Isocitrate dehydrogenase
3. A-ketoglutarate dehydrogenase
4. Fumarate
5. Malate dehydrogenase.

“respiration in plants NEET questions and answers PDF”

Question 8. Name the enzymes present in the inner mitochondrial membrane, which take part in cellular respiration.
Answer:

The enzymes present in the inner mitochondrial membrane that take part in cellular respiration are—

1. Cytochrome C reductase,
2. NADH dehydrogenase,
3. Succinate dehydrogenase,
4. Glycerol 3-phosphate dehydrogenase and
5. ATP synthase.

Question 9. Name the inhibitors of the Krebs cycle.
Answer:

Some compounds that act as inhibitors of the Krebs cycle are—

1. Fluoroacetate which inhibits the action of aconitase enzyme;
2. Arsenite which inhibits dehydrogenase;
3. Malonate inhibits the action of succinate dehydrogenase.

“short answer questions on respiration in plants”

Question 10. Why is aerobic respiration more important than anaerobic respiration?
Answer: 686 kcal energy is released by oxidation of 1 molecule of glucose during aerobic respiration whereas, only 28-40 kcal energy is released during anaerobic respiration. Again, during aerobic respiration, CO₂ and water are released as byproducts.

But during anaerobic respiration, ethyl alcohol is produced in plants, and lactic acid is produced in animals, as a byproduct. These products are harmful to the respective organisms. Hence, aerobic respiration is more important than anaerobic respiration.

Question 11. How does gaseous exchange occur in plants, though they do not have any special respiratory organs?
Answer: In plants, gaseous exchange occurs throughout the body surface. The amount of gaseous exchange is low in plants as compared to animals. Gaseous exchange also occurs in plants through some special openings like stomata and lenticels. The gaseous exchange takes place in different parts of the plants by diffusion, through intercellular space present between the matured parenchyma cells.

Question 12. Why is carbon dioxide not produced during glycolysis?
Answer: Carbon dioxide is not produced during glycolysis because decarboxylation of carbohydrates does not occur in the process of glycolysis.

Question 13. What is oxidative decarboxylation?
Answer: The process where pyruvic acid is transported to the mitochondrial matrix from the inner mitochondrial membrane by a specific transport protein and is oxidized to produce carbon dioxide is known as oxidative decarboxylation.

Question 14. What is the Crabtree effect?
Answer: The oxygen consumption is suppressed by a high concentration of glucose in the living cells. This phenomenon is known as the Crabtree effect.

“MCQs on respiration in plants with answers”

Class 11 Biology WBCHSE Respiration In Plants VeryShort Answer Type Questions

Question 1. Name the site of oxidative phosphorylation.
Answer: Oxysomes are the sites of oxidative phosphorylation.

Question 2. Why is fructose 6-phosphate known as fructose monophosphate?
Answer: As it contains a single phosphate group at carbon 6, it is known as fructose monophosphate.

Question 3. What is the alternate name for fructose bisphosphate?
Answer: Fructose 1,6-bisphosphate or fructose 2,6-bisphosphate.

Question 4. How many highly energized phosphates are present in 1 molecule of ATP?
Answer: There are 2 highly energized phosphates in ATP— phosphate and y phosphate.

Question 5. Write down the elementary difference between 3-phosphoglycerate and 2-phosphoglycerate.
Answer: In 3-PGA, the phosphate group remains at carbon number 3, while in 2-PGA the same is enzymatically shifted to carbon 2 of the molecule.

Question 6. What is the unit of oxidative photophosphorylation?
Answer: The unit of oxidative phosphorylation is kJ/mol.

Question 7. How many ATP molecules are synthesized during the glycolysis phase of anaerobic respiration?
Answer: 2 ATP molecules are formed in anaerobic glycolysis.

Question 8. What is the site for terminal respiration?
Answer: In prokaryotes, it occurs in the cell membrane, and in eukaryotes, it occurs in the cristae of the inner mitochondrial membrane

“previous year respiration in plants questions and answers”

Question 9. Name the special structures present on leaves that are responsible for gaseous exchange in plants.
Answer: Stomata are special structures present in the leaf epidermis and are responsible for gaseous exchange

Question 10. AnsweGive the location of enzymes involved in the Krebs cycle.
Answer: All the enzymes participate actively in the Krebs cycle, except succinate dehydrogenase, which remains dissolved in the mitochondrial matrix. It is one of the components of Complex II of ETS present on the inner mitochondrial membrane

Question 11. Mention the location of coenzymes of ETS in mitochondria.
Answer: The coenzymes remain dissolved in the mitochondrial matrix.

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Question 12. What is the other name for TCA Cycle?
Answer: The other name of TCA cycle is the Citric Acid Cycle or Krebs cycle.

Question 13. What is the full form of ETS? Where does it occur?
Answer: ETS stands for electron transport system. It occurs in the inner mitochondrial membrane.

Question 14. What are respiratory substrates?
Answer: The organic substances that are catabolized or broken down enzymatically in cellular respiration to release energy are known as respiratory substrates.

Question 15. How many highly energized phosphate compounds (ATP) can be obtained from one molecule of glucose?
Answer: 38 highly energized phosphate compounds (ATP) are obtained from 1 molecule of glucose.

Question 16. What are the raw materials for cellular respiration?
Answer: The energy fuels for cellular respiration are carbohydrates (usually glucose). Lipids and proteins may also be used as substrates for respiration under certain conditions.

Question 17. What is the function of ATP?
Answer: It provides energy for the cellular activities. So, it is often referred to as energy currency.

Question 18. How many molecules of ATP are net gained in Krebs cycle and glycolysis?
Answer: 12 ATP in the Krebs cycle and 2 ATP in glycolysis.

Question 19. What is zymosis?
Answer: The process of anaerobic respiration in yeast is known as zymosis.

Question 20. Which phase connects glycolysis and the TCA cycle?
Answer: The oxidative decarboxylation of pyruvate to acetyl CoA in the mitochondrial matrix is the connecting step of glycolysis and the TCA cycle.

Question 21. Name the stage of respiration that releases 1 molecule of H₂O as one of the respiratory products.
Answer: During terminal respiration, one molecule of H₂O is one of the respiratory products.

Question 22. Which compound acts as energy currency in plants and animals?
Answer: ATP functions as an energy currency in plants and animals.

“difference between aerobic and anaerobic respiration questions”

Question 23. What is synthesized by the F₀-F₁ complex?
Answer: They constitute the ATP synthase enzyme and synthesize ATP if a proton gradient is available across the mitochondrial membrane.

Question 24. Name the main compound produced during glycolysis in skeletal muscles and fermentation in yeast.
Answer: Lactate (lactic acid) is formed in skeletal muscle during glycolysis and ethanol (ethyl alcohol) is formed during fermentation in yeast.

Question 25. How many grams of glucose is oxidized during aerobic respiration?
Answer: 180 gm of glucose are oxidized during aerobic respiration.

Question 26. What is RQ?
Answer: RQ or respiratory quotient is the ratio of the volume of carbon dioxide liberated in respiration with the volume of oxygen consumed by a respiring tissue (or organism) for the same time period.

Question 27. Which type of respiration has an infinite RQ value?
Answer: In the fermentation process, the RQ value of glucose is infinity (oo) .

Question 28. Mention the significance of RQ.
Answer: The chemical nature of the respiratory substrate can be determined by knowing the RQ value.

Question 29. What is terminal oxidation?
Answer: Terminal oxidation is the final step in aerobic respiration which involves the oxidation of protons (H+) released by the coenzymes during oxidative phosphorylation, by the final acceptor of protons, i.e., oxygen, which also accepts electrons coming from ETS 4H⁺ + O₂ + 4e^– —> 2H₂O

Question 30. Name one compound produced during the anabolic phase of the Krebs cycle.
Answer: Cis-aconitate.

Question 31. Who observed the similarities between respiration and combustion?
Answer: Lavoisier observed the similarities between respiration and combustion

Question 32. Which plant shows zero RQ value?
Answer: During the night, the respiratory CO₂ is utilized to synthesize organic acid by CAM plants (such as Bryophyllum). O₂ consumption, therefore, takes place without concomitant CO₂ evolution and the RQ value becomes zero.

Question 33. Name the first complex of the electron transport chain or ETC.
Answer: The name of the first complex of the electron transport chain is NADH dehydrogenase.

“Krebs cycle and glycolysis questions with answers

Question 34. In which process does zymase act as an essential enzyme?
Answer: In the fermentation of sugar into ethanol and carbon dioxide, zymase acts as an essential enzyme.

Question 35. Name the two main compounds produced in heterotactic fermentation.
Answer: In heterotactic fermentation ethanol and lactic acid are produced.

Question 36. What type of substrates have an RQ of 1?
Answer: Carbohydrates are the respiratory substrate having an RQ of 1.

Question 37. Where does anaerobic respiration occur in the human body?
Answer: Anaerobic respiration occurs in skeletal muscle cells of the human body when they lack sufficient oxygen supply.

Question 38. Which phase of glycolysis directly produces water?
Answer: Dehydration of 2-phosphoglycerate to phosphoenolpyruvate catalyzed by enolase, directly produces water molecules.

“respiration in plants long answer questions for board exams”

Question 39. Mention the step of the citric acid cycle, which is not mediated by dehydrogenase enzyme.
Answer: Conversion of oxaloacetic acid to citric acid is not mediated by dehydrogenase enzyme.

Question 40. What is oxidative phosphorylation?
Answer: The process of ATP formation, as a result of the transportation of electrons from NADH or FADH₂ to O₂ through a series of electron carriers is known as oxidative phosphorylation.

Respiration In Plants Multiple Choice Questions

Question 1. Which statement is wrong for the Krebs cycle?

1. There is one point in the cycle where FAD+ is reduced to FADH₂
2. During the conversion of succinyl CoA to succinic acid, a molecule of GTP is synthesized
3. The cycle starts with the condensation of the acetyl group (acetyl CoA) with pyruvic acid to yield citric acid
4. There are three points in the cycle where NAD+ is reduced to NADH + H⁺

Answer: 4. There are three points in the cycle where NAD+ is reduced to NADH + H⁺

Question 2. Oxidative phosphorylation is

1. Formation of ATP by transfer of phosphate group from a substrate to ADP
2. Oxidation of phosphate group in ATP
3. Addition of phosphate group to ATP
4. Formation of ATP by energy released from electrons removed during substrate oxidation

Answer: 1. Formation of ATP by transfer of phosphate group from a substrate to ADP

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Question 3. Which of the following biomolecules is common to the respiration-mediated breakdown of fats carbohydrates and proteins?

1. Glucose 6-phosphate
2. Fructose 1,6-bisphosphate
3. Pyruvic acid
4. Acetyl CoA

Answer: 4. Acetyl CoA

“respiration in plants MCQ with answers”

Question 4. In which one of the following processes CO₂ is not released?

1. Aerobic respiration in plants
2. Aerobic respiration in animals
3. Alcoholic fermentation
4. Lactate fermentation

Answer: 4. Lactate fermentation

Question 5. There are three major ways in which different cells handle pyruvic acid produced by glycolysis. These are–

1. Lactic acid fermentation, alcoholic fermentation, aerobic respiration
2. Oxaloacetic acid fermentation, lactic acid
   fermentation, aerobic respiration
3. Alcoholic fermentation, oxaloacetic acid fermentation, citric acid fermentation
4. Citric Acid fermentation, lactic acid fermentation, alcoholic fermentation

Answer: 1. Lactic acid fermentation, alcoholic fermentation, aerobic respiration

“multiple choice questions on respiration in plants for NEET”

Question 6. The Respiratory Quotient (RQ) of glucose is—

1. 0.5
2. 0.7
3. 1.0
4. 1.5

Answer: 3. 1.0

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Class 11 Biology MCQs	Class 11 Physics MCQs
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Question 7. How much ATP is produced when 1 molecule of FADH₂ is oxidized to FAD through an electron transport system?

1. 2
2. 3
3. 1
4. 4

Answer: 1. 2

Question 8. Out of 38 molecules of ATP produced upon aerobic respiration of glucose, the break up of ATP production in glycolysis (P), pyruvate to acetyl CoA formation (Q), and Krebs cycle (R) is as follows

1. P=1,Q=6, R= 30
2. P=8,Q=6, R= 24
3. P=8,Q=10, R= 20
4. P=2,Q=12, R=24

Answer: 4. P=2,Q=12, R=24

“respiration in plants quiz with answers”

Question 9. How many NAD molecules get reduced in complete oxidation of one glucose molecule?

1. 2
2. 5
3. 10
4. 12

Answer: 1. 2

Question 10. Acetylation of pyruvate takes place in the—

1. Perimitochondrial space
2. Mitochondrial matrix
3. Cristae
4. F particles

Answer: 2. Mitochondrial matrix

Question 11. Enzyme enolase catalyzes the conversion of 2PGA to phosphoenol pyruvic acid in the presence of which is the cofactor.

1. Mn²⁺
2. Fe²⁺
3. Mg²⁺
4. Zn²⁺

Answer: 3. Mg²⁺

“important MCQs on respiration in plants with explanations”

Question 12. When the respiratory quotient is less than 1.0 in respiratory metabolism, it means that—

1. Carbohydrates are Used As Respiratory Substrate
2. The volume of carbon dioxide evolved is less than the volume of oxygen consumed
3. The volume of carbon dioxide evolved is more than the volume of oxygen consumed
4. The volume of carbon dioxide evolved is equal to the volume of oxygen consumed

Answer: 4. Volume of carbon dioxide evolved is equal to the volume of oxygen consumed

respiration in plants

Question 13. A small protein attached to the outer surface of the inner membrane and which acts as a mobile carrier for the transfer of electrons between complex 3 and 4 is

1. Cytochrome-D
2. Cytochrome-B
3. Cytochrome-C
4. Cytochrome-A

Answer: 2. Cytochrome-B

Question 14. During glycolysis, fructose 1,6-bisphosphate is split into

1. Dihydroxyacetone phosphate and 2-phosphoglyceraldehyde
2. Dihydroxyacetone phosphate and1-phosphoglyceraldehyde
3. Dihydroxyacetone phosphate and 2-phosphoglycerate
4. Dihydroxyacetone phosphate and 3-phosphoglyceraldehyde

Answer: 4. Dihydroxyacetone phosphate and 3-phosphoglyceraldehyde

“respiration in plants class 11 MCQ PDF download”

Question 15. Assertion (A): The RQ value of fats is less than one. Reason (R): The amount of CO₂ released is less than the O₂ consumed when fats are used in respiration

1. Both A and R are correct and R is the correct explanation of A.
2. Both A and R are correct and R is not the correct explanation of A.
3. A is correct R is incorrect
4. A is incorrect R is correct

Answer: 1. Both A and R are correct and R is the correct explanation of A.

“net gain of atp in krebs cycle “

Question 16. In which of the following steps of the citric acid cycle CO₂ is evolved?

1. Citric acid→or-ketoglutarate
2. Succinic acid →Malic acid
3. Malic acid →Oxaloacetic acid
4. α-ketoglutaric acid → Succinyl CoA

Choose the correct answer

1. 1 and 2
2. 2 and 3
3. 3 and 4
4. 1 and 4
5. 2 and 4

Answer: 2. 2 and 3

Question 17. Match the organic compounds listed under column I with the explanations given under column II. Choose the appropriate option from the given choices.

1. 1-3, 2 – 4, 3-5, 4-1
2. 1-2, 2 —3, 3 — 4,4— 5
3. 1 — 5, 2-4,3-3, 4-2
4. 1—5,2-1, 3-2,4-3

Answer: 3. 1 — 5, 2-4,3-3, 4-2

“objective questions on respiration in plants for competitive exams”

Question 18. Oxidative decarboxylation of pyruvic acid results in the formation of

1. Acetyl CoA
2. CO₂
3. Atp
4. NADH+H⁺

Choose the correct answer

1. Only 1
2. 1 and 2
3. 1,2 and 3
4. 1,2, and 4
5. 3 and 4

Answer: 5. 3 and 4

Question 19. Select the correct order of reactions in glycolysis—

1. Conversion of 3-phosphoglyceraldehyde to 1,3-bisphosphoglycerate.
2. Conversion of 3-phosphoglyceric acid to 2-phosphoglycerate.
3. Conversion of 1,3-BPGA to 3-phosphoglyceric acid.
4. Splitting of fructose 1,6-bisphosphate into dihydroxy acetone phosphate and 3-phosphoglyceraldehyde.

Choose the correct answer

1. 4,3,1 and 2
2. 2, 3, 1 and 4
3. 4, 2, 1 and 3
4. 1, 4, 3 and 2
5. 4, 1, 3 and 2

Answer: 5. 4, 1, 3 and 2

Question 20. Oxygen content reduction makes the glycolysis (glycogenesis) intensity increase due to

1. Increase of ADP concentration in cell
2. Increase of NAD+ concentration in cell
3. Increase of ATP concentration in cell
4. Increase in concentration of peroxides and free radicals

Answer: 1. Increase of ADP concentration in cell

Question 21. The process by which ATP is produced in the inner membrane of a mitochondrion. The electron transport system transfers protons from the inner compartment to the outer as the protons flow back to the inner compartment; the energy of their movement is used to add phosphate to ADP, forming ATP.

1. Chemiosmosis
2. Phosphorylation
3. Glycolysis
4. Fermentation

Answer: 1. Chemiosmosis

“glycolysis, Krebs cycle, and ETC MCQs with answers”

Question 22. Biological oxidation in the Krebs cycle involves—

1. O₂
2. CO₂
3. O₃
4. NO₂

Answer: 1. O₂

Question 23. In which of the following reactions of glycolysis, oxidation takes place?

1. Glucose 6-phosphate to fructose 6-phosphate
2. Glyceraldehyde 3-phosphate to 1,3-diphosphoglycerate
3. 1,3-diphosphoglycerate to 3-phosphoglycerate
4. 2-diphosphoglycerate to phosphoglycerate

Answer: 2. Glyceraldehyde 3-phosphate to 1,3-diphosphoglycerate

Question 24. The three boxes in this diagram represent the three major biosynthetic pathways in aerobic respiration. Arrows represent net reactants or products.
Answer:

Arrows numbered 4, 8, and 12 can all be—

1. NADH
2. ATP
3. H₂O
4. FAD⁺ or FADH₂

Answer: 2. ATP

“previous year respiration in plants MCQs for NEET and board exams”

Question 25. Which of the metabolites is common to respiration-mediated carbohydrates and proteins?

1. Glucose 6-phosphate
2. Fructose 1,6-bisphosphate
3. Pyruvic acid
4. Acetyl CoA

Answer: 4. Acetyl CoA

Question 26. Which one of the following reactions is an example of oxidative decarboxylation?

1. Conversion of succinate to fumarate
2. Conversion of fumarate to malate
3. Conversion of pyruvate to acetyl CoA
4. Conversion of citrate to isocitrate

Answer: 3. Conversion of pyruvate to acetyl CoA

Crassulacean Acid Metabolism

Crassulacean Acid Metabolism

This metabolic pathway was first discovered in plants of the family Crassulaceae.

Crassulacean Acid Metabolism Definition: The metabolic pathway by which mainly the members of the family Crassulaceae assimilate carbon while preventing water loss by evaporation is called Crassulacean add metabolism (CAM)

The pathway is also common in Cactaceae, Euphorbiaceae, Rhizoaceae, Liliaceae, Bromeliaceae, Orchidaceae, etc., families. The plants which show CAM pathways are called CAM plants. E.g., A few economically important plants, including pineapple, Bryophyllum sp, Sedum sp., etc., are CAM plants.

Characteristics of CAM plants:

1. These plants are generally found in dry and desert regions.
2. In these plants, stomata remain open at night and closed during the day. These are called photoactive stomata.
3. These plants have low compensation points.
4. Decarboxylation of malate during the day yields CO₂ inside the photosynthetic tissues. This CO₂ is fixed normally by RuBisCO in C₃ cycle. This permits CO₂ assimilation without letting in CO₂ inside the cell directly from the air.
5. Transpiration and photorespiration are greatly reduced in CAM plants.

Pathway of CAM

Cam Plants Stomata

The CAM pathway, consisting of dark acidification and light deacidification reactions, is divided into the following phases

Phase-1 (Dark acidification): The main aim of this phase is to produce malic acid in the dark. As the stomata remain open at night, CO₂ diffuses in. This CO₂ requires temporary storage as an intermediate carbon compound. CAM pathway requires the breakdown of starch in the dark to produce phosphoenol pyruvate (PEP) through glycolysis. PEP is the substrate for carboxylation by PEP-carboxylase. The product generated is oxaloacetic acid (OAA).

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Class 11 Biology	Class 11 Physics Notes

⇒ \(\text { PEP } \underset{\text { dehydrogenase }}{\stackrel{\text { Malate }}{\longrightarrow}} \mathrm{OAA}+\mathrm{Pi}\)

During this period, PEP-carboxylase is active and fixation of C02 takes place irrespective of the presence or absence of oxygen. OAA is then reduced to malate by NAD-dependent malate dehydrogenase.

⇒ \(\text { OAA } \underset{\text { dehydrogenase }}{\stackrel{\text { Malate }}{\longrightarrow}} \text { Malate + NADP }{ }^{+}\)

Malate accumulates as malic acid in the vacuole towards the end of the dark period, when the rate of CO₂ fixation declines. This is due to the inhibition of PEP-case by accumulated malate and a decrease in the cytosolic pH.

Phase-2 (Light de-acidification): The intensity of light is high during the day. Malic acid gets released from the vacuoles as malate. Malate gets converted to pyruvate by malate decarboxylase. Decarboxylation of malate occurs with a low rate of CO₂ fixation. CO₂ enters C₃ cycle during the synthesis of PGA.

Pyruvate resulting from malate decarboxylation is converted to PEP by pyruvate orthophosphate dikinase, present in the chloroplast.

Crassulacean acid metabolism (CAM) notes PDF

⇒ \(\text { Malate }+\mathrm{NADP}^{+} \stackrel{\text { Malic enzyme }}{\rightleftharpoons} \text { Pyruvate }+\mathrm{CO}_2+\mathrm{NADPH}+\mathrm{H}^{+}\)

CO₂ produced by any of the decarboxylation reactions gets fixed by RuBisCO through C₃ cycle. The pyruvate or PEP resulting from malate decarboxylation may be oxidised to C02 by the mitochondrial TCA cycle. This CO₂ will get fixed by C₃ cycle.

Significance of CAM:

CAM is an adaptation to an extremely xerophytic environment. Even under conditions of severe water stress, carbon dioxide uptake continues in CAM plants.

CAM plants can eliminate the loss of CO₂ as they can retain and fix the released CO₂

Chemosynthesis

1. Some bacteria do not use light energy to carry out the synthesis of food.
2. Instead, they oxidise biochemical compounds to release energy that is utilised during food synthesis. This energy, along with CO₂, is used to produce food for the plants. This process by which food is synthesised, using the energy released by oxidation of chemical compounds is known as chemosynthesis. Different types of bacteria, that carry out chemosynthesis, are known as chemosynthetic bacteria.
3. Iron bacteria like Leptothrix spv Ferrobacillus sp., etc., oxidise ferrous salts to ferric salts. The energy released in the process is used up for chemosynthesis.
4. On the other hand, sulphur bacteria like Thiothrix sp., etc., oxidise HZS to S and the energy released is used for chemosynthesis.
5. Similarly, nitrifying bacteria like Nitrosomonas sp. convert ammonia to nitrate, while Nitrobacter sp. converts nitrites to nitrates, to carry out chemosynthesis.

Factors Affecting Photosynthesis

The external and internal factors that affect photosynthesis are discussed under the following heads.

The external factors influencing photosynthesis are—

Light: Both quality and intensity of light influence the rate of photosynthesis.

intensity:

1. The rate of photosynthesis is directly proportional to the rate of photosynthesis.
2. However, very high intensity of light oxidises chlorophylls (photooxidation of chlorophyll) which photosynthesis. This phenomenon is called solarisation.
3. The amount of light intensity at which the rate of respiration is equal to that of photosynthesis is called the light compensation point.

Quality:

1. A wavelength of light between 400 nm and 700 nm is most effective for photosynthesis. This light is called photosynthetically active radiation (PAR).
2. Comparatively more photosynthesis occurs in red and blue regions of PAR though others show significant photosynthesis.

Co₂ concentration:

1. It is found that if the atmospheric CO₂ concentration (0.03-0.04%) increases by 0.01%, the rate of photosynthesis increases significantly.
2. This is achieved in the greenhouses under controlled conditions.
3. If the CO₂ concentration increases further, the rate of photosynthesis decreases. The following graph shows how different CO₂ concentrations affect the rate of photosynthesis.

Water: A deficiency of water causes the stomata to close, thereby reducing the C02 availability. Besides, water deficit stress also causes wilting of leaves, thus reducing the surface area of the leaves and their metabolic activity as well.

CAM pathway in plants: steps and significance notes

Temperature: The optimum temperature for photosynthesis is generally 20-30°C. Generally, the rate of photosynthesis increases with the rise in temperature. This effect is seen within the temperature range of 6 to 37 c by this, the rate of photosynthesis decreases and ceases at 43c photosynthesis of different plants also depends on their habitat. Some bacteria can carry out photosynthesis at 70°C while some at -35 °C.

The following graph shows changes in the rate of photosynthesis with temperature.

Temperature coefficient or Q₁₀

Scientist Vant Hoff postulated this law. According to this law, the rate of a biochemical reaction doubles with every 10°C rise, within a specific temperature range (0-30°C). It is known as the temperature coefficient. This coefficient may be written in the following way, in the case of photosynthesis—

⇒ \(\mathrm{Q}_{10}=\frac{\text { Rate of photosynthesis at } \mathrm{T}^{\circ} \mathrm{C}+10^{\circ} \mathrm{C}}{\text { Rate of photosynthesis at } \mathrm{T}^{\circ} \mathrm{C}}\)

In this case, T°C is a specific temperature.

Oxygen concentration: Increased O₂ concen¬ traction is known to inhibit the activity of the photosynthesis enzymes. The rate of photosynthesis declines when atmospheric oxygen concentration rises above its normal value i.e. 21%. This effect is known as the Warburg effect. However, some plants do not show this effect.

Presence of chemical substances: Chemical substances like gaseous and metallic pollutants decrease the rate of photosynthesis. For example, ozone, sulphur dioxide, fluorides, hydrogen sulphide, chloroform, etc., have an inhibitory effect on photosynthesis.

Low Limiting Factor

Blackman’s law of limiting factor is a modification of Leibig’s law of minimum. It states that if a biochemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value. This factor is called the limiting factor. A limiting factor is a factor, whose change may directly affect the process.

Difference between C3, C4, and CAM pathways

For example, despite optimal light and CO₂ conditions, a green leaf may not photosynthesise, if the temperature is very low. This leaf, if given the optimal temperature, will carry on the process of photosynthesis.

Cam Plant

The theory of three cardinal points, which is related to the law of limiting factors, was given by Sachs in 1860. According to this concept, there is minimum, optimum and maximum value for each factor.

For every factor, there is a minimum value when no photosynthesis occurs, an optimum value showing the highest rate of photosynthesis and a maximum value, above which photosynthesis fails to take place. The law can be explained best by an illustration.

1. Light intensity provided to a leaf is sufficient to allow it to utilise a fixed concentration of CO₂. Initially, at level A, no photosynthesis occurs due to non-availability of CO₂.
2. If the concentration of CO₂ is increased further, the rate of photosynthesis will increase up to a maximum value (from level A to level D).
3. If the CO₂ concentration is further increased, the rate of photosynthesis will remain constant. Further increase in the rate of photosynthesis beyond level D is possible only when light intensity is increased, which at this point, is working as a limiting factor.

The factor which is quantitatively the least, may not be the limiting one. Instead, the factor which is relatively less than the amount actually required will act as the limiting factor. This law may also be named as ‘Law of relatively limiting factor’ or ‘Law of most significant factor’.

Internal Factors

The internal factors regulating photosynthesis are as follows—

Chlorophyll concentration: The concentration of chlorophyll affects the rate of reaction as it is the pigment that absorbs the light energy. Chlorophyll deficiency results in chlorosis. It can occur due to disease, mineral deficiency or the natural process of ageing (senescence). Lack of iron, magnesium, nitrogen and light affects the formation of chlorophyll and thereby causes chlorosis.

Internal structure of the leaves: The efficiency of mesophyll tissues, stomata, guard cells, etc., determines the rate of photosynthesis. Any change in the diameter of the stomata influences the rate of photosynthesis.

Accumulation of photosynthetic products: Accumulation of photosynthetic products, such as starch, within the mesophyll tissues, decreases the rate of photosynthesis. Hence, the products of photosynthesis need to be removed from the leaves, regularly.

NEET biology CAM pathway notes with important points

Ageing of the leaves: As the leaves begin ageing, the number of chloroplasts within the mesophyll tissues also decreases. This, in turn, decreases the rate of photosynthesis.

Enzymes: Photosynthesis is an enzyme-catalysed process. Hence, the presence and activity of enzymes affect the rate of photosynthesis.

Hormones: Auxins, gibberelins, cytokinin, etc., increase the rate of photosynthesis. Abscisic acid, on the other hand, decreases the rate of photosynthesis.

Relation Between Photosynthesis And Respiration

During the process of respiration, food is oxidised and energy is released in the utilisable form which remains stored as ATP. Using this ATP, all the cellular activities are performed. CO₂ and water are also released during respiration. The overall equation is—

⇒ \(\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{O}_2 \stackrel{\text { Aerobic cell }}{\longrightarrow} 6 \mathrm{CO}_2+6 \mathrm{H}_2 \mathrm{O}+673 \mathrm{kcal}\)

The equation for respiration is the reverse of that of photosynthesis. In photosynthesis, CO₂ is consumed from the atmosphere, while in respiration CO₂ is released.

Crassulacean Acid

These two processes exist in precise balance in nature. By these opposing processes, the concentration of carbon dioxide in the atmosphere is maintained at a nearly constant amount (0.03%). Approximately sixteen billion tonnes of carbon is processed in this way every year.

Note:

Carbon scavenging: Process by which the element carbon (C) is used up or removed.

Chanosis: Loss of green colouration of leaves in a plant.

Chromatic adaptation: Modification of photosynthetic apparatus according to different wavelengths of incident light, resulting in absorption of energy.

Facultative: Capable of switching to any other pathway other than its usual if the need arises.

Feedback control: Process by which the concentration of the product generated during a reaction controls the above-mentioned reaction.

Mechanism of CAM photosynthesis with diagram

Free energy: Energy available in a system that can be converted to work.

Proton pump: An integral membrane protein that allows protons to pass across a cell membrane.

Spectrophotometer: An instrument used to measure the absorption spectrum of different pigments with respect to different wavelengths of light.

Stratosphere: The second layer of the atmosphere.

Photorespiration Or C₂-Cycle

Photorespiration is the light-dependent oxidation of intermediates of carbon assimilation which is accompanied by absorption of O₂ and release of CO₂. It was discovered by Dicker and Tio (1959) in a tobacco plant. The. the term ‘photorespiration’ was coined by scientist Gleb Krotkov.

Definition: The oxidation process in plants, that takes place in bright light and high O₂ concentration, producing 2C compound (phosphoglycolic acid) and CO₂ is called photorespiration.

Site of occurrence: This cycle takes place in chloroplasts, peroxisomes and mitochondria.

It is also called the glycolate cycle or C₂ because, the 2C compound, glycolate, is produced as the first intermediate product of this metabolic pathway.

“photorespiration process and significance notes for class 11”

Mechanism Of Photorespiration

Photorespiration involves the initial fixation of O₂ followed by further O₂ uptakes and CO₂ evolution.

Reactions occurring in chloroplast (first step)

Reactions of photorespiration in chloroplast take place in two steps.

RuBP cleavage, synthesis of phosphoglycolate and its oxidation: The C₂ cycle starts in chloroplasts with phosphoglycolate produced from RuBP due to the oxygenase action of RuBisCO. It converts RuBP to 3-phosphoglycerate and 2-phosphoglycolate.

⇒ \(\text { RuBP }+\mathrm{O}_2 \stackrel{\text { RuBisCO }}{\longrightarrow} \text { 3-PGA + 2-Phosphoglycolate }\)

Conversion of phosphoglycolate to glycolate: 3-phosphoglycerate enters the Calvin cycle. On the other hand, 2-phosphoglycolate undergoes dephosphorylation by phosphoglycolate phosphatase enzyme to form glycolate. This glycolate leaves the chloroplast and enters the peroxisome.

⇒ \(\text { 2-Phosphoglycolate }+\mathrm{H}_2 \mathrm{O} \stackrel{\begin{array}{c} \text { Phosphoglycolate } \\ \text { phosphatase } \end{array}}{\longrightarrow} \text { Glycolate }+\mathrm{Pi}\)

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Reactions occurring in peroxisome (second step)

Reactions of photorespiration in peroxisome takes place in three steps. Those steps are discussed below along with their chemical reactions.

Conversion of glycolate to glyoxylate: Glycolate enters peroxisome where it is oxidised to glyoxylate and H202 by enzyme glycolate oxidase and sunlight.

Hydrolysis of H₂O₂: The other product of glycolate oxidation is H₂O₂ which is decomposed to H₂O and O₂. This reaction is catalyzed by the enzyme catalase present in the peroxisome.

⇒ \(\begin{aligned} & \text { Glycolate }+\mathrm{O}_2 \underset{\substack{\text { Glycolate } \\ \text { reductase }}}{\stackrel{\text { Glycolate }}{\rightleftharpoons}} \text { Glyoxylate }+\mathrm{H}_2 \mathrm{O}_2 \\ & 2 \mathrm{H}_2 \mathrm{O}_2 \stackrel{\text { Catalase }}{\longrightarrow} \mathrm{O}_2+\mathrm{H}_2 \mathrm{O} \\ & \end{aligned}\)

It is possible that some of the glyoxylates may return to the chloroplast. There it may get reduced back to glycolate at the expense of photogenerated NADPH by glyoxylate reductase enzyme. Such shuttle reactions, involving glycolate-glyoxylate, are used to dissipate the light-generated reducing power. This is useful in protecting the photosystems when CO₂ supply is limited. Photorespiration is observed in C₃ plants which photosynthetically fix CO₂ exclusively via the Calvin cycle in the mesophyll cells.

Synthesis of glycine: Glyoxylate reacts with glutamate in the presence of glutamate-glyoxylate aminotransferase enzyme to produce glycine (amino acid) and a-ketoglutarate.

⇒ \(\text { Glyoxylate + Glutamate } \stackrel{\begin{array}{c} \text { Glutamate } \\ \text { glyoxylate } \\ \text { aminotransferase } \end{array}}{\longrightarrow} \alpha \text {-Ketoglutarate }\)

Reactions occurring in mitochondria

Glycine enters the mitochondrion from the peroxisome and the cycle moves further.

Synthesis of serine, NH3 and CO₂: The glycine then moves to mitochondrion. Two molecules of glycine are converted to one molecule each of serine, CO₂ and NH₃ in a two-step reaction. The reaction requires NAD⁺ as an oxidant and the resultant NADH is reoxidised by the mitochondrial electron transport chain with the generation of ATP. These reactions are catalysed by glycine decarboxylase and serine hydroxymethyl transferase respectively.

“detailed notes on photorespiration and its importance”

Reactions occurring in peroxisome (last step)

Serine moves back to peroxisome and gets converted to glycerate.

Conversion of serine to hydroxy pyruvate: After being synthesised in mitochondria, serine moves to peroxisome. Here it reacts with or-ketoglutarate to produce glutamate and hydroxypyruvate. This is catalysed by the enzyme glyoxylate aminotransferase.

Reduction of hydroxypyruvate and synthesis of glycerate: Hydroxypyruvate then undergoes reduction to produce glycerate. This reaction is catalysed by the enzyme hydroxy pyruvate reductase.

Reactions occurring in chloroplast

The last step involved moving glycerate into the chloroplast.

Phosphorylation of glycerate: The glycerate then moves into the chloroplast where it is phosphorylated to form 3-phosphoglycerate. This reaction is catalysed by the enzyme glycerate kinase.

“photorespiration pathway “

3-phosphoglycerate now enters the C₃ cycle where it is used for RuBP synthesis. Thus, the photorespiration or C₂ cycle is completed.

Effect of O₂ on photorespiration

When the concentration of O₂ is higher, RuBP carboxylase causes RuBP to bind to O₂ instead of CO₂. This leads to the production of phosphoglycolate, which reduces the rate of carbon assimilation during photosynthesis. The concentration of O₂ in the environment is about 21%, which is maintained by photosynthesis.

“step-by-step process of photorespiration in plants”

But this O₂ content becomes harmful for the C₃ plants, as more and more RuBP will bind O₂, with no RuBP left for binding CO₂. This reduces photosynthesis further. No such carboxylase has been discovered yet, that does not have any affinity to O₂.

Significance Of Photorespiration

1. Photorespiration regenerates CO₂ and PGA which are ultimately used up in the Calvin cycle.
2. It produces amino acids and carbohydrates and maintains CO₂ balance in nature.
3. Photorespiration serves to protect the photochemical apparatus from damage caused by light. This takes place through neutralisation of harmful effects of otherwise damaging products of light reaction. These products tend to accumulate when a low CO₂ concentration limits the progress of the Calvin cycle.
4. Since no ATP is produced in photorespiration, it is not considered true respiration. Instead, ATP is used up during this process along with NADH⁺H⁺.

“significance of photorespiration “

C₃ And C₄ Cycle And Pathway

According to the number of carbon atoms in the intermediate product, the pathway of the Calvin cycle may be of three types—C₃, C₄ and CAM.

C₃ Cycle or Pathway

Definition: The biochemical pathway, within the dark phase, during which carbon is assimilated and phosphoglyceric acid (3C) is produced as the first stable product is called C₃ pathway or Calvin cycle.

Site of occurrence: Stroma of the chloroplast.

Characteristics of C₃ plants:

1. The plants which show the C₃ cycle are called C₃ plants. In most of the plants, it takes place using the RuBisCO enzyme.
2. The first stable compound obtained is the 3-carbon compound phosphoglyceric acid (PGA).
3. RuBP binds CO₂ in the atmosphere and thereby maintains the balance of O₂-CO₂ within the environment.
4. All the compounds produced within the C₃ cycle can be re-synthesised.
5. During hot and dry summers, the stomata of C₃ plants remain closed. Hence, CO₂ cannot enter the plants. So, the C₃ cycle slows down and glucose production is inhibited temporarily. example Paddy, wheat, soybean, etc.

C₄ Cycle Or Pathway

Definition: The pathway of photosynthesis in which carbon assimilation takes place and oxaloacetic acid (4C) is produced as the first stable product is called the C₄ pathway.

Site of occurrence: Cells (mainly chloroplasts) in mesophyll tissue and bundle sheath.

Types of chloroplast involved in the C₄ cycle: Chloroplasts are of two types—

• Mesophyll chloroplast (MC): Chloroplast present in the mesophyll cells.
• Bundle sheath chloroplast (BSC): Chloroplast present in the bundle sheath cells.

Characteristics of C₄ plants:

• The plants which show C₄ cycle are called C₄ plants. Most of the C₄ species are monocots, especially grasses, although more than 300 are dicots.
• They are generally found in tropical and subtropical regions.
• They have more bundle sheath cells.

“difference between photosynthesis and photorespiration notes”

• Only spongy parenchyma is present in mesophyll cells.
• The initial products of C₂ fixations are the 4-carbon dicarboxylic acids—oxalate, malate and aspartate. Hence the pathway is known as C₄ pathway. The first stable compound formed in this pathway is a 4-carbon compound, oxaloacetic acid (OAA).
• The rate of transpiration is more than C₃ plants.

“photorespiration in C3 and C4 plants explained”

• Their ability to photosynthesise is high, as compared to C₃ plants.
• Generally, photorespiration is absent in these plants.
• Photosynthesis continues even in bright sunlight, water stress and high temperature.
• The presence of a prominent layer of bundle sheath cells containing chloroplasts, around the vascular tissue of the leaf, is the feature of C₄ plants. This feature is called Kranz anatomy.
• The stroma in the chloroplasts within bundle sheath cells is more organised than the grana.
• The stroma of chloroplast in mesophyll cells is less organised than the grana. Moreover, there are differences in the ultrastructures of chloroplasts between mesophyll cells and bundle sheath cells. example Sugarcane, maize, jowar, bajra, etc.

“photorespiration diagram “

C₄ plants and photorespiration

C₄ cycle effectively pumps CO₂ from the atmosphere into the bundle sheath cells. This transport process generates a much higher concentration of CO₂ in the bundle sheath cells than would occur in equilibrium with the external atmosphere. This elevated concentration of CO₂ at the site of carboxylation of RuBP, results in suppression of the oxygenation of RuBP. Hence, photorespiration is prevented.

Description of C₄ Cycle: C₄ cycle consists of four stages—

1. Fixation of CO₂ by the carboxylation of phosphoenolpyruvate (PEP) in the mesophyll cells to form 4-carbon acid.
2. Transport of the 4C acid to the bundle sheath cells.
3. Decarboxylation of the 4C acid within the bundle sheath cells and generation of CO₂, which is then reduced to carbohydrates via the Calvin cycle.
4. Transport of the 3C acid (pyruvate or alanine). that is formed by the decarboxylation, back to the mesophyll cells for regeneration of CO₂ acceptor, PEP.

Reactions in mesophyll cells

1. Carbon dioxide present in the air enters the mesophyll cells and reacts with water to form carbonic acid. This reaction is catalysed by the enzyme carbonic anhydrase.

⇒ \(\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \stackrel{\text { Carbonic anhydrase }}{\longrightarrow} \mathrm{H}^{+}+\mathrm{HCO}_3^{-}\)

“biochemical pathway of photorespiration with diagram”

The primary carboxylation of the C₄ cycle is done by phosphoenol pyruvate carboxylase (PEP carboxylase) using HCO_3^– as the substrate to yield oxaloacetate (OAA). PEP carboxylase is found in the cytosol of mesophyll cells. It is activated by Mg2+ and inhibited by malate and aspartate feedback control. OAA (4C) is the first stable compound formed in C₄ cycle.

“photorespiration definition “

⇒ \(\text { PEP } \underset{\text { dehydrogenase }}{\stackrel{\text { Malate }}{\longrightarrow}} \mathrm{OAA}+\mathrm{Pi}\)

OAA formed now enters the mesophyll cells. It is reduced to malate in the chloroplast at the expense of NADPH by the enzyme malate dehydrogenase. In the case of some C₄ plants, aspartate is generated from OAA.

⇒ \(\text { OAA } \underset{\text { dehydrogenase }}{\stackrel{\text { Malate }}{\longrightarrow} \text { Malate + NADP }}{ }^{+}\)

Malate so formed is then exported to the bundle sheath cell chloroplast.

Reactions in bundle sheath cells

1. CO₂ removal and decarboxylation:

1. Malate dehydrogenase present in bundle sheath cells, acts upon malate to produce pyruvate and release CO₂.
2. Pyruvate so formed is transported to mesophyll cells,
3. The released CO₂ reacts with RuBP to form PGA, which enters the C₃ cycle. This is catalysed by the enzyme RuBP carboxylase. Instead of malate, if aspartate is generated, it is catalysed by PEP carboxykinase.

⇒ \(Malic acid +\mathrm{NADPH}+\mathrm{H}^{+} \underset{\text { dehydrogenase }}{\longrightarrow} Pyruvic acid + NADP\)

⇒ \(\begin{aligned} & \text { Aspartate }+\alpha \text {-ketoglutaric acid } \frac{\text { Iransaminase }}{\text { OAA }+ \text { Glutamic acid }} \\ & \mathrm{OAA}+\mathrm{ATP} \stackrel{\text { Carboxykinase }}{\longrightarrow} \mathrm{PEP}+\mathrm{CO}_2+\mathrm{ADP} \\ & \text { PEP } \stackrel{\begin{array}{c} \text { Pyruvate } \\ \text { kinase } \end{array}}{\longrightarrow} \text { Pyruvate } \stackrel{\begin{array}{c} \text { Alanine } \\ \text { transferase } \end{array}}{\longrightarrow} \text { Alanine } \\ & \end{aligned}\)

“photorespiration and its role in plant metabolism”

Types of C₄ plants

There are three subgroups according to the different mechanisms by which decarboxylation takes place in bundle sheath cells.

1. NADP*-malic enzyme (NAD⁺-ME) type: In this type, malic acid is formed from oxaloacetic acid in the presence of NADPH⁺H⁺. This is catalysed by the enzyme malate dehydrogenase. Malate is then transported to bundle sheath cells from the mesophyll cell. Since NADP-dependent malate dehydrogenase is the main enzyme involved, hence the name NADP⁺-ME type.
2. PEP-carboxykinase (PEP-CK or PCK) type: In this type, OAA is directly decarboxylated by the enzyme PEP-carboxykinase in bundle sheath cell chloroplast. This provides for assimilation through a cycle. The formed PEP is converted by pyruvate kinase to pyruvate, which is then converted to alanine by alanine aminotransferase. This alanine is returned to the mesophyll cell. Since PEP-carboxykinase is the main enzyme involved, hence the name PEP-carboxykinase type.
3. NAD+-malic enzyme (NAD⁺+-ME) type: In this type, transfer of aspartate and return of alanine takes place. In this case, malate is directly decarboxylated to form by NAD-dependent malic enzyme, hence the name NAD⁺+-ME-type. Pyruvate moving from mitochondria is then converted to alanine in cytoplasm by alanine aminotransferase.

Re-formation of PEP: The pyruvate sent to the chloroplast of mesophyll cells, is converted to PEP at the expense of ATP by a unique enzyme named pyruvate orthophosphate dikinase. Alanine that enters the mesophyll cells also gets converted to PEP.

This is the final step of the C₄ cycle.

Significance of C₄ cycle:

• The rate of photosynthesis is higher than C₃ plants. Hence, they can produce more glucose than C₃ plants.
• C₄ plants are partially adapted to drought conditions, where a high rate of CO₂ fixation is maintained even with almost closed stomata. Hence, they can grow and produce more seeds than C₃ plants.
• The C4 photosynthesis is more efficient at high temperatures. Such high-temperature tolerance of C₄ plants is due to the stability of some enzymes like PEP-carboxylase.
• Oxygen has no inhibitory effect on C₄ photosynthesis because PEPcase is insensitive to oxygen and photorespiration is absent.

“significance and disadvantages of photorespiration notes”

• C₄ plants have low CO₂ compensation points. They can rapidly take up CO₂ even at reduced C02 levels, with almost closed stomata and thus they can conserve water.
• The C₄ pathway is commonly found in tropical plants, which are normally exposed to abundant sunlight. This pathway supports a higher rate of photosynthesis and growth in these plants.
• Photorespiration is not observed in C₄ plants.
• An adequate amount of nitrogen assimilation enzymes and an efficient capacity to use nitrogen for biomass production are additional features associated with C₄ pathway.

Photophosphorylation

Cyclic And Noncyclic Photophosphorylation

Photophosphorylation Definition: The synthesis of ATP from ADP and Pi using the energy of light is called photophosphorylation.

It can be of two types

1. Cyclic and
2. Non-cyclic photophosphorylation.

Cyclic Photophosphorylation:

The photophosphorylation process which occurs along with cyclic electron transport is known as cyclic photophosphorylation.

Cyclic Photophosphorylation

Photophosphorylation Process:

1. Only PS 1 or P is involved in the process.
2. Chlorophyll dimers of the reaction centre absorb light rays of wavelength more than 680 nm.
3. After absorbing light in the form of a photon, an electron is released, leading to the oxidation of the reaction centre.
4. The reaction centre becomes positively charged and the electron released now forms ferredoxin reducing substance (FRS).
5. The electron is carried by the electron carriers like quinone (Q), plastoquinone (PQ), FeS protein and finally ferredoxin (Fd). Now the electron, from Fd, returns to P700, via Cyt b6f and plastocyanin.
6. The electron creates a proton gradient which leads to the formation of 2 ATP molecules from 2ADP and Pi.
7. Due to the absence of photolysis of water, O₂ and NADPH are not produced.

Cyclic and non-cyclic photophosphorylation notes PDF

Limitations of cyclic photophosphorylation

1. It is an incomplete mechanism, that occurs only when non-cyclic photophosphorylation is prevented.
2. It is active only within PS I.
3. As the non-cyclic photophosphorylation stops, carbon assimilation no longer takes place. This reduces the rate of photosynthesis.
4. O₂ is not produced, hence NADPH is also not formed.

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Non-cyclic photophosphorylation: The photophosphorylation process which occurs along with non-cyclic electron transport is known as non-cyclic photophosphorylation.

Non-cyclic photophosphorylation Process:

1. Photosystem 1, photosystem 2 and cytochrome b6f complex are involved in the transport of protons and electrons.
2. PS 2 absorbs light of 680 nm wavelength (in the red part of the spectrum) and its reaction centre, P₆₈₀, gets excited. It releases a pair of electrons and becomes P_680⁺. This reaction centre can, later on, absorb electrons released by the splitting of water.
3. The electrons released by P₆₈₀ are accepted by the primary electron acceptor Pheo,
4. The electrons are transferred from Pheo to PCT. Simultaneously, PQ- also accepts 2H⁺ from stroma to form PQH₂.
5. PQH2 is oxidised and the two protons are released into the lumen and form semireduced plastosemiquinone (PQH). One electron is given to cytochrome f, in cyt b6f complex, via a Fe-S protein.
6. PQH is now further oxidised to form PQ. This electron is now transferred to cytochrome b6, in cyt b6f complex.
7. The electron of cytochrome f is transferred to a Cu-containing electron carrier, plastocyanin (PC).
8. This electron is now transferred to PS 1.
9. Simultaneously, PS 1 absorbs light having a wavelength of 700 nm (in the far-red part of the spectrum) and its reaction centre P₇₀₀ gets excited. It expels the electrons, which are accepted by a Fe-S protein. P₇₀₀ becomes P₇₀₀⁺.
10. These electrons are accepted by ferredoxin (Fd), which is also a Fe-S protein.
11. P₇₀₀+ pair in PS 1 accepts two electrons from reduced plastocyanin and becomes P₇₀₀–
12. By the catalytic activity of Fd-NADP oxidoreductase, electrons are transferred to NADP⁺, forming NADPH⁺ H⁺, thereby completing non-cyclic electron transport.
13. A continuous supply of water is essential for this process. O₂ is released by this process.

Experiments by different scientists to prove— ‘Water releases O₂ during photosynthesis’

In 1931, Van Niel demonstrated that H2S is required for stabilising CO₂ in photosynthetically active bacteria. In these bacteria, sulphur is formed instead of O₂.

⇒ \(6 \mathrm{CO}_2+12 \mathrm{H}_2 \mathrm{~S} \longrightarrow \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+12 \mathrm{~S}+6 \mathrm{H}_2 \mathrm{O}\)

In 1937, Robert Hill observed that isolated chloroplasts can evolve oxygen in the absence of CO₂. His finding was one of the first indications that the source of the electrons in the light reactions was in fact water. In his experiment, he used an artificial electron acceptor.

Difference between cyclic and non-cyclic photophosphorylation

The artificial electron acceptor intercepts the electrons before they cascade down to P₇₀₀ (the reaction centre of PS 1), but after they have gone down the electron transport chain. Thus, the Hill reaction is formally defined as the photo-reduction of an electron acceptor by the electrons of water, with the evolution of oxygen. Various dyes can be used as artificial electron acceptors (A). The general equation, known as the Hill Reaction can be written as follows—

Non-Cyclic Photophosphorylation

⇒ \(2 \mathrm{~A}+2 \mathrm{H}_2 \mathrm{O} \underset{\text { chlorophyll }}{\stackrel{\text { sunlight }}{\longrightarrow}} 2 \mathrm{AH}_2+\mathrm{O}_2\)

In vivo, or in the organism, the final electron acceptor is NADP⁺. However, during the experiment, a dye is used as an artificial electron acceptor. It changes colour as it is reduced. DCIP (2,6-dichlorophenolindophenol) is a dye which is blue in its oxidized form and colourless in its reduced form. It is called the Hill Reagent.

In 1941, Samuel Ruben and Martin Kamen used radioactive oxygen (O¹⁸)-containing water, to prove that O₂ is released from H20 (H₂O¹⁸)

⇒ \(12 \mathrm{H}_2 \mathrm{O}^{18}+6 \mathrm{CO}_2 \underset{\text { chlorophyll }}{\stackrel{\text { sunlight }}{\longrightarrow}} \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{O}_2^{18}+6 \mathrm{H}_2 \mathrm{O}\)

Later, in 1952, Arnon and Emerson proved that the hydrogen acceptor in photosynthesis is NADP⁺. So, NADP+ is the natural Hill reagent.

The growth of weeds can be reduced by blocking photophosphorylation

Herbicides such as chlorophenyl dimethyl urea (DCMU) and chlorophenyl dimethyl urea (CMU) can prevent electron transport during non-cyclic photophosphorylation. As a result, on the application of these chemicals, the light-independent phase is blocked, and no more glucose is synthesised by photosynthesis. This reduces the growth of the weeds.

Significance of photophosphorylation

Liberation of oxygen: Splitting of water releases oxygen, during photophosphorylation.

ATP production: Cyclic photophosphorylation produces 2 molecules of ATP, while non-cyclic photophosphorylation produces 1 molecule of ATP.

Reduction of NADP: Non-cyclic photophosphorylation reduces NADP⁺ to NADPH and H⁺.

Cyclic Electron Transport Chain

 

The chemiosmotic hypothesis of synthesis of ATP

The chemiosmotic mechanism of ATP formation was first proposed by Peter Mitchell (1966). He received the Nobel Prize in 1978 for proposing the above hypothesis. According to this theory, a proton concentration gradient is established across the thylakoid membrane due to photosynthetic electron transport.

The chemiosmotic mechanism of ATP formation is as follows—

• H⁺ ions, released through the splitting of water (photolysis), accumulate within the thylakoid lumen.
• Primary electron acceptors or carriers are present outside the thylakoid membrane.
• These primary electron carriers carry the electrons to the H-acceptor.
• At the same time, these primary electron carriers also carry H⁺ ions from the stroma into the thylakoid lumen.
• As the H⁺ ion from the carrier is released into the thylakoid lumen, the electron bound to the carrier is transferred to the next carrier.
• NADP reductase is present outside the thylakoid membrane. It is the last of the series of electron carriers that carries electrons from PS 1 to NADPH. It accepts the electron from the previous carrier and a proton from the stroma to reduce NADP⁺ into NADPH⁺H⁺.
• Due to this reaction, the concentration of H+ ions decreases in the stroma but increases in the thylakoid lumen. This causes the pH to decrease within the thylakoid lumen.
• A proton gradient is created due to the difference in the concentration of protons across the thylakoid membrane.
• The potential energy stored in the form of a proton gradient is electrical as well as chemical in nature.

Cyclic and non-cyclic photophosphorylation mechanism with diagram

• As the concentration of hydrogen ions in the lumen increases further, the ions move through the ATP synthase enzyme to the stroma. This movement of the proton generates a kind of energy called proton motive force, which is used to phosphorylate ADP to ATP.
• Towards the end of the electron transport chain, specific enzyme molecules synthesise ATP by combining ADP and Pi, using this proton motive force. These are known as CF₀-CF₁ particles (ATP synthase or ATPase).
• These CF₀-CF-₁ particles are structurally similar to the F₀-F₁ particles of mitochondria.
• CF0 part is rod-like and is strongly attached to the thylakoid membrane. The CF-L part is a spherical structure placed above the CF₀ part.
• Since the H+ ions are transported through the CF₀ part, it is known as the proton channel. The H+ ions are transported through this transmembrane channel by facilitated diffusion.
• Energy is released for every 3H⁺ ions transported through the CF₀ to the stroma. This energy is utilised to cause a conformational change in the CF₀ particle. This enables it to catalyse the synthesis of 1 molecule of ATP from ADP and Pi.
• Hence, it is observed that a membrane, proton pump, proton gradient and CF₀-CF₁ particles are required for the chemiosmotic mechanism.

 

Photosystem1(PS 1)

• The photocentre, LHC 1 and electron carriers are present within PS 1, over thylakoid membrane proteins.
• The light absorption centre present within PS 1 is a dimer of chlorophyll a. It absorbs a wavelength of 700 nm, hence called P₇₀₀– Besides this dimer, there are other chlorophyll molecules within PS 1.
• Chlorophyll a is more abundantly found than chlorophyll b in PS 1.
• Both the dimers bind a 4Fe-4S iron-sulfur centre, called FeSx, at an interface region. Between P₇₀₀ and FeS_x, two additional chlorophyll molecules are present.
• Reducing agents A₀, A1 (belongs to a class of cyclic organic compounds called quinones), FeSx, FeSA, FeSB (iron-sulphur centres), Fd (Ferredoxin), cytochrome b6f complex and plastocyanine are present in PS 1.
• Cyclic and non-cyclic photophosphorylation both take place in PS 1. Cyclic phosphorylation can take place in PS 1, independently.
• PS 1 takes an electron from PS 1 and transfers it to NADP⁺. There are two molecules of phylloquinone (vitamin K₁) present per heterodimer, with one molecule bound to each subunit.

“photosystem notes for class 11 biology”

Photosystem 2(PS 2)

1. P₆₈₀ is the reaction centre in PS 2. Its reaction centre contains six molecules of chlorophyll a, two molecules of Pheophytin-a, two molecules of 8-carotene and one cytochrome b559 (a protein that is an important component of PS 2).
2. It contains a complex in the central portion that produces oxygen. It also contains LHC 2 and some electron carriers.
3. The reaction centre within PS 2 contains a dimer of two proteins, that absorbs light of wavelength 680nm. Hence, it is called P₆₈₀
4. Other important components within PS include pheophytin (a chemical compound similar to chlorophyll), plastoquinone (a type of quinone molecule), cytochrome b6f (an iron-containing protein), plastocyanin, etc.
5. It accepts electrons produced by the photolysis of water (splitting of water using light).
6. PS 2 is associated with non-cyclic phosphorylation.

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“detailed notes on photosystem 1 and photosystem 2”

Similarities between PS 1 and PS 2

Both photosystems consist of a complex of pigment molecules, proteins and other prosthetic groups (inorganic or organic groups tightly bound to proteins) embedded in the thylakoid membranes of the chloroplast.

photosystem 1 and 2 diagram

Cytochrome B₆f Complex

1. The cytochrome b6f complex is an enzyme found in the thylakoid membrane of chloroplasts. It consists of four major polypeptides—cytochrome f (33 kDa), cytochrome b6 (heme-containing protein, 23 kDa), the ‘Rieske’ iron-sulfur protein (20 kDa) and subunit 4 (a 17 kDa protein made up of four small subunits).
2. The complex catalyses the transfer of electrons between plastoquinol (in PS 2) and plastocyanin (in PS 1). This, in turn, reduces the plastocyanin in the thylakoid lumen.
3. Two protons are transported into the thylakoid lumen for every electron transferred to plastocyanin. This facilitates the formation of a proton gradient that drives ATP synthesis.

“photosystems “

Mechanism Of Photosynthesis

Photosynthesis is divided into two phases

1. Photochemical or light phase and
2. Dark Or light-independent phase.

“difference between photosystem 1 and photosystem 2 notes”

Light Or Photochemical Phase

Definition: The part of photosynthesis that produces a reducing agent (NADPH and H⁺), along with ATP and O₂, in the thylakoid of chloroplast, in the presence of light, is called the light phase.

Site of occurrence: It takes place in the grana of the chloroplast.

Components: The process requires sunlight and chlorophyll as the main components. It also requires ADP and NADP as accessory components.

Significance:

“what is a photosystem “

The significance of the light phase in plants is as follows—

Conversion of energy: The solar energy gets converted into chemical energy (ATP and NADPH) during this phase.

Liberation of oxygen: Due to the oxidation of water, O₂ is released as a byproduct. Oxygen is further required for aerobic respiration.

Production of components required for the dark phase: NADPH and H⁺ ions produced during this phase are required during the dark phase.

Stages of photochemical phases: The photochemical part of photosynthesis begins with light absorption. When an atom or molecule absorbs light, it gains the whole energy of the photon (i.e., quantum), and becomes excited. The stages of the photochemical phase are discussed separately.

“photosystem structure and function notes”

Absorption of solar energy by chlorophyll molecules

1. Absorption of energy in the form of photons causes the chlorophyll molecules to move to their energised state.
2. The electrons remain in this state for a relatively short time, nearly 1 picosecond (= =1×10^-12 second). These can return to the lower excited singlet state by releasing the absorbed energy either as heat or as light.
3. The excited electron may also return to another excited state of lower potential energy but of greater stability, known as metastable triplet state (T).
4. Using the energy of chlorophyll a 680 and chlorophyll a 700, present in a metastable triplet state, a photochemical reaction takes place.

Chemiluminescence

The phenomenon where energy is released by a chemical reaction, in the form of light is called chemiluminescence.

Electron transport chain

Robert Hill was the first to describe the electron in this phase. transport chain. The electron transport may be of two types—non-cydic and cyclic.

“photosystem one and two “

Non-cyclic electron transport: Non-cyclic electron transport involves the following steps

1. Light energy reaches P₆₈₀ through resonance (by vibrations) of accessory pigments. This leads to the excitation (activation) of P₆₈₀ to a metastable triplet state.
2. P₆₈₀ now releases an e“ that is carried through the different electron carriers such as pheophytin (Pheo), quinone (Q), plastoquinone (PQ), cytochrome-f (Cyt f) plastocyanine (PC), etc.
3. Finally, the electron reaches the PS 1 reaction centre, while PS 2 remains positively charged due to the loss of electrons.
4. P_680⁺ (in positively charged PS 2) now oxidizes water to gain the lost electron. Thus water acts as an exogenous electron donor. This oxidation of water is catalyzed by the Mn-protein present in PS 2.
5. on the other hand, the photochemical events that follow the excitation of PS 1 (P₇₀₀) are similar to those of PS photosynthetic pigments in PS 1 absorb light of various wavelengths and transfer it to P₇₀₀ chlorophyll a- p₇₀₀ become excited (P₇₀₀).
6. The excited reaction centre P₇₀₀ loses an electron to an electron carrier protein. Due to the loss of electrons, PS 1 becomes positively charged.
7. This electron is transferred to Fd (ferredoxin, an iron-containing protein) and finally to NADP⁺. NADP collects protons from the medium and forms NADPH in the presence of an enzyme ferredoxin-NADP⁺ oxidoreductase.

⇒ \(2 \mathrm{H}_2 \mathrm{O} \underset{\mathrm{P}_{680}}{\stackrel{\text { chlorophyll a }}{\longrightarrow}} 2 \mathrm{H}^{+}+\mathrm{OH}^{-}\)

⇒ \(2 \mathrm{OH}^{-} \longrightarrow 2 \mathrm{OH}^{-}+2 \mathrm{e}^{-}\)

Cyclic electron transport: It occurs when there is a limited supply of CO₂. Hence, the synthesis of carbohydrates is decreased. As a result, NADPH starts accumulating. So, electron transport must occur, without the formation of more NADPH. So, this transport takes place. It involves the following steps

1. P₇₀₀ absorbs light and releases an electron that is captured by the primary electron acceptor (A).
2. This electron is then transported to Fd.
3. The reduced Fd is unable to reduce NADP+. Therefore, it transfers electrons to cyt b₆, PQ, cyt f and PC.
4. Finally, the electron reaches back to P₇₀₀ in PS 1, thereby completing cyclic electron transport.

Production of assimilatory power: Arnon (1956) used the term assimilatory power to refer to ATP and NADPH. The process of reduction of NADP⁺ to NADPH through the transfer of electrons is called photosynthetic electron transport. The process of formation of ATP from ADP and Pi, utilising light energy is called photophosphorylation.

“photosystem notes for NEET exam”

This also indicates that in photosynthesis a portion of light energy absorbed by the chlorophyll is captured as phosphate bond energy of ATP. The remaining is utilised for the reduction of NADP⁺.

Experiment to prove that oxygen is released during photosynthesis

A Hydrilla plant is placed in a beaker containing water. A small amount of NaHCO₃ is added to water, so as to increase the CO₂ available. Now, an inverted glass funnel is placed above the beaker, with a test tube placed at its open end. This whole set-up is left under sunlight.

When observed after several hours, bubbles are seen within the test tube and a gas is seen to have collected on top. On adding potassium pyrogallate solution to this water, it turns brown and the water level rises. As a result, the tube gets filled again.

“photosystem I and II mechanism explained”

This proves that the gas collected is oxygen, which has been released by Hydrilla during photosynthesis. formation of ATP from ADP and Pi, utilising light energy is called photophosphorylation. This also indicates that in photosynthesis a portion of light energy absorbed by the chlorophyll is captured as phosphate bond energy of ATP. The remaining is utilised for the reduction of NADP⁺

Chlorophyll

Chlorophyll Definition: The green-coloured, primary photosynthetic pigment, present in the green leaves, that traps the sun’s rays during photosynthesis, is known as chlorophyll.

Chlorophyll Distribution: It is found in the thylakoid and stroma lamellae of chloroplast in green plants.

Chlorophyll Types: There are five types of chlorophyll present in green plants. These are—chlorophyll a, chlorophyll b, chlorophyll c, chlorophyll d and chlorophyll e. In higher plants, mainly chlorophyll a and chlorophyll b are present. Two types of chlorophyll are seen in the bacteria— bacteriochlorophyll and bacterioviridin (also known as chromium chlorophyll).

Chlorophyll Chemical Formulae

1. Chlorophyll a—C₅₅H₇₂O₅N₄Mg
2. Chlorophyll b-C₅₅H₇₀O₆N₄Mg
3. Bacteriochlorophyll—C₅₅H₇₄O₆N₄Mg

Chlorophyll structure and function notes PDF 

Chlorophyll Characteristics:

1. The chemical structure of chlorophyll a and b are well established. They are porphyrin compounds containing magnesium at the centre.
2. The porphyrin consists of four pyrrole rings joined by -CH bridges. In addition to it, a fifth isocyclic ring is also present.
3. Each pyrrole ring is made up of 4 carbon and 1 nitrogen atom.
4. The carbon atoms present towards the periphery of the pyrrole ring are numbered C1-C8. The Cl, C3, C5 and C8 have methyl groups attached to them.
5. A long chain of C and H atoms called the phytol chain or phytol tail is attached to the fourth pyrrole ring.
6. Chlorophyll b has a slightly different structure. It has – CHO group attached to the third carbon of the pyrrole ring.

Role of chlorophyll in photosynthesis with mechanism

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Chlorophyll Functions:

1. Chlorophyll is the main photosynthetic pigment to absorb light energy. Accessory photosynthetic pigments absorb the energy of a particular wavelength of light and transmit the energy to chlorophyll a molecule.
2. P₇₀₀> P₆₈₀ function as reaction centres within chlorophyll a. These are regions containing pigments that absorb light of wavelength 700 nm and 680 nm, respectively. The solar energy is converted to electrical energy within these reaction centres, during photosynthesis.

Chlorophyll Structure

Albino Plant

Chlorophyll is synthesised in plants due to the presence of a specific gene within their chromosomes. In some plants, this gene may be absent and chlorophyll synthesis is prevented. Such plants are known as albino plants.

Carotenoids

Carotenoids Definition: The red or yellow coloured pigments, that act as the accessory pigments are called carotenoids

Carotenoids Types: Carotenoids are of two types—

1. Carotenes and
2. Xanthophylls.

Carotenoids Distribution: They are present either conjugated with chlorophyll, in -the chloroplastid or present separately within the chromoplastid.

Chemical formula: Carotene (C₄H₅₆), Xanthophyll (C₄H₅₆O₂).

Class 11 biology chloroplast and chlorophyll notes with diagrams

Carotenoids Characteristics:

1. All the carotenoids are tetraterpenoids. Carotenes contain long hydrocarbon chains and their oxygen derivatives are called xanthophylls.
2. Generally, carotenoids are yellow or orange in colour. They can absorb light of wavelength ranging from 400 to 500 nm.
3. Carotenoids are insoluble in water but soluble in chloroform, ethyl ether and alcohol.
4. The major carotene in higher plants is yS-carotene with a small amount of or-carotene. The special carotene, responsible for the red colour of tomatoes, watermelon, etc., is known as lycopene.
5. The major xanthophylls found in higher plants are lutein, violaxanthin and neoxanthin.

Chlorophyll Diagram

Carotenoids Functions:

1. Carotenoids protect the chlorophyll against the photodynamic action of light andO₂ (destruction due to light, in the presence of O₂).
2. Carotenoids act as accessory pigments in photosynthesis. They absorb and transfer radiant energy to chlorophyll during photosynthesis.
3. They provide colour to flowers and fruits.
4. β-carotene acts as the precursor of vitamin A.

Phycobilins

Phycobilins Definition: The proteinaceous pigments of blue-green algae and red algae that indirectly take part in photosynthesis are called phycobilins.

Phycobilins Types: Phycobilins are generally of three types— phycocyanin, phycoerythrin and allophycocyanin.

Phycobilins Location: These pigments are found attached to the chloroplast lamellae of algae, as small granules called phycobilisomes. Phycocyanin is found in blue-green algae while phycoerythrin is found in red algae.

Short notes on chlorophyll and chloroplast for quick revision

Phycobilins Chemical formulae: Phycocyanin (C₃₄H₄₄0₈N₄), phycoerythrin (C₃₄H₄₆0₈N₄).

Phycobilins Characteristics:

1. These pigments are water-soluble open-chain tetrapyrroles without magnesium at the centre. They also do not possess any phytol tail
2. They remain conjugated with a protein molecule, hence called phycobiliproteins.
3. The pigment phytochrome of higher plants, which is involved in light absorption for flowering and seed germination, is chemically similar to phycobilins.

Chlorophyll Biology

Phycobilins Functions:

1. Phycobilins absorb light during photosynthesis and may be regarded as accessory pigments. The light absorbed by the phycobiliproteins is transferred to chlorophyll during photosynthesis.
2. These pigments help in chromatic adaptation in plants.
3. They also function as antennae molecules

Separation Of Chloroplast Pigment By Paper Chromatography

1. Some fresh green spinach leaves were ground in 15-20 ml of acetone with the help of a mortar and pestle. The green-coloured extract was filtered and concentrated by evaporation of acetone. It was used as a sample containing photosynthetic pigment.
2. A narrow glass jar with a split cork was taken. A strip of chromatographic paper was cut (narrower and shorter than the glass jar). Two lateral notches were cut at one end of the paper (at a little distance from each other).
3. The sample was poured drop by drop over the notched area. A mixture of 92% petroleum ether and 8% acetone was left at the bottom of the jar.
4. The chromatographic paper was suspended in the jar by a hook in such a way, that the notched area remained well above the solvent mixture while the other end dipped in it. The set-up was allowed to stand for a few hours.
5. After a few hours, the solvent moved up the chromatographic paper.
6. The pigment got dissolved in the solvent and ascended to various heights on the paper.
7. Four pigment bands are observed over the paper strip in the following order from top to base orange, yellow, blue-green and green.
8. Leaves contain four types of photosynthetic pigments. They separate over the chromatographic paper on the basis of their solubility and rate of diffusion.
9. The four pigments are carotene (orange), xanthophyll (yellow), chlorophyll a (blue-green) and chlorophyll b (green).

Photosynthesis In Higher Plants Multiple Choice Questions

Question 1. Phosphoenol pyruvate (PFP) is the primary CO₂ acceptor in—

1. C₄ plants
2. C₂ plants
3. C₃ and C4 plants
4. C₃ plants

Answer: 1. C₄ plants

Question 2. With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct?

1. Increasing atmospheric CO₂ concentration up to 0.05% can enhance CO₂ fixation rate
2. C₃ plants respond to higher temperatures with enhanced photosynthesis while C₄ plants have much lower temperature optimum
3. Tomato is a greenhouse crop which can be grown in CO₂ enriched atmosphere for a higher yield
4. Light saturation for CO₂ fixation occurs at 10% of full sunlight

“photosynthesis in higher plants MCQ with answers”

Answer: 2. C₃ plants respond to higher temperatures with enhanced photosynthesis while C₄ plants have much lower temperature optimum’

Read and Learn More WBCHSE Multiple Choice Question and Answers for Class 11 Biology

Question 3. The process which makes a major difference between C₃ and C₄ plants—

1. Photorespiration
2. Respiration
3. Glycolysis
4. Calvin cycle

Answer: 3. Glycolysis

Question 4. Mitochondria and chloroplast are—

1. Semi-autonomous organelles
2. Formed by the division of pre-existing organelles they contain DNA but lack protein-synthesizing machinery

Choose the correct Answer

1. Both [1] and [2] are correct
2. [2] is true but [1] is false
3. [1] is true but [2] is false
4. Both [1] and [2] are false

Answer: 3. [1] is true but [2] is false

Question 5. Emerson’s enhancement effect and Red drop have been instrumental in the discovery of

1. Two photosystems operating simultaneously
2. Photophosphorylation and cyclic electron transport
3. Oxidative phosphorylation
4. Photophosphorylation and non-cyclic electron transport

Answer: 1. Two photosystems operating simultaneously

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Question 6. In a chloroplast, the highest number of protons are found in

1. Stroma
2. Lumen of thylakoids
3. Intermembrane space
4. Antennae complex

Answer: 2. Lumen of thylakoids

Question 7. The oxygen that evolved during photosynthesis comes from water molecules. Which one of the following pairs of elements is involved in this reaction?

1. Magnesium and Chlorine
2. Manganese and Chlorine
3. Manganese and Potassium
4. Magnesium and Molybdenum

Answer: 2. Manganese and Chlorine

“multiple choice questions on photosynthesis in higher plants”

Question 8. In photosynthesis, the light-independent reactions take place at—

1. Stromal matrix
2. Thylakoid lumen
3. Photosystem-1
4. Photosystem-2

Answer: 1. Stromal matrix

Question 9. Anoxygenic photosynthesis is characteristic of—

1. Rhodospirillum
2. Spirogyra
3. Chlamydomonas
4. Ulva

Answer: 1. Rhodospirillum

Question 10. Identify the incorrect statement(s) in relation to C₄-photosynthesis—

1. Kranz Anatomy is an essential feature for C₄ plants
2. C₄ plants have higher water use efficiency than C₃ plants
3. Photorespiration can be minimised when the C₄ pathway is in operation
4. Conversion of oxaloacetate to malate occurs in the bundle sheath cells

Answer: 4. Conversion of oxaloacetate to malate occurs in the bundle sheath cells

“photosynthesis in higher plants quiz with answers”

Question 11. Photosynthetic Active Radiation (PAR) has the following range of wavelengths

1. 340-450 nm
2. 400-700 nm
3. 500-600 nm
4. 450-950 nm

Answer: 2. 400-700 nm

Question 12. The products of the light reaction are

1. Xanthophyll, NADPH and oxygen
2. Chlorophyll, ATP and NADPH
3. ATP, NADPH and oxygen
4. None of the above

Answer: 3. ATP, NADPH and oxygen

Question 13. The C₄-photosynthetic system is present in plants which are found in

1. Cold region
2. Hot region
3. Both A and B
4. Dry tropical region

Answer: 4. Dry tropical region

“MCQ on photosynthesis in higher plants for NEET”

Question 14. Which element plays a vital role in the splitting of water to liberate oxygen during photosynthesis?

1. Copper
2. Boron
3. Chlorine
4. Manganese

Answer: 4. Manganese

Question 15. Synthesis of one glucose molecule requires

1. 6
2. 12
3. 18
4. 24

Answer: 2. 12

Question 16. Gross primary productivity is the rate of production during photosynthesis

1. Organic matter
2. Oxygen
3. Carbon dioxide
4. Chlorophyll

Answer: 1. Organic matter

“important MCQs on photosynthesis in higher plants”

Question 17. Enzymes required for phosphorylation are located in of chloroplast.

1. Peristomium
2. Plastidome
3. Stroma
4. Quaantasome

Answer: 4. Quaantasome

Question 18. C4-plants have bundle sheath cells which possess—

1. Few chloroplasts with thin walls so that gaseous exchange can take place
2. Large number of chloroplasts with thick walls impervious to gaseous exchange
3. A large number of chloroplasts with thick walls and no intercellular spaces
4. None of the above

Answer: 5. None of the above

Question 19. Statement (A): Photorespiration decreases photosynthetic output.

Statement (B): In the photorespiratory pathway, neither ATP nor NADPH is produced.

1. Both the statements A and B are correct
2. Both the statements A and B are incorrect
3. Statement A is correct and statement B is incorrect
4. Statement B is correct and statement A is incorrect

Answer: 1. Both the statements A and B are correct

“photosynthesis in higher plants objective questions”

Question 20. Which of the following statements regarding the cycle flow of electrons during the light reaction is false?

1. This process takes place in stromal lamellae
2. ATP synthesis takes place
3. NADPH⁺ H⁺ is synthesised
4. Takes place when light of wavelength beyond 680 nm is available for excitation
5. PS 2 is not involved in the process

Answer: 3. NADPH⁺ H⁺ is synthesised

Question 21. Find out the mismatched pair

1. C₄-plants— Kranz anatomy
2. Primary CO₂ fixation product of C₄-plants—OAA
3. Primary CO₂ acceptor of C₃-plants— RuBP
4. Calvin pathway of C₄-plants occurs in—Bundle sheath
5. C₃-plants—Maize

Answer: 5. C₃-plants—Maize

Question 22. Cyclic photophosphorylation links to—

1. PS 2
2. PS 1
3. dark reaction
4. Both A and B

Answer: 2. PS 1

Question 23. Thylakoids occur inside—

1. Mitochondria
2. Chloroplast
3. Golgi apparatus
4. Endoplasmic reticulum

Answer: 2. Chloroplast

Question 24. In the C₄ pathway, the CO₂ fixation in mesophyll cells is carried out by the enzyme

1. Pyruvate dehydrogenase
2. Pyruvate decarboxylase
3. PEP-carboxylase
4. RuBisCO

Answer: 4. RuBisCO

Question 25. photosynthetic bacteria have—

1. Pigment system-1
2. Pigment system-2
3. Both A and B
4. Some other kinds of pigments (P890)

Answer: 4. Some other kinds of pigments (P890)

Question 26. In C₃ plants, the first stable product of photosynthesis during the dark reaction is

1. PAGAL
2. RuB
3. PGA
4. OAK

Answer: 3. PGA

Question 27. In C₄ plants, the carbon dioxide fixation occurs in—

1. Guard cells
2. Spongy cells
3. Palisade
4. Bundle sheath cells

Answer: 4. Bundle sheath cells

Question 28. Photolysis of water is caused by—

1. PS 1
2. PS 2
3. PS 1 and PS 2
4. None of these

Answer: 2. PS 2

Question 29. CAM pathway is observed in—

1. Pineapple
2. Maize
3. Sunflower
4. Sugarcane

Answer: 1. Pineapple

Question 30. Which one of the following statements about the events of non-cyclic photophosphorylation is not correct?

1. Photolysis of water takes place
2. Oxygen is released
3. Only one photosystem participates
4. ATP and NADPH are produced

Answer: 3. Only one photosystem participates