Assertion Reason Questions for Biology Chapter 13 Photosynthesis in Higher Plants

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Directions: In the following questions, a statement of assertion is followed by a statement of reason.
Mark the correct choice as:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Q.1. Assertion: Chloroplasts mostly occur in mesophyll cells along their walls inside the leaves.
Reason : The membrane system of chloroplast is responsible for trapping the light energy and also for the synthesis of ATP and NADPH.

Answer Answer: (b) Chloroplasts function as the site of photosynthesis in eukaryotic photoautotrophs. Inside the leaves, the chloroplasts occur mostly in the mesophyll cells along their walls for easy diffusion of gases and receiving optimum quantity of incident light. Within the chloroplast there is the membranous system consisting of grana, the stroma lamellae, and the fluid stroma. The membrane system is responsible for trapping the light energy and also for the synthesis of ATP and NADPH.

Q.2. Assertion : Rhoeo leaves contain anthocyanin pigments in epidermal cells.
Reason : Anthocyanins are accessory photosynthetic pigments. [AIIMS 2002]

Answer Answer: (c) Anthocyanin pigments only give colouration since the epidermal cells mainly have potential colouring pigments. It is responsible for blue, red, pink and purple colours, observed in different parts of plants such as petals, stamens and fruits etc.
Anthocyanins are also important for attracting insects for pollination and seed dispersal. Hence, anthocyanin pigments are not accessory photosynthetic pigments.

Q.3. Assertion: Leaf colouration is due to the presence of four pigments – Chlorophyll a, chlorophyll b, xanthophylls and carotenoids.
Reason : Chlorophyll b is the chief pigment associated with photosynthesis.

Answer Answer: (c) Chlorophyll a is found in all photosynthetic plants except bacteria. Hence, it is called as universal photosynthetic pigment. It is also called primary photosynthetic pigment because it performs primary reaction of photosynthesis which involves conversion of light into chemical energy. Other photosynthetic pigments like chlorophyll b, carotenes and xanthophylls are called accessory pigments.

Q.4. Assertion: Bacterial photosynthesis occurs by utilizing wavelength longer than 700 nm.
Reason: Here reaction centre is B-890. [AIIMS 2002]

Answer Answer: (b) In bacteria, photosynthesis utilizes light of wavelength more than 700 nm and their reaction centre is B-890.

Q.5. Assertion : There is a decrease in photosynthesis, if the photosynthetic cells are illuminated by light
of P680 nm or more wavelength.
Reason : In red drop phenomenon the rate of photosynthesis decreases.

Answer Answer: (b) Although the efficiency of photosynthesis is uniform over most of the spectrum, it declines significantly in the red, i.e., at wavelength of 680 nm and above. This phenomenon is called red drop. However, it was shown by Emerson that if light at 680 nm is supplemented with light of a shorter wavelength (< 600 nm), the quantum efficiency of photosynthesis in the red can be restored to normal.

Q.6. Assertion : 6 molecules of CO2 and 12 molecules of NADPH+ + H+ and 18 ATP are used to form one hexose molecule.
Reason : Light reaction results in formation of ATP and NADPH2.

Answer Answer: (b) Six molecules of CO2 enter Calvin cycle to produce one hexose molecule whereas 18 ATP, 12 NADPH + and H+ molecules are used up. The light reaction of photosynthesis results in ATP and NADPH2 formation.

Q.7. Assertion : Cyclic pathway of photosynthesis first appeared in some eubacterial species.
Reason : Oxygen started accumulating in the atmosphere after the non-cyclic pathway of photosynthesis evolved.

Answer Answer: (b) Cyclic pathway of photosynthesis appeared first in some eubacterial species. It is supposed to be the first evidence of production of ATP in the presence of light. During non-cyclic photophosphorylation photolysis of water takes place. Under the influence of light energy and the catalytic action of chlorophyll, water a substance of low energy value, is split up into oxygen and hydrogen. Oxygen is used in the chloroplast. Non-cyclic photophosphorylation is the only natural process which adds molecular oxygen to the atmosphere.

Q.8. Assertion : Cyclic photophosphorylation synthesizes ATP.
Reason : ATP synthesise in cyclic photophos￾phorylation is not associated with NADPH formation.

Answer Answer: (b) In case of cyclic photophosphorylation, the electron, while passing between ferredoxin and plastoquinone and/or over the cytochrome complex the electron loses sufficient energy to form ATP from ADP and inorganic phosphate.

Q.9. Assertion : Each molecule of ribulose-1, 5- bisphosphate fixes one molecule of CO2.
Reason : Three molecules of NADPH and two ATP are required for fixation of one molecule of CO2.

Answer Answer: (c) Each molecule of ribulose-1, 5-biphosphate fixes one molecule of carbon dioxide with the addition of water, thereby resulting in the formation of two molecules of 3-phosphoglyceric acid (3-PGA). The fixation and reduction of one molecule of CO2 requires three molecules of ATP and two of NADPH, coming from the photochemical reactions.

Q.10. Assertion :The stromal thylakoids are rich in both PS I and PS II.
Reason : The granal membranes are rich in ATP synthetase.

Answer Answer: (d) The grana stacks of membranes are enriched in PS II and LHC (Light harvesting centre), while there is little ATP synthetase. On the other hand, a fraction of stroma thylakoids is rich in PS I and ATPase and poor in PS II and LHC.

Q.11. Assertion :Cyclic photophosphorylation synthesizes ATP.
Reason : ATP synthesise in cyclic photophosphorylation is not associated with NADPH formation.

Answer Answer: (b) In case of cyclic photophosphorylation, the electron, while passing between ferredoxin and plastoquinone and/or over the cytochrome complex the electron loses sufficient energy to form ATP from ADP and inorganic phosphate.

Q.12. Assertion : Oxidative phosphorylation requires oxygen.
Reason : Oxidative photophosphorylation occurs in mitochondria.

Answer Answer: (b) The synthesis of ATP via electron flow through the ETS, with oxygen as the terminal electron acceptor, is known as oxidative phosphorylation and takes place in mitochondria. In contrast to the oxidative phosphorylation of mitochondria, O2 is not used in photophosphorylation of chloroplasts and NADP+ is the last electron acceptor.

Q.13. Assertion : Plants utilize 5-10 of the absorbed water in photosynthesis.
Reason : Reduced leaf hydration decrease the photosynthesis.

Answer Answer: (d) Less than 1% of the total water absorbed is utilized in photosynthesis. The rest is lost in transpiration. Even a slight increase in transpiration reduces the leaf hydration that cuts down photosynthesis by causing stomatal closure and hence decreased CO2 absorption, loss of leaf turgidity, reduced absorption of solar radiations and decrease in enzymatic activity.

Q.14. Assertion: Six molecules of CO2 are fixed to form a hexose.
Reason: One molecule of CO2 is fixed to produce 686 kcal in photosynthesis.

Answer Answer: (c)

Q.15. Assertion: 686,000 calories energy are produced in the formation of one molecule of glucose.
Reason: The energy is provided by a total of 12 NADPH and 18 ATP.

Answer Answer: (a)

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