NEET Biology Photosynthesis in Higher Plants Important Questions Set 01

These Class 11 NEET Biology important questions on Photosynthesis in Higher Plants give 45 questions with step-by-step answers, arranged as very short, short and long answer types, as asked in school and board examinations. They help NEET aspirants revise the definitions, structures, differences and key terms of the chapter.

Very Short Answer Type Questions

Question 1. Who provided evidence for production of glucose when plants grow?
Answer: Julius Von Sachs.

Question 2. What are pigments and which is the chief pigment associated with photosynthesis?
Answer: Pigments are substances that have an ability to absorb light at specific wavelengths. The chief pigment associated with photosynthesis is chlorophyll a.

Question 3. Define photophosphorylation.
Answer: The process of ATP formation from ADP and Pi in the presence of light in chloroplasts is called photophosphorylation.

Question 4. Expand RuBisCO.
Answer: RuBisCO stands for Ribulose Bisphosphate Carboxylase Oxygenase.

Question 5. What is photorespiration?
Answer: Photorespiration is loss of fixed carbon as CO₂ in the presence of light due to oxygenase activity of RuBisCO.

Question 6. Name the technique used to separate leaf pigments.
Answer: Paper chromatography is used to separate leaf pigments.

Question 7. What is the first stable product of C₄ cycle?
Answer: First stable product of C₄ cycle is oxaloacetic acid.

Question 8. Name two photosynthetic pigments belonging to carotenoids.
Answer: Carotenoids include carotene and xanthophyll.

Question 9. Give the chemical equation of photosynthesis.

Answer:

Overall equation for photosynthesis is :

6CO₂ + 12H₂O —Sunlight →C₆H₁₂O₆ + 6O₂ + 6H₂O Chlorophyll

Question 10. Who gave the law of limiting factors?
Answer: Law of limiting factors was given by Blackmann (1905).

Short Answer Type Questions

Question 11. Describe photosynthetic unit.
Answer: Photosynthetic unit is smallest group of pigment molecules that absorb light and promote release of electrons.

Question 12. Describe briefly the contribution of Joseph Priestley.
Answer: Joseph Priestley in 1770 performed a series of experiments that revealed the essential role of air in the growth of green plants. He hypothesised that plants restore to the air whatever the breathing animals and the burning candles remove.

Question 13. Complete the given below sequence of C₄ pathway? CO₂ fixation → A → Transport → Decarboxylation → B.
Answer: CO₂fixation —→ C₄acid —→ Transport —→ C₃ acid + CO₂

Question 14. Differentiate between photorespiration and aerobic respiration.

Answer:

Question 15. What is RuBisCO? Where is it present in C₃ and C₄ plants?
Answer: RuBisCO is the most abundant enzyme. This enzyme catalyses the carboxylation reaction for the fixation of CO₂ into a stable organic intermediate. In C₃ plants, RuBisCO is present in all photosynthetic cells and in C₄ plants, this enzyme is present in bundle sheath cells.

Question 16. Why do the leaves appear green in colour?
Answer: Chlorophyll, the chief pigment of leaves, absorbs mainly the blue and red wavelengths of visible spectrum. It reflects the green wavelength of light and that is why the leaves appear green.

Question 17. What are light harvesting complexes?
Answer: The light harvesting complexes are made up of hundreds of photosynthetic pigment molecules bound to proteins. They help to make photosynthesis more efficient by absorbing different wavelengths of light.

Question 18. What is Blackman's law of limiting factors?

Answer:

Blackman's Law of Limiting Factors states that :

If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value : It is the factor which directly affects the process if its quantity is changed.

Question 19. Give comparison between the cyclic and non-cyclic photophosphorylation.

Answer:

4. External source of electrons is not required External source of electrons is required

Question 20. How many ATP and NADPH molecules will be required to make one molecule of glucose through the Calvin pathway?
Answer: To make one molecule of glucose, 6 turns of Calvin cycle are required. It utilizes 18 ATP and 12 NADPH molecules.

Question 21. What is the advantage of having more than one pigment molecule in the photosynthetic unit?
Answer: Though chlorophyll-a is the major pigment responsible for trapping light, other thylakoid pigments like chlorophyll b, xanthophylls and carotenoids which are accessory pigments also absorb light and transfer it to chlorophyll
a. They enable a wider range of wavelengths of incoming light to be utilised for photosynthesis and also protect chlorophyll a from photo-oxidation.

Question 22. Briefly describe the contribution of Jan Ingenhousz, which led to gradual development in our understanding of photosynthesis.
Answer: Jan Ingenhousz (1730–1799) showed that sunlight is essential to the plant process that somehow purifies the air fouled by the burning candles or the breathing animals. In an experiment with an aquatic plant, he showed that in bright sunlight, small bubbles were formed around the green parts of plant, while in the dark, they did not. Later he identified these bubbles to be of oxygen. Hence, he showed that it is only the green parts of the plants that could release oxygen in the presence of light.

Question 23. List the processes which occur during the photochemical phase of photosynthesis.

Answer:

Light reaction or photochemical phase includes :

(i) Light absorption

(ii) Water splitting

(iii) Oxygen release

(iv) Formation of high energy chemical intermediates, ATP and NADPH.

Question 24. Briefly describe the Z-scheme and why is it called so?
Answer: The whole scheme of transfer of electrons, starting from the PS II, uphill to the acceptor, down the electron transport chain to PS I, excitation of electrons, transfer to another acceptor, and finally down hill to NADP⁺ causing it to be reduced to NADPH + H⁺ is called the Z-scheme, due to its characteristic shape. This characteristic shape is formed when all the carriers are placed in a sequence on a redox potential scale.

Question 25. How does PS II supply electrons continuously in noncyclic ETS?
Answer: During the non-cyclic photophosphorylation, a continuous supply of electrons is needed, The electrons that were moved from photosystem II must be replaced. This is achieved by electrons available due to splitting of water. The splitting of water is associated with the PS II, water molecule is split into hydrogen ions (H⁺), [0] and electrons. The oxygen released is one of the net products of photosynthesis. The electrons needed to replace those removed from photosystem I are provided by photosystem II. 2H₂O —→4H⁺+O₂+4e–

Question 26. Give the diagrammatic explanation for ATP synthesis through chemiosmosis.
Answer: A well-labelled diagram should show these parts: H⁺; NADP⁺; NADPH; Lumen; Thylakoid; F₀ membrane; Stroma; F₁; ADP; ATP.

Question 27. Give the significance of photosynthesis.
Answer: Photosynthesis is a vital physico-chemical process by which the green plants use light energy to drive the synthesis of organic compounds. This process links the physical and biological world. The plants biomass (dry matter), derived through photosynthesis, supports humans and all other organisms (hetrotrophic) living in biosphere. During photosynthesis, O₂ is released, which is helpful to living organisms for aerobic respiration and also in making of ozone in outer layer of atmosphere.

Question 28. Write a short note on photosynthetic pigments.

Answer:

Photosynthetic pigments:

These photosynthetic pigments (chlorophyll) give green colour to the leaves. They have an ability to absorb light at specific wavelengths necessary for photosynthesis.

Question 29. List the various external and internal factors affecting photosynthesis.

Answer:

External factors : Availability of sunlight, temperature, CO₂ concentration and water.

Internal factors : Number, size, age and orientation of leaves, mesophyll cells, chloroplasts.

Question 30. What is PEP? What is its role in the biosynthetic process?
Answer: PEP is phosphoenol pyruvate. It plays a very vital role in CO₂ fixation in C₄ plants. The primary CO₂ acceptor is PEP and the enzyme responsible for this CO₂ fixation is PEP carboxylase or PEPcase. PEP is regenerated during the Hatch and Slack pathway in the mesophyll cells.

Long Answer Type Questions

Question 31. Explain the significance of the three phases of Calvin cycle.

Answer:

The three phases are :

Carboxylation : Calvin cycle is the only process for synthesis of photosynthate. This is the most crucial step of the Calvin cycle where CO₂ is utilized for the carboxylation of RuBP. This reaction is catalysed by the enzyme RuBisCO which results in the formation of two molecules of 3-PGA (first stable compound).

Reduction : These are a series of reaction that lead to the formation of glucose. The steps involve utilization of 2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO₂ molecule fixed. Six turns of the cycle are required for the removal of one molecule of glucose from the pathway.

Regeneration : Regeneration of the CO₂ acceptor molecule RuBP is crucial if the cycle is to continue uninterrupted. The regeneration step requires one ATP for phophorylation to form RuBP.

Question 32. Mention the site of occurrence of following events in maize plant.
(a) Regeneration of RuBP
(b) RuBP + CO₂ —→ 3PGA
(c) PEP + CO₂ —→ OAA
(d) C₄ acid formation
(e) C₃ acid formation

Answer:

(a) Stroma – Bundle sheath cells

(b) Stroma – Bundle sheath cells

(c) Cytoplasm – Mesophyll cells

(d) Mesophyll cells

(e) Bundle sheath cells

Question 33. (a) Mention the photosystems and other components involved in non-cyclic photophosphorylation.
(b) Name the components involved in Cyclic ETS.
(c) Which is the major limiting factor for photosynthesis.
(d) What is the CO₂ saturation point for C₃ & C₄ plants.
(e) Which abiotic factor affects the photosynthesis indirectly.

Answer:

(a) Water splitting complex, PS II, H-carrier, Cytochrome b - f complex, PS I, NADP reductase.

(b) PS I, cytochrome b-f complex, H-carrier.

(c) CO₂ is the major limiting factor for photosynthesis.

(d) C₄ – 360 ppm C₃ > 450 ppm.

(e) Water is one of the reactants in the light reaction but the effect of water as a factor is more through its effect on the plant, rather than directly on photosynthesis.

Question 34. Give the schematic sketches of cyclic and non-cyclic photophosphorylation.
Answer: A well-labelled diagram should show these parts: Photosystem I; Photosystem II; Photosystem I e– acceptor; NADPH; Light e– acceptor; ATP; ADP +iP ATP; NADP⁺; P+iP; Electron; Electron transport; AD transport system system; LHC; Chlorophyll P₇₀₀; H₂O → 2e– + 2H⁺ + [O].

Question 35. Describe the Calvin cycle diagrammatically.
Answer: A well-labelled diagram should show these parts: Atmosphere; CO₂ + H₂O; Ribulose-1,5- bisphosphate; ADP; 1 Carboxylation; 3; The; Regeneration; Calvin; 3-phosphoglycerate cycle; ATP; 2; Reduction; +; NADPH; Triose phosphate; Pi + NADP⁺; Sucrose, starch.

Question 36. Describe how the C₄ pathway is an adaptive advantage to the C₄ plants like sugarcane.

Answer:

 C₄ plants are adapted to dry tropical regions. These have better tolerance towards high temperature conditions (40–45°C).

 These keep their stomata partially closed during hot day and PEPcase fix whatever low amount of CO₂ available.

 These have a mechanism to increase the concentration of CO₂ at enzyme (RuBisCO) site. Thus, oxygenase activity is minimised.

 Kranz anatomy with thick-walled bundle sheath cells do not allow entry of O₂ into them. Bundle sheath cells themselve do not generate O₂ (non-cyclic photophosphorylation being absent). Thus, photorespiration is absent.

Question 37. Distinguish between Bundle sheath and Mesophyll cells of C₄ plant.

Answer:

Question 38. How are ATP, NADPH and oxygen produced in non-cyclic photophosphorylation?

Answer:

Non-cyclic Photophosphorylation involves both Photosystem I and Photosystem II. The two photosystems are connected through an electron transport chain. Both ATP and NADPH + H⁺ are synthesised by this kind of electron flow. Oxygen is released due to splitting of water molecule during the process.

First in PS II, the P₆₈₀ molecule absorbs 680 nm wavelength of red light causing electrons to become excited and jump into an orbit which is farther from the atomic nucleus. These electrons are picked up by an electron acceptor which passes them to an electron transport system of cytochromes. This movement of electrons is downhill on redox potential scale. The electrons are then passed onto the pigments of PS I, simultaneously, electrons in the reaction center of PS I (P₇₀₀) are excited when they receive light of wavelength 700 nm and these electrons are transferred to an other acceptor molecule that has a greater redox potential. These electrons are then moved downhill again to a molecule of NADP⁺. The addition of these electrons reduces the NADP⁺ to NADPH + H⁺. This whole scheme of transfer of electrons is called the Z-scheme due to its characteristic shape. This shape is formed when all the carriers are placed in a sequence on a redox potential scale.

Question 39. Compare Photosystem I and Photosystem II.

Answer:

Photosystem I / Pigment system I Photosystem II / Pigment system II
1. PS-I absorb maximally at 700 nm of 1. PS-II absorb maximally at 680 nm of

3. PS-I is present on non-appressed side of 3. PS-IIis presentin appressedpart of Grana. Granaandstromalamellae.
4. Foundinbothgranaandstromalamellae. 4. Foundingranalamellaeonly.
5. Molecular oxygen is not released when this 5. Molecular oxygen is released by photolysis systemoperates individually. of water whenthis systemoperates.
6. Participates in both cyclic as well as 6. It is involved only in non-cyclic flow of non-cyclic flowofelectrons. electrons.

Question 40.

(a) Describe cyclic photophosphorylation.

(b) Give the following information about photorespiration.

Answer:

Cyclic Photophosphorylation

(a) The process of cyclic photophosphorylation involves only PS I and this process takes place in the stroma lamella membrane. When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation occurs due to cyclic flow of electrons. The excited electron does not pass on to NADP⁺ and is cycled back to the PS I complex through the electron transport chain. ATP is produced by this process but NADPH + H⁺ is not produced. Cyclic photophosphorylation also occurs when only light of wavelength beyond 680 nm are available for excitation.

(b) (i) RuBP —RuBisCO →3 PGA + Phosphoglycolate
(ii) ATP is required

(iii) C₃ plants

(iv) Chloroplast, Peroxisomes Mitochondria

Question 41. Give an account of external factors affecting photosynthesis.

Answer:

External factors affecting photosynthesis

(a) Light : It is an essential factor for photosynthesis.

(i) Light intensity : There is a linear relationship between incident light and CO₂ fixation at low light intensities. At higher light intensities, gradually the rate does not show further increase as other factors become limiting. The light saturation occurs at 10 percent of the total sunlight available to plants. Increase in incident light beyond a point causes the breakdown of chlorophyll and thus resulting in decrease in photosynthesis.
(ii) Light quality : Light between 400–700 nm wavelength constitute the photosynthetically active radiation (PAR). Maximum photosynthesis takes place in red and blue light of the visible spectrum and minimum photosynthesis takes place in green light.

(iii) Duration of light : Light duration does not affect the rate of photosynthesis, but it affects the overall photosynthesis.

(b) Carbon dioxide concentration : It is a major limiting factor influencing the rate of photosynthesis.

The C₃ and C₄ plants respond differently to CO₂ concentration. At low light intensities neither type responds to high CO₂ concentration. At high light intensities, both C₃ and C₄ plants show increase in the rate of photosynthesis. The C₄ plants show saturation at about 360 mlL–1 (ppm), while C₃ plants show saturation only beyond 450 mlL–1 (ppm), thus, the current concentration of CO₂ is limiting for C₃ plants.

(c) Temperature : Photosynthesis can take place over a wide range of temperatures. The light reactions are temperature senstive but they are affected to a much lesser extent. The dark reaction being enzymatic are temperature controlled. Again, the temperature optimum for photosynthesis of different plants also depends on the habitat that they are adapted to. Tropical plants have a higher temperature optimum than the plants adapted to temperate climates.

The C₄ plants respond to higher temperatures and they show higher rate of photosynthesis, while C₃ plants have much lower temperature optimum. Optimum temperature in C₃ plant is 20–25°C and for C₄ plant is 30–45°C.

(d) Water : Water is one of the raw materials utilized for the process of photosynthesis. Photosynthetic process utilizes less than 1% of the water absorbed by a plant, hence it is rarely a limiting factor in photosynthesis. Water stress causes the stomata to close, hence reducing the CO₂ availability as gaseous exchange could not occur. Also, water stress makes leaves wilt, thus reducing the surface area of the leaves and the metabolic activity reduces as well.

Question 42. (a) What are the requirements of chemiosmosis.
(b) Mention the features of bundle sheath cells associated with Kranz anatomy.

Answer:

(a) Chemiosmosis process requires a membrane, a proton pump, a proton gradient and ATPase enzyme. Energy is used to pump protons across the membrane into the lumen, which creates a proton gradient across the membrane. ATPase enzyme has transmembrane channel that allows diffusion of protons back across the membrane, this releases energy to activate ATPase enzyme which catalyses the formation of ATP.

(b) ● May form several layers around vascular bundles

● Large size cells

● Thick walls impervious to gases

● No intercellular spaces

● Have large number of chloroplasts

Question 43. Give a diagrammatic representation of a section of chloroplast.
Answer: A well-labelled diagram should show these parts: Outer membrane; Inner membrane; Stromal lamella; Grana; DNA segments; Stroma; Ribosomes; Starch granule; Lipid droplet.

Question 44. (a) Give the diagrammatic representation of light-harvesting complex.
(b) Mention the experimental material used by the following
(i) Van Niel
(ii) Melvin Calvin
(iii) Englemann
(iv) Joseph Priestley
Answer: A well-labelled diagram should show these parts: (a); Primary acceptor; Photon; Reaction center; Pigment molecules; (b) (i); Purple and green bacteria; (ii) Cladophora , aerobic bacteria; (iii) Green alga – Chlorella; (iv) Mouse, Mint plant.

Question 45. Give the diagrammatic representation of Hatch and Slack pathway.
Answer: A well-labelled diagram should show these parts: Atmospheric CO2; Mesophyll; Plasma cell membrane; Cell wall; Phosphoenol; HCO3– pyruvate; Fixation; Regeneration; C4 acid; C3 acid; Plasmodesmata; Bundle sheath cell; Transport; Fixation by; Calvin cycle; CO2; Decarboxylation.