LifeProcess-D Explained - Kashmir Study

📘 Welcome

Hi User, you have selected Read Mode. This is Time Free (Unlimited) for your ease to understand every question as per your Ease and Time.

Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main window designed with Exam Features.

🔊 Voice Sound ON

Q1. What is the first event that happens during photosynthesis when sunlight falls on a leaf?

A. Carbon dioxide is reduced to glucose

B. Light energy is absorbed by chlorophyll

C. Water molecules are split into hydrogen and oxygen

D. Stomata open automatically

Light energy is absorbed by chlorophyll

The very first event is the absorption of light photons by chlorophyll pigments. This absorption excites electrons and initiates all subsequent steps. CO₂ reduction occurs later in the Calvin cycle, water splitting happens after light absorption, and stomatal opening is a separate regulated process.

Q2. Which pigment present in green plants is primarily responsible for the absorption of light energy during photosynthesis?

A. Carotene

B. Xanthophyll

C. Chlorophyll

D. Anthocyanin

Chlorophyll

Chlorophyll is the primary photosynthetic pigment that absorbs light energy, mainly in the blue and red wavelengths. Carotene and xanthophyll are accessory pigments that capture other wavelengths and pass energy to chlorophyll. Anthocyanin is a non-photosynthetic pigment responsible for red/purple colors in fruits and flowers.

Q3. What happens immediately after chlorophyll absorbs light energy during photosynthesis?

A. Carbon dioxide is fixed into carbohydrates

B. The energy is used to split water molecules

C. The energy is converted into chemical energy and electrons become excited

D. Stomata close to prevent water loss

The energy is converted into chemical energy and electrons become excited

Upon light absorption, chlorophyll molecules enter an excited state where electrons jump to a higher energy level. This excited energy is then converted into chemical potential energy as the electrons are passed through an electron transport chain. Water splitting is driven by this excited electron deficit, not directly.

Q4. During the conversion of light energy to chemical energy, which two energy-rich molecules are produced?

A. Glucose and oxygen

B. ATP and NADPH

C. Carbon dioxide and water

D. Chlorophyll and carotene

ATP and NADPH

Light reactions convert solar energy into chemical energy stored in ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). These molecules are then used in the Calvin cycle to reduce CO₂ to glucose. Glucose and oxygen are end products, not the immediate energy carriers.

Q5. What happens during the splitting of water molecules (photolysis) in photosynthesis?

A. Water molecules combine with carbon dioxide to form glucose

B. Water molecules are broken down into hydrogen and oxygen using light energy

C. Water molecules are transported from roots to leaves

D. Water molecules are converted into ATP directly

Water molecules are broken down into hydrogen and oxygen using light energy

Photolysis is the light-driven reaction: 2H₂O → 4H⁺ + 4e⁻ + O₂. The electrons replace those lost from photosystem II, protons contribute to ATP synthesis, and oxygen is released. Water is not directly converted to ATP, nor does it combine directly with CO₂.

Q6. What is the fate of the oxygen produced during the splitting of water molecules in photosynthesis?

A. It is used to break down glucose

B. It is combined with hydrogen to form water again

C. It is released into the atmosphere through stomata

D. It is stored in the chloroplast for later use

It is released into the atmosphere through stomata

Oxygen is a byproduct of photolysis and is not used further in photosynthesis. It diffuses out of the leaf through open stomata. This oxygen is essential for aerobic respiration in plants and other organisms.

Q7. What happens to the hydrogen produced from the splitting of water molecules?

A. It is released as hydrogen gas into the atmosphere

B. It is used to reduce carbon dioxide into carbohydrates

C. It combines with oxygen to make water inside the leaf

D. It is stored in the vacuole of the plant cell

It is used to reduce carbon dioxide into carbohydrates

The hydrogen (protons and electrons) from water splitting ends up in NADPH. NADPH then donates these hydrogens (as H atoms) to reduce carbon dioxide into carbohydrates in the Calvin cycle. Hydrogen is not released as gas.

Q8. What is the reduction of carbon dioxide to carbohydrates?

A. The process of adding oxygen to carbon dioxide

B. The process of removing hydrogen from carbon dioxide

C. The process of adding hydrogen to carbon dioxide to form glucose

D. The process of breaking down glucose into carbon dioxide

The process of adding hydrogen to carbon dioxide to form glucose

In chemical terms, reduction means gaining electrons (often accompanied by hydrogen). CO₂ (low in hydrogen) is reduced to glucose (C₆H₁₂O₆) by addition of hydrogen atoms from NADPH. Removing hydrogen would be oxidation, and adding oxygen is not what happens.

Q9. Where does the reduction of carbon dioxide to carbohydrates take place inside a plant cell?

A. In the thylakoid membrane of the chloroplast

B. In the stroma of the chloroplast

C. In the nucleus of the cell

D. In the mitochondria

In the stroma of the chloroplast

The stroma is the fluid-filled space surrounding the thylakoids. It contains the enzymes of the Calvin cycle, including RuBisCO, where CO₂ is fixed and reduced to carbohydrates. Thylakoid membranes host light reactions, mitochondria perform cellular respiration, and the nucleus stores DNA.

Q10. Which enzyme is responsible for fixing carbon dioxide during its reduction to carbohydrates?

A. Pepsin

B. Trypsin

C. RuBisCO (Ribulose bisphosphate carboxylase-oxygenase)

D. Amylase

RuBisCO (Ribulose bisphosphate carboxylase-oxygenase)

RuBisCO catalyzes the first step of the Calvin cycle: combining CO₂ with RuBP (ribulose bisphosphate) to form an unstable 6-carbon intermediate that splits into two molecules of 3-PGA. Pepsin and trypsin are digestive enzymes, and amylase breaks down starch.

Q11. What is the first stable product formed when carbon dioxide is reduced to carbohydrates in C3 plants?

A. Glucose

B. Starch

C. 3-phosphoglyceric acid (PGA)

D. Oxaloacetic acid (OAA)

3-phosphoglyceric acid (PGA)

After RuBisCO fixes CO₂ onto RuBP, the unstable 6C intermediate immediately splits into two molecules of 3-phosphoglyceric acid (3PGA), a 3-carbon compound. Glucose and starch are end products much later. OAA is the first stable product in C4 plants, not C3.

Q12. During the reduction of carbon dioxide to carbohydrates, what is the role of ATP?

A. ATP provides oxygen for the reaction

B. ATP provides the energy needed to convert PGA into glucose

C. ATP splits water molecules

D. ATP absorbs light energy

ATP provides the energy needed to convert PGA into glucose

ATP from light reactions provides the chemical energy to drive the endergonic (energy-requiring) steps of the Calvin cycle, specifically converting 3-PGA into G3P (glyceraldehyde-3-phosphate). ATP does not split water (photolysis does) nor absorb light.

Q13. During the reduction of carbon dioxide to carbohydrates, what is the role of NADPH?

A. NADPH absorbs sunlight

B. NADPH provides the hydrogen atoms to reduce carbon dioxide

C. NADPH splits water molecules

D. NADPH closes the stomata

NADPH provides the hydrogen atoms to reduce carbon dioxide

NADPH is the reducing agent. It donates electrons and hydrogen ions (H⁺) to convert 3-PGA into G3P, effectively adding hydrogen to reduce carbon dioxide into carbohydrate form. Without NADPH, carbon fixation cannot proceed to sugar formation.

Q14. Which of the following correctly represents the overall chemical equation for the reduction of carbon dioxide to carbohydrates?

A. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

B. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

C. 6CO₂ + 6O₂ → C₆H₁₂O₆ + 6H₂O

D. C₆H₁₂O₆ + 6H₂O → 6CO₂ + 6H₂O

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

This is the overall photosynthesis equation. Six molecules of carbon dioxide and six of water are converted into one glucose molecule and six oxygen molecules. Option B is cellular respiration (reverse reaction). Options C and D are incorrect.

Q15. What are stomata?

A. Green pigments present in leaves

B. Tiny pores present on the surface of leaves

C. Roots that absorb water

D. Cells that perform photosynthesis

Tiny pores present on the surface of leaves

Stomata (singular: stoma) are microscopic pores, primarily on leaf surfaces (and some stems), that allow gas exchange. Each stoma is surrounded by two guard cells. They are not pigments, roots, or photosynthetic cells themselves.

Q16. What is the function of open stomatal pores during photosynthesis?

A. To prevent water loss from the leaf

B. To allow carbon dioxide to enter the leaf for reduction and oxygen to exit

C. To absorb light energy for chlorophyll

D. To transport glucose to other parts of the plant

To allow carbon dioxide to enter the leaf for reduction and oxygen to exit

Stomata are the primary route for gas exchange. CO₂ enters for the Calvin cycle, and O₂ (produced in photolysis) exits. Glucose transport occurs through phloem, not stomata. Open stomata actually allow water loss (transpiration), not prevent it.

Q17. Which cells are responsible for the opening and closing of stomatal pores?

A. Epidermal cells

B. Mesophyll cells

C. Guard cells

D. Xylem cells

Guard cells

Each stoma is surrounded by two specialized guard cells that change shape to open or close the pore. They do so by gaining or losing water (turgor pressure). Epidermal cells are the leaf surface cells, mesophyll cells perform photosynthesis, and xylem transports water.

Q18. What happens to the guard cells when water enters them?

A. They become flaccid and the stomatal pore closes

B. They become turgid (swollen) and the stomatal pore opens

C. They divide to form more guard cells

D. They lose chlorophyll and become colorless

They become turgid (swollen) and the stomatal pore opens

When water enters guard cells via osmosis (due to ion uptake), they become turgid. Their unevenly thickened cell walls cause them to bow apart, creating an open pore. Flaccid guard cells close the pore. Guard cells do not divide or lose chlorophyll for normal opening/closing.

Q19. What happens to the guard cells when they lose water?

A. They become turgid and the stomatal pore opens

B. They become flaccid (shriveled) and the stomatal pore closes

C. They become longer and wider

D. They start performing photosynthesis rapidly

They become flaccid (shriveled) and the stomatal pore closes

When guard cells lose water (due to ion loss or water stress), their turgor pressure drops, making them flaccid. The cells relax and the pore closes to prevent further water loss. This is the opposite of the turgid/open state.

Q20. Why do stomata generally remain open during the daytime?

A. Because the plant wants to lose as much water as possible

B. Because light triggers the guard cells to take up water and open, allowing CO₂ for photosynthesis

C. Because the plant wants to store oxygen inside the leaves

D. Because the temperature is lower during the day

Because light triggers the guard cells to take up water and open, allowing CO₂ for photosynthesis

Light activates proton pumps in guard cell membranes, leading to ion uptake, water influx, and turgor increase. This opens stomata specifically to allow CO₂ entry for the Calvin cycle. Water loss is an unavoidable consequence, not the purpose.

Q21. Why do stomata often close at night?

A. Because the plant does not need carbon dioxide at night since no light means no reduction of CO₂ to carbohydrates

B. Because the plant wants to absorb more oxygen

C. Because the guard cells lose chlorophyll at night

D. Because the roots stop supplying water at night

Because the plant does not need carbon dioxide at night since no light means no reduction of CO₂ to carbohydrates

At night, light reactions stop, so no ATP/NADPH is produced. The Calvin cycle cannot run, so CO₂ is not needed. Closing stomata conserves water when gas exchange is unnecessary. Guard cells retain chlorophyll; roots supply water continuously.

Q22. What happens to the absorption of light energy by chlorophyll if the stomata are closed?

A. Absorption increases because more light enters

B. Absorption decreases because chlorophyll becomes inactive

C. Absorption of light energy can still occur, but without CO₂, the reduction step cannot proceed

D. Chlorophyll changes its color and stops absorbing light

Absorption of light energy can still occur, but without CO₂, the reduction step cannot proceed

Light absorption by chlorophyll is independent of stomatal state. However, if stomata are closed, CO₂ cannot enter. Light reactions may still produce ATP and NADPH, but without CO₂, the Calvin cycle stops, and photorespiration or photodamage may occur.

Q23. During the conversion of light energy to chemical energy, where are the ATP and NADPH produced?

A. In the stroma of the chloroplast

B. In the thylakoid membrane of the chloroplast

C. In the nucleus of the cell

D. In the cell wall

In the thylakoid membrane of the chloroplast

ATP is synthesized by ATP synthase located in the thylakoid membrane, driven by proton gradient formed across it. NADPH is produced on the stroma side of the thylakoid membrane. The stroma is where these molecules are used, not produced.

Q24. What is the immediate source of electrons for the reduction of carbon dioxide to carbohydrates?

A. Chlorophyll directly

B. Oxygen gas

C. NADPH (which gets electrons from the splitting of water)

D. Carbon dioxide itself

NADPH (which gets electrons from the splitting of water)

NADPH carries high-energy electrons (originally from water splitting) to the Calvin cycle. It donates these electrons to reduce 3-PGA to G3P. Chlorophyll provides excited electrons but not directly to CO₂ reduction; oxygen is not a source.

Q25. If a plant is kept in an environment with no carbon dioxide but plenty of sunlight and water, what will happen?

A. Absorption of light energy and splitting of water will continue, but reduction of CO₂ to carbohydrates will stop

B. All steps of photosynthesis will continue normally

C. Only the reduction of CO₂ will happen using stored carbon

D. Splitting of water will stop immediately

Absorption of light energy and splitting of water will continue, but reduction of CO₂ to carbohydrates will stop

Light reactions (absorption and photolysis) can proceed without CO₂ because they only require light and water. However, without CO₂, the Calvin cycle cannot operate. Electrons may instead go to oxygen (photorespiration) causing stress.

Q26. During the reduction of carbon dioxide to carbohydrates, how many molecules of CO₂ are needed to make one molecule of glucose (C₆H₁₂O₆)?

A. 1 molecule

B. 3 molecules

C. 6 molecules

D. 12 molecules

6 molecules

One glucose molecule contains 6 carbon atoms. Each CO₂ molecule provides one carbon atom. Therefore, 6 CO₂ molecules are required per glucose. The Calvin cycle fixes 3 CO₂ to produce a 3-carbon G3P; two G3Ps combine to form glucose, requiring 6 CO₂ total.

Q27. What happens to the carbohydrates produced after the reduction of carbon dioxide?

A. They are immediately broken down back into CO₂

B. They are converted into other organic compounds like starch, cellulose, and oils for storage, energy, and growth

C. They are stored only as glucose in the vacuole

D. They are excreted out through stomata

They are converted into other organic compounds like starch, cellulose, and oils for storage, energy, and growth

The initial carbohydrate product (G3P) is used to synthesize glucose, which is then converted to starch (storage), cellulose (cell walls), sucrose (transport), and oils (seeds). Free glucose is not stored in vacuoles; it would cause osmotic problems.

Q28. How do open stomatal pores help in the splitting of water molecules?

A. They directly split water using light energy

B. They allow carbon dioxide to enter, which indirectly creates a demand for the products of water splitting (hydrogen for CO₂ reduction)

C. They prevent oxygen from leaving, which speeds up water splitting

D. They absorb light for the guard cells only

They allow carbon dioxide to enter, which indirectly creates a demand for the products of water splitting (hydrogen for CO₂ reduction)

Stomata do not split water. However, by allowing CO₂ entry, they enable the Calvin cycle to consume NADPH, which in turn drives the need for electrons from water splitting. Without CO₂, the demand for water splitting decreases.

Q29. In very hot and dry conditions, plants close their stomata. What happens to the reduction of carbon dioxide to carbohydrates under these conditions?

A. It increases because the plant saves water

B. It decreases or stops because carbon dioxide cannot enter the leaf

C. It continues using oxygen instead of carbon dioxide

D. It happens only at night

It decreases or stops because carbon dioxide cannot enter the leaf

Closed stomata block CO₂ entry. Without CO₂, the Calvin cycle cannot fix carbon, so carbohydrate production stops or drastically reduces. The plant may switch to photorespiration (using O₂ instead of CO₂), which is wasteful and does not produce carbohydrates.

Q30. Arrange the following events of photosynthesis in the correct order:

A. 2 → 4 → 3 → 1

B. 2 → 3 → 4 → 1

C. 1 → 2 → 3 → 4

D. 4 → 2 → 3 → 1

2 → 3 → 4 → 1

The correct sequence is: (2) Light absorption by chlorophyll → (3) Water splitting (photolysis) replaces excited electrons → (4) Light energy converts to chemical energy (ATP/NADPH) via electron transport → (1) ATP/NADPH drive CO₂ reduction to carbohydrates in Calvin cycle.