Question
▶️Answer/Explanation
A. Incorrect – At low light intensity, light is still a limiting factor. Temperature affects the rate only when light and CO₂ are sufficient.
B. Correct – At 0.1% CO₂ and low light, the graph would show a low photosynthesis rate. Since CO₂ is relatively high and light is low, light intensity is the limiting factor.
C. Incorrect – While CO₂ is low at 0.03%, if light intensity is also low, it remains the main limiting factor. We can’t assume temperature is also limiting without further data.
D. Incorrect – Even above 0.1% CO₂, if light or temperature are low, they can still limit the rate of photosynthesis. So other limiting factors can exist.
Question
A group of students studied the impact of auxins on shoots exposed to various treatments. The diagrams illustrate one of these treatments (T1) and the control (C) at both the start of the experiment and after one week. During the experiment, light was provided from all directions. What might explain the results observed for T1 after one week?
A. Cell division along the shoot was inhibited due to a lack of auxins.
B. Mitosis stopped in the apical meristem due to a low auxin concentration.
C. Cell elongation did not occur as auxins could not diffuse downwards.
D. Cell differentiation slowed down as auxins were not synthesized in apical meristems.
▶️Answer/Explanation
Answer: C. Cell elongation did not occur as auxins could not diffuse downwards.
Explanation:
Role of Auxins in Shoots
Auxins are plant hormones produced in the apical meristem (shoot tip) and move down the stem. They promote cell elongation, which is essential for shoot growth. If the tip is removed or damaged, auxin production stops, and shoot growth slows or halts.
A. Incorrect – Cell division may still occur, but elongation, which depends on auxins, is affected more directly.
B. Incorrect – Mitosis occurs in the apical meristem itself. If the meristem is removed, it no longer divides but this isn’t due to low auxin.
C. Correct – Without the apical tip, auxins are not produced and cannot diffuse downward, so cell elongation does not happen.
D. Incorrect – Auxins are normally synthesized in apical meristems. If the meristem is gone, synthesis stops but this doesn’t slow differentiation, it stops the signal for elongation.
Question
Which of the following processes require(s) ATP during photosynthesis?
I. The splitting of water molecules
II. The regeneration of ribulose bisphosphate (RuBP)
III. The maintenance of a proton gradient between the thylakoid space and the stroma
A. I only
B. II only
C. I and II
D. II and III
▶️Answer/Explanation
Answer: B. II only
Explanation:
ATP Use in Photosynthesis
Photosynthesis occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).
- ATP is produced during the light-dependent reactions.
- It is then used in the Calvin cycle for two main steps: conversion of 3-carbon compounds and regeneration of RuBP.
- The splitting of water (photolysis) does not require ATP it is driven by light energy.
- Proton gradients are created by the electron transport chain, not by ATP input.
Evaluation of options:
I. Incorrect – The splitting of water is driven by light energy absorbed by photosystem II, not by ATP.
II. Correct – Regeneration of RuBP in the Calvin cycle requires ATP, which is used to rearrange molecules into the 5-carbon RuBP.
III. Incorrect – The proton gradient forms as electrons move through the electron transport chain, actively pumping protons using the energy of electrons, not using ATP directly.
Question
The graph illustrates the impact of increasing light intensity on the rate of photosynthesis in an experiment conducted at optimal temperature and normal atmospheric CO2 concentration.
Which factor might be limiting photosynthesis at point X on the graph?
A. Light intensity
B. Carbon dioxide concentration
C. Temperature
D. Nutrient availability
▶️Answer/Explanation
Answer: B. Carbon dioxide concentration
Explanation:
Identifying Limiting Factors
As light intensity increases, so does the photosynthesis rate until it levels off. That plateau (like at point X) means light is no longer the limiting factor, so something else is.
A. Incorrect – The rate is no longer increasing with light, so light is not limiting.
B. Correct – If light is sufficient and temperature is optimal, then CO₂ is likely limiting the rate at point X.
C. Incorrect – The experiment is done at optimal temperature, so it’s not a limiting factor.
D. Incorrect – Nutrients are not directly related to short-term photosynthesis rate in such experiments.
Question
If a plant is exposed to light, which colour of light would lead to the lowest rate of oxygen release by a green plant?
Blue
Red
Green
White
▶️Answer/Explanation
Answer: C. Green
Explanation:
Light Absorption in Photosynthesis
Chlorophyll absorbs blue and red light well, but reflects green light, which is why plants look green. Photosynthesis, and therefore oxygen production, is lowest under green light.
Let’s analyze the options:
Blue: Incorrect – Blue light is strongly absorbed and supports high photosynthesis.
Red: Incorrect – Red light is also absorbed effectively.
Green: Correct – Green light is reflected, not absorbed, so it contributes the least to photosynthesis.
White: Incorrect – White light includes all wavelengths, so supports photosynthesis well.
Question
What do chloroplasts and mitochondria have in common?
Both are found in the cells of Filicinophyta.
Both contain grana.
Both occur in all eukaryotic cells.
Both are found in a Paramecium.
▶️Answer/Explanation
Answer: A. Both are found in the cells of Filicinophyta.
Explanation:
Similarities and Differences Between Chloroplasts and Mitochondria
Chloroplasts and mitochondria are both double-membraned organelles involved in energy transformations in cells.
- Mitochondria carry out aerobic respiration and are found in all eukaryotic cells, including animals, plants, fungi, and protists.
- Chloroplasts carry out photosynthesis and are only found in plant cells and some photosynthetic protists (like algae).
- Both organelles have their own DNA, ribosomes, and can replicate independently of the nucleus.
- Grana are structures unique to chloroplasts, not mitochondria.
Evaluation of Options:
A. Correct – Filicinophyta (ferns) are plants. Their cells have both mitochondria and chloroplasts, so this is true.
B. Incorrect – Only chloroplasts have grana (stacks of thylakoid membranes). Mitochondria do not contain grana.
C. Incorrect – While mitochondria are found in all eukaryotic cells, chloroplasts are not (e.g., animal and fungal cells lack chloroplasts).
D. Incorrect – Paramecium is a heterotrophic protist and does not perform photosynthesis. It contains mitochondria, but not chloroplasts.
Question
What does the Rf value in thin layer chromatography represent?
The distance travelled by the pigment front in a fixed time period
The distance from the origin to the solvent front at the end of the experiment
The ratio of distances travelled by the pigment and solvent fronts
The concentration of the pigment applied to the chromatography plate
▶️ Answer/Explanation
Answer: C. The ratio of distances travelled by the pigment and solvent fronts
Explanation:
Rf (Retention Factor)
The Rf value is used to identify pigments based on their movement in chromatography. It’s the ratio of the distance a pigment travels to the distance the solvent front moves. It is unitless and helps compare pigments in different conditions.
A. Incorrect – Rf isn’t based on time.
B. Incorrect – That describes the solvent front, not the Rf.
C. Correct – Rf = distance pigment travelled ÷ distance solvent front travelled.
D. Incorrect – Rf doesn’t measure concentration.