Question
▶️Answer/Explanation
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 synthesised in apical meristems.
▶️Answer/Explanation
Ans. C
Auxin (IAA) is transported down to the root tip from the shoot in the vascular cylinder. Here it is redistributed to the root cortex and epidermis, and transported back up the root to the elongation zone, where it regulates the rate of cell elongation.
The plant hormone auxin causes cell elongation by loosening cell walls, which allows the cells to grow:
Auxin can cause rapid cell elongation in higher plants. In some plant species, auxin can start promoting cell elongation within 10–15 minutes, and reach its maximum rate within 30–45 minutes.
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
Ans. B
In photosynthesis, ATP is required for the following processes:
1. The Calvin Cycle (Light-independent reactions):
– ATP is used in the Calvin cycle to convert 3-phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate** (G3P), a sugar. Specifically, ATP provides the energy needed for the phosphorylation of intermediates in the cycle.
2. The regeneration of RuBP:
– ATP is also used to regenerate ribulose bisphosphate (RuBP) from G3P, which is necessary for the Calvin cycle to continue. This process involves the enzyme RuBP carboxylase/oxygenase (RuBisCO) and ATP for further enzymatic reactions.
However, ATP is not required during the light-dependent reactions themselves to generate high-energy molecules like NADPH or to drive the photolysis of water. The light reactions primarily involve the use of light energy to generate ATP and NADPH, which are then used in the Calvin cycle.
So, to summarize:
– ATP is used in the Calvin cycle (light-independent reactions) to drive carbon fixation and regenerate RuBP.
– ATP is not directly required in the light-dependent reactions, but it is produced by them.
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
Ans. B
At the given point light intensity is maximum so the CO2 concentration acts as a limiting factor .
-
Light
At low light intensities, light is the limiting factor because increasing light increases the rate of photosynthesis. However, at higher light intensities, the rate of photosynthesis levels off and another factor becomes limiting.
-
Temperature
At higher temperatures, the rate of photosynthesis increases until it reaches an optimum point. After that, the rate decreases as the enzymes denature and can no longer catalyze the reaction.
-
Carbon dioxide
Increasing the concentration of carbon dioxide increases the rate of photosynthesis, as long as the plant has enough light, water, and is warm enough.
-
Chlorophyll
As the amount of chlorophyll increases, more light can be trapped by the chloroplasts to drive the reaction. However, once there is enough chlorophyll, it will no longer be a limiting factor
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
Ans: C
Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.
Plants have a pigment called chlorophyll that gives them their green color and helps them absorb energy from light. Chlorophyll absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green. Therefore, green light is the least effective for plants because they cannot use it to photosynthesize.
So, if a plant is exposed to the light, which colour of light would lead to the lowest rate of oxygen release by a green plant? The answer is green light because it is mostly reflected by the plant and not used for photosynthesis.
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
Phylum filicinophyta Fonds (pinnate leaves) Sporangia Rhizoid Roots Mitochondria and chloroplasts are organelles that are involved in energy production in eukaryotic cells. Mitochondria break down fuel molecules and capture energy in cellular respiration, while chloroplasts capture light energy and make sugars in photosynthesis. Both organelles have their own DNA and ribosomes, and are thought to have evolved from bacteria that were engulfed by larger cells.
Flilicinophyta is another name for ferns, a group of vascular plants that reproduce by spores. Ferns have both mitochondria and chloroplasts in their cells, as they are photosynthetic plants that also need to respire. Ferns belong to the clade Polypodiopsida, which is a sister group to seed plants.
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
Ans: C
RF value stands for retardation factor or relative front. It is a ratio of the distance travelled by a solute (the substance being separated) to the distance travelled by the solvent (the liquid carrying the solute) on a chromatography paper. It is a characteristic of the solute and can be used to identify it in a chromatographic system.
The RF value formula is: Distance travelled by the solute divided by the distance travelled by the solvent
The RF value is important because it indicates how well the solute is separated by the solvent and how strongly it interacts with the stationary phase (the paper or other material that does not move) and the mobile phase (the solvent that moves) . Different solutes have different RF values depending on their polarity, relative mass, and relative solubility. The RF value can also be affected by factors such as temperature, solvent composition, and paper quality.