RN Pre-Entrance Exam ,Biology practice questions , challenging
multiple-choice questions for each of these three categories:
1.Cell Structure,
2.Cell Division
3. Enzyme and Metabolism
4. Cellular Respiration and Photosynthesis
5. Genetics 6.Human Body systems
7. DNA & RNA
8. Ecology & Environment
9. Circulatory & Respiratory System
10. Immune System
11.Endocrine System
12. Reproductive System
Each question includes a correct answer and an explanation.
Photosynthesis
1. What are the two main stages of photosynthesis?
o Answer: Light-dependent reactions and the Calvin cycle.
o Explanation: Photosynthesis consists of light-dependent reactions, which
capture energy from sunlight, and the Calvin cycle, which uses this energy to
synthesize glucose.
2. Where in the cell does the light-dependent reaction of photosynthesis occur?
o Answer: Thylakoid membranes of the chloroplasts.
o Explanation: The light-dependent reactions take place in the thylakoid
membranes, where light energy is converted into chemical energy.
3. What is the primary pigment involved in photosynthesis?
o Answer: Chlorophyll a.
o Explanation: Chlorophyll a absorbs light energy, primarily in the blue and red
wavelengths, to drive photosynthesis.
4. What is the primary product of the light-dependent reactions of photosynthesis?
o Answer: ATP and NADPH.
o Explanation: The light-dependent reactions produce ATP and NADPH,
which are used in the Calvin cycle to synthesize glucose.
,5. What gas is released as a byproduct of photosynthesis?
o Answer: Oxygen (O₂).
o Explanation: Oxygen is produced as a byproduct of the splitting of water
molecules during the light-dependent reactions.
6. What is the main purpose of the Calvin cycle?
o Answer: To convert carbon dioxide into glucose.
o Explanation: The Calvin cycle uses ATP and NADPH from the light-
dependent reactions to fix carbon dioxide into glucose.
7. Which enzyme catalyzes the fixation of carbon dioxide in the Calvin cycle?
o Answer: Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase).
o Explanation: Rubisco is responsible for catalyzing the first step of the Calvin
cycle, where carbon dioxide is attached to a 5-carbon sugar.
8. What is the role of water in photosynthesis?
o Answer: To provide electrons and protons, and produce oxygen.
o Explanation: Water molecules are split during the light-dependent reactions
to provide electrons, protons, and oxygen.
9. How does the light intensity affect the rate of photosynthesis?
o Answer: The rate of photosynthesis increases with light intensity up to a
point, then levels off.
o Explanation: Light intensity affects the rate of photosynthesis by providing
more energy, but once all the pigments are saturated, further increases in light
do not affect the rate.
10. What is the role of NADP+ in photosynthesis?
o Answer: To carry electrons and hydrogen ions.
o Explanation: NADP+ accepts electrons and hydrogen ions to form NADPH,
which is used in the Calvin cycle.
11. What are the main products of photosynthesis?
o Answer: Glucose and oxygen.
o Explanation: Photosynthesis produces glucose for energy and oxygen as a
byproduct.
12. How do temperature changes affect photosynthesis?
o Answer: Photosynthesis rate increases with temperature up to an optimal
point, then decreases if the temperature is too high.
o Explanation: Enzymes involved in photosynthesis work efficiently at optimal
temperatures; extreme temperatures can denature them.
13. What is the significance of the photosystems in the light-dependent reactions?
o Answer: They capture and convert light energy into chemical energy.
o Explanation: Photosystems are complexes of chlorophyll and proteins that
absorb light and initiate the electron transport chain.
14. How does carbon dioxide concentration influence photosynthesis?
o Answer: Increasing carbon dioxide concentration increases the rate of
photosynthesis up to a certain point.
o Explanation: Carbon dioxide is a raw material in the Calvin cycle, so higher
concentrations can enhance the rate of photosynthesis.
15. What is the role of ATP synthase in photosynthesis?
o Answer: To synthesize ATP from ADP and inorganic phosphate.
o Explanation: ATP synthase utilizes the proton gradient generated by the
electron transport chain to produce ATP.
16. Which part of the chloroplast contains the enzymes for the Calvin cycle?
o Answer: The stroma.
, o Explanation: The stroma is the fluid-filled space in chloroplasts where the
Calvin cycle takes place.
17. What is a photon?
o Answer: A particle of light.
o Explanation: Photons are the units of light energy that are absorbed by
chlorophyll during the light-dependent reactions.
18. What is the main difference between C3 and C4 photosynthesis?
o Answer: C4 photosynthesis has a mechanism to concentrate carbon dioxide
and is more efficient in hot, dry conditions.
o Explanation: C4 plants have an additional step to fix carbon dioxide into a 4-
carbon compound, which helps reduce photorespiration.
19. What is photorespiration?
o Answer: A process where oxygen competes with carbon dioxide for the active
site of rubisco, leading to reduced photosynthetic efficiency.
o Explanation: Photorespiration occurs when rubisco fixes oxygen instead of
carbon dioxide, which can waste energy.
20. What is the role of the electron transport chain in photosynthesis?
o Answer: To transfer electrons and create a proton gradient that drives ATP
synthesis.
o Explanation: The electron transport chain moves electrons through a series of
proteins, creating a proton gradient used by ATP synthase to produce ATP.
Enzymes
1. What is an enzyme?
o Answer: A biological catalyst that speeds up chemical reactions.
o Explanation: Enzymes lower the activation energy of reactions, making them
proceed faster without being consumed.
2. How does an enzyme's active site function?
o Answer: It binds to specific substrates and facilitates their conversion into
products.
o Explanation: The active site of an enzyme is a specific region where
substrates bind and undergo a chemical reaction.
3. What is the difference between competitive and non-competitive inhibition?
o Answer: Competitive inhibition occurs when an inhibitor competes with the
substrate for the active site; non-competitive inhibition occurs when an
inhibitor binds elsewhere, altering the enzyme's activity.
o Explanation: Competitive inhibitors reduce enzyme activity by blocking the
active site, while non-competitive inhibitors reduce activity by changing the
enzyme's shape.
4. What is the role of cofactors in enzyme activity?
o Answer: Cofactors are non-protein molecules that assist enzymes in
catalyzing reactions.
o Explanation: Cofactors, such as metal ions or vitamins, are required for the
proper functioning of many enzymes.
5. How does temperature affect enzyme activity?
o Answer: Enzyme activity increases with temperature up to an optimal point,
then decreases if the temperature is too high.
o Explanation: Higher temperatures increase molecular movement, enhancing
reaction rates, but extreme temperatures can denature enzymes.
, 6. What is an enzyme-substrate complex?
o Answer: A temporary molecule formed when an enzyme binds to its
substrate.
o Explanation: The enzyme-substrate complex is the intermediate state in
which the substrate is held in place for a reaction to occur.
7. What is meant by enzyme specificity?
o Answer: Enzymes are specific to their substrates due to the precise fit
between the enzyme's active site and the substrate.
o Explanation: Enzyme specificity refers to the ability of an enzyme to choose
the exact substrate from a group of similar molecules.
8. What happens to an enzyme after a reaction is complete?
o Answer: The enzyme is released unchanged and can catalyze another
reaction.
o Explanation: Enzymes are not consumed in the reaction and can be used
repeatedly to catalyze multiple reactions.
9. What is the effect of pH on enzyme activity?
o Answer: Enzyme activity is optimal at a specific pH, and deviating from this
pH can reduce activity or denature the enzyme.
o Explanation: pH affects the charge and structure of the enzyme and its
substrate, influencing the reaction rate.
10. What is an enzyme inhibitor?
o Answer: A substance that decreases the activity of an enzyme.
o Explanation: Inhibitors can bind to the enzyme and prevent it from catalyzing
its reaction, either by blocking the active site or altering enzyme structure.
11. What is an allosteric site?
o Answer: A site on an enzyme other than the active site that can regulate
enzyme activity.
o Explanation: Binding to an allosteric site can change the enzyme’s shape and
activity, either activating or inhibiting its function.
12. What are enzyme activators?
o Answer: Molecules that increase the activity of an enzyme.
o Explanation: Activators enhance enzyme function by binding to the enzyme
and improving its ability to catalyze reactions.
13. How does substrate concentration affect enzyme activity?
o Answer: Increasing substrate concentration increases the reaction rate until
the enzyme is saturated.
o Explanation: As substrate concentration rises, more enzyme-substrate
complexes form, speeding up the reaction, but eventually, all active sites are
occupied.
14. What is the Michaelis-Menten constant (Km)?
o Answer: The substrate concentration at which the reaction rate is half of the
maximum velocity (Vmax).
o Explanation: Km is a measure of the affinity of the enzyme for its substrate; a
low Km indicates high affinity.
15. What is the turnover number (kcat) of an enzyme?
o Answer: The number of substrate molecules converted to product per enzyme
molecule per unit time.
o Explanation: The turnover number indicates the efficiency of an enzyme in
catalyzing reactions.
16. What is enzyme denaturation?
