Skip to content
CNMS ICSE - 7 Std
Share
Explore

Answers to textbook exercises

Prepared by: learnloophq@gmail.com

Chapter: 04. Photosynthesis

⁠

Check Point

Write True or False.

Photosynthesis provides carbon dioxide for all living organisms.
False. Photosynthesis provides oxygen and organic food for living organisms, while consuming carbon dioxide.
Presence of starch is tested with the help of iodine solution.
True.
Stomata remain open at night.
False. Stomata get closed at night to prevent water loss when photosynthesis is not taking place.
Starch synthesised in leaves is transported to different plant parts.
False. Glucose is the water-soluble form of sugar that is transported (translocated) to different plant parts; starch is insoluble and used primarily for storage.
Plants are called autotrophs.
True.
⁠

Test Yourself

A. Multiple Choice Questions

This is the milk sugar. (a) Starch (b) Lactose © Sucrose (d) Glucose
Answer: (b) Lactose
This is used to test the presence of starch in food. (a) Iodine solution (b) Copper sulphate solution © Caustic soda (d) Benedict’s solution
Answer: (a) Iodine solution
Which set is correct for photosynthesis? (a) Carbon dioxide, sunlight, oxygen, chlorophyll (b) Nitrogen, water, carbon dioxide, chlorophyll © Carbon dioxide, water, sunlight, chlorophyll (d) Oxygen, nitrogen, water, chlorophyll
Answer: © Carbon dioxide, water, sunlight, chlorophyll
The green pigment in the leaves is (a) Chloroplast (b) Chlorophyll © Anthocyanin (d) Phycoerythrin
Answer: (b) Chlorophyll
Stomata are pores present on the surface of leaves surrounded by (a) Guard cells (b) Epidermal cells © Mesophyll cells (d) None of these
Answer: (a) Guard cells
⁠

B. Assertion-Reason Type Questions

(a) Both Assertion [A] and Reason [R] are true. ​(b) Both Assertion [A] and Reason [R] are false. ​© Assertion [A] is true but Reason [R] is false. ​(d) Assertion [A] is false but Reason [R] is true.
Assertion [A]: The second major product of photosynthesis is oxygen. ​Reason [R]: Oxygen is actually not a product of photosynthesis but a by-product or waste product.
Answer: (a) Both Assertion [A] and Reason [R] are true.
Assertion [A]: Plants and animals are called producers. ​Reason [R]: Organisms that produce their own food are called autotrophs or producers.
Answer: (d) Assertion [A] is false but Reason [R] is true. (Animals are consumers/heterotrophs, not producers).
Assertion [A]: Chlorophyll acts as a catalyst for photosynthesis to take place. ​Reason [R]: A catalyst is the substance that causes a chemical reaction to start and to continue.
Answer: © Assertion [A] is true but Reason [R] is false. (A catalyst accelerates a reaction without being consumed, rather than initiating or “causing it to start and continue”).
⁠

C. Fill in the blanks with suitable words.

Chlorophyll traps energy from _______________
sunlight (or solar energy)
___________ nutrition is found in nongreen plants.
Heterotrophic
The occurrence of photosynthesis can be confirmed by testing the presence of ___________ in the leaf.
starch
Starch turns colour of ___________ from purple to bluish-black.
iodine solution
⁠

D. State whether these statements are true or false. If false, rewrite the correct form of statements.

All plant cells carry out photosynthesis.
False. Only green plant cells containing chloroplasts (such as those in leaves and green stems) carry out photosynthesis. Non-green cells (like root cells) cannot.
Oxygen, during photosynthesis is released from carbon dioxide.
False. Oxygen is released from the splitting of water molecules (photolysis of water) during photosynthesis.
Chlorophyll is contained in chloroplasts.
True.
Optimum temperature for photosynthesis is 35°C.
False. The optimum temperature for photosynthesis is 20°C to 30°C.
Presence of starch in the leaves is tested using iodine solution.
True.
⁠

E. Give one word for the following.

Green plants that prepare their own food
Autotrophs
Microscopic openings on the under surface of leaf
Stomata
Hydrolysis of water into H⁺ and OH⁻ ions with the use of solar energy
Photolysis of water
End product of photosynthesis
Glucose
Presence of starch in the leaves is tested using iodine solution.
Iodine test
⁠

F. Encircle the odd one out and give reasons for your choice.

Protein, starch, cellulose, glucose
Protein. Reason: Starch, cellulose, and glucose are carbohydrates, whereas protein is a macromolecule composed of amino acids and containing nitrogen.
Starch, iodine, caustic soda
Caustic soda. Reason: Starch and iodine are associated with the starch test, whereas caustic soda is used in the test for proteins.
Chlorophyll, stomata, sulphur, carbon dioxide
Sulphur. Reason: Chlorophyll, stomata, and carbon dioxide are actively involved in the process of photosynthesis, while sulphur is not.
Leaves, chloroplasts, chlorophyll, roots
Roots. Reason: Leaves, chloroplasts, and chlorophyll are directly associated with the process of photosynthesis, whereas roots are underground structures primarily involved in water absorption.
⁠

G. Match the columns.

Column A (Question)
Column B (Matching Answer)
1. Product of photosynthesis
© Glucose
2. Chlorophyll
(e) Solar energy
3. Starch
(a) Storage
4. Water
(b) Source of oxygen
5. Stomata
(d) Closed at night
⁠
⁠

H. Answer these questions.

Why is glucose converted into starch immediately after its formation in the cells?
Answer: Glucose is highly soluble in water and chemically active, which can affect the osmotic pressure of the plant cells. Converting it into starch—which is insoluble in water and osmotically inactive—makes it safe and easy to store.
Too much bright light and high temperature above 45°C slow down photosynthesis. Why?
Answer: Too much bright light destroys chlorophyll molecules, while high temperatures above 45°C denature (deform) the enzymes (being proteins) that facilitate the chemical reactions of photosynthesis, rendering them inactive.
What is the role of carbon dioxide and water in the process of photosynthesis?
Answer:
Carbon dioxide acts as the source of carbon and oxygen to synthesize glucose molecules.
Water undergoes photolysis to release oxygen into the atmosphere and provides hydrogen ions (H⁺) which combine with carbon dioxide to form glucose.
How do chlorophyll and sunlight affect photosynthesis?
Answer:
Chlorophyll is the pigment that traps solar energy. Without it, light cannot be captured to drive the reaction.
Sunlight provides the energy required to split water molecules. Variations in sunlight duration, intensity, and quality directly determine the rate of photosynthesis.
Why are green plants called autotrophs?
Answer: Green plants are called autotrophs because they synthesize their own organic food (glucose) from simple inorganic compounds (carbon dioxide and water) using solar energy trapped by chlorophyll.
What does ‘photo’ represent in photosynthesis?
Answer: ‘Photo’ is derived from the Greek word meaning light.
Name the raw materials needed for photosynthesis.
Answer: The primary raw materials are carbon dioxide and water.
Write equation to represent the basics of photosynthesis.
Answer:
math
⁠
​(Or simplified as:
math
⁠
)
Which form of energy is utilised by chlorophyll? In which form is this energy converted during photosynthesis and stored in glucose?
Answer: Chlorophyll utilizes solar energy (light energy). This energy is converted into chemical energy during photosynthesis and stored within the chemical bonds of glucose.
⁠

I. Diagram-based Questions

Look at the picture of leaf and answer the questions. (a) Label the parts 1-4.
Answer:
1: Leaf blade (Lamina)
2: Vein
3: Leaf margin
4: Petiole (Leaf stalk) (b) How does a leaf get carbon dioxide from air?
Answer: Carbon dioxide from the atmosphere diffuses into the leaf through tiny microscopic pores called stomata present in the epidermis of the leaf. © Which part of the leaf carries out photosynthesis?
Answer: Photosynthesis is carried out in the mesophyll cells (such as the palisade layer and spongy parenchyma) of the leaf blade, which contain chloroplasts.
Draw and label open and closed stomata.
Answer: ​(Student-drawn diagram)
Key Labels for Open Stoma: Guard cells (turgid/swollen), Stomatal pore (open), Chloroplasts, Epidermal cells, Inner thick wall, Outer thin wall.
Key Labels for Closed Stoma: Guard cells (flaccid/shrunk), Stomatal pore (closed), Chloroplasts, Epidermal cells.
Observe the experimental set-up and answer the following questions: (a) Why is an aquatic plant used in the experiment?
Answer: An aquatic plant (like Hydrilla) is used because the oxygen produced during photosynthesis is released into the water as visible bubbles, allowing them to be collected and measured. (b) Why have these bubbles appeared in the set-up?
Answer: The bubbles appear because the Hydrilla plant is performing photosynthesis under sunlight and releasing oxygen gas, which travels upward through the water. © How is this gas evolved? Give the reaction.
Answer: This gas is evolved during the photolysis of water, where light energy splits water molecules.
Reaction:
math
⁠
math
⁠
⁠

J. Complete the words with the help of clues provided:

The presence of this substance is taken as evidence that photosynthesis has occurred.
S T A R C H
Structures present on the undersurface of leaves for exchange of gases.
S T O M A T A
Pigment necessary for photosynthesis.
C H L O R O P H Y L L
Presence of starch in leaf is tested by using this solution.
I O D I N E
⁠

K. Case-based Questions

The primary reason that leaves are green because their cells have: (a) Nucleus (b) Chloroplasts © Carotinoids (d) Photosynthesis
Answer: (b) Chloroplasts
The by-product of photosynthesis is: (a)
math
⁠
(b) Water © Oxygen (d) Hydrogen
Answer: © Oxygen
During photosynthesis, solar energy is used: (a) in splitting carbon dioxide to release oxygen. (b) in splitting water molecule into hydrogen and oxygen. © in the synthesis of glucose. (d) in all these processes.
Answer: (b) in splitting water molecule into hydrogen and oxygen.
⁠

ThinkZone

Why do the leaves of a plant kept in dark become yellow?
Answer: Chlorophyll synthesis requires light energy. When a plant is kept in the dark, it cannot produce new chlorophyll, and the existing chlorophyll breaks down over time, exposing the underlying yellow pigments (carotenoids).
Photosynthesis slows down above 40°C. Why?
Answer: Photosynthesis relies on specialized enzymes, which are proteins. At temperatures above 40°C, these enzymes denature (lose their shape and function), significantly reducing the rate of photosynthesis.
Gallery
 
Want to print your doc?
This is not the way.
Try clicking the ··· in the right corner or using a keyboard shortcut (
CtrlP
) instead.