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Chapter 4

Photosynthesis and Respiration

Class 7 - Concise Biology Selina


Multiple Choice Questions

Question 1

Carbohydrates are stored by plants in the form of:

  1. Starch
  2. Proteins
  3. Fats
  4. Glucose

Answer

Starch

Reason — Glucose is formed in leaves very rapidly during the photosynthesis and it cannot be transported to other parts with the same rapidity. So, several molecules of glucose join together to form insoluble starch for temporary storage.

Question 2

Stomata are present on the surface of:

  1. Leaves
  2. Roots
  3. Stem
  4. Flower petals

Answer

Leaves

Reason — Stomata are present on the surface of leaves to facilitate exchange of gases between the leaf and the atmosphere.

Question 3

Which one of the following is the immediate end-product of photosynthesis?

  1. Fructose
  2. Glucose
  3. Cellulose
  4. Lactose

Answer

Glucose

Reason — Fructose, Cellulose and lactose are polymers of glucose.

Short Answer Questions

Question 1

Why do leaves generally look green?

Answer

Leaves generally look green because of the presence of chlorophyll, a pigment that imparts green colour to leaves.

Question 2

Which four of the following are needed for photosynthesis in a leaf?

  1. Carbon dioxide
  2. Oxygen
  3. Nitrates
  4. Water
  5. Chlorophyll
  6. Soil
  7. Light

Answer

Following are the four things which are needed for photosynthesis in a leaf:

  1. Carbon dioxide
  2. Water
  3. Chlorophyll
  4. Light

Question 3

What is the source of energy for photosynthesis?

Answer

The source of energy for photosynthesis is Sunlight.

Question 4

Which gas is taken in and which one is given out by a green leaf in bright sunlight?

(i) Taken in: ............... (ii) Given out: ...............

Answer

(i) Taken in: Carbon dioxide (ii) Given out: Oxygen

Question 5

Suppose we compare the leaf with a factory, match the items in Column A with those in Column B.

Sl.
No.
Column AColumn B
1.Cells in the leafRaw materials
2.ChloroplastPower
3.SunlightMachinery
4.Oxygen and waterEnd product
5.Carbon dioxide and waterBy product
6.GlucoseWork room

Answer

Sl.
No.
Column AColumn B
1.Cells in the leafWork room
2.ChloroplastMachinery
3.SunlightPower
4.Oxygen and waterBy product
5.Carbon dioxide and waterRaw materials
6.GlucoseEnd product

Question 6

State whether the following statements are True or False:

(i) Green plants prepare their food by using two raw materials, oxygen and water.

(ii) The chlorophyll enables the plants to use light energy.

(iii) The free oxygen in the atmospheric air is the result of photosynthesis.

(iv) Photosynthesis occurs only in chlorophyll-containing parts of the plant.

Answer

(i) False
Corrected Statement — Green plants prepare their food by using two raw materials; Carbon dioxide and water.

(ii) True

(iii) True

(iv) True

Question 7

Differentiate between aerobic and anaerobic respiration. Write the overall chemical equations of the two kinds of respiration in plants.

(i) Aerobic: ...............

(ii) Anaerobic: ...............

Answer

Sl.
No.
Aerobic RespirationAnaerobic Respiration
1.It utilizes oxygen.It does not utilize oxygen.
2.Food molecules (glucose) completely break down.Food molecules (glucose) partially break down.
3.Carbon dioxide and water are formed.Ethanol along with carbon dioxide (in plants) and lactic acid (in animals) are formed.
4.More energy is released (38 ATP molecules).Less energy is released (2 ATP molecules).

Chemical equations of the two kinds of respiration in plants are:

(i) Aerobic:

Glucose + Oxygen Enzymes\xrightarrow{\text{Enzymes}} Carbon dioxide + water + Energy (38 ATP)

(ii) Anaerobic:

Glucose Enzymes\xrightarrow{\text{Enzymes}} Ethanol + Carbon dioxide + Energy (2 ATP)

Question 8

Explain how photosynthesis is different from respiration.

Answer

The differences between Photosynthesis and Respiration are explained below:

Sl.
No.
PhotosynthesisRespiration
1.Food is synthesized.Food is broken down.
2.Oxygen is released as a by-product.Carbon dioxide is released as a by-product.
3.Occurs in plant cells containing chlorophyll.Occurs in all cells of both plants and animals.
4.Occurs only during the day.Occurs both during the day and the night.

Question 9

Do the plants respire all day and night or only during the day? Give reasons.

Answer

Plants respire all day and night as plants require a constant supply of energy for all the different processes that go on inside the cells of the plant body. Energy is required for the growth of the plant, for root cells to penetrate the soil and absorb water and minerals and so many other such activities. Thus, Respiration occurs continuously in plants, during both day and night.

Question 10

What happens to the energy liberated during respiration?

Answer

The energy liberated during respiration is utilized for all the different processes that go on inside the cells of the plant body. Energy is required for the growth of the plant, for root cells to penetrate the soil and absorb water and minerals.

Long Answer Questions

Question 1

In order to carry out photosynthesis, what are the substances that a plant must take in? Also mention their sources.

Answer

In order to carry out photosynthesis, the substances that a plant must take in are Carbon dioxide and Water. Photosynthesis also require the presence of Chlorophyll and Sunlight.

Following are their sources:

  • Carbon dioxide — Atmosphere
  • Water — Soil
  • Sunlight — Sun
  • Chlorophyll — contained in the leaves.

Question 2

What is the role of chlorophyll in photosynthesis?

Answer

Chlorophyll is found in mesophyll cells of leaf, inside the plastids called chloroplast. Chlorophyll is very important as it absorbs the sunlight which provides energy for the process of photosynthesis. This energy is used to split water molecules (H2O) into hydrogen ions (H+) and hydroxyl ions (OH-). Oxygen from the hydroxyl ion is released into the air and hydrogen ions combine with carbon dioxide to form glucose.

Question 3

Do plants need oxygen? If so, what is its source?

Answer

Plants need oxygen for respiration. The source of oxygen is atmosphere.

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