Selina Chapter 4 Photosynthesis and Respiration Questions Answers Class 7 Biology

ICSE Solutions for Chapter 4 Photosynthesis and Respiration Class 7 Biology Selina Publisher

Review Questions

Multiple Choice Questions

1. Put a tick (✓ ) against the most appropriate alternative in the following statements.

(i) Carbohydrates are stored by plants in the form of:
(a) Vitamins
(b) Proteins
(c) Fats
(d) Glucose

Answer

(d) Glucose 

(ii) Stomata are present on the surface of:
(a) Leaves
(b) Roots
(c) Stem
(d) Flower petals

Answer

(a) Leaves

(iii) Which one of the following is an end-product of photosynthesis ?
(a) Fructose
(b) Glucose
(c) Cellulose
(d) Lactose

Answer

(b) Glucose

Short Answer Questions

1. Why do leaves generally look green ?
Answer
The green colour of a leaf is due to the presence of chlorophyll.

2. Which four of the following are needed for photosynthesis in a leaf:
(i) Carbon dioxide:
(ii) Oxygen:
(iii) Nitrates :
(iv) Water:
(v) Chlorophyll:
(vi) Soil:
(vii) Light:
Answer
(i) Carbon dioxide: from air
(iv) Water: from soil
(v) Chlorophyll: contained in leaf
(vii) Light: from sunlight

3. What is the source of energy for photosynthesis ?
Answer
Light is the ultimate source of energy in photosynthesis because plants take in the sunlight CO₂ and H₂O and converts it into glucose.

4. Which gas is taken in and which one is given out by the leaf in bright sunlight ?
(i) Taken in :
(ii) Given out:
Answer
(i) Carbon dioxide
(ii) Oxygen

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

Leaf	Factory
(i) Cells in the leaf	(c) Machinery(a) Raw materials
(ii) Chloroplast	(f) Work room
(iii) Sunlight	(b) Power
(iv) Oxygen and water	(e) By product
(v) Carbon dioxide and water	(a) Raw materials
(vi) Glucose	(d) End product

Answer

Leaf	Factory
(i) Cells in the leaf	(c) Machinery
(ii) Chloroplast	(f) Work room
(iii) Sunlight	(b) Power
(iv) Oxygen and water	(e) By product
(v) Carbon dioxide and water	(a) Raw materials
(vi) Glucose	(d) End product

6. State whether the following statements are True or False:

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

Green plants prepare their food by using raw materials, CO, chlorophyll and water.

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

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

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

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

Aerobic respiration	Anaerobic respiration
1. It occurs in the presence of oxygen.	1. It occurs in the absence of oxygen.
2. Here there is complete breakdown of glucose releasing carbon-di-oxide, water and energy.	2. There is partial breakdown of glucose into ethyl alcohol, carbon-di-oxide and energy.
3. More energy is released (38 ATP).	3. Lesser energy is released (2 ATP).

(i) Aerobic respiration:

(ii) Anaerobic respiration:

8. Explain how photosynthesis is different from respiration.
Answer

Photosynthesis	Respiration
1. Anabolic process	1. Catabolic process
2. Food is produced here.	2. Food is broken down form here to release energy
3. Oxygen is by-product.	3. Carbon-di-oxide is the by-product.
4. Chlorophyll and sunlight are required.	4. Chlorophyll and sunlight are not required.
5. Occur only during daytime.	5. Occurs all the time
6. Occurs in green plants only.	6. Occurs in all living beings including plants.

Photosynthesis :
6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂ 

Respiration:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

9. Do the plants respire all day and night or only during the night ?
Answer

The plants respire only during the night. Plants take in oxygen and give out carbon dioxide. Hence, there is some truth in the belief that one should not sleep under the trees at night.

10. What happens to the energy liberated during respiration?
Answer

The energy liberated during respiration is utilized for carrying out various life processes. Some of the energy liberated during the breakdown of 03 the glucose molecule, is in the form of heat, but a large part of it is converted into chemical energy called Adenosine Triphosphate (ATP). Any activity inside the cell is carried out by the energy released by these ATP molecules.

Long Answer Questions

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

For preparing food, the plants require the following :

1. Water (from soil)
2. Carbon dioxide (from air)
3. Chlorophyll (contained in the leaf)
4. Energy (from sunlight)

The process of preparing or synthesising food using water from the soil and carbon
dioxide from the air, together chlorophyll and sunlight is called photosynthesis. This
entire process is a series of complex chemical reactions Photosynthesis is represented
as follows:

2. What is the role of chlorophyll in photosynthesis ?
Answer

This pigment is of utmost importance as it absorbs the sunlight which provides energy for the process of photosynthesis occurs inside the chloroplast of the leaf.

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

Yes plants need oxygen, all the free oxygen in the atmospheric air is the result of photosynthesis. No animal can survive without oxygen as it is needed for respiration. Even the plants use the same oxygen in dark for their own respiration.

Additional Questions

Check Your Progress

Answer these questions.

1. What is external respiration ?
Answer

External respiration or breathing is a mechanical or physical process that involves inhaling (breathing in) air rich in oxygen and exhaling (breathing out) air rich in carbon dioxide.

2. Write the equation showing the process of respiration.

Answer

3. In what form is the energy released during respiration stored ?
Answer

The energy released is stored in the form of an energy-rich chemical substance called ATP (Adenosine triphosphate).

4 . Name the two types of respiration.
Answer

Aerobic respiration and anaerobic respiration.

5. Name the organ of respiration in fishes.
Answer

Gills

6. What are the holes on the sides of the body of insects called ?
Answer

Spiracles

Answer the following in one word.

1. What is the muscular sheet below the lungs called ?
Answer

Diaphragm

2. Which organ is called the voice box ?
Answer

Larynx

3. Which membrane covers the lungs ?
Answer

Pleural membrane

4. Where does exchange of gases takes place ?
Answer

Lungs (alveoli)

5. What is formed when oxygen combines with hemoglobin ?
Answer

Oxy haemoglobin

6. What is carbamino haemoglobin ?
Answer

Carbon-dioxide combines with hemoglobin to form carbamino hemoglobin.

Exercises

A. Tick the most appropriate answer.

1. The products of respiration are :
a. carbon dioxide and oxygen
b. oxygen and energy
c. carbon dioxide, water and energy
d. carbon dioxide, oxygen and energy.

Answer

c. carbon dioxide, water and energy

2. Glucose is oxidized to produce ethyl alcohol during
a. excretion
b. aerobic respiration
c. anaerobic respiration
d. photosynthesis

Answer

c. anaerobic respiration

3. In insects like grasshopper, there is a well-developed system of air tubes called
a. tracheae
b. gills
c. lungs
d. alveoli

Answer

a. tracheae

4. Frogs breathe through the
a. moist skin
b. lungs
c. mouth cavity
d. all of these

Answer

d. all of these

5. Inside the chest, the trachea divides into two branches called
a. bronchi
b. bronchioles
c. bronchus
d. alveolus

Answer

a. bronchi

6. In humans beings, during inhalation the diaphragm.
a. moves up
b. moves down
c. remains at its position
d. moves down moves up

Answer

b. moves down

7.Exhaled air contains
a. more carbon dioxide
b. more oxygen
c. more nitrogen
d. more hydrogen

Answer

a. more carbon dioxide

8. Plants have these for exchange of gases.
a. spiracles and stomata
b. lenticels and spiracles
c. lenticels and stomata
d. buds and flowers

B. Fill in the blanks.
1. The two respiration of respiration are _______ and _______.
2. Muscles of human beings switch to anaerobic ________ in the absence of oxygen.
3. In _______respiration, food is completely oxidized into carbon dioxide, water and energy.
4. Below the lungs is a muscular sheet called _______.
5. Bronchi divide into smaller tubes called ________.
6. In human beings, exchange of gases takes place in _______ (lungs).

Answer

1. The two respiration of respiration are aerobic and anaerobic.
2. Muscles of human beings switch to anaerobic respiration in the absence of oxygen.
3. In aerobic respiration, food is completely oxidized into carbon dioxide, water and energy.
4. Below the lungs is a muscular sheet called diaphragm.
5. Bronchi divide into smaller tubes called bronchioles.
6. In human beings, exchange of gases takes place in alveoli (lungs).

C. State if the following statements are true or false. Correct the statement if it is false.

1. The oxidation pf food to release energy and water is called breathing.
False. 

The oxidation of food to release energy and water is called Respiration.

2. Anaerobic respiration takes place in our bones.
False. 

Anaerobic respiration takes place in our muscles.

3. The microscopic air sacs present in the lungs are called bronchi.
False. 

The microscopic air sacs present in the lungs are called alveolar sacs.

4. Respiration that takes place through skin is called pulmonary respiration.
False. 

Respiration that takes place through skin is called cutaneous respiration.

5. Stomata are present on mature roots and woody stems.
False. 

Lenticels are present on mature roots and woody stems.

6. In photosynthesis oxygen is released as a by-product
True

D. Match the following.

Column A (Organism)	Column B (Organ of Respiration)
1. Fish	a. Lungs
2. Human beings	b. Tracheae
3. Frog	c. Gills
4. Cockroach	d. Moist skin, mouth cavity and lungs
5. Bird	e. Lungs

Answer

Column A (Organism)	Column B (Organ of Respiration)
1. Fish	c. Gills
2. Human beings	a. Lungs
3. Frog	d. Moist skin, mouth cavity and lungs
4. Cockroach	b. Tracheae
5. Bird	e. Lungs

E. Differentiate between

 

(i) Difference between Aerobic respiration and Anaerobic respiration.

 

Aerobic Respiration	Anaerobic Respiration
1. It takes place in the presence of oxygen.	1. It takes place in the absence of oxygen.
2. Complete oxidation of food takes place.	2. Incomplete oxidation of food takes place.
3. 38 molecules of ATP are produced by oxidation of one gram mole of glucose.	3. 2 molecules of ATP are produced by oxidation of gram mole of glucose.
4. CO2 and H2O are the end products.	4. Ethyl alcohol (C6H5OH) and CO2 are the end products.

(ii) Difference between External respiration and Internal respiration

 

External respiration	Internal respiration
1. It is the mechanical process of inhaling and exhaling air It does not involve any enzymes.	1. It is a complex biochemical process in which enzymes are involved.
2. It involves taking in oxygen and giving out carbon dioxide.	2. It involves the oxidation of glucose into carbon dioxide, water and energy.
3. No energy is released.	3. Energy is released and stored in the form of ATP.
4. It takes place outside the cell.	4. It takes place inside the cell.

(iii) Difference between Photosynthesis and Respiration

 

Photosynthesis	Respiration
1. It is an anabolic process.	1. It is a catabolic process Sunlight is not necessary for the respiration.
2. It takes place in the presence of sunlight.	2. Carbon dioxide is released as the by product.
3. Oxygen is released as the by product.	3. It takes place in all the parts of a plant.
4. It takes place in the green parts of the plant that is green leaves, young green stems.	4. Food is oxidized using oxygen to release energy.
5. Food is synthesized by plants using CO2 and H2O

F. Answer the following in short.

1. Define respiration.
Answer

The process of conversion of glucose molecules in food into energy rich molecules, carbon dioxide and water with the help of oxygen is known as respiration.

2. What is the full form of ATP ?
Answer

ATP is the energy currency of cell. Its full form is Adenosine Triphosphate.

3. What is respiratory tract ?
Answer

The path through which the air travels to the lungs and back to the atmosphere in humans is called the respiratory tract

4. Define cutaneous respiration ?
Answer

The exchange of gases through moist skin and blood capillaries underneath is called cutaneous respiration. e.g. in frogs.

5. What is the function of pleural fluid ?
Answer

Pleural fluid keeps the surface of the lungs moist for easy diffusion of gases (oxygen and carbon dioxide).

6. What is the role of the diaphragm in breathing mechanism ?
Answer

Diaphragm moves up and down and helps in the exchange of air between the atmosphere and lungs.

G. Answer the following in detail.

1. How is the process of cellular respiration different from breathing ?
Answer

Respiration	Breathing
1. It is a complex bio-chemical process which involves enzymes.	1. It is a mechanical process without the involvement of enzymes.
2. It involves oxidation of glucose in to CO2, water and energy.	2. It involves only the exchange of oxygen and CO2.
3. Energy is released and stored in the form of ATP.	3. No energy is released.
4. It takes place inside the cell.	4. It takes place outside the cell.

2. Explain the process of Cellular Respiration.
Answer

Cellular Respiration is a biochemical process which involves the oxidation of glucose to release energy, carbon dioxide and water are released as by products. 

It involves a series of chemical reactions controlled by different enzymes. The energy released in the process is stored in the form of energy rich substance called ATP (Adenosine triphosphate). The ATP molecules are stored in the cells and later on can be broken down to release energy for various metabolic activities. The entire process takes place partially in the cytoplasm and partially in the mitochondria of our body cells. The process of conversion of glucose molecules in food in to energy rich molecules, CO₂ and water with the help of oxygen is known as respiration.

3. In human beings, what happens to oxygen after it is inhaled through the nose ?
Answer

Air rich in oxygen, enters the body through the nostrils (nose). From the nose, air enters the phaiynx which leads to larynx and then trachea (windpipe). From trachea, it enters the bronchi and enters the lungs. From bronchi, it enters bronchioles and finally the alveoli. The oxygen diffuses through the thin walls of blood capillaries (surrounding) into the blood and combines with hemoglobin to form oxy hemoglobin. The oxygen in blood is carried to all body cells where internal respiration takes place in a series of chemical reactions and food (in the form of glucose) is converted into carbon-dioxide water and energy in the form of ATP, using the oxygen.

4. Show the mechanism of breathing in human beings.
Answer

The process of taking in oxygen and giving out carbon dioxide is called breathing. It is a physical process and carried out by the movement of the various body parts.
1. Inhalation : When we inhale air our ribs move upwards and outwards and the diaphragm moves downwards. The volume of chest cavity increases and the air pressure is reduced, as a result of which air flows in to the lungs.
2. Exhalation : When we exhale air, that is breathe out air, the diaphragm moves upwards and the ribs move downwards and inwards. The space inside the chest cavity decreases and the air pressure is increased as, a result the air rushes out.

5. Explain the process of exchange of gases in plants.
Answer

In plants, exchange of gases takes place through stomata and lenticels.

1. Stomata – They are tiny pores present on the lower surface of leaves and young green stems. The gaseous exchange takes place in plants mostly through stomata. They remain open during the day and close at night. 

2. Lenticels – In certain trees, the mature roots and woody stems have tiny openings called lenticels which enable the oxygen to reach the intercellular spaces of interior tissues and carbon dioxide to be released into the atmosphere. 

The exchange of gases (oxygen and carbon dioxide) in plants takes place by two processes – photosynthesis and respiration

Photosynthesis occurs during the day. It takes in carbon dioxide and gives out oxygen. A part of oxygen formed is used by plants for respiration and rest is given out through stomata
Respiration occurs throughout day and night. Oxygen is used and carbon dioxide is given out. This carbon dioxide is used by the plant for photosynthesis during the day. At night, in the absence of photosynthesis, carbon dioxide is released into the air through stomata.

H. Number the following organs in the correct order to show the path taken by fresh air at the time of inhalation.
trachea, nose, bronchioles, bronchi, larynx, alveoli, pharynx, lungs
Answer
nose → pharynx → larynx → trachea→ bronchi → lungs →bronchioles →alveoli.