NCERT Solutions for Class 7 Science Chapter 7 Transportation in Animals and Plants (blood)

Circulatory System

We all know that blood flows out whenever we get a cut. Blood is defined as the fluid that flows through the blood vessels. It transports oxygen from the lungs to various parts of the body. It also transports digested food from the alimentary canal (small intestine) to other parts. It is also the means of transport of waste material from different parts of the body to the excretory system. Blood contains several types of cells. The fluid component of blood is called plasma.

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Amongst the different types of cells present in the blood, red blood cells (RBCs) form the major part. RBC contains haemoglobin, which imparts a red colour to the blood. The main function of haemoglobin is to bind and transfer oxygen to different parts of the body. Without haemoglobin, oxygen will not be transported efficiently.

Blood also contains white blood cells. The main function of the white blood cells is to maintain immunity against germs and pathogens that can enter our bodies by various means.

Two types of vessels are present in the human body. They are called veins and arteries. Arteries mainly carry blood to different parts of the body. Veins carry blood from different parts of the body to the heart. As we inhale, the lung is filled with oxygen. The oxygen is taken up from the lungs by the veins and transported to the heart. The heart pumps the oxygenated blood to different parts of the body through the arteries.

Similarly, the different cells of the body use this oxygen and release carbon dioxide. The carbon dioxide is taken up by the veins and is returned to the heart. Another set of arteries carries the deoxygenated blood from the heart to the lungs. The pressure at which the heart pumps the blood is very high. For that reason, arteries have thick muscular and elastic walls.

However, the veins do not have to endure the high pressure of blood flow through them. That is why veins have thin walls. Moreover, the veins contain valves that ensure that the blood flows in one direction only, i.e., towards the heart. 

When the arteries reach the tissues, they divide into smaller, finer vessels called arterioles, which further subdivide to form extremely thin capillaries. These capillaries are the site of the exchange of oxygen and carbon dioxide between the blood and the cells of the tissue. These capillaries then rejoin and form venules, which further rejoin to form veins. The veins then empty the blood into the heart. 

The heart is an essential organ of the body which pumps blood to different parts of the body in a non-stop manner. It is located in the middle of the chest cavity. However, you will feel your heartbeat on the left side of your chest. You observe this phenomenon because its lower tip is tilted towards the left. You will find that your heart and your fist are almost the same size.

There are four chambers of the heart. The upper two chambers are called the auricles (or the atria, singular atrium). The lower two chambers are called the ventricles. These chambers function together to prevent the mixing of the oxygenated and the deoxygenated blood with the help of the partition between the chambers. 

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The walls of the four chambers of the heart are made up of muscles that relax and contract in a rhythmic manner. This process of contraction and relaxation in a rhythm forms the heartbeat. You can feel the heartbeat by placing your hand on the left side of your heart. Doctors listen to the heartbeat with the help of a stethoscope. The stethoscope amplifies the heartbeat. It has a chest piece carrying a sensitive diaphragm, and a tube connecting the chest piece with two earpieces. By listening to the amplified heartbeat, doctors can identify any change in the heartbeat pattern, which can be linked to conditions of any disease. 

Other organisms can also contain blood, despite not having a proper circulatory system. For example, in hydra and sponges, water entering the body brings food and oxygen and picks up carbon dioxide and waste products as it leaves the body. Water performs the function of the blood in the body of these organisms.

1. Match structures given in Column I with functions given in Column II.

Column- I	Column-II
(i) Stomata	(a) Absorption of water
(ii) Xylem	(b) Transpiration
(iii) Root hairs	(c) Transport of food
(iv) Phloem	(d) Transport of water
	(e) Synthesis of carbohydrates

Solution:

Column- I	Column-II
(i) Stomata	(b) Transpiration
(ii) Xylem	(d) Transport of water
(iii) Root hairs	(a) Absorption of water
(iv) Phloem	(c) Transport of food

2. Fill in the blanks.

(i) The blood from the heart is transported to all parts of the body by the _____________.

(ii) Haemoglobin is present in _____________ cells.

(iii) Arteries and veins are joined by a network of _____________.

(iv) The rhythmic expansion and contraction of the heart is called the _____________.

(v) The main excretory product in human beings is _____________.

(vi) Sweat contains water and _____________.

(vii) Kidneys eliminate the waste materials in the liquid form called _____________.

(viii) Water reaches great heights in the trees because of suction pull caused by _____________.

Solution:

(i) The blood from the heart is transported to all parts of the body by the arteries.

(ii) Haemoglobin is present in red blood cells.

(iii) Arteries and veins are joined by a network of capillaries.

(iv) The rhythmic expansion and contraction of the heart is called the heartbeat.

(v) The main excretory product in human beings is urea.

(vi) Sweat contains water and salts.

(vii) Kidneys eliminate the waste materials in the liquid form called urine.

(viii) Water reaches great heights in the trees because of suction pull caused by transpiration.

3. Choose the correct option:

(a) In plants, water is transported through

(i) xylem

(ii) phloem

(iii) stomata

(iv) root hair

(b) Water absorption through roots can be increased by keeping the plants

(i) in the shade

(ii) in dim light

(iii) under the fan

(iv) covered with a polythene bag

Solution:

a) i) xylem

b) iii) under the fan

4. Why is the transport of materials necessary in a plant or in an animal? Explain.

Solution:

Transport of materials is necessary for both plants and animals as every cell needs a regular supply of nutrients and oxygen to release energy through respiration.

The food that we eat is broken down into smaller components to be absorbed by cells. The oxygen we inhale also has to be transported to all the cells of the body. Our body also requires the constant removal of waste materials such as carbon dioxide.

For the transport of all these materials (nutrients, oxygen and waste products), our body has a specialised transport system. 

Similarly, in plants, the transport of water and food is accomplished with the help of vascular tissues (xylem and the phloem). 

5. What will happen if there are no platelets in the blood?

Solution:

If there are no platelets, then blood will not clot as platelets release blood clotting factor at the site of injury and stop further bleeding.

6. What are stomata? Give two functions of stomata.

Solution:

Tiny pores present on the leaf surface are known as stomata.

Functions of stomata

• It helps in the exchange of gases
• Evaporation of water through leaves occurs due to stomata.

7. Does transpiration serve any useful function in plants? Explain.

Solution:

Transpiration serves the following functions in plants

• It helps in lowering the temperature of plants, thus preventing heat injury to plants.
• It helps in transpiration pull, which helps in raining water on higher plants.
• It also causes loss of water absorbed by plants.

8. What are the components of blood?

Solution:

The components are red blood cells, white blood cells, platelets and plasma.

9. Why is blood needed by all the parts of a body?

Solution:

It is a significant part of the transport system in our body, and we need blood for the following reasons:

• For the transport of oxygen to all parts of our body
• To expel carbon dioxide from our body
• To transmit heat, thus helping in the regulation of body temperature.
• It is required to fight out infections and diseases.

10. What makes the blood look red?

Solution:

The presence of a red pigment called haemoglobin in red blood cells (RBC) makes the blood appear red.

11. Describe the function of the heart.

Solution:

The heart is an organ which beats continuously to act as a pump for the transport of blood, which carries other substances with it. The heart has four chambers. The two upper chambers are called the atria (singular: atrium), and the two lower chambers are called the ventricles. The partition between the chambers helps to avoid mixing up blood in oxygen with the blood in carbon dioxide. Blood flows from the heart to the lungs and back to the heart, from where it is pumped to the rest of the body.

12. Why is it necessary to excrete waste products?

Solution:

When the cells in the body perform their functions, certain waste products are released. These are toxic and hence need to be removed from the body.

13. Draw a diagram of the human excretory system and label the various parts.

Solution: