NCERT Class X Science Solutions: Chapter 6 – Life Processer Part 3

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Question 11:

Describe double circulation in human beings. Why is it necessary?


Because both oxygen and carbon dioxide have to be transported by the blood, the heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide. The human heart is divided into four chambers − the right atrium, the right ventricle, the left atrium and the left ventricle.

Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, the left atrium. The left atrium relaxes when it is collecting this blood. It then contracts, while the next chamber, the left ventricle, expands, so that the blood is transferred to it. When the muscular left ventricle contracts in its turn, the blood is pumped out to the body.

This diagram shows circulation in human beings

Circulation in Human Beings

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De-oxygenated blood comes from the body to the upper chamber on the right, the right atrium, as it expands. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates. This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation. During this process blood goes twice through the heart. That’s why it is known as double circulation.

Double Circulation is necessary:

The separation of oxygenated and de-oxygenated blood allows a more efficient supply of oxygen to the body cells. This efficient system of oxygen supply is very useful in warm-blooded animals such as human beings. As we know, warm-blooded animals have to maintain a constant body temperature by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment. Hence, they require more O2 for more respiration so that they can produce more energy to maintain their body temperature.

Thus, the circulatory system of humans is more efficient because of the double circulatory heart.

Question 12:

What are the differences between the transport of materials in xylem and phloem?


Difference between Xylem and Phloem:

Xyleum vs Phloem




Xylem tissue helps in the transport of water and minerals.


Phloem tissue helps in the transport of food.


Water is transported upwards from roots to all other plant parts.


Food is transported in both upward and downward directions.


Transport in xylem occurs with the help of simple physical forces such as transpiration pull.


Transport of food in phloem requires energy in the form of ATP.

Question 13:

Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.


Alveoli vs. Nephron




Alveoli are tiny balloon like structures present inside the lungs.


Nephrons are tubular structures present inside the kidneys.


The walls of the alveoli are one cell thick and it contains an extensive network of blood capillaries.


Nephrons are made of glomerulus, bowman’s capsule, and a long renal tube. It also contains a cluster of thin walled capillaries.


The exchange of O2 and CO2 takes place between the blood of the capillaries that surround the alveoli and the gases present in the alveoli.

Alveoli are the site of gaseous exchange.


The blood enters the kidneys through the renal artery which branches into many capillaries in the glomerulus. The water and solute are transferred to the nephron at Bowman’s capsule. Then the filtrate moves through the proximal tubule, distal tubule and collecting duct. The collecting duct collects the urine from many nephrons and passes it to the ureter. During the flow of filtrate, some substances such as glucose, amino acids, and water are selectively reabsorbed.

Nephrons are the basic filtration unit.