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Life Process

Autotrophic Nutrition in plants (Group A)

What is blood and what are its functions?

Blood is a fluid connective tissue that flows in blood vessels. Its main function is to transport substances such as digested food and oxygen (from the small intestine and lungs respectively) to all parts of the body. It also takes part in the removal of waste materials from the body. How does blood perform all these functions? Does it have some special components that perform these functions? Blood is made up of various types of cells that are suspended in a fluid part called plasma. Let us study the various components of blood.

Blood consists of three types of cells. These are as follows.

  • Red Blood Cells or Erythrocytes - They contain a red pigment called haemoglobin, which transports oxygen to all cells of the body by combining with oxygen to form a compound called oxyhaemoglobin. The mature erythrocytes do not have a nucleus.

  • White Blood Cells or Leukocytes - They are larger than RBCs and do not have haemoglobin. They fight against germs that enter the body. Thus, they protect the body from diseases.

  • Blood Platelets or Thrombocytes - You must have noticed that when you get injured, bleeding stops after some time. This happens because of the activity of platelets. Platelets help in the clotting of blood during an injury. The platelets are smaller than the RBCs.

Some interesting facts:

  • After blood donation, the fluid gets replaced in few hours and the red blood cells within four weeks. It takes around eight weeks to restore the iron lost after donation.
  • Platelets are produced at the rate of 200 billion per day in the human body.

Functions of blood:

  • It transports nutrients and oxygen to the different parts of the body

  • It also carries waste materials (from the different parts of the body) to be removed by the excretory organs.

  • Chemical messengers like hormones are transported by the blood.

  • Protects the body from disease carrying germs.

  • Helps to maintain a constant body temperature.


Lymph is a watery clear fluid. It is blood minus RBC. This fluid distributes immune cells and other factors throughout the body. It also interacts with the blood circulatory system to drain fluid from cells and tissues. The lymphatic system contains immune cells called lymphocytes, which protect the body against foreign antigens (viruses, bacteria, etc.) that invade the body.

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Blood transfusion and blood groups

Sometimes when we get seriously wounded and lose a lot of blood, this lost blood is replaced by blood taken from another person but we cannot just take blood from any person and hence the characteristics of the blood are to be studied before. The process of transfer of blood from one person to another is called blood transfusion.

Blood groups

Based on the presence or absence of certain substances called antigens on the surface of the RBCs , the blood of human beings can be divided into four blood groups, they are A, B, AB and O.

  • Blood group A has A antigen

  • Blood group B has B antigen

  • Blood group AB has both A and B antigens

  • Blood group O has neither A nor B antigens.

Do You Know?

  • Blood group O is known as the universal donor since it can be transfused into any person with any blood group
  • Blood group AB is known as the universal acceptor since it can receive any blood group


There is another antigen present on the surface of the RBCs which is known as the Rh- factor. About 85% of the people have Rh factor and are called Rh positive and those who do not have the Rh factor are known as Rh negative.

Before blood transfusion, the Rh factor as well as the blood group of the donor and the recipient have to be matched or it may lead to serious illness.

You know that all activities performed by the body require energy. Where does the body get energy from? The food we eat contains stored energy.

How is the energy stored in food released to be used by the body?

You know that during the process of breathing, we take in air. Oxygen is taken in, while carbon dioxide is released out of the body during breathing. Oxygen is then circulated to all cells of the body. Food (glucose) is broken down in the cells with the help of oxygen.

The process in which food is broken down in the cells to release energy is known as cellular respiration.

Have you ever wondered what will happen if no or very little oxygen is available to cells? Will the process of cellular respiration stop?

Two types of respiration take place in the cells. One occurs in the presence of oxygen, while the other occurs in the absence of it. The process of breakdown of food (glucose) in the presence of oxygen is known as aerobic respiration. It takes place in all organisms and leads to the production of carbon dioxide, water, and energy.

Food is also broken down in the absence of oxygen. This process is known as anaerobic respiration. It occurs in organisms such as yeast. This process leads to the production of alcohol and carbon dioxide.

Difference between Aerobic and Anaerobic respiration

Aerobic respiration Anaerobic respiration

It occurs in the presence of O2.

It occurs in the absence of O2.

It involves the exchange of gases between an organism and outs...

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