IV. Answer the following questions in two sentences.

1. Describe the function of blood platelets.

Ans:- When a blood vessel is damaged, blood flows out from it. The body can not afford to let blood flow out of the body. The blood platelets present in the blood helps to clot the blood and seal the wound to prevent bleeding.

2. Why does your heart beat increase when you run?

Ans:- When we run, our heart beat increases. This is because at such times, the body needs more oxygen to release more energy through respiration. To supply more oxygen, the blood flows faster. 

3. What is transpiration?

Ans:- Transpiration is the evaporation of water from the leaves through stomata present on the leaves.

4. What is the function of the lymph nodes?

Ans:- Lymph nodes contain special types of cells. These cells protect the human body from disease-causing organisms and harmful substances.

5. List the organs of the excretory system.

Ans:- The organs of the excretory system are kidneys, ureters, urinary bladder and urethra.

V. Answer the following questions in about four to five sentences.

1. Describe the structure of the human heart with a diagram.

Ans:- 


Our heart is a fist sized muscular organ. Our heart is divided into four chambers. The upper two chambers are called right atrium and left atrium and the lower chambers are called the left ventricle and right ventricle. The muscular wall that separates the right and left sides of our heart is called septum. The blood vessels that carries blood are called arteries and veins. Arteries carry oxygen rich blood from the heart to the rest of the body and the veins bring back the carbon dioxide rich blood from all parts of the body to the heart.

2. How does oxygen-rich blood reach every part of the body? 

Ans:- Our heart functions as a pump. It pumps the impure blood to the lungs. In the lungs the blood gives off the carbon dioxide and takes  in oxygen. The oxygen rich blood is now carried to the left atrium by the pulmonary vein. From here the blood enters the left ventricle. The left ventricle pumps the oxygen rich blood to every part of the body through the aorta. 

3. Explain the composition of blood.

Ans:- The blood of vertebrate is made up of red blood cells (RBC), white blood cells (WBC) and blood platelets. The fluid portion of the blood is called plasma. 

Red blood cells:- Oxygen and carbon dioxide gases readily bind to haemoglobin of the RBCs. The blood transport gases in the body with the help of RBCs.

White blood cells:- It is colourless. They kill the germs and defend the body against infectious diseases.

Blood platelets:- When a blood vessel is damaged, blood flows out from it. So to prevent the bleeding blood platelets present in blood help the blood to clot and seal the wound.

4. Differentiate between arteries and veins.

Ans:- 

Arteries:- 1. Carry blood away from the heart.

                  2. Carry oxygenated blood.

Veins:- 1. Carry blood towards the veins.

             2. Carry deoxygenated blood.

5. How is blood purified in the kidneys?

Ans:-  A human being has two kidneys. Each kidney contains thousands of tiny tubules which work like filters.

As blood flows through the kidneys, the tiny tubules filter the blood and separate waste from it as urine. 

6. Describe the vascular system in plants.

Ans:- The transport system in plants is called the vascular system. It is made up of two types of narrow tubes called the xylem and the phloem. Each of these tubes are organised into bundles called vascular bundles and form a continuous network in the entire plant. The xylem carries the water from the roots to the leaves. While the phloem transports the food made by the leaves to the stem, branches, flowers, fruits and roots.