(A) Think and tell.
Q. Why do we pant when we have been running hard for some time ?
Ans. During running our heart pumps blood to our muscles and lungs pumps more air to the body. As more work is done during running than normal condition our heart beats faster due to excitation or exertion and we pant.
(B) Answer the following questions.
1. What is meant by ‘internal organ’ ?
Ans. An organ that is situated inside the body and cannot be seen from the outside is called an internal organ.
2. Name the two cavities in the abdomen.
Ans. The cavity inside the abdomen has two parts, the abdominal cavity and the pelvic cavity.
3. Which important organs are situated in the ribcage in the thoracic cavity ?
Ans. The important organs situated in the ribcage in the thoracic cavity are the heart and the lungs.
4. Why does the chest swell when we breathe in ?
Ans. When we breathe in air, the lungs expand a little. That is why our chest swells up when we breathe in.
5. Why is the brain situated in the casing of the skull ?
Ans. The brain, is a very important internal organ. Injury to the brain can make one disabled for life and can even cause death. Hence, the brain is situated in a casing formed by skull around it.
(C) Fill in the blanks.
1. The internal organs that help digest food are present in the alimentary canal.
2. We have two lungs.
3. Every contraction of the heart is called a heartbeat.
4. We become aware of all our emotions in the brain.
5. The structure of the human body is very complex .
(D) True or false ?
1. The oesophagus is in the thoracic cavity. True
2. The heart is a little bigger than our fist. True
3. The food in the mouth forms a moist lump. True
4. In the brain, we interpret the information collected by the sensory organs. True
(E) Give reasons why.
1. The structure of the body is such that all internal organs remain secure in their
Ans. The structure of our body is such that our internal organs can remain secure in their places no matter how much we move. This is because there are hollow spaces for protection of these organs inside the head and the torso, called cavities.
2. Blood must be kept flowing in the blood vessels throughout the body.
Ans. Our blood carries the air to all parts of the body. The food that we eat gets digested. It is blood that carries the digested part to every particle of the body. For these purposes,
it is necessary to keep blood flowing through the blood vessels that spread throughout the body.
3. The brain has to be kept completely safe.
Ans. The brain, is a very important internal organ. Injury to the brain can make one disabled for life and can even cause death. Hence, the brain has to be kept completely safe.
(F) Match the following :