NCERT Solutions For Class 7 Science Chapter 2 Nutrition in Animals

Blood appears red because of the presence of a red-coloured pigment in red blood cells called haemoglobin. This pigment binds with oxygen and carries it to all parts of body.

Waste products need to be excreted because these are toxic in nature and their circulation or presence in body cause damage to various organs of the body.

Blood is the only means of supplying oxygen and nutrients derived from digested food to all parts of the body and removing waste products from them. As blood is the sole means of transport of materials, it is needed by all parts of the body.

There are four major components of blood:

1. Plasma
2. Red blood cells
3. White blood cells
4. Platelets

Transpiration is the loss of water molecules from stomata that causes a suction pull on the water column in xylem. Due to this suction pressure, water is transported to a great height in large trees through the xylem.

(a) In plants, water is transported through (i) xylem

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

The correctly matched contents of Column I with Column II are as follows:

Heart is a muscular organ that pumps blood to each and every organ of the body. It helps in pumping the blood to lungs for oxygenation. Pumping action of heart keeps blood circulating in the vessels through which various important substances, like respiratory gases and nutrients, are transported. Heart consists of two atria and two ventricles, which contract and relax rhythmically to give rise to the pumping action.

Stomata are small pores present on the surface of the leaves forming an opening for exchange of materials. Two important functions of stomata are as follows:

1. Stomata allow exchange of gases, that is, intake of carbon dioxide and release of oxygen through it.
2. Stomata regulate rate of evaporation of water from the leaf surface, which is called transpiration.

In the absence of platelets, clot formation will not take place that will result in severe blood loss in case of injury. When a blood vessel is injured, platelets form blood clot that covers the wound protecting it from disease causing microorganisms and preventing blood loss.

The transport of materials is necessary in all organisms because it allows exchange of gases, supply of nutrients and removal of waste materials. All plants and animals have well developed transport systems to ensure continuous supply of oxygen, water and food to all parts of the body. Also, the toxic waste materials generated due to various activities is removed from the body by means of transport system only.

A well-labelled diagram of human excretory system is as follows:

(i) arteries

(ii) Red blood

(iii) capillaries

(iv) Heartbeat

(v) urea

(vi) salts

(vii) Urine

(viii) transpiration