The contraction and expansion movements of the walls of food-pipe are called peristaltic movements. This movement pushes the food in forward direction in the alimentary cana
The small intestine is the main region for the absorption of digested food. The inner lining of small intestine has millions of tiny finger-like projections called villi. The presence of villi gives the inner walls of the small intestine a very large surface area for absorption of digested food. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body.
ammals and birds are warm-blooded animals. They constantly use energy to maintain their body temperature. They have higher energy need and so they require more oxygen to produce energy. Thus, it is important that their oxygenated blood does not get mixed up with deoxygenated blood.
The components of the transport system of highly organized plants consist of xylemand phloem. Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. Phloem consists of sieve tubes, companion cells, phloem fibres and phloem parenchyma.
Thus a large amount of air is brought in contact with the air in the lungs. More than millions of alveoli are present in the lungs. The presence of millions of alveoli in the lungs provides a very large surface area for the exchange of gases. The availability of large surface area maximizes the exchange of gases.
Absorbed water from the soil also contains dissolved minerals (nitrates, phosphates, etc) and hence it is called sap. This sap moves upwards due to the transpiration pull’developed in the xylem elements. Thus, transportation of sap from roots to the leaves at the top is called ascent of sap.
Water in the mesophyll cells of leaves (cells located below the stomata) is in contact with water or sap in xylem of leaf petiole, stem and root. This water evaporates by the process of transpiration. Thus, due to transpiration water is pulled upward which creates an upward suction force called ‘transpiration pull’.
