Class 7 Science Transportation in Animals and Plants Notes

RBC. RBC’s are non nucleated disc-shaped cells. The red colour of RBC is due to the presence of the protein haemoglobin. There are about 5- 5.5 million RBC’s in one ml of oxygen blood and are responsible to different parts of the body. Oxygen combines with haemoglobin to form oxyhemoglobin.

Oxygen + haemoglobin ‡ˆ ˆreversible reaction †ˆOxyhaemoglobin

When oxygen rich blood reaches the tissue and cells of the body, oxygen is released for use in cellular respiration. Hence the haemoglobin free to carry more oxygen.

Anaemia is a very common disorder in which the amount of haemoglobin gets lowered. This leads to decrease in the oxygen carrying capacity of blood.

WBC: The number of WBCs in blood is less than the number of RBCs. They are comparatively bigger in size than RBCs and are meant for protecting the body against harmful bacteria and diseases. They show Amoeba like movements and are capable of ingesting foreign material. WBCs are the first ones to reach an infected or injured part of the body by passing through the walls the blood vessels.

Platelets: These help in blood clotting at the area of injury and block blood flow. Hence they prevent blood loss. These are smaller in size than RBCs. Haemophilia or bleeder’s disease is a genetic platelet disorder. In a person suffering from haemophilia, there is no clotting of blood. Even a small wound or cut can prove fatal for such people as they can bleed to death.

Functions of Blood

1. It is a medium for exchange of oxygen and carbondioxide in the alveoli of lungs and body cell

2. Blood capillaries present in the villi of small intestine help in the absorption of food.

3. Harmones secreted by different endocrine glands in the body are also circulated throughout the body via blood.

4. Plalelets present in the blood help in blood clotting and thus prevent excessive blood lo

5. Blood circulates in the body and perform the function of collecting and transporting waste materials to the excretory organs for excretion

6. Blood circulation also maintains a constant internal body temperature.

7. WBCs present in blood protect us from germ and infection

TRANSPORT OF SUBSTANCES IN PLANTS

Different flowering plants herb, shrub and trees draw water from soil through their roots. Many of the outer cells at the root extend to form root hairs.

Root Hairs

The root hairs absorb water along with dissolved minerals and transport it to the leaves through xylem part of vascular system (Fig.3). Leaves are known as the “Food factories”. Food is prepared here by the process of photosynthesis. The raw materials required are water from soil, carbondioxide from atmosphere, chlorophyll present in leaves, sunlight from the sun.

Food that is prepared in the leaves is in the form of glucose. It is converted into a soluble sugar and transported through phloem to storage organs like seed, fruits, stem and root. Thus xylem and phloem are present as vascular system in plants throughout their body, that is from roots to leaves covering the stem and the branches.

Note: A group of cells, mostly of similar type performing specialised function. Group of tissues make an organ. Xylem and phloem are examples of plant tissues.

Conduction of Water and Minerals through Xylem

The process by which water and minerals salts are transported from xylem of root and carried upward to the stem, branches and leaves is called Ascent of sap. There are two important forces responsible for the uptake of water and minerals in plants — one arising from the roots and the other by the leaves from the top. The mode of transport in different kinds of plants – herbs, shrubs and trees is almost the same. [Fig. 4]

The two kinds of forces are:

1. Root pressure           2. Transpiration pull

Root Pressure: The roots of a plant are in direct contact with water in the soil. The branching nature of root hairs provide a large surface area for absorption of water and mineral salts. Root cells contain large vacuoles filled with a fluid, the cell sap. The cell sap has a higher concentration of salt than the soil water such a feature enable the root hair cells to draw water from soil, through a process known as osmosis. The continuous absorption of water by root hairs build up sufficient force to push the water upwards through the xylem vessels.

Xylem are complex tissues composed of more than one type of cells they consist mainly of dead elements tracheids, vessels, xylem fibres and a living element xylem parenchyma.

Transpiration Pull: The loss of water from the aerial parts of plants in the form of water vapours is known as transpiration. Water evaporates through stomata, the tiny pores present on leaf surfaces. When water is lost from the leaves either due to transpiration or consumed in the process of photosynthesis, the water column becomes greatly stretched and creates a pull. The continuity of water column does not break due to the forces operating between the water molecules and also between the water molecules and the wall of the xylem vessels. The transpiration pull is sufficient to raise water in leaves of the tallest trees.

Thus due to combined effect of push force due to root pressure and pull force due to transpiration by leaf cells, water moves upwards along the xylem vessel (Fig,. 5).