CBSE Class 10 Science Life Processes Transportation in Humans and Plants Notes Set 10

Why do organisms need a transport system?

A single-celled organism such as Amoeba exchanges materials directly with its surroundings through the cell surface, and diffusion carries them within the cell. In large multicellular organisms, the cells that absorb, make or use materials are far apart, so diffusion alone is too slow. These organisms need a transport system that carries food, oxygen, water, minerals, hormones and wastes quickly to and from every cell.

Transportation in human beings

The human transport system is the circulatory system. It has three parts: blood (the fluid medium), the heart (the pump) and blood vessels (the tubes).

Blood

Blood is a fluid connective tissue made of plasma and cells.

1. Plasma is the straw-coloured liquid. It carries dissolved food, carbon dioxide in the form of bicarbonate, nitrogenous wastes, salts and hormones.

2. Red blood cells (RBCs) contain haemoglobin, a pigment that has a high affinity for oxygen and carries it from the lungs to the tissues. A shortage of haemoglobin causes anaemia.

3. White blood cells (WBCs) fight infection by engulfing germs and by making antibodies.

4. Platelets help blood to clot at a cut so that blood loss is stopped.

The heart

The heart is a muscular organ about the size of a fist, placed in the chest slightly to the left. It has four chambers: two upper atria, which receive blood, and two lower ventricles, which pump blood out. The ventricles have thicker walls than the atria because they must push blood to the lungs and the whole body. Valves between the chambers and at the exits ensure that blood flows in one direction only. Oxygen-rich and oxygen-poor blood are kept separate by the wall between the right and left halves, which is essential in birds and mammals since they have high energy needs and maintain a constant body temperature.

Path of blood: body, then the right atrium, right ventricle, lungs (where it picks up oxygen), left atrium, left ventricle and back to the body.

Double circulation

Blood passes through the heart twice in one complete round: once in the pulmonary circulation (heart to lungs and back) and once in the systemic circulation (heart to body and back). This is why human circulation is called double circulation.

Blood vessels

1. Arteries carry blood away from the heart. They have thick, elastic walls to withstand high pressure. They carry oxygenated blood except the pulmonary artery.

2. Veins bring blood back to the heart. They have thinner walls and contain valves to stop backflow. They carry deoxygenated blood except the pulmonary vein.

3. Capillaries are very thin, one-cell-thick vessels linking arteries to veins; exchange of materials between the blood and the cells occurs here.

Blood pressure

Blood pressure is the force exerted by blood on the walls of the vessels. Systolic pressure, measured while the ventricles contract, is about 120 mm Hg in a healthy adult. Diastolic pressure, measured while the ventricles relax, is about 80 mm Hg. High blood pressure (hypertension) can lead to rupture of arteries and internal bleeding.

Lymph

Some plasma, proteins and blood cells leak through the capillary walls into the tissue spaces. This colourless fluid, called lymph, drains back into the blood through lymph vessels. It carries digested fat from the intestine and helps in defence against infection.

Transportation in plants

Plants have a lower energy need, and their transport is carried out by the vascular tissues, xylem and phloem.

Xylem is made of vessels, tracheids, fibres and parenchyma and carries water and minerals from the roots to the leaves. Flow is one-way (upward). Roots take in ions actively, which makes water enter by osmosis and creates root pressure that pushes water up a short distance. The major force for tall plants is transpiration pull: water evaporating from leaf stomata creates suction that pulls a continuous column of water up from the roots. At night when stomata are closed, root pressure is the chief force.

Transpiration also cools the plant and helps in the absorption of water and minerals.

Phloem is made of sieve tubes, companion cells, fibres and parenchyma and carries soluble food, mainly sucrose, and also amino acids from the leaves to all parts of the plant, such as the roots, fruits and growing tips. This is translocation. Sucrose is loaded into the phloem by using energy from ATP, which makes water move in by osmosis; the resulting pressure moves the material to the regions where it is needed. Flow in phloem can occur in both directions.

Worked examples

Example 1. Why is the right side of the heart separated from the left side? Answer: it prevents the oxygen-rich blood from mixing with the oxygen-poor blood, so the body gets a fully oxygenated supply, which supports high energy needs.

Example 2. Which force raises water in a tall tree during the day, and which at night? Answer: during the day, the transpiration pull; at night, when stomata are closed, the root pressure.

Example 3. Trace the path of a molecule of oxygen from the lungs to the body. Answer: lungs, pulmonary vein, left atrium, left ventricle, aorta, arteries and capillaries, and then to the body cells.

Quick Check Questions