5. Life Processes

In multi-cellular organisms, most cells are not in direct contact with the air outside. Diffusion is a very slow process. It cannot supply oxygen quickly to all the cells deep inside the body. So special organs like lungs and a transport system are needed.

Living things show movement, which may be visible or at the molecular level. They also carry out life processes like nutrition, respiration, transportation and excretion. These help to maintain and repair the body. If these are present, we say the thing is alive.

Outside raw materials such as food, water and oxygen are used for:

• getting energy,
• growth and development of the body,
• making proteins and other substances needed by the body,
• repair and maintenance of the body.

Nutrition, respiration, transportation and excretion are essential for maintaining life.

• Carbon dioxide: from the atmosphere, through the stomata of leaves.
• Water: from the soil, absorbed by the roots.
• Sunlight: from the Sun.
• Chlorophyll: present in the chloroplasts of green leaves.

Plants also take minerals like nitrogen and phosphorus from the soil.

• Hydrochloric acid creates an acidic medium. This helps the enzyme pepsin to act on proteins.
• It also kills germs that enter the stomach with food.

Digestive enzymes break down complex food molecules into simple, soluble molecules. For example, proteins into amino acids, carbohydrates into glucose and fats into fatty acids and glycerol. These simple molecules can be absorbed by the body.

The inner lining of the small intestine has many finger-like projections called villi. Villi increase the surface area for absorption. They are richly supplied with blood vessels. These blood vessels take the absorbed food to every cell of the body.

The amount of oxygen dissolved in water is very low compared to air. So aquatic organisms breathe much faster to get oxygen. Terrestrial organisms take oxygen from air, which has a much higher amount of oxygen. So they do not have to breathe so fast.

Glucose is first broken into pyruvate in the cytoplasm. Then it is broken down in three ways:

• In yeast (absence of oxygen): pyruvate → ethanol + carbon dioxide + energy
• In muscle cells (lack of oxygen): pyruvate → lactic acid + energy
• In mitochondria (presence of oxygen): pyruvate → carbon dioxide + water + energy

Oxygen: Haemoglobin in red blood cells has a high affinity for oxygen. It carries oxygen from the lungs to all the tissues.

Carbon dioxide: It is more soluble in water. So it is mostly carried in dissolved form in the blood plasma, from the tissues to the lungs.

In the lungs, the air passage divides into smaller and smaller tubes. These end in balloon-like structures called alveoli. The alveoli give a very large surface area for exchange of gases. Their walls are thin and have a network of blood vessels.

• Heart: It pumps blood to all parts of the body.
• Blood vessels (arteries, veins and capillaries): Arteries carry blood away from the heart. Veins bring blood back to the heart. Capillaries allow exchange of materials between blood and cells.
• Blood: Plasma carries food, carbon dioxide and nitrogenous wastes. RBCs carry oxygen. Platelets help in clotting of blood.
• Lymph: It carries digested fats and drains extra fluid from tissues back into the blood.

Mammals and birds need a lot of energy because they maintain a constant body temperature. Separating the two types of blood gives a highly efficient supply of oxygen to the body. So they can get enough energy.

• Xylem: It carries water and minerals from the roots to the leaves.
• Phloem: It carries food made in the leaves to other parts of the plant.

Xylem tissue carries water and minerals. Root cells take ions from the soil. This creates a difference in concentration, so water moves into the root and pushes up the xylem.

Transpiration (loss of water vapour from leaves) creates a suction. This pulls water from the roots to the leaves. This is the main force during the day.

The transport of food is called translocation. It takes place through phloem. Food like sucrose is moved into phloem using energy from ATP. This increases the pressure in the phloem. Then food moves to other parts of the plant where it is needed.

Structure: Nephron is the basic filtering unit of the kidney. It has a cup-shaped part called Bowman’s capsule. It holds a cluster of thin-walled blood capillaries called the glomerulus. A long tubule from the capsule ends in a collecting duct.

Functioning:

• Oxygen and carbon dioxide are removed through stomata.
• Extra water is removed by transpiration.
• Some wastes are stored in leaves, which fall off.
• Some wastes are stored as resins and gums in old xylem.
• Some wastes are given out into the soil around the roots.

It depends on the amount of excess water and dissolved wastes in the body. If there is more water in the body, more urine is produced. If there is less water, more water is reabsorbed and less urine is formed. Hormones also help to control this.

Answer: (c) excretion.

Answer: (a) transport of water.

Answer: (d) all of the above.

Answer: (b) mitochondria.

Fats are digested in the small intestine.

Saliva wets the food and makes swallowing easy. It contains an enzyme called salivary amylase. This enzyme breaks down starch into simple sugar.

Necessary conditions: sunlight, chlorophyll, carbon dioxide and water.

By-products: oxygen is released. Carbohydrates are stored as starch.

Organisms that use anaerobic respiration: yeast, some bacteria and parasitic worms (like tapeworm). Our muscle cells also use it during heavy exercise.

• Alveoli are balloon-like and very large in number. So they give a very large surface area. If spread out, it would cover about 80 m².
• Their walls are very thin.
• They are surrounded by a dense network of blood capillaries.

Haemoglobin carries oxygen to the cells. If it is less, cells get less oxygen. So less energy is produced. The person feels tired and weak and gets breathless easily. This condition is called anaemia.

In human beings, blood passes through the heart twice in one complete cycle. This is called double circulation.

Why necessary: It keeps oxygenated and deoxygenated blood separate. This gives an efficient supply of oxygen. Our body needs a lot of energy to keep a constant body temperature.