NCERT Solutions: Class 10 Science Chapter 5 - Life Processes

In multicellular organisms, all cells are not in direct contact with the external environment. Diffusion is too slow to transport oxygen over long distances and cannot meet the high oxygen demand of many cells, so specialised transport and respiratory systems are needed.

We look for life processes such as nutrition, respiration, transport, excretion, growth, response to stimuli and reproduction. Even when visible movement is absent, molecular movement and maintenance processes continue in living organisms.

Outside raw materials are used to build the body, repair tissues and release energy. They include food as a source of carbon and energy, oxygen for respiration, and water and minerals for biochemical processes.

The essential life processes are nutrition, respiration, transport and excretion. These processes supply energy and materials, move them through the body and remove wastes.

In autotrophic nutrition, organisms make their own food from CO₂ and water using light energy and chlorophyll, as green plants do. In heterotrophic nutrition, organisms depend on other organisms for ready-made organic food, as animals, fungi and many bacteria do.

Plants get carbon dioxide from the air through stomata, water from the soil through roots, and sunlight from the Sun. Chlorophyll present in the leaves traps light energy.

Hydrochloric acid in the stomach creates an acidic medium needed for the enzyme pepsin to digest proteins. It also helps kill many microbes that enter with food.

Digestive enzymes break down complex food molecules into simpler soluble molecules that can be absorbed. For example, amylase breaks starch into sugars, pepsin digests proteins and lipase breaks fats.

The inner lining of the small intestine has many finger-like projections called villi. Villi greatly increase surface area and contain blood capillaries and lymph vessels, so digested nutrients can be absorbed efficiently and transported through the body.

Air contains a much higher concentration of oxygen than water. Therefore terrestrial organisms can obtain oxygen more easily than aquatic organisms, which must extract dissolved oxygen from water.

Glucose first breaks down in the cytoplasm to pyruvate. In the presence of oxygen, pyruvate is completely oxidised in mitochondria to CO₂ and water with a large release of energy. In yeast, anaerobic breakdown forms ethanol, CO₂ and energy. In muscle cells during lack of oxygen, pyruvate is converted to lactic acid with a smaller release of energy.

Oxygen is transported mainly by haemoglobin in red blood cells as oxyhaemoglobin. Carbon dioxide is more soluble in water and is transported mostly in dissolved form as bicarbonate in the blood plasma, with some carried by haemoglobin.

The lungs contain millions of alveoli. Each alveolus has a thin wall and is surrounded by blood capillaries, giving a very large surface area and a short diffusion distance for exchange of oxygen and carbon dioxide.

The human transport system consists of the heart, blood and blood vessels. The heart pumps blood. Blood transports oxygen, carbon dioxide, nutrients, hormones and wastes. Arteries carry blood away from the heart, veins bring blood back to the heart, and capillaries allow exchange with tissues.

Mammals and birds maintain a constant body temperature and need a high, efficient energy supply. Separation of oxygenated and deoxygenated blood ensures that tissues receive oxygen-rich blood and respiration is efficient.

Highly organised plants have xylem and phloem as transport tissues. Xylem transports water and minerals from roots to aerial parts, while phloem transports food from leaves to other parts of the plant.

Water and minerals are absorbed by root hairs and move into xylem vessels. They rise through xylem due to root pressure and mainly due to transpiration pull created by evaporation of water from leaves.

Food is transported by phloem in a process called translocation. Sugars made in leaves are actively loaded into phloem using energy from ATP; water enters by osmosis, creating pressure that moves the food solution to storage and growing tissues.

A nephron has a cup-shaped Bowman's capsule containing a glomerulus, followed by a long tubular part that joins a collecting duct. Blood entering the glomerulus is filtered under pressure, so water, salts, glucose, amino acids and urea enter Bowman's capsule. As the filtrate passes through the tubule, useful substances such as glucose, amino acids, required salts and most water are selectively reabsorbed into the blood. The remaining fluid, containing urea and excess water and salts, becomes urine and passes into the collecting duct.

Plants remove wastes by diffusion of gases through stomata and lenticels, by storing wastes in leaves, bark or old xylem that later fall off, by converting wastes into resins and gums, and by excreting some substances into the surrounding soil.

The amount of urine depends on how much excess water and dissolved waste must be removed. If the body has plenty of water, less water is reabsorbed and more urine is produced. If water is scarce, more water is reabsorbed in the nephrons, producing less concentrated urine. Hormones also regulate this reabsorption.

(c) excretion.

(a) transport of water.

(d) all of the above.

(b) mitochondria.

Fat digestion takes place mainly in the small intestine. Bile salts from the liver emulsify large fat globules into smaller droplets, increasing the surface area. Lipase enzymes then break fats into fatty acids and glycerol.

Saliva moistens food and helps in swallowing. It contains salivary amylase, which begins digestion by breaking starch into simpler sugars.

Autotrophic nutrition requires carbon dioxide, water, chlorophyll and sunlight. In photosynthesis, glucose is formed and oxygen is released as a by-product.

Aerobic respiration occurs in the presence of oxygen and completely breaks down glucose to CO₂ and water, releasing more energy. Anaerobic respiration occurs without oxygen and releases less energy, producing ethanol and CO₂ in yeast or lactic acid in muscle cells. Yeast and some bacteria use anaerobic respiration.

Alveoli are numerous tiny sacs that provide a very large surface area. Their walls are thin and moist, and each alveolus is surrounded by a network of capillaries, allowing rapid diffusion of oxygen into blood and carbon dioxide out of blood.

Haemoglobin carries oxygen in blood. Its deficiency reduces oxygen transport to tissues, so cells release less energy by respiration. The person may feel tired, weak and breathless, a condition associated with anaemia.

In double circulation, blood passes through the heart twice during one complete round. In pulmonary circulation, deoxygenated blood from the right side of the heart goes to the lungs and returns oxygenated to the left side. In systemic circulation, oxygenated blood from the left side goes to the body and returns deoxygenated to the right side. It is necessary because it keeps oxygenated and deoxygenated blood separate and supplies oxygen efficiently to meet the high energy needs of humans.

Xylem transports water and minerals mainly upward from roots to leaves, largely by transpiration pull and root pressure. Phloem transports food from leaves to storage or growing regions; movement can be upward or downward and requires energy from ATP for loading.

Alveoli are thin-walled air sacs surrounded by capillaries; they provide a large surface for diffusion of gases, allowing oxygen to enter blood and carbon dioxide to leave it. Nephrons are tubular filtration units with Bowman's capsule, glomerulus and tubule; they filter blood, reabsorb useful substances and form urine. Both have thin walls and rich blood supply, but alveoli exchange gases while nephrons remove soluble nitrogenous wastes and regulate water and salts.