The big picture
Four jobs, done in plants and in animals.
| Idea | The rule |
|---|---|
| Four processes, one body | Life processes keep a body in repair. Nutrition brings in food. Respiration releases the food’s energy. Transport carries things around. Excretion removes harmful wastes. |
| Makers and eaters | An autotroph makes its own food from simple things. Carbon dioxide and water are two of them. Green plants use sunlight to do it. A heterotroph depends on food made by other living things. |
| A meal taken apart in steps | Food is broken down step by step along the alimentary canal. Enzymes do the breaking down. Digested food is absorbed in the small intestine. |
| Respiration is chemistry | Respiration breaks glucose down to release energy. Aerobic respiration uses oxygen and releases much more energy. Anaerobic respiration works without oxygen. |
| Why big bodies need a pump | Blood goes through the heart twice in one round of the body. This is double circulation. The right side sends blood to the lungs. The left side sends it to the body. |
| Moving water in plants | By day, transpiration pulls water up the xylem. At night, root pressure matters more. The phloem carries food both up and down. |
| Filtering the blood | A nephron filters blood. It takes back glucose, amino acids, salts and much of the water. What is left leaves as urine. |
| Where urine goes | Urine is made in the kidneys. Urine flows down the ureters to the bladder. The bladder stores urine. Urine leaves the body through the urethra. |
| What plants do with waste | Plants let gases out and lose extra water as vapour. A falling leaf carries some waste away. Old wood stores waste as gums and resins. Some waste goes out into the soil. |
| How a leaf makes food | Photosynthesis needs carbon dioxide, water, sunlight and chlorophyll. It makes glucose and oxygen. Extra glucose is stored as starch. |
| Test a leaf for starch | Iodine turns blue-black where there is starch. A leaf needs chlorophyll, light and carbon dioxide to make starch. |
| The path of air | Air passes through the nostrils, throat and windpipe. Then it passes down smaller and smaller tubes to the alveoli. |
| Where gases swap | Alveoli are tiny balloon-like sacs with thin walls. Blood vessels wrap round them. Oxygen passes into the blood. Carbon dioxide passes out. |
| What blood carries | Plasma is the liquid part of blood. It carries food, wastes and much of the carbon dioxide. Red cells carry oxygen with haemoglobin. Platelets help blood clot at a cut. |
| White cells and lymph | White cells fight germs. Fat that you digest travels in lymph. Lymph also returns spare liquid to the blood. |
| Three kinds of tube | Blood leaves the heart in arteries, under high pressure. Artery walls are thick and elastic to stand it. Veins bring blood back. Many veins have valves that keep it moving one way. Capillaries are the tiniest tubes. Food, oxygen and wastes cross their one-cell wall. |
| How much urine? | Both kidneys together filter about 180 L of liquid in a day. Just 1 to 2 L leaves as urine. The rest is taken back. The amount taken back depends on the body’s water. It also depends on the wastes to remove. |
Now open Chapter 5, Life Processes, in your NCERT Science book.