Science Class 07 part-II NCERT

7. Weather and climate
1. All the changes in the weather are driven by the sun. Rainfall is measured by an instrument called the rain gauge.
2. Polar bears are so well-insulated that they have to move slowly and rest often to avoid getting overheated.
3. Birds must remain warm to survive. They migrate to warmer regions when winter sets in.
4. Some evidence that birds may use the magnetic field of the earth to find direction. And it is not only birds that migrate; mammals, many types of fish and insects are also known to migrate seasonally in search of more hospitable climates
5. Lion-tailed macaque (also called Beard ape) lives in the rainforests of Western Ghats. Its most outstanding feature is the silver-white mane, which surrounds the head from the cheeks down to its chin. It rarely comes down on the ground
8. Winds and storms
1. Increased wind speed is accompanied by a reduced air pressure. Air moves from the region where the air pressure is high to the region where the pressure is low. The greater the difference in pressure, the faster the air moves.
2. On heating the air expands and occupies more space. When the same thing occupies more space, it becomes lighter. The warm air is, therefore, lighter than the cold air. That is the reason that the smoke goes up.
3. Wind currents are generated due to uneven heating on the earth.
1. Uneven heating between the equator and the poles
2. Uneven heating of land and water
4. Thunderstorms develop in hot, humid tropical areas like India very frequently. The rising temperatures produce strong upward rising winds.
1. These winds carry water droplets upwards, where they freeze, and fall down again. Swift movement of the falling water droplets along with the rising air create lightning and sound.
9. Soil
1. The rotting dead matter in the soil is called humus.
2. If soil contains greater proportion of big particles it is called sandy soil. If the proportion of fine particles is relatively higher, then it is called clayey soil.
1. If the amount of large and fin particles is about the same, then the soil is called loamy. (sandy > loamy > clayey)
3. Sand is well aerated. Water can drain quickly through the spaces between the sand particles. So, sandy soils tend to be light, well aerated and rather dry.
4. Clay particles, being much smaller, pack tightly together, leaving little space for air. Unlike sandy soil, water can be held in the tiny gaps between the particles of clay. So clay soils have little air. But they are heavy as they hold more water than the sandy soils.
5. Best topsoil for growing plants is loam. Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. Silt occurs as a deposit in river beds. The size of the silt particles is between those of sand and clay.
6. Clayey and loamy soils are both suitable for growing cereals like wheat, and gram.
7. For paddy, soils rich in clay and organic matter and having a good capacity to retain water are ideal. For lentils (masoor) and other pulses, loamy soils, which drain water easily, are required.
8. Crops such as wheat are grown in the fine clayey soils, because they are rich in humus and are very fertile.
9. Percolation rate of water is different in different types of soil. It is highest in the sandy soil and least in the clayey soil.
10. Respiration
1. In the cells, oxygen in the air helps in the breakdown of food. The process of breakdown of food in the cell with the release of energy is called cellular respiration. Cellular respiration takes place in the cells of all organisms.
2. When breakdown of glucose occurs with the use of oxygen it is called aerobic respiration. Food can also be broken down, without using oxygen.
3. This is called anaerobic respiration. In the absence of oxygen, glucose breaks down into alcohol and carbon dioxide.
1. Yeasts are single-celled organisms. They respire anaerobically and during this process yield alcohol. They are used to make wine and beer
2. Anaerobic respiration takes places in the muscle cells to fulfil the demand of energy, releasing lactic acid.
4. Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs.
1. Inhaled air is by volume 78% nitrogen, 21% oxygen and small amounts include argon, carbon dioxide, neon, helium, and hydrogen.
2. The gas exhaled is 4-5% by volume of carbon dioxide, about a 100 fold increase over the inhaled amount (oxygen comes down by 4-5%)
5. In earthworm, the exchange of gases occurs through the moist skin. In fishes it takes place through gills and in insects through the tracheae (spiracles).
6. In plants each part can independently take in oxygen from the air and give out carbon dioxide.
11. Transportation in animals
1. Blood is the fluid which flows in blood vessels. It transports substances like digested food from the small intestine to the other parts of the body. Fluid part of the blood is called plasma.
1. One type of cells are the red b lood cells (RBC) which contain a red pigment called haemoglobin.
2. Haemoglobin binds with oxygen and transports it to all the parts of the body and ultimately to all the cells.
2. Clot is formed because of the presence of another type of cells in the blood called platelets. Only in mammals.
3. Arteries carry oxygen-rich blood from the heart to all parts of the body. Since the blood flow is rapid and at a high pressure, the arteries have thick elastic walls. Veins are the vessels which carry carbon dioxide-rich blood from all parts of the body back to the heart. The veins have thin walls.
1. There are valves present in veins which allow blood to flow only towards the heart.
2. On reaching the tissues, arteries divide further into extremely thin tubes called capillaries. The capillaries join up to form veins which empty into the heart.
4. Animals such as sponges and Hydra do not posses any circulatory system.
5. Urine consists of 95% water, 2.5% urea and 2.5% other waste products. Fish excrete waste substances such as ammonia which directly dissolve in water
6. Root hair increase the surface area of the root for the absorption of water and mineral nutrients dissolved in water.
7. Nutrients are transported along with water to the entire plant via the vascular tissue called xylem.
8. The vascular tissue for the transport of food to the various parts of the plant is phloem.
12. Reproduction in plants - covered in class 12
1. There are several methods of asexual reproduction such as fragmentation, budding, spore formation and vegetative propagation. Plants such as moss and ferns reproduce by means of spores.
2. Flowers which contain either only the pistil or only the stamens are called unisexual flowers. The flowers which contain both stamens and pistil are called bisexual flowers
3. Pollen grains have a tough protective coat which prevents them from drying up.
4. Seed dispersal is aided by wind, water and animals. Seed dispersal helps the plants to (i) prevent overcrowding, (ii) avoid competition for sunlight, water and minerals and (iii) invade new habitats
13. Current
1. When an electric current flows through a wire, the wire gets heated. It is the heating effect of current. This effect has many applications.
2. When electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current.
14. Light
1. Light travels along straight lines.
2. An image which can be obtained on a screen is called a real image. An image which cannot be obtained on a screen is called a virtual image
3. Image formed by a plane mirror is erect. It is virtual and is of the same size as the object. The image is at the same distance behind the mirror as the object is in front of it.
4. Convex mirror uses - side view mirror in cars, accidental security mirror
   Concave mirror uses - telescope, shaving mirrors, reflectors in head light
5. A convex lens converges (bends inward) the light generally falling on it, called a converging lens. A convex lens can form real and inverted image.
6. When the object is placed very close to the lens, the image formed is virtual, erect and magnified. When used to see objects magnified, the convex lens is called a magnifying glass.
7. On the other hand, a concave lens diverges (bends outward) the light and is called a diverging lens. Image formed by a concave lens is always virtual, erect and smaller in size than the object
8. Sunlight consists of seven colors. The sunlight is said to be white light. This means that the white light consists of seven colors