Second stage of urine formation is called selective re-absorption. Why?

Explain the significance of peristalsis.

When a person eats sugary food, then organisms A present in his mouth act on sugar to produce a substance B. The substance B first dissolves the calcium salts from the top part C of the tooth and then from its middle part D forming holes E. These holes ultimately reach the part F in the lower part of tooth which contains nerves and blood vessels. The substance B irritates the nerve endings inside the tooth causing toothache.

1. What are (i) organisms A, and (ii) substance B?
2. What are (i) part C, and (ii) part D, of tooth known as?
3. By what name are the holes E in the tooth known?
4. Name the part F of the tooth.
5. What will happen if organisms A reach part F of the tooth known?

Mention the major events during photosynthesis.

Outline the functioning of kidney dialysis machine?

There are four organisms A, B, C and D. The organism A eats only the flesh of other animals as food. The organism B can eat grains, fruits and vegetables as well as meat and fish. The organism C can make the food itself from simple inorganic substances present in the environment by utilising sunlight energy. On the other hand, organism D eats only plants and their products as food.

1. Which organism is

1. Omnivore,
2. Herbivore,
3. Carnivore?

2. Which organism is an autotroph?
3. Which organism is/ are heterotroph (s)?
4. Which organism can be a producer?
5. Which organism is/ are consumer (s)?

Give one example each of organisms which could be like A, B, C and D.

If the teeth are not cleaned regularly, they become covered with a sticky yellowish layer W of food particles and bacteria. Since layer W covers the teeth, the alkaline liquid X secreted by glands Y inside the mouth cannot reach the teeth surface to neutralise the acid formed by the action of organisms Z on sugary food, and hence tooth decay sets in.

1. What is W known as?
2. What is (i) X, and (ii) Y?
3. What are organisms Z?
4. State one way of removing layer W from the teeth.

Draw a labelled diagram of:

1. A xylem vessel.
2. A sieve tube (or phloem).

Name the conducting structures present in plants.

Describe the working of human blood circulatory system with the help of a suitable diagram which shows all the steps involved.