21.

Select the correct statement about biosphere reserves

• These are the areas which help to maintain the biodiversity and culture of the areas

• These are the protected areas reserved for wildlife where they can freely use the habitats and natural resources

• These are the protected areas meant for the conservation of endemic species

• These are the areas meant only for the conservation of plants and animals

Study the following statements.

1. Prokaryotes do not have a nucleus.
2. A single cell can perform all the functions in a unicellular organism.
3. Blue-green algae are examples of prokaryotes.
4. Eukaryotes do not have a well-organized nucleus with a nuclear membrane.

The correct statements are

• A, C and D

• B, C and D

• A, B and C

• A, B and D

In the given diagram, positions of four endocrine glands in the human body are marked by the letters A, B, C and D. The correct labeling of A, B, C and D is

• A - adrenal gland

  B - thyroid gland

  C - pancreas

  D - pituitary gland

• A - pituitary gland

  B - pancreas

  C - thyroid gland

  D - adrenal gland

• A - pituitary gland

  B - thyroid gland

  C - adrenal gland

  D - pancreas

• A - adrenal gland

  B - pituitary gland

  C - pancreas

  D - thyroid gland

A rectangular container given below is filled with a liquid heavier than water.

Select the correct statement from the following about the liquid pressure.

• Pressure at C > Pressure at B = Pressure at A

• Pressure at C > Pressure at B > Pressure at A

• Pressure at A = Pressure at B = Pressure at C

• Pressure at A > Pressure at B > Pressure at C

Light is falling on the surfaces S₁, S₂ and S₃ as shown below

The surfaces on which the angle of incidence is equal to the angle of reflection are

• S₁ and S₃

• All the three surfaces

• S₁ and S₂

• S₂ and S₃

In the diagram of human eye given below, the parts marked by A, B, C and D should be labeled as

• A-iris, B-cornea, C-pupil, D-lens

• A-ciliary muscle, B-iris, C-lens, D-cornea

• A-ciliary muscle, B-pupil, C- lens, D-cornea

• A-iris, B-pupil, C-lens, D-cornea

Impression of an image persists on the retina of human eye for about

• $\frac{1}{15}\mathrm{s}$

• $\frac{1}{25}\mathrm{s}$

• 1 s

• $\frac{1}{2}\mathrm{s}$

Study the following statements.

1. Germination of seeds does not take place under dry conditions.
2. Nutrients get transported to each part of the plant in a dissolved form.
3. The supply of water to crops at different intervals improves the texture of the soil.
4. The supply of water to crops makes the soil porous due to which exchange of gases becomes easy.
5. Water protects the crops from both frost and hot air currents.

The statements which justify the need to irrigate crops are

• C, D and E

• A, B and E

• A, B and C

• B, C and D

Study the following statements

1. Chromosomes are located in the nucleolus.
2. Genes are located in the chromosomes.
3. Unicellular organisms respire and reproduce.
4. The most important function of the cell membrane is to control the entry and exit of materials from cells.

The correct statements are

• A, C and D

• A, B and D

• A, B and C

• B, C and D

The ultrasound equipments used for investigating medical problems work at frequency

• between 2000 Hz and 20000 Hz

• above 20000 Hz

• below 20 Hz

• between 20 Hz and 200000 Hz