Test Paper 2

A neuron is the longest cell of our body. It has three parts — cell body, axon and dendrites.

1. The cell body called cyton contains the nucleus.
2. Many short fibres called dendrons arise from the cell. They further divide to form dendrites. Dendrites receive messages from other neurons.
3. A single, long fibre called axon extends from the other side of the cell body. It is covered by a sheath called myelin sheath.

Below diagram shows the structure of a neuron:

An automatic, spontaneous and mechanical response to a stimulus; controlled by the spinal cord without the involvement of the brain is called a reflex action.
For example, if we step on a sharp object, we instantly withdraw our foot. This reaction is automatic and does not involve thinking about it.

The various physical changes that occur during adolescence are:

1. Sexual maturation — In males testes start producing testosterone and sperms. In females, the ovaries start releasing eggs and produce the female hormones, oestrogen and progesterone. Sex organs develop fully and secondary sexual characteristics like enlargement of external genital organs in males and enlargement of breasts in females also start.
2. Increase in height — There is a spurt in growth hormone leading to sudden increase in height due to the elongation of the bones of the legs and arms. Age by which full height is attained is 14 to 15 years for girls and 18 to 19 years for boys.
3. Change in body appearance — In males, the shoulders become broad and the chest becomes wide.The muscles also grow and develop more than in girls. In females, there is widening of the pelvic region and broadening of the hips. The breasts also develop and enlarge in size. Also in both males and females, hair starts growing in the armpit and pubic area. In males, facial hair (as beard and mustache) grows.
4. Change in voice — There is growth in the voice box or larynx. It grows more in males than in females. As a result, males develop deep voice whereas females develop a high-pitched voice.

HIV stands for Human Immuno-deficiency Virus. It is a virus which causes AIDS. AIDS stands for Acquired Immuno deficiency Syndrome.
The difference between HIV and AIDS is that HIV is a virus which acts as the vector or causative agent for the disease that is called AIDS.

Following are the ways to prevent AIDS:

1. Screening of blood before transfusion
2. Avoiding sharing and reuse of blades, needles and syringes and surgical instruments.
3. Avoiding pregnancy if mother is HIV positive
4. Safe sex
5. Educating people

Five ways in which fungi help us are:

1. They decompose the dead, decaying bodies of plants and animals. Fungi also helps in making the soil fertile.
2. Morels and some mushrooms are consumed as delicacies.
3. Yeast is used in baking industry.
4. Alcohol and alcoholic drinks are produced by the fermentation of grapes, barley etc. by yeast.
5. Yeast is also used for manufacturing vitamins. Penicillin, an antibiotic, is obtained from Penicillium, a fungi.

The membranes enveloping the brain are called meninges.

The message that travels along a nerve in the form of a wave of chemical disturbance is called impulse.

Endocrine glands are also called ductless glands because they do not have their own duct.

The hormone thyroxine is released by thyroid gland.

BCG vaccine is given to children as a preventive measure against tuberculosis.

The process of treating animal skin to produce leather is called tanning.

The breeding and management of silkworms for the production of silk is called sericulture.

Increased level of thyroxine due to over secretion increases rate of metabolism and cellular respiration. This causes weight loss.

We get a variety of products from animals. Animals are beneficial to us in following ways:

1. They provide us milk, meat and eggs.
2. We can use the drought animals for work in field.
3. They also provide us wool, hide, leather etc.
4. Other products like honey, silk, pearl and lac are derived from animals.

The labelled parts of brain are:

a → Cerebrum

b → Cerebellum

c → Medulla Oblongata

False

Corrected statement — Motor nerves carry impulses from the spinal cord to the sense organs.

True

False

Corrected statement — The chemicals secreted by endocrine glands are called hormones.

True

False

Corrected statement — Communicable diseases are also called infectious diseases.

True

True