BIOLOGY [3 marks Question Answer]

Pancreas is both an exocrine as well as endocrine gland. It has a duct which secretes pancreatic juice which helps in digestion. Pancreas also contains an endocrine tissue called Islets of Langerhans which produce a number of hormones of which one important hormone is insulin. Insulin controls the amount of glucose in the blood. Extra glucose is converted into glycogen by insulin and stored in the liver. In some people enough insulin is not released, as a result of which excess glucose collects in the blood and is excreted along with urine. This condition is called diabetes mellitus.

Thyroid gland is present in the throat region. It produces thyroxine hormone which controls the speed of cellular metabolism especially, the rate at which oxygen is consumed and energy is produced. Thyroxine hormone is an iodine containing hormone. Too little of this hormone makes a person sleepy and sluggish and brings an increase in weight, since the food taken in is stored rather than being oxidized to release energy. Insufficient secretion of thyroxine is called hypothyroidism. The prominent symptom of hypothyroidism is the swelling of thyroid gland. This condition is called goitre.

The functions of:
Iris : Iris is the opaque disc of muscular tissue, which expands and contracts in response to intensity of light.
Retina : It acts as a screen. The image of an object is formed at retina.
Pupil : It is a small hole in the Iris. It regulate and controls the amount of light entering the eye.
Optic Nerve : The optic nerve connect the eye to the brain. It transfer nerve impulses to the brain, which in turn interprets these impulses and we are able to see.

Cerebrum : It is the uppermost and the largest part of the brain. It fills most of the skull. The surface of the cerebrum shows ridges and grooves. These increase the surface area of the brain to have more nerve cells. It is divisible into right and left cerebral hemispheres with a deep furrow in between. It is responsible for sensation of pain, temperature, touch, sight, sound, taste and smell. It is also the centre for mental activities involved in memory, intelligence, thinking and reasoning.

The basic structural unit of the nervous system is a nerve cell or a neutron. The message that travels along a neutron is called an impulse. It is like an electrical signal. Each nerve cell consists of a cell body called cyton. The cell body contains the nucleus. Many short fibres called dendrons extend from the cell body which further divide to form dendrites. They receive messages from other neurons. A single long fibre called axon extends from the other side of the cell. Axon carries the message from the cell body of one neuron to another. The axon is covered by a sheath called myelin sheath.