[5 Mark Question Answer]

Question 14 Marks

What are endocrine glands ?

Answer

The specialised tissues that release, chemical substances that is hormones in trace amounts are called endocrine glands.$-$ The endocrine glands do not have ducts, so they are called ductless glands. These glands put their secrefrous directly into the blood. Hormones are the chemical messengers which help to control and
coordinate various activities in the body. The various endocrine glands are.
$(a)$ Pituitary gland : It is called the master gland as it secretes many hormones and some of these hormones control other endocrine glands. It is present at the base of the brain. It releases the growth hormone which controls the growth of the body.
$(b)$ Thyroid gland : It 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.
$(c)$ Parathyroid glands : Parathyroid glands are four small glands attached to the thyroid gland. It releases parathyroxine or parathormone. This hormone controls the amount of calcium and phosphorus in the body, which plays an important role in muscle contraction.
$(d)$ Pancreas : Pancreas is both exocrine as well as endocrine gland. It has a duct w’hich secretes pancreatic juice which helps in digestion. Pancreas also contains an endocrine tissue called Islets of Langerhans which produce insulin. Insulin controls the amount of glucose in the blood.
$(e)$ Adrenal glands : One adrenal gland is present above each of the two kidneys. Adrenal glands produce the hormone adrenalin. Adrenalin is released when person is under stress or involved in intensive exercise. It makes the heart beat faster, increases the flow of blood to the brain and helps to cope with stress.
$(f)$ Ovaries and testes : Ovaries produces female hormones progesterones and oestrogen. Testes produces male hormone testosterone. These hormones control growth, development and reproductive behaviour. These hormones are related to appearance of secondary sexual- character in both males and females.

Gland	Location	Main Hormone secreted by it	Functions
pituitary	at the base of the brain	growth hormone	regulates growth
thyroid	throat region	thyroxine	regulates rate of growth and metabolism
parathyroid	throat region	parathormone	Regulates calcium and phosphorus level
pancreas	abdomen $($near the small intenstine$)$	insulin in blood	regulates amount of glucose in blood
adrenal	above kidneys	Adrenalin	helps a person to cope with an emergency
Ovaries $($females$)$	lower abdomen	Oestrogen. progesterone	Control reproductive growth and development, and reproductive behavior.
Testes $($males$)$	scrotum	testosterone	Controls reproductive growth and development, and reproductive behaviour

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Question 24 Marks

Explain the structure of an eye. Draw a labelled diagram to show the structure of the eye.

Answer

Each eyeball is almost spherical. Tluman eye consists of three layers$-$the outermost layer called scleroid, middle layer called choroid and the innermost layer called retina.

Scleroid : It gives shape and protects the inner delicate parts of the eye. It is white and thick except in front, where it is transparent for light to enter. This region is termed as cornea. It is protectively covered by a transparent conjunctiva.
Choroid : It is a thin layer, just behind the rim of cornea. The choroid layer is raised into a number of ridges or ciliary processes which surround the lens. The lens divides the cavity between cornea and the lens is filled with a fluid called aqueous homour. The larger back or posterior cavity behind the lens is filled with a thicker fluid called vitreous humour. The choroid layer is not continuous as it terminates in front of the eye near the iris.
Iris : The iris is an opaque disc of muscular tissue containing blood capillaries and pigments. It forms the coloured part of the eye. This ring of muscles expands and contracts in response to intensity of light. The pupil is the opening in the middle of the iris. The size of the pupil controls the amount of light that enters the eye.
Retina : The innermost layer consists of nerve cells sensitive to light. There are two types of light sensitive cells$-$rods and cones. Cones are the receptors responsible for coloured vision and for seeing when the light is strong. Rods are receptors for seeing in dim light. Behind the iris is a biconvex lens. Light passes through the pupil to the lens. The lens is a clear, flexible structure. Muscles attached to the lens cause it to get thicker or thinner. As the lens changes shape, it focuses light from near or far objects on to the retina and forms an image.
The rods and cones of the retina are connected to sensory neurons that form the optic nerve. The optic nerve connects the eye to the brain. When light stimulates rods and cones, nerve impulses are sent along the optic nerve to the brain. The brain interprets these impulses and we are able to see, .Eyes are provided with lacrymal glands $($tear glands$)$ which produce tears. Tears wash away foreign materials, irritants and prevent injury.

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Question 34 Marks

What does central nervous system consist of ?

Answer

Central nervous system in human beings is highly ’ developed. It consist of $(a)$ brain $(b)$ spinal cord.
$(a)$ Brain : Brain is the main control centre of the nervous system. It is situated within the skull. It is enveloped by three membranes called meninges. The membranes have a fluid called cerebrospinal fluid between them. The brain is divided in to three regions.
$(i)$ Cerebrum : It is the uppermost and the largest part of the brain. It consists of two cerebral hemispheres. It is responsible for the sensation of pain, temperature, touch, sight, sound, taste and smell. It is also involved in memory, intelligence, thinking and reasoning.
$(ii)$ Cerebellum : It is a small egg shaped organ, placed under the cerebrum at the back of the head. It is involved is muscle coordination and balance of body.
$(iii)$ Medulla Oblongata : It emerges out from the base of the brain and joins the spinal cord to the brain. It is also called the brain stem. It is the regulating centre for swallowing, coughing, sneezing and vomiting.
$(b)$ Spinal cord : It is the continuations of the medulla oblongata. It is like a cord coming out from a hole at the base of the skull, running through the vertebral column. A cross sections of the spinal cord shows two similar halves fused together to form a small canal in the centre called central canal.
It contains cerebrospinal fluid. The $H-$shaped area in central canal is called grey matter, which consist of cell bodies of neurons. The outer portion is white matter which consists of nerve fibres. A part from regulating normal function of the body, many activities of the internal organs like heart, blood vessels and glands are controlled by spinal cord. It also serves as a reflex centre.

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BIOLOGY [5 Mark Question Answer]

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