Science M.C.Q

Photo means light and tropism means movement. The bending of plant shoots in response to light is called phototropism.

Insulin is produced in the pancreas. It regulates blood sugar level and its deficiency causes diabetes. The growth and development of the body is regulated by the growth hormone.

It is a non-directional movement of plant parts in response to light.

Testosterone is the male sex hormone which is associated with male puberty.

The growth of pollen tubes towards the ovule caused by a sugary substance is an example of chemotropism.

The stimulus in thigmotropism is touch which causes movement.

Under-secretion of thyroxine hormone from the thyroid gland can lead to goitre.

The pituitary gland secretes a hormone known as growth hormone which controls the growth of the human body. Deficiency of growth hormone can make the person very short, while excess of this hormone can make a person very tall.

Roots do not respond to touch.

Roots bend away from the light source and show negative phototropism.

The hindbrain consists of three centres called the pons, the cerebellum and the medulla.
The forebrain consists mainly of the cerebrum.
The midbrain does not have any further divisions.
The spinal cord is a cylindrical structure.

The olfactory receptors which detect smell are located in the nose.

In a synapse, a chemical signal is transmitted from the axon end of one neuron to the dendrite end of the adjacent neuron.

The contraction of the pupil of the eye in the presence of a bright light is an example of cerebral reflex. A reflex action that involves the brain is called cerebral reflex. It is found in the organs present in the head that are directly connected to the brain.

The growth of tendrils in pea plants is due to the rapid cell division and elongation in tendril cells in contact with the support.

Adrenaline is secreted by the adrenal glands which are located on top of the kidneys.

Statement (a) is incorrect. Iodine is required for the synthesis of thyroxine hormone by the thyroid gland.

The pathway taken by a nerve impulse in a reflex action is called reflex arc. The correct sequence of the components in a reflex arc is given below:
Receptors → Sensory neuron → Spinal cord → Motor neuron → Muscle.

This is an example of thigmotropism.

Dwarfism is characterised by retarded physical growth and a normal brain. It is caused due to the hypo - secretion of growth hormone.

The rolling up of plant leaves on touching is a thigmonastic movement and it is not related to growth.

It is advised to use iodised salt to prevent goitre. It is because the thyroid gland requires iodine to synthesise thyroxine hormone. Deficiency of iodine in the body can lead to the under-secretion of thyroxine hormone which, in turn, can lead to goitre.

A synapse is a functional junction between the axon of a neuron and the dendrites of the next neuron. It is separated by a small gap known as the synaptic cleft.

Abscisic acid causes abscission, i.e., falling of leaves and fruits from the plant body.

Cerebral reflexes are those reflex actions which involve the brain. They occur in the organs present in the head as these organs are directly connected to the brain.

A receptor is a cell (or a group of cells) which present in a sense organ and is sensitive to a particular type of stimulus such as light, sound, smell, taste, heat or pressure.

The bending of the top part of the seedling towards the burning candle is an example of phototropism.

Statement (a) is incorrect. Iodine is required for the synthesis of thyroxine hormone by the thyroid gland.

Gustatory receptors detect taste; olfactory receptors detect smell; while auditory receptors detect sound.

The pancreas acts as an exocrine as well as an endocrine gland. The salivary, pituitary and parathyroid glands are endocrine glands.

The cerebellum is a part of the hindbrain which helps in maintaining posture and balance of the body.

The life processes in humans are controlled and regulated by the endocrine and the digestive system. They work together to communicate, integrate and coordinate the functions of various organs and other systems of the body.

The dramatic changes in the body features associated with puberty are mainly due to the secretion of testosterone from the testes (in male) and estrogen from the ovary (in female).

The movement of plant parts in response to the force of gravity is called geotropism.

Abscisic acid inhibits growth in plants.

Water or hydrogen oxide acts as a stimulus in the process of hydrotropism.

It is because a plant stem grows towards the light in the upward direction against the force of gravity.

As many as 31 pairs of nerves arise from the spinal cord.

The response of dandelion flowers to light that involves the movement of the petals is an example of photonasty.

The medulla controls various involuntary actions such as heart beat, breathing, blood pressure and peristaltic movement in the body.

Abscisic acid mainly functions as a growth inhibitor.

The pituitary gland does not occur in pairs, while the adrenal gland, testis (in male) and ovary (in female) do.

The liver is the target organ for both adrenaline and insulin. Target organs and target cells are specific organs and cells upon which hormones act and produce their effects.

Insulin controls the blood sugar level. Hence, the doctor advised him to take an injection of insulin to bring his sugar level to normal.

Sense organs contain receptors. The ear, nose and eye are sense organs, a muscle is not.

In a neuron, the electrical impulse travels from the dendrites to the cell body and from the cell body to the axon and, then, to the axon end.

All the voluntary actions of our body are controlled by the cerebrum. The cerebrum is the largest and the most prominent part of the brain.

The pons take part in the regulation of respiration in the human body.

The pituitary gland is an endocrine gland, while the ovary, testis and pancreas are heterocrine glands. Those glands which are partly exocrine (with duct) and partly endocrine (without duct) are known as heterocrine glands. Here, the exocrine part releases secretion into the duct, while the endocrine part releases hormones into blood.