Science [1 Mark Questions]

Iodine is necessary for the synthesis of the hormone thyroxine in the human body. Thyroxine is produced by the thyroid gland and plays a key role in regulating metabolism.

An example of a plant hormone that promotes growth: Auxin.

Plant hormones are chemical compounds produced by plant itself and help to coordinate growth, development and responses to the environment.

Cerebellum is the part of the brain that maintains posture and equilibrium of the body.

A reflex arc is the pathway taken by nerve impulses during a reflex action. It involves a simple, automatic response to a stimulus without involving the brain. The components of a reflex arc include:

1. Receptor – Detects the stimulus (e.g., skin receptor).
2. Sensory neuron – Carries the impulse from the receptor to the spinal cord.
3. Interneuron – Located in the spinal cord, it processes the signal and transmits it to the motor neuron.
4. Motor neuron – Carries the response from the spinal cord to the effector (muscle or gland).
5. Effector – The muscle or gland that produces the response (e.g., muscle contracts).

This process helps in quick reactions to stimuli, often without conscious thought.

A controlling and coordinating system of body which consists of brain and spinal cord is called central nervous system.

The specialised structures that receive stimuli from external environment are called receptors.

The ductless glands that secret hormones are called endocrine gland.

The growth related movement in the plant organs, which are induced as a response to directional stimulus is called tropism.

The reaction of living organisms against the stimulus induced by the change in the external environment is called response.

Growth hormone releasing factor: Secretory site: Hypothalamus.
Function: Stimulates the pituitary gland to release growth hormone.

Secretion of testosterone in males is responsible for the development of beard and moustache.

Auxin is synthesised at the shoot tip and it diffuses towards the side of the shoot which is in shade.

Hormones, secreted by endocrine system constitute a second way of control and coordination in our body.

In higher animals, electrical impulses bring immediate response to only those cells that are connected by nervous tissue while chemical signals reaching to each and every cells of body.

Abscisic acid - a plant hormone that inhibits growth. It affects wilting of leaves.

Hormones are called chemical messengers because they carry information in the form of chemicals that regulate the biological processes of body.

The leaves of the sensitive plant chhui- mui move very quickly in response to touch stimulus.

Muscle cells have special proteins that change both their shape and arrangement in cells, so muscle cells change their shape.

Muscle cells move by changing their shape either shortening or elongating.

When a nerve impulse reaches the muscle, the muscle fibre can move due to stimulation.

Involuntary actions such as blood pressure, salivation, vomiting are controlled by medulla in the hind-brain.

The sensation of feeling full is because of a centre that is associated with hunger, located In separate part of the fore-brain.

Thinking is called a complex activity, because it is bound to involve a complicated interaction of many nerve impulses from many neurons.

There are separate areas specialised for hearing, smell, sight, etc. in fore - brain.

The peripheral nervous system consists of cranial nerves arising from brain and spinal nerves arising from the spinal cord.

When bright light is focussed on eyes, we constrict pupils, we pull our hand when we touch a hot object. These are the examples of movement in order to protect ourselves.

The nervous tissue is made-up of an organised network of neurons. It is specialised for conducting information via electrical impulses.

The receptors which detect taste are called gustatory receptors. They are located on the surface of tongue.

Information that is transmitted through the nerves in form of electro-chemical signals are called Impulse.

A stem moves towards light. This phenomenon is known as positive phototropism.

A root give positive response to gravity, this phenomenon is called positive geotropism.

Sensitive plant: Touch-me-not (Mimosa pudica).

One of the hormones secreted by the pituitary gland is GH (Growth Hormone).

The neuron (nerve cell) is the structural and functional unit of nervous system.

Function of medulla : It maintains the rhythm of various involuntary processess such as breathing, heartbeats, peristalsis of the alimentary canal, etc.

The most important part of the human brain is cerebrum which is the largest part of the brain.

The three components of a nerve cell are a cyton, an axon and one or more dendrons.

The nervous system and the endocrine system are the two systems of control and coordination in higher animals.

a - growth hormone releasing factor
b - pituitary gland

Backbone (vertebral column)

(i) Phototropism
(ii) Geotropism
(iii) Chemotropism
(iv) Hydrotropism
(v) Thigmotropism

(iii) Movement of our leg - very slow

Cerebellum

Dwarfism, Insulin

Positive phototropism in shoot is indicated in the diagram. Auxin is responsible for it.

Drooping of leaves of chhui-mui

Cytokinin