[4 marks Questions]

Question 14 Marks

State the names of plant hormones and their effects.

Answer

Plant hormones: They help to coordinate growth, development and response to environment.
They are synthesised at places away from where they act and simply diffuse to the area of action.
$(i)$ Growth promoting hormones:
$(1)$ Auxin:
It is synthesised at the shoot tip.
It helps cells to grow longer.
When light is coming from one side of the plant, auxin diffuses towards the side of the shoot which is in shade.
Specific concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus plant appears to bend towards light.
The auxin is responsible for phototropism.
$(2)$ Gibberellin:
It helps in the growth of the stem.
$(3)$ Cytokinin:
It is naturally present in higher concentration in areas where rapid cell division occurs.
In fruits and seeds, it is found in more concentration.
It promotes cell division.
$(ii)$ Growth inhibiting hormone
Abscisic acid:
It inhibits plant growth.
Its effects include wilting of leaves.

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Question 24 Marks

Describe plant hormones.

Answer

Plant hormones: They help to coordinate growth, development and response to environment.
They are synthesised at places away from where they act and simply diffuse to the area of action.
$(i)$ Growth promoting hormones:
$(1)$ Auxin:
It is synthesised at the shoot tip.
It helps cells to grow longer.
When light is coming from one side of the plant, auxin diffuses towards the side of the shoot which is in shade.
Specific concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus plant appears to bend towards light.
The auxin is responsible for phototropism.
$(2)$ Gibberellin:
It helps in the growth of the stem.
$(3)$ Cytokinin:
It is naturally present in higher concentration in areas where rapid cell division occurs.
In fruits and seeds, it is found in more concentration.
It promotes cell division.
$(ii)$ Growth inhibiting hormone
Abscisic acid:
It inhibits plant growth.
Its effects include wilting of leaves.

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Question 34 Marks

Explain: Human brain

Answer

Human brain has three major regions or parts : $(1)$ Fore-brain, $(2)$ Mid-brain and $(3)$ Hind-brain.
(1) Fore-brain:
It consists mainly of cerebrum, which is a main thinking part of the brain.
It receives sensory impulses from various receptors.
The fore-brain has separate areas specialised for hearing, smell, sight and so on.
There are separate areas of association where sensory information is interpreted by putting it together with information from other receptors as well as with information already stored in the brain.
Based on all this, a decision is made about how to respond.
It has motor areas which control the movement of voluntary muscles.
It has a separate centre associated with hunger.
(2) Mid-brain:
Corpora quadrigemina is a part of mid-brain.
Centres for visual and auditory reflexes are located there.
(3) Hind-brain:
Pons, medulla and cerebellum are the parts of hind-brain.
Involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla.
Cerebellum is responsible for precision of voluntary actions and maintaining the posture and balance (Equilibrium) of the body.

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Question 44 Marks

Describe human brain with specific functions of its different parts.

Answer

Human brain has three major regions or parts : $(1)$ Fore-brain, $(2)$ Mid-brain and $(3)$ Hind-brain.
(1) Fore-brain:
It consists mainly of cerebrum, which is a main thinking part of the brain.
It receives sensory impulses from various receptors.
The fore-brain has separate areas specialised for hearing, smell, sight and so on.
There are separate areas of association where sensory information is interpreted by putting it together with information from other receptors as well as with information already stored in the brain.
Based on all this, a decision is made about how to respond.
It has motor areas which control the movement of voluntary muscles.
It has a separate centre associated with hunger.
(2) Mid-brain:
Corpora quadrigemina is a part of mid-brain.
Centres for visual and auditory reflexes are located there.
(3) Hind-brain:
Pons, medulla and cerebellum are the parts of hind-brain.
Involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla.
Cerebellum is responsible for precision of voluntary actions and maintaining the posture and balance (Equilibrium) of the body.

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Question 54 Marks

Explain how is hand pulled away from the hot object reflexly.

Answer

A connection between the input (sensory) nerve and output (motor) nerve along with spinal cord is called reflex arc. OR
It is a path of reflex action which consists of receptor, sensory neuron, relay neuron and motor neuron connected to effector organ.
Thus a neural pathway for the sensory and motor messages that pass through the spinal cord forms the reflex arc.
A very rapid response is shown through it.
The following example can clarify the meaning of reflex arc:
Suppose by mistake and unknowingly one touches a hot object by one’s hand.
One would withdraw the hand all of a sudden without giving a slightest thought.
Here the hot object is the source of stimulus.
This stimulus activates the sensory nerve fibre in the hand and carry that impulse to the spinal cord.
The sensory centres in the spinal cord receive the stimulus and transmits the response to the motor centre of the spinal cord.
This motor message is transmitted through the motor nerve fibre to definite muscles of the hand, which upon contraction, withdraws the hand.
The hand or its muscles act as effector organ.
This entire neural path from the sensory or receptor organ, to the effector organ is a reflex arc.

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Question 64 Marks

Explain reflex arc. Explain spinal reflex.

Answer

A connection between the input (sensory) nerve and output (motor) nerve along with spinal cord is called reflex arc. OR
It is a path of reflex action which consists of receptor, sensory neuron, relay neuron and motor neuron connected to effector organ.
Thus a neural pathway for the sensory and motor messages that pass through the spinal cord forms the reflex arc.
A very rapid response is shown through it.
The following example can clarify the meaning of reflex arc:
Suppose by mistake and unknowingly one touches a hot object by one’s hand.
One would withdraw the hand all of a sudden without giving a slightest thought.
Here the hot object is the source of stimulus.
This stimulus activates the sensory nerve fibre in the hand and carry that impulse to the spinal cord.
The sensory centres in the spinal cord receive the stimulus and transmits the response to the motor centre of the spinal cord.
This motor message is transmitted through the motor nerve fibre to definite muscles of the hand, which upon contraction, withdraws the hand.
The hand or its muscles act as effector organ.
This entire neural path from the sensory or receptor organ, to the effector organ is a reflex arc.

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Question 74 Marks

What is meant by ‘Tropisms’? Explain with an example.

Answer

If the movement in a plant organ is induced by an external and directional stimulus, then it is called tropism or tropic movement.
The process induced by a stimulus is called a response or reaction.
If the growth of the plant organ is towards the direction of the stimulus, it is called positive tropism and if the growth of the plant organ is in the opposite direction of the stimulus, it is called negative tropism.
Factors inducing stimulus:
Light, gravitational force, water, chemical and physical touch are the common factors that induce stimuli.
Types of tropisms based on response shown by the plant organs:
$(1)$ Phototropism:
The reaction of plant organ in response to stimulus in the form of light is called phototropism or phototropic movement.
e.g. Root system of plant shows negative phototropism and the shoot system shows positive phototropism.
$(2)$ Geotropism:
The reaction of plant organ in response to the direction of the gravitational force is called geotropism.
e.g., Root system shows positive geotropism and the shoot system shows negative geotropism.
$(3)$ Hydrotropism:
The reaction or response of plant organ in response to the direction of water is called hydrotropism.
e.g., The root system shows positive hydrotropism and the stem and leaves show negative hydrotropism.
$(4)$ Chemotropism:
The reaction of plant organ in response to the direction of chemical substance is called chemotropism.
e.g., The elongation of the pollen tube in the direction of the micropyle of the ovule during fertilisation is the example of positive chemotropism.
$(5)$ Thigmotropism:
The reaction of plant organ in response to the direction of touch is called thigmotropism.
e.g., The tendrils coil spirally along the supporting object that comes in contact with the tendril.
It is an example of positive thigmotropism.

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Question 84 Marks

Explain how nervous impulses travel in the body.

Answer

Nervous impulses travel through neuron, nerve fibre and synapse.
Generation of impulse:
Sense organs have specific receptors with the dendritic tip of a nerve cell.
The information of external stimulus is received at the end of the dendritic tip.
An electric impulse is generated by sets of chemical reactions.
Transmission of impulse:
The nerve impulse generated at dendritic tip, travels from the dentrite to cell body.
This impulse travels from cell body to axon and finally reaches to nerve ending.
Synapse:
Synapse is a gap between nerve ending of an axon of one neuron and dendrites of the next neuron.
When impulse reaches the nerve ending of an axon, neurochemicals (neurotransmitters) are released and such chemicals cross the synapse and start a similar impulse in a dendrite of the next neuron.
A similar synapse finally deliver such impulses from neuron to muscles cells or gland.

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Question 94 Marks

What is a movement? What are the different purposes for which movements are seen in organisms? Give suitable examples.

Answer

Change in position of an organism is called movement.
Movement is one characteristic feature of living beings.
Movements are seen for following purposes in organisms:
$(1)$ Some movements are growth related.
e.g., a seed germinates and grows.
Seedling develops and shoot system comes out from soil.
$(2)$ Running, playing, chewing, etc. are the examples of movement which are not related to growth but for other functions.
$(3)$ Some movements are seen as a response to change in the environment of the organism or for their advantage.
e.g., amoeba expands pseudopodia to ingest food particles, buffaloes chew cud to break-up tough food for better digestion.
$(4)$ Some movements are seen for protection.
e.g., our pupils constricted when bright light falls on eyes, we pull our hand instantly while touching a hot object.

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