What is meant by reflex-action ? With the help of a labelled diagram trace the sequence of events which occur when we touch a hot object.
Stimulus: In the example above, the stimulus is the contact with the hot pot. This contact causes a nerve impulse that will travel to the spinal cord via the sensory neurons.
Sensory neurons: These neurons carry the nerve impulse to the spinal cord. Similar to the interneuron and motor neuron, sensory neurons receive incoming impulses at the dendrites. The impulses move away from the cell body along the axon to the synaptic terminal where the impulse is sent to the next interneuron with the help of a neurotransmitter (acetylcholine). Interneurons: The interneuron is also known as relay neuron. These neurons are fully contained in the central nervous system. The interneuron serves as the connection between the sensory neurons and the motor neurons. Synapse: The synapse is a tiny space between two neurons. When an impulse gets to the end of one neuron and has to be sent down to the next neuron, the synapse acts as a bridge. The signal arrives at the end of one neuron (close to the synapse) as an electrical signal, crosses the synapse as a chemical signal (with the help of a neurotransmitter known as acetylcholine released by the synaptic vesicles at the synaptic terminal) and continues as an electrical signal in the next neuron.
Motor neurons: These neurons send nerve impulses away from the central nervous system to effector organs or muscle fiber in our example above. This causes the muscle fiber to contract, resulting in you snatching your hand away from the hot pot.
Response: To respond to the stimulus of the reflex arc, the muscle needs to contract to pull the hand quickly away from the hot pot. For this to happen, the impulse travels to the synaptic terminal of the motor neuron. Synaptic vesicles at the synaptic . terminal will then release acetylcholine which will cross the synapse and bind to the receptors on the muscle fibers to trigger the muscle contraction known as the ‘response'.
State the functions of any three of the structural and functional unit of nervous system.
A young green plant receives sunlight from one direction only. What will happen to its shoots ?
Which of the following is a growth movement and which is not ?
(a) folding up of leaves of sensitive plant on touching with hand.
(b) folding up of petals of dandelion flower when light fades.
What are meanings? What are their functions? Name the fluid, which is filled in between meanings.
(i) Name the hormones that are released in human males and females when they reach puberty.
(ii) Name a gland associated with brain. Which problem is caused due to the deficiency of the hormone released by this gland ?
Name, the two main organs of our central nervous system. Which one of them plays a major role in sending command to muscles to act without involving thinking process? Name the phenomenon involved.
(a) Name the two main constituents of the Central Nervous System in human beings.
(b) What is the need for a system of control and coordination in human beings?
Give one example of the movement of a plant part which is caused by the loss of water (or migration of water).
Fill in the following blanks :
(a) A plant’s response to light is called…………..
(b) A plant’s response to gravity is called…………..
(c) Plant shoot grows upward in response to…………….
(d) Plant roots grow downward in response to…………..
(e) Tendrils wind around a support in response to……………
(f) Plant roots grow towards…….. and in the direction of force of……………
(g) A root of a plant grows downward. This is known as…………..
(h) ……….is the hormone that causes phototropism in plants
(i) The response of leaves to the sunlight is called……………
(a) What does a root do in response to gravity ? What is this phenomenon known as ?
(b) What does a stem (or shoot) do in response to light ? What is this phenomenon known as ?
Distinguish between tropic movements and nastic movements in plants. Give examples to illustrate your answer.
(a) What are the various sense organs in our body ?
(b) What is meant by receptors and effectors ? Give two examples of each.
State the functions of the following hormones :
(a) Thyroxine (b) Adrenaline (c) Growth hormone
(a) Name the hormone which is released into the blood when its sugar level rises. Explain the need of Chemical communication in multicellular organisms the organ which produces this hormone and its effect on blood sugar level. Also mention the digestive enzymes secreted by this organ with one function of each.
(b) Explain the need of Chemical communication in multicellular organisms.
(a) Draw the structure of neuron and label cell body and axon.
(b) Name the part of neuron:
(i) where information is acquired
(ii) through which information travels as an electrical impulse.
Name and explain the function of the hormone secreted by the pituitary gland in humans.
Name one example of the movement of a plant part which is very quick and can be observed easily.
Which of the following is a growth movement and which is not ?
(a) folding up of leaves of sensitive plant on touching with hand.
(b) folding up of petals of dandelion flower when light fades.
What is a tendril ? Name the two types of tendrils. What does a tendril do in response to the touch of a support ? What is this phenomenon known as ?
Define chemotropism. Give one example of chemotropism. State whether this example is of positive chemotropism or negative chemotropism.
Why is the folding up of the leaves of a sensitive plant on touching with a finger not a tropism ?
(a) What is meant by positive tropism and negative tropism ? Explain with examples.
(b) Define thigmotropism. Give one example of thigmotropism.
(c) What is the difference between thigmotropism and thigmonasty ? Name one plant which exhibits thigmotropism and one plant which exhibits thigmonasty. What behaviour (or responses) of these plants make you think that they exhibit thigmotropism and thigmonasty respectively ?
If we happen to touch a hot object unknowingly, we immediately pull back our hand. What is this type of action known as ?
a) What are the short fibres of a neuron known as ?
What is the long fibre of a neuron known as ?
Which halogen element is necessary for the making of thyroxine hormone by the thyroid gland ?
