Ch. 7 Control and Coordination Questions-Answers

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Q. What is a stimulus?

A. It is any change in the surrounding of an organism that elicits a response.

Q. What is Response?

A. Movements or actions done by organisms in reaction to stimuli.

Q. How do we perceive stimulus?

A. Stimulus is perceived with the help of receptors. Receptors are specialised dendritic tips of a neuron that are found in different sense organs and detect different information.
Eg. Auditory Receptors (Ears)  : detect sound
      Photo Receptors (Eyes)      : detect light
      Olfactory Receptors (Nose) : detect smell
      Gustatory Receptors (Tongue) : detect taste

Q. What is Nerve Impulse?

A. Nerve impulse refers to the information transmitted in the neuron in the form of chemical or electrical signal.

Q. How is the information acquired at the end of the dendritic tip of the cell transmitted along the neuron?

A. The information acquired at the dendritic tip of the nerve cell sets off a chemical reaction that creates an electrical impulse. This impulse travels from dendrite to the cell body, and then along the axon to its ends. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap, or synapse and start a similar electrical impulse in a dendrite of the next neuron.

This is general scheme of how nervous impulses travel in the body.

Q. Enlist the types of Responses.

A.    Voluntary
       Involuntary
       Reflex

Q. What is Reflex Arc?

A.     Receptors         →            Spinal Cord          →               Effectors
         (Skin)               (Sensory Neurons)                                    (Motor Neurons)        (Muscles)

Q. What is Reflex Action?

A. It is an involuntary and instantaneous movement in response to a stimulus. Most of these actions are formed mainly from the spinal cord.

Q. Describe the sequence of events which occur when you touch a hot plate and also explain the process.

A. At the point of contact with the hot plate, skin receptors quickly send nerve impulses (electrical) to the spinal cord via sensory neurons. In the spinal cord, the impulses are processed and a response is relayed back. The relay neurons (in the spinal cord) make the connects between the sensory neurons and the motor neurons. From the relay neurons, the response is relayed to the motor neurons which project out of the spinal cord to stimulate your muscles (effector) to contract, causing you to snatch your hand away from the plate.

Q. Why are reflex arcs more evolved in animals?

A. Reflex arcs have evolved in animals because the thinking process of the brain is not fast enough. In fact, many animals have very little or none of the complex neuron networks needed for thinking. So it is quite likely that reflex arc has evolved as efficient ways of functioning in the absence of true thought process.

Q. Differentiate between Nastic and Tropic Movements.

A. 
Nastic Movement Tropic Movement
The movements are independent of growth The movements are dependent on growth
They are not directional movements. Part of the plant does not respond towards/away from stimulus i.e. movement happens at a point different from touch These are directional movements due to growth and are either towards stimulus or away from it (i.e. positive or negative tropism respectively)
These are fast These are slow
Eg: Touch me not plant Eg: Phototropic, geotropism etc.

Q. Explain the types of Nastic Movements.

A.
i) Thigmonasty: Response to touch. Eg. Venus Fly Trap, Touch Me Not Plant
ii) Photonasty: Response to light. Eg. Dandelion Flower, Moonflower.

Q. Explain the steps in Phototropism.

A. i) Detection of light by growing plants.
ii) Synthesis of auxin at shoot tip.
iii) Diffusion of auxin towards the shady side of the root.
iv) This hormone helps the cells to grow hormone on the side of the shoot which is away from the light.

Q. How is the information that a touch has occurred in touch me not plant communicated? How is response brought?

A. Information that a touch has occurred must be communicated. The plants also use electrical and chemical means to convey this information from cell to cell, but unlike in animals, there is no specialised tissue in plants for the conduction of information. Finally, again as in animals, some cells must change shape in order for the movement to happen. Instead of specialised proteins found in animal muscle cells, plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.

Q. Name the regions in plants where cytokinin is present in higher concentration.

A. Cytokinins promote cell division, and it is natural that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds.

Q. Name the plant hormones and write about their functions.

A. i) Auxin: 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 the light.

ii) Gibberellins: Help in the growth of the stem.

iii) Cytokinins: Promote cell division.

iv) Abscisic Acid: Inhibits growth. Its effects include wilting of leaves.

Q. Differentiate between Electrical signals and chemical signals.

A. 
Electrical signals Chemical signals
Cant reach each and every cell in the animal body as they will reach only those cells connected by neuron tissue.
Can reach all cells of the body.
Involves generation of electrical impulses.
Cells are stimulated through the release of a chemical compound by the stimulated cell. The compound can diffuse all around cells, which in turn is deflected by other cells using special molecules (receptor proteins) on their surfaces.
It gets the response immediately.
Gets response usually slowly.
Cells cant continually create and transmit electrical impulse in cell and transmit it. The cell will take some time to reset its mechanism.
Can be done steadily and slowly.
Information travels rapidly.
Information travels slowly.
Limited responses
Permits different kinds of responses as these compounds show a great deal of diversity

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