NCERT Solutions for Class 10 Science Chapter 7 Control and Coordination
Control and co-ordination in animals and plants: Tropic movements in plants; Introduction to plant hormones; Control and co-ordination in animals, nervous system; voluntary, involuntary and reflex action; Chemical co-ordination: animal hormones.
What is the function of receptors in our body?
Receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So gustatory receptors will detect taste while olfactory receptors will detect smell.
Draw the structure of neuron and explain its function.
The specialised tips of some nerve cells detect all information from our environment. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So gustatory receptors will detect taste while olfactory receptors will detect smell. This information, acquired at the end of the dendritic tip of a nerve cell, sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the axon to its end. 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 a general scheme of how nervous impulses travel in the body. A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscles cells or gland. It is thus no surprise that nervous tissue is made up of an organized network of nerve cells or neurons, and is specialised for conducting information via electrical impulses from one part of the body to another.
How does phototropism occur in plants?
Phototropism is a growth movement induced by a light stimulus. Growth towards a source of light is called positive phototropism, that away from the source is termed negative phototropism. The tips of shoots are usually positively, that of roots negatively phototropic.
Charles Darwin and his son Francis discovered (in 1880) that the phototropic stimulus is detected at the tip of the plant.
The Darwins used grass seedlings for some of their experiments. When grass seeds germinate, the primary leaf pierces the seed coverings and the soil while protected by the coleoptile, a hollow, cylindrical sheath that surrounds it. Once the seedling has grown above the surface, the coleoptile stops growing and the primary leaf pierces it.
The Darwins found that the tip of the coleoptile was necessary for phototropism but that the bending takes place in the region below the tip.
If they placed an opaque cover over the tip, phototropism failed to occur even though the rest of the coleoptile was illuminated from one side.
However, when they buried the plant in fine black sand so that only its tip was exposed, there was no interference with the tropism – the buried coleoptile bent in the direction of the light.
From these experiments, it seemed clear that
- The stimulus (light) was detected at one location (the tip)
- The response (bending) was carried out at another (the region of elongation).
- This implied that the tip was, in some way, communicating with the cells of the region of elongation.
How does chemical coordination occur in plants?
It has been found that the growth of plants is regulated by certain chemical substances which are synthesized by the plants in very small amounts. These are known as plant hormones or phytohormones.
They are the organic substances which either promote or inhibit growth. A phytohormones can be defined as a chemical substances which are produced naturally in plants and are capable of translocation and regulating one or more physiological processes when present in low concentration. Main categories of plant hormones are:
- Abscisic acid
Auxins and Gibbrerellins stimulate cell elongations, cytokinins stimulate cell division ethylene promotes transverse or isodiametric growth and abscisic acid is a growth inhibitor.
What is the need for a system of control and coordination in an organism?
Co-ordination in this sense refers to the regulation or control of body activity.
Plants need very little in the way of a control system. Since growth and reproduction are about the only things that are regulated, a rapid control system is not required and hormonal control is all they possess.
Animals are continually moving through new environments that may pose all types of changes and threatening situations to the organism. This requires the rapid and precise control of a nervous system. Hormones regulate slower activities, such as growth, development and reproduction.
How are involuntary actions and reflex actions different from each other?
All reflex actions are involuntary in nature but all involutary actions are not reflexes as the beating of heart is an involuntary action but is not reflex action.
Reflex actions are very quick but all involutary actions may not be very fast as in heart beating.
A reflex action may involve any muscle or a gland as we withdraw our hand on touching a hot object but all involuntary actions involve only smooth i.e., involuntary or cardiac muscles.
Reflex actions are at the level of spinal cord whereas the involuntary actions generally involve brain too.
Nerves and autonomious nervous system can increase or decrease the rate of involuntary actions but reflex actions can be controlled by great will only and are not usually controllable.
Reflex actions are done to meet emergencies where as an inv.action may or may not be for just meeting an emergency but may be a critical lie process as circulation of blood, swallowing of food, movement of food in food pipe, etc.
Multiple Choice Questions (MCQs) [1 Mark each]
What is the correct direction of flow of electrical impulses ? [NCERT Exemplar]
(c) Direction of flow of electrical impulse.
Impulse —> Dendrite —> Cell body —> Axon —> Release of chemicals that cross synapse —> Dendrite of next neuron.
Three directions in which nerve impulses can travel in the nervous system are listed below:
(i) Away from the central nervous system
(ii) Towards the central nervous system
(iii) Within the central nervous system
In which direction do impulses in sensory and relay (intermediate) neurons travel?
(d) Sensory neuron transmits impulses towards CNS, (i.e. brain and spinal cord) while, the relay neurons occur within the CNS and serve as links between other neurons.
In a nerve pathway, the following events take place in a coordinated order.
(i) Activation of muscle
(ii) Activation of receptor
(iii) Passage of impulses along a motor neuron
(iv) Passage of impulses along a sensory neuron
Read the events given and identify the correct order of these events from the table given below:
(b) The sequence of events in a typical nerve pathway is receptor —> passage of impulse along sensory neuron —> passage of impulse along motor neuron —> activation of muscle (effector). Thus, the correct sequence is (ii), (iv), (iii) and (i).
The diagram shows a section of the brain and different parts labelled as W,X, Y and Z.
Study the figure and correlate the regions which control balance, heart rate and temperature in human body?
(b) Out of the options given, the region X, (i.e. cerebellum) controls balance, region Y (i.e. medulla oblongata) controls heartbeat and region Z, (i.e. hypothalamus) controls temperature in human body.
Which of the following endocrine glands is unpaired? [NCERT Exemplar]
(c) There are two adrenal glands, one on top of each kidney that make adrenaline hormone. Testes are paired glands present in males and secrete male sex hormone. Pituitary gland is present just below the brain and is unpaired. It is also called master gland as it secretes a number of hormones. Ovaries are paired glands present in females and secrete female sex hormones.
Dramatic changes of body features associated with puberty are mainly because of secretion of [NCERT Exemplar]
(a) oestrogen from testes and testosterone from ovary
(b) oestrogen from adrenal gland and testosterone from pituitary gland
(c) testosterone from testes and oestrogen from ovary
(d) testosterone from thyroid gland and oestrogen from pituitary gland
|Testosterone||To control the development
of male sex organs and male features such as deep voice, etc., i.e. changes associated with puberty.
|Oestrogen||To control the development
of female sex organs and
female features such as soft skin, etc.
|Progesterone||To control uterus changes during menstrual cycle and helps in maintenance of pregnancy.|