Control and Co-ordination 16
CONTROL AND COORDINATION
1. Explain with
examples how living things act in response to their environment.
Ans. (1) Every living
thing responds to factors of the environment such as light, heat, cold,
pressure, etc.
(2) Various life processes
are carried on in the bodies of living things. These life processes are
dependent upon one another.
(3) Several changes occur
in our everyday life. Sometimes we eat more, sometimes less, sometimes sweet
and sometimes spicy, hot foods.
(4) Depending on these
changes the process of digestion also undergoes changes, and food gets digested
properly.
(5) In summer the
temperature is high while in winter it is very low. Even then our body
temperature is maintained at about 37°C in any season. In winter, the body must
produce more energy. So, we eat foods that provide more energy.
(6) On the other hand, in
summer, the higher temperature of the air raises the temperature of our skin,
too. To reduce this temperature, the skin produces sweat. When sweat
evaporates, it helps to lower the skin temperature. As the body loses water due
to sweating, we feel thirsty. That is why we drink more water in summer.
(7) It means that even as
conditions inside and outside the body change all the time, changes in life
processes also take place in accordance with them.
2. Name the main parts
of the nervous system.
ANS: Brain, spinal cord
and nerve fibers are the main parts of the nervous system.
3. What is meant by
growth?
ANS: Growth is a
reversible process occurring in living things. In the growth, the parts of a
living organism grow in length, weight and size.
4. Explain the
movements in plants with examples.
ANS: The movements of
plants are not noticeable like animals. However, control and co-ordination of
growth and movements is seen in plants, too.
Examples (1) When you
touch the mimosa’s leaves they react by closing up. After some time, they open
again. (2) The blossoming of a bud into a flower (3) The flowers of the Night
Blooming Jasmine (ratrani) blossoming only at night (4) The growth of roots
deep into the soil in search of water (5) The stem growing towards sunlight.
(6) The characteristic movements of the drossera and pitcher plant to catch
their prey.
5. Define.
Reflex action
Reflex action is instant,
involuntary reaction of the body carried out by spinal cord in response to a
stimulus requiring immediate attention. The message of afferent nerves does not
reach brain during reflex action.
(b) Hormones
Hormones are the chemical
substances secreted by the endocrine glands for controlling the life processes
and for maintaining the homeostasis.
6. Write notes.
(a) Homeostasis
ANS: (1) Every living
thing responds to factors of the environment such as light, heat, cold,
pressure, etc.
(2) Various life processes
are carried on in the bodies of living things. These life processes are
dependent upon one another.
(3) Several changes occur
in our everyday life. Sometimes we eat more, sometimes less, sometimes sweet
and sometimes spicy, hot foods.
(4) Depending on these
changes the process of digestion also undergoes changes, and food gets digested
properly.
(5) These changes are
always in accordance with the surrounding changes.
(6) For example, though
there is a change in the surrounding temperatures, the body temperature of
human beings is always at 37
.
.
(7) Thus, the optimum
level of the body in the given conditions is maintained in all circumstances.
This continuous process of adjustment is called homeostasis.
(b) Endocrine system
ANS: (1) The endocrine
system consists of various glands called endocrine glands. (2) They secrete
hormones. Chemical substances that control the life processes and movements of
animals are called hormones.
(3) Even though the
endocrine glands are situated only at specific places in the human body the
hormones bring about effects all over the body. Their function is carried out
at places at a distance from where they are secreted.
(4) These glands do not
have ducts. The hormones enter the blood directly and spread throughout the
body through the blood.
(5) The pituitary,
thyroid, adrenal, pineal, thymus are the endocrine glands in the human body.
7. Give the function of
(1) Afferent nerves: Nerves which bring different information from all the
body parts to the brain and the spinal cord are called afferent nerves.
(2) Efferent nerves: Nerves which carry commands of the brain and the
spinal cord to all the body parts are called efferent nerves.
8. Give four examples
of reflex actions.
Examples of reflex action:
(1) Watering of mouth at
the sight of tamarind.
(2) covering the ears when
someone is lighting a fire-cracker.
(3) Instantly pulling away
of the hand when it touches something hot.
(4)
Screaming 'ouch' (ow) and pulling away of the hand when a needle pricks the
finger.
