Lesson: Control and Coordination
What
is the difference between a reflex action and walking?
A reflex action
is an unconscious involuntary action. It is a rapid and automatic response to
an external stimulus. On the other hand, walking is a voluntary action. It is
under our control.
What
happens at the synapse between two neurons?
A synapse is
the gap between two neurons. At the synapse, electrical signals are converted
into chemicals. These chemicals can easily cross the gap and pass on to the
next neuron. Here it is again converted into electrical signals. The impulses
or signals are transmitted in one direction only.
Which
part of the brain maintains posture and equilibrium of the body?
Cerebellum which is a part of hind brain
is responsible for maintaining posture and equilibrium of a body.
How do we
detect smell of an agarbatti (incense stick)?
When the smell
of an incense stick reaches our nose, the olfactory receptors present in our
nose detect it. These receptors send information to the fore-brain in the form
of electrical signals. The fore-brain interprets this information, from stored
memory, as the smell of an incense stick.
What
is the role of brain in reflex action?
A brain
has no direct involvement in reflex action. Reflex actions are very quick. They
do not require thinking. They are mainly controlled by the spinal cord.
What
are plant hormones?
Plant
hormones:
(a) Are known as phytohormones.
(b) Are chemical substances that are
secreted within a plant
(c) Regulate the growth and development
of a plant.
There are five major types of plant
hormones; auxin, gibberellins, cytokinins, abscisic acid and ethylene etc.
How
is the movement of leaves of a sensitive plant different from the movement of a
shoot towards light?
The movement of leaves of a sensitive
plant is touch sensitive and does not depend on the direction of the stimulus
and is growth independent. On the other hand, movement of a shoot depends on
the direction of light and is known as phototropism. This movement is
directional and growth dependent.
Give
an example of a plant hormone that promotes growth.
Auxins
promote stem elongation, growth and movement.
How
do auxins promote the growth of a tendril around a support?
Auxin
increases in concentration in part of the tendril that is away from support.
This results in increased cell division in that part. Lesser auxin occurs on
the side of contact as compared to the free side. As a result, auxin promotes
growth on the free side and the tendrils coil around the support.
Design
an experiment to demonstrate hydrotropism.
Experiment
to demonstrate hydrotropism
Take two small beakers and label them
as A and B.
(a) Take a beaker A with water.
(b) Now make a cylindrical-shaped roll
from a filter paper and keep it as a bridge between beaker A and beaker B, as
shown in the figure.
(c) Attach few germinating seeds in the
middle of the filter paper bridge.
(d) Now, cover the entire set-up with a
transparent plastic container so that moisture is retained.
Observation:
The
roots of germinating seeds will grow towards beaker A.
This
experiment demonstrates the phenomenon of hydrotropism.
How
does chemical coordination take place in animals?
Chemical coordination in animals takes place
through hormones. These hormones are chemical messengers. They are secreted by
glands and directly released in the bloodstream. The blood carries them to
specific tissues or organs called target tissues/organs. In the target, they
trigger a biochemical or physiological activity. The hormones are of different
types and perform different functions.
Why
is the use of iodised salt advisable?
Iodine is an important constituent of the hormone
thyroxine that regulates carbohydrate, fat and protein metabolism in our body.
If there is a deficiency of this hormone, it may
result in enlargement of the thyroid gland. This can lead to goitre, a disease
characterized by swollen neck. Therefore we should use iodised salt to avoid deficiency
of thyroxine hormone.
How does our body respond when adrenaline is
secreted into the blood?
Adrenal gland
secretes adrenaline hormone when someone is in an emergency situation. It is
secreted directly into the blood and is transported to different parts of a body.
It increases the rate of heartbeat and breathing rate, so that more oxygen
could be supplied to the muscles. It also increases blood pressure. This
enables a person to fight an emergency situation.
Why are some patients of diabetes treated by giving
injections of insulin?
Insulin is a hormone. It plays an important role in sugar metabolism. It converts extra sugar present in the blood into glycogen. Diabetes is caused due to poor or no secretion of insulin by pancreas. Thus, patients suffering from diabetes are given insulin injection to control their blood sugar level.