Coordination and control: Class 10 Biology

Key points

Coordination is the working together of different organs of the body to respond to changes in the environment. In humans it is done by the nervous system, which gives fast responses through nerve impulses, and by the endocrine system, which gives slower and longer lasting responses through hormones. In plants coordination is done by plant hormones.

The nervous system has the central nervous system (brain and spinal cord) and the peripheral nervous system (cranial and spinal nerves). The basic unit is the neuron, or nerve cell. A neuron has a cell body with a nucleus, short branches called dendrites that receive impulses, and a long axon that carries impulses away. Many axons are covered by a fatty myelin sheath that speeds up the impulse.

Neurons are of three types according to function:

• Sensory neurons carry impulses from receptors to the central nervous system.
• Relay (connector) neurons lie inside the brain and spinal cord and link sensory and motor neurons.
• Motor neurons carry impulses from the central nervous system to effectors such as muscles and glands.

A synapse is the gap between the axon end of one neuron and the dendrite of the next. The impulse crosses the gap by chemicals called neurotransmitters, which are released from the first neuron and bind to the second. This makes the impulse travel in one direction only.

A reflex action is a quick, automatic response to a stimulus, and it does not need thinking. The path of the impulse is the reflex arc: receptor, sensory neuron, relay neuron in the spinal cord, motor neuron, effector. Pulling the hand away from a hot object is an example. Reflexes protect the body from harm because they are very fast.

The human brain has three main regions:

• Cerebrum: the largest part, controlling thinking, memory, speech, learning and voluntary movement.
• Cerebellum: controls balance and coordinates muscular movement.
• Medulla oblongata: controls involuntary actions such as heartbeat, breathing and swallowing. It joins the brain to the spinal cord.

The eye is the organ of sight. The cornea is a transparent front layer that begins to bend light. The iris controls the size of the pupil, so it controls the amount of light entering. The lens focuses light on the retina, which holds rod cells (dim light) and cone cells (colour and bright light). The optic nerve carries impulses to the brain. For near objects the ciliary muscles contract and the lens becomes thicker, and for distant objects the lens becomes thinner.

Common eye defects are short sight (myopia), where distant objects look blurred and the image forms in front of the retina, and long sight (hypermetropia), where near objects look blurred and the image forms behind the retina. Short sight is corrected with concave lenses and long sight with convex lenses.

Endocrine glands are ductless glands that release hormones directly into the blood. A hormone is a chemical messenger that affects target organs. The pituitary is called the master gland because it controls other glands. The thyroid makes thyroxine, which controls metabolic rate. The pancreas makes insulin and glucagon. The adrenal glands make adrenaline, which prepares the body for fight or flight. The testes make testosterone and the ovaries make oestrogen and progesterone.

Blood glucose is controlled by insulin and glucagon. Insulin lowers blood glucose by helping cells take it up and by converting extra glucose to glycogen in the liver. Glucagon raises blood glucose by breaking glycogen down. In diabetes mellitus the pancreas does not make enough insulin, or the body does not respond to it, so blood glucose stays high. Patients are managed by controlled diet, exercise and, where needed, insulin injections.

Plant coordination depends on hormones and on tropisms:

• Auxins promote cell elongation in shoots and cause bending towards light.
• Gibberellins promote stem growth and seed germination.
• Cytokinins promote cell division.
• Abscisic acid closes stomata and keeps buds and seeds dormant.
• Ethene promotes fruit ripening.
• A tropism is growth of a plant part in response to a stimulus. Shoots show positive phototropism and negative geotropism. Roots show positive geotropism and positive hydrotropism.

Study tip: Compare nervous and hormonal control in a short table of speed, path and duration, because this is a favourite question. Learn the hormone with its gland and function as a list, and practise labelled diagrams of the neuron, the reflex arc, the brain and the eye.

Definitions and flashcards

Say the meaning first, then open the card to check.

Short questions with model answers

These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.

Common mistakes

• Saying that hormones travel through nerves. They travel in the blood.
• Drawing the reflex arc with the brain in it. The relay neuron is in the spinal cord.
• Mixing up the corrections for eye defects. Short sight uses concave lenses and long sight uses convex lenses.
• Writing that insulin raises blood glucose. It lowers it.
• Confusing phototropism with geotropism. Photo means light and geo means gravity.

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Practice questions and timed test Printable worksheet