Control and Coordination Class 10: Notes and Questions

These Control and Coordination Class 10 notes explain how animals and plants sense changes around them and respond in a controlled way. You will go through the chapter in order, from neurons and reflexes to the brain, plant movements and hormones, and finish with a revision list, important questions with model answers, and common mistakes to avoid.

Why living things need control and coordination

Movement in living things is not random. It is a controlled response to stimuli, which are changes in the environment.

• Growth-dependent movement: a germinating seedling pushes through the soil because it is growing. Stop the growth and the movement stops.
• Growth-independent movement: a cat running or a buffalo chewing its cud has nothing to do with getting larger. These are responses to the environment.

We blink at a bright light and pull our hand back from a hot object. Such precise responses need special tissues. In animals, this is the job of nervous and muscular tissue.

The neuron and the synapse

The nervous system is a network of neurons. A neuron has three parts: dendrites, a cell body and an axon.

Information is picked up by receptors, specialised tips of nerve cells in sense organs. Gustatory receptors detect taste; olfactory receptors detect smell.

How a signal travels:

1. Information is acquired at the dendritic tip, setting off a chemical reaction that creates an electrical impulse.
2. The impulse travels to the cell body and along the axon to its end.
3. At the axon's end, the impulse releases chemicals.
4. The chemicals cross a tiny gap, the synapse, and start a new electrical impulse in the dendrite of the next neuron.

Impulses finally reach effector cells, muscles or glands, which act. The synapse makes sure impulses travel in only one direction.

Reflex actions and the reflex arc

A reflex action is a sudden, involuntary response to a stimulus, without conscious thought, like pulling your hand away from a flame. Thinking takes time, because it involves dense networks of neurons in the brain. In an emergency, that delay could mean a serious burn.

The shortcut is the reflex arc, where the sensory nerve connects to the motor nerve in the spinal cord:

The information still goes to the brain for recording, but the response is handled by the spinal cord.

The human brain

The brain and spinal cord form the central nervous system. The brain has three regions:

The fore-brain has association areas where new sensory information is compared with stored memories. Riding a bicycle or walking in a straight line depends on the cerebellum.

Protection: the brain sits in a bony box, the skull, cushioned by a fluid-filled balloon that absorbs shocks. The spinal cord is protected by the vertebral column.

Muscles: muscle cells contain special proteins that change their shape and arrangement when a nerve impulse arrives, so the cell shortens and contracts. Voluntary muscles (arms) are controlled by the fore-brain; involuntary muscles (heart, gut) by the mid-brain and hind-brain.

Coordination in plants

Plants have no nervous system or muscles, but they still respond.

Immediate response (growth-independent): the leaves of the sensitive plant, Mimosa pudica, fold and droop almost at once when touched. Plant cells pass information by electrical-chemical means and change shape by changing the amount of water inside them: losing water makes cells shrink, gaining water makes them swell. The point of touch can differ from the point of movement, showing that information travels through the plant.

Tropisms (growth-dependent, directional):

Tendrils: in climbing plants like peas, the side of the tendril touching a support grows slower than the side away from it, so the tendril circles and clings to the support.

Plant hormones

Plant hormones are made in one part of the plant and diffuse to other parts.

How a shoot bends towards light: when light falls from one side, auxin diffuses to the shady side. Cells there grow longer, so the shoot bends towards the light.

Hormones in animals: the endocrine system

Hormones are chemical messengers secreted directly into the blood. They reach every cell and give a wide, lasting response. Nerves give quick, local responses; hormones give broader, longer-lasting coordination.

Adrenaline (adrenal glands) prepares the body for fight or flight: the heart beats faster, blood is diverted from the digestive system and skin to the skeletal muscles, and breathing speeds up.

Lack of iodine in the diet can cause goitre, a swollen neck. Too little insulin raises blood sugar, causing diabetes.

Feedback mechanism: after a meal, blood sugar rises. Pancreas cells detect this and release more insulin. As sugar falls towards normal, insulin secretion is reduced. Similarly, the hypothalamus releases a releasing factor that makes the pituitary produce more growth hormone when levels are low.

Remember this

• Impulse path: dendrite → cell body → axon → synapse → next neuron.
• Reflex arcs are in the spinal cord.
• Cerebellum: balance and posture. Medulla: blood pressure, salivation, vomiting.
• Plant cells move by changing water content; animal muscles by changing proteins.
• Auxin moves to the shady side; abscisic acid inhibits growth.
• Iodine for thyroxine; insulin for blood sugar.

Important questions with model answers

1. How is the movement of a germinating seed different from a cat running? The seed's movement depends on growth: it moves because it is getting bigger. The cat's movement is independent of growth: it is a quick response to a stimulus.

2. What happens at a synapse? The impulse at the end of the axon releases chemicals. These cross the gap and start a new electrical impulse in the dendrite of the next neuron.

3. Why are reflex arcs in the spinal cord and not the brain? The spinal cord is where nerves from all over the body meet first. Connecting sensory and motor nerves there skips the slower thinking process of the brain and gives a faster response.

4. Which part of the brain keeps your balance while cycling? The cerebellum, a part of the hind-brain.

5. How does a shoot bend towards light? Auxin made at the shoot tip diffuses to the shady side. Cells on the shady side grow longer than those on the lit side, so the shoot bends towards light.

6. How do Mimosa leaves fold without muscles? Cells change shape by changing their water content. When water moves out of certain cells, they shrink and the leaves fold. It is a growth-independent movement.

7. Why is chemical communication sometimes better than electrical impulses? Impulses reach only cells connected by nervous tissue and need time to reset. Hormones travel in the blood to almost every cell and give a steady, lasting signal.

8. Why is iodised salt advisable? The thyroid needs iodine to make thyroxine, which regulates metabolism. Without enough iodine, a person may develop goitre.

9. How is insulin secretion controlled? By feedback. When blood sugar rises, the pancreas releases more insulin; as sugar falls towards normal, insulin secretion is reduced.

Common mistakes to avoid

• Saying the brain handles a reflex action. The spinal cord does; the brain only records it.
• Mixing up positive and negative geotropism. Roots: positive. Shoots: negative.
• Writing that auxin collects on the lit side. It moves to the shady side.
• Calling abscisic acid a growth promoter. It is an inhibitor.

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