Class 10 Science Notes Chapter 6 — Control and Coordination#

Animals coordinate their activities with the nervous system and hormones. Plants use only hormones.

Nervous tissue#

Receptors — specialised tips of nerve cells that detect information from the environment (in the sense organs). For example, gustatory receptors detect taste and olfactory receptors detect smell.
Neuron (nerve cell) — the unit of the nervous system.

Path of a nerve impulse:
dendrite → cell body → axon → nerve ending → synapse → next neuron or muscle

The impulse travels as an electrical signal along the neuron.
At the end of the axon, it releases chemicals that cross the gap (synapse) and start a new electrical impulse in the next neuron. So impulses travel in one direction only.

Reflex action#

A reflex action is a sudden, automatic response to a stimulus, without thinking. Example: pulling your hand back from a hot object.
Reflex arc: receptor → sensory neuron → relay neuron (in the spinal cord) → motor neuron → effector (muscle or gland).
Reflex arcs form in the spinal cord so the response is quick, before the brain thinks about it. The information also goes on to the brain.

Reflex arc: the spinal cord connects the input nerve to the output nerve, so the response is quick and does not wait for the brain.

Human nervous system#

The central nervous system is the brain and spinal cord. The peripheral nervous system is the cranial nerves (from the brain) and spinal nerves (from the spinal cord).

Part of the brain	Main parts	Functions
Fore-brain	Cerebrum	Thinking, intelligence, memory; sensory areas (sight, hearing, smell); voluntary movements; hunger
Mid-brain	—	Involuntary actions, such as eye movements
Hind-brain	Pons, medulla	Involuntary actions: blood pressure, salivation, vomiting (medulla), breathing
	Cerebellum	Precision of voluntary actions; posture and balance (walking straight, riding a bicycle)

The brain is protected by the bony cranium (skull) and a fluid-filled balloon that absorbs shocks. The spinal cord is protected by the vertebral column (backbone).
Muscles move because proteins in muscle cells change their shape and arrangement in response to nerve impulses.

Coordination in plants#

Plants have no nervous system or muscles. They respond in two ways:

Movement	Type	Example
Immediate, not growth-related	Cells change shape by changing their water content	Leaves of the touch-me-not (Mimosa) fold when touched
Growth-related (tropisms)	Directional growth towards or away from a stimulus	Shoots bending towards light

Tropism	Stimulus	Example
Phototropism	Light	Shoot grows towards light (positive); root away from it (negative)
Geotropism	Gravity	Root grows down (positive); shoot grows up (negative)
Hydrotropism	Water	Roots grow towards water
Chemotropism	Chemicals	Pollen tube grows towards the ovule

Tendrils coil around a support because the part away from the support grows faster than the part touching it.

Plant hormones#

Hormone	Function
Auxin	Made at the shoot tip. It moves to the shady side and makes those cells grow longer, so the shoot bends towards light
Gibberellins	Help the stem grow
Cytokinins	Promote cell division; found where cells divide rapidly, such as in fruits and seeds
Abscisic acid	Inhibits growth; causes wilting of leaves

Hormones in animals#

Hormones are chemicals secreted by endocrine (ductless) glands directly into the blood. They act on target organs away from where they are made.

Gland	Hormone	Function
Adrenal	Adrenaline	Prepares the body for an emergency (“fight or flight”): faster heartbeat, more oxygen to muscles, blood diverted from digestion and skin
Thyroid	Thyroxin	Regulates carbohydrate, protein and fat metabolism. Needs iodine; lack of it causes goitre (swollen neck)
Pituitary	Growth hormone	Regulates growth. Too little in childhood → dwarfism; too much → gigantism
Pancreas	Insulin	Regulates blood sugar. Too little → diabetes
Testes	Testosterone	Changes in males at puberty
Ovaries	Oestrogen	Changes in females at puberty
Hypothalamus	Releasing factors	Controls the pituitary (for example, growth hormone releasing factor)

Iodised salt gives the iodine needed to make thyroxin.
Feedback mechanism — the timing and amount of hormone released are controlled by feedback. For example, when blood sugar rises, the pancreas releases more insulin; when it falls, insulin release goes down.

Nervous vs hormonal control#

Nervous	Hormonal
Electrical impulses along neurons	Chemicals carried in blood
Very fast	Slower
Reaches only cells connected by nerves	Reaches every cell in the body
Short-lived effect	Longer-lasting effect

Common mistakes#

Saying the cerebellum controls thinking. Thinking is the cerebrum; the cerebellum controls balance and precision.

Saying reflex actions are controlled by the brain. The reflex arc is in the spinal cord.

Saying auxin makes the lit side grow more. Auxin moves to the shady side.

Saying the touch-me-not response is a growth movement. It is not growth-related.

6. Control and Coordination