Control and Coordination Notes | Class 10 Science

1. Introduction

Every living organism responds to its environment. A plant bends towards light, an animal moves away from danger, and our body maintains a constant temperature. These responses are made possible by the coordination of various organs and systems. In animals, control and coordination are carried out by two systems: the nervous system and the endocrine system (hormones). The nervous system provides quick, short-lived responses through electrical and chemical signals, while hormones provide slow but long-lasting effects through chemical messengers carried in the blood.

Control and coordination are essential for survival. Without them, an organism would not be able to respond appropriately to changes in its surroundings, such as finding food, escaping danger, or adjusting to temperature changes. In plants, coordination is achieved mainly through chemical substances called plant hormones, since plants do not have a nervous system.

In this chapter, we will study the structure and function of the neuron, reflex action, the human brain, the central and peripheral nervous systems, the structure and working of the human eye, the endocrine glands and their hormones, and plant movements such as phototropism, geotropism and chemotropism, along with the plant hormones.

2. The Nervous System

The basic unit of the nervous system is the neuron (nerve cell). A neuron consists of a cell body (cytoplasm and nucleus), dendrites (short branched fibres that receive messages) and a single long axon (which conducts messages away from the cell body). The axon ends in nerve endings called axon terminals.

A nerve impulse is an electrical signal that travels along the neuron. At the synapse (the gap between two neurons), the impulse is transmitted through chemicals called neurotransmitters. The flow of impulses is always from dendrites → cell body → axon → synapse → next neuron.

Reflex Action

A reflex action is a quick, automatic response to a stimulus that does not involve conscious thought. It is controlled by the spinal cord. For example, when we touch a hot object, we withdraw our hand instantly. The pathway through which the impulse travels in a reflex action is called the reflex arc:

$$\text{Receptor (skin)} \rightarrow \text{Sensory neuron} \rightarrow \text{Spinal cord} \rightarrow \text{Motor neuron} \rightarrow \text{Effector (muscle)}$$

The reflex arc enables the spinal cord to respond quickly before the brain is involved, protecting the body from injury.

The Human Brain

The human brain is the main coordinating centre of the body. It is protected by the cranium (skull) and is covered by three membranes called meninges. The brain has three main parts:

Forebrain: the largest part, consisting of the cerebrum, which controls thinking, memory, reasoning and voluntary actions. The forebrain also contains centres for hunger, thirst and body temperature.
Midbrain: connects the forebrain and hindbrain, and relays messages between them.
Hindbrain: consists of the cerebellum (which controls balance and coordination of voluntary movements), the medulla (which controls involuntary actions such as breathing, heartbeat and blood pressure) and the pons.

The Peripheral Nervous System

Nerves that arise from the brain and spinal cord are called cranial nerves and spinal nerves. Together with the central nervous system (brain and spinal cord), they form the peripheral nervous system. Reflex actions are controlled by the spinal cord; some reflex actions, such as blinking, salivation and sneezing, are controlled by the brain.

3. The Human Eye

The human eye is a natural optical instrument that allows us to see. Its structure includes:

Cornea: the transparent bulge on the front of the eye that refracts light.
Iris: the coloured part that controls the size of the pupil and hence the amount of light entering the eye.
Pupil: the black opening in the centre of the iris.
Eye lens: a convex lens that forms an inverted, real image of objects on the retina.
Retina: the light-sensitive layer containing rods and cones (photoreceptors).
Ciliary muscles: adjust the focal length of the eye lens to focus objects at different distances.

Accommodation

The ability of the eye lens to change its focal length to focus objects at varying distances is called accommodation. The power of accommodation of a normal eye is about 4 dioptres; it can clearly see objects from infinity down to about 25 cm (the least distance of distinct vision). Rods help in seeing in dim light and in black-and-white vision, while cones help in seeing colours and bright light.

Persistence of Vision

The image formed on the retina persists for about 1/16th of a second. This is called the persistence of vision. It is the principle behind movies, which are a rapid succession of still pictures.

Common Defects of the Eye

Myopia (short-sightedness): the image is formed in front of the retina because the eyeball is too long or the lens is too convex. It is corrected with a concave lens.
Hypermetropia (long-sightedness): the image is formed behind the retina because the eyeball is too short or the lens is too flat. It is corrected with a convex lens.
Presbyopia: the power of accommodation decreases with age because the ciliary muscles weaken or the lens becomes inflexible. It is corrected with bifocal lenses.
Cataract: clouding of the eye lens, treated by surgical removal and lens replacement.

4. Coordination in Plants

Plants do not have a nervous system; they respond to stimuli through hormones and movements.

Types of Plant Movements

Tropic movements: growth movements of a plant part in response to a stimulus, directed towards or away from it. For example, phototropism (response to light), geotropism (response to gravity), chemotropism (response to chemicals) and hydrotropism (response to water). Growth of roots towards water is chemotropism/hydrotropism, and the growth of pollen tubes towards ovules is chemotropism.
Nastic movements: movements which do not depend on the direction of the stimulus, for example the folding of the leaves of the touch-me-not plant (Mimosa pudica) when touched. This movement is due to changes in the amount of water in the cells.

Plant Hormones

Auxin: promotes cell elongation, controls phototropism (helps in the growth of shoots towards light) and geotropism (root growth downwards). It is present in the tips of shoots and roots.
Gibberellin: promotes stem elongation and helps in flowering and seed germination.
Cytokinin: promotes cell division in plants.
Abscisic acid (ABA): inhibits growth, promotes dormancy and closure of stomata during water shortage (stress hormone).

5. Hormones in Animals

Hormones are chemical messengers secreted by endocrine (ductless) glands and carried in the blood to target organs. The study of endocrine glands and hormones is called endocrinology. The main endocrine glands and their functions are:

Gland	Hormone	Function
Pituitary	Growth hormone	Controls growth, called the master gland
Thyroid	Thyroxine	Regulates metabolism, growth and development
Pancreas	Insulin	Regulates blood sugar (glucose) level
Adrenal	Adrenaline	Prepares body for emergency (fight or flight)
Testis	Testosterone	Controls male reproductive organs
Ovary	Oestrogen and progesterone	Controls female reproductive organs
Parathyroid	Parathormone	Regulates calcium and phosphate level in blood

Feedback Mechanism

The functioning of hormones is regulated by feedback mechanisms. For example, when the blood sugar level rises, the pancreas secretes insulin, which lowers the sugar level. When the sugar level falls too low, insulin secretion is reduced. This is a negative feedback mechanism. Similarly, the thyroid gland's secretion is controlled by the pituitary through a feedback loop. Hormone deficiency or excess leads to diseases such as goitre (thyroxine deficiency) and diabetes (insulin deficiency).

Quick Revision Tables

Table 1: Comparison of Nervous System and Hormones

Feature	Nervous System	Hormones
Nature of signal	Electrical (nerve impulse)	Chemical (hormones)
Speed	Very fast	Slow
Duration of effect	Short-lived	Long-lasting
Mode of transport	Through neurons	Through blood
Site of action	Specific organs/muscles	Target organs

Table 2: Plant Hormones and their Functions

Plant Hormone	Function
Auxin	Cell elongation, phototropism, geotropism
Gibberellin	Stem elongation, flowering, seed germination
Cytokinin	Cell division
Abscisic acid	Inhibition of growth, dormancy, stomatal closure

Mind Map

flowchart TD A[Control and Coordination] --> B[Animal: Nervous System] B --> B1[Neuron: dendrites, cell body, axon] B --> B2[Reflex arc: receptor to effector via spinal cord] B --> B3[Brain: forebrain, midbrain, hindbrain] B --> B4[Human eye: cornea, lens, retina, accommodation] A --> C[Animal: Endocrine System] C --> C1[Pituitary: growth] C --> C2[Thyroid: metabolism] C --> C3[Pancreas: insulin for blood sugar] C --> C4[Adrenal: adrenaline for emergency] A --> D[Plant: Coordination] D --> D1[Tropic movements: phototropism, geotropism] D --> D2[Nastic movements: Mimosa pudica] D --> D3[Plant hormones: auxin, gibberellin, cytokinin, ABA]

Important Diagrams (SVG)

Diagram 1: Structure of a Neuron

Diagram 2: Structure of the Human Eye

Common Mistakes

Confusing the direction of the nerve impulse; the impulse always travels from dendrites to axon, not the reverse.
Saying that reflex actions are controlled by the brain; most reflex actions are controlled by the spinal cord.
Mixing up the functions of the cerebellum and medulla; the cerebellum controls balance while the medulla controls heartbeat and breathing.
Believing that the eye forms an upright image on the retina; the image formed on the retina is real and inverted.
Confusing myopia and hypermetropia: myopia needs a concave lens (image in front of retina), hypermetropia needs a convex lens (image behind retina).
Thinking plants have a nervous system; plants coordinate through hormones and movements only.
Confusing auxin and abscisic acid; auxin promotes growth while abscisic acid inhibits growth.

Exam Tips

Learn the reflex arc pathway in order: stimulus → receptor → sensory neuron → spinal cord → motor neuron → effector → response.
Memorise the three brain parts and at least one function of each: cerebrum (thinking), cerebellum (balance), medulla (involuntary actions).
Know the eye defects with their causes and correcting lenses, which is a very common board question.
For the neuron, be able to draw and label dendrites, cell body, nucleus, axon and axon terminals.
Remember that rods are for dim light and black-and-white vision, while cones are for bright light and colour vision.
Memorise the table of endocrine glands and their hormones, especially insulin (pancreas), thyroxine (thyroid) and adrenaline (adrenal).
For plant hormones, link each hormone to one function: auxin (growth), gibberellin (elongation), cytokinin (cell division), ABA (inhibition).

Conclusion

Control and coordination are what make organisms respond intelligently to their surroundings. The nervous system provides lightning-fast responses through neurons and reflex arcs, while the endocrine system regulates long-term changes through hormones. The human eye, with its ability to accommodate and its complex structure, is a remarkable organ that connects us to the world of light and colour. Plants, though lacking nerves, display elegant tropic and nastic movements and regulate their growth through hormones. Together, the nervous and hormonal systems maintain the internal balance of the body, keep us safe from harm, and allow us to perceive and interact with the environment. A clear understanding of the structure and function of neurons, the brain, the eye, glands and plant hormones will prepare you well for the examination and for future studies in biology and medicine.

Control and Coordination — Study Notes