1. Coordination and Control
Organisms need to detect changes in their surroundings and respond appropriately. In multicellular organisms, different organs and tissues must also work together. The processes that help an organism receive information, process it and produce a suitable response are part of control and coordination.
2. Coordination in Plants
Plants do not have a nervous system or muscles like animals. They coordinate responses through chemical substances called plant hormones and through growth or movement responses.
2.1 Plant Hormones
| Hormone | Main role / effect |
|---|---|
| Auxin | Promotes cell growth, especially in shoots; helps coordinate phototropic growth. |
| Gibberellins | Promote growth of stems and other plant parts. |
| Cytokinins | Promote cell division and support growth. |
| Abscisic acid (ABA) | Generally inhibits growth; involved in dormancy and responses such as stomatal closure during water stress. |
2.2 Tropic Movements
Tropic movement is a directional growth movement of a plant part in response to an external stimulus. The direction of the response is related to the direction of the stimulus.
| Type | Stimulus | Typical example |
|---|---|---|
| Phototropism | Light | Shoot bends towards light. |
| Geotropism / gravitropism | Gravity | Roots generally grow downward; shoots generally grow upward. |
| Hydrotropism | Water | Roots grow towards a source of water. |
| Chemotropism | Chemicals | Pollen tube grows towards the ovule due to chemical signals. |
Phototropism and Auxin
When light falls from one side, auxin distribution in a shoot becomes uneven. In shoots, the shaded side generally has more auxin, causing greater cell elongation there. The resulting unequal growth bends the shoot towards light.
2.3 Nastic Movements
Some plant movements do not depend on the direction of the stimulus. For example, the leaves of Mimosa pudica fold and droop when touched. Such movements are often rapid and may involve changes in water content or turgor pressure in cells.
3. Nervous System in Animals
Animals need fast communication because they move and interact actively with their environment. The nervous system detects stimuli, transmits information and coordinates responses.
3.1 Neuron
A neuron or nerve cell is the structural and functional unit of the nervous system.
| Part | Function |
|---|---|
| Dendrites | Receive information or signals. |
| Cell body | Contains nucleus and maintains the cell. |
| Axon | Carries nerve impulse away from cell body. |
| Axon terminal | Passes signal to the next neuron or effector across a synapse. |
3.2 How Does a Nerve Impulse Travel?
A stimulus can generate an electrical change in a receptor or neuron. The impulse travels along the neuron. At a synapse, chemicals released from the axon terminal cross the small gap and initiate an electrical signal in the next neuron.
4. Reflex Action and Reflex Arc
A reflex action is a quick, automatic response to a stimulus. It helps protect the body from potentially harmful situations.
Reflex Arc
In many reflexes, the spinal cord provides a rapid pathway for the response. The brain receives information too, allowing awareness of what happened.
Voluntary and Involuntary Actions
| Voluntary action | Involuntary action |
|---|---|
| Under conscious control, e.g. writing or walking. | Not normally under conscious control, e.g. heartbeat and many digestive movements. |
5. Human Brain
The brain is the main coordinating centre of the nervous system. It receives sensory information, processes it and controls responses.
| Region | Major functions |
|---|---|
| Forebrain / cerebrum | Thinking, reasoning, memory, interpreting sensory information and voluntary actions. |
| Midbrain | Participates in certain visual and auditory reflexes and pathways. |
| Hindbrain | Includes cerebellum, pons and medulla; involved in posture, balance, coordination and involuntary functions. |
Important Brain Areas
Protection of Brain
The brain is protected by the skull and by membranes and cerebrospinal fluid. The spinal cord is protected by the vertebral column.
6. Coordination Through Hormones in Animals
Hormones are chemical messengers produced by endocrine glands. They are released into the blood and act on specific target tissues or organs.
Major Endocrine Glands and Hormones
| Gland | Hormone | Major role |
|---|---|---|
| Pituitary | Growth hormone and others | Regulates growth and controls several other endocrine glands. |
| Thyroid | Thyroxine | Regulates metabolism and supports normal growth and development. |
| Pancreas | Insulin | Helps regulate blood glucose level. |
| Adrenal glands | Adrenaline | Prepares body for emergency or stressful situations. |
| Testes | Testosterone | Supports male reproductive development and secondary sexual characteristics. |
| Ovaries | Oestrogen and progesterone | Regulate female reproductive development, menstrual cycle and related functions. |
Adrenaline and Emergency Response
When a person is frightened or stressed, the adrenal glands release adrenaline. It increases heart rate and breathing rate and directs more blood towards muscles, helping the body respond quickly.
Thyroxine and Iodine
The thyroid gland requires iodine to make thyroxine. Iodine deficiency can reduce thyroxine production and may lead to enlargement of the thyroid gland, called goitre.
Feedback Regulation
Hormone levels are regulated so that the body maintains suitable internal conditions. For example, when blood glucose rises, insulin helps cells take up glucose and lowers blood glucose towards the normal range.
7. Nervous vs Hormonal Coordination
| Feature | Nervous coordination | Hormonal coordination |
|---|---|---|
| Signal | Electrical impulses and chemical transmission at synapses. | Chemical hormones carried mainly by blood. |
| Speed | Generally very fast. | Generally slower to start. |
| Duration | Often brief and targeted. | Can have longer-lasting effects. |
| Examples | Reflex action, voluntary movement. | Growth, metabolism, blood glucose regulation. |
8. Key Terms for Exams
9. Quick Revision
10. 30 Practice Questions
- Why do organisms need control and coordination?
- What is a stimulus? Give two examples.
- What is a plant hormone?
- Name four plant hormones and state one function of each.
- Define phototropism.
- Explain how auxin causes bending of a shoot towards light.
- Differentiate tropic and nastic movements.
- What is geotropism? Give one example.
- What is hydrotropism?
- What is chemotropism? Give an example.
- What is a neuron? Name its main parts.
- What is the function of dendrites?
- What is a synapse?
- Explain how a nerve impulse is transmitted across a synapse.
- Define reflex action.
- Explain the pathway of a reflex arc.
- Differentiate voluntary and involuntary actions.
- What are the main regions of the human brain?
- State two functions of the cerebrum.
- What is the role of the cerebellum?
- Which part of the brain controls several involuntary functions?
- Why is the spinal cord important in reflex actions?
- What are hormones?
- Why are endocrine glands called ductless glands?
- State the function of thyroxine.
- Why is iodine necessary for our body?
- What is the role of insulin?
- What happens in the body when adrenaline is released?
- Differentiate nervous and hormonal coordination.
- Explain why coordination is essential for survival.
11. CBSE PYQ / PYQ-Based Practice
These questions are designed around recurring CBSE concepts and competency-style applications. They are suitable for written practice and viva preparation.
- A plant is placed near a window. After several days, its shoot bends towards the light. Explain the mechanism responsible.
- Why is the movement of a Mimosa leaf after touching it different from the growth of a shoot towards light?
- What would happen to a plant if auxin production or distribution were significantly disturbed? Explain using growth coordination.
- Explain how a nerve impulse travels through a neuron and across a synapse.
- Draw a labelled reflex arc and explain how it produces a quick response.
- Why is a reflex action generally faster than a consciously planned response?
- A person accidentally touches a hot object and immediately withdraws the hand. Explain the pathway involved.
- What could be the effect on body coordination if the cerebellum is damaged? State relevant functions.
- Why is the medulla important even though many of its functions are not under conscious control?
- Explain how the nervous system and endocrine system together maintain coordination in the human body.
- Why does the heart beat faster during fear or an emergency?
- Explain the role of adrenaline in preparing the body for an emergency.
- Why can iodine deficiency affect normal body functioning? Relate your answer to thyroxine.
- How does insulin help maintain a stable blood glucose level?
- Compare nervous coordination and hormonal coordination with respect to speed, signal and duration.
- What are tropic movements? Explain any two with examples.
- How do plant hormones help plants respond to their environment even without a nervous system?
- Suppose the receptor cells in a particular sense organ are unable to detect a stimulus. How would this affect coordination?
- Why is a feedback mechanism important in maintaining hormone levels and internal balance?
- Explain how damage to different parts of the brain can affect different functions, using the specialised roles of brain regions.