Control and Coordination
Control and coordination is how an organism responds to changes around it in a controlled way. In animals this is done by the nervous system and hormones; in plants, only by hormones and growth movements. This chapter covers neurons, reflex action, the brain, the endocrine system and plant hormones, and is a steady source of marks in Class 10 biology.
Learning objectives
- Describe the structure of a neuron and how a nerve impulse travels.
- Explain reflex action and the reflex arc.
- Identify the main parts of the human brain and their functions.
- List important animal hormones and their roles.
- Describe plant hormones and tropic movements.
Key concepts
Neurons and nerve impulses
A neuron (nerve cell) is the basic unit of the nervous system. Information is picked up by dendrites, travels as an electrical impulse along the axon, and is passed to the next neuron across a tiny gap called a synapse using chemicals.
Reflex action
A reflex is a quick, automatic response to a stimulus, such as pulling the hand away from a hot object. It travels through a reflex arc — receptor → sensory neuron → spinal cord → motor neuron → muscle — without waiting for the brain to decide.
The human brain
The brain has three main parts: the cerebrum (thinking, memory, voluntary actions), the cerebellum (balance and posture), and the medulla / brain stem (involuntary actions like heartbeat and breathing). It is protected by the skull and fluid.
Hormones in animals and plants
Animal hormones (from endocrine glands) include insulin (controls blood sugar), adrenaline (prepares the body for emergencies), thyroxine and growth hormone. Plant hormones (phytohormones) such as auxin, gibberellin, cytokinin and abscisic acid control growth and tropic movements (phototropism, geotropism).
Key definitions
- Neuron
- A nerve cell — the structural and functional unit of the nervous system.
- Synapse
- The tiny gap between two neurons across which impulses are passed chemically.
- Reflex arc
- The path travelled by nerve impulses during a reflex action.
- Hormone
- A chemical messenger secreted in small amounts that controls a specific body process.
- Tropism
- A directional growth movement of a plant in response to a stimulus such as light or gravity.
Solved examples
Q1. Why is reflex action faster than a normal voluntary response?
Solution: In a reflex, the impulse is processed directly at the spinal cord through a short reflex arc, without travelling up to the brain for a decision, so the response is much quicker.
Q2. How does a plant shoot bend towards light?
Solution: Light makes the hormone auxin move to the shaded side of the shoot. More auxin there causes faster cell growth on that side, so the shoot bends towards the light — this is positive phototropism.
Q3. What happens in the body when adrenaline is released?
Solution: Adrenaline increases the heartbeat and breathing rate and directs more blood to muscles, preparing the body to deal with an emergency ('fight or flight').
Common mistakes to avoid
- Saying the brain controls reflex action — it is handled by the spinal cord.
- Confusing the cerebrum (thinking) with the cerebellum (balance).
- Mixing up the functions of insulin and adrenaline.
- Thinking plants have a nervous system — they coordinate only through hormones.
Control and Coordination — MCQ Quiz
10 questions with instant feedback. Use number keys 1–4 to answer.
The structural and functional unit of the nervous system is the:
Practice questions
Short answer
What is a stimulus?
Any change in the environment to which an organism responds.
Name the gland that secretes insulin.
The pancreas.
Which plant hormone inhibits growth and causes wilting?
Abscisic acid.
Long answer
Describe the path of a reflex arc when you touch a hot object.
Heat (stimulus) is detected by receptors in the skin. A sensory neuron carries the impulse to the spinal cord, which immediately passes it through a relay to a motor neuron. The motor neuron signals the arm muscles to contract, pulling the hand away — all before the brain consciously feels the pain.
Explain how hormonal coordination in plants differs from nervous coordination in animals.
Animals coordinate quickly using both electrical impulses (nervous system) and hormones, allowing fast, specific responses. Plants have no nervous system; they coordinate only through hormones, producing slower responses seen as growth movements (tropisms) rather than rapid actions.
HOTS (Higher Order Thinking)
A person's hand is on a hot plate. Why do they pull it away before they 'feel' the heat?
The protective reflex acts through the spinal cord and moves the hand instantly, while the slower signal to the brain that produces the conscious feeling of heat arrives a moment later.
Why is feedback control important for hormones like insulin?
Feedback keeps hormone levels balanced: when blood sugar rises, more insulin is released; when it falls, less is released. This self-regulation prevents the level from going too high or too low.
Quick revision
Revision notes
- Neuron: dendrite → axon → synapse; impulses are electrical then chemical.
- Reflex arc handled by the spinal cord (fast, automatic).
- Brain: cerebrum (thinking), cerebellum (balance), medulla (involuntary).
- Hormones: insulin (sugar), adrenaline (emergency); plants use auxin etc.
Key takeaways
- Reflexes are spinal, not brain-controlled.
- Match each brain part and hormone to its function.
- Plants coordinate only with hormones and tropic movements.
Frequently asked questions
What is the difference between nervous and hormonal control?
Nervous control is fast and short-lived using electrical impulses; hormonal control is slower and longer-lasting using chemical messengers.
What is a reflex action?
A quick, automatic response to a stimulus that travels through a reflex arc via the spinal cord.
Do plants have hormones?
Yes — plant hormones (phytohormones) like auxin, gibberellin, cytokinin and abscisic acid control growth and movements.