Introduction

Every living organism needs to respond to its surroundings to survive. A stimulus (change in environment, response trigger), such as touching a hot object, results in a response (reaction to stimulus, survival mechanism). Animals coordinate their actions using the nervous system (brain, spinal cord, nerves, fast response) and the endocrine system (hormones, glands, slow response), while plants rely on hormones and environmental responses. This chapter explores these mechanisms in detail.
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1. Control and Coordination in Animals
Animals regulate their body functions using:
Nervous System – Controls rapid responses via neurons (nerve cells, structural & functional unit).
Endocrine System – Controls long-term changes using hormones (chemical messengers).
These systems work together to maintain homeostasis and respond to environmental changes.

2. The Nervous System
The nervous system detects, processes, and responds to stimuli. It consists of:
Brain – Controls bodily functions.
Spinal Cord – Relays messages and handles reflex actions.
Nerves – Carry signals throughout the body.

(i) Neurons – The Nerve Cells
Neurons have three main parts:
Dendrites (receive signals, sensory input).
Axon (transmits signals, electrical impulse).
Synapse (gap between neurons, signal transmission).
Neurons communicate via electrical and chemical signals.

3. Human Nervous System
The nervous system is divided into:

(i) Central Nervous System (CNS)
Includes Brain and Spinal Cord.
Acts as the coordination center.

The Human Brain:
Cerebrum (thinking, memory, voluntary actions).
Medulla Oblongata (breathing, heartbeat, reflexes).

(ii) Peripheral Nervous System (PNS)
Includes nerves.
Relays messages between CNS and body.

4. Reflex Actions – Quick Responses
A reflex action is an automatic, quick response to a stimulus, controlled by a reflex arc (pathway of reflex action, quick response).

Example:
Pulling a hand away from a hot object.
Blinking when an object comes close.

The reflex arc involves:
Sensory Neuron (carries message to spinal cord).
Motor Neuron (sends response to muscles).
Effector (muscle or gland, performs action).

5. Hormonal Control and Coordination in Animals
The endocrine system uses hormones for slow but long-lasting responses. Endocrine glands (hormone-secreting, no ducts, blood transport) play key roles in body regulation.

Major Endocrine Glands:
Pituitary Gland (master gland, growth hormone, controls other glands).
Thyroid Gland (thyroxine, metabolism, iodine requirement).
Pancreas (insulin, blood sugar regulation, diabetes control).
Ovaries (estrogen & progesterone, female reproductive hormones).

6. Control and Coordination in Plants
Plants respond to environmental changes using hormones and specialized growth movements.

(i) Plant Hormones (Phytohormones)
Auxins – Control phototropism (light response, sunflower bending).
Gibberellins – Help stem elongation and seed germination.
Cytokinins – Promote cell division and fruit growth.

(ii) Types of Plant Movements

Plants exhibit:
Tropic Movements (Directional Growth Response)
Phototropism (light response, plant bending towards light).
Geotropism (gravity response, roots down, shoots up).
Thigmotropism (touch response, tendrils in climbers).
Nastic Movements (Non-Directional Movements)
Seismonastic (touch response, mimosa plant closing leaves).
Nyctinasty (sleep movements, flowers opening & closing).

 FAQs – Frequently Asked Questions

Q1: What is control and coordination?
It is the ability of an organism to detect changes in the environment and respond.

Q2: What are the two systems that control body functions in humans?
Nervous System (fast response, short-term effects).
Endocrine System (slow response, long-term effects).

Q3: What is a reflex action?
A quick, automatic response controlled by the reflex arc.

Q4: Why is the brain important?
The brain controls thinking, memory, movement, and involuntary actions.

Q5: What is the function of the pancreas in hormonal control?
It secretes insulin, which helps regulate blood sugar levels.

Q6: How do plants respond without a nervous system?
They use phytohormones and tropisms like phototropism and geotropism.

Q7: What does adrenaline do in our body?
It is the fight or flight hormone, preparing the body for emergencies.

Q8: What is the role of auxins in plants?
They regulate stem elongation and directional growth towards light.

Q9: How does the thyroid gland influence metabolism?
The thyroid produces thyroxine, which controls metabolic activities.

Q10: What is the difference between fast and slow responses in the body?
Fast Response (Nervous System): Uses electrical impulses for immediate actions.
Slow Response (Endocrine System): Uses hormones for long-term control.