CONTROL AND COORDINATION IN ORGANISMS

Control and Coordination

Control and coordination is the process by which different organs of the body work together in a systematic and balanced way to perform various functions efficiently.

It helps an organism to sense changes (stimuli) in its environment and to respond appropriately through nervous and hormonal systems.

1. The Nervous System – The Fast Electrical Messenger

2. The Endocrine System – The Slow Chemical Messenger

The Nervous System: The Electrical Network

The nervous system coordinates all voluntary and involuntary actions using neurons, which transmit impulses at a lighting speed.

The nervous system is the electrical network of our body that controls and coordinates all activities by transmitting messages between the brain, spinal cord, and other parts through nerve impulses.

Functions of the Nervous System

1. Receives information from the surroundings (stimulus).
2. Processes the information in the brain or spinal cord.
3. Sends instructions to muscles or glands (effectors) for response.
4. Maintains coordination between all body parts.

Parts of the Nervous System

Neuron

A neuron is a nerve cell that transmits messages in the form of electrical impulses.

Parts of a Neuron:

Dendrites: Receive messages

Cell body (Cyton): Processes messages

Axon: Carries impulse away from cell body

Synapse: Small gap between neurons where impulse passes chemically.

Mnemonic to Remember Divisions: ‘CAP’

C – Central Nervous System
A – Autonomic Nervous System
P – Peripheral Nervous System

Structure of a Neuron

A neuron consists of:
– Dendrites: Receive messages
– Cell Body (Cyton): Controls neuron activities
– Axon: Carries impulse away
– Axon Terminals: Transmit to next neuron or effector

Flowchart: Pathway of Nerve Impulse

Stimulus → Receptor → Sensory Neuron → Spinal Cord/Brain → Motor Neuron → Effector → Response

Human Nervous System

The human nervous system is divided into three major parts:
1. Forebrain – Controls voluntary actions and intelligence.
2. Midbrain – Controls reflexes related to sight and sound.
3. Hindbrain – Controls involuntary actions like heartbeat and balance.

Main Division	Parts	Functions
1. Central Nervous System (CNS)	Brain and Spinal cord	Controls all body activities; processes information
2. Peripheral Nervous System (PNS)	Cranial and Spinal nerves	Carries messages between CNS and body parts
3. Autonomic Nervous System (ANS)	Sympathetic & Parasympathetic systems	Controls involuntary actions (heartbeat, breathing, digestion)

Human Brain:The Control Centre of the Body

The human brain is the main coordinating and controlling organ of the nervous system.
It receives information from the sense organs, interprets it, stores it as memory, and sends instructions to the body for appropriate action.

It is protected by:

Cerebrospinal fluid (CSF): Cushions the brain and protects it from shock.

Cranium (skull): Hard bony covering.

Meninges: Three protective membranes.

The brain is divided into three main regions:

1. Forebrain (Thinking Part)

Parts: Cerebrum, Thalamus, Hypothalamus

Cerebrum – The Largest Part

• It forms about 80% of the total brain.
• It is divided into two hemispheres (left and right) connected by the corpus callosum.
• The surface (cerebral cortex) is folded to increase area for information storage.

Functions of Cerebrum:

• Controls voluntary actions (walking, writing, speaking, etc.)
• Controls intelligence, memory, learning, reasoning, emotions.
• Receives impulses from sense organs (sight, sound, touch, taste, smell).
• Interprets sensory information and makes decisions.

Thalamus

• Relays sensory and motor signals between different parts of the brain.
• Acts as a relay centre for messages going to and from the cerebrum.

Hypothalamus

• Controls involuntary functions such as hunger, thirst, sleep, temperature, and emotions.
• Maintains homeostasis (internal balance) of the body.
• Controls pituitary gland, hence regulating hormone secretion.

2. Midbrain (Relay Centre)

• Located between the forebrain and hindbrain.
• Small but important portion.

Functions:

• Controls reflex movements of the head, neck, and eyes in response to light or sound.
  (Example: Turning your head when you hear a sound.)
• Connects forebrain with hindbrain and acts as a transmission link.

3. Hindbrain (Movement and Balance Control)

Parts: Cerebellum, Pons, Medulla Oblongata

Cerebellum

• Located below the cerebrum, at the back of the skull.
• Maintains balance and posture of the body.
• Coordinates smooth and precise movements of muscles.

Example: While cycling, cerebellum helps maintain balance and control leg movement.

 Pons

• Lies in front of the cerebellum and above the medulla.
• Acts as a bridge connecting different parts of the brain.
• Helps in controlling breathing rate and communication between brain parts.

Medulla Oblongata

• Located at the base of the brain and continuous with the spinal cord.
• Controls involuntary activities such as:
  • Heartbeat
  • Breathing
  • Blood pressure
  • Digestion and swallowing

Part of Brain	Main Function(s)
Cerebrum (Forebrain)	Intelligence, memory, learning, voluntary actions
Thalamus	Relay centre for sensory messages
Hypothalamus	Controls temperature, hunger, emotions, hormones
Midbrain	Controls reflexes of eyes and head
Cerebellum (Hindbrain)	Maintains body balance and muscle coordination
Pons	Controls breathing and connects brain parts
Medulla Oblongata	Controls involuntary actions like heartbeat, respiration

Reflex Action

A reflex action is an automatic, quick, and involuntary response of the body to a stimulus, without the involvement of the brain in the decision-making process.
It is controlled by the spinal cord to protect the body from harm.

Example:

• Withdrawing hand from a hot object.
• Blinking of eyes when an object comes close.
• Sneezing or coughing when dust enters the nose

Mechanism of Reflex Action

The pathway through which nerve impulses travel during a reflex action is called the Reflex Arc.
It ensures a quick, automatic, and protective response without the delay of sending messages to the brain.

1. Stimulus

A stimulus is a sudden change in the environment that triggers a response.
Example: Touching a hot object (heat acts as the stimulus).

2. Receptor

The receptor is a sense organ (like skin) that detects the stimulus.
It converts the external change (like heat, pressure, pain) into an electrical signal (impulse).

3. Sensory Neuron

The sensory neuron carries the nerve impulse from the receptor to the spinal cord.

4. Interneuron (Relay Neuron)

Located inside the spinal cord, the interneuron (also called association neuron) receives the message from the sensory neuron, processes it, and passes it to the motor neuron.

5. Motor Neuron

The motor neuron carries the command from the spinal cord to the effector organ (usually a muscle).

6. Effector (Muscle or Gland)

The effector performs the actual response.
Muscles contract or glands secrete as instructed by the motor neuron.

Example: When a person touches a hot object (stimulus), heat is detected by skin receptors.
The sensory neuron carries this message to the spinal cord.
The spinal cord (interneuron) immediately sends a command through the motor neuron to hand muscles (effector) to withdraw.
The hand moves away instantly to avoid injury, this quick action is called a reflex action.

Flowchart: Reflex Arc Pathway

Stimulus → Receptor → Sensory Neuron → Spinal Cord → Motor Neuron → Effector → Response

What is Reflex Arc?

• The reflex arc is the pathway of nerve impulse during a reflex action.
• It ensures instant response by bypassing the brain for immediate protection.

Importance of Reflex Action

1. Prevents injury and protects the body from danger.
2. Allows the body to respond quickly to harmful stimuli.
3. Maintains body posture and balance automatically.

Coordination in Plants

Plants lack a nervous system but show coordination using hormones (phytohormones) and movements called tropisms.

Coordination in plants is the process by which different parts of a plant respond to various internal and external stimuli in a well-organized way.
Unlike animals, plants do not have a nervous system or muscles, they coordinate their activities using plant hormones and growth movements.

Types of Plant Movements (Responses to Stimuli)

1. Tropic Movements (Directional Movements)

Definition: Movement of a plant part in response to a stimulus, which is directional (towards or away from the stimulus).

Controlled by: Plant hormones (auxins)

In tropic movements, direction of response depends on direction of stimulus.

Type of Tropism	Stimulus	Example	Direction of Movement
Phototropism	Light	Bending of shoot towards light	Positive (towards light)
Geotropism	Gravity	Roots grow downward	Roots: Positive; Shoots: Negative
Hydrotropism	Water	Root grows towards water	Positive
Thigmotropism	Touch	Tendrils coil around support	Positive
Chemotropism	Chemicals	Growth of pollen tube towards ovule	Positive

2. Nastic Movements (Non-directional Movements)

Nastic movements are non-directional movements in plants that occur in response to external stimuli, but not dependent on the direction from which the stimulus comes.

Cause of Nastic Movements

These movements are caused by changes in turgor pressure (water pressure) inside the cells of the pulvinus (a swollen region at the base of the leaf or leaflet).

• When a plant cell gains water → it becomes turgid (swollen).
• When it loses water → it becomes flaccid (shrunken).
• This change in turgidity of cells results in movement of plant parts.

Hence, nastic movements are physiological movements caused by water pressure, not by growth.

Examples of Nastic Movements

Thigmonasty (Response to Touch)

• Seen in Mimosa pudica (Touch-me-not plant).
• When touched, the leaves fold inward and droop instantly.
• This happens due to loss of turgor pressure in the pulvinus cells at the base of the leaf.

Mechanism:

1. Touch (stimulus) → electrical & chemical signal travels to the pulvinus.
2. Water moves out from lower cells → cells lose turgor → shrink.
3. Upper cells remain turgid → leaflets fold downwards.
4. After some time, water returns → leaves reopen.

Photonasty (Response to Light)

• Seen in flowers like Dandelion and Tulip.
• The opening and closing of petals depend on intensity of light.

Examples:

• Dandelion flowers open in sunlight and close in darkness.
• Moonflowers open at night and close during the day.

Reason:

• Cells on different sides of the petals gain or lose water depending on light conditions.
• This change in turgor pressure causes opening or closing of the flower.

Difference Between Tropic and Nastic Movements

Feature	Tropic Movement	Nastic Movement
Direction of Response	Depends on direction of stimulus	Independent of direction
Cause	Growth of cells	Turgor pressure change
Example	Phototropism (bending towards light)	Thigmonasty (folding on touch)
Speed	Slow	Fast
Controlled by	Hormones (like Auxin)	Turgor changes in pulvinus cells

Plant Hormones and Functions

Plant hormones, also called phytohormones, are chemical substances produced naturally in plants that control and coordinate various growth and developmental processes like germination, flowering, ripening, and response to stimuli.

They are secreted in very small amounts and are transmitted from one part of the plant to another where they exert their effects.

Types of Plant Hormones

Plant hormones are classified into five major types based on their functions:

Type of Hormone	Main Function	Example / Extra Info
Auxins	Promote growth by cell elongation	Responsible for phototropism and geotropism
Gibberellins	Promote stem elongation and seed germination	Help in breaking seed dormancy
Cytokinins	Promote cell division and delay aging	Found in areas of active growth (buds, fruits, seeds)
Abscisic Acid (ABA)	Inhibits growth, causes wilting	Called the stress hormone
Ethylene	Promotes fruit ripening and leaf fall	A gaseous hormone found in ripe fruits.

Auxins – The Growth Hormones

• Discovered by F.W. Went.
• Synthesized mainly in shoot tips and young leaves.

Functions:

• Promotes cell elongation (helps stems and roots grow longer).
• Helps in phototropism (bending of shoot towards light).
• Helps in geotropism (roots grow towards gravity).
• Prevents falling of leaves and fruits (delays abscission).
• Used in agriculture for rooting of cuttings and weed control.

Example: In sunlight, auxin moves to the shaded side of the shoot → causes more cell elongation on that side → shoot bends towards light.

Gibberellins – The Growth Promoters

• Discovered from a fungus Gibberella fujikuroi.
• Present in young leaves, embryos, and roots.

Functions:

• Promotes stem elongation (especially in dwarf plants).
• Helps in seed germination by breaking dormancy.
• Promotes flowering and fruit growth.
• Stimulates enzyme production in germinating seeds.

Example: Gibberellins are sprayed on grapes to make them bigger and longer.

Cytokinins – The Cell Division Hormones

• Discovered in coconut milk and germinating seeds.
• Found in regions of active cell division (like buds, fruits, and seeds).

Functions:

• Promote cell division (cytokinesis).
• Delay senescence (aging) of leaves and fruits.
• Promote shoot formation in tissue culture.
• Work together with auxins for growth and development.

Example: Cytokinins keep vegetables like lettuce fresh and green for longer.

Abscisic Acid (ABA) – The Growth Inhibitor

• Also known as the stress hormone.
• Found in leaves, stems, and unripe fruits.

Functions:

• Inhibits plant growth.
• Promotes wilting and leaf fall (abscission).
• Closes stomata during water stress (to prevent water loss).
• Helps plants to tolerate stress conditions like drought, cold, or high salinity.

Example: In dry conditions, ABA causes stomata to close — reducing water loss.

Ethylene – The Ripening Hormone

• Only gaseous plant hormone.
• Produced in ripening fruits, old leaves, and flowers.

Functions:

• Promotes ripening of fruits (like bananas, tomatoes).
• Promotes abscission (falling of leaves, flowers, fruits).
• Stimulates flowering in plants like pineapples.
• Breaks dormancy of buds and seeds.

Example: Fruits like mangoes or bananas ripen faster when kept with ripe fruits — due to ethylene gas.

Chemical Coordination in Humans – The Endocrine System

Hormones are chemical messengers secreted by endocrine glands directly into the blood. They regulate processes such as metabolism, growth, and reproduction.

The endocrine system consists of endocrine glands that secrete hormones directly into the bloodstream. These hormones regulate the activities of different organs and maintain homeostasis (internal balance).

Hormones are chemical messengers secreted by endocrine glands in very small quantities into the blood, which regulate the functioning of specific organs or tissues of the body.

Major Endocrine Glands and Their Functions

Endocrine Gland	Hormone Secreted	Main Function / Role	Disorder due to Imbalance
Pituitary gland (Master gland)	Growth hormone (GH), TSH, FSH, LH, ADH	Controls growth, stimulates other glands (thyroid, adrenal, gonads)	Dwarfism / Gigantism
Thyroid gland	Thyroxine	Controls metabolism, growth, and development	Goitre (due to iodine deficiency)
Parathyroid glands	Parathormone	Regulates calcium and phosphorus levels in blood	Muscle cramps, weak bones
Adrenal glands	Adrenaline (emergency hormone), Cortisol	Prepares body for stress (“fight or flight”), controls metabolism	High BP, anxiety if over-secretion
Pancreas (Islets of Langerhans)	Insulin and Glucagon	Regulates blood sugar level	Diabetes mellitus (insulin deficiency)
Testes (in males)	Testosterone	Controls development of male reproductive organs and secondary sexual characters	Reduced masculinity if deficient
Ovaries (in females)	Oestrogen and Progesterone	Control female reproductive cycle, development of female characteristics	Menstrual irregularities
Pineal gland	Melatonin	Regulates sleep and biological rhythm	Sleep disorders
Thymus gland	Thymosin	Develops immunity in early life	Weak immune response in deficiency

Pituitary Gland – “Master Gland”

• Located at the base of the brain.
• Controls other endocrine glands (thyroid, adrenals, gonads).
• Secretes:
  • Growth hormone (GH): Controls height and body growth.
  • TSH: Stimulates thyroid gland.
  • FSH & LH: Control reproductive organs.
  • ADH: Controls water balance.

Disorders:

• Less GH: Dwarfism (short height)
• Excess GH: Gigantism (abnormally tall)

Thyroid Gland

• Located in the neck region.
• Secretes thyroxine, which contains iodine.

Functions:

• Regulates metabolism (rate of energy use).
• Controls growth and development.

Disorders:

• Iodine deficiency → Goitre (enlargement of thyroid gland).
• Excess thyroxine → Hyperthyroidism (increased metabolism).

 Parathyroid Glands

• Four small glands located behind the thyroid.
• Secretes parathormone.

Function:
Regulates calcium and phosphate balance in blood.

 Adrenal Glands – “Emergency Hormone Gland”

• Located on top of both kidneys.
• Secretes adrenaline (epinephrine) and cortisol.

Functions:

• Adrenaline:
  • Increases heart rate and blood pressure.
  • Prepares body for fight or flight during stress or danger.
• Cortisol: Controls metabolism of fats, proteins, and carbohydrates.

Pancreas – Dual Gland (Endocrine + Exocrine)

• Contains Islets of Langerhans which secrete hormones:
  • Insulin: Lowers blood sugar level.
  • Glucagon: Raises blood sugar level.

Disorder:

• Lack of insulin → Diabetes mellitus.
  Symptoms: Frequent urination, thirst, fatigue, and high blood sugar.

Gonads – Sex Glands

(a) Testes (in males)

• Secretes testosterone.
• Controls development of male reproductive organs and secondary sexual characteristics (voice change, facial hair).

(b) Ovaries (in females)

• Secrete oestrogen and progesterone.
• Control menstrual cycle, ovulation, and female body features.
• Progesterone helps in maintaining pregnancy.

Pineal Gland

• Located deep in the brain.
• Secretes melatonin.
• Regulates sleep-wake cycle and biological rhythms (day-night cycle).

Thymus Gland

• Located near the heart, large in childhood and shrinks after puberty.
• Secretes thymosin, which helps in the development of immunity.

Gland	Hormone	Function	Disorder (If Deficient)
Pituitary	Growth hormone	Controls body growth	Dwarfism
Thyroid	Thyroxine	Regulates metabolism	Goitre
Adrenal	Adrenaline	Fight or flight response	Weak stress response
Pancreas	Insulin	Controls sugar level	Diabetes
Testes	Testosterone	Male characteristics	Infertility, less masculinity
Ovaries	Oestrogen, Progesterone	Female characteristics, pregnancy	Menstrual issues
Pineal	Melatonin	Sleep rhythm	Sleep imbalance
Thymus	Thymosin	Immunity development	Weak immunity

Importance of Endocrine System

Works in coordination with the nervous system to regulate body functions.

Maintains internal balance (homeostasis).

Controls growth, metabolism, reproduction, and emotions.

Flowchart: Endocrine Coordination

Stimulus → Gland → Hormone → Target Organ → Response

Feedback Mechanism of Hormones

The feedback mechanism is a self-regulating system in the human body that helps to maintain the right level of hormones.

It ensures that:

• Hormones are secreted only when needed, and
• Their secretion stops once the desired effect is achieved.

It prevents the over-secretion or under-secretion of hormones and helps maintain homeostasis (internal balance) in the body.

How It Works

The feedback mechanism works mainly between:

• The endocrine glands (which secrete hormones), and
• The brain (especially the hypothalamus and pituitary gland), which act as control centers.

There are two types of feedback mechanisms:

1. Negative Feedback Mechanism
2. Positive Feedback Mechanism

Negative Feedback Mechanism

Definition:

In a negative feedback, the rise in the level of a hormone inhibits further secretion of that hormone.
Similarly, a fall in its level triggers more secretion.

It maintains a constant internal balance by reducing excess or restoring deficiency.

Example 1: Regulation of Thyroxine (Thyroid Hormone)

1. The pituitary gland secretes TSH (Thyroid Stimulating Hormone).
2. TSH stimulates the thyroid gland to release thyroxine.
3. When thyroxine level increases in blood, it inhibits the pituitary gland from secreting more TSH.
4. As a result, the thyroid stops releasing extra thyroxine.

If thyroxine level decreases → pituitary releases more TSH → thyroid releases more thyroxine again.

Conclusion:

The level of thyroxine is maintained automatically by a negative feedback mechanism involving the pituitary and thyroid glands.

LETS RECALL

Q1. Explain the feedback mechanism of hormonal control in humans with a suitable example.

Answer:
The feedback mechanism helps to maintain a stable level of hormones in the human body.
When the level of a particular hormone rises above normal, its further secretion is stopped; and when it falls below normal, secretion increases again.

Example – Regulation of Thyroxine:

1. The pituitary gland secretes TSH (Thyroid-Stimulating Hormone).
2. TSH stimulates the thyroid gland to produce thyroxine.
3. When thyroxine level in blood increases, it inhibits the pituitary from releasing more TSH.
4. Thus, the thyroid stops releasing excess thyroxine.
5. When thyroxine level decreases, TSH secretion increases again.

Hence, the thyroxine level remains constant through a negative feedback mechanism.
 This mechanism prevents hormonal imbalance and maintains homeostasis.

Q2. Describe the structure and function of the human brain.

Answer:
The human brain is the control centre of the nervous system.
It is protected by the cranium, meninges, and cerebrospinal fluid (CSF).

Main Parts and Functions:

1. Forebrain (Cerebrum, Thalamus, Hypothalamus):
   • Cerebrum – controls intelligence, memory, learning, voluntary actions.
   • Thalamus – relays sensory messages.
   • Hypothalamus – regulates hunger, thirst, emotions, and hormone control.
2. Midbrain: Controls reflex movements of eyes and head.
3. Hindbrain (Cerebellum, Pons, Medulla):
   • Cerebellum – maintains balance and coordination.
   • Pons – controls breathing rate.
   • Medulla oblongata – controls involuntary actions like heartbeat and digestion.

Q3. Explain coordination in plants and describe the role of plant hormones.

Answer:
Plants coordinate their activities through chemical control using plant hormones since they lack a nervous system.

Plant Hormones and Their Functions:

1. Auxin: Promotes cell elongation and helps in phototropism and geotropism.
2. Gibberellin: Stimulates stem elongation and seed germination.
3. Cytokinin: Promotes cell division and delays aging.
4. Abscisic Acid (ABA): Inhibits growth; causes wilting and dormancy.
5. Ethylene: Promotes fruit ripening and leaf fall.

Thus, plants show coordination through growth-related chemical signals (phytohormones) and tropic movements.

Q4. What is reflex action? Explain its pathway with the help of a labeled diagram of reflex arc.

Answer:
A reflex action is an automatic, quick, and involuntary response of the body to a stimulus, controlled by the spinal cord.
It helps protect the body from injury.

Pathway (Reflex Arc):

1. Stimulus: Detected by receptor (skin).
2. Sensory Neuron: Carries impulse to spinal cord.
3. Interneuron: Processes information.
4. Motor Neuron: Sends message to effector organ (muscle).
5. Effector: Produces response (withdraws hand).

 Stimulus → Receptor → Sensory Neuron → Spinal Cord → Motor Neuron → Effector → Response.

Q5. Compare and contrast nervous control and chemical (hormonal) control in humans.

Feature	Nervous Control	Chemical (Hormonal) Control
Nature of Message	Electrical impulses	Chemical messengers (hormones)
Speed	Very fast	Slow but long-lasting
Duration	Short term	Long term
Organs Involved	Brain, spinal cord, nerves	Endocrine glands
Type of Action	Voluntary and reflex actions	Growth, metabolism, reproduction
Example	Withdrawal of hand from flame	Regulation of blood sugar by insulin

Exam Tips

Focus on definitions and diagrams.
Write in points with subheadings (functions, examples).
Underline key terms (e.g., thyroxine, negative feedback, adrenaline).
For 5-mark questions, include examples and labeled diagrams.