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Control and Coordination in Living Organisms
1. Introduction
- In the previous chapter, we studied life processes involved in maintenance functions.
- A common idea is that movement signifies life.
- Some movements result from growth (e.g., a seedling emerging from the soil).
- Other movements are independent of growth (e.g., animals running, children playing).
2. Why is Movement Associated with Life?
- Movement is often a response to changes in the environment.
- Examples:
- A cat running after seeing a mouse.
- Plants growing toward sunlight.
- Buffaloes chewing cud to aid digestion.
- Movement helps organisms use environmental changes to their advantage.
- Reflex actions like blinking or withdrawing from heat are also protective responses.
3. Control and Coordination in Living Organisms
- Movement in response to stimuli is carefully controlled.
- Organisms recognize changes in their environment and respond accordingly.
- Example:
- We whisper instead of shouting in class to avoid disturbance.
- The type of response depends on the stimulus (triggering event).
4. Need for Control and Coordination
- Organisms require systems for proper control and coordination.
- In multicellular organisms, specialized tissues handle control and coordination.
- These systems ensure that responses to stimuli are appropriate and efficient.
Conclusion
- Movement is an important sign of life and is often a response to environmental changes.
- Living organisms need control and coordination systems to ensure the right response to stimuli.
- Specialized tissues in multicellular organisms play a key role in these processes.
7.1 ANIMALS – NERVOUS SYSTEM
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In animals, control and coordination are carried out by nervous and muscular tissues. The nervous system plays a crucial role in detecting stimuli, processing information, and generating appropriate responses.
1. Nervous System and Its Role
- The nervous system enables animals to detect stimuli and respond quickly.
- It is composed of nerve cells (neurons) that transmit information in the form of electrical impulses.
- Example: Touching a hot object triggers an immediate reaction due to the nervous system’s rapid response mechanism.
2. Sensory Reception and Detection of Stimuli
-
Specialized nerve endings (receptors) detect changes in the environment.
-
These receptors are present in sense organs such as:
- Skin (touch, temperature, pain)
- Tongue (taste – gustatory receptors)
- Nose (smell – olfactory receptors)
- Ears (hearing, balance)
- Eyes (vision)
-
Example: When we touch a hot object, receptors in our skin detect the heat and send signals to the brain.
3. Structure and Function of a Neuron
(a) Structure of a Neuron
A neuron is the fundamental unit of the nervous system, designed for receiving and transmitting electrical signals.
Parts of a Neuron:
- Dendrites: Receive information from the environment or other neurons.
- Cell body (Cyton/Soma): Processes the information and contains the nucleus.
- Axon: A long fiber that carries impulses away from the cell body.
- Axon terminals: Transmit signals to the next neuron or an effector (muscle or gland).
- Synapse: The gap between two neurons where chemical transmission occurs.
(b) Transmission of Nerve Impulses
The nervous system uses electrical and chemical signals for communication.
-
Detection of Stimulus
- Receptors in sense organs detect the stimulus.
- This information is received at the dendritic tip of a neuron.
-
Generation of Electrical Impulse
- A chemical reaction at the dendrites generates an electrical impulse.
- The impulse moves from dendrite → cell body → axon → axon terminals.
-
Transmission Across Synapse
- At the axon terminal, the electrical impulse triggers the release of neurotransmitters (chemical messengers).
- Neurotransmitters cross the synapse and generate a new impulse in the next neuron.
-
Response by Effector Organs
- The final neuron transmits the impulse to muscles or glands, triggering an appropriate response.
- Example: Muscles contract to pull the hand away from a hot object.
4. Role of Synapse in Neural Communication
- A synapse is a small gap between two neurons.
- The electrical signal from one neuron is converted into a chemical signal to pass through the gap.
- Once it reaches the next neuron, it is converted back into an electrical signal.
- This process ensures one-way transmission of nerve impulses.
5. Function of the Nervous System
The nervous system is responsible for:
- Receiving stimuli from the external or internal environment.
- Processing information in the brain or spinal cord.
- Generating responses to stimuli through muscles or glands.
- Coordinating voluntary and involuntary actions.
6. Activity 7.1 – Understanding the Role of Receptors
Experiment:
- Step 1: Put some sugar in your mouth and observe its taste.
- Step 2: Block your nose and eat sugar again. Observe any difference in taste.
- Step 3: Try blocking your nose while eating a full meal and see if food tastes different.
Observations & Explanation:
- When the nose is blocked, the sense of taste is reduced.
- This is because smell and taste are closely linked.
- Olfactory receptors in the nose help in detecting flavors along with gustatory receptors in the tongue.
- A similar effect occurs when we have a cold, making food taste bland.
7. Summary
- The nervous system is responsible for detecting, processing, and responding to stimuli.
- Neurons are the basic units of the nervous system that conduct electrical impulses.
- Receptors in sense organs detect environmental changes.
- Synapses enable communication between neurons using chemical signals.
- The nervous system coordinates body movements and responses efficiently.
7.1.1 What Happens in Reflex Actions?
1. Introduction to Reflex Actions
- Reflex actions are sudden, automatic, and involuntary responses to stimuli.
- Examples:
- Jumping away from a moving bus.
- Pulling the hand back from a hot object.
- Salivating at the sight of food.
- Reflex actions occur without conscious thought, ensuring quick responses to environmental changes.
2. Importance of Reflex Actions
- Prevents injury (e.g., withdrawing from a hot object before getting burnt).
- Helps in survival by enabling rapid responses.
- Reduces reaction time by bypassing complex thinking processes.
3. How Reflex Actions Work?
- If we had to think before responding, it would take too long, increasing the risk of injury.
- The nervous system has a shortcut to quickly process urgent stimuli – this is called a Reflex Arc.
4. Reflex Arc – The Neural Pathway
A reflex arc is the pathway through which a reflex action occurs. It involves:
- Receptor – Detects stimulus (e.g., heat, pain).
- Sensory neuron – Carries impulse from receptor to the spinal cord.
- Interneuron (Relay Neuron) – Processes impulse and transmits it to a motor neuron.
- Motor neuron – Sends impulse to an effector organ (muscle/gland).
- Effector – Responds (e.g., muscle contracts to pull hand away).
Example of Reflex Arc in Action
- Touching a hot object:
- Heat is detected by skin receptors.
- Sensory neurons carry the impulse to the spinal cord.
- The spinal cord processes the impulse and immediately signals the motor neuron.
- Motor neurons activate muscles to pull the hand away.
- The brain later receives the signal to understand what happened.
Key Features of Reflex Actions
- Involuntary – Happens without conscious effort.
- Fast – Saves time by bypassing the brain initially.
- Protective – Prevents damage and enhances survival.
5. Evolutionary Significance of Reflex Arcs
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- Reflex arcs evolved in simple organisms before the brain developed.
- Many animals lack complex brains, relying solely on reflexes for survival.
- Even after brain evolution, reflexes remain useful due to their speed.
6. Example: Pupil Reflex to Bright Light
- When bright light is focused on the eyes:
- The retina (receptor) detects high light intensity.
- The optic nerve (sensory neuron) sends the impulse to the brain.
- The brain processes the impulse and sends a signal to eye muscles.
- The pupil contracts to reduce light entry, protecting the retina.
7.1.2 Human Brain
1. Introduction
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- The spinal cord is not just for reflex actions; it also helps transmit information to the brain.
- The brain is the main coordinating center of the body.
- The Central Nervous System (CNS) includes the brain and spinal cord, which receive and process information from all parts of the body.
- The Peripheral Nervous System (PNS) consists of cranial nerves (from the brain) and spinal nerves (from the spinal cord) that connect the CNS to the body.
- The brain controls both voluntary and involuntary actions through its complex structure.
2. Structure of the Human Brain
The human brain is divided into three major regions:
- Forebrain – Thinking, decision-making, voluntary actions.
- Midbrain – Relaying signals and controlling some involuntary actions.
- Hindbrain – Balance, posture, and involuntary functions like breathing and heartbeat.
3. Functions of Different Parts of the Brain
(a) Forebrain – The Thinking Center
- Largest and most developed part of the brain.
- Responsible for thoughts, memory, emotions, and voluntary movements.
- Receives sensory inputs and processes them.
- Divided into:
- Sensory Areas – Receive impulses from sense organs (e.g., sight, smell, hearing).
- Association Areas – Interpret sensory information by linking it to stored memories.
- Motor Areas – Control voluntary movements (e.g., walking, lifting objects).
Examples:
- The hunger center in the forebrain helps us know when we are full.
- The motor area sends signals to leg muscles for movement.
(b) Midbrain – The Communication Bridge
- Acts as a relay center between the forebrain and hindbrain.
- Controls some reflex actions related to vision and hearing.
- Plays a role in coordinating eye movement and posture.
(c) Hindbrain – The Control Center for Body Functions
- Regulates basic functions like breathing, balance, and coordination.
- Divided into:
- Cerebellum – Controls balance, posture, and precision of movements.
- Medulla Oblongata – Regulates heartbeat, breathing, digestion, and involuntary reflexes like vomiting.
- Pons – Helps in respiration and relays signals between brain regions.
Examples:
- The cerebellum allows us to walk in a straight line, ride a bicycle, or pick up objects with accuracy.
- The medulla controls involuntary actions like blood pressure regulation and salivation.
4. Voluntary vs. Involuntary Actions
| Feature | Voluntary Actions | Involuntary Actions |
|---|---|---|
| Control | Conscious effort | Automatic, without thought |
| Brain Part Involved | Forebrain (motor areas) | Midbrain, Hindbrain (Medulla, Cerebellum) |
| Examples | Writing, talking, moving objects | Heartbeat, digestion, breathing, salivation |
5. Reflex vs. Thought-Out Actions
- Some actions, like pulling the hand from a flame, are reflexes (controlled by the spinal cord).
- Other actions, like moving a chair or writing, require thinking and planning (controlled by the forebrain).
- Certain involuntary actions, like salivation and heartbeat, are regulated by the hindbrain and midbrain.
6. Summary
- The brain is the control center of the body, handling both voluntary and involuntary functions.
- It consists of three main parts:
- Forebrain – Thinking, decision-making, voluntary actions.
- Midbrain – Relays sensory information and controls some reflexes.
- Hindbrain – Maintains balance, posture, and automatic functions.
- Reflexes, involuntary movements, and thought-out actions are controlled by different brain regions.
- The CNS and PNS work together to process information and coordinate responses efficiently.
Final Thought
- The human brain is highly specialized, allowing us to think, learn, react, and survive efficiently.
- Its complex design ensures smooth coordination between thought, movement, and automatic body functions.
7.1.3 How are these Tissues Protected?
1. Protection of the Brain
- The brain is a delicate and vital organ, requiring strong protection.
- It is enclosed within a bony structure called the skull (cranium), which acts as a hard protective shell.
- Inside the skull, the brain is further protected by a fluid-filled balloon, known as the cerebrospinal fluid (CSF).
- Functions of cerebrospinal fluid (CSF):
- Shock absorption – Protects the brain from sudden impacts.
- Nourishment – Provides essential nutrients to brain cells.
- Waste removal – Helps remove waste products from brain metabolism.
2. Protection of the Spinal Cord
- The spinal cord is protected by the vertebral column (backbone).
- The vertebrae are stacked bones forming a protective structure around the spinal cord.
- Like the brain, the spinal cord is also surrounded by cerebrospinal fluid, which acts as a cushion.
3. Summary of Nervous System Protection
| Part | Protective Structure | Function |
|---|---|---|
| Brain | Skull (Cranium) | Provides a hard protective covering. |
| Brain | Cerebrospinal Fluid (CSF) | Absorbs shocks, nourishes, and cleans. |
| Spinal Cord | Vertebral Column (Backbone) | Provides a strong bony cover. |
| Spinal Cord | Cerebrospinal Fluid | Prevents damage from sudden impact. |
7.1.4 How does the Nervous Tissue Cause Action?
1. Role of Nervous Tissue in Movement
- The nervous system collects information, processes it, and sends signals to muscles for movement.
- Final execution of movement is done by muscles – the nervous system only sends commands.
2. How do Muscles Move?
- Muscle movement occurs when a nerve impulse reaches a muscle fiber.
- This impulse triggers a response inside the muscle cell, causing it to contract.
- Movement at the cellular level happens when muscle cells change their shape and shorten.
- Special proteins inside muscle cells change their shape in response to electrical signals from neurons.
- The new protein arrangement makes the muscle shorter, resulting in contraction.
3. Types of Muscles and Their Control
| Type of Muscle | Control | Example |
|---|---|---|
| Voluntary Muscles (Skeletal Muscles) | Under conscious control | Moving arms, walking, writing |
| Involuntary Muscles (Smooth Muscles) | Not under conscious control | Digestive system, blood vessels |
| Cardiac Muscles (Heart Muscles) | Involuntary but rhythmic | Heartbeat |
- Voluntary muscles work when we think and decide to move.
- Involuntary muscles work automatically without conscious thought (e.g., heartbeat, digestion).
4. Summary of Muscle Action
- Nerve impulses trigger muscle contraction.
- Muscle movement occurs by shortening of muscle fibers.
- Different types of muscles work under voluntary or involuntary control.
- The brain and spinal cord coordinate muscle activity for smooth and efficient movements.
Final Thought
- The nervous system and muscular system work together to produce movement.
- The brain, spinal cord, and nerves send signals, while muscles execute the actions.
- Proper protection of the nervous system ensures smooth functioning of body movements.
Q U E S T I O N S & A N S W E R S
1. What is the difference between a reflex action and walking?
Answer:
- Reflex action is an involuntary and automatic response to a stimulus, such as pulling a hand away from a hot object. It is controlled by the spinal cord and occurs without conscious thought.
- Walking is a voluntary action, meaning it is under conscious control and coordinated by the brain (forebrain and cerebellum).
2. What happens at the synapse between two neurons?
Answer:
- A synapse is the junction between two neurons where nerve impulses are transmitted.
- When an electrical impulse reaches the axon terminal of the first neuron, it triggers the release of neurotransmitters (chemical messengers).
- These chemicals cross the synaptic gap and generate a new electrical impulse in the next neuron.
3. Which part of the brain maintains posture and equilibrium of the body?
Answer:
- The cerebellum, a part of the hindbrain, is responsible for maintaining posture and equilibrium of the body.
- It helps in coordinating muscle movements and balancing the body during activities like walking, running, and cycling.
4. How do we detect the smell of an agarbatti (incense stick)?
Answer:
- The olfactory receptors in the nose detect the scent molecules from the agarbatti.
- These receptors send signals through the olfactory nerve to the forebrain, which processes the smell and helps us recognize it.
5. What is the role of the brain in reflex action?
Answer:
- Reflex actions are primarily controlled by the spinal cord, allowing quick responses without involving the brain.
- However, the brain receives information about the reflex action for awareness and learning.
- In some complex reflexes, the brain can modify or override reflex responses if needed.
7.2 COORDINATION IN PLANTS
1. Introduction
- Unlike animals, plants do not have a nervous system or muscles for coordination.
- However, they still respond to stimuli such as touch, light, gravity, and chemicals.
- Plants show two types of movement:
- Movement independent of growth (e.g., folding of the touch-me-not plant).
- Movement dependent on growth (e.g., bending of shoots towards light).
7.2.1 Immediate Response to Stimulus
1. Non-Growth Movements in Plants
- Example: The touch-me-not plant (Mimosa pudica) folds its leaves when touched.
- This movement is not related to growth but occurs due to changes in water pressure in cells.
2. How Do Plants Respond Without a Nervous System?
- No specialized tissues for impulse conduction like animals.
- Information is transmitted via electrical-chemical signals.
- Some plant cells change shape by gaining or losing water, causing movement.
- Example: When touched, the base of the sensitive plant's leaves loses water, making the leaves fold.
7.2.2 Movement Due to Growth
1. Growth-Related Movements
- Plants grow in specific directions based on external stimuli like light, gravity, water, and chemicals.
- Example: Pea plants use tendrils to climb by wrapping around support.
2. Types of Tropic Movements (Tropisms)
Plants show directional movements in response to stimuli, known as tropisms.
| Type of Tropism | Stimulus | Example |
|---|---|---|
| Phototropism | Light | Shoots grow towards light, roots grow away. |
| Geotropism | Gravity | Roots grow downward, shoots grow upward. |
| Hydrotropism | Water | Roots grow towards water. |
| Chemotropism | Chemicals | Pollen tubes grow towards ovules. |
| Thigmotropism | Touch | Tendrils wrap around support. |
3. Example of Phototropism Experiment
- A conical flask filled with water is covered with wire mesh, and germinated bean seeds are placed on top.
- The setup is placed in a box with one open side facing light.
- Observation: Shoots bend towards light, roots grow away.
- Conclusion: Plants grow towards light due to the action of plant hormones.
7.2.3 Role of Chemical Coordination in Plants
1. Why Do Plants Use Chemical Signals?
- Electrical impulses work well for animals but are not suitable for plants.
- Limitations of electrical impulses:
- They only reach connected cells.
- They cannot be continuously generated.
- Instead, plants use chemical messengers called hormones to coordinate activities.
2. Plant Hormones (Phytohormones)
| Hormone | Function | Example |
|---|---|---|
| Auxin | Promotes cell elongation in shoots, bending towards light. | Phototropism in plants. |
| Gibberellins | Stimulates stem growth and seed germination. | Increases height in sugarcane. |
| Cytokinins | Promotes cell division, delays aging. | Found in fruits and seeds. |
| Abscisic Acid (ABA) | Inhibits growth, causes wilting of leaves. | Helps plants survive drought. |
3. Example of Auxin in Action
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- Auxin is a hormone that controls plant bending towards light.
- It accumulates on the shaded side of the plant, causing those cells to grow longer.
- This leads to the plant bending towards the light source.
7.2.4 Summary
- Plants lack a nervous system but respond to stimuli through chemical coordination.
- Non-growth movements occur due to changes in water pressure in plant cells.
- Growth-related movements (tropisms) help plants grow in favorable conditions.
- Plant hormones (phytohormones) regulate growth, development, and responses to stimuli.
- Auxin, gibberellins, cytokinins, and abscisic acid play crucial roles in plant coordination.
Final Thought
Plants may not have brains or nerves, but their chemical communication system allows them to adapt, survive, and thrive in different environments. 🌿
Q U E S T I O N S & A N S W E R S
1. What are plant hormones?
Answer:
- Plant hormones (phytohormones) are chemical messengers that regulate plant growth, development, and responses to stimuli.
- They are produced in one part of the plant and transported to other parts where they take action.
- Examples: Auxins, Gibberellins, Cytokinins, Abscisic Acid (ABA).
2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Answer:
- The movement of the sensitive plant (Mimosa pudica) is not dependent on growth; it occurs due to changes in water pressure in plant cells.
- The movement of a shoot towards light (phototropism) is dependent on growth, caused by unequal cell elongation due to the hormone auxin.
| Feature | Sensitive Plant (Touch Response) | Shoot Towards Light (Phototropism) |
|---|---|---|
| Type of Movement | Rapid, immediate response | Slow, growth-dependent |
| Cause of Movement | Water movement in cells | Unequal growth due to auxin |
| Example | Folding of Mimosa leaves | Shoot bending towards light |
3. Give an example of a plant hormone that promotes growth.
Answer:
- Auxins promote cell elongation, root development, and bending of shoots toward light.
- Gibberellins stimulate stem elongation and seed germination.
- Cytokinins promote cell division and delay aging.
Example: Gibberellins help in increasing the height of sugarcane plants.
4. How do auxins promote the growth of a tendril around a support?
Answer:
- Tendrils of climbing plants show thigmotropism (response to touch).
- When a tendril touches a support, the auxin concentration increases on the opposite side of the contact.
- This unequal growth causes the tendril to bend and wrap around the support.
5. Design an experiment to demonstrate hydrotropism.
Answer:
Aim: To demonstrate hydrotropism (growth of roots towards water).
Materials Required:
- A potted plant with young roots.
- A large glass container.
- A porous pot filled with water.
- Moist cotton or sawdust.
Procedure:
- Take a potted plant with small roots.
- Place the plant inside a glass container filled with dry soil.
- Keep a porous pot filled with water on one side of the container.
- Observe the direction of root growth after a few days.
Observation:
- The roots will bend towards the porous pot containing water.
Conclusion:
- The roots grow towards water, proving that plants exhibit hydrotropism.
7.3 HORMONES IN ANIMALS
1. Introduction
- Animals use hormonal (chemical) coordination to regulate body functions.
- Hormones are chemical messengers that travel through blood and affect target organs.
- Unlike nerve impulses, hormones cause long-lasting, widespread effects in the body.
- Example: When a squirrel senses danger, its body prepares to either fight or flee using the hormone adrenaline.
2. Endocrine System in Animals
- The endocrine system consists of glands that secrete hormones directly into the bloodstream.
- These hormones regulate growth, metabolism, reproduction, and stress responses.
Key Features of Hormones
✔ Produced by endocrine glands (ductless glands).
✔ Transported through blood to target organs.
✔ Act in small amounts but have significant effects.
✔ Regulated by feedback mechanisms.
3. Adrenaline – The "Fight or Flight" Hormone
- Secreted by: Adrenal glands (located above the kidneys).
- Function: Prepares the body to respond to stress by:
- Increasing heart rate → More oxygen to muscles.
- Increasing breathing rate → More oxygen intake.
- Diverting blood from digestive organs to muscles → More energy for movement.
- Example: When an animal faces danger, adrenaline levels rise to prepare for fight or flight.
4. Important Endocrine Glands and Their Hormones
| Endocrine Gland | Hormone | Function | Deficiency/Excess Disorder |
|---|---|---|---|
| Pituitary Gland (Master Gland) | Growth Hormone (GH) | Controls body growth | Deficiency: Dwarfism; Excess: Gigantism |
| Thyroid Gland | Thyroxine | Regulates metabolism (carbohydrates, proteins, fats) | Deficiency: Goitre (due to lack of iodine) |
| Adrenal Glands | Adrenaline | Prepares body for stress (fight or flight response) | Overactivity causes high blood pressure |
| Pancreas | Insulin | Controls blood sugar levels | Deficiency: Diabetes |
| Testes (Male) | Testosterone | Controls male puberty changes | Low levels may affect reproductive health |
| Ovaries (Female) | Oestrogen | Regulates female reproductive cycle and puberty changes | Low levels may cause menstrual problems |
5. Role of Hormones in Growth and Development
(a) Growth Hormone (GH) and Body Growth
- Secreted by the pituitary gland.
- Regulates height and overall development.
- Deficiency in childhood → Dwarfism.
- Excess in childhood → Gigantism.
(b) Thyroxine and Metabolism
- Thyroid gland produces thyroxine, which controls energy production and metabolism.
- Requires iodine for production → Deficiency causes goitre (swollen neck).
- Iodised salt is recommended to prevent thyroid disorders.
(c) Puberty and Reproductive Hormones
- At 10-12 years of age, boys and girls undergo puberty changes due to:
- Testosterone (males) – Deepens voice, facial hair, muscle growth.
- Oestrogen (females) – Regulates menstrual cycle, breast development.
6. Role of Insulin in Blood Sugar Regulation
- Secreted by the pancreas.
- Maintains normal blood sugar levels.
- If insulin is not produced properly → Diabetes occurs.
- Diabetic patients need insulin injections or controlled sugar intake.
7. Feedback Mechanism in Hormone Regulation
- Hormone secretion is controlled by feedback mechanisms to prevent imbalances.
- Example:
- If blood sugar rises, the pancreas releases more insulin.
- Once sugar levels drop, insulin secretion decreases.
8. Summary
- Hormones are chemical messengers secreted by endocrine glands.
- They regulate growth, metabolism, stress response, and reproduction.
- Adrenaline helps in stress response, thyroxine regulates metabolism, and insulin controls blood sugar.
- Hormones are regulated by a feedback mechanism to maintain balance.
Final Thought
The endocrine system ensures that our body functions smoothly by maintaining internal balance, allowing us to grow, respond to stress, and stay healthy. 🔬
Q U E S T I O N S & A N S W E R S
1. How does chemical coordination take place in animals?
Answer:
- Chemical coordination in animals is controlled by the endocrine system, which consists of glands that secrete hormones.
- Hormones are chemical messengers that travel through the bloodstream to regulate various body functions.
- Examples of hormonal coordination:
- Adrenaline prepares the body for stress.
- Thyroxine regulates metabolism.
- Insulin controls blood sugar levels.
2. Why is the use of iodised salt advisable?
Answer:
- Iodine is essential for the thyroid gland to produce thyroxine hormone.
- Thyroxine regulates carbohydrate, protein, and fat metabolism for proper growth and energy balance.
- Deficiency of iodine causes goitre, a condition where the thyroid gland swells, leading to a swollen neck.
- Using iodised salt prevents thyroid-related disorders.
3. How does our body respond when adrenaline is secreted into the blood?
Answer:
- Adrenaline (fight-or-flight hormone) is released by the adrenal glands in response to stress or danger.
- It triggers several changes in the body:
- Increases heart rate → More oxygen reaches muscles.
- Increases breathing rate → More oxygen intake.
- Redirects blood to muscles → More energy for action.
- Enhances alertness → Quick decision-making in emergencies.
4. Why are some patients of diabetes treated by giving injections of insulin?
Answer:
- Diabetes occurs when the pancreas does not produce enough insulin or the body cannot use insulin effectively.
- Insulin is a hormone that regulates blood sugar levels by allowing glucose to enter cells.
- Diabetic patients are given insulin injections to control blood sugar and prevent complications like kidney failure, blindness, and nerve damage.
E X E R C I S E S
1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin ✅
Answer:
- Cytokinin is a plant hormone that promotes cell division and growth.
- The other options (insulin, thyroxin, oestrogen) are animal hormones.
2. The gap between two neurons is called a:
(a) Dendrite
(b) Synapse ✅
(c) Axon
(d) Impulse
Answer:
- A synapse is the small gap between two neurons where electrical impulses are converted into chemical signals for transmission.
3. The brain is responsible for:
(a) Thinking
(b) Regulating the heartbeat
(c) Balancing the body
(d) All of the above ✅
Answer:
- The brain controls thinking, heartbeat regulation, and body balance, making option (d) correct.
4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer:
-
Receptors detect stimuli (changes in the environment) and send signals to the nervous system.
-
Examples of receptors:
- Photoreceptors (eyes) → Detect light.
- Olfactory receptors (nose) → Detect smell.
- Thermoreceptors (skin) → Detect temperature.
-
Problems if receptors do not work properly:
- Blindness if photoreceptors fail.
- Loss of smell/taste if olfactory receptors malfunction.
- Inability to feel pain/temperature, leading to injuries.
5. Draw the structure of a neuron and explain its function.
Answer:
-
Neurons are nerve cells that transmit electrical impulses.
-
Parts of a Neuron:
- Dendrites – Receive signals.
- Cell Body (Cyton) – Processes signals.
- Axon – Transmits impulses away.
- Axon Terminals – Pass signals to the next neuron/muscle.
-
Function: Neurons carry messages between the brain, spinal cord, and body to control actions.
6. How does phototropism occur in plants?
Answer:
- Phototropism is the growth of plants in response to light.
- Auxin hormone accumulates on the shady side of the plant, causing faster cell growth on that side.
- This results in bending of the shoot towards light.
7. Which signals will get disrupted in case of a spinal cord injury?
Answer:
- The spinal cord carries signals between the brain and the body.
- Injury to the spinal cord can cause:
- Loss of sensation in body parts.
- Paralysis (loss of movement).
- Disrupted reflex actions.
8. How does chemical coordination occur in plants?
Answer:
- Plants use hormones (phytohormones) for coordination.
- Examples of plant hormones:
- Auxin – Promotes growth towards light.
- Gibberellins – Stimulate stem growth.
- Cytokinins – Help in cell division.
- Abscisic Acid (ABA) – Inhibits growth and causes leaf fall.
9. What is the need for a system of control and coordination in an organism?
Answer:
- Organisms need control and coordination to:
- Respond to stimuli (e.g., withdrawing hand from heat).
- Maintain balance (e.g., walking).
- Regulate internal functions (e.g., digestion, heartbeat).
- Ensure survival by adapting to the environment.
10. How are involuntary actions and reflex actions different from each other?
| Feature | Involuntary Actions | Reflex Actions |
|---|---|---|
| Control | Controlled by the brain (medulla, cerebellum) | Controlled by the spinal cord |
| Speed | Slower | Very fast |
| Examples | Heartbeat, digestion, breathing | Pulling hand from fire, knee-jerk reaction |
Answer: Reflex actions are immediate and protective, whereas involuntary actions are automatic but not necessarily fast.
11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
| Feature | Nervous System | Hormonal System |
|---|---|---|
| Type of Signal | Electrical impulses | Chemical messengers (hormones) |
| Speed | Very fast | Slow |
| Duration of Response | Short-lived | Long-lasting |
| Examples | Reflex actions, voluntary movements | Growth, metabolism, stress response |
Answer:
- The nervous system works through neurons, while the hormonal system uses endocrine glands to release hormones into the blood.
12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
| Feature | Sensitive Plant Movement | Leg Movement (Humans) |
|---|---|---|
| Type of Movement | Involuntary, occurs due to changes in water pressure in cells | Voluntary, controlled by nervous and muscular system |
| Example | Folding of leaves in Mimosa pudica | Walking, running, jumping |
| Control | Chemical and water-based signals | Electrical nerve impulses |
Answer:
- In plants, movement occurs due to water pressure changes, whereas in animals, movement is controlled by nerves and muscles.
