In-Chapter Questions
Section 6.1 - Animals - Nervous System
1. What is the difference between a reflex action and walking?
A reflex action is an involuntary, automatic, and rapid response to a stimulus that does not involve conscious thought. It is mediated by the spinal cord. For example, pulling your hand away from a hot object.
Walking is a voluntary action that involves conscious thought and is controlled by the brain. It requires coordination of multiple muscle groups and continuous adjustment based on sensory feedback.
2. What happens at the synapse between two neurons?
At the synapse between two neurons:
- The electrical impulse from the axon terminal of the presynaptic neuron triggers the release of chemical neurotransmitters.
- These neurotransmitters cross the synaptic cleft and bind to receptors on the dendrites of the postsynaptic neuron.
- This binding generates a new electrical impulse in the postsynaptic neuron.
- The synapse ensures that nerve impulses travel in only one direction.
3. Which part of the brain maintains posture and equilibrium of the body?
The cerebellum, located in the hind-brain, maintains posture and equilibrium of the body. It is responsible for the precision of voluntary actions and coordination of body movements.
4. How do we detect the smell of an agarbatti (incense stick)?
We detect the smell of an agarbatti through the following process:
- Chemical particles from the burning agarbatti enter our nose.
- These particles dissolve in the mucus lining of the nasal cavity.
- Olfactory receptors in the nose detect these chemicals.
- The receptors generate electrical impulses that are transmitted to the olfactory bulb.
- From there, the impulses are sent to the brain where they are interpreted as smell.
5. What is the role of the brain in reflex action?
In most reflex actions, the brain is not directly involved in the immediate response. The reflex arc passes through the spinal cord, allowing for a quick response. However, the brain receives information about the reflex action after it has occurred and can modify future responses. In some cases, the brain may become involved if the reflex needs to be consciously overridden.
Section 6.2 - Coordination in Plants
1. What are plant hormones?
Plant hormones (phytohormones) are chemical compounds produced in plants that regulate growth, development, and responses to environmental stimuli. They are synthesized in one part of the plant and transported to other parts where they exert their effects. Examples include auxins, gibberellins, cytokinins, and abscisic acid.
2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
The movement of leaves of the sensitive plant (Mimosa pudica) is:
- A rapid response to touch (thigmonasty)
- Not dependent on growth
- Caused by changes in turgor pressure in specialized cells
- Reversible
The movement of a shoot towards light (phototropism) is:
- A slow directional growth response
- Dependent on growth
- Caused by unequal distribution of auxin hormone
- Permanent
3. Give an example of a plant hormone that promotes growth.
Auxin is a plant hormone that promotes growth. It is synthesized at the shoot tip and helps cells to grow longer. Auxin is responsible for phototropism (growth towards light) by accumulating on the shaded side of the plant and stimulating cell elongation there.
4. How do auxins promote the growth of a tendril around a support?
When a tendril comes in contact with a support:
- The part of the tendril in contact with the support grows slower due to reduced auxin concentration.
- The part away from the support grows faster due to higher auxin concentration.
- This differential growth causes the tendril to curl around the support.
- Once the tendril has coiled around the support, it provides stability for the climbing plant.
5. Design an experiment to demonstrate hydrotropism.
Experiment to demonstrate hydrotropism:
- Take a porous pot filled with water and place it in a large tray containing dry soil.
- Plant a germinating seed in the soil near the porous pot.
- Observe the growth of roots over several days.
- You will notice that the roots grow towards the porous pot containing water, demonstrating positive hydrotropism (growth towards water).
- As a control, set up another tray without the porous pot to show that roots grow randomly in the absence of a water gradient.
Section 6.3 - Hormones in Animals
1. How does chemical coordination take place in animals?
Chemical coordination in animals occurs through the endocrine system:
- Endocrine glands secrete hormones directly into the bloodstream.
- Hormones are chemical messengers that travel to target organs or tissues.
- Target cells have specific receptors that recognize and respond to particular hormones.
- Hormones regulate various physiological processes including growth, metabolism, reproduction, and stress responses.
- The timing and amount of hormone release are regulated by feedback mechanisms.
2. Why is the use of iodised salt advisable?
The use of iodised salt is advisable because:
- Iodine is essential for the synthesis of thyroxin hormone by the thyroid gland.
- Thyroxin regulates carbohydrate, protein, and fat metabolism in the body.
- It provides the best balance for growth and development.
- Iodine deficiency can lead to goitre, a condition characterized by a swollen neck due to an enlarged thyroid gland.
- Iodine is also crucial for proper brain development, especially in children.
3. How does our body respond when adrenaline is secreted into the blood?
When adrenaline is secreted into the blood, our body responds with the "fight or flight" reaction:
- The heart beats faster to supply more oxygen to muscles.
- Blood flow to the digestive system and skin is reduced.
- Blood is diverted to skeletal muscles.
- Breathing rate increases due to contractions of the diaphragm and rib muscles.
- Pupils dilate to improve vision.
- Blood sugar levels increase to provide immediate energy.
- These responses prepare the body to deal with emergency situations.
4. Why are some patients of diabetes treated by giving injections of insulin?
Some diabetes patients are treated with insulin injections because:
- Diabetes is characterized by high blood sugar levels due to insufficient insulin production or ineffective use of insulin.
- Insulin is a hormone produced by the pancreas that helps regulate blood sugar levels.
- In type 1 diabetes, the pancreas produces little or no insulin.
- Insulin injections help maintain normal blood sugar levels by facilitating the uptake of glucose by cells.
- This treatment prevents the harmful effects of persistently high blood sugar, such as damage to blood vessels, nerves, and organs.
End-Chapter Exercises
1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
Answer: (d) Cytokinin
Cytokinin is a plant hormone that promotes cell division. Insulin and thyroxin are animal hormones, and oestrogen is a human hormone.
2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
Answer: (b) synapse
The synapse is the junction between two neurons where nerve impulses are transmitted chemically.
3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
Answer: (d) all of the above
The brain is responsible for thinking (cerebrum), regulating heart beat (medulla), and balancing the body (cerebellum).
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?
Function of receptors: Receptors are specialized tips of nerve cells that detect information from the environment. They are usually located in sense organs and are sensitive to specific stimuli like light, sound, smell, taste, heat, pressure, etc.
Situations where receptors don't work properly and associated problems:
- Damage to olfactory receptors: Loss of smell (anosmia)
- Damage to taste receptors: Loss of taste (ageusia)
- Damage to photoreceptors in retina: Vision problems or blindness
- Damage to auditory receptors: Hearing impairment
- Damage to skin receptors: Inability to feel pain, temperature, or touch, which can lead to injuries
5. Draw the structure of a neuron and explain its function.
[Neuron Diagram Would Appear Here]
Typical neuron structure includes:
- Dendrites - receive information
- Cell body - contains nucleus
- Axon - transmits electrical impulses
- Axon terminals - release neurotransmitters
Figure: Structure of a neuron
Function of a neuron: Neurons are specialized cells that transmit nerve impulses. They receive information through dendrites, process it in the cell body, and transmit electrical impulses along the axon to the axon terminals, where neurotransmitters are released to pass the signal to the next neuron or effector cell.
6. How does phototropism occur in plants?
Phototropism occurs in plants through the following mechanism:
- The shoot tip produces auxin hormone.
- When light comes from one direction, auxin diffuses towards the shaded side of the shoot.
- Higher concentration of auxin on the shaded side stimulates cells to elongate more.
- This causes the shoot to bend towards the light source.
- This response is positive phototropism (growth towards light).
- Roots typically show negative phototropism (growth away from light).
7. Which signals will get disrupted in case of a spinal cord injury?
In case of a spinal cord injury, the following signals will get disrupted:
- Sensory signals from body parts below the injury site to the brain
- Motor signals from the brain to body parts below the injury site
- Reflex actions involving the affected segments of the spinal cord
- Coordination between different parts of the body
- Autonomic functions like bladder and bowel control if the injury is severe
The extent of disruption depends on the location and severity of the injury.
8. How does chemical coordination occur in plants?
Chemical coordination in plants occurs through plant hormones (phytohormones):
- Hormones are synthesized in specific parts of the plant.
- They diffuse to other parts where they exert their effects.
- Different hormones coordinate various growth and developmental processes:
- Auxins: Promote cell elongation, phototropism, geotropism
- Gibberellins: Stem growth, seed germination
- Cytokinins: Cell division, delay aging
- Abscisic acid: Growth inhibition, stress response
- Ethylene: Fruit ripening, leaf fall
- Hormones help plants respond to environmental stimuli like light, gravity, touch, etc.
9. What is the need for a system of control and coordination in an organism?
A system of control and coordination is essential for organisms because:
- It allows the organism to respond appropriately to changes in the environment.
- It ensures different organs and tissues work together in a synchronized manner.
- It maintains homeostasis (stable internal environment).
- It enables growth and development to occur in an organized way.
- It allows for efficient utilization of resources.
- It provides protection against harmful stimuli.
- In complex organisms, it enables learning, memory, and complex behaviors.
10. How are involuntary actions and reflex actions different from each other?
Involuntary actions:
- Controlled by the autonomic nervous system
- Regulate internal body functions like heartbeat, digestion, breathing
- Generally continuous and rhythmic
- Not under conscious control
- Mediated by the brain stem and spinal cord
Reflex actions:
- Rapid, automatic responses to specific stimuli
- Protective in nature (e.g., pulling hand from hot object)
- Occur without conscious thought
- Mediated mainly by the spinal cord
- Can be somatic (involving skeletal muscles) or autonomic (involving smooth muscles and glands)
11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
| Aspect |
Nervous System |
Endocrine System |
| Nature of message |
Electrical impulses |
Chemical hormones |
| Transmission |
Through neurons |
Through bloodstream |
| Speed |
Very fast |
Relatively slow |
| Duration of effect |
Short-lived |
Long-lasting |
| Area of effect |
Localized (specific cells) |
Widespread (target organs) |
| Response |
Immediate and precise |
Slow and generalized |
| Components |
Brain, spinal cord, nerves |
Endocrine glands |
12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Movement in sensitive plant (Mimosa pudica):
- Non-growth movement (nastic movement)
- Rapid response to touch (thigmonasty)
- Caused by changes in turgor pressure in specialized cells
- Not controlled by nervous tissue
- Involves electrical-chemical signaling between cells
- Reversible movement
Movement in our legs:
- Voluntary movement controlled by nervous system
- Involves contraction and relaxation of muscles
- Controlled by brain and spinal cord
- Involves electrical impulses transmitted through neurons
- Requires coordination between nervous system and muscular system
- Can be consciously controlled and modified