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Chapter 6 Control And Coordination
In the previous chapter, we explored the essential life processes that maintain organisms. We observed that movement is often associated with life, but this movement can be related to growth (like a seedling pushing through soil) or independent of growth (like an animal running). These movements are frequently responses to changes in the environment, aimed at benefiting the organism (finding food, seeking shelter, avoiding danger, optimizing light exposure).
The ability to make appropriate movements in response to specific environmental changes suggests a system for detecting these changes and coordinating the correct response. This requires **control and coordination**. In multicellular organisms, specialized tissues are responsible for these functions.
Animals – Nervous System
In animals, control and coordination are primarily carried out by the **nervous system** and the **muscular system**. The nervous system is specialized for quickly collecting information, processing it, and transmitting instructions.
How do animals detect changes in the environment? Specialized tips of some nerve cells, called **receptors**, are located in our sense organs (eyes, ears, nose, tongue, skin). Different receptors detect different stimuli: gustatory receptors detect taste, olfactory receptors detect smell, photoreceptors detect light, etc.
When a receptor detects a stimulus (e.g., touch, smell, light), it triggers a chemical reaction in the nerve cell that generates an **electrical impulse**. This impulse is a form of information. It travels from the dendrite (the branched tip receiving the signal) across the cell body and along the axon (the long part of the neuron) to its end.
At the end of the axon, the electrical impulse causes the release of certain **chemicals** (neurotransmitters). These chemicals cross a tiny gap called a **synapse**, located between two neurons or between a neuron and another cell (like a muscle cell or gland cell). These chemicals bind to receptors on the next cell's dendrite (or surface), triggering a new electrical impulse in that cell.
This allows nervous impulses to travel as a chain of electrical signals, relayed chemically across synapses, forming an organized network specialized for transmitting information rapidly from one part of the body to another.
What Happens In Reflex Actions?
**Reflex actions** are sudden, rapid, involuntary responses to stimuli. They occur without conscious thought or control, often to protect the body from harmful situations (e.g., pulling your hand away from a hot object).
Why do we need reflexes? Thinking consciously about a dangerous stimulus and deciding on a response takes time. The thinking process involves complex interactions in the brain. If we had to consciously process every potentially harmful stimulus, the delay could lead to injury (e.g., getting burnt before pulling your hand away).
To solve this problem, the body has evolved **reflex arcs**. A reflex arc is a neural pathway that allows for a rapid response by creating a direct connection between the sensory neuron (detecting the stimulus) and the motor neuron (instructing a muscle to act) at the level of the **spinal cord**, bypassing the brain for initial processing. Nerves from receptors all over the body converge in the spinal cord on their way to the brain. The reflex arc connection is made in the spinal cord itself, although the signal also continues to the brain, making us aware of the stimulus after the reflex action has occurred.
Reflex arcs enable very quick responses, which are crucial for survival, especially in animals with less complex brains. They remain highly efficient even in animals with complex nervous systems.
Human Brain
While reflex actions are handled by the spinal cord, more complex processing, thinking, and voluntary actions are controlled by the **brain**. The brain and the spinal cord together form the **Central Nervous System (CNS)**. The CNS receives information, integrates it, and sends out instructions.
The brain is the main coordinating centre. It is responsible for thought, decision-making for voluntary actions, processing sensory information (sight, hearing, smell, taste, touch), regulating involuntary actions, and maintaining posture and balance.
The human brain has three main regions:
- **Forebrain:** The main thinking part. It has specific areas for receiving sensory information from different receptors. Areas of association interpret this information, combining it with stored data to make decisions. Motor areas in the forebrain send instructions to voluntary muscles (e.g., limb muscles). Centres for sensations like hunger are also located here.
- **Midbrain and Hindbrain:** These regions control many **involuntary actions** (actions not under conscious control), such as heartbeat, breathing, digestion, salivation, and blood pressure. The **medulla** in the hindbrain controls many of these vital involuntary functions.
- **Cerebellum:** A part of the hindbrain responsible for the **precision of voluntary actions** (e.g., walking in a straight line, riding a bicycle, picking up a pencil) and for maintaining **posture and balance** of the body.
Communication between the CNS and the rest of the body is carried out by the **Peripheral Nervous System (PNS)**. The PNS consists of **cranial nerves** (arising from the brain) and **spinal nerves** (arising from the spinal cord), which connect the CNS to all parts of the body.
How Are These Tissues Protected?
Delicate and vital organs like the brain and spinal cord are well-protected within the body:
- The **brain** is protected by the bony skull. Inside the skull, it is cushioned by a fluid-filled sac (cerebrospinal fluid) which absorbs shocks and protects it from mechanical injury.
- The **spinal cord** is protected by the vertebral column (backbone), a hard, bony structure running down the back.
How Does The Nervous Tissue Cause Action? (Muscle Movement)
The nervous system ultimately causes action by instructing muscles to move. Muscle tissue is specialized for movement. When a nerve impulse (electrical signal) reaches a muscle fiber at a **neuromuscular junction**, it triggers events within the muscle cell that cause it to change shape and shorten.
Muscle cells contain special **proteins** that change their shape and arrangement in response to the electrical impulse from the nerve. This rearrangement of proteins causes the muscle fiber to contract (shorten), resulting in muscle movement. Different types of muscles (voluntary, involuntary) are controlled by different parts of the nervous system, but the fundamental mechanism of contraction involves these specialised proteins responding to neural signals.
Question 1. What is the difference between a reflex action and walking?
Answer:
| Feature | Reflex Action | Walking |
|---|---|---|
| Nature | Involuntary (occurs automatically without conscious thought). | Voluntary (initiated and controlled consciously). |
| Pathway | Involves a reflex arc, typically processed at the spinal cord level, bypassing the brain for immediate decision. | Controlled by the brain (cerebrum and cerebellum), involves complex neural pathways. |
| Speed | Very rapid. | Relatively slower than reflex actions, controlled. |
| Purpose | Often protective, immediate response to stimuli. | Goal-oriented, planned movement. |
| Awareness | Awareness comes after the action. | Awareness precedes and accompanies the action. |
Question 2. What happens at the synapse between two neurons?
Answer:
A synapse is the tiny gap between the axon terminal of one neuron and the dendrite (or cell body) of the next neuron (or other cell). When an electrical impulse reaches the axon terminal of the first neuron, it triggers the release of **neurotransmitters** (chemical substances) into the synapse. These neurotransmitters diffuse across the gap and bind to specific receptors on the membrane of the next neuron (postsynaptic neuron). This binding triggers the generation of a new electrical impulse in the postsynaptic neuron, effectively transmitting the signal from one neuron to the next.
Question 3. Which part of the brain maintains posture and equilibrium of the body?
Answer:
The part of the brain that maintains posture and equilibrium of the body is the **Cerebellum**, located in the hindbrain.
Question 4. How do we detect the smell of an agarbatti (incense stick)?
Answer:
We detect the smell of an agarbatti (incense stick) through the process involving **olfactory receptors** in our nose. Scent molecules from the agarbatti travel through the air and enter our nostrils. These molecules reach the olfactory epithelium in the nasal cavity, where they are detected by specialized olfactory receptors (tips of nerve cells). Detection by these receptors generates an electrical impulse, which is transmitted by sensory neurons via the olfactory nerve to the olfactory areas in the forebrain. The brain processes this information and interprets it as the smell of agarbatti.
Question 5. What is the role of the brain in reflex action?
Answer:
In most simple reflex actions (like withdrawing from heat), the brain is **not directly involved in the immediate decision-making or initiation of the response**. The reflex arc is completed at the spinal cord level, allowing for a rapid, involuntary action. However, the sensory information from the reflex arc is *also* transmitted upwards to the brain. The brain becomes aware of the stimulus and the action *after* the reflex has occurred. This allows us to feel pain, learn from the experience, and potentially modify future responses.
Coordination In Plants
Plants, unlike animals, do not have a nervous system or muscles. However, they still respond to stimuli and coordinate their activities. Plant movements can be classified into two main types: those dependent on growth and those independent of growth.
Immediate Response To Stimulus (Independent of Growth)
Some plant movements happen quickly in response to stimuli and do not involve growth. A classic example is the rapid folding and drooping of the leaves of the 'touch-me-not' plant (Mimosa pudica) when touched (Fig 6.4 in textbook).
Mechanism of rapid plant movement (independent of growth):
- Detection of stimulus (touch) happens at a specific point.
- Information about the touch is communicated rapidly from cell to cell. Plants use electrical-chemical means for this information transfer, similar to animal nerve impulses but without specialized nervous tissue.
- Finally, cells in the part of the plant that moves change shape. Unlike animal muscle cells using specialized proteins, plant cells change shape by altering the amount of **water** in them. Changes in water content lead to swelling or shrinking of cells, causing the plant part to move (e.g., leaves folding).
Movement Due To Growth (Tropism)
Many plant responses involve growth in a particular direction in response to a stimulus. These directional growth movements are called **tropic movements** or **tropisms**. Tropisms can be either towards the stimulus (positive tropism) or away from the stimulus (negative tropism).
Examples of tropisms:
- **Phototropism:** Growth response to light. Shoots typically grow towards light (positive phototropism), which helps leaves maximize light absorption for photosynthesis. Roots typically grow away from light (negative phototropism).
- **Geotropism (Gravitropism):** Growth response to gravity. Roots grow downwards towards the Earth (positive geotropism), anchoring the plant and accessing water and minerals. Shoots grow upwards, away from the Earth (negative geotropism).
- **Hydrotropism:** Growth response to water. Roots grow towards sources of water (positive hydrotropism).
- **Chemotropism:** Growth response to chemicals. Example: Growth of pollen tubes towards ovules in a flower, guided by chemical signals.
- **Thigmotropism:** Growth response to touch. Tendrils in climbing plants are sensitive to touch; the part of the tendril in contact with a support grows slower than the part away from the support, causing the tendril to coil around the object and cling to it.
Plant growth and development, including tropic movements, are coordinated by chemical substances called **plant hormones** or **phytohormones**. These hormones are synthesised in one part of the plant and diffuse to other parts where they act.
Examples of plant hormones and their functions:
- **Auxins:** Synthesised at shoot tips. Promote cell elongation (growth of stems and shoots). Involved in phototropism and geotropism. In phototropism, auxin accumulates on the shady side, stimulating cells there to grow longer, causing the shoot to bend towards light.
- **Gibberellins:** Promote growth of the stem.
- **Cytokinins:** Promote cell division. Found in areas of rapid cell division (fruits, seeds, root tips).
- **Abscisic acid:** An inhibitory hormone. Inhibits growth, promotes dormancy, and causes wilting of leaves.
While electrical impulses allow for fast communication in animals, chemical communication via hormones is slower but can reach all cells and provide persistent signals, which is suitable for the slower processes like growth and development in plants. Animals also use chemical communication (hormones) for coordination, especially for widespread or slower responses.
Question 1. What are plant hormones?
Answer:
Plant hormones (or phytohormones) are chemical substances produced in one part of a plant body that are transported (usually by diffusion or through vascular tissues) to other parts, where they influence or control specific physiological processes like growth, development, flowering, fruiting, dormancy, and responses to environmental stimuli.
Question 2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Answer:
The movement of leaves of the sensitive plant (Mimosa pudica) is a **rapid, immediate response to touch (thigmonasty)**. It is a type of movement **independent of growth**. It occurs due to rapid changes in the water content and turgor pressure of cells in the pulvini (swollen bases) of the leaf stalks. This movement is non-directional relative to the stimulus.
The movement of a shoot towards light (phototropism) is a **slower, directional growth movement (tropism)**. It occurs due to the differential growth of cells on one side of the shoot, stimulated by the hormone auxin in response to light. This movement is dependent on the growth of the plant and is directional relative to the stimulus (towards the light source).
Question 3. Give an example of a plant hormone that promotes growth.
Answer:
Examples of plant hormones that promote growth are **Auxins** (promote cell elongation in shoots and roots), **Gibberellins** (promote stem elongation, break dormancy), and **Cytokinins** (promote cell division).
Question 4. How do auxins promote the growth of a tendril around a support?
Answer:
Auxins play a role in the thigmotropic response of tendrils. When a tendril touches a support, the cells on the side of the tendril in contact with the support grow slower than the cells on the side away from the support. This differential growth is influenced by auxin. Auxin moves to the side of the tendril away from the point of contact and stimulates cell elongation on that side. This causes the tendril to curve and grow around the support, helping the plant to climb.
Question 5. Design an experiment to demonstrate hydrotropism.
Answer:
Experiment to demonstrate hydrotropism (root growth towards water):
**Materials:** Two small potted plants of similar size, two porous pots (like clay pots), water, dry soil, a flat container or tray.
**Procedure:**
- Take the two small porous pots and fill them with water. Seal the top of the porous pots so water can only seep through the sides.
- Place each porous pot in the center of a flat container or tray.
- Around each porous pot, fill the flat container with dry soil.
- Plant a seedling or germinated seed in the dry soil, a few centimeters away from the porous pot, in both setups. Ensure the root of the seedling is pointing away from the porous pot initially.
- Maintain the setups in a location with adequate sunlight and temperature for growth. Do not water the dry soil directly, but keep the porous pots filled with water.
- Observe the direction of root growth over a few days or a week.
**Observation:** The roots of the seedlings will be observed to bend and grow towards the porous pot containing water, even though the rest of the soil is dry.
**Conclusion:** This demonstrates hydrotropism, showing that plant roots grow in the direction of a water source.
Hormones In Animals
Animals also use chemical communication for control and coordination, alongside the nervous system. These chemical messengers are called **hormones**. Hormones are produced by specialized glands called **endocrine glands**. They are secreted directly into the bloodstream and transported to target tissues or organs in different parts of the body, where they exert specific effects.
The endocrine system constitutes a second system of control and coordination in animals.
Example: Response to a scary situation (e.g., a squirrel facing danger).
In a stressful situation, the body needs to prepare for a 'fight or flight' response. This requires widespread physiological changes to make energy available and prepare muscles for intense activity. While the nervous system provides rapid signals for immediate muscle action, hormonal signals provide broader, sustained preparation.
A key hormone in this response is **adrenaline**, secreted by the **adrenal glands** (located on top of the kidneys). Adrenaline is released into the blood and affects multiple target organs, including the heart, lungs, digestive system, and muscles:
- Heart beats faster, increasing blood flow and oxygen supply to muscles.
- Breathing rate increases due to diaphragm and rib muscle contractions.
- Blood flow to the digestive system and skin decreases (arterioles constrict), diverting blood to skeletal muscles.
- Glucose is released from the liver into the blood, increasing available energy.
These coordinated responses prepare the body for intense physical activity (fighting or running away).
Animal hormones also coordinate growth and development in a controlled manner, unlike the directional growth in plants.
Examples of animal hormones and their functions:
- **Thyroxin:** Produced by the **thyroid gland** (in the neck). Requires iodine for synthesis. Regulates carbohydrate, protein, and fat metabolism, essential for balanced growth. Deficiency of iodine leads to insufficient thyroxin and can cause **goitre** (swollen neck).
- **Growth hormone:** Produced by the **pituitary gland** (in the brain). Regulates growth and development of the body. Deficiency in childhood leads to dwarfism; excess can lead to gigantism.
- **Insulin:** Produced by the **pancreas** (near the stomach). Regulates blood sugar levels. Insufficient insulin leads to increased blood sugar, causing **diabetes**. Insulin injection is a treatment for diabetes.
- **Testosterone:** Produced by **testes** (in males). Controls development and changes associated with male puberty.
- **Oestrogen:** Produced by **ovaries** (in females). Controls development and changes associated with female puberty, regulates menstrual cycle.
- **Adrenaline:** Produced by **adrenal glands** (on kidneys). Prepares the body for 'fight or flight' response in stressful situations.
- **Releasing hormones:** Produced by the **hypothalamus** (in the brain). Control the release of hormones from the pituitary gland.
The timing and amount of hormone release are often regulated by **feedback mechanisms**. For example, if blood sugar levels rise, the pancreas releases more insulin to lower it. As sugar levels fall, insulin secretion decreases. This is a negative feedback mechanism maintaining homeostasis (stable internal environment).
Question 1. How does chemical coordination take place in animals?
Answer:
Chemical coordination in animals takes place through **hormones**. Hormones are chemical messengers secreted by endocrine glands directly into the bloodstream. Blood carries these hormones to specific target cells, tissues, or organs in different parts of the body. Hormones bind to specific receptors on these target cells, triggering specific responses or changes in cellular activity. This process is slower than nervous coordination but can have widespread and prolonged effects, coordinating processes like growth, development, metabolism, and reproduction.
Question 2. Why is the use of iodised salt advisable?
Answer:
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, which is crucial for normal growth and development. Deficiency of iodine in the diet leads to insufficient production of thyroxin, causing a disorder called **goitre**, which manifests as a swollen neck. Iodised salt provides the necessary dietary iodine to prevent this deficiency and maintain proper thyroid function.
Question 3. How does our body respond when adrenaline is secreted into the blood?
Answer:
When adrenaline (the 'fight or flight' hormone) is secreted into the blood, it causes a rapid, widespread response throughout the body, preparing it for intense physical activity:
- The **heartbeat increases**, pumping more blood and oxygen to the muscles.
- The **breathing rate increases**, and bronchioles in the lungs dilate, increasing oxygen intake.
- Blood flow to the digestive system and skin is reduced as small arteries supplying these organs constrict, diverting more blood to the skeletal muscles.
- Glucose stored in the liver is converted into readily available glucose and released into the blood, increasing energy supply.
- Pupils dilate.
- Hair stands on end (piloerection).
These coordinated responses make the body ready to either confront the threat or escape from it.
Question 4. Why are some patients of diabetes treated by giving injections of insulin?
Answer:
Some patients of diabetes (specifically Type 1 diabetes, or Type 2 when the pancreas does not produce enough insulin) are treated by giving injections of insulin because their pancreas does not produce sufficient amounts of insulin hormone. **Insulin is crucial for regulating blood sugar levels** by promoting the uptake of glucose from the blood into cells and its storage as glycogen in the liver and muscles. Without enough insulin, glucose accumulates in the blood, leading to high blood sugar levels, which can cause serious long-term health complications. Injecting insulin supplements the body's deficient supply, helping to lower and regulate blood sugar levels.
Intext Questions
Page No. 105
Question 1. What is the difference between a reflex action and walking?
Answer:
Question 2. What happens at the synapse between two neurons?
Answer:
Question 3. Which part of the brain maintains posture and equilibrium of the body?
Answer:
Question 4. How do we detect the smell of an agarbatti (incense stick)?
Answer:
Question 5. What is the role of the brain in reflex action?
Answer:
Page No. 108
Question 1. What are plant hormones?
Answer:
Question 2. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Answer:
Question 3. Give an example of a plant hormone that promotes growth.
Answer:
Question 4. How do auxins promote the growth of a tendril around a support?
Answer:
Question 5. Design an experiment to demonstrate hydrotropism.
Answer:
Page No. 111
Question 1. How does chemical coordination take place in animals?
Answer:
Question 2. Why is the use of iodised salt advisable?
Answer:
Question 3. How does our body respond when adrenaline is secreted into the blood?
Answer:
Question 4. Why are some patients of diabetes treated by giving injections of insulin?
Answer:
Exercises
Question 1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin.
Answer:
Question 2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
Answer:
Question 3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
Answer:
Question 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:
Question 5. Draw the structure of a neuron and explain its function.
Answer:
Question 6. How does phototropism occur in plants?
Answer:
Question 7. Which signals will get disrupted in case of a spinal cord injury?
Answer:
Question 8. How does chemical coordination occur in plants?
Answer:
Question 9. What is the need for a system of control and coordination in an organism?
Answer:
Question 10. How are involuntary actions and reflex actions different from each other?
Answer:
Question 11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer:
Question 12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer: