Control And Coordination

Namaste students, welcome to today's science class. Today we are going to study Chapter 6 which is about Control and Coordination. This is a very important chapter that will help you understand how your body works and how living organisms respond to changes in their environment. So let's begin.

Students, think about this. You are sitting in your classroom and suddenly someone throws a ball at you. What do you do? You automatically catch it or duck away, right? But have you ever wondered how your body knows to do this so quickly? Or think about what happens when you touch a hot vessel by mistake. You immediately pull your hand back, don't you? This happens even before you think about it. This is because of control and coordination in our body.

Now, let me ask you another question. Have you seen a plant called chhui-mui, also known as the touch-me-not plant? When you touch its leaves, they fold up immediately. How does this happen? Plants don't have a nervous system like us, so how do they respond to touch?

In this chapter, we will learn how both animals and plants control and coordinate their activities. We will understand the nervous system in animals, how reflex actions work, the role of the brain, and how plants use hormones to respond to their environment. So let's start with animals.

## 6.1 Animals – Nervous System

Students, in animals, control and coordination are provided by nervous and muscular tissues. You have already studied these tissues in Class IX. Let me remind you that nervous tissue is made up of specialised cells called neurons that can conduct electrical impulses.

Now, imagine you are touching a hot object. How do you detect that it is hot? All information from our environment is detected by specialised tips of some nerve cells. These receptors are usually located in our sense organs. For example, gustatory receptors in your tongue detect taste, olfactory receptors in your nose detect smell, and so on.

So students, when you taste something sweet, when you smell your mother's cooking, when you see your teacher entering the classroom, all this information is detected by receptors in your sense organs.

Now, what happens when these receptors detect information? Let me explain this step by step. The information acquired at the end of the dendritic tip of a nerve cell sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron.

So students, this is how nervous impulses travel in the body. The synapse is the gap between two neurons. The chemicals released at the synapse are called neurotransmitters. This is a general scheme of how information travels in our nervous system. A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscle cells or gland cells.

Now, let me ask you to look at Figure 6.1(a) in your textbook. Can you identify the parts of a neuron? Where is information acquired? That would be the dendrites. Through which part does information travel as an electrical impulse? That would be the axon. And where is this impulse converted into a chemical signal for onward transmission? That happens at the axon terminal, at the synapse.

So students, to summarise what we have learned so far: nervous tissue is made up of an organised network of nerve cells or neurons, and it is specialised for conducting information via electrical impulses from one part of the body to another.

Now, let me tell you about an interesting activity that you can try at home. This is Activity 6.1 from your textbook.

Put some sugar in your mouth. How does it taste? It tastes sweet, right? Now, block your nose by pressing it between your thumb and index finger. Now eat sugar again. Is there any difference in its taste? Most of you will notice that the sugar does not taste as sweet when your nose is blocked. Similarly, while eating lunch, block your nose in the same way and notice if you can fully appreciate the taste of the food you are eating.

Why does this happen? This is because a large part of what we call "taste" is actually smell. When we eat food, the aroma of the food reaches our olfactory receptors through the back of our throat. When we have a cold and our nose is blocked, we cannot smell the food properly, and therefore we cannot fully appreciate its taste. This is why food seems bland when we have a cold. This shows that our sense of smell and taste work together.

Now students, let us move on to a very important concept - reflex actions.

### 6.1.1 What happens in Reflex Actions?

Students, the word 'reflex' is something we use very commonly. We say 'I jumped out of the way of the bus reflexly', or 'I pulled my hand back from the flame reflexly', or 'I was so hungry my mouth started watering reflexly'. What exactly do we mean by this?

A common idea in all such examples is that we do something without thinking about it, or without feeling in control of our reactions. Yet these are situations where we are responding with some action to changes in our environment. So the question is, how is control and coordination achieved in such situations?

Let us consider the example of touching a flame. This is an urgent and dangerous situation. How would we respond to this? One seemingly simple way is to think consciously about the pain and the possibility of getting burnt, and therefore move our hand. But an important question is, how long will it take us to think all this?

The answer depends on how we think. If nerve impulses are sent around the way we have talked about earlier, then thinking is also likely to involve the creation of such impulses. Thinking is a complex activity, so it is bound to involve a complicated interaction of many nerve impulses from many neurons.

If this is the case, it is no surprise that the thinking tissue in our body consists of dense networks of intricately arranged neurons. It sits in the forward end of the skull, and receives signals from all over the body which it thinks about before responding to them. Obviously, in order to receive these signals, this thinking part of the brain in the skull must be connected to nerves coming from various parts of the body. Similarly, if this part of the brain is to instruct muscles to move, nerves must carry this signal back to different parts of the body. If all of this is to be done when we touch a hot object, it may take enough time for us to get burnt!

So how does the design of the body solve this problem? Students, the answer is reflex arcs. Rather than having to think about the sensation of heat, if the nerves that detect heat were to be connected to the nerves that move muscles in a simpler way, the process of detecting the signal or the input and responding to it by an output action might be completed quickly.

Such a connection is commonly called a reflex arc. Where should such reflex arc connections be made between the input nerve and the output nerve? The best place would be at the point where they first meet each other. Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain.

So students, when you touch a hot object, the nerve impulse from your hand travels to the spinal cord, and immediately a signal is sent back to your muscles to pull your hand away. This happens so quickly that you don't even think about it. This is a reflex action.

Now, why have reflex arcs evolved? They have evolved because the thinking process of the brain is not fast enough. In fact, many animals have very little or none of the complex neuron network needed for thinking. So it is quite likely that reflex arcs have evolved as efficient ways of functioning in the absence of true thought processes. However, even after complex neuron networks have come into existence, reflex arcs continue to be more efficient for quick responses.

So students, to summarise what we have learned about reflex actions: reflex actions are quick, automatic responses to stimuli that do not involve the brain. They are controlled by the spinal cord through reflex arcs. This helps protect our body from danger quickly.

Now, let us move on to the human brain.

### 6.1.2 Human Brain

Students, is reflex action the only function of the spinal cord? Obviously not, since we know that we are thinking beings. The spinal cord is made up of nerves which supply information to think about. Thinking involves more complex mechanisms and neural connections. These are concentrated in the brain, which is the main coordinating centre of the body.

The brain and spinal cord constitute the central nervous system. They receive information from all parts of the body and integrate it.

We also think about our actions. Writing, talking, moving a chair, clapping at the end of a programme are examples of voluntary actions which are based on deciding what to do next. So, the brain also has to send messages to muscles. This is the second way in which the nervous system communicates with the muscles.

The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord.

The brain thus allows us to think and take actions based on that thinking. As you will expect, this is accomplished through a complex design, with different parts of the brain responsible for integrating different inputs and outputs.

The brain has three major parts or regions, namely the fore-brain, mid-brain and hind-brain.

Let me explain each part to you, students.

The fore-brain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing, smell, sight and so on. There are separate areas of association where this sensory information is interpreted by putting it together with information from other receptors as well as with information that is already stored in the brain. Based on all this, a decision is made about how to respond and the information is passed on to the motor areas which control the movement of voluntary muscles, for example, our leg muscles.

However, certain sensations are distinct from seeing or hearing. For example, how do we know that we have eaten enough? The sensation of feeling full is because of a centre associated with hunger, which is in a separate part of the fore-brain.

Now, students, let me tell you about another use of the word 'reflex'. Our mouth waters when we see food we like without our meaning to. Our hearts beat without our thinking about it. In fact, we cannot control these actions easily by thinking about them even if we wanted to. Do we have to think about or remember to breathe or digest food?

So, in between the simple reflex actions like change in the size of the pupil, and the thought out actions such as moving a chair, there is another set of muscle movements over which we do not have any thinking control. Many of these involuntary actions are controlled by the mid-brain and hind-brain. All these involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain.

Now, students, think about activities like walking in a straight line, riding a bicycle, picking up a pencil. These are possible due to a part of the hind-brain called the cerebellum. It is responsible for precision of voluntary actions and maintaining the posture and balance of the body. Imagine what would happen if each of these events failed to take place if we were not thinking about it. You would not be able to walk properly or balance yourself. This shows how important the cerebellum is.

So students, to summarise what we have learned about the brain: the brain has three main parts - fore-brain, mid-brain, and hind-brain. The fore-brain is responsible for thinking, receiving sensory information, and making decisions. The mid-brain and hind-brain control involuntary actions. The cerebellum maintains posture and balance.

Now, let us see how these tissues are protected.

### 6.1.3 How are these Tissues protected?

Students, a delicate organ like the brain, which is so important for a variety of activities, needs to be carefully protected. For this, the body is designed so that the brain sits inside a bony box. This bony box is your skull. Inside the box, the brain is contained in a fluid-filled balloon which provides further shock absorption. This fluid is called cerebrospinal fluid.

If you run your hand down the middle of your back, you will feel a hard, bumpy structure. This is the vertebral column or backbone which protects the spinal cord. The vertebral column is made up of many small bones called vertebrae that are stacked on top of each other. Between these bones, there are discs that act as cushions. This protects the spinal cord from damage.

So students, our body has natural protective mechanisms for the nervous system - the skull protects the brain, and the vertebral column protects the spinal cord.

### 6.1.4 How does the Nervous Tissue cause Action?

Students, so far we have been talking about nervous tissue, and how it collects information, sends it around the body, processes information, makes decisions based on information, and conveys decisions to muscles for action. In other words, when the action or movement is to be performed, muscle tissue will do the final job.

How do animal muscles move? When a nerve impulse reaches the muscle, the muscle fibre must move. How does a muscle cell move? The simplest notion of movement at the cellular level is that muscle cells will move by changing their shape so that they shorten. This is called contraction.

So the next question is, how do muscle cells change their shape? The answer must lie in the chemistry of cellular components. Muscle cells have special proteins that change both their shape and their arrangement in the cell in response to nervous electrical impulses. When this happens, new arrangements of these proteins give the muscle cells a shorter form. This is how muscles contract and cause movement.

Students, you might remember from Class IX that there are different kinds of muscles, such as voluntary muscles and involuntary muscles. Voluntary muscles are those that we can control consciously, like the muscles in our arms and legs. Involuntary muscles are those that we cannot control consciously, like the muscles in our stomach and intestines. Based on what we have discussed so far, can you think what the differences between these would be?

Voluntary muscles are controlled by the somatic nervous system, which is under our conscious control. Involuntary muscles are controlled by the autonomic nervous system, which works automatically without our conscious thought. This is the difference between voluntary and involuntary muscles.

Now students, let me ask you some questions to check your understanding.

Question 1: What is the difference between a reflex action and walking?

Reflex action is an automatic, quick response to a stimulus that does not involve the brain. It is controlled by the spinal cord. Walking, on the other hand, is a voluntary action that involves conscious thought and decision-making. We think about walking and decide to walk. It is controlled by the brain.

Question 2: What happens at the synapse between two neurons?

At the synapse, the electrical impulse from one neuron is converted into a chemical signal. Chemicals called neurotransmitters are released from the axon terminal of one neuron. These chemicals cross the synapse and bind to receptors on the dendrite of the next neuron, thereby converting the chemical signal back into an electrical impulse.

Question 3: Which part of the brain maintains posture and equilibrium of the body?

The cerebellum, which is part of the hind-brain, maintains posture and equilibrium of the body.

Question 4: How do we detect the smell of an agarbatti (incense stick)?

When an agarbatti is burned, it releases fragrant particles into the air. These particles enter our nose when we breathe. They are detected by olfactory receptors in our nose. These receptors then send electrical impulses through olfactory nerves to the brain, where the smell is interpreted.

Question 5: What is the role of the brain in reflex action?

The brain receives information about the stimulus through the spinal cord, but the actual reflex action occurs at the level of the spinal cord without the involvement of the brain. However, the brain is still informed about the event, which is why we become aware of the reflex action after it has occurred. The brain also helps in modulating or modifying reflex actions based on past experience.

Now students, let us move on to the next section - Coordination in Plants.

## 6.2 Coordination in Plants

Students, animals have a nervous system for controlling and coordinating the activities of the body. But plants have neither a nervous system nor muscles. So, how do they respond to stimuli?

When we touch the leaves of a chhui-mui (the 'sensitive' or 'touch-me-not' plant of the Mimosa family), they begin to fold up and droop. When a seed germinates, the root goes down, the stem comes up into the air. What happens?

Firstly, the leaves of the sensitive plant move very quickly in response to touch. There is no growth involved in this movement. On the other hand, the directional movement of a seedling is caused by growth. If it is prevented from growing, it will not show any movement.

So students, plants show two different types of movement – one dependent on growth and the other independent of growth. Let us understand both of these.

### 6.2.1 Immediate Response to Stimulus

Let us think about the first kind of movement, such as that of the sensitive plant. Since no growth is involved, the plant must actually move its leaves in response to touch. But there is no nervous tissue, nor any muscle tissue. How does the plant detect the touch, and how do the leaves move in response?

If we think about where exactly the plant is touched, and what part of the plant actually moves, it is apparent that movement happens at a point different from the point of touch. So, information that a touch has occurred must be communicated.

Students, the plants also use electrical-chemical means to convey this information from cell to cell, but unlike in animals, there is no specialised tissue in plants for the conduction of information. Finally, again as in animals, some cells must change shape in order for movement to happen. Instead of the specialised proteins found in animal muscle cells, plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.

So when you touch the sensitive plant, the touch is detected at one point, and this information is passed to other cells through electrical-chemical signals. These cells then lose water and shrink, causing the leaves to fold up. This happens very quickly, within seconds.

### 6.2.2 Movement Due to Growth

Now students, let us understand the second type of movement - movement due to growth.

Some plants like the pea plant climb up other plants or fences by means of tendrils. These tendrils are sensitive to touch. When they come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.

More commonly, plants respond to stimuli slowly by growing in a particular direction. Because this growth is directional, it appears as if the plant is moving. Let us understand this type of movement with the help of an example.

This is Activity 6.2 from your textbook. Let me explain it to you.

First, fill a conical flask with water. Cover the neck of the flask with a wire mesh. Keep two or three freshly germinated bean seeds on the wire mesh. Take a cardboard box which is open from one side. Keep the flask in the box in such a manner that the open side of the box faces light coming from a window. After two or three days, you will notice that the shoots bend towards light and roots away from light.

Now, turn the flask so that the shoots are away from light and the roots towards light. Leave it undisturbed in this condition for a few days. Have the old parts of the shoot and root changed direction? No, they have not changed direction. Are there differences in the direction of the new growth? Yes, the new growth of the shoot will bend towards light, and the new growth of the root will bend away from light.

What can we conclude from this activity? This activity shows that plants respond to light. The shoot grows towards light (positive phototropism), and the root grows away from light (negative phototropism). This is because of the direction of growth, not because the plant is moving as a whole.

Students, environmental triggers such as light, or gravity will change the directions that plant parts grow in. These directional, or tropic, movements can be either towards the stimulus, or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it. How does this help the plant?

This helps the plant because shoots need light for photosynthesis, so they grow towards light. Roots need water and minerals from the soil, so they grow downwards towards gravity to find water and nutrients.

Students, plants show tropism in response to other stimuli as well. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth. This upward and downward growth of shoots and roots, respectively, in response to the pull of earth or gravity is, obviously, geotropism.

If 'hydro' means water and 'chemo' refers to chemicals, what would 'hydrotropism' and 'chemotropism' mean? Hydrotropism is movement or growth towards water, and chemotropism is movement or growth towards chemicals.

Can we think of examples of these kinds of directional growth movements? One example of chemotropism is the growth of pollen tubes towards ovules. When a pollen grain lands on the stigma of a flower, it grows a tube towards the ovule to deliver the sperm cells. This is guided by chemicals secreted by the ovule.

Now students, let me summarise what we have learned so far about plant movements. Plants show two types of movements:

1. Immediate response to stimulus - like the movement of sensitive plant leaves when touched. This is not related to growth and happens quickly.

2. Movement due to growth - like the bending of shoots towards light and roots away from light. This is slow and related to growth.

Now, let me tell you about how information is communicated in multicellular organisms. The movement of the sensitive plant in response to touch is very quick. The movement of sunflowers in response to day or night, on the other hand, is quite slow. Growth-related movement of plants will be even slower.

Even in animal bodies, there are carefully controlled directions to growth. Our arms and fingers grow in certain directions, not haphazardly. So controlled movements can be either slow or fast. If fast responses to stimuli are to be made, information transfer must happen very quickly. For this, the medium of transmission must be able to move rapidly.

Electrical impulses are an excellent means for this. But there are limitations to the use of electrical impulses. Firstly, they will reach only those cells that are connected by nervous tissue, not each and every cell in the animal body. Secondly, once an electrical impulse is generated in a cell and transmitted, the cell will take some time to reset its mechanisms before it can generate and transmit a new impulse. In other words, cells cannot continually create and transmit electrical impulses.

It is thus no wonder that most multicellular organisms use another means of communication between cells, namely, chemical communication.

If, instead of generating an electrical impulse, stimulated cells release a chemical compound, this compound would diffuse all around the original cell. If other cells around have the means to detect this compound using special molecules on their surfaces, then they would be able to recognise information, and even transmit it. This will be slower, of course, but it can potentially reach all cells of the body, regardless of nervous connections, and it can be done steadily and persistently.

These compounds, or hormones, used by multicellular organisms for control and coordination show a great deal of diversity, as we would expect.

Different plant hormones help to coordinate growth, development and responses to the environment. They are synthesised at places away from where they act and simply diffuse to the area of action.

Now students, let us learn about plant hormones.

When growing plants detect light, a hormone called auxin, synthesised at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

This is how phototropism works in plants. The auxin hormone is produced on the side of the plant that is away from light, causing those cells to elongate more, which makes the plant bend towards light.

Another example of plant hormones are gibberellins which, like auxins, help in the growth of the stem. Cytokinins promote cell division, and it is natural then that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds. These are examples of plant hormones that help in promoting growth.

But plants also need signals to stop growing. Abscisic acid is one example of a hormone which inhibits growth. Its effects include wilting of leaves. This hormone helps the plant to survive in adverse conditions by slowing down growth.

So students, to summarise what we have learned about plant hormones:

1. Auxin - promotes cell elongation and is responsible for phototropism and geotropism. 2. Gibberellins - promote stem growth. 3. Cytokinins - promote cell division. 4. Abscisic acid - inhibits growth and causes wilting of leaves.

Now, let me answer the questions from this section.

Question 1: What are plant hormones?

Plant hormones are chemical substances produced by plants that help in coordinating growth, development, and responses to the environment. They are synthesised at places away from where they act and simply diffuse to the area of action.

Question 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 is a quick response to touch and is not related to growth. It happens due to changes in water content in cells, causing them to swell or shrink. On the other hand, the movement of a shoot towards light is a slow response that is related to growth. It happens due to the hormone auxin, which causes differential growth on different sides of the shoot.

Question 3: Give an example of a plant hormone that promotes growth.

Auxin is an example of a plant hormone that promotes growth. Gibberellins and cytokinins are also plant hormones that promote growth.

Question 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 does not grow as rapidly as the part away from the support. This is because auxin moves to the side away from the support, causing those cells to elongate more. This causes the tendril to curve and wrap around the support.

Question 5: Design an experiment to demonstrate hydrotropism.

To demonstrate hydrotropism, you can take two beakers. In one beaker, place some germinated seeds on moist cotton or soil. In the second beaker, place similar seeds but keep the water at a distance. Place both beakers in a dark place. After a few days, you will observe that the roots of the seeds in the first beaker grow towards the water, while the roots in the second beaker grow in a random direction. This shows hydrotropism - the growth of roots towards water.

Now students, let us move on to the next section - Hormones in Animals.

## 6.3 Hormones in Animals

Students, we have learned how chemical coordination works in plants. Now let us learn about how chemical coordination works in animals.

How are such chemical, or hormonal, means of information transmission used in animals? What do some animals, for instance squirrels, experience when they are in a scary situation? Their bodies have to prepare for either fighting or running away. Both are very complicated activities that will use a great deal of energy in controlled ways. Many different tissue types will be used and their activities integrated together in these actions. However, the two alternate activities, fighting or running, are also quite different! So here is a situation in which some common preparations can be usefully made in the body. These preparations should ideally make it easier to do either activity in the near future. How would this be achieved?

If the body design in the squirrel relied only on electrical impulses via nerve cells, the range of tissues instructed to prepare for the coming activity would be limited. On the other hand, if a chemical signal were to be sent as well, it would reach all cells of the body and provide the wide-ranging changes needed.

This is done in many animals, including human beings, using a hormone called adrenaline that is secreted from the adrenal glands. Look at Figure 6.7 in your textbook to locate these glands. The adrenal glands are located on top of the kidneys.

Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation.

Such animal hormones are part of the endocrine system which constitutes a second way of control and coordination in our body.

Students, the endocrine system is a system of glands that produce and secrete hormones directly into the bloodstream. These hormones then travel to different parts of the body and regulate various functions.

Now, let me tell you about Activity 6.3. Look at Figure 6.7 in your textbook. Identify the endocrine glands mentioned in the figure. Some of these glands have been listed in Table 6.1 and discussed in the text. Consult books in the library and discuss with your teachers to find out about other glands.

Remember that plants have hormones that control their directional growth. What functions do animal hormones perform? On the face of it, we cannot imagine their role in directional growth. We have never seen an animal growing more in one direction or the other, depending on light or gravity! But if we think about it a bit more, it will become evident that, even in animal bodies, growth happens in carefully controlled places. Plants will grow leaves in many places on the plant body, for example. But we do not grow fingers on our faces. The design of the body is carefully maintained even during the growth of children.

Now, let us examine some examples to understand how hormones help in coordinated growth.

We have all seen salt packets which say 'iodised salt' or 'enriched with iodine'. Why is it important for us to have iodised salt in our diet? Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck. Can you correlate this with the position of the thyroid gland in Figure 6.7? The thyroid gland is located in the neck, so when it enlarges due to iodine deficiency, it causes a swollen neck.

Sometimes we come across people who are either very short (dwarfs) or extremely tall (giants). Have you ever wondered how this happens? Growth hormone is one of the hormones secreted by the pituitary. As its name indicates, growth hormone regulates growth and development of the body. If there is a deficiency of this hormone in childhood, it leads to dwarfism. If there is excess of this hormone in childhood, it leads to gigantism.

You must have noticed many dramatic changes in your appearance as well as that of your friends as you approached 10–12 years of age. These changes associated with puberty are because of the secretion of testosterone in males and oestrogen in females.

Testosterone is produced by the testes in males and is responsible for the development of male secondary sexual characteristics like facial hair, deepening of voice, etc. Oestrogen is produced by the ovaries in females and is responsible for the development of female secondary sexual characteristics like breast development, etc.

Do you know anyone in your family or friends who has been advised by the doctor to take less sugar in their diet because they are suffering from diabetes? As a treatment, they might be taking injections of insulin. This is a hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted in proper amounts, the sugar level in the blood rises causing many harmful effects.

If it is so important that hormones should be secreted in precise quantities, we need a mechanism through which this is done. The timing and amount of hormone released are regulated by feedback mechanisms. For example, if the sugar levels in blood rise, they are detected by the cells of the pancreas which respond by producing more insulin. As the blood sugar level falls, insulin secretion is reduced. This is an example of negative feedback, which is a very important mechanism in hormone regulation.

Now students, let me tell you about Activity 6.4. Hormones are secreted by endocrine glands and have specific functions. Complete Table 6.1 based on the hormone, the endocrine gland or the functions provided.

Let me help you complete this table:

| S.No. | Hormone | Endocrine Gland | Functions | |-------|---------|-----------------|-----------| | 1. | Growth hormone | Pituitary gland | Stimulates growth in all organs | | 2. | Thyroxin | Thyroid gland | Regulates metabolism for body growth | | 3. | Insulin | Pancreas | Regulates blood sugar level | | 4. | Testosterone | Testes | Development of male sex organs and secondary sexual characteristics | | 5. | Oestrogen | Ovaries | Development of female sex organs, regulates menstrual cycle, etc. | | 6. | Adrenaline | Adrenal gland | Prepares body for fight or flight response | | 7. | Releasing hormones | Hypothalamus | Stimulates pituitary gland to release hormones |

Now students, let me answer the questions from this section.

Question 1: How does chemical coordination take place in animals?

In animals, chemical coordination takes place through hormones. Hormones are secreted by endocrine glands directly into the bloodstream. They travel to different parts of the body and regulate various functions. Hormones act on specific target organs or tissues that have receptors for them.

Question 2: Why is the use of iodised salt advisable?

Iodised salt is advisable because iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates metabolism in the body. Iodine deficiency can lead to goitre, which is characterised by a swollen neck. Iodised salt helps prevent iodine deficiency disorders.

Question 3: How does our body respond when adrenaline is secreted into the blood?

When adrenaline is secreted into the blood, it prepares the body for a fight or flight response. The heart beats faster to supply more oxygen to muscles. Blood is diverted from the digestive system and skin to skeletal muscles. Breathing rate increases. These responses help the body deal with stressful or dangerous situations.

Question 4: Why are some patients of diabetes treated by giving injections of insulin?

Diabetes is a condition where the pancreas does not produce enough insulin, or the body does not respond properly to insulin. As a result, blood sugar levels rise, causing various health problems. Patients with diabetes are treated with insulin injections to help regulate their blood sugar levels.

Now students, let us go through the exercises at the end of the chapter.

## Exercises

Let me solve each exercise question for you.

Exercise 1: Which of the following is a plant hormone? (a) Insulin (b) Thyroxin (c) Oestrogen (d) Cytokinin.

The correct answer is (d) Cytokinin. Insulin and thyroxin are animal hormones, oestrogen is also an animal hormone, while cytokinin is a plant hormone that promotes cell division.

Exercise 2: The gap between two neurons is called a (a) dendrite. (b) synapse. (c) axon. (d) impulse.

The correct answer is (b) synapse. The gap between two neurons is called a synapse. Dendrite is the part of a neuron that receives information, axon is the part that transmits information, and impulse is the electrical signal that travels along neurons.

Exercise 3: The brain is responsible for (a) thinking. (b) regulating the heart beat. (c) balancing the body. (d) all of the above.

The correct answer is (d) all of the above. The brain is responsible for thinking (fore-brain), regulating heart beat (medulla in hind-brain), and balancing the body (cerebellum).

Exercise 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?

Receptors are specialised cells that detect information from the environment. They are usually located in sense organs like eyes, ears, nose, tongue, and skin. When receptors detect stimuli, they send this information to the brain through nerve impulses.

If receptors do not work properly, we would not be able to detect changes in our environment properly. For example, if the receptors in our eyes do not work, we cannot see. If the receptors in our ears do not work, we cannot hear. If the receptors for touch and temperature do not work properly, we might not detect danger like heat or sharp objects, which could lead to injuries.

Exercise 5: Draw the structure of a neuron and explain its function.

Students, I want you to draw a neuron in your notebook. A neuron has three main parts:

1. Cell body (soma): This contains the nucleus and other cell organelles. It integrates information received from dendrites.

2. Dendrites: These are short, branched extensions from the cell body that receive information from other neurons or from sensory receptors.

3. Axon: This is a long, thin extension from the cell body that transmits electrical impulses away from the cell body to other neurons or to effector cells like muscles or glands.

The function of a neuron is to transmit information in the form of electrical impulses. When a stimulus is detected by receptors, it creates an electrical impulse that travels through the neuron from dendrites to the cell body and then along the axon to the synapse, where it triggers the release of neurotransmitters that pass the signal to the next neuron or to an effector organ.

Exercise 6: How does phototropism occur in plants?

Phototropism occurs due to the hormone auxin. When light falls on a plant from one side, auxin, which is synthesised at the shoot tip, moves to the shaded side of the shoot. This causes the cells on the shaded side to elongate more than the cells on the light side. As a result, the plant bends towards the light. This is how phototropism occurs.

Exercise 7: Which signals will get disrupted in case of a spinal cord injury?

In case of a spinal cord injury, the signals between the brain and the rest of the body will get disrupted. This means that:

1. Reflex actions below the level of injury will be affected because the reflex arc passes through the spinal cord.

2. Voluntary movements below the injury will be affected because the brain cannot send signals to muscles through the spinal cord.

3. Sensory information from below the injury may not reach the brain.

4. Involuntary functions like bladder and bowel control may also be affected.

Exercise 8: How does chemical coordination occur in plants?

Chemical coordination in plants occurs through plant hormones or phytohormones. These are chemical substances produced by plants that help in coordinating growth, development, and responses to the environment. They are synthesised at places away from where they act and simply diffuse to the area of action.

Examples of plant hormones include auxin (promotes cell elongation), gibberellins (promotes stem growth), cytokinins (promotes cell division), and abscisic acid (inhibits growth). These hormones help plants respond to stimuli like light, gravity, touch, etc.

Exercise 9: What is the need for a system of control and coordination in an organism?

Organisms need a system of control and coordination to respond to changes in their environment and to maintain homeostasis. This system helps organisms:

1. Detect changes in the environment through receptors.

2. Process this information in the nervous system or through hormones.

3. Respond appropriately to these changes.

4. Coordinate the activities of different parts of the body so that they work together efficiently.

Without control and coordination, organisms would not be able to adapt to their environment, maintain internal balance, or carry out complex activities.

Exercise 10: How are involuntary actions and reflex actions different from each other?

Involuntary actions are those that we cannot control consciously, like heartbeat, digestion, breathing, etc. These are controlled by the autonomic nervous system and are essential for maintaining basic body functions.

Reflex actions are quick, automatic responses to stimuli that do not involve the brain. They are controlled by the spinal cord and are protective in nature, like pulling hand away from a hot object.

The main difference is that involuntary actions are ongoing processes that are always happening to maintain body functions, while reflex actions are specific responses to particular stimuli. Also, some involuntary actions are controlled by the brain (like breathing can be consciously controlled), while reflex actions bypass the brain entirely.

Exercise 11: Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

Similarities: - Both are mechanisms for control and coordination in animals. - Both help in responding to changes in the environment. - Both involve chemical signals (neurotransmitters in nervous system, hormones in endocrine system).

Differences: - Nervous system uses electrical impulses, while hormonal system uses chemical substances (hormones). - Nervous system transmits information quickly, while hormonal system transmits information slowly. - Nervous system effects are short-lived, while hormonal effects are long-lasting. - Nervous system transmits information through neurons, while hormones are secreted into the bloodstream. - Nervous system is specific in its action (specific neurons), while hormones can affect all cells that have receptors for them. - Nervous system is under our conscious control (to some extent), while hormonal system is automatic.

Exercise 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 a sensitive plant (like chhui-mui): - It is a quick response to touch. - It is not related to growth. - It happens due to changes in water content in cells, causing them to swell or shrink. - It does not involve nervous tissue or muscles. - It is an immediate response to stimulus.

Movement in our legs: - It is a voluntary action controlled by the brain. - It involves muscles and nerves. - It happens due to contraction and relaxation of muscle fibers. - It is slower than the movement in sensitive plants. - It requires the nervous system to send signals to muscles.

So students, the main difference is that the sensitive plant movement is rapid and does not involve growth or nervous tissue, while leg movement involves the nervous system and muscles and is under our conscious control.

Now students, let me give you a summary of everything we have learned in this chapter.

## What you have learnt

- Control and coordination are the functions of the nervous system and hormones in our bodies.

- The responses of the nervous system can be classified as reflex action, voluntary action or involuntary action.

- The nervous system uses electrical impulses to transmit messages.

- The nervous system gets information from our sense organs and acts through our muscles.

- Chemical coordination is seen in both plants and animals.

- Hormones produced in one part of an organism move to another part to achieve the desired effect.

- A feedback mechanism regulates the action of the hormones.

Students, in this chapter, we have learned how living organisms control and coordinate their activities. We learned about the nervous system in animals, how reflex actions work, the structure and function of the brain, and how plants and animals use hormones for chemical coordination. We also learned about various hormones in animals and their functions, and about plant hormones like auxin, gibberellins, cytokinins, and abscisic acid.

This is a very important chapter that will help you understand how your body works. Make sure you revise this chapter thoroughly and practice the diagrams.

Thank you for listening. See you in the next class. Goodbye and take care!