Life Processes

Hello students, welcome to today's science lesson. I'm so happy to see you all here, ready to learn about one of the most fascinating chapters in your science textbook. Today, we're going to study Chapter 5: Life Processes. This is an extremely important chapter because it tells us how living organisms function, how they obtain energy, how they transport materials within their bodies, and how they get rid of waste. This knowledge will help you understand your own body better and also appreciate how other living beings around you survive. So let's begin our journey into the world of life processes.

First, let me ask you a question. How do we tell the difference between what is alive and what is not alive? If you see a dog running in the park, or a cow chewing cud in a field, or a man shouting loudly on the street, you would immediately say these are living beings. But what if the dog or the cow or the man were asleep? You would still think they are alive, but how do you know that? You would say because you can see them breathing. What about plants? How do we know that plants are alive? Some of you might say because they are green. But what about plants that have leaves of other colours? Some would say because they grow over time. In other words, we tend to think of some sort of movement, either growth-related or not, as common evidence for being alive.

But here's something interesting, students. A plant that is not visibly growing is still alive, and some animals can breathe without visible movement. So using visible movement as the defining characteristic of life is not enough. There are movements over very small scales that are invisible to the naked eye - movements of molecules, for example. Is this invisible molecular movement necessary for life? If we ask this question to professional biologists, they will say yes. In fact, viruses do not show any molecular movement in them until they infect some cell, and that is partly why there is a controversy about whether viruses are truly alive or not.

Now, why are molecular movements needed for life? You have seen in earlier classes that living organisms are well-organised structures. They can have tissues, tissues have cells, cells have smaller components in them, and so on. Because of the effects of the environment, this organised, ordered nature of living structures is very likely to keep breaking down over time. If order breaks down, the organism will no longer be alive. So living creatures must keep repairing and maintaining their structures. Since all these structures are made up of molecules, they must move molecules around all the time. This is a very important point, students - life requires constant maintenance at the molecular level.

Now let us explore what are the maintenance processes in living organisms. The maintenance functions of living organisms must go on even when they are not doing anything particular. Even when you are just sitting in class, even if you are just asleep, this maintenance job has to go on. The processes which together perform this maintenance job are called life processes.

Since these maintenance processes are needed to prevent damage and break-down, energy is needed for them. This energy comes from outside the body of the individual organism. So there must be a process to transfer a source of energy from outside the body of the organism, which we call food, to the inside - a process we commonly call nutrition. If the body size of the organisms is to grow, additional raw material will also be needed from outside. Since life on earth depends on carbon-based molecules, most of these food sources are also carbon-based. Depending on the complexity of these carbon sources, different organisms can then use different kinds of nutritional processes.

The outside sources of energy could be quite varied since the environment is not under the control of the individual organism. These sources of energy, therefore, need to be broken down or built up in the body, and must be finally converted to a uniform source of energy that can be used for the various molecular movements needed for maintaining living structures, as well as to the kind of molecules the body needs to grow. For this, a series of chemical reactions in the body are necessary. Oxidising-reducing reactions are some of the most common chemical means to break down molecules. For this, many organisms use oxygen sourced from outside the body. The process of acquiring oxygen from outside the body, and to use it in the process of break-down of food sources for cellular needs, is what we call respiration.

In the case of a single-celled organism, no specific organs for taking in food, exchange of gases or removal of wastes may be needed because the entire surface of the organism is in contact with the environment. But what happens when the body size of the organism increases and the body design becomes more complex? In multi-cellular organisms, all the cells may not be in direct contact with the surrounding environment. Thus, simple diffusion will not meet the requirements of all the cells.

We have seen previously how, in multi-cellular organisms, various body parts have specialised in the functions they perform. We are familiar with the idea of these specialised tissues, and with their organisation in the body of the organism. It is therefore not surprising that the uptake of food and of oxygen will also be the function of specialised tissues. However, this poses a problem since the food and oxygen are now taken up at one place in the body of the organisms, while all parts of the body need them. This situation creates a need for a transportation system for carrying food and oxygen from one place to another in the body.

When chemical reactions use the carbon source and the oxygen for energy generation, they create by-products that are not only useless for the cells of the body, but could even be harmful. These waste by-products are therefore needed to be removed from the body and discarded outside by a process called excretion. Again, if the basic rules for body design in multi-cellular organisms are followed, a specialised tissue for excretion will be developed, which means that the transportation system will need to transport waste away from cells to this excretory tissue.

So students, let me recap what we have learned so far. The essential life processes that maintain life are nutrition, respiration, transportation, and excretion. We will study each of these processes in detail in this chapter. Now let's move on to the first life process - nutrition.

When we walk or ride a bicycle, we are using up energy. Even when we are not doing any apparent activity, energy is needed to maintain a state of order in our body. We also need materials from outside in order to grow, develop, synthesise protein and other substances needed in the body. This source of energy and materials is the food we eat.

Now, how do living things get their food? The general requirement for energy and materials is common in all organisms, but it is fulfilled in different ways. Some organisms use simple food material obtained from inorganic sources in the form of carbon dioxide and water. These organisms, the autotrophs, include green plants and some bacteria. Other organisms utilise complex substances. These complex substances have to be broken down into simpler ones before they can be used for the upkeep and growth of the body. To achieve this, organisms use bio-catalysts called enzymes. Thus, the heterotrophs survival depends directly or indirectly on autotrophs. Heterotrophic organisms include animals and fungi.

Let me explain this more clearly. Autotrophs are organisms that can make their own food. Green plants are the best example of autotrophs. They use sunlight, carbon dioxide, and water to make food through photosynthesis. Heterotrophs, on the other hand, cannot make their own food. They depend on other organisms for food. Animals and fungi are heterotrophs. When you eat a chapatti or rice, you are getting food that originally came from a plant. So even as a heterotroph, you depend on autotrophs for your food.

Now let's study autotrophic nutrition in more detail. Carbon and energy requirements of the autotrophic organism are fulfilled by photosynthesis. It is the process by which autotrophs take in substances from the outside and convert them into stored forms of energy. This material is taken in the form of carbon dioxide and water which is converted into carbohydrates in the presence of sunlight and chlorophyll. Carbohydrates are utilised for providing energy to the plant. The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant. A somewhat similar situation is seen in us where some of the energy derived from the food we eat is stored in our body in the form of glycogen.

The overall equation for photosynthesis can be written as:

6CO₂ + 12H₂O →[Chlorophyll][Sunlight] C₆H₁₂O₆ + 6O₂ + 6H₂O

This equation shows that carbon dioxide and water are converted into glucose and oxygen in the presence of chlorophyll and sunlight.

Now let us see what actually happens during the process of photosynthesis. The following events occur during this process:

First, absorption of light energy by chlorophyll. Second, conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen. Third, reduction of carbon dioxide to carbohydrates.

These steps need not take place one after the other immediately. For example, desert plants like cactus take up carbon dioxide at night and prepare an intermediate which is acted upon by the energy absorbed by the chlorophyll during the day. This is an adaptation that helps desert plants conserve water during the hot daytime.

Now, let us see how each of the components of the above reaction are necessary for photosynthesis. If you carefully observe a cross-section of a leaf under the microscope, you will notice that some cells contain green dots. These green dots are cell organelles called chloroplasts which contain chlorophyll. Chlorophyll is the green pigment that absorbs light energy for photosynthesis.

Now students, let's do an activity to demonstrate that chlorophyll is essential for photosynthesis. This is Activity 5.1 from your textbook.

Take a potted plant with variegated leaves - for example, money plant or crotons. Keep the plant in a dark room for three days so that all the starch gets used up. This is called destarching. Now keep the plant in sunlight for about six hours. Pluck a leaf from the plant. Mark the green areas in it and trace them on a sheet of paper. Dip the leaf in boiling water for a few minutes to kill the cells. After this, immerse it in a beaker containing alcohol. Carefully place the above beaker in a water-bath and heat till the alcohol begins to boil. This is done to remove the chlorophyll from the leaf, which is called decolourisation. What happens to the colour of the leaf? The leaf becomes colourless or pale. What is the colour of the solution? The solution becomes green because chlorophyll dissolves in alcohol. Now dip the leaf in a dilute solution of iodine for a few minutes. Iodine is used to test for starch. Take out the leaf and rinse off the iodine solution. Observe the colour of the leaf and compare this with the tracing of the leaf done in the beginning. What can you conclude about the presence of starch in various areas of the leaf?

The areas that were green before will show the presence of starch (they turn blue-black with iodine), while the areas that were not green (like white or yellow areas in variegated leaves) will not show the presence of starch. This experiment clearly demonstrates that chlorophyll is essential for photosynthesis because only the green areas, which contain chlorophyll, can produce starch.

Now, let us study how the plant obtains carbon dioxide. In Class IX, we had talked about stomata which are tiny pores present on the surface of the leaves. Massive amounts of gaseous exchange takes place in the leaves through these pores for the purpose of photosynthesis. But it is important to note here that exchange of gases occurs across the surface of stems, roots and leaves as well. Since large amounts of water can also be lost through these stomata, the plant closes these pores when it does not need carbon dioxide for photosynthesis. The opening and closing of the pore is a function of the guard cells. The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly, the pore closes if the guard cells shrink. This is a very important mechanism that helps plants conserve water.

Now let's do another activity, Activity 5.2, to understand the role of carbon dioxide in photosynthesis.

Take two healthy potted plants which are nearly the same size. Keep them in a dark room for three days to destarch them. Now place each plant on separate glass plates. Place a watch-glass containing potassium hydroxide by the side of one of the plants. Potassium hydroxide is used to absorb carbon dioxide. Cover both plants with separate bell-jars. Use vaseline to seal the bottom of the jars to the glass plates so that the set-up is air-tight. Keep the plants in sunlight for about two hours. Pluck a leaf from each plant and check for the presence of starch as in the above activity. Do both the leaves show the presence of the same amount of starch? What can we conclude from this activity?

The plant kept with potassium hydroxide will not show the presence of starch because potassium hydroxide absorbed all the carbon dioxide from the air inside the bell-jar. This proves that carbon dioxide is necessary for photosynthesis.

Based on the two activities performed above, can we design an experiment to demonstrate that sunlight is essential for photosynthesis? Yes, we can. We can keep two plants - one in sunlight and one in a dark room. After some time, we can test leaves from both plants for starch. The plant kept in sunlight will show the presence of starch, while the one in darkness will not. This proves that sunlight is essential for photosynthesis.

So far, we have talked about how autotrophs meet their energy requirements. But they also need other raw materials for building their body. Water used in photosynthesis is taken up from the soil by the roots in terrestrial plants. Other materials like nitrogen, phosphorus, iron and magnesium are taken up from the soil. Nitrogen is an essential element used in the synthesis of proteins and other compounds. This is taken up in the form of inorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen.

Now let's move on to heterotrophic nutrition. Each organism is adapted to its environment. The form of nutrition differs depending on the type and availability of food material as well as how it is obtained by the organism. For example, whether the food source is stationary (such as grass) or mobile (such as a deer), would allow for differences in how the food is accessed and what is the nutritive apparatus used by a cow and a lion. There is a range of strategies by which the food is taken in and used by the organism. Some organisms break-down the food material outside the body and then absorb it. Examples are fungi like bread moulds, yeast and mushrooms. Others take in whole material and break it down inside their bodies. What can be taken in and broken down depends on the body design and functioning. Some other organisms derive nutrition from plants or animals without killing them. This parasitic nutritive strategy is used by a wide variety of organisms like cuscuta (amar-bel), ticks, lice, leeches and tape-worms.

Cuscuta, also known as amar-bel in India, is a plant that lacks chlorophyll and cannot photosynthesise. It wraps around other plants and absorbs nutrients from them. This is an example of parasitism.

Now let's see how organisms obtain their nutrition. Since the food and the way it is obtained differ, the digestive system is different in various organisms. In single-celled organisms, the food may be taken in by the entire surface. But as the complexity of the organism increases, different parts become specialised to perform different functions.

For example, Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole. Inside the food-vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out. In Paramecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface of the cell.

Now let's study nutrition in human beings in detail. The alimentary canal is basically a long tube extending from the mouth to the anus. The tube has different parts. Various regions are specialised to perform different functions. What happens to the food once it enters our body? We shall discuss this process here.

Let's do an activity, Activity 5.3. Take 1 mL starch solution (1%) in two test tubes (A and B). Add 1 mL saliva to test tube A and leave both test tubes undisturbed for 20-30 minutes. Now add a few drops of dilute iodine solution to the test tubes. In which test tube do you observe a colour change? What does this indicate about the presence or absence of starch in the two test tubes? What does this tell us about the action of saliva on starch?

The test tube with saliva (test tube A) will not show a blue-black colour with iodine, indicating that starch has been broken down. The test tube without saliva (test tube B) will show a blue-black colour, indicating the presence of starch. This tells us that saliva contains an enzyme called salivary amylase that breaks down starch into simpler sugars.

We eat various types of food which has to pass through the same digestive tract. Naturally the food has to be processed to generate particles which are small and of the same texture. This is achieved by crushing the food with our teeth. Since the lining of the canal is soft, the food is also wetted to make its passage smooth. When we eat something we like, our mouth 'waters'. This is actually not only water, but a fluid called saliva secreted by the salivary glands. Another aspect of the food we ingest is its complex nature. If it is to be absorbed from the alimentary canal, it has to be broken into smaller molecules. This is done with the help of biological catalysts called enzymes. The saliva contains an enzyme called salivary amylase that breaks down starch which is a complex molecule to give simple sugar. The food is mixed thoroughly with saliva and moved around the mouth while chewing by the muscular tongue.

It is necessary to move the food in a regulated manner along the digestive tube so that it can be processed properly in each part. The lining of canal has muscles that contract rhythmically in order to push the food forward. These peristaltic movements occur all along the gut.

From the mouth, the food is taken to the stomach through the food-pipe or oesophagus. The stomach is a large organ which expands when food enters it. The muscular walls of the stomach help in mixing the food thoroughly with more digestive juices.

The digestion in stomach is taken care of by the gastric glands present in the wall of the stomach. These release hydrochloric acid, a protein digesting enzyme called pepsin, and mucus. The hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin. What other function do you think is served by the acid? The acid also helps in killing bacteria that might come with food. The mucus protects the inner lining of the stomach from the action of the acid under normal conditions. We have often heard adults complaining about 'acidity'. Can this be related to what has been discussed above? Yes, when excess acid is produced, it can cause discomfort and damage to the stomach lining.

The exit of food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine. From the stomach, the food now enters the small intestine. This is the longest part of the alimentary canal which is fitted into a compact space because of extensive coiling. The length of the small intestine differs in various animals depending on the food they eat. Herbivores eating grass need a longer small intestine to allow the cellulose to be digested. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.

The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas for this purpose. The food coming from the stomach is acidic and has to be made alkaline for the pancreatic enzymes to act. Bile juice from the liver accomplishes this in addition to acting on fats. Fats are present in the intestine in the form of large globules which makes it difficult for enzymes to act on them. Bile salts break them down into smaller globules increasing the efficiency of enzyme action. This is similar to the emulsifying action of soaps on dirt that we have learnt about in Chapter 4. The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats. The walls of the small intestine contain glands which secrete intestinal juice. The enzymes present in it finally convert the proteins to amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol.

Digested food is taken up by the walls of the intestine. The inner lining of the small intestine has numerous finger-like projections called villi which increase the surface area for absorption. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body, where it is utilised for obtaining energy, building up new tissues and the repair of old tissues.

The unabsorbed food is sent into the large intestine where its wall absorb more water from this material. The rest of the material is removed from the body via the anus. The exit of this waste material is regulated by the anal sphincter.

Now students, let me tell you about dental caries, which is a very common problem in India. Dental caries or tooth decay causes gradual softening of enamel and dentine. It begins when bacteria acting on sugars produce acids that softens or demineralises the enamel. Masses of bacterial cells together with food particles stick to the teeth to form dental plaque. Saliva cannot reach the tooth surface to neutralise the acid as plaque covers the teeth. Brushing the teeth after eating removes the plaque before the bacteria produce acids. If untreated, microorganisms may invade the pulp, causing inflammation and infection. So always remember to brush your teeth twice a day!

Now let's answer the questions from this section.

Question 1: What are the differences between autotrophic nutrition and heterotrophic nutrition?

In autotrophic nutrition, organisms prepare their own food from simple inorganic substances like carbon dioxide and water, using sunlight as the energy source. Green plants and some bacteria are autotrophs. In heterotrophic nutrition, organisms depend on other organisms for food. They cannot prepare their own food. Animals and fungi are heterotrophs.

Question 2: Where do plants get each of the raw materials required for photosynthesis?

Plants get carbon dioxide from the atmosphere through stomata. They get water from the soil through their roots. They get sunlight through chlorophyll present in chloroplasts in leaf cells.

Question 3: What is the role of the acid in our stomach?

The hydrochloric acid in our stomach creates an acidic medium which facilitates the action of the enzyme pepsin for protein digestion. It also helps in killing bacteria that come with food.

Question 4: What is the function of digestive enzymes?

Digestive enzymes break down complex food molecules into simpler ones that can be absorbed by the body. For example, salivary amylase breaks down starch into sugars, pepsin breaks down proteins into amino acids, and lipase breaks down fats into fatty acids and glycerol.

Question 5: How is the small intestine designed to absorb digested food?

The small intestine is designed to maximise absorption in several ways. First, it is very long and coiled to provide a large surface area. Second, its inner lining has numerous finger-like projections called villi, which further increase the surface area. Third, each cell on the surface of the villi has even smaller projections called microvilli, which create even more surface area. Fourth, the villi are richly supplied with blood vessels that transport the absorbed food to all parts of the body.

Now let's move on to the next section: Respiration.

We have discussed nutrition in organisms in the last section. The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Diverse organisms do this in different ways - some use oxygen to break-down glucose completely into carbon dioxide and water, some use other pathways that do not involve oxygen. In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm. Further, the pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration. Break-down of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this aerobic process is a lot greater than in the anaerobic process. Sometimes, when there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is taken. Here the pyruvate is converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

Let me write this more clearly:

In the presence of absence of oxygen in yeast, pyruvate converts to ethanol and carbon dioxide. This is anaerobic respiration in yeast.

In the presence of oxygen in mitochondria, pyruvate converts to carbon dioxide and water. This is aerobic respiration.

In the absence of oxygen in our muscle cells, pyruvate converts to lactic acid. This is anaerobic respiration in humans during heavy exercise.

The energy released during cellular respiration is immediately used to synthesise a molecule called ATP which is used to fuel all other activities in the cell. In these processes, ATP is broken down giving rise to a fixed amount of energy which can drive the endothermic reactions taking place in the cell.

Now let me tell you more about ATP. ATP is the energy currency for most cellular processes. The energy released during the process of respiration is used to make an ATP molecule from ADP and inorganic phosphate. We can write it as:

ADP + phosphate plus energy gives ATP.

Endothermic processes in the cell then use this ATP to drive the reactions. When the terminal phosphate linkage in ATP is broken using water, the energy equivalent to 30.5 kJ/mol is released.

Think of how a battery can provide energy for many different kinds of uses. It can be used to obtain mechanical energy, light energy, electrical energy and so on. Similarly, ATP can be used in the cells for the contraction of muscles, protein synthesis, conduction of nervous impulses and many other activities.

Now, since the aerobic respiration pathway depends on oxygen, aerobic organisms need to ensure that there is sufficient intake of oxygen. We have seen that plants exchange gases through stomata, and the large inter-cellular spaces ensure that all cells are in contact with air. Carbon dioxide and oxygen are exchanged by diffusion here. They can go into cells, or away from them and out into the air. The direction of diffusion depends upon the environmental conditions and the requirements of the plant. At night, when there is no photosynthesis occurring, CO₂ elimination is the major exchange activity going on. During the day, CO₂ generated during respiration is used up for photosynthesis, hence there is no CO₂ release. Instead, oxygen release is the major event at this time.

Animals have evolved different organs for the uptake of oxygen from the environment and for getting rid of the carbon dioxide produced. Terrestrial animals can breathe the oxygen in the atmosphere, but animals that live in water need to use the oxygen dissolved in water.

Let's do an activity, Activity 5.6. Observe fish in an aquarium. They open and close their mouths and the gill-slits behind their eyes also open and close. Are the timings of the opening and closing of the mouth and gill-slits coordinated in some manner? Count the number of times the fish opens and closes its mouth in a minute. Compare this to the number of times you breathe in and out in a minute.

You will notice that fish breathe much faster than humans. This is because the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air. So the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. Fishes take in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood.

Now students, I want to tell you something very important about tobacco. Using tobacco directly or any product of tobacco in the form of cigar, cigarettes, bidis, hookah, gutkha, etc., is harmful. Use of tobacco most commonly affects the tongue, lungs, heart and liver. Smokeless tobacco is also a major risk factor for heart attacks, strokes, pulmonary diseases and several forms of cancers. There is a high incidence of oral cancer in India due to the chewing of tobacco in the form of gutkha. Stay healthy; just say NO to tobacco and its products!

Now let's study the human respiratory system in detail. Terrestrial organisms use the oxygen in the atmosphere for respiration. This oxygen is absorbed by different organs in different animals. All these organs have a structure that increases the surface area which is in contact with the oxygen-rich atmosphere. Since the exchange of oxygen and carbon dioxide has to take place across this surface, this surface is very fine and delicate. In order to protect this surface, it is usually placed within the body, so there have to be passages that will take air to this area. In addition, there is a mechanism for moving the air in and out of this area where the oxygen is absorbed.

In human beings, air is taken into the body through the nostrils. The air passing through the nostrils is filtered by fine hairs that line the passage. The passage is also lined with mucus which helps in this process. From here, the air passes through the throat and into the lungs. Rings of cartilage are present in the throat. These ensure that the air-passage does not collapse.

Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures which are called alveoli. The alveoli provide a surface where the exchange of gases can take place. The walls of the alveoli contain an extensive network of blood-vessels. As we have seen in earlier years, when we breathe in, we lift our ribs and flatten our diaphragm, and the chest cavity becomes larger as a result. Because of this, air is sucked into the lungs and fills the expanded alveoli. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body. During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

When the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body. Instead, respiratory pigments take up oxygen from the air in the lungs and carry it to tissues which are deficient in oxygen before releasing it. In human beings, the respiratory pigment is haemoglobin which has a very high affinity for oxygen. This pigment is present in the red blood corpuscles. Carbon dioxide is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood.

Now let me tell you some interesting facts. If the alveolar surface were spread out, it would cover about 80 square metres. How much do you think the surface area of your body is? Consider how efficient exchange of gases becomes because of the large surface available for the exchange to take place. If diffusion were to move oxygen in our body, it is estimated that it would take 3 years for a molecule of oxygen to get to our toes from our lungs. Aren't you glad that we have haemoglobin?

Now let's answer the questions from this section.

Question 1: What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

Terrestrial organisms can breathe oxygen directly from the atmosphere, which has much more oxygen compared to water. Aquatic organisms have to use oxygen dissolved in water, which is limited. That's why fish breathe faster than land animals.

Question 2: What are the different ways in which glucose is oxidised to provide energy in various organisms?

Glucose can be oxidised in three ways. First, aerobic respiration - in the presence of oxygen, glucose is completely broken down into carbon dioxide and water in mitochondria, releasing a lot of energy. Second, anaerobic respiration in yeast - in the absence of oxygen, glucose is broken down into ethanol and carbon dioxide. Third, anaerobic respiration in muscles - during heavy exercise when oxygen is insufficient, glucose is broken down into lactic acid.

Question 3: How is oxygen and carbon dioxide transported in human beings?

Oxygen is transported by haemoglobin in red blood cells. Haemoglobin has a high affinity for oxygen and forms oxyhaemoglobin. Carbon dioxide is more soluble in water, so it is mostly transported in the dissolved form in plasma. Some carbon dioxide is also carried by haemoglobin as carbaminohaemoglobin.

Question 4: How are the lungs designed in human beings to maximise the area for exchange of gases?

The lungs are designed to maximise the area for exchange of gases in several ways. First, the bronchi branch repeatedly to form bronchioles, which finally end in alveoli. Second, each lung contains millions of alveoli, which are tiny balloon-like structures. Third, the alveoli have very thin walls and are surrounded by a dense network of capillaries. This provides a large surface area (about 80 square metres) for efficient exchange of gases.

Now let's move on to the next section: Transportation.

We have seen in previous sections that blood transports food, oxygen and waste materials in our bodies. In Class IX, we learnt about blood being a fluid connective tissue. Blood consists of a fluid medium called plasma in which the cells are suspended. Plasma transports food, carbon dioxide and nitrogenous wastes in dissolved form. Oxygen is carried by the red blood corpuscles. Many other substances like salts are also transported by the blood. We thus need a pumping organ to push blood around the body, a network of tubes to reach all the tissues and a system in place to ensure that this network can be repaired if damaged.

Let's do an activity, Activity 5.7. Visit a health centre in your locality and find out what is the normal range of haemoglobin content in human beings. Is it the same for children and adults? Is there any difference in the haemoglobin levels for men and women? Visit a veterinary clinic in your locality. Find out what is the normal range of haemoglobin content in an animal like the buffalo or cow. Is this content different in calves, male and female animals? Compare the difference seen in male and female human beings and animals. How would the difference, if any, be explained?

Generally, adult males have higher haemoglobin than adult females. This is because males generally have more muscle mass and higher metabolic rate. During pregnancy, females may have different haemoglobin levels. In animals, similar differences may be observed based on age, sex, and physiological state.

Now let's study our pump - the heart. The heart is a muscular organ which is as big as our fist. Because both oxygen and carbon dioxide have to be transported by the blood, the heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide. The carbon dioxide-rich blood has to reach the lungs for the carbon dioxide to be removed, and the oxygenated blood from the lungs has to be brought back to the body. This oxygen-rich blood is then pumped to the rest of the body.

We can follow this process step by step. Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, the left atrium. The left atrium relaxes when it is collecting this blood. It then contracts, while the next chamber, the left ventricle, relaxes, so that the blood is transferred to it. When the muscular left ventricle contracts in its turn, the blood is pumped out to the body. De-oxygenated blood comes from the body to the upper chamber on the right, the right atrium, as it relaxes. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates. This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation. Since ventricles have to pump blood into various organs, they have thicker muscular walls than the atria do. Valves ensure that blood does not flow backwards when the atria or ventricles contract.

The separation of the right side and the left side of the heart is useful to keep oxygenated and de-oxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body. This is useful in animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature. In animals that do not use energy for this purpose, the body temperature depends on the temperature in the environment. Such animals, like amphibians or many reptiles have three-chambered hearts, and tolerate some mixing of the oxygenated and de-oxygenated blood streams. Fishes, on the other hand, have only two chambers to their hearts, and the blood is pumped to the gills, is oxygenated there, and passes directly to the rest of the body. Thus, blood goes only once through the heart in the fish during one cycle of passage through the body. On the other hand, it goes through the heart twice during each cycle in other vertebrates. This is known as double circulation.

Now let me tell you about blood pressure. The force that blood exerts against the wall of a vessel is called blood pressure. This pressure is much greater in arteries than in veins. The pressure of blood inside the artery during ventricular systole (contraction) is called systolic pressure and pressure in artery during ventricular diastole (relaxation) is called diastolic pressure. The normal systolic pressure is about 120 mm of Hg and diastolic pressure is 80 mm of Hg. Blood pressure is measured with an instrument called sphygmomanometer. High blood pressure is also called hypertension and is caused by the constriction of arterioles, which results in increased resistance to blood flow. It can lead to the rupture of an artery and internal bleeding.

Now let's study the blood vessels. Arteries are the vessels which carry blood away from the heart to various organs of the body. Since the blood emerges from the heart under high pressure, the arteries have thick, elastic walls. Veins collect the blood from different organs and bring it back to the heart. They do not need thick walls because the blood is no longer under pressure, instead they have valves that ensure that the blood flows only in one direction.

On reaching an organ or tissue, the artery divides into smaller and smaller vessels to bring the blood in contact with all the individual cells. The smallest vessels have walls which are one-cell thick and are called capillaries. Exchange of material between the blood and surrounding cells takes place across this thin wall. The capillaries then join together to form veins that convey the blood away from the organ or tissue.

Now let's talk about maintenance by platelets. What happens if this system of tubes develops a leak? Think about situations when we are injured and start bleeding. Naturally the loss of blood from the system has to be minimised. In addition, leakage would lead to a loss of pressure which would reduce the efficiency of the pumping system. To avoid this, the blood has platelet cells which circulate around the body and plug these leaks by helping to clot the blood at these points of injury.

Now let's talk about lymph. There is another type of fluid also involved in transportation. This is called lymph or tissue fluid. Through the pores present in the walls of capillaries some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form the tissue fluid or lymph. It is similar to the plasma of blood but colourless and contains less protein. Lymph drains into lymphatic capillaries from the intercellular spaces, which join to form large lymph vessels that finally open into larger veins. Lymph carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood.

Now let's study transportation in plants. We have discussed earlier how plants take in simple compounds such as CO₂ and photosynthesise energy stored in their chlorophyll-containing organs, namely leaves. The other kinds of raw materials needed for building plant bodies will also have to be taken up separately. For plants, the soil is the nearest and richest source of raw materials like nitrogen, phosphorus and other minerals. The absorption of these substances therefore occurs through the part in contact with the soil, namely roots. If the distances between soil-contacting organs and chlorophyll-containing organs are small, energy and raw materials can easily diffuse to all parts of the plant body. But if these distances become large because of changes in plant body design, diffusion processes will not be sufficient to provide raw material in leaves and energy in roots. A proper system of transportation is therefore essential in such situations.

Energy needs differ between different body designs. Plants do not move, and plant bodies have a large proportion of dead cells in many tissues. As a result, plants have low energy needs, and can use relatively slow transport systems. The distances over which transport systems have to operate, however, can be very large in plants such as very tall trees.

Plant transport systems will move energy stores from leaves and raw materials from roots. These two pathways are constructed as independently organised conducting tubes. One, the xylem moves water and minerals obtained from the soil. The other, phloem transports products of photosynthesis from the leaves where they are synthesised to other parts of the plant. We have studied the structure of these tissues in detail in Class IX.

Now let's study the transport of water in plants. In xylem tissue, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plant. At the roots, cells in contact with the soil actively take up ions. This creates a difference in the concentration of these ions between the root and the soil. Water, therefore, moves into the root from the soil to eliminate this difference. This means that there is steady movement of water into root xylem, creating a column of water that is steadily pushed upwards.

However, this pressure by itself is unlikely to be enough to move water over the heights that we commonly see in plants. Plants use another strategy to move water in the xylem upwards to the highest points of the plant body.

Let's do an activity, Activity 5.8. Take two small pots of approximately the same size and having the same amount of soil. One should have a plant in it. Place a stick of the same height as the plant in the other pot. Cover the soil in both pots with a plastic sheet so that moisture cannot escape by evaporation. Cover both sets, one with the plant and the other with the stick, with plastic sheets and place in bright sunlight for half an hour. Do you observe any difference in the two cases?

You will observe that the plant loses water through transpiration, while the stick does not. This demonstrates the process of transpiration.

Provided that the plant has an adequate supply of water, the water which is lost through the stomata is replaced by water from the xylem vessels in the leaf. In fact, evaporation of water molecules from the cells of a leaf creates a suction which pulls water from the xylem cells of roots. The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.

Thus, transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves. It also helps in temperature regulation. The effect of root pressure in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.

Now let's study the transport of food and other substances in plants. So far we have discussed the transport of water and minerals in plants. Now let us consider how the products of metabolic processes, particularly photosynthesis, are moved from leaves, where they are formed, to other parts of the plant. This transport of soluble products of photosynthesis is called translocation and it occurs in the part of the vascular tissue known as phloem. Besides the products of photosynthesis, the phloem transports amino acids and other substances. These substances are especially delivered to the storage organs of roots, fruits and seeds and to growing organs. The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.

Unlike transport in xylem which can be largely explained by simple physical forces, the translocation in phloem is achieved by utilising energy. Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material according to the plant's needs. For example, in the spring, sugar stored in root or stem tissue would be transported to the buds which need energy to grow.

Now let's answer the questions from this section.

Question 1: What are the components of the transport system in human beings? What are the functions of these components?

The transport system in human beings consists of the heart, blood, and blood vessels. The heart is a pumping organ that pumps blood throughout the body. Blood is the fluid that carries substances. Blood vessels are tubes that carry blood - arteries carry blood away from the heart, veins bring blood back to the heart, and capillaries allow exchange of materials between blood and tissues.

Question 2: Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Mammals and birds are warm-blooded animals that have high energy needs to maintain their body temperature. Separating oxygenated and deoxygenated blood ensures that oxygen-rich blood is efficiently delivered to all parts of the body, providing maximum oxygen for energy production.

Question 3: What are the components of the transport system in highly organised plants?

The transport system in highly organised plants consists of xylem and phloem. Xylem transports water and minerals from roots to leaves. Phloem transports products of photosynthesis (sugars) from leaves to other parts of the plant.

Question 4: How are water and minerals transported in plants?

Water and minerals are transported in plants through xylem tissue. This process involves root pressure (pressure created by water moving into roots from soil) and transpiration pull (suction force created by evaporation of water from leaves). The continuous column of water in xylem vessels helps in upward movement of water.

Question 5: How is food transported in plants?

Food is transported in plants through phloem tissue. This process is called translocation. Sugars are actively loaded into phloem tubes using ATP, which creates osmotic pressure. This pressure pushes the food solution to other parts of the plant where it is needed or stored.

Now let's move on to the final section: Excretion.

We have already discussed how organisms get rid of gaseous wastes generated during photosynthesis or respiration. Other metabolic activities generate nitrogenous materials which need to be removed. The biological process involved in the removal of these harmful metabolic wastes from the body is called excretion. Different organisms use varied strategies to do this. Many unicellular organisms remove these wastes by simple diffusion from the body surface into the surrounding water. As we have seen in other processes, complex multi-cellular organisms use specialised organs to perform the same function.

Now let's study excretion in human beings. The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. Kidneys are located in the abdomen, one on either side of the backbone. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.

How is urine produced? The purpose of making urine is to filter out waste products from the blood. Just as CO₂ is removed from the blood in the lungs, nitrogenous waste such as urea or uric acid are removed from blood in the kidneys. It is then no surprise that the basic filtration unit in the kidneys, like in the lungs, is a cluster of very thin-walled blood capillaries. Each capillary cluster in the kidney is associated with the cup-shaped end of a coiled tube called Bowman's capsule that collects the filtrate. Each kidney has large numbers of these filtration units called nephrons packed close together. Some substances in the initial filtrate, such as glucose, amino acids, salts and a major amount of water, are selectively re-absorbed as the urine flows along the tube. The amount of water re-absorbed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted. The urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder. Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra. The bladder is muscular, so it is under nervous control, as we have discussed elsewhere. As a result, we can usually control the urge to urinate.

Now let me tell you about artificial kidney or hemodialysis. Kidneys are vital organs for survival. Several factors like infections, injury or restricted blood flow to kidneys reduce the activity of kidneys. This leads to accumulation of poisonous wastes in the body, which can even lead to death. In case of kidney failure, an artificial kidney can be used. An artificial kidney is a device to remove nitrogenous waste products from the blood through dialysis.

Artificial kidneys contain a number of tubes with a semi-permeable lining, suspended in a tank filled with dialysing fluid. This fluid has the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes. The patient's blood is passed through these tubes. During this passage, the waste products from the blood pass into dialysing fluid by diffusion. The purified blood is pumped back into the patient. This is similar to the function of the kidney, but it is different since there is no re-absorption involved. Normally, in a healthy adult, the initial filtrate in the kidneys is about 180 litres daily. However, the volume actually excreted is only a litre or two a day, because the remaining filtrate is re-absorbed in the kidney tubules.

Now let's talk about organ donation. Organ donation is a generous act of donating an organ to a person who suffers from non-function of organ(s). Donation of an organ may be done by the consent of the donor and his/her family. Anyone regardless of age or gender can become an organ and tissue donor. Organ transplants can save or transform the life of a person. Transplantation is required because recipient's organ has been damaged or has failed by disease or injury. In organ transplantation the organ is surgically removed from one person (organ donor) and transplanted to another person (the recipient). Common transplantations include corneas, kidneys, heart, liver, pancreas, lungs, intestines and bone marrow. Most organ and tissue donations occur just after the donor has died or when the doctor declares a person brain dead. But some organs such as kidney, part of a liver, lung, etc., and tissues can be donated while the donor is alive.

Now let's study excretion in plants. Plants use completely different strategies for excretion than those of animals. Oxygen itself can be thought of as a waste product generated during photosynthesis! We have discussed earlier how plants deal with oxygen as well as CO₂. They can get rid of excess water by transpiration. For other wastes, plants use the fact that many of their tissues consist of dead cells, and that they can even lose some parts such as leaves. Many plant waste products are stored in cellular vacuoles. Waste products may be stored in leaves that fall off. Other waste products are stored as resins and gums, especially in old xylem. Plants also excrete some waste substances into the soil around them.

Now let's answer the questions from this section.

Question 1: Describe the structure and functioning of nephrons.

Each nephron consists of a Bowman's capsule and a long tubule. The Bowman's capsule contains a cluster of capillaries called glomerulus. Blood is filtered through the glomerulus into the Bowman's capsule. This filtrate contains water, glucose, amino acids, salts, and waste products like urea. As this filtrate passes through the tubule, useful substances like glucose, amino acids, and water are re-absorbed back into the blood. The remaining fluid, containing urea and other waste products, becomes urine. This urine passes through the collecting duct and enters the ureter.

Question 2: What are the methods used by plants to get rid of excretory products?

Plants get rid of waste products through several methods. They get rid of oxygen through stomata during photosynthesis. They get rid of excess water through transpiration. They store waste products in cellular vacuoles or in leaves that fall off. They also store waste as resins and gums in old xylem. Some waste substances are excreted into the soil around them.

Question 3: How is the amount of urine produced regulated?

The amount of urine produced is regulated by the hormone ADH (antidiuretic hormone). When the body has excess water, less ADH is released, so less water is re-absorbed in the kidneys, producing more dilute urine. When the body is low on water, more ADH is released, so more water is re-absorbed, producing concentrated urine. This helps maintain water balance in the body.

Now let's solve the exercise questions at the end of the chapter.

Question 1: The kidneys in human beings are a part of the system for (a) nutrition. (b) respiration. (c) excretion. (d) transportation.

The answer is (c) excretion. Kidneys filter waste products from the blood and produce urine, which is the excretory function.

Question 2: The xylem in plants are responsible for (a) transport of water. (b) transport of food. (c) transport of amino acids. (d) transport of oxygen.

The answer is (a) transport of water. Xylem transports water and minerals from roots to leaves.

Question 3: The autotrophic mode of nutrition requires (a) carbon dioxide and water. (b) chlorophyll. (c) sunlight. (d) all of the above.

The answer is (d) all of the above. Autotrophic nutrition requires carbon dioxide, water, chlorophyll (or other pigments), and sunlight for photosynthesis.

Question 4: The breakdown of pyruvate to give carbon dioxide, water and energy takes place in (a) cytoplasm. (b) mitochondria. (c) chloroplast. (d) nucleus.

The answer is (b) mitochondria. The complete breakdown of pyruvate (through Krebs cycle) occurs in mitochondria during aerobic respiration.

Question 5: How are fats digested in our bodies? Where does this process take place?

Fats are digested in the small intestine. The process begins in the small intestine where bile juice from the liver emulsifies fats, breaking them into smaller globules. Then, pancreatic lipase breaks down emulsified fats into fatty acids and glycerol. These are then absorbed by the villi in the small intestine.

Question 6: What is the role of saliva in the digestion of food?

Saliva contains an enzyme called salivary amylase that breaks down starch (a complex carbohydrate) into simpler sugars like maltose. Saliva also moistens food, making it easier to chew and swallow. It helps in cleaning the mouth and killing some bacteria.

Question 7: What are the necessary conditions for autotrophic nutrition and what are its by-products?

The necessary conditions for autotrophic nutrition are: presence of chlorophyll (or other photosynthetic pigments), sunlight, carbon dioxide, and water. The by-products of photosynthesis are oxygen and glucose (which is stored as starch).

Question 8: What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

Aerobic respiration occurs in the presence of oxygen and completely breaks down glucose into carbon dioxide and water, releasing more energy. Anaerobic respiration occurs in the absence of oxygen and partially breaks down glucose, releasing less energy. The products can be ethanol and carbon dioxide (in yeast) or lactic acid (in muscles).

Organisms that use anaerobic respiration include yeast (which performs fermentation), some bacteria, and our muscle cells during heavy exercise.

Question 9: How are the alveoli designed to maximise the exchange of gases?

Alveoli are designed to maximise gas exchange in several ways. First, there are millions of alveoli in each lung, providing a huge surface area (about 80 square metres). Second, the walls of alveoli are very thin (only one cell thick), allowing easy diffusion. Third, each alveolus is surrounded by a dense network of capillaries that carry blood for efficient exchange. Fourth, the alveoli always contain some residual air, ensuring continuous exchange.

Question 10: What would be the consequences of a deficiency of haemoglobin in our bodies?

Deficiency of haemoglobin leads to a condition called anaemia. In anaemia, the blood cannot carry enough oxygen to all parts of the body. This causes fatigue, weakness, pale skin, shortness of breath, and reduced immunity. Children and pregnant women are particularly vulnerable to anaemia.

Question 11: Describe double circulation of blood in human beings. Why is it necessary?

Double circulation means that blood passes through the heart twice in one complete cycle. Deoxygenated blood from the body enters the right atrium, goes to the right ventricle, and is pumped to the lungs for oxygenation. Oxygenated blood from the lungs enters the left atrium, goes to the left ventricle, and is pumped to the rest of the body. This separation ensures that oxygen-rich blood does not mix with oxygen-poor blood. It is necessary for warm-blooded animals like mammals and birds to efficiently supply oxygen to all parts of the body to meet their high energy needs for maintaining body temperature.

Question 12: What are the differences between the transport of materials in xylem and phloem?

Xylem transports water and minerals from roots to leaves. This is a one-way transport. It is driven by physical forces like root pressure and transpiration pull. Xylem consists of vessels and tracheids.

Phloem transports products of photosynthesis (sugars) from leaves to other parts of the plant. This is a two-way transport (both upward and downward). It requires energy (ATP) and is driven by osmotic pressure. Phloem consists of sieve tubes and companion cells.

Question 13: Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

Both alveoli and nephrons are designed for exchange of materials. Alveoli are for gas exchange - oxygen from inhaled air diffuses into blood, and carbon dioxide from blood diffuses into alveolar air. They have thin walls and a large surface area surrounded by capillaries.

Nephrons are for filtering blood - they filter waste products from blood and re-absorb useful substances. Each nephron has a Bowman's capsule, glomerulus, and a long tubule. Blood is filtered under pressure, and then useful substances are re-absorbed.

Both are adaptations that increase surface area for efficient exchange or filtration.

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

In this chapter, we studied life processes, which are essential for maintaining life. We learned that movement of various types can be taken as an indication of life, and maintenance of life requires processes like nutrition, respiration, transport of materials within the body, and excretion of waste products.

We studied autotrophic nutrition, where organisms like green plants make their own food using carbon dioxide, water, sunlight, and chlorophyll. We learned about photosynthesis and the equation for it. We also studied heterotrophic nutrition, where organisms depend on other organisms for food.

We studied nutrition in human beings, including the alimentary canal and the process of digestion. We learned about the mouth, oesophagus, stomach, small intestine, and large intestine. We learned about various enzymes and their functions.

We studied respiration, including aerobic and anaerobic respiration. We learned about the breakdown of glucose into pyruvate and then into carbon dioxide and water (aerobic) or ethanol and carbon dioxide (anaerobic in yeast) or lactic acid (anaerobic in muscles). We learned about ATP as the energy currency of cells.

We studied the human respiratory system, including the lungs, alveoli, and the mechanism of breathing. We learned about haemoglobin and its role in oxygen transport.

We studied transportation in human beings, including the heart, blood vessels (arteries, veins, capillaries), and blood. We learned about double circulation and the importance of separating oxygenated and deoxygenated blood.

We studied transportation in plants, including xylem (for water and mineral transport) and phloem (for food transport). We learned about transpiration and translocation.

We studied excretion in human beings, including the kidneys, nephrons, and the process of urine formation. We learned about the structure and functioning of nephrons. We also learned about artificial kidney (hemodialysis) and organ donation.

We studied excretion in plants, including how they get rid of oxygen, water, and other waste products.

This is a very important chapter that helps us understand how our body works and how other living organisms function. I hope you all have understood these concepts well. Thank you for your attention, and keep studying!