Life Processes
Why This Matters
How do you know a dog is alive but a stone is not? You might say a dog moves and breathes. But a plant stands perfectly still, and it is alive too. A sleeping person hardly moves, and they are alive too. So “can I see it moving?” is not the real test of life.
The real test is hidden inside. Every living body is built in a neat, ordered way. Organs are made of tissues. Tissues are made of cells. Cells are made of tiny molecules. Everything around us is slowly trying to break this order down. Think of how food rots, iron rusts, and old things fall apart. To stay alive, a body must keep repairing and rebuilding itself all the time, even while you sleep.
Before we see how that repair happens, let us quickly recall what a body is actually built from — the ladder of cells, tissues and organs you met in Class 9.
This repair work needs two things from outside. It needs energy. It needs raw material to build with. The body must also throw out its waste.
The jobs that do all this maintenance are called the life processes. A “life process” is simply a basic job a body must keep doing to stay alive. This chapter covers the four big ones: nutrition, respiration, transportation and excretion. We will see how your body, a plant, and even a single-celled Amoeba (a tiny animal made of just one cell) each manage to do them.
The Big Idea
A living body is built in a neat, ordered way, and that order is always trying to break down. To stay alive, the body must keep fixing itself. For that it needs food (nutrition), a way to get energy out of that food (respiration), a way to move things around inside the body (transportation), and a way to throw out waste (excretion).
In a tiny organism made of just one cell, the whole outer surface touches the outside world. So food, gases and waste can simply seep in and out through the surface. This slow seeping is called diffusion (diffusion means molecules spreading on their own from where there are many of them to where there are few). For example, the smell of agarbatti spreads across a room by diffusion.
But your body is huge and made of billions of cells. Most of your cells are deep inside, far from your skin. Diffusion is far too slow to reach them. This one problem is the reason big living things slowly developed special systems to do the work: a digestive system for food, lungs for air, a heart-and-blood system to carry things around, and kidneys to clean out waste.
But why exactly does being big spoil the trick that works fine for a tiny cell? The reason is a simple matter of shape. As something grows bigger, its inside (its volume) shoots up much faster than its outside (its surface). So in a big body the centre ends up sitting very far from any surface — and diffusion only works over tiny distances. Figure 5.1 below makes this clash visible.
Hold on to this one idea: the body’s order must be kept up, and in a big body diffusion alone is too slow to do it. Once you remember that, every system in this chapter will make sense.
Let’s Break It Down
Nutrition: getting food
Nutrition means taking in food and using it for energy and growth. For example, when you eat a roti, that is nutrition. Every living thing needs energy and raw material. The difference is in how they get their food.
- Autotrophs make their own food. (“Auto” means self, so an autotroph is a “self-feeder”.) They build food from simple things around them: carbon dioxide gas (CO₂) and water, using the energy of sunlight. Green plants and some bacteria are autotrophs.
- Heterotrophs cannot make their own food. (“Hetero” means other, so a heterotroph is an “other-feeder”.) They take in ready-made food and break it down. Animals and fungi (like mushrooms) are heterotrophs. In the end, they all depend on autotrophs for food, either directly or indirectly.
The way autotrophs make their own food is called photosynthesis. “Photo” means light and “synthesis” means making, so photosynthesis is “making food using light”. Here is the reaction:
6CO₂ + 12H₂O →[chlorophyll, sunlight] C₆H₁₂O₆ + 6O₂ + 6H₂O
Three things happen during photosynthesis. First, a green colour inside the leaf called chlorophyll soaks up sunlight. Second, the energy from that light splits water apart, and this is where the oxygen gas (O₂) comes from. Third, the CO₂ is turned into a sugar called glucose (C₆H₁₂O₆). The plant joins many glucose units together and stores them as starch (the same starch in rice and potatoes).
The CO₂ gets into the leaf through tiny holes called stomata (one hole is a “stoma”). These holes can open and close. The water reaches the leaf by travelling up from the roots.
Slice a leaf open and you can see all these parts working together. Figure 5.2 below shows how the chloroplasts, air spaces, vein and stoma are arranged.
A stoma is the little hole itself. On each side of it sits a curved, bean-shaped cell called a guard cell. These two guard cells control the hole. When they fill up with water, they swell and bend apart, and the hole opens, so gases can move in and out. When they lose water, they go soft and limp, and the hole closes, which stops water from escaping the leaf. This is how a plant decides when to let gases pass.
Figure 5.3 below shows the same stoma both ways — wide open and shut tight — so you can see exactly how the guard cells change shape.
Nutrition in human beings
In humans, food travels down one long tube that runs from the mouth to the back end of the body. This tube is called the alimentary canal (it is also just called the food pipe and gut). As food moves along it, the food is broken down step by step. Breaking food down into simple parts the body can use is called digestion. But before we trace that journey, there is one helper that shows up at almost every step — the enzyme. Let us see what it is.
Now follow a mouthful of food from start to finish. This table lays out each stop — mouth, stomach, small and large intestine — and what gets done to the food there.
| Place | What happens | Key juice / enzyme |
|---|---|---|
| Mouth | Teeth crush food; saliva wets it and starts digesting starch | Salivary amylase (starch → sugar) |
| Stomach | Muscular walls churn; acid kills germs & activates enzyme | HCl + pepsin (proteins) + mucus |
| Small intestine | Complete digestion of carbs, proteins & fats; absorption | Bile (emulsifies fat), pancreatic juice (trypsin, lipase), intestinal juice |
| Large intestine | Absorbs water from the leftover | — |
The small intestine is where most of the digestion and absorption happens. (“Absorption” means the digested food passing from the gut into the blood.) A juice called bile comes here from the liver. Bile does two jobs. It makes the food alkaline (the opposite of acidic), which the next enzymes need. It also breaks large blobs of fat into many tiny droplets. Breaking big fat blobs into small droplets is called emulsification. It works just like soap breaking up oily grease on a dirty plate (you saw this in Chapter 4).
The inside wall of the small intestine is not smooth. It is covered with millions of tiny finger-like bumps called villi (one bump is a “villus”). These bumps give the wall a much larger surface, so the digested food can pass into the blood quickly. Think of how a folded towel can soak up far more water than a flat sheet.
But how does folding add surface without making the gut any wider? Picture running a thread along a flat wall, then along the same wall after it has been crumpled into ridges — the second thread is far longer even though the wall is the same width. The villi crumple the gut wall in exactly this way, and food touches every part of that longer surface. Figure 5.4 below makes the difference clear.
Figure 5.5 below shows the whole digestive system in one picture — trace the tube from the mouth right down to the large intestine, and spot where the liver and pancreas join in.
Respiration: releasing the energy
Eating food is not enough. The energy is locked up inside the food, and the body must release it to use it. Respiration is the process that breaks down food inside cells to set this energy free. The energy comes out in a usable form called ATP. You can think of ATP as the energy “money” of the cell. The cell makes ATP from food, then spends ATP to do its work.
The first step is always the same. A glucose molecule (which has 6 carbon atoms) is split into two smaller molecules called pyruvate (each has 3 carbon atoms). This happens in the cytoplasm, the jelly-like fluid that fills the cell. What happens to the pyruvate next depends on whether oxygen is present:
| Pathway | Where / when | Products | Energy |
|---|---|---|---|
| Aerobic (with O₂) | Mitochondria | CO₂ + water | A lot |
| Anaerobic — fermentation | Yeast cells | Ethanol + CO₂ | Less |
| Anaerobic — in our muscles | Muscle cells, low O₂ | Lactic acid | Less |
When you run hard, your muscles cannot get oxygen fast enough. So they switch to the third pathway and make lactic acid. This lactic acid is what builds up and gives you those painful muscle cramps.
Now, where does the oxygen come from? It comes from breathing. Breathing means taking air in and pushing it out. In humans, air enters through the nostrils, goes down the throat, and reaches the lungs. The throat is held open by stiff rings of cartilage (cartilage is the firm but bendy stuff you can feel at the tip of your nose and in your ears) so the air passage never collapses shut.
Inside the lungs, the air ends up in millions of tiny balloon-like bags called alveoli (one bag is an “alveolus”). If you spread all of them out flat, they would cover about 80 square metres, roughly the size of a small flat!
But why do the gases move at all? And why so fast? There are two reasons, and NCERT rushes past both.
The first reason is diffusion, the same slow seeping we met at the start of the chapter. Gases always drift from where there are many of them to where there are few. The fresh air you breathe in is packed with O₂ and has almost no CO₂. The blood arriving from your body is the exact opposite — it is low on O₂ and loaded with CO₂. So O₂ drifts from the air into the blood, and CO₂ drifts from the blood into the air. Nobody pushes them. They just even themselves out.
The second reason is distance. Diffusion is hopelessly slow over long distances, but it is very fast over short ones. And here the distance is almost nothing. The wall between the air and the blood is only two cells thick — one cell of the air sac, one cell of the blood vessel. On top of that, the blood is right there: every alveolus has a capillary hugging its outside. So the gases have barely any distance to cross.
Put those together and you get the design of a lung: an enormous surface (80 m²), an extremely thin barrier, and blood flowing right past it. Figure 5.6 below shows all three at once.
The oxygen is then carried around by a red-coloured substance called haemoglobin, found in the red blood cells. CO₂ dissolves in water more easily, so it is carried mostly dissolved in the watery part of blood (the plasma). Fish live in water, which holds far less oxygen than air, so fish breathe faster and use gills instead of lungs to take in oxygen from the water.
Pause here and test the big idea of the chapter — why a large animal cannot just rely on gases seeping in on their own.
Why is diffusion alone not enough to supply oxygen to all the cells of a large animal like a human?
In a big body, most cells are buried deep inside, far from the skin where the air is. Diffusion (oxygen slowly seeping on its own) is far too slow to cover such a long distance. In fact, people have worked out that an oxygen molecule would take about 3 years to diffuse from the lungs all the way to the toes! That is why big animals need a transport system (blood with haemoglobin) to carry oxygen quickly to every cell.
One more quick check before we move on — make sure you have the steps of respiration in the right order.
In which order does glucose get broken down to release energy with oxygen?
Glucose is first split into pyruvate in the cytoplasm. This happens the same way in everyone. When oxygen is present, the pyruvate is then broken down in the mitochondria into CO₂ and water. This releases a lot of energy, and we call it aerobic respiration.
Transportation in human beings
Transportation means carrying things from one part of the body to another. In humans, blood does this carrying. Blood is a flowing tissue. It has a watery part called plasma, which carries dissolved food, CO₂ and waste. It also has cells floating in it: red blood cells carry the oxygen, and platelets help seal a cut by forming a clot (this is why a wound stops bleeding and forms a scab).
To push the blood around, the body has a pump called the heart. The heart has four rooms inside it, called chambers. The four chambers keep oxygen-rich blood and oxygen-poor blood apart, so the two never get mixed together. Figure 5.7 below looks inside the heart to show those four chambers, the big vessels that join them, and which side handles which kind of blood.
Let us follow the blood step by step. The upper chambers are called atria (one is an “atrium”) and the lower ones are called ventricles. Oxygen-rich blood comes from the lungs into the left atrium. It drops into the left ventricle. From there it is pumped out to the whole body. After the body uses up the oxygen, the now oxygen-poor blood (full of CO₂) comes back into the right atrium. It drops into the right ventricle. From there it is pumped to the lungs to pick up fresh oxygen.
Notice that in one full round, the blood passes through the heart two times (once on the way to the body, once on the way to the lungs). Because of this, we call it double circulation. This double trip keeps the oxygen-rich and oxygen-poor blood completely separate. This matters most for warm-blooded animals like birds and mammals (such as us), because they use a lot of energy to keep their body warm and need a steady, full supply of oxygen.
Figure 5.8 below traces both loops at once — follow the arrows to see how blood crosses the heart twice on one full journey around the body.
Blood travels through three kinds of tubes:
- Arteries carry blood away from the heart. The heart pushes blood into them with great force, so they have thick, stretchy walls to handle that high pressure.
- Veins carry blood back to the heart. They have small flaps called valves inside that stop the blood from flowing backward.
- Capillaries are the tiniest tubes. Their walls are just one cell thick. This is where the blood actually hands over oxygen and food to the body’s cells and takes back their waste.
But why do veins need valves when arteries do not? In an artery the heart’s strong push keeps the blood moving forward, so there is little danger of it slipping back. A vein is different: by the time blood reaches it, the heart’s push has almost worn off, and in your legs the blood must even climb upward against gravity to get back to the heart. With such a gentle, slow flow, the blood could easily drift backward. A valve solves this with a pair of tiny flaps that act like a one-way gate. Figure 5.9 below shows how they swing open and shut depending on which way the blood tries to move.
Transportation in plants
Plants also need to move things around, but they do it slowly. A plant does not run or jump, and many of its cells are dead, so it does not need much energy and is in no hurry. But a tall tree must still lift water all the way up from its roots to its top leaves, which can be very high.
But first, how does the water even get into the plant? Roots do not have a pump, so they use a clever trick called osmosis — worth a quick refresher.
Once water is inside, the plant uses two separate pipelines to move things around — one going up, one going both ways:
- Xylem carries water and minerals upward from the roots. First, the root cells pull in minerals, and water follows them in. This builds up a small push from below called root pressure. But the main force is a pull from above called transpiration. Transpiration means water evaporating (turning to vapour) out of the leaves. As water leaves the top, it pulls the whole column of water up behind it, just like sucking a drink up through a straw.
- Phloem carries food (the sugar made in the leaves) down and across to the rest of the plant. Moving this food around is called translocation. Unlike water movement, this needs energy (ATP), and the food can be sent either up or down, wherever the plant needs it.
Excretion: removing wastes
Excretion means throwing out the harmful waste that the body makes. When the body breaks down proteins (found in foods like dal, eggs and paneer), it produces waste containing nitrogen, such as a chemical called urea. These nitrogenous wastes are poisonous, so the body must clear them out. In humans, the set of organs that does this is the excretory system. It is made of a pair of kidneys, two tubes called ureters, a urinary bladder, and one more tube called the urethra.
The real cleaning happens inside the kidney, in a tiny unit called a nephron. Figure 5.10 below zooms right in to show how one nephron filters blood and saves the good stuff.
Each kidney holds millions of tiny filtering units called nephrons. The blood is first filtered in a small ball of capillaries called the glomerulus, which sits inside a cup-shaped part called the Bowman’s capsule. The filtered liquid then flows along a long, thin tube. As it flows, the useful things in it (glucose, amino acids, salts and most of the water) are taken back into the blood. Taking the useful things back is called reabsorption. What is left behind (urea, extra water and extra salts) becomes urine. If a person’s kidneys stop working, a machine called an artificial kidney can clean the blood instead. This cleaning process is called dialysis.
Plants get rid of waste in their own way. The oxygen made during photosynthesis is a waste product for the plant, and it lets it out. Extra water leaves through transpiration. Other waste is stored inside the plant in little storage bags called vacuoles, or kept in old leaves that later drop off, or turned into resins and gums, or simply passed out into the soil.
Back to the nephron for a moment — here is a question that catches many students out about what ends up in the urine.
In a nephron, why is glucose normally absent from the urine of a healthy person?
Glucose does get filtered into the nephron at the glomerulus. But as the liquid flows along the tubule, useful things like glucose are taken back into the blood (reabsorbed). So in a healthy person, no glucose is left to show up in the urine.
Common Mistakes
Plants only respire during the day, and they only photosynthesise — they don't really 'breathe'.
We are taught that plants 'take in CO₂ and give out O₂', so it sounds like the opposite of breathing.
Plants respire ALL the time, day and night, just like us. During the day, photosynthesis is so fast that it uses up the CO₂ the plant makes by respiring and gives out extra O₂. This hides the respiration from view, but respiration never stops.
Arteries always carry oxygen-rich blood, and veins always carry oxygen-poor blood.
This is true for most blood vessels, so people assume it is true for all of them.
The real rule is about direction, not oxygen. Arteries carry blood AWAY from the heart. Veins carry blood BACK to the heart. There are two exceptions: the pulmonary artery carries CO₂-rich blood (from heart to lungs), and the pulmonary vein carries O₂-rich blood (from lungs to heart).
Xylem carries food, and phloem carries water.
The two names sound similar, so they are easy to mix up.
It is the other way around. Xylem carries WATER and minerals UP from the roots (pulled by transpiration). Phloem carries FOOD (sugar) made in the leaves to all parts of the plant (this is translocation, and it uses energy). An easy way to remember: phloem = food.
Bile is a digestive enzyme that breaks down fat.
Bile acts on fat, so it sounds like it must be an enzyme.
Bile has NO enzymes at all. It does two other jobs. It makes the food alkaline, so the pancreatic enzymes can work. And it emulsifies fat, meaning it breaks big fat blobs into tiny droplets. This lets the fat-digesting enzyme (lipase) work on them much faster.
Quick Check
Why is the small intestine longer in herbivores than in carnivores?
Grass and leaves are full of cellulose, which is hard to break down. So plant-eaters (herbivores) need a longer small intestine and more time to digest it. Meat is much easier to digest, so meat-eaters (carnivores) like tigers have a shorter one.
The contraction-and-relaxation waves that push food along the alimentary canal are called:
The muscle in the wall of the gut squeezes and relaxes again and again in waves. These waves are called peristaltic movements (peristalsis). They push the food forward along the whole digestive tube, the same way you squeeze toothpaste along the tube.
Practice Problems
These are written by Curriv and are completely free. Try before revealing.
Easy
What is the role of saliva in the digestion of food?
Saliva does two main jobs. First, it wets the food so it becomes soft and slides down the throat easily. Second, it carries an enzyme called salivary amylase, which starts breaking starch down into simple sugar right there in the mouth. The tongue helps by mixing the food and saliva together while you chew.
Name the parts of the human excretory system in the order urine passes through them.
Kidneys (these make the urine) → ureters (these carry it down) → urinary bladder (this stores it) → urethra (this lets it out of the body).
Medium
What are the differences between aerobic and anaerobic respiration? Name an organism that uses anaerobic respiration.
- Aerobic respiration uses oxygen, takes place in the mitochondria, and breaks glucose fully into CO₂ + water, releasing a lot of energy.
- Anaerobic respiration happens without oxygen, in the cytoplasm, and gives products like ethanol + CO₂ (or lactic acid in our muscles), releasing much less energy.
An organism using anaerobic respiration: yeast (during fermentation).
Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Mammals and birds are warm-blooded. This means they keep using energy all the time to hold their body at a steady, warm temperature. So they have high energy needs. A four-chambered heart keeps the two blood streams apart, so the body cells always receive fully oxygen-rich blood. This gives the cells the most efficient oxygen supply, which is exactly what their high energy demand needs.
Challenge
How is the small intestine designed to absorb digested food efficiently? Give two features.
- It is very long and coiled up. This gives the food a long path and plenty of time to be absorbed.
- Its inner wall is covered with millions of finger-like bumps called villi. These bumps give a much larger surface area for absorption. Each villus is full of blood vessels, which take the absorbed food away to every cell of the body.
Compare the alveoli in the lungs and the nephrons in the kidneys — how are they similar in design?
They share a lot in common. Both are tiny units. Both are present in huge numbers. Both are built to give a very large surface area for their work. And both are wrapped in a fine net of thin-walled blood capillaries:
- Alveoli swap gases — they let O₂ into the blood and CO₂ out.
- Nephrons filter the blood — they take out nitrogenous waste while putting the useful substances back.
So both designs do the same trick: pack in a large surface and wrap it in capillaries. The alveoli use this to exchange gases, and the nephrons use it to clean out liquid waste.
Summary
- Life processes keep a living body’s order maintained: nutrition, respiration, transportation, excretion. Big bodies need specialised systems because diffusion alone is too slow.
- Nutrition: autotrophs make food by photosynthesis (CO₂ + water + sunlight → glucose, via chlorophyll; stomata let gases in/out). Heterotrophs eat ready-made food. In humans, food is digested along the alimentary canal (amylase in mouth → HCl + pepsin in stomach → bile + pancreatic + intestinal juices in the small intestine, absorbed by villi).
- Respiration: glucose → pyruvate (cytoplasm); then aerobic (mitochondria, O₂ → CO₂ + water, lots of ATP) or anaerobic (yeast → ethanol+CO₂; muscles → lactic acid → cramps). Breathing uses alveoli + haemoglobin.
- Transport in humans: four-chambered heart, double circulation; arteries (away), veins (back), capillaries (exchange).
- Transport in plants: xylem (water up, by transpiration pull); phloem (food, by translocation, using energy).
- Excretion: kidneys’ nephrons filter blood and reabsorb the useful parts; dialysis replaces failed kidneys. Plants use vacuoles, falling leaves, resins, gums and the soil.
What’s Next
You have now seen how a body keeps itself running. It takes in food, releases energy, moves things around, and clears out waste. But how does the body manage all of this together, and how does it react to the world around it? In Chapter 6: Control and Coordination, you will meet the nervous system, reflexes, the brain, and the hormones that quietly control everything. In short, you will learn how a living body senses what is happening, decides what to do, and then acts.
Frequently Asked Questions
What are the four main life processes in Class 10 Science?
The four main life processes are nutrition, respiration, transportation, and excretion. Nutrition provides raw materials and energy; respiration releases that energy from food; transportation moves nutrients, gases, and waste around the body; and excretion removes the waste products. Every living thing — animal, plant, or single-celled organism — must carry out all four to stay alive.
What is the difference between aerobic and anaerobic respiration?
Aerobic respiration uses oxygen to break down glucose completely, releasing a large amount of energy along with carbon dioxide and water. Anaerobic respiration happens without oxygen — it only partly breaks down glucose, so it releases much less energy and produces different waste products (lactic acid in muscles, or alcohol and CO₂ in yeast). Your muscles switch to anaerobic respiration during intense exercise when oxygen runs short, which is why they ache afterwards.
Why do we breathe out carbon dioxide?
When cells burn glucose for energy (respiration), carbon dioxide is produced as a waste gas. This CO₂ builds up in body cells, passes into the blood, travels to the lungs, and is breathed out. If CO₂ were allowed to build up inside cells, it would make the cell fluid acidic and damage the cell, so the body must remove it continuously.
How does the heart achieve double circulation in humans?
In double circulation, blood passes through the heart twice for every one full trip around the body. First, the right side of the heart pumps oxygen-poor blood to the lungs (pulmonary circuit), where it picks up oxygen. Then the blood returns to the left side of the heart, which pumps the now oxygen-rich blood out to the rest of the body (systemic circuit). Keeping the two circuits separate ensures that oxygenated and deoxygenated blood never mix, so every organ gets blood with the maximum possible oxygen.
What is the role of nephrons in the kidney?
A nephron is the tiny filtering unit inside each kidney — you have about a million nephrons per kidney. Blood flows into a cup-like structure at one end (the Bowman's capsule), and the nephron filters out waste, excess water, salts, and urea from the blood. As the filtered liquid travels along the nephron tube, useful substances like glucose and most of the water are reabsorbed back into the blood. What is left — concentrated urine — drains out to the bladder.