Life Processes — Class 10 Science Notes & Practice

A rock sitting in the sun does nothing to stay a rock. A living body is the opposite: it has to work continuously just to stay alive. It pulls in raw material, releases energy from it, moves that material to every cell, and pushes the waste out. Those four jobs — nutrition, respiration, transportation and excretion — are what this chapter calls life processes.

Life Processes is Chapter 5 of the current NCERT Class 10 Science textbook and it sits inside Unit II: World of Living, which carries 25 marks in the 80-mark theory paper. It is one of the largest chapters in the book, and it is generous in the exam: diagrams, definitions, comparisons and reasoning questions all come from here. The trap is that it looks like pure memorisation. It is not. Almost every fact in this chapter is an answer to the question “why is it built that way?” — and if you learn it that way, you will not forget it.

What This Chapter Covers

• Nutrition: autotrophic and heterotrophic modes
• Nutrition in human beings: the alimentary canal
• Respiration: aerobic, anaerobic and the human respiratory system
• Transportation in human beings and in plants
• Excretion in animals and in plants
• Dialysis and the artificial kidney
• Practice worksheet with answers

Your Game Plan for This Chapter

This chapter rewards drawing more than it rewards reading. Work through it in this order:

1. Learn the four processes as a set first. Before any detail, be able to say in one line each what nutrition, respiration, transportation and excretion do. Everything else hangs off that frame.
2. Draw five diagrams until you can do them from memory: the human digestive system, a section of the human respiratory system showing alveoli, the human heart with the four chambers labelled, a nephron, and an open stoma with its guard cells. These five carry a lot of marks.
3. Attack it in plant/animal pairs. Do nutrition in plants and nutrition in animals together, then transportation in plants and in animals together. The comparison is where the exam lives.
4. Turn every structure into a reason. Alveoli are folded — why? The left ventricle wall is thick — why? Do this out loud and long-answer questions stop being scary.
5. Finish with the worksheet below and only open an answer after you have written yours down.

Study Notes

1. Nutrition: Autotrophic and Heterotrophic Modes

Nutrition is how an organism takes in and uses food. Organisms split into two camps by where their food comes from. Autotrophs build their own food from simple inorganic material using an outside energy source — green plants and some bacteria. Heterotrophs cannot build it and must take in food made by others — all animals, all fungi, and most bacteria.

In green plants, autotrophic nutrition happens by photosynthesis: carbon dioxide and water are converted into carbohydrate using sunlight captured by chlorophyll, with oxygen released as a by-product.

The carbon dioxide enters mainly through stomata — tiny pores on the leaf surface, each guarded by a pair of bean-shaped guard cells. When water flows into the guard cells they swell, curve apart and the pore opens. When water flows out they shrink, straighten and the pore closes. Because open stomata also lose a lot of water, plants keep them shut when photosynthesis is not happening.

Heterotrophs differ in how they get the ready-made food:

Worked Example 1. A potted plant is kept in a completely dark cupboard for three days, then one leaf is partly covered with black paper and the plant is moved into sunlight for a day. The leaf is tested for starch. Which part turns blue-black, and why?
Only the uncovered part turns blue-black. Three days in the dark used up the starch already stored in the leaf, so the plant started from zero. In sunlight, only the exposed part could absorb light, so only there could photosynthesis run and fresh starch form. The covered part had chlorophyll, carbon dioxide and water but no light — proving light is essential.

Worked Example 2. Cuscuta grows twined around a host plant and has no chlorophyll of its own; a mushroom grows on a rotting log. Both depend on other organisms. Why is only one of them called a parasite?
The test is whether the food source is alive. Cuscuta draws nutrition from a living host through specialised structures, so it is parasitic. The mushroom secretes enzymes onto dead, decaying wood and absorbs the products, so it is saprophytic. Same dependence, different source — living versus dead.

2. Nutrition in Human Beings: The Alimentary Canal

Human nutrition is holozoic and it happens along one long tube — the alimentary canal, running from mouth to anus. Food is moved along by rhythmic muscular contractions of the wall called peristalsis, and at each station a specific enzyme works on a specific food type at a specific pH.

Digestion finishes in the small intestine, and so does absorption. Its inner lining is thrown into thousands of finger-like projections called villi, which multiply the surface area enormously and are richly supplied with blood vessels. The large intestine digests nothing; it absorbs most of the remaining water, and the rest is removed through the anus.

Worked Example 1. Bile contains no digestive enzyme at all. Explain why fat digestion becomes very inefficient if bile stops reaching the small intestine.
Fat arrives in the intestine as large globules. Lipase can only act on the surface of a globule, so a few large globules offer very little working area. Bile does two things without being an enzyme: it makes the acidic food coming from the stomach alkaline, which is the pH pancreatic lipase needs, and it emulsifies the fat, breaking large globules into many tiny droplets with a far greater total surface area. Remove bile and lipase is left working slowly on a small surface in the wrong pH.

Worked Example 2. A person has a section of the small intestine surgically removed. Predict two effects and give the reason.
First, poorer absorption of nutrients, leading to weakness and weight loss — the small intestine is where villi absorb the digested food, so less length means less absorbing surface. Second, incomplete digestion of some food — the small intestine is where bile, pancreatic juice and intestinal juice finish the job, so food may pass on before it is fully broken down. Both effects trace back to the same cause: reduced surface and reduced time.

3. Respiration: Aerobic, Anaerobic and the Human Respiratory System

Digestion delivers glucose. Respiration is the process that releases the energy locked inside it. The first step is the same everywhere: in the cytoplasm, a six-carbon glucose molecule is broken into two three-carbon molecules of pyruvate. What happens to the pyruvate next depends on whether oxygen is available.

In humans, the oxygen for aerobic respiration arrives through the respiratory system. Air enters through the nostrils, where hair and mucus filter it, passes down the trachea — held permanently open by rings of cartilage — and branches into bronchi, then finer bronchioles, ending in balloon-like alveoli.

The alveoli are where the actual exchange happens. Their walls are one cell thick and covered in a dense net of blood capillaries. Together, the alveoli of an adult provide a gas-exchange surface of roughly 80 square metres — an area many times that of the skin, packed into the chest.

Worked Example 1. After sprinting hard, your leg muscles ache and you keep breathing heavily even after stopping. Explain both observations.
During a sprint, the muscles demand energy faster than the blood can deliver oxygen. Pyruvate is then broken down without enough oxygen into lactic acid, which accumulates in the muscle and causes cramps and aching. The heavy breathing afterwards supplies the extra oxygen needed to clear that accumulated lactic acid — which is why the panting continues even though you have stopped running.

Worked Example 2. Why do terrestrial organisms have a much smaller respiratory surface, relative to body size, than aquatic organisms need — and why do fish die when taken out of water?
Air contains far more oxygen per unit volume than water does. A land animal can therefore meet its needs with a comparatively compact organ. An aquatic organism, drawing oxygen dissolved in water, must pass large volumes over a large surface and so breathes faster. A fish has gills, which are adapted to absorb dissolved oxygen from water; in air the delicate gill filaments stick together and collapse, the exchange surface is lost, and the fish cannot absorb oxygen even though it is surrounded by it.

4. Transportation in Human Beings and in Plants

Digestion and respiration are useless if the products stay where they were made. Transportation moves them. In humans the carrier is blood, pushed by the heart through a closed network of vessels.

The human heart has four chambers: two upper atria and two lower ventricles. Deoxygenated blood from the body enters the right atrium, passes to the right ventricle, and is pumped to the lungs. Oxygenated blood returns from the lungs to the left atrium, passes to the left ventricle, and is pumped out to the whole body. Valves between and beyond the chambers make sure blood only ever moves forward.

Alongside blood runs lymph — a pale yellow fluid that escapes from capillaries into the surrounding tissue, carries digested fat absorbed from the intestine, and drains back into the veins. Blood also carries platelets, which plug leaks by clotting so blood is not lost from a wound.

Plants have no heart. They run two separate one-way pipelines instead:

Worked Example 1. Why is the wall of the left ventricle much thicker than the wall of the right ventricle?
Both ventricles pump, but not the same distance. The right ventricle sends blood only to the lungs, which are close by and need gentle pressure. The left ventricle must push blood through the entire body, all the way to the toes and the brain, against much greater resistance. Generating that higher pressure requires more muscular force, so its wall is thicker. Structure follows workload.

Worked Example 2. A ring of bark is removed from all the way around a tree trunk. Over the following weeks the region above the ring swells and the tree eventually dies. Explain.
The bark contains the phloem; the xylem lies deeper in the wood and is untouched. So water still travels up from the roots and the leaves keep photosynthesising — but the food they make can no longer travel down past the cut. It accumulates just above the ring, causing the swelling. The roots, receiving no food, cannot respire or grow, so they die; without roots the tree loses its water supply and dies too.

5. Excretion in Animals and in Plants

Every chemical reaction inside a cell leaves residue. Breaking down proteins in particular produces nitrogenous wastes, which are toxic if allowed to build up. Excretion is the removal of these harmful metabolic wastes from the body.

In humans the job belongs to the excretory system: a pair of kidneys, a pair of ureters, the urinary bladder and the urethra. Inside each kidney are around a million microscopic filtering units called nephrons.

A nephron works in two stages. First, blood arrives at a cluster of capillaries — the glomerulus — sitting inside a cup-shaped Bowman’s capsule. Pressure forces water and small dissolved substances out of the blood into the capsule. This filtration is indiscriminate: useful glucose, amino acids and salts pass out along with the wastes. Second, as the filtrate travels down the long tubule, the substances the body still needs are selectively reabsorbed back into the surrounding blood capillaries. What remains is urine, which collects in a duct and passes to the bladder.

How much water is reabsorbed is not fixed. It depends on how much surplus water the body has and on how much dissolved waste needs to be flushed out — which is why urine output rises after drinking a lot of water and falls on a hot day when you have been sweating.

Plants face the same problem with far less urgency, because they produce waste more slowly and can afford to store it. Their strategies:

• Gaseous wastes — oxygen from photosynthesis and carbon dioxide from respiration — leave through the stomata and through pores in the stem.
• Excess water is removed by transpiration.
• Many wastes are stored in cell vacuoles, or in leaves that are about to fall.
• Resins and gums are stored in old xylem that is no longer transporting anything.
• Some waste is simply secreted into the soil around the roots.

Worked Example 1. Glucose is present in the filtrate that enters a nephron, but a healthy person’s urine contains no glucose. Explain.
Glucose is a small molecule, so during filtration at the glomerulus it passes out of the blood along with water and salts — it is not screened out at that stage. But glucose is far too valuable to waste. As the filtrate moves along the tubule, glucose is selectively reabsorbed back into the blood capillaries wrapped around it. In a healthy person the reabsorption is complete, so none appears in urine. Glucose in urine therefore signals that the amount in the blood has exceeded what the tubule can reclaim.

Worked Example 2. On a hot day spent playing outdoors, a student passes a small volume of dark urine. On a cool day after drinking several glasses of water, the volume is large and pale. Explain using the working of the nephron.
The nephron adjusts water reabsorption to the body’s needs. On the hot day, a lot of water was lost as sweat, so the body is short of water; the tubule reabsorbs as much as it can, leaving a small volume of urine in which the wastes are concentrated — hence the dark colour. On the cool day there is surplus water and little sweating, so less is reabsorbed; a large volume of dilute, pale urine is produced. The quantity of waste removed is similar in both cases — only the water carrying it changes.

6. Dialysis and the Artificial Kidney

Kidneys can fail through infection, injury or restricted blood flow. When they do, nitrogenous waste — especially urea — builds up in the blood and quickly becomes dangerous. Dialysis is the artificial process used to remove it.

In a dialysis machine, blood is drawn from an artery, cooled slightly, and passed through tubes made of a selectively permeable membrane. These tubes sit in a tank of dialysing fluid, which has the same concentration of glucose and salts as normal blood plasma but contains no nitrogenous waste at all. Because of that difference, urea and other wastes diffuse out of the blood into the fluid, while glucose and salts — being at equal concentration on both sides — have no reason to move. The cleaned blood is then returned to a vein.

Worked Example 1. Why does the dialysing fluid contain glucose and salts at all? Would pure water not remove the waste faster?
Pure water would indeed remove urea quickly — but it would also strip out glucose, amino acids and essential salts, because each of those would have a steep concentration gradient from blood into water. The patient would lose vital substances along with the waste. Matching the fluid to normal plasma removes that gradient, so those substances stay in the blood while only urea, absent from the fluid, diffuses out.

Worked Example 2. A dialysis patient must attend sessions several times a week, whereas healthy kidneys work continuously. Why can dialysis not simply be done once a month?
Waste is produced continuously by the body’s ongoing metabolism, and a machine only removes it during a session. Between sessions, urea accumulates steadily in the blood with nothing to clear it. Leaving too long a gap would allow it to reach toxic levels. Frequent sessions are the compromise that keeps the waste concentration within a safe range without a permanently attached machine.

Practice Worksheet

Write your answer down before opening the accordion. Reading an answer you have not attempted teaches you almost nothing.

Aim for one more correct answer than yesterday. That is the whole method — small, repeated, honest improvement. Kaizen.