Life Processes — Complete Grade 10 Biology Guide

Part 1: learn by doing — your own body is the laboratory · five exam diagrams you will learn to draw · Part 2: going further, referenced to NIH, NASA and NOAA

Which syllabus are you studying?

Check your foundations first

This topic defeats students whose earlier basics are shaky. Fewer than three right? Read the refresher below.

1. What is diffusion?
2. How does osmosis differ from diffusion?
3. Give one function of the cell membrane.
4. Which organelle is the chloroplast, and which pigment does it hold?
5. What do enzymes do?

1. What are life processes?

A stone and a sleeping child are both motionless. Which is alive, and how would you tell?

Sit perfectly still for one minute — move nothing. Now write down every job your body carried on with during that minute.

Visible movement is not required — but molecular movement never stops. Body structures are constantly breaking down, so repair must be constant. That repair is called maintenance, and the processes that together carry it out are life processes.

This is why multicellular organisms need specialised organs — their inner cells are not in direct contact with the outside, so diffusion alone cannot serve them.

Level 1 Name the four life processes.

Level 2 What is maintenance, and why is it necessary?

Level 3 Why does Amoeba need no heart or lungs, while a human does?

2. Autotrophic nutrition — photosynthesis

Where does a tree's mass come from? If it is the soil, why does the soil in a pot never run out?

Keep a potted plant in the dark for three days. Cover half of one leaf with black paper and put the plant in sunlight. After six hours boil that leaf in alcohol to remove the green colour, then add iodine. Predict which half turns blue-black.

Organisms that make their own food from simple inorganic substances are autotrophs.

The three events of photosynthesis:

1. absorption of light energy by chlorophyll
2. conversion of light energy to chemical energy, and splitting of water into hydrogen and oxygen
3. reduction of carbon dioxide to carbohydrate

Most gas exchange happens through tiny pores on the leaf surface — stomata. Water also escapes through them as vapour, which is transpiration. When CO₂ is not needed the pores close, saving water. The opening and closing is done by water entering or leaving the guard cells.

Plants also take up nitrogen, phosphorus, iron and magnesium dissolved in the soil.

Answer: most of a tree's mass is carbohydrate built from carbon dioxide in the air and water, not from soil. The soil supplies water and a few minerals — which is why the pot does not empty.

Level 1 Which gas is released in photosynthesis?

Level 2 Why do stomata close, and how does the plant benefit?

Level 3 Why is the plant kept in the dark for three days first? What if that step were skipped?

3. Heterotrophic nutrition

Dodder has no green colour yet lives well. Mould eats bread without a mouth. How?

Dampen a piece of bread slightly and keep it covered for two days. Predict — mould grows, but what happens to the bread itself?

Nutrition in Amoeba: it surrounds food with pseudopodia, forming a food vacuole; complex substances are broken down there, absorbed, and the remainder is thrown out. In Paramecium food is taken in at a fixed spot, where cilia push it in.

In one line: a saprotroph digests outside and absorbs, a parasite takes what another has made, a holozoic feeder takes food in and digests it inside.

Level 1 What type of nutrition does dodder show?

Level 2 Describe nutrition in Amoeba from intake to egestion.

Level 3 Fungi and Amoeba are both heterotrophs. Why does a fungus need no food vacuole?

4. Nutrition in human beings

Chew a piece of bread for a long time without swallowing — why does it start to taste sweet?

Take a mouthful of bread or rice and chew for one whole minute without swallowing. What changed?

This is why you are told to chew your food — chewing increases surface area and gives salivary amylase a chance to work.

Level 1 Which acid is secreted in the stomach?

Level 2 Give two functions of bile.

Level 3 The stomach wall is itself made of protein, and pepsin digests protein. Why is the stomach not digested?

5. Respiration

Why do your calf muscles cramp after running — and why does the cramp fade once you rest?

In respiration glucose is broken down to release energy. The first step is the same in all organisms — glucose (6 carbons) breaks down in the cytoplasm to pyruvate (3 carbons). After that there are two routes:

Air enters through the nostrils, where hairs and mucus filter it, then passes down the windpipe into bronchi and bronchioles, ending in the alveoli. Alveolar walls are extremely thin and carry a net of blood capillaries — this is where gases are exchanged.

Oxygen is carried by the respiratory pigment haemoglobin, which has a high affinity for it. CO₂ is more soluble in water, so it travels back mostly dissolved.

In aquatic animals: fish take oxygen dissolved in water. Because water holds very little oxygen, their breathing rate is faster than that of land animals.

Alveoli are so numerous that their combined surface is vast — and diffusion is faster the more surface it has. The whole body follows one rule: wherever exchange is needed, increase the surface. Villi do it, alveoli do it.

Level 1 What three-carbon molecule is formed when glucose breaks down?

Level 2 Give three differences between aerobic and anaerobic respiration.

Level 3 A fish dies out of water, although air holds far more oxygen than water does. Why?

6. Transportation

How does water reach the topmost leaf of a 30-metre tree? There is no pump up there.

The heart is a pump with four chambers. The upper two, the atria, receive blood; the lower two, the ventricles, push it onward. Ventricle walls are thicker, and the left ventricle's is thickest because it must send blood to the whole body.

Double circulation: blood passes through the heart twice in one complete cycle — once for the lungs, once for the rest of the body. Oxygenated and deoxygenated blood therefore never mix, and the body gets energy efficiently.

Valves stop blood from flowing backwards.

Lymph — fluid that leaks out of capillaries; it carries digested fat and returns excess fluid to the blood.

Transport in plants

Answer: not a pump but a pull. Transpiration during the day draws the water column upward through the narrow xylem tubes. At night, when transpiration is low, root pressure takes over.

Level 1 Which chamber of the heart has the thickest wall?

Level 2 Give two differences between an artery and a vein.

Level 3 What if the heart had no septum? Which animals does this matter most to, and why?

7. Excretion

You pass more urine in winter than in summer, though you drink much the same. Why?

A tea strainer holds back the leaves and lets the liquid through. Now think — if the body filtered blood that way, glucose and useful salts would wash out too. How might the body save them?

Removing nitrogenous waste made by metabolism is excretion. In humans the kidneys do it; each kidney holds millions of filtering units called nephrons.

1. Filtration — blood arrives at the glomerulus under high pressure and is filtered into Bowman's capsule.
2. Selective reabsorption — as the filtrate passes along the tubule, glucose, amino acids, salts and most of the water are taken back into the blood.
3. Urine — what remains goes through the collecting duct to the ureter and bladder.

Artificial kidney (dialysis): when kidneys fail, blood is passed through a machine with semi-permeable tubes that absorb the waste. There is no reabsorption — which is why it is not a full substitute for a kidney.

Excretion in plants: excess oxygen and water leave through stomata; some waste is stored as gum and resin in old xylem; some is shed with falling leaves; and some is released into the surrounding soil.

Answer: in summer much water leaves as sweat, so the kidneys reabsorb more and the urine is less and more concentrated. In winter there is little sweating, so the spare water must go — more urine.

Level 1 Name the functional unit of the kidney.

Level 2 What is selective reabsorption, and which substances are taken back?

Level 3 Glucose is found in someone's urine. Which stage of the nephron has gone wrong, and why?

Your ladder — score yourself

The five diagrams — how to draw them

Diagrams carry the most marks in this topic. Draw along on paper. Each comes with the mistake examiners see most often.

How examiners award marks

(Typical examiner practice, not any board's official scheme.)

The trap table

Final test — mixed, including earlier topics

8+ correct = solid.

1. Write the balanced equation for photosynthesis.
2. How do stomata open and close?
3. What does salivary amylase digest?
4. What causes muscle cramp?
5. Which heart chamber has the thickest wall, and why?
6. Which artery carries deoxygenated blood?
7. What does transpiration pull do?
8. Which stage is missing in an artificial kidney?
9. (acids topic) How would you prove exhaled air contains CO₂?
10. (carbon topic) Ethanol from anaerobic respiration in yeast belongs to which homologous series?

Glossary

For parents and teachers

A. Mitochondria — where the energy actually goes

Part 1 said aerobic respiration "releases far more energy". More of what, exactly?

The energy is not released as heat and lost — it is captured in a molecule called ATP, adenosine triphosphate, which cells use as a universal energy currency. ^[1] Breaking one of its phosphate bonds powers muscle contraction, protein building and nerve signalling. This is why mitochondria are called the powerhouse of the cell: they are where most ATP is made. ^[1] Anaerobic respiration yields only a small fraction of the ATP that the aerobic route does — the difference you feel as exhaustion.

B. One rule, three organs

Look back at Part 1 and notice how often the same solution appears:

Diffusion and filtration both work faster across a larger area, so evolution keeps arriving at the same answer: fold, branch, or flatten until the surface is enormous while the volume stays small. Recognise this pattern and half of biology stops being memory work.

C. What a dialysis machine still cannot do

Part 1 noted that an artificial kidney has no reabsorption stage. The National Institute of Diabetes and Digestive and Kidney Diseases, part of the US National Institutes of Health, describes how the machine works: blood is pumped out through a filter called a dialyzer — sometimes called an artificial kidney — where it is forced through many very thin hollow fibres, and the cleaned blood is returned to the body. ^[2]

The same institute notes that haemodialysis at a centre is usually done three times a week, about four hours each session. ^[3]

D. Who makes the oxygen you are breathing?

Ask where Earth's oxygen comes from and most people say "forests". The measurements say something else.

NASA reports that scientists estimate at least 50 per cent of the oxygen in our atmosphere has been produced by phytoplankton — microscopic drifting organisms that photosynthesise in the sunlit surface of the sea. ^[4] The US National Oceanic and Atmospheric Administration gives a similar figure, and adds that one single species, Prochlorococcus, may produce up to 20 per cent of the oxygen in the entire biosphere — more than all tropical rainforests combined. ^[5]

Either way, the equation you learned in section 2 is not only a plant's business. It is the reaction that keeps the atmosphere breathable.

E. Where this leads

References

Only universities and government agencies are cited. Each link was checked when this guide was written.

1. Biology / Chemistry LibreTexts — open textbook project hosted by the University of California, Davis. Chapters on cellular respiration, ATP and mitochondria. libretexts.org
2. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health, USA. "Hemodialysis." niddk.nih.gov
3. NIDDK, National Institutes of Health, USA. "Choosing a Treatment for Kidney Failure." niddk.nih.gov
4. NASA Earth Observatory. "Oxygen Factories in the Southern Ocean." science.nasa.gov
5. National Oceanic and Atmospheric Administration (NOAA), Ocean Service, USA. "How much oxygen comes from the ocean?" oceanservice.noaa.gov
6. National Council of Educational Research and Training (NCERT), Government of India. Science — Textbook for Class X. ncert.nic.in

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