Class 10 › Science › Chapter 5

Life Processes

Nutrition, respiration, transportation and excretion: how organisms maintain themselves, in plants and in human beings.

1. What are Life Processes?

Life processes: the basic maintenance processes that go on in living organisms, even at rest or asleep, to repair and maintain their organised structures.

Visible movement alone cannot define life (a plant may not visibly grow). Molecular movement is needed, since living structures keep breaking down and must be repaired. Viruses show no molecular movement until they infect a cell, so whether they are alive is debated.
Nutrition: bringing in food (carbon-based) for energy and raw material for growth. Respiration: taking in O₂ to break down food for cellular energy. Transportation: carrying food and O₂ to all cells. Excretion: removing harmful waste by-products.
Why diffusion is not enough: in multicellular organisms, not all cells touch the environment, so specialised organs and a transport system are needed.

2. Nutrition: Autotrophic

Autotrophs

Make their own food

Use simple inorganic CO₂ and water. Green plants and some bacteria.

Heterotrophs

Depend on others

Break down complex substances using enzymes (bio-catalysts). Animals and fungi. Survival depends directly or indirectly on autotrophs.

6CO₂ + 12H₂O chlorophyll, sunlight → C₆H₁₂O₆ + 6O₂ + 6H₂OPhotosynthesis: carbohydrates (glucose) are made; excess is stored as starch in plants (glycogen in animals).

Events in photosynthesis

1. Absorption of light energy by chlorophyll (in chloroplasts).

2. Conversion of light to chemical energy and splitting of water into hydrogen and oxygen.

3. Reduction of CO₂ to carbohydrates. These steps need not occur one after the other (desert plants take up CO₂ at night and use the intermediate during the day).

Raw materials: CO₂ enters through stomata (tiny leaf pores); water and minerals (N, P, Fe, Mg) come from the soil through roots. Nitrogen is taken as nitrates or nitrites, or as organic compounds made by bacteria from atmospheric nitrogen.
Stomata: guard cells swell when water flows in (pore opens) and shrink to close it. Closing prevents large water loss when CO₂ is not needed.
Chlorophyll needed (Act. 5.1): in a variegated leaf, only the green parts turn blue-black with iodine, showing starch only where chlorophyll was present.
CO₂ needed (Act. 5.2): the plant in a bell jar with KOH (absorbs CO₂) shows no starch; the one without KOH does.
Sunlight needed: plants kept in the dark lose their starch (kept in the dark for three days to destarch).

3. Nutrition: Heterotrophic

Break down outside, then absorb: fungi (bread mould, yeast, mushrooms).
Take in whole food and digest inside the body: most animals.
Parasites: derive nutrition from a host without killing it: cuscuta (amar-bel), ticks, lice, leeches, tapeworms.
Amoeba: finger-like pseudopodia fuse over the food particle to form a food vacuole; digestion occurs inside it and undigested material is thrown out through the cell surface.
Paramoecium: definite shape; food enters at a specific spot, moved there by cilia.
The digestive system differs with food and body complexity.

4. Nutrition in Human Beings

Part	What happens
Mouth	Teeth crush food; saliva (salivary glands) wets it. Salivary amylase breaks starch to simple sugar. Tongue mixes food.
Oesophagus	Food moves by peristalsis (rhythmic muscle contractions along the gut).
Stomach	Gastric glands release HCl (acidic medium for pepsin; also kills bacteria), pepsin (digests proteins) and mucus (protects lining). A sphincter releases food in small amounts.
Small intestine	Complete digestion. Bile (liver) makes food alkaline and emulsifies fats. Pancreatic juice: trypsin (proteins), lipase (fats). Intestinal juice finally gives amino acids, glucose, fatty acids and glycerol. Villi absorb food.
Large intestine	Absorbs water; the rest leaves via the anus (anal sphincter).

Villi: finger-like projections that increase surface area for absorption and are richly supplied with blood vessels.
The small intestine is the longest part of the canal; it is longer in herbivores (to digest cellulose) than in carnivores like tigers.
Dental caries: bacteria act on sugars to form acid that softens enamel; plaque stops saliva neutralising it. Brush after eating.
Enzymes: amylase (starch), pepsin and trypsin (protein), lipase (fat).

5. Respiration

Respiration: acquiring O₂ and using it to break down food for cellular energy.

Breakdown of glucose

Step 1 (cytoplasm, all cases): glucose (6C) → pyruvate (3C) + energy.

Anaerobic, in yeast (no O₂): pyruvate → ethanol (2C) + CO₂ + energy. This is fermentation.

Anaerobic, in muscle (lack of O₂): pyruvate → lactic acid (3C) + energy. Build-up causes cramps.

Aerobic (in mitochondria, with O₂): pyruvate → 3CO₂ + H₂O + much more energy.

ATP (energy currency): energy released in respiration makes ATP from ADP + inorganic phosphate. Breaking the terminal phosphate bond releases ~30.5 kJ/mol, used for muscle contraction, protein synthesis and nerve impulses.
Evidence: exhaled air turns lime water milky faster than air pumped by syringe (more CO₂); fermenting yeast also turns lime water milky.
Anaerobic organisms: yeast and some bacteria.

6. Gas Exchange: Plants, Fish, Humans

Plants

Stomata + diffusion

Gases diffuse through stomata and across stems and roots; intercellular spaces reach all cells. Night: CO₂ released. Day: CO₂ used in photosynthesis, O₂ released.

Fish

Gills

Take in water through mouth and pass it over gills. Dissolved O₂ is low, so aquatic animals breathe faster than terrestrial ones.

Humans

Lungs

Nostrils (hairs, mucus) → pharynx → larynx → trachea (cartilage rings keep it open) → bronchi → bronchioles → alveoli.

Alveoli: balloon-like, thin walls, richly supplied with blood capillaries; the surface where O₂ enters and CO₂ leaves blood. Alveolar surface ≈ 80 m². A residual volume of air stays so exchange continues.
Breathing in: ribs lift, diaphragm flattens, chest cavity enlarges, air is sucked in.
Haemoglobin (in red blood corpuscles, high affinity for O₂) carries oxygen. CO₂ is more soluble in water, so it is mostly carried dissolved in blood. Deficiency of haemoglobin reduces O₂ supply to tissues.
Cilia in the upper tract trap germs and dust; smoking destroys cilia and can lead to lung cancer. Tobacco harms the tongue, lungs, heart and liver.

7. Transportation in Human Beings

Blood: fluid connective tissue. Plasma carries food, CO₂ and nitrogenous waste dissolved; RBCs carry O₂.

The heart and double circulation

The heart has four chambers: two thin-walled atria (upper) and two thick-walled ventricles (lower). Separation keeps oxygenated and deoxygenated blood from mixing.

Path: lungs → (oxygen-rich) left atrium → left ventricle → body. Body → (deoxygenated) right atrium → right ventricle → lungs.

Double circulation: blood passes through the heart twice in one full cycle. It is necessary in birds and mammals, which have high energy needs and keep a constant body temperature.

Valves prevent backward flow. Ventricles have thicker walls because they pump blood to organs.

Animal	Heart chambers	Note
Fish	2	Single circulation: blood goes through the heart once per cycle
Amphibians, many reptiles	3	Some mixing tolerated (low energy needs)
Birds, mammals	4	Complete separation; double circulation

Arteries

Away from heart

Thick, elastic walls (blood under high pressure).

Veins

Towards heart

Thin walls, valves ensure one-way flow.

Capillaries

One cell thick

Exchange of material between blood and cells.

Blood pressure: force of blood on vessel walls. Systolic ≈ 120 mm Hg (ventricular contraction), diastolic ≈ 80 mm Hg (relaxation). Measured by a sphygmomanometer. High pressure is hypertension (constricted arterioles).
Platelets clot blood at injuries, plugging leaks and preserving pressure.
Lymph: colourless fluid, like plasma with less protein; formed when plasma, proteins and cells escape capillaries. Carries digested fat from the intestine and drains excess fluid back to blood.

8. Transportation in Plants

Xylem

Water and minerals

Vessels and tracheids form continuous channels from roots to leaves. Moves upward only. Mostly dead cells.

Phloem

Food (translocation)

Sieve tubes with companion cells carry photosynthesis products and amino acids both upward and downward, to roots, fruits, seeds and growing parts.

How water moves up

Root pressure: root cells actively take up ions, so water moves in from the soil; this pushes a column of water upward. More important at night.

Transpiration pull: evaporation of water from leaf cells through open stomata creates suction that pulls water up the xylem. The main driving force during the day.

Transpiration = loss of water vapour from aerial parts. It helps absorption, upward movement of water and minerals, and temperature regulation.

Translocation in phloem uses energy: sucrose is loaded into phloem using ATP, raising osmotic pressure so water enters; pressure then moves material to tissues of lower pressure. In spring, sugar stored in roots goes to buds.

9. Excretion

Excretion: removal of harmful metabolic (nitrogenous) wastes from the body. Unicellular organisms excrete by simple diffusion.

Human system

Path of urine

Pair of kidneys → pair of ureters → urinary bladder (stored) → urethra. Kidneys filter nitrogenous waste (urea, uric acid) from blood.

Nephron

Filtration unit

Cluster of thin-walled capillaries (glomerulus) + cup-shaped Bowman's capsule + tubule. Collects filtrate.

Selective reabsorption: glucose, amino acids, salts and a major amount of water are reabsorbed as the filtrate flows along the tubule. How much water is reabsorbed depends on the body's excess water and the amount of dissolved waste to excrete; this regulates urine volume.
Initial filtrate ≈ 180 L/day, but only 1 to 2 L is excreted. The bladder is muscular and under nervous control.
Artificial kidney (haemodialysis): blood is passed through tubes with a semi-permeable lining in a dialysing fluid; wastes diffuse out and purified blood returns. No reabsorption, unlike a real kidney.
Plants excrete by transpiration (water), O₂ and CO₂ through stomata; storing waste in cell vacuoles; shedding leaves; storing as resins and gums in old xylem; and releasing wastes into the soil.
Organ donation: kidneys, heart, liver, cornea, etc., can be donated with consent; a kidney, part of a liver or lung can even be donated while alive.

10. Quick Revision

Process	Key organs / ideas
Autotrophic nutrition	Photosynthesis in chloroplasts; CO₂ via stomata, water via roots
Digestion	Amylase → pepsin → bile, trypsin, lipase; absorption by villi
Aerobic respiration	Mitochondria; most energy; CO₂ + H₂O
Anaerobic respiration	Yeast gives ethanol + CO₂; muscle gives lactic acid
Gas exchange (human)	Alveoli; haemoglobin carries O₂
Circulation	4-chambered heart, double circulation; arteries, veins, capillaries
Plant transport	Xylem (water, up) vs phloem (food, both ways)
Excretion	Nephron: filtration, selective reabsorption; urine to bladder

Common mistakes:
• Writing the photosynthesis equation without chlorophyll and sunlight, or forgetting 6H₂O on the right.
• Saying digestion of fats happens in the stomach; it happens in the small intestine (bile and lipase).
• Mixing up atria (receive blood) and ventricles (pump blood), or left and right sides.
• Saying phloem transports water; it carries food (and amino acids). Xylem carries water.
• Calling lactic acid fermentation; lactic acid forms in muscle, ethanol in yeast.
• Saying haemodialysis includes reabsorption; it does not.