Life Processes — Detailed Notes

Chapter 5 | NCERT Class 10 Science

5.1 What Are Life Processes?

NRTE map — Life processes decision map (NRTE)

Visible movement (running, growing, breathing) is a common clue that something is alive, but it is incomplete: sleeping animals and non-growing plants are still alive. Biologists emphasise molecular movement inside cells. Viruses show little molecular activity until they infect a cell — one reason their “living” status is debated.

Living structures are ordered. The environment tends to break that order down. Organisms must therefore repair and maintain themselves continuously. The processes that perform this maintenance job — even when the organism appears inactive — are life processes.

Energy and materials come from outside as food (nutrition). Outside carbon sources are broken down or rebuilt into a usable form; many organisms use oxygen in oxidising–reducing reactions (respiration). In multicellular organisms, specialised uptake sites create a need for a transport system. Harmful by-products of metabolism must leave the body (excretion).

In unicellular organisms, the whole surface contacts the environment, so specialised organs may be unnecessary. In multicellular bodies, most cells are not in direct contact with surroundings, so diffusion alone is insufficient for oxygen, food and waste needs of all cells.

Better Method / Strategy

Start every long answer with: maintenance → energy/materials → specialised tissues → transport of wastes.

For “why diffusion fails” questions, stress distance + large body size + specialised uptake sites.

5.2 Nutrition

All organisms need energy and materials for order, growth and synthesis. Autotrophs (green plants, some bacteria) use simple inorganic sources (CO₂, water). Heterotrophs (animals, fungi) use complex organic food made by others and break it down with enzymes. Heterotrophs depend directly or indirectly on autotrophs.

5.2.1 Autotrophic Nutrition

Photosynthesis converts CO₂ and water into carbohydrates using sunlight and chlorophyll. Unused carbohydrate is stored as starch (plants) — comparable to glycogen storage in humans.

Events of photosynthesis:

Absorption of light energy by chlorophyll
Conversion of light energy to chemical energy and splitting of water into hydrogen and oxygen
Reduction of CO₂ to carbohydrates

These need not occur immediately in sequence. Desert plants may take up CO₂ at night and process an intermediate by day.

Chloroplasts in leaf cells contain chlorophyll. Stomata are pores for gaseous exchange; gases also exchange across stem, root and leaf surfaces. Guard cells swell with water → pore opens; shrink → pore closes — balancing CO₂ need against water loss.

Terrestrial plants take water via roots. Minerals (N, P, Fe, Mg) come from soil; nitrogen (for proteins) as nitrates/nitrites or as organic compounds prepared by bacteria from atmospheric N₂.

Diagram — leaf cross-section:

Leaf cross-section — epidermis, mesophyll, vascular bundle

Diagram — stomata:

two kidney-shaped guard cells enclosing a pore; open when turgid, closed when flaccid.

5.2.2 Heterotrophic Nutrition

Strategies match food type and availability:

External digestion then absorption — fungi (bread moulds, yeast, mushrooms)
Intake of whole food, digested inside — many animals
Parasitic nutrition without killing the host — Cuscuta (amar-bel), ticks, lice, leeches, tapeworms

5.2.3 How Organisms Obtain Nutrition

Amoeba: temporary finger-like extensions engulf food → food vacuole → digestion → diffusion into cytoplasm → undigested waste expelled
Paramoecium: definite shape; food taken at a specific spot; cilia move food to that spot

5.2.4 Nutrition in Human Beings

Alimentary canal: mouth → oesophagus → stomach → small intestine → large intestine → anus. Food is crushed, moistened and moved by peristalsis.

Region	Key secretions / action	Result
Mouth	Salivary amylase	Starch → simple sugar
Stomach	HCl, pepsin, mucus	Acidic medium for pepsin; mucus protects lining; protein digestion begins
Small intestine	Bile (liver); pancreatic trypsin + lipase; intestinal enzymes	Complete digestion of carbs, proteins, fats
Large intestine	Water absorption	Faeces formed; anal sphincter controls exit

Stomach detail: gastric glands release HCl (acidic medium for pepsin; also helps kill microbes), pepsin (protein), mucus (protects lining). A sphincter regulates exit into the small intestine in small amounts.

Small intestine: longest coiled region; longer in herbivores (cellulose) than carnivores. Acidic food made alkaline by bile; bile salts emulsify fats into smaller globules. Final products: amino acids, glucose, fatty acids + glycerol. Villi increase surface area; rich blood supply carries absorbed food to cells.

Dental caries (awareness): bacteria on sugars make acids that demineralise enamel; plaque blocks saliva; brushing removes plaque.

Better Method / Strategy

Always pair enzyme → substrate → product → site.

For absorption questions, lead with villi → surface area → blood vessels.

5.3 Respiration

Food provides energy via break-down of glucose. First step (all pathways): glucose (6C) → pyruvate (3C) in cytoplasm.

Pathway	Conditions	Products	Notes
Anaerobic (yeast)	No O₂	Ethanol + CO₂	Fermentation
Aerobic	O₂ present	CO₂ + H₂O + much energy	In mitochondria
Muscle (O₂ lack)	Temporary O₂ debt	Lactic acid	Can cause cramps

ATP is the energy currency. Respiration energy makes ATP from ADP + inorganic phosphate. Breaking the terminal phosphate of ATP (with water) releases about 30.5 kJ/mol, driving endothermic cell work (muscle contraction, protein synthesis, nerve impulses).

Plants: gas exchange mainly by diffusion via stomata and intercellular spaces. At night, CO₂ elimination dominates; by day, photosynthetic use of respiratory CO₂ means O₂ release is the major net event.

Animals: aquatic organisms use dissolved O₂ (low concentration → faster breathing rate); fish force water over gills. Terrestrial animals use atmospheric O₂; exchange surfaces are large, delicate and usually internal.

Human respiratory path: nostrils (hairs + mucus filter) → throat (cartilage rings keep passage open) → lungs → bronchioles → alveoli. Breathing in: ribs lift, diaphragm flattens → chest volume ↑ → air sucked in. Blood releases CO₂ into alveoli and takes up O₂. Residual volume of air remains so exchange has time. Haemoglobin in RBCs carries O₂; CO₂ is mostly carried dissolved in blood (more soluble than O₂).

Diagram — human respiratory system:

nasal passage → pharynx/trachea → bronchi → branching tubes ending in clusters of thin-walled alveoli surrounded by capillaries; diaphragm below lungs.

Better Method / Strategy

Memorise the glucose tree before naming organs.

For “maximise exchange”, list: thin walls, large surface (alveoli), rich capillary network, residual air.

5.4 Transportation

5.4.1 Transportation in Human Beings

Blood: plasma (food, CO₂, nitrogenous wastes dissolved) + cells; O₂ mainly on RBCs (haemoglobin). Needs a pump, vessel network and repair system.

Heart (fist-sized, four chambers):

Oxygenated blood from lungs → left atrium → left ventricle → body
Deoxygenated blood from body → right atrium → right ventricle → lungs

Ventricles have thicker walls than atria. Valves prevent backflow. Separation of sides keeps O₂-rich and CO₂-rich blood apart — efficient supply for high-energy animals (birds, mammals) that maintain body temperature. Amphibians/many reptiles: three-chambered hearts, some mixing. Fish: two chambers; blood through heart once per cycle. Other vertebrates: blood through heart twice per cycle = double circulation.

Blood pressure: force on vessel walls; higher in arteries. Systolic (ventricular contraction) ≈ 120 mm Hg; diastolic (relaxation) ≈ 80 mm Hg. Hypertension: narrowed arterioles → high resistance; risk of vessel rupture.

Vessels:

Arteries: away from heart; thick elastic walls (high pressure)
Veins: to heart; thinner walls; valves for one-way flow
Capillaries: one-cell-thick walls; site of exchange

Platelets help clot blood at injury sites (limit loss and pressure drop).

Lymph (tissue fluid): plasma/proteins/cells escaping capillaries into intercellular spaces; colourless, less protein than plasma. Lymph vessels return fluid to veins; lymph also carries digested fat from intestine.

Diagram — heart section:

left/right atria above; left/right ventricles below; valves between chambers; septum separating left and right.

5.4.2 Transportation in Plants

Plants have low energy needs (many dead cells; no locomotion) but may need long-distance transport. Two pathways:

Tissue	Carries	Direction / drive
Xylem	Water + minerals from soil	Upward; root pressure + transpiration pull
Phloem	Photosynthates (e.g. sucrose), amino acids	Up and down (translocation); uses ATP

Water: root cells actively take ions → osmotic water entry → column pushed up (root pressure, more important at night). By day, stomatal water loss creates suction — transpiration pulls xylem water up; also cools the plant.

Food: sucrose loaded into phloem using ATP → osmotic pressure rises → water enters → pressure flow to low-pressure sinks (roots, fruits, growing tips). In spring, stored sugar can move to buds.

Better Method / Strategy

Tag every transport answer: what + where from/to + energy needed?.

Xylem ≈ physical forces; phloem ≈ active, bidirectional as needed.

5.5 Excretion

Excretion removes harmful metabolic wastes (especially nitrogenous). Unicellular organisms often use diffusion across the body surface.

5.5.1 Excretion in Human Beings

Organs: kidneys (filter blood) → ureters → urinary bladder → urethra.

Nephron (filtration unit): cluster of thin capillaries (glomerulus) in cup-shaped Bowman’s capsule collects filtrate. As fluid flows in the tubule, glucose, amino acids, salts and much water are selectively reabsorbed. Water reabsorption depends on excess water in the body and amount of dissolved waste. Urine stored in bladder (muscular; nervous control of urge).

Artificial kidney (haemodialysis): blood passed through tubes with semi-permeable lining in dialysing fluid (same osmotic pressure as blood, no nitrogenous wastes). Wastes diffuse out; purified blood returned. Unlike natural kidney, no selective reabsorption. Healthy adult: ~180 L filtrate/day but only ~1–2 L urine excreted.

Diagram — nephron:

afferent vessel → glomerular capillary knot in Bowman’s capsule → long coiled tubule with capillary network → collecting duct toward ureter.

5.5.2 Excretion in Plants

O₂ (photosynthetic by-product) and CO₂ handled via stomatal exchange
Excess water: transpiration
Other wastes: stored in vacuoles; in falling leaves; as resins/gums (old xylem); excreted into surrounding soil

Chapter Closing Strategy

Build one master map: In (food/O₂) → Process (digest/respire) → Circulate → Out (CO₂/urine/faeces).
Practise four comparison tables until you can write them without looking.
For 5-markers, use labelled-in-words diagrams plus two functions each.

Deep Dive Add-On — Comparison Tables (Board Ready)

Autotrophic vs Heterotrophic Nutrition

Point	Autotrophs	Heterotrophs
Food source	Make organic food from inorganic (CO₂, H₂O)	Depend on organic food made by others
Energy capture	Light (photosynthesis) or chemical (some bacteria)	Chemical energy already in food
Examples	Green plants, some bacteria	Animals, fungi, many parasites
Key organs/structures	Chloroplasts, stomata (plants)	Digestive enzymes / gut / specialised intake

Aerobic vs Anaerobic Respiration

Point	Aerobic	Anaerobic (yeast)	Muscle (O₂ debt)
Oxygen	Required	Not required	Temporarily lacking
End products	CO₂ + H₂O	Ethanol + CO₂	Lactic acid
Energy yield	High (much ATP)	Low	Low
Site (after pyruvate)	Mitochondria	Cytoplasm (pathway continues without mito aerobic steps)	Muscle cells
Exam phrase	“Complete oxidation”	Fermentation	Causes cramps

Arteries vs Veins vs Capillaries

Feature	Artery	Vein	Capillary
Direction	Away from heart	Toward heart	Connect arteries ↔ veins
Wall	Thick, elastic	Thinner	One-cell thick
Pressure	High	Lower	Lowest exchange pressure
Valves	Generally absent (except base of aorta/pulmonary)	Present (prevent backflow)	—
Role	Rapid distribution	Return + reservoir	Exchange of materials

Xylem vs Phloem

Feature	Xylem	Phloem
Carries	Water + minerals	Sucrose, amino acids (food)
Main direction	Upward (roots → shoot)	Up and down as needed
Driving force	Root pressure + transpiration pull	Pressure flow after ATP-powered loading
Living status of conducting cells (NCERT idea)	Often described with physical column / pull	Needs living phloem tissue + energy

Alveoli vs Nephron (Exchange / Filter Design)

Feature	Alveoli	Nephron
Main job	Gas exchange (O₂ ↔ CO₂)	Filter blood; form urine
Key design	Thin walls, large surface, capillary net	Glomerulus + capsule + tubule
What enters/leaves	O₂ into blood; CO₂ out to air	Filtrate out of blood; useful substances reabsorbed
Linked organ	Lungs	Kidney

Human Digestion — Enzyme Snapshot

Digestive system — Human digestive system — main organs

Site	Enzyme / juice	Substrate → product
Mouth	Salivary amylase	Starch → simple sugar
Stomach	Pepsin (+ HCl medium)	Proteins → simpler peptides
Duodenum / SI	Bile (not enzyme)	Fat emulsification
Pancreas → SI	Trypsin	Proteins / peptides
Pancreas → SI	Lipase	Fats → fatty acids + glycerol
Intestinal enzymes	Various	Complete digestion to absorbable ends

Deep Dive Add-On — Word Diagrams (Expand if Thin)

Stomata (labelled figure)

Open: guard cells take up water → become turgid → pore widens.
Closed: guard cells lose water → become flaccid → pore shrinks.
Trade-off: open stomata help CO₂ entry for photosynthesis but increase water loss (transpiration).

Alveoli (labelled figure)

Why efficient? (i) enormous total surface area, (ii) thin barrier, (iii) rich blood supply, (iv) residual air keeps exchange going between breaths.

Nephron (labelled figure)

Nephron — filtration and selective reabsorption

Filtration at glomerulus/capsule; selective reabsorption along tubule; urine volume depends on water/waste load.
Dialysis contrast: artificial kidney removes wastes by diffusion into dialysing fluid but does not perform selective reabsorption like a living nephron.

Double Circulation (arrow checklist)

Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs
Lungs → pulmonary vein → left atrium → left ventricle → aorta → body
Blood through heart twice per full circuit = double circulation.