CLASS 10 SCIENCE · CHAPTER 5 · STUDY NOTES
Life Processes
A comprehensive study of the fundamental biological functions that maintain life in living organisms, covering nutrition, respiration, transportation, and excretion in both plants and animals.
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Defining Life Processes and Molecular Movement
Explain why maintenance continues even when visible movement stops.LOOK INSIDE THE PROCESS
Even a resting cell stays busy.
Predict: which jobs still happen in a resting cell?
Food supplies raw materials and an energy source to the cell.
- Life processes
- Functions that maintain and repair a living organism.
A sleeping organism still needs energy, raw materials and removal of metabolic waste. Nutrition, respiration, transport and excretion support this maintenance.
Cells deep inside a large body are far from the surroundings. Specialised surfaces take in materials; transport systems deliver them and carry wastes away.
Go deeper: Visible movement is only a clue
Growth or movement can suggest life, but a still plant or sleeping animal remains alive. Molecular maintenance continues without obvious movement.
A unicellular organism can exchange materials over its exposed surface. In a large multicellular body, long distances and many interior cells make simple diffusion alone inadequate.
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Question
A person rests motionless after a meal. Does their lack of movement mean their cells no longer need respiration? Explain.
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Autotrophic Nutrition: The Process of Photosynthesis
Connect each photosynthesis requirement to what the leaf makes.LOOK INSIDE THE PROCESS
A leaf captures light and builds food.
Predict the starch result before changing one condition.
Light + chlorophyll + CO₂ + water → carbohydrate production. Excess carbohydrate can be stored as starch.
Compare initially destarched leaves with enough water and otherwise matched conditions. Blue-black is the iodine observation after treatment, not a colour the living leaf develops in sunlight.
- Photosynthesis
- Using light energy to build carbohydrates from carbon dioxide and water.
Chlorophyll absorbs light energy. Carbon dioxide supplies carbon and water supplies raw material; the process builds carbohydrates and releases oxygen. Excess carbohydrate can be stored as starch.
A destarched-leaf comparison tests one condition at a time. After iodine treatment, blue-black regions indicate starch; green leaf colour itself is not the test result.
The Chemical Equation of Photosynthesis
Sunlight and chlorophyll
6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂OSix molecules of carbon dioxide and twelve molecules of water react in the presence of sunlight and chlorophyll to produce one molecule of glucose, six molecules of oxygen, and six molecules of water.
Go deeper: What does the comparison establish?
Green regions of a variegated leaf contain chlorophyll; under suitable conditions they form starch, while non-green regions do not. Removing CO₂ with potassium hydroxide supplies a separate comparison.
Photosynthesis includes light-energy capture, water splitting and carbon-dioxide reduction. These events are not necessarily immediate consecutive steps; some desert plants take up CO₂ at night and use captured light energy during the day. Roots also supply minerals needed for growth.
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Question
Two destarched plants receive the same light and water. One is sealed with a CO₂ absorber. Why must the other plant be kept under otherwise matching conditions?
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Stomata and Gas Exchange in Plants
Relate guard-cell water content to pore opening and water loss.LOOK INSIDE THE PROCESS
Two guard cells control one tiny opening.
Predict: what else changes when the pore closes to save water?
Water enters guard cells; they become turgid and the pore opens. CO₂ uptake and water-vapour loss can occur together.
- Stoma
- A pore controlled by two guard cells; stomata is the plural.
Water entering guard cells makes them turgid and opens the pore. Losing water reduces turgidity and narrows the pore.
The opening allows CO₂ uptake and gas exchange, while water vapour can leave. Closing it reduces water loss but also limits gas exchange.
Go deeper: Opening is a trade-off
A plant needs CO₂ for photosynthesis but also needs to conserve water. The pore is controlled by the guard cells, not by a lid pushed across it.
Gas exchange also occurs across stems and roots. Plants respire throughout day and night; the net exchange through a leaf depends on the balance of photosynthesis, respiration and conditions.
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Question
A leaf reduces water loss by closing its stomata. Identify one benefit and one cost of this change.
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Heterotrophic Nutrition and Single-Celled Organisms
Distinguish digestion inside an organism from digestion outside it.LOOK INSIDE THE PROCESS
Different bodies. Different ways to get food.
Compare where digestion occurs before nutrients are absorbed.
Pseudopodia surround food; a food vacuole forms. Digestion inside the vacuole releases soluble nutrients into the cytoplasm.
- Heterotrophic nutrition
- Obtaining organic food made by other organisms.
Amoeba extends pseudopodia around food to form a food vacuole. Digestion releases soluble nutrients into the cytoplasm; undigested remains leave at the surface.
Fungi release enzymes onto food and absorb soluble products. Parasites obtain nourishment from a living host; these strategies differ in how food is obtained and digested.
Go deeper: Body design changes the route
Paramecium uses its cilia to move food towards a particular entry region. It does not engulf food with Amoeba-like pseudopodia.
Nutrition supplies energy sources and building materials. Absorbing small molecules after digestion is different from taking in an intact food particle; fungal external digestion is not photosynthesis.
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Question
A mould releases enzymes onto bread and then absorbs dissolved nutrients. Has it swallowed a piece of bread like Amoeba engulfs a particle?
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Human Digestion: The Upper Alimentary Canal
Follow food movement while separating mechanical and chemical digestion.LOOK INSIDE THE PROCESS
Follow food through the upper digestive tract.
Follow the contraction behind food, not a gravity arrow.
Teeth break food physically; salivary amylase begins starch digestion.
- Peristalsis
- Coordinated muscular contractions that move food along the alimentary canal.
Teeth break food into smaller pieces and saliva moistens it. Salivary amylase begins starch digestion; the tongue mixes food and helps form a bolus.
Peristalsis moves the bolus through the oesophagus. In the stomach, HCl provides an acidic medium for pepsin, while mucus helps protect the lining.
Go deeper: Transport is not digestion
A contraction behind the bolus pushes it forward; gravity is not the sole cause of swallowing. Peristalsis continues through the gut.
HCl is not an enzyme. Pepsin acts on proteins under acidic conditions; protective mucus and controlled release through the stomach sphincter have different roles.
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Question
Food moves along the oesophagus even when its starch has not yet been fully broken down. Which process moves it, and which process changes the starch?
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The Small Intestine: Site of Complete Digestion
Explain how digestion prepares molecules for absorption across villi.LOOK INSIDE THE PROCESS
Break down food, then cross the intestinal wall.
Predict: do smaller fat droplets mean chemical digestion is complete?
Bile breaks large fat globules into smaller droplets. Emulsification is a physical change; bile is not a digestive enzyme.
Particle sizes show breakdown qualitatively; the dots are not a count of molecules or a volume measurement.
- Emulsification
- Breaking large fat globules into smaller droplets without chemically digesting the fat.
| Enzyme/Secretion | Source | Function |
|---|---|---|
| Bile Salts | Liver | Emulsification of fats |
| Salivary Amylase | Salivary Glands | Breakdown of starch to sugar |
| Pepsin | Stomach | Digestion of proteins in acidic medium |
| Trypsin | Pancreas | Digestion of proteins in alkaline medium |
| Lipase | Pancreas | Breakdown of emulsified fats |
Bile from the liver helps provide suitable intestinal conditions and emulsifies fats. Pancreatic and intestinal enzymes complete digestion into absorbable products.
Villi increase the area for absorption. Nutrients enter blood or lymph and reach tissues; the large intestine absorbs further water, and undigested remains leave by egestion.
Go deeper: Surface area and chemical change
Smaller fat droplets expose more surface to lipase. Bile salts help make that surface available; they are not themselves fat-digesting enzymes.
At this level, carbohydrate products are described as glucose, protein products as amino acids, and fat products as fatty acids and glycerol. Absorption follows digestion; removing undigested food is egestion, not excretion of a metabolic waste.
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Question
A large fat droplet becomes many small droplets before lipase acts. Has bile already converted the fat into its final digestion products?
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Respiration: Pathways of Glucose Breakdown
Account for carbon as glucose follows different respiratory pathways.LOOK INSIDE THE PROCESS
Six carbon atoms. Three possible pathways.
Count all six carbon atoms in each possible outcome.
Two pyruvate molecules enter oxygen-dependent breakdown in mitochondria: CO₂ + water, with more ATP than fermentation.
- ATP
- A molecule used to transfer energy to cellular processes.
| Pathway | Conditions | End Products | Energy Yield |
|---|---|---|---|
| Aerobic | Presence of O₂ | CO₂ + H₂O | High |
| Anaerobic (Yeast) | Absence of O₂ | Ethanol + CO₂ | Low |
| Muscle Cells | Lack of O₂ | Lactic Acid | Low |
One six-carbon glucose forms two three-carbon pyruvate molecules in the cytoplasm. Subsequent pathways depend on the cell and conditions.
Oxygen-dependent breakdown produces CO₂ and water with a greater ATP yield. Yeast fermentation forms ethanol and CO₂; muscle cells can form lactate when oxygen supply is insufficient.
Go deeper: Energy transfer and carbon accounting
The carbon count is six throughout: six CO₂, two ethanol plus two CO₂, or two three-carbon lactate molecules. Carbon dots show accounting, not the full molecular structures.
Respiration transfers energy that helps form ATP from ADP and phosphate. ATP hydrolysis can drive cellular work; a drawn phosphate bond is not a container that releases energy simply because a bond is broken. The pathways shown do not claim one universal ATP yield.
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Question
A yeast cell converts one glucose into two ethanol molecules and two CO₂ molecules. Count the carbon atoms in the products.
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