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Step-by-step answers for all textbook questions in this chapter
What are Life Processes?
All living organisms perform certain basic activities to survive and maintain themselves. These are called life processes:
1. Nutrition — obtaining food and energy 2. Respiration — releasing energy from food 3. Transportation — moving substances within the body 4. Excretion — removing metabolic wastes
Nutrition
Autotrophic Nutrition (Plants)
Plants make their own food using sunlight, CO₂ and water — this is called photosynthesis.
Equation: 6CO₂ + 6H₂O + Light energy →(chlorophyll) C₆H₁₂O₆ + 6O₂
Where Does Photosynthesis Occur?
- In chloroplasts, which contain the green pigment chlorophyll
- Chlorophyll absorbs light energy (mainly red and blue wavelengths)
Factors Affecting Photosynthesis
- Light intensity — more light = faster photosynthesis (to a limit)
- CO₂ concentration — more CO₂ = faster photosynthesis (to a limit)
- Temperature — optimum 25–35°C; extremes slow it down
- Water — shortage closes stomata, stopping CO₂ entry
How Leaves are Adapted for Photosynthesis
- Broad, flat — maximum surface for light absorption
- Stomata — pores for CO₂ entry and O₂ exit; opened and closed by guard cells
- Thin — short distance for CO₂ to diffuse to cells
- Chloroplasts in mesophyll cells — packed with chlorophyll
Heterotrophic Nutrition (Animals)
| Type | Description | Example |
|---|---|---|
| Holozoic | Takes in solid food, digests inside | Humans, amoeba |
| Saprotrophic | Feeds on dead organic matter | Fungi, bacteria |
| Parasitic | Lives on host, harms it | Cuscuta plant, tapeworm |
Human Digestive System
Food travels: Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus
| Organ | Secretion | Action |
|---|---|---|
| Mouth | Salivary amylase | Starch → maltose |
| Stomach | HCl + Pepsin | Kills bacteria; protein digestion begins |
| Liver | Bile (stored in gall bladder) | Emulsifies fats |
| Pancreas | Amylase, lipase, trypsin | Digests carbohydrates, fats, proteins |
| Small intestine | Intestinal enzymes | Final digestion; absorption through villi |
| Large intestine | — | Absorbs water; forms faeces |
Villi: Finger-like projections on small intestine wall that greatly increase the surface area for absorption. Each villus has blood capillaries and lymph capillaries.
Respiration
Aerobic Respiration (with oxygen)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (38 ATP)
Occurs in mitochondria — the "powerhouse of the cell". Produces maximum energy.
Anaerobic Respiration (without oxygen)
In yeast: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + small energy Used in: bread-making (CO₂ makes dough rise), wine/beer production
In human muscles during heavy exercise: C₆H₁₂O₆ → 2C₃H₆O₃ (lactic acid) + small energy Lactic acid accumulates → causes cramps. Hot bath/massage helps remove it.
Breathing in Humans
Inhalation: Diaphragm flattens (moves down) + rib cage expands → lung volume increases → air rushes in
Exhalation: Diaphragm relaxes (moves up) + rib cage contracts → lung volume decreases → air pushed out
Gas Exchange in Alveoli
- Alveoli are tiny air sacs — thin walls + rich blood supply
- O₂ diffuses from alveolar air → into blood
- CO₂ diffuses from blood → into alveolar air
- Alveoli have a very large total surface area (~70 m²) for efficient exchange
Respiration in Plants
Plants also respire continuously (aerobic). During the day, the O₂ produced by photosynthesis is much more than the O₂ used in respiration — so net O₂ is released. At night (no photosynthesis), CO₂ is released.
Transportation
In Plants
Water and minerals — Xylem:
- Root hair cells absorb water by osmosis
- Water moves through xylem tissue (dead hollow tubes) up to leaves
- Driving force: Transpiration pull — evaporation from leaves creates suction that pulls water up through xylem
Food — Phloem:
- Glucose made in leaves is transported via phloem (living cells)
- Moves in both directions (leaves → roots, leaves → fruits)
- Mechanism: Pressure flow — sugar loaded into phloem at leaves; water follows by osmosis, creating pressure that pushes the solution downward
| Xylem | Phloem |
|---|---|
| Dead cells | Living cells |
| Moves water and minerals | Moves food (sugars, amino acids) |
| Moves only upward | Moves up and down |
| No energy needed | Requires energy |
In Humans — The Circulatory System
The Heart: 4-chambered pump
- Right atrium → receives deoxygenated blood from body
- Right ventricle → pumps blood to lungs (pulmonary circuit)
- Left atrium → receives oxygenated blood from lungs
- Left ventricle → pumps oxygenated blood to all body parts (systemic circuit)
Double Circulation:
- Pulmonary circulation: Right heart → Lungs (blood oxygenated) → Left heart
- Systemic circulation: Left heart → Body organs (O₂ delivered) → Right heart
Blood Vessels:
- Arteries — thick walls; carry blood away from heart (usually oxygenated)
- Veins — thin walls; carry blood toward heart; have valves to prevent backflow
- Capillaries — one cell thick; site of exchange of O₂, nutrients, CO₂ between blood and tissues
Components of Blood:
| Component | Function |
|---|---|
| Red Blood Cells (RBCs) | Carry O₂ via haemoglobin |
| White Blood Cells (WBCs) | Fight infections; immune defence |
| Platelets | Blood clotting |
| Plasma | Liquid; carries nutrients, hormones, CO₂, waste |
Blood pressure: Normal = 120/80 mmHg. Measured using a sphygmomanometer.
Excretion
In Humans — The Kidneys
Two kidneys, each containing ~1 million nephrons.
Steps in urine formation in one nephron:
1. Glomerular filtration: Blood enters glomerulus (a capillary knot in Bowman's capsule) under high pressure. Water, glucose, urea, salts are filtered out.
2. Tubular reabsorption: As filtrate passes through the renal tubule, all glucose, most water, salts, and amino acids are reabsorbed back into blood.
3. Tubular secretion: Additional waste products (H⁺ ions, urea) are secreted from blood into the tubule.
4. Urine: Remaining concentrated waste (urea + water + salts) flows into collecting duct → ureter → urinary bladder → urethra.
Composition of urine: Water ~96%, urea ~2%, uric acid, creatinine, salts ~2%
Kidneys also regulate:
- Blood water balance (osmoregulation)
- Blood pH
- Blood pressure (through water/salt balance)
Dialysis (Artificial Kidney): When kidneys fail, blood is passed through a dialysis machine. Waste substances (urea) diffuse out through a semi-permeable membrane into dialysis fluid. Clean blood is returned to the patient.
Excretion in Plants
- CO₂ and excess water through stomata (transpiration)
- O₂ (produced during photosynthesis) released through stomata
- Waste stored in old leaves → shed in autumn
- Waste stored in bark, resins, gums
- Some waste excreted into soil around roots
Board Exam Tips
- 10–12 marks typically from the Biology section — highest scoring area
- Photosynthesis equation must be balanced and written correctly
- Human digestive system — labelled diagram often required (3–5 marks)
- Nephron diagram with explanation — very common 5-mark question
- "Compare aerobic and anaerobic respiration" in a table — 3 marks, appears almost every year
- Xylem vs Phloem comparison table — 2 marks, very common
- Learn double circulation: which side of heart receives/pumps oxygenated vs deoxygenated blood
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Intext Questions
Page 95, Q1: Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
Page 101, Q1: What criteria do we use to decide whether something is alive?
The most fundamental criterion is molecular movement — even seeds that appear dormant show internal chemical activity.
- Movement (not necessarily visible — internal molecular movement always occurs)
- Growth — increase in mass over time
- Reproduction — ability to produce offspring
- Metabolism — chemical reactions that maintain life (nutrition, respiration, excretion)
- Response to stimuli — reacting to environment
Page 105, Q1: What are the differences between autotrophic and heterotrophic nutrition?
| Feature | Autotrophic | Heterotrophic |
|---|---|---|
| Food source | Make their own food | Depend on others |
| Process | Photosynthesis | Ingestion/digestion of organic matter |
| Examples | Green plants, algae, some bacteria | Animals, fungi, most bacteria |
| Raw materials | CO₂, H₂O, sunlight | Carbohydrates, proteins, fats from food |
Page 111, Q1: Why is the small intestine in herbivores longer than in carnivores?
Chapter-End Exercise
Q1. What are the differences between aerobic and anaerobic respiration?
| Feature | Aerobic respiration | Anaerobic respiration |
|---|---|---|
| Oxygen needed | Yes | No |
| Location | Cytoplasm + mitochondria | Cytoplasm only |
| Glucose breakdown | Complete | Incomplete |
| End products | CO₂ + H₂O | Lactic acid (animals) or ethanol + CO₂ (yeast) |
| Energy released | 38 ATP (high) | 2 ATP (very low) |
| Examples | Most organisms | Yeast, bacteria; muscles during intense exercise |
Equation (aerobic): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (38 ATP) Equation (anaerobic in yeast): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy (2 ATP)
Q2. How are fats digested in our bodies? Where does this process take place?
Steps: 1. Emulsification by bile: Bile (from liver, stored in gall bladder) breaks large fat globules into smaller droplets — this is emulsification. Bile does not chemically digest fat; it increases surface area. 2. Enzyme action: Lipase enzyme (secreted by the pancreas) acts on the emulsified fat and breaks it down into fatty acids and glycerol. 3. Absorption: Fatty acids and glycerol are absorbed into the small intestine wall through villi and enter the lymph (lacteals), then into the bloodstream.
Q3. What is the role of the kidney in the human body?
Functions: 1. Filtration: Blood enters the kidney under pressure. The glomerulus in each nephron filters blood — water, glucose, amino acids, urea, salts all pass into the Bowman's capsule. 2. Selective reabsorption: As filtrate moves through the tubule, useful substances (glucose, amino acids, most water, salts) are reabsorbed back into the blood. 3. Urine formation: The remaining fluid (urea, excess water, salts) becomes urine. 4. Water balance: Kidneys regulate the amount of water in the blood (osmoregulation). Urine flows from kidneys → ureters → urinary bladder → excreted through urethra.
Q4. What are the components of the transport system in plants?
Together, xylem and phloem form the vascular tissue of plants.
Q5. Describe double circulation in human beings. Why is it necessary?
Two circuits: 1. Pulmonary circulation: Right side of heart → lungs (for oxygenation) → back to left side of heart 2. Systemic circulation: Left side of heart → body organs → back to right side of heart
Why it is necessary:
- Separates oxygenated and deoxygenated blood completely
- Maintains high blood pressure for efficient delivery of oxygen to all body tissues
- Without separation, oxygenated and deoxygenated blood would mix, reducing oxygen supply to organs
- Warm-blooded animals need a constant high-energy supply — double circulation ensures this
Q6. What are the methods used by plants to get rid of waste products?
Methods: 1. Stomata and lenticels: O₂ (waste from respiration) and CO₂ (from photosynthesis in leaves) diffuse out through stomata. 2. Transpiration: Excess water is lost through stomata as water vapour. 3. Autumn leaf fall: Metabolic waste stored in leaves is got rid of when leaves fall. 4. Bark: Resins, gums, tannins — stored in old bark and shed periodically. 5. Excretion into soil: Some plants excrete waste through their roots into the surrounding soil.