1. Life Processes
Living organisms continuously perform activities needed to maintain and sustain life. These maintenance activities are called life processes.
Main life processes
- Nutrition — obtaining and utilising food.
- Respiration — releasing energy from food.
- Transportation — distributing useful substances and carrying wastes.
- Excretion — removing harmful metabolic wastes.
Key idea: Even when an organism appears inactive, its internal maintenance processes continue.
2. Nutrition
Nutrition provides organisms with energy and materials needed for growth, repair and maintenance.
Types of nutrition
A. Autotrophic nutrition
Organisms make their own food from simple inorganic substances.
Examples: Green plants and some bacteria.
Photosynthesis
Plants use:
- Carbon dioxide
- Water
- Sunlight
- Chlorophyll
to produce carbohydrates.
Simplified equation:
CO₂ + H₂O → Carbohydrate + O₂
(in the presence of sunlight and chlorophyll)
Major events
- Chlorophyll absorbs light energy.
- Light energy is converted into chemical energy and water is split.
- Carbon dioxide is converted into carbohydrates.
Role of stomata
- Tiny pores mainly present on leaves.
- Allow exchange of gases.
- Guard cells regulate their opening and closing.
- They also provide a route through which water can be lost.
Other minerals
Plants also require substances such as nitrogen, phosphorus, iron and magnesium from the soil.
B. Heterotrophic nutrition
Organisms obtain complex food from other organisms.
Examples: Animals and fungi.
Different organisms use different methods:
- Fungi: digest food outside the body and absorb it.
- Animals: generally ingest food and digest it internally.
- Parasites: obtain nutrition from living hosts.
3. Human Nutrition
The human alimentary canal is a continuous digestive tube from the mouth to the anus.
Flow of food
Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Anus
Mouth
- Teeth mechanically break food.
- Saliva moistens food.
- Salivary amylase begins digestion of starch.
- Tongue mixes and helps move food.
Oesophagus
Food moves towards the stomach through peristalsis — rhythmic muscular contractions of the digestive tract.
Stomach
Gastric glands release:
- Hydrochloric acid (HCl) — provides an acidic medium.
- Pepsin — helps digest proteins.
- Mucus — protects the stomach lining.
Small intestine
This is the major site of complete digestion and absorption.
- Bile from liver helps neutralise acidity and emulsifies fats.
- Trypsin helps digest proteins.
- Lipase helps digest fats.
- Intestinal enzymes complete digestion.
Final products include:
- Carbohydrates → glucose
- Proteins → amino acids
- Fats → fatty acids + glycerol
Villi
Finger-like projections lining the small intestine.
Importance: Increase surface area for absorption and contain blood vessels that transport absorbed nutrients.
Large intestine
- Absorbs additional water.
- Remaining waste is eliminated through the anus.
4. Respiration
Respiration is the process through which food is broken down to release energy for cellular activities.
First stage
Glucose → Pyruvate
This occurs in the cytoplasm.
After that, pyruvate can follow different pathways:
Aerobic respiration
Occurs in the presence of oxygen.
Pyruvate → CO₂ + H₂O + large amount of energy
Further breakdown occurs in the mitochondria.
Anaerobic respiration
Occurs without oxygen.
In yeast:
Pyruvate → Ethanol + CO₂ + less energy
In human muscle cells during insufficient oxygen:
Pyruvate → Lactic acid + energy
Accumulation of lactic acid can contribute to muscle cramps during sudden activity.
ATP — Energy currency
Energy released during respiration is used to form ATP.
ATP supplies usable energy for processes such as:
- Muscle contraction
- Protein synthesis
- Nervous impulses
- Other cellular activities.
Aerobic vs Anaerobic
| Aerobic | Anaerobic |
|---|---|
| Requires oxygen | Does not require oxygen |
| More energy released | Less energy released |
| Produces CO₂ and water | Products depend on organism/pathway |
| Major breakdown occurs in mitochondria after glycolysis | Further breakdown does not use the aerobic mitochondrial pathway |
5. Human Respiratory System
Air pathway
Nostrils → Throat → Air passages → Lungs → Alveoli
Alveoli
Tiny balloon-like structures in lungs where gas exchange occurs.
They are efficient because they have:
- Very large surface area.
- Thin walls.
- Extensive blood-vessel network.
Gas exchange
- Oxygen passes from alveolar air into blood.
- Carbon dioxide passes from blood into alveoli and is exhaled.
Haemoglobin
Present in red blood cells and carries oxygen to tissues.
Aquatic vs terrestrial respiration
Water contains much less dissolved oxygen than atmospheric air. Therefore, aquatic organisms such as fish generally need to pass water rapidly over their gills to obtain sufficient oxygen.
6. Transportation in Human Beings
The circulatory system consists mainly of:
Heart + Blood + Blood vessels
Blood transports:
- Oxygen
- Food/nutrients
- Carbon dioxide
- Nitrogenous wastes
- Salts and other substances.
Heart
The human heart has four chambers:
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
Blood pathway
Body → Right atrium → Right ventricle → Lungs → Left atrium → Left ventricle → Body
Why four chambers?
They help prevent oxygenated and deoxygenated blood from mixing and allow efficient oxygen supply.
Valves
Prevent backward flow of blood.
Double circulation
In humans, blood passes through the heart twice during one complete cycle:
- Heart → lungs → heart
- Heart → body → heart
This provides efficient oxygen delivery.
Blood vessels
Arteries
- Carry blood away from heart.
- Thick, elastic walls.
- Blood is under relatively high pressure.
Veins
- Carry blood towards heart.
- Have valves to prevent backflow.
- Walls are less thick than arteries.
Capillaries
- Extremely small vessels.
- Walls are about one cell thick.
- Allow exchange of substances between blood and tissues.
Platelets
Help in blood clotting, reducing blood loss when vessels are damaged.
Lymph
- Tissue fluid formed from material escaping through capillary walls.
- Returns excess fluid to blood.
- Helps transport absorbed fats from the intestine.
7. Transportation in Plants
Plants need transport systems because diffusion alone is insufficient when the distance between roots and leaves becomes large.
Two main tissues
| Tissue | Main function |
|---|---|
| Xylem | Transports water and minerals |
| Phloem | Transports products of photosynthesis and other substances |
Water transport — Xylem
Water enters roots and moves upward through xylem.
Transpiration
Loss of water vapour from aerial parts of the plant, mainly through stomata.
Transpiration pull
Evaporation of water from leaves creates a suction force that helps pull water upward through xylem.
Importance:
- Helps upward movement of water and minerals.
- Helps regulate plant temperature.
Food transport — Phloem
Movement of soluble products of photosynthesis is called translocation.
- Takes place through phloem.
- Can occur upward or downward, according to the plant’s needs.
- Uses energy from ATP.
Xylem vs Phloem
| Xylem | Phloem |
|---|---|
| Water and minerals | Food/products of photosynthesis |
| Mainly root → aerial parts | Can move in either direction |
| Movement largely driven by physical forces | Transport requires energy |
8. Excretion
Excretion is the removal of harmful metabolic wastes from an organism.
In complex organisms, specialised organs perform this function.
Human Excretory System
Main parts:
- Two kidneys
- Two ureters
- Urinary bladder
- Urethra
Path of urine
Kidneys → Ureters → Urinary bladder → Urethra → Outside
Kidney
The kidney filters wastes from blood.
Nephron
The nephron is the basic filtration unit of the kidney.
Main idea:
- Blood is filtered.
- Useful substances such as glucose, amino acids, salts and much water are selectively reabsorbed.
- Remaining waste forms urine.
- Urine passes into the ureter.
The amount of water reabsorbed depends partly on the body’s water requirement and the amount of dissolved waste that must be removed.
Artificial kidney / haemodialysis
When kidneys fail to adequately remove nitrogenous wastes, dialysis can remove these wastes from blood using a semipermeable membrane and dialysing fluid.
9. Excretion in Plants
Plants have different strategies because many of their tissues contain dead cells.
They can:
- Remove excess water through transpiration.
- Store wastes in cell vacuoles.
- Store wastes in leaves that later fall.
- Store substances such as gums and resins.
- Release some wastes into the surrounding soil.
- Release gases through exchange with the environment.
⭐ Ultra-Important Exam Connections
Remember these chains
Nutrition → Food → Respiration → ATP → Life activities
Roots → Xylem → Water + minerals → Leaves
Leaves → Phloem → Food → Growing/storage regions
Blood → Kidneys → Nephrons → Filtration + reabsorption → Urine
Lungs → Alveoli → O₂ into blood + CO₂ out
High-priority topics for revision
Excretion in plants
Photosynthesis and its requirements
Human digestion and functions of digestive organs
Aerobic vs anaerobic respiration
ATP and cellular energy
Structure and working of alveoli
Four-chambered heart and double circulation
Arteries, veins and capillaries
Xylem vs phloem
Transpiration pull
Nephron and urine formation