Life Processes
Explore nutrition, respiration, circulation, excretion, and how living organisms sustain life.
Chapter Notes
1. What are Life Processes?
- The maintenance functions that keep an organism alive even when it is not doing anything visible are called life processes: nutrition, respiration, transportation, excretion, along with control and coordination.
- Living organisms need an energy source and raw materials because their molecular structures keep breaking down due to the effects of the environment; repair and maintenance need energy.
- Unicellular organisms exchange materials directly with the environment by diffusion. Multicellular organisms have specialised tissues and organ systems because their inner cells are not in direct contact with the surroundings.
Board-style practice questions
Q1.Why is diffusion insufficient to meet the oxygen requirement of multicellular organisms like humans?
2 marks2. Nutrition — Autotrophic
- Autotrophs (green plants, some bacteria) make their own food from CO₂ and water using sunlight and chlorophyll.
- Steps of photosynthesis: absorption of light energy by chlorophyll, conversion of light energy to chemical energy and splitting of water into hydrogen and oxygen, and reduction of carbon dioxide to carbohydrates.
- Gaseous exchange occurs through stomata; each stoma is guarded by two guard cells that swell (open) when water flows in and shrink (close) when water is lost — this also prevents excess water loss.
- Plants also need nitrogen, phosphorus, iron and magnesium, taken from soil as minerals.
6CO₂ + 6H₂O →(light, chlorophyll) C₆H₁₂O₆ + 6O₂Watch it happen — Photosynthesis Rate Lab
Controls
60 %
50 %
25 °C
Live result
Relative rate
35.7%
Limiting factor
CO₂ concentration
Glucose produced
2.98mg/h
Rate35.71
Photosynthesis inside the leafRelative rate: 35.7 %
6CO₂ + 6H₂O →(light, chlorophyll) C₆H₁₂O₆ + 6O₂. The slowest factor limits the whole rate.
Board-style practice questions
Q1.Describe the events occurring during photosynthesis. Write the overall equation.
3 marks3. Nutrition — Heterotrophic and Human Digestion
- Heterotrophic nutrition types: saprophytic (fungi, on dead matter), parasitic (Cuscuta, ticks, leeches) and holozoic (Amoeba, humans).
- Amoeba engulfs food with pseudopodia into a food vacuole; Paramoecium uses cilia.
- Human alimentary canal: mouth → oesophagus → stomach → small intestine → large intestine → anus. Salivary amylase digests starch; peristaltic movements push food along.
- Stomach: HCl makes the medium acidic and kills germs, pepsin digests protein, mucus protects the stomach lining.
- Small intestine is the site of complete digestion — bile from the liver emulsifies fat and makes the medium alkaline, pancreatic juice supplies trypsin and lipase, intestinal juice completes digestion. Villi increase surface area for absorption.
- Large intestine absorbs water; the remaining waste is expelled through the anus.
Starch →(amylase) Maltose →(intestinal juice) GlucoseWatch it happen — Digestive Enzyme Matcher
Controls
Live result
Enzyme(s)
Salivary amylase
Action
Starch → maltose
Optimum pH
pH ~7 (slightly alkaline)
Digestion — enzymes breaking food downEnzyme(s): Salivary amylase
Bile does not contain enzymes — it emulsifies fat and makes the medium alkaline for lipase.
4. Respiration
- Glucose is first broken in the cytoplasm into pyruvate (glycolysis). In the presence of oxygen, pyruvate is broken in the mitochondria into CO₂ and water releasing much more energy.
- Anaerobic in yeast gives ethanol + CO₂ (fermentation); in our muscle cells during vigorous exercise, lack of oxygen gives lactic acid, which causes cramps.
- Energy released is used to make ATP, the energy currency of the cell.
- Human respiratory system: nostrils → nasal passage → pharynx → larynx → trachea (supported by cartilage rings) → bronchi → bronchioles → alveoli. Alveoli provide a huge surface area (about 80 m²) for exchange of gases; haemoglobin in RBCs carries oxygen and CO₂ is mostly carried dissolved in plasma.
- Terrestrial animals get oxygen from air; aquatic animals use gills and breathe faster because dissolved oxygen in water is low.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP (aerobic)Watch it happen — Aerobic vs Anaerobic Respiration
Controls
5
Live result
ATP produced
190
End products
CO₂ + H₂O
Site
Cytoplasm + mitochondria
ATP190
Respiration — glucose to energyATP produced: 190
Lactic acid build-up in muscles during heavy exercise causes cramps.
Board-style practice questions
Q1.Differentiate between aerobic and anaerobic respiration with equations and site of occurrence.
3 marks5. Transportation in Humans
- The human heart has four chambers so that oxygenated and deoxygenated blood do not mix — this keeps the oxygen supply efficient for warm-blooded animals.
- Path: body → vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body. Blood passes through the heart twice in one cycle — double circulation.
- Ventricles have thicker walls because they pump blood out with pressure; valves prevent backflow.
- Blood components: plasma, RBCs (haemoglobin), WBCs (defence), platelets (clotting). Arteries carry blood away from the heart, veins bring it back and have valves, capillaries allow exchange of materials.
- Lymph is a colourless fluid that carries digested fat and returns extra tissue fluid to the blood.
- High blood pressure (hypertension) is caused by constriction of arterioles; normal BP is 120/80 mm Hg.
Cardiac output = Stroke volume × Heart rateWatch it happen — Heart & Circulation
Controls
72 bpm
70 mL
Live result
Cardiac output
5.04L/min
State
Normal resting
Output (L/min)5.04
Double circulation — heart pumpingCardiac output: 5.04 L/min
Humans have double circulation: blood passes through the heart twice in one complete cycle.
Board-style practice questions
Q1.Explain double circulation in human beings. Why is it necessary?
5 marks6. Transportation in Plants
- Xylem carries water and minerals upward from the roots; phloem translocates food from leaves to storage and growing parts.
- Root pressure pushes water up at night; during the day, transpiration pull from the leaves is the main driving force. Transpiration also cools the plant and helps in mineral absorption.
- Translocation in phloem is bidirectional and uses energy — sucrose is loaded using ATP, water enters by osmosis, and the resulting pressure moves material to tissues of lower pressure.
Watch it happen — Transpiration Pull
Controls
28 °C
50 %
8 km/h
Live result
Transpiration rate
24.7mL/h per plant
Stomata
Open
Rate24.73
Transpiration pull — water up the plantTranspiration rate: 24.7 mL/h per plant
Transpiration pull created in the leaves drags water up the xylem from the roots.
7. Excretion
- Human excretory system: two kidneys, two ureters, urinary bladder and urethra.
- The nephron is the filtration unit. Blood is filtered in the glomerulus (Bowman's capsule); useful substances like glucose, amino acids, salts and most water are reabsorbed in the tubule; the remaining fluid is urine.
- Amount of water reabsorbed depends on how much excess water there is in the body and on the amount of dissolved waste to be excreted.
- Kidney failure is treated by haemodialysis using an artificial kidney.
- Plants excrete by storing wastes in vacuoles, in leaves that fall off, as resins and gums in old xylem, and by releasing some waste into the soil.
Watch it happen — Nephron Filtration Lab
Controls
2 L/day
180 L/day
Live result
Urine output
1.1L/day
Water reabsorbed
99.39%
Urine concentration
Dilute (pale)
Nephron — filtration & reabsorptionUrine output: 1.1 L/day
Selective reabsorption in the tubule returns glucose, amino acids and most water to the blood.
Board-style practice questions
Q1.Draw/describe the structure of a nephron and explain how urine is formed.
3 marks