Health & Life Processes
Pathogens
Disease-causing organisms
What is a Pathogen?
A pathogen is a microorganism that causes disease. There are four main types:
Viruses
Structure: Genetic material (DNA or RNA) inside a protein coat. Not made of cells.
Reproduction: Invade host cells and use them to copy themselves, destroying the cell.
Examples: Influenza (flu), HIV, COVID-19, measles, chickenpox.
Important: Antibiotics do NOT kill viruses! Vaccines can prevent some viral diseases.
Body Defences
How we fight disease
💊 Antibiotics
Medicines that kill bacteria or stop them growing.
- • Effective against: Bacterial infections
- • NOT effective against: Viruses
- • Must complete the full course even if you feel better
Antibiotic resistance: Overuse means bacteria evolve resistance - a serious problem!
💉 Vaccination
Introduces dead or weakened pathogens to train your immune system.
- • Your body makes antibodies without getting the disease
- • Memory cells remain for rapid future response
- • Can prevent many dangerous diseases
Herd immunity: When enough people are vaccinated, disease can't spread easily.
Movement of Molecules
Diffusion and surface area to volume ratio
Factors Affecting Diffusion
Diffusion is the net movement of particles from high concentration to low concentration. Several factors affect the rate:
Temperature
Higher temperature = faster diffusion. Particles have more kinetic energy and move faster.
Concentration Gradient
Steeper gradient = faster diffusion. Bigger difference means more net movement.
Surface Area to Volume Ratio
Small organisms have a larger SA:Volume ratio than large organisms. This affects how easily substances can diffuse in and out.
Small cube
SA:V = 6:1
Fast diffusion
Medium cube
SA:V = 3:1
Medium diffusion
Large cube
SA:V = 1.5:1
Slow diffusion
This is why cells are small - they need a large SA:Volume for efficient diffusion!
Respiration
Releasing energy from food
Aerobic Respiration
The process that releases energy from glucose using oxygen. Happens in mitochondria of all living cells.
Glucose + Oxygen → Carbon Dioxide + Water + ENERGY (ATP)
What is ATP?
ATP (Adenosine Triphosphate) is the energy currency of cells. The energy released during respiration is used to make ATP from ADP.
- • ATP provides energy for: muscle contraction, nerve impulses, protein synthesis, active transport
- • ATP can be quickly converted back to ADP to release energy when needed
Photosynthesis
How plants make food
The Word Equation
Photosynthesis is the process by which plants make glucose using light energy.
Carbon Dioxide + Water + Light Energy → Glucose + Oxygen
Leaf Adaptations
- ● Broad, flat surface: Maximum light absorption
- ● Thin: Short distance for gases to diffuse
- ● Stomata: Pores for gas exchange (CO₂ in, O₂ out)
- ● Chloroplasts: Contain chlorophyll to absorb light
Factors Affecting Rate
- ☀️ Light intensity: More light = faster photosynthesis (up to a point)
- 💨 CO₂ concentration: More CO₂ = faster photosynthesis (up to a point)
- 🌡️ Temperature: Optimum around 25-35°C for most plants
These factors are called limiting factors.
Circulatory System
Transport around the body
Double Circulation
Humans have a double circulatory system - two separate circuits:
Pulmonary Circuit
Heart → Lungs → Heart
Deoxygenated blood picks up oxygen and releases CO₂ in the lungs.
Systemic Circuit
Heart → Body → Heart
Oxygenated blood delivers oxygen to all body cells.
The Heart
Right side: Receives deoxygenated blood from body, pumps to lungs
Left side: Receives oxygenated blood from lungs, pumps to body
Valves: Prevent backflow of blood
Coronary arteries: Supply the heart muscle with oxygen
Arteries
- • Carry blood away from heart
- • Thick, muscular walls
- • High pressure
- • No valves
Veins
- • Carry blood to heart
- • Thinner walls
- • Lower pressure
- • Contain valves
Capillaries
- • Tiny, thin-walled vessels
- • One cell thick
- • Exchange of materials
- • Connect arteries to veins
Ecosystems
Energy flow and the carbon cycle
Pyramids of Biomass
Shows the total mass of organisms at each trophic (feeding) level. Always pyramid-shaped because energy is lost at each level.
Energy Loss: Only about 10% of energy is passed to the next level. The rest is lost as heat, used for movement, or in waste.
The Carbon Cycle
Carbon is constantly recycled in ecosystems. Decomposers (bacteria and fungi) play a vital role.
Photosynthesis: Plants take in CO₂ and convert it to glucose
Respiration: All organisms release CO₂ back into the air
Decomposition: Breaks down dead material, releasing CO₂
Combustion: Burning fossil fuels releases CO₂
Human Impact: Burning fossil fuels and deforestation are increasing CO₂ levels, contributing to climate change.
Practice Questions
Test your understanding
Pathogens [4 marks]
a) What is a pathogen? [1 mark]
b) Explain why antibiotics cannot treat viral diseases. [2 marks]
c) Name one way to prevent viral diseases. [1 mark]
Answer:
a) A pathogen is a microorganism that causes disease. [1 mark]
b) Antibiotics work by damaging bacterial cell walls or stopping bacterial reproduction. [1 mark] Viruses do not have cells or cell walls - they live inside host cells, so antibiotics cannot affect them. [1 mark]
c) Vaccination OR avoiding infected people OR good hygiene. [1 mark]
Respiration Equations [3 marks]
Write the word equation for aerobic respiration.
Answer:
Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)
Award 1 mark each for: reactants correct, products correct, energy/ATP included.
Circulatory System [3 marks]
Explain the difference in structure between arteries and veins and relate this to their functions.
Answer:
Arteries: Have thick, muscular walls to withstand high pressure from the heart pumping blood. [1 mark]
Veins: Have thinner walls because blood pressure is lower. Contain valves to prevent backflow of blood. [1 mark]
Function link: Structure relates to pressure - arteries carry high-pressure blood away from heart; veins carry low-pressure blood back to heart. [1 mark]
Photosynthesis [3 marks]
Describe how the structure of a leaf is adapted for photosynthesis.
Answer (any three adaptations for 3 marks):
• Broad and flat: Large surface area for light absorption
• Thin: Short distance for light to penetrate and gases to diffuse
• Stomata: Pores that allow CO₂ to enter and O₂ to exit
• Chloroplasts in palisade layer: Large number near surface to capture light
• Vascular bundles (veins): Transport water to leaf and glucose away
Year 9 Biology Complete!
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