AQA GCSE (Combined Science) Unit 4: Bioenergetics Higher

Photosynthesis

• Chemical reaction in plants converting CO2 and water into glucose and oxygen.
• Light energy absorbed by chlorophyll in chloroplasts.
• Endothermic reaction.
• Carbon dioxide enters through stomata; water via roots and xylem.
• Glucose used for respiration, stored as starch/fats/oils, or for protein synthesis.

Rate of Photosynthesis and Limiting Factors

• Limiting factors: temperature, light intensity, CO2 levels.
• Temperature increase boosts reaction rate until enzymes denature (~45°C).
• Higher light intensity and CO2 levels increase reaction rate.

Effect of Light Intensity (RPI)

• More light = more photosynthesis; no light = no photosynthesis.
• Method:
  • Use sodium hydrogen carbonate, pondweed, lamp, measure bubbles.
  • Independent variable: light intensity.
  • Dependent variable: number of bubbles.
  • Control variables: time, amount of pondweed.

Interaction of Limiting Factors (HT only)

• Limiting factor changes with conditions (e.g., light at night, temperature in winter).
• Increasing one factor increases rate until another becomes limiting.

Greenhouse Economics (HT only)

• Greenhouses trap heat and control light/CO2 for optimal conditions.
• Costly but improves crop health and growth.
• Control pests/diseases better in enclosed conditions.

Respiration

• Occurs in mitochondria, releasing energy for functions.
• Exothermic reaction.
• Aerobic (with oxygen) vs. anaerobic (without oxygen, less energy).
• Anaerobic in plants and yeast = fermentation (used in bread/beer).

Inverse Square Law and Light Intensity

• Light intensity inversely proportional to square of distance from source.
• Worked Example:
  • Light source at different distances affects intensity reaching plant.

Effect of Exercise

• Muscles need more energy; increased respiration.
• Heart rate, breathing rate/volume increase to supply oxygen.
• Anaerobic respiration if oxygen demand exceeds supply.
• Produces lactic acid, causing oxygen debt and fatigue.

Metabolism

• Combination of all reactions in the body.
• Energy from respiration used in metabolic processes (e.g., synthesizing molecules).

Oxygen Debt (HT only)

• During exercise, anaerobic respiration produces lactic acid.
• Oxygen needed to convert lactic acid back to glucose.

AQA GCSE Biology (Combined Science) Unit 2: Organisation

Principles of Organisation

• Cells, tissues, organs, organ systems, organisms hierarchy.
• Food tests for sugar, starch, protein, lipids using different reagents.

The Digestive System

• Breaks down large molecules for absorption into bloodstream.
• Enzymes increase reaction rates in digestion.
• Effect of pH on Amylase: Measuring time to digest starch at different pH levels.

The Heart and Blood Vessels

• Heart pumps blood; gas exchange in lungs.
• Blood vessels adapted for specific functions (arteries, veins, capillaries).

The Heart as a Double Pump

• Pulmonary and systemic circulation.
• Pacemaker cells control heart rate.

Enzymes

• Biological catalysts, specific to reactions.
• Work optimally at specific pH/temperature.
• Denature at extremes.

Coronary Heart Disease

• Caused by fatty deposits in coronary arteries.
• Lifestyle factors (diet, smoking, stress) increase risk.

Blood

• Components: red blood cells, white blood cells, platelets suspended in plasma.
• Plasma transports cells, CO2, nutrients, hormones.
• Red blood cells transport oxygen; white blood cells defend against pathogens.

Cancer

• Uncontrolled cell growth results in tumors.

Plant Tissues, Organs, and Systems

• Leaves absorb sunlight for photosynthesis.
• Xylem and phloem transport water, nutrients, and glucose.

Transpiration and Translocation

• Transpiration: water loss by evaporation from leaves.
• Environmental factors affect rate.
• Translocation: transport of food substances in phloem.

Health and Disease

• Health: state of being free from illness.
• Diseases influenced by lifestyle (diet, smoking, stress).
• Interactions between diseases (immune disorders, viral infections).

Heart Disease (Treatments)

• Treatments: statins, stents, heart transplant.
• Each has advantages and disadvantages.

AQA Combined Science: Physics Topic 2 Electricity

Investigating Resistance

• Variables: length of wire (independent), resistance (dependent).
• Conclusion: Resistance increases with wire length.

Investigating Circuits

• Series vs. parallel circuits' effects on resistance.

Equations and Maths

• Charge, potential difference, energy, and power calculations.

Circuit Devices

• LDRs and thermistors: dependent on light and temperature.

Series and Parallel Circuits

• Series: shared potential difference, total resistance adds up.
• Parallel: same potential difference, total current is sum of individual currents.

Electricity in the Home

• Role of different wires (live, neutral, earth) in safety and circuit function.

The National Grid

• Transfers electrical power from power stations to consumers using transformers to manage voltage.