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Topic 4.1: Cell biology

Subtopic 4.1.1: Cell structure

4.1.1.1 - Eukaryotes, Prokaryotes and Cell Scale

4.1.1.2a - Animal and Plant Cell Structures

4.1.1.2b - Microscopy of Plant and Animal Cells

4.1.1.3 - Cell Specialisation

4.1.1.4 - Cell Differentiation

4.1.1.5 - Microscopy, Magnification and Resolution

4.1.1.6a - Culturing Microorganisms and Bacterial Growth

4.1.1.6b - Aseptic Technique and Zones of Inhibition

Subtopic 4.1.2: Cell division

4.1.2.1 - Chromosomes, DNA and Genes

4.1.2.2 - Mitosis and the Cell Cycle

4.1.2.3 - Stem Cells

Subtopic 4.1.3: Transport in cells

4.1.3.1a - Diffusion and Factors Affecting Its Rate

4.1.3.1b - Surface Area to Volume Ratio and Exchange Surfaces

4.1.3.2a - Osmosis and Water Movement

4.1.3.2b - Required Practical - Osmosis in Plant Tissue

4.1.3.3 - Active Transport

Topic 4.2: Organisation

Subtopic 4.2.1: Principles of organisation

4.2.1 - Principles of Organisation

Subtopic 4.2.2: Animal tissues, organs and organ systems

4.2.2.1a - Digestive System, Enzymes and Digestion

4.2.2.1b - Required Practical - Food Tests

4.2.2.1c - Required Practical - Amylase and pH

4.2.2.2 - The Heart and Blood Vessels

4.2.2.3 - Blood

4.2.2.4 - Coronary Heart Disease and Treatments

4.2.2.5 - Health Issues and Disease Interactions

4.2.2.6 - Lifestyle Risk Factors and Non-Communicable Disease

4.2.2.7 - Cancer

Subtopic 4.2.3: Plant tissues, organs and systems

4.2.3.1 - Plant Tissues

4.2.3.2a - Plant Transport Organs And Transpiration

4.2.3.2b - Translocation and Plant Transport Data

Topic 4.3: Infection and response

Subtopic 4.3.1: Communicable diseases

4.3.1.1 - Communicable Diseases

4.3.1.2 - Viral Diseases

4.3.1.3 - Bacterial Diseases

4.3.1.4 - Fungal Diseases - Rose Black Spot

4.3.1.5 - Protist Diseases - Malaria

4.3.1.6 - Human Defence Systems

4.3.1.7 - Vaccination

4.3.1.8 - Antibiotics and Painkillers

4.3.1.9 - Discovery and Development of Drugs

Subtopic 4.3.2: Monoclonal antibodies

4.3.2.1 - Producing Monoclonal Antibodies

4.3.2.2 - Uses of Monoclonal Antibodies

Subtopic 4.3.3: Plant disease

4.3.3.1 - Detection And Identification Of Plant Diseases

4.3.3.2 - Plant Defence Responses

Topic 4.4: Bioenergetics

Subtopic 4.4.1: Photosynthesis

4.4.1.1 - Photosynthetic Reaction

4.4.1.2a - Rate of Photosynthesis and Limiting Factors

4.4.1.2b - Required Practical - Light Intensity and Photosynthesis

4.4.1.3 - Uses of Glucose from Photosynthesis

Subtopic 4.4.2: Respiration

4.4.2.1a - Aerobic and Anaerobic Respiration

4.4.2.1b - Anaerobic respiration in muscles and fermentation

4.4.2.2 - Response to Exercise

4.4.2.3 - Metabolism

Topic 4.5: Homeostasis and response

Subtopic 4.5.1: Homeostasis

4.5.1 - Homeostasis

Subtopic 4.5.2: The human nervous system

4.5.2.1a - The Nervous System and Reflex Arcs

4.5.2.1b - Required Practical - Reaction Time

4.5.2.2 - The Brain

4.5.2.3a - The Eye and Accommodation

4.5.2.3b - Vision Defects And Their Correction

4.5.2.4 - Control of Body Temperature

Subtopic 4.5.3: Hormonal coordination in humans

4.5.3.1 - Human Endocrine System

4.5.3.2a - Blood glucose control

4.5.3.2b - Diabetes and Blood Glucose Treatments

4.5.3.3a - Water, ions and urea balance

4.5.3.3b - Kidney Failure, Dialysis and Transplants

4.5.3.4 - Hormones in Human Reproduction

4.5.3.5 - Contraception

4.5.3.6 - Hormones to Treat Infertility

4.5.3.7 - Negative feedback

Subtopic 4.5.4: Plant hormones

4.5.4.1a - Plant Hormones and Tropisms

4.5.4.1b - Required Practical - Plant Responses

4.5.4.2 - Use of Plant Hormones

Topic 4.6: Inheritance, variation and evolution

Subtopic 4.6.1: Reproduction

4.6.1.1 - Sexual and Asexual Reproduction

4.6.1.2 - Meiosis

4.6.1.3 - Advantages and Disadvantages of Sexual and Asexual Reproduction

4.6.1.4 - DNA and the Genome

4.6.1.5 - DNA structure

4.6.1.6a - Genetic Inheritance Terms and Gametes

4.6.1.6b - Genetic crosses and Punnett squares

4.6.1.7a - Inherited Disorders

4.6.1.7b - Embryo Screening

4.6.1.8 - Sex Determination

Subtopic 4.6.2: Variation and evolution

4.6.2.1 - Variation

4.6.2.2 - Evolution

4.6.2.3 - Selective breeding

4.6.2.4a - Genetic Engineering Process

4.6.2.4b - Genetic Engineering Applications and Risks

4.6.2.5a - Plant Cloning by Cuttings and Tissue Culture

4.6.2.5b - Animal cloning and embryo transplants

Subtopic 4.6.3: The development of understanding of genetics and evolution

4.6.3.1 - Theory of evolution

4.6.3.2 - Speciation

4.6.3.3 - Development of Genetics

4.6.3.4 - Evidence for evolution

4.6.3.5 - Fossils

4.6.3.6 - Extinction

4.6.3.7 - Resistant Bacteria

Subtopic 4.6.4: Classification of living organisms

4.6.4 - Classification of living organisms

Topic 4.7: Ecology

Subtopic 4.7.1: Adaptations, interdependence and competition

4.7.1.1 - Communities and Interdependence

4.7.1.2 - Abiotic factors

4.7.1.3 - Biotic factors

4.7.1.4 - Adaptations

Subtopic 4.7.2: Organisation of an ecosystem

4.7.2.1a - Ecosystem Levels and Food Chains

4.7.2.1b - Required Practical - Sampling Populations

4.7.2.2 - Water and carbon cycles

4.7.2.3a - Decomposition and Decay Factors

4.7.2.3b - Investigating Decay Using Milk pH

4.7.2.4 - Impact of Environmental Change

Subtopic 4.7.3: Biodiversity and the effect of human interaction on ecosystems

4.7.3.1 - Biodiversity

4.7.3.2 - Waste Management

4.7.3.3 - Land Use

4.7.3.4 - Deforestation

4.7.3.5 - Global warming

4.7.3.6 - Maintaining biodiversity

Subtopic 4.7.4: Trophic levels in an ecosystem

4.7.4.1 - Trophic levels

4.7.4.2 - Pyramids of biomass

4.7.4.3 - Transfer of Biomass

Subtopic 4.7.5: Food production

4.7.5.1 - Factors affecting food security

4.7.5.2 - Farming Techniques

4.7.5.3 - Sustainable fisheries

4.7.5.4 - Role of Biotechnology

Topic 4.8: Key ideas

Synoptic connections across biology

4.8 - Key Ideas in Biology

4.4.1.1 - Photosynthetic Reaction

4.4.1.1 - Photosynthetic Reaction

Photosynthesis is the reaction that plants and algae use to make glucose. At AQA GCSE depth, the core is not a detailed biochemical pathway: it is the reaction equation, the chemical symbols, and the idea that light transfers energy to chloroplasts. This lesson keeps the focus on those exam-ready statements.

Reaction summary

Photosynthesis uses carbon dioxide and water to make glucose and oxygen. In a chemical equation, the substances on the left of the arrow are the reactants, and the substances on the right are the products.

Reactant

A reactant is a substance that is used up in a chemical reaction.

The word equation for photosynthesis is:

Photosynthesis word equation

\text{carbon dioxide} + \text{water} \xrightarrow{\text{light}} \text{glucose} + \text{oxygen}

Carbon dioxide and water are the reactants. Glucose and oxygen are the products. Light is written above the arrow because it transfers energy for the reaction; it is not one of the substances being rearranged into glucose and oxygen.

Symbols and balanced equation

AQA expects you to recognise the chemical symbols in the photosynthesis equation. The capital letters matter: CO2 is carbon dioxide, but Co would mean the element cobalt, so Co2 is not a correct way to write carbon dioxide.

Substance	Chemical symbol	Role in photosynthesis
Carbon dioxide	`CO2`	Reactant
Water	`H2O`	Reactant
Glucose	`C6H12O6`	Product
Oxygen	`O2`	Product

You may also see the balanced symbol equation:

Balanced symbol equation

6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2

The large numbers in front, such as the 6 before CO2, balance the equation. They show how many molecules are involved in the summary equation. The smaller numbers inside a formula, such as the 2 in CO2 or the 6, 12 and 6 in C6H12O6, are part of the chemical formula and must not be changed casually.

Endothermic energy transfer

Photosynthesis is an endothermic reaction. At GCSE, that means energy is transferred from the environment to the reaction.

Endothermic reaction

An endothermic reaction is a reaction in which energy is transferred from the surroundings or environment to the reacting substances.

For photosynthesis, AQA's exact biology wording is that energy is transferred from the environment to the chloroplasts by light. Chloroplasts are the sub-cellular structures where photosynthesis takes place in plant cells and algal cells.

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