AQA GCSE Combined Science: Trilogy 8464 Biology Revision

Biology Paper 1 & 2 Revision Notes

4.1 Cell Biology

• Eukaryotes and Prokaryotes

  • Eukaryotic cells (plant and animal cells):
    • Have genetic material enclosed in a nucleus to control cell activity.
    • Have a cell membrane to control what enters and exits.
    • Contain cytoplasm for reactions.
  • Prokaryotic cells (bacterial cells):
    • Smaller than eukaryotic cells.
    • Genetic material is not enclosed in a nucleus; it's a single DNA loop.
    • May contain small DNA rings called plasmids.
    • Have cytoplasm and a cell membrane.
    • Have a cell wall for strength and support.

• Animal and Plant Cells

  • Animal Cells:
    • Nucleus
    • Cytoplasm
    • Cell membrane
    • Mitochondria (for aerobic respiration, releasing energy)
    • Ribosomes (for protein synthesis)
  • Plant Cells (in addition to animal cell parts):
    • Chloroplasts (with chlorophyll for photosynthesis)
    • Permanent vacuole (filled with cell sap for support)
    • Cell wall (made of cellulose for strength)

• Required Practical 1: Light Microscopy

  • Light Microscope:
    • Shines light through a thin, dead, stained specimen.
    • Resolution and magnification are sufficient to view the nucleus and cell membrane.
    • Most organelles are too small to see.
  • Drawings:
    • Use a pencil for drawings.
    • Include labels.
  • Maths Skills:
    • Size \, of \, image \, (mm) = Magnification \times Size \, of \, real \, object \, (mm)

• Cell Specialisation

  • Cells are specialised to perform specific functions.
  • Examples:
    • Sperm cells, nerve cells, and muscle cells in animals.
    • Root hair cells, xylem, and phloem cells in plants.
  • Examples of cell specializations (Name of Cell, Picture, Structure, Function):
    • PHLOEM CELLS: Consists of long hollow tubes. Transports dissolved sugars around a plant.
    • ROOT HAIR CELLS: Have hairs on the tops of cells to increase surface area. Absorb nutrients from the small intestine.
    • NERVE CELLS: Has a large surface area because of a long finger-like projection. Allows electrical impulses to pass around the body
    • SPERM CELLS: Has a long flagella and lots of mitochondria. Fertilises an egg cell
    • XYLEM CELLS: Consists of long hollow tubes strengthened with lignin. Transports water and mineral ions around a plant
    • MUSCLE CELLS: Have lots of mitochondria to release extra energy. Control movement of the skeleton in animals
    • CILIATED CELLS: Has a long axon and a cell body found in the CNS. Absorb water for a plant

• Cell Differentiation

  • Cells differentiate to form different cell types as an organism develops.
  • Animal cells differentiate early.
  • Plant cells can differentiate throughout life.
  • Cell division in mature animals is mainly for repair and replacement.
  • Differentiation leads to specialised cells with specific sub-cellular structures.
  • Meristem tissue in plants allows for continuous differentiation.

4.1.3 Cell Transport

• Diffusion

  • Definition: Spreading of particles in a solution or gas from high to low concentration.
  • Examples: Molecules diffusing in and out of cells.
  • Factors Affecting Rate: Concentration gradient, temperature, surface area.
  • Surface Area: Volume Ratio: Higher ratio increases the rate of diffusion.
  • Adaptations for exchanging materials:
    • Lungs
    • Small intestine
    • Gills
    • Leaves
    • Roots

• Osmosis

  • Definition: Diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

• Required Practical 2: Osmosis in Plant Tissue

  • Plant tissue can measure water uptake rate in different solutions.
  • Only water moves; salt and sugar molecules are too large.
  • Higher salt/sugar concentration means lower water concentration.

• Active Transport

  • Moves substances against a concentration gradient (from dilute to concentrated).
  • Requires energy from respiration.
  • Examples:
    • Mineral ions absorbed into plant root hairs.
    • Sugar molecules absorbed from the gut into the blood.

4.2 Organisation

• Principles of Organisation

  • Cells are the basic building blocks.
  • A tissue is a group of similar cells with a similar function.
  • Organs are tissues performing specific functions.
  • Organ systems are organs working together.
  • Hierarchy: Cell -> Tissue -> Organ -> Organ System -> Organism
  • Example of a plant organ and its function.

• The Heart and Blood Vessels

  • Heart pumps blood in a double circulatory system.
    • Right ventricle pumps blood to the lungs for gas exchange.
    • Left ventricle pumps blood to the rest of the body.
  • Natural resting heart rate is controlled by cells in the right atrium (pacemaker).
  • Artificial pacemakers correct irregularities.
  • Blood vessels: Arteries, veins, and capillaries.
  • Heart valves

• The Lungs

  • Specialised organs for efficient gas exchange.
  • Large surface area: volume ratio to maximise gas exchange rate.

• Blood

  • Tissue consisting of plasma, red blood cells, white blood cells, and platelets.

• Plant Tissues

  • Epidermal tissues, palisade mesophyll, spongy mesophyll, xylem, phloem, and meristem tissue.
  • Leaf is a plant organ adapted for photosynthesis.
  • Xylem
  • Phloem

• Plant Organ Systems

  • Transpiration: Water movement from roots to atmosphere via xylem and leaves.
  • Xylem vessels transport water.
  • Phloem tissue transports dissolved sugars (sucrose) via translocation.
  • Stomata: Used to control gas exchange and water loss.
  • How the structure of the root hair cell is adapted to its function.

• The Stomata

  • Stomata and guard cells are found on the underside of the leaf and are used to control gas exchange and water loss.

4.4 Bioenergetics

• Photosynthesis – The Reaction

  • Photosynthesis is an endothermic reaction where energy is transferred from the environment to chloroplasts by light to produce glucose.
  • Word equation:
    • Carbon dioxide + Water → Glucose + Oxygen
  • Symbol equation:
    • 6CO2 + 6H2O \rightarrow C6H{12}O6 + 6O2

• The Rate of Photosynthesis

  • Limiting factors: Light intensity, carbon dioxide concentration, temperature, water availability.
  • Effect of temperature on the rate of photosynthesis

• The Rate of Photosynthesis (HIGHER TIER ONLY)

  • Farmers use knowledge of limiting factors to design greenhouses for increased photosynthesis and profits.
    • Light \, Intensity \propto \frac{1}{Distance^2}

• Required Practical 5: Photosynthesis and Aquatic Organisms

  • Investigating the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed.
  • Name the equipment needed for this experiment.

• Uses of Glucose from Photosynthesis

  • Glucose is required by plants for various processes and converted into different molecules.
  • Uses: Respiration, making cellulose, making amino acids, stored as oils or fats, stored as starch.
  • Plants need nitrate ions to produce proteins.

• Aerobic and Anaerobic Respiration

  • Cellular respiration is an exothermic reaction in living cells.
    • Word equation:
      • Glucose + Oxygen → Carbon dioxide + Water
    • Symbol Equation:
      • C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O
  • Respiration releases energy for living processes.
  • Anaerobic respiration in yeast is fermentation.
    • In muscles:
      • Glucose → Lactic acid
    • In plants/yeast:
      • Glucose → Ethanol + Carbon dioxide
  • Uses of Fermentation

• Response to Exercise

  • Increased energy demand during exercise leads to increased heart rate, breathing rate, and breath volume.
  • Insufficient oxygen leads to anaerobic respiration and lactic acid build-up, causing muscle fatigue.
  • Lactic acid is transported to the liver and converted back into glucose.
  • Oxygen debt is the extra oxygen needed to react with lactic acid and remove it from cells.

• Metabolism

  • Metabolism is the sum of all reactions in a cell or the body.
  • Examples of monomers:
    • Carbohydrates:
    • Lipids:
    • Proteins:

4.5 Homeostasis and Response

• Homeostasis

  • Homeostasis is the regulation of internal conditions inside a cell or organism.
  • Controlled variables: Body temperature, water content, blood glucose.

• Structure and Function of The Human Nervous System

  • The nervous system enables humans to react to their surroundings and coordinate their behavior.
  • Reflex actions are rapid; they do not involve the conscious part of the brain.
  • Components of a reflex arc: Stimulus, receptor, coordinator (CNS), effector, response.

• Required Practical 6: Human Reaction Time

  • Investigating the effect of a factor on human reaction time.

• Human Endocrine System

  • The endocrine system secretes hormones directly into the bloodstream.
  • Hormones are transported to target organs to produce an effect.
  • The pituitary gland is a ‘master gland’ which secretes several hormones.

• Contraception

  • Contraceptive methods and how they work:
    • Oral contraceptives (the pill)
    • Injection/Implant/Patch
    • Barrier method e.g. condoms/ diaphragms
    • Intrauterine Devices e.g. coil
    • Spermicidal agents
    • Timed abstinence
    • Surgical sterilisation e.g. vasectomy

• The Use of Hormones to Treat Infertility (HT ONLY)

  • Fertility drugs can be given to women to help them become pregnant naturally.
  • In Vitro Fertilisation (IVF) is an alternative method used by couples unable to get pregnant.

• Negative Feedback (HT ONLY)

  • Negative feedback processes ensure internal conditions are maintained within a narrow range.

4.6 Inheritance, Variation and Evolution

• Chromosomes

  • The nucleus of a cell contains chromosomes made of DNA molecules.
  • Each chromosome carries a large number of genes.
  • In body cells the chromosomes are normally found in pairs.
  • Hierarchy: Cell -> Nucleus -> Chromosome -> Gene

• Mitosis and The Cell Cycle

  • Cells divide in a series of stages called the cell cycle.
  • Genetic material is doubled and then divided into two genetically identical daughter cells.
  • Mitosis is important in the growth, repair, and development of multicellular organisms.

• Stem Cells

  • A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.
  • Stem cells from embryos can be cloned and made to differentiate into most different types of human cells. Stem cells from adult bone marrow can form many types of cells including blood cells. Treatment with stem cells may be able to help conditions such as diabetes and paralysis. Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of a plant.

• Cancer

  • Cancer is the result of changes in cells that lead to uncontrolled growth and division.
  • Tumours can be malignant or benign.
  • Both genetic factors and lifestyle choices can affect an individual’s likelihood of developing cancer.

• DNA and The Genome

  • The genetic material in the nucleus is composed of a chemical called DNA. DNA is a polymer made up of two strands forming a double helix. The DNA is contained in structures called chromosomes.
  • Genes code for a particular sequence of amino acids which make a specific protein.
  • The genome of an organism is the entire genetic material of that organism. The whole human genome has now been studied and this will have great importance for medicine in the future.

• Inherited Disorders

  • Some disorders are caused by the inheritance of certain alleles, e.g. cystic fibrosis and polydactyly.

• Sex Determination

  • Human body cells contain a pair of chromosomes, which carry the genes that determine sex.

• Variation

  • There is extensive variation within a population of a species.
  • The phenotype (observable characteristics) of an organism is affected by both genetics and the environment.
  • Mutations occur continuously. Very rarely, a mutation will lead to a new characteristic. If the new characteristic is advantageous it can lead to a change in the species.

• Evolution

  • The theory of evolution states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
  • Evolution is a change in the inherited characteristics of a population over time through a process of natural selection, which may result in the formation of a new species.
  • If two populations of one species become so different that they are no longer able to interbreed to produce fertile offspring, they have formed two new species.

• Selective Breeding

  • Selective breeding is the process by which humans breed plants and animals for particular genetic characteristics. Humans have been doing this for thousands of years since they first bred food crops from wild plants and domesticated animals.
  • Selective breeding can lead to ‘inbreeding’, where some breeds are particularly prone to disease or inherited defects.

• Classification of Living Organisms

  • Traditionally living things have been classified into groups depending on their structure and characteristics in a system developed by Carl Linnaeus.
  • As evidence of internal structures become more developed due to improvements in microscopes, and the understanding of biochemical processes progressed, new models of classification were proposed.
  • Due to evidence available from chemical analysis there is now a three domain system developed by Carl Woese.

4.7 Ecology

• Communities

  • An ecosystem is the interaction of a community of living organisms with the non-living parts of their environment.
  • Organisms require a supply of materials from their surroundings and other living organisms there.
  • Plants compete with each other for light, space, water and mineral ions.
  • Animals compete with each other for food, mates and territory.
  • Interdependence means that communities of species depend on other species for food, shelter, pollination, water etc. If one species is removed, it can affect the whole community.
  • In a stable community, all the species and environmental factors are in balance and population sizes remain fairly constant.
  • Pollinators: Describe the importance of bees to plants within a community.

• Biotic and Abiotic Factors

  • Non-living factors which affect a community are known as abiotic factors.
  • Examples include: light intensity (photosynthesis), temperature (enzymes), moisture levels, soil pH and mineral content, wind intensity and direction, carbon dioxide levels (plants), oxygen levels (aquatic animals).
  • Living factors which affect a community are known as biotic factors.
  • Examples include: availability of food, new predators arriving, new pathogens, one species outcompeting another so the numbers are no longer sufficient to breed.

• Adaptations

  • Adaptations are features that enable them to survive in the conditions in which they normally live. These adaptations may be structural, behavioural or functional.
  • Extremophiles live in environments that are very extreme, such as at high temperature, pressure, or salt concentration.

• Levels of Organisation

  • Photosynthetic organisms (plants and algae) are the producers of biomass for life on Earth.
  • Transects and quadrats are used to determine the distribution and abundance of species in an ecosystem.
  • All organisms are part of a food chain:
    • Producer → Primary consumer → Secondary consumer → Tertiary consumer

• Required Practical 7: Population Size

  • Measure the population size of a common species in a habitat. Use sampling techniques to investigate the effect of a factor on the distribution of this species.

• How Materials Are Cycled

  • The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis.
  • The water cycle provides fresh water for plants and animals on land before draining into the seas. Water is continuously evaporated and precipitated.
  • Microorganisms cycle materials through an ecosystem through the process of decay. As the microorganisms respire, they release the carbon trapped in materials as carbon dioxide into the atmosphere. At the same time, mineral ions are released to the soil.

• Biodiversity

  • Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem.
  • A great biodiversity ensures the stability of ecosystems by increasing the availability of food and shelter for organisms.
  • Many human activities, such as deforestation, are reducing biodiversity. Only recently have measures been taken to try and stop this reduction. One way is carbon sequestration.

• Waste Management

  • Rapid growth in the human population and an increase in the standard of living mean that increasingly more resources are used and more waste is produced.
  • Pollution kills plants and animals which can reduce biodiversity.
  • Water pollution can occur from sewage, fertiliser or toxic chemicals.
  • Air pollution can occur from smoke and acidic gases.
  • Land pollution can occur from landfill and from toxic chemicals.

• Land Use

  • Humans reduce the amount of land available for other animals and plants by building, quarrying, farming and dumping waste.
  • Peat bogs are wetland areas made up of partially decomposing material. Peat is used as garden compost because it contains a high concentration of mineral ions. The destruction of peat bogs results in a loss of biodiversity.
  • The decay or burning of peat releases carbon dioxide into the environment.

• Deforestation

  • Large-scale deforestation in tropical areas has occurred in order to provide land for cattle and rice fields, and grow crops for biofuel.

• Global Warming

  • Global warming is the observed increase in the average surface temperature due to the effect of greenhouse gases. Increasing levels of the two main greenhouse gases, carbon dioxide and methane, are contributing to global warming.
  • Scientific publications are always peer-reviewed. Scientists review each other’s work regularly in order to understand more about global warming and climate change. During this process, scientists try and repeat each other’s work in order to check its validity and give each other feedback.

• Maintaining Biodiversity

  • Scientists and concerned citizens have put in place programmes to reduce the negative effects of humans on ecosystems and biodiversity. These include breeding programmes for endangered species, protection and regeneration of rare habitats, re-introduction of hedgerows in agricultural areas where farmers grow only one type of crop, reduction of deforestation and carbon dioxide emissions and recycling initiatives.

Microbes and Health

• The Human Digestive System

  • The digestive system is an organ system where several organs work together to absorb and digest food.
  • Digestive enzymes convert large insoluble molecules into smaller soluble ones so they can be absorbed into the blood stream.
  • Complete the table to summarise the role of the organs in the digestive system
  • What does a digestive enzyme do?
  • Complete the table about enzymes
  • Explain enzyme action using the lock and key theory.
  • Describe the 2 functions of bile and state where it is made and where it is stored

• Required Practical 3: Testing for Carbohydrates, Lipids, and Proteins

  • Outlines how to prepare a sample of solid food for a food test
  • Summarizes the 4 food tests
    • Benedict’s Test
    • Iodine Solution
    • Biuret Test
    • Sudan III Test

• Required Practical 4: Effect of pH on Amylase Activity

  • Details method for practical using continuous sampling technique.
  • Suggests experiment hypothesis outlined above.
  • Identifies 3 possible sources of error in the experiment and identifies how we would control or monitor them.

• Coronary Heart Disease: A Non-Communicable Disease

  • Describes what has happened inside the body of someone who has coronary heart disease.
  • Describes the consequence of a person having a faulty valve and the methods used to treat it.
  • Summary of some treatments for CHD

• Health Issues and The Effect of Lifestyle on Some Non-Communicable Diseases

  • States 3 lifestyle factors that can affect both mental and physical health.
  • Which type of pathogen, living in cells, can be a trigger for cancer?
  • What can immune reactions (originally caused by a pathogen) be a trigger for?
  • What mental illness can severe physical health problems cause?
  • What physical problems can smoking cause?
  • Which organs does drinking alcohol affect the most?

• Cancer

  • Describes what is happening to cells in someone with cancer.
  • What is a benign tumour?
  • How are malignant tumours different to benign tumours?
  • Suggest three factors that are linked with an increased risk of getting cancer.

• Communicable Diseases

  • Pathogens are microorganisms that can cause disease. They can infect plants or animals and can be spread by direct contact, water or air.

• Viral and Bacterial Diseases

  • The flu (influenza), measles, HIV and tobacco mosaic virus (TMV) are all examples of viral diseases.
  • Salmonella which causes food poisoning and Gonorrhoea (a sexually transmitted infection) are caused by bacteria.

• Fungal and Protist Diseases

  • Rose black spot is a fungal disease affecting plant growth.
  • Malaria is caused by protists.

• Human Defence Systems

  • Complete the table to summarize the defence systems of the human body:
    • Skin
    • Nose
    • Trachea and bronchi
    • Stomach
  • Describe the 3 ways that white blood cells defend the body against pathogens

• Vaccination

  • Spread of pathogens can be reduced by vaccinating a large amount of the population.
  • A vaccine prevents an individual becoming infected with and spreading a specific pathogen.
  • Vaccinations work by introducing small amounts of dead/inactive pathogens into the body causing the white blood cells to respond.

• Antibiotics and Painkillers

  • What is an antibiotic? Give an example.
  • Why are doctors being encouraged to reduce the amount of antibiotics they are prescribing?
  • Why can antibiotics not be used to treat the flu?
  • Why is it difficult to create a drug that kills the flu?
  • What is a painkiller? How is it different to an antibiotic?

• Detection and Identification of Plant Diseases (biology only - HT only)

  • List 7 ways plant diseases can be detected.
  • List 3 Ways an Identification of a Plant Disease Can Be Made.
  • Other than pathogens, how else can plants get infected? Give an example.
  • Complete the table to summarise the problems plants have with mineral deficiency

• Plant Defence Responses

  • Describe in detail 3 physical defence responses that plants have to resist invasion of microorganisms.
  • Describe 2 chemical plant defence responses.
  • Suggest 3 mechanical adaptations plants may have to defend against being eaten by animals.

• Graph Drawing

  • List the top tips for getting full marks in graph-drawing questions
  • Explain what is bar charts used for
  • Explain what is line graph used for
  • Define Independent variable
  • Define Dependent variable
  • Define Categoric variable
  • Define Continuous variable