AQA GCSE Biology Specification Breakdown
AQA GCSE Biology is assessed through a combination of two written exams.
This page will break down the specification for the written exams, including in-depth analysis of the last three Biology Higher Tier exams:
- Average marks per paper for each unit
- Number of marks for each topic for the last three series, including Assessment Objective breakdown and whether it was in the Extended Question.
These insights will provide guidance on the relative frequency of topics in exams. Currently, only data on Paper 1 is available but Paper 2 will be added very soon.
Note: You may notice that the marks allocated to each topic do not cumulatively add up to the total marks for a given paper. This is because questions with more than one topic required for the marks are included in both topic tallies.
Paper 1
B1 – Cell Biology
Average marks available per series: 35.3
Eukaryotes and Prokaryotes
Understand that:
- Plant and animal cells are eukaryotic cells. They have a cell membrane, cytoplasm and nucleus containing genetic material.
- Bacterial cells are prokaryotic cells. They are much smaller in comparison and have cytoplasm and a cell membrane surrounded by a cell wall and a single DNA loop and some plasmids (small rings of DNA) loop.
Demonstrate:
- Understanding of the scale and size of cells to make order of magnitude calculations (requires standard form).
- Ability to use the prefixes centi, milli, micro, nano.
Animal and Plant Cells
Explain how the main subcellular structures are related to their function:
- Nucleus, cell membrane, mitochondria, chloroplasts (plant cells) and plasmids (bacterial cells)
Recognise, draw and interpret images of animal and plant cells.
Use estimations and explain why they should be used to judge relative size or area of sub-cellular structures.
Use estimations and explain why they should be used to judge relative size or area of sub-cellular structures.
Cell Specialisation
Explain how:
- The structure of different types of cell relate to their function in a tissue, an organ, an organ system, or the whole organism (using information provided)
- The following cells are specialised to carry out a particular function: sperm, nerve and muscle cells (animals) and root hair cells, xylem and phloem cells (plant).
Cell Differentiation
Understand that:
- As an organism develops, cells form different types of cells through cell differentiation
- Cell differentiation enables cell specialisation as it acquires different sub-cellular structures so it can carry out a specific function.
- In animals, cells can differentiate at an early stage – in mature animals, cell division is structured to repair and replacement.
- In plants, many cells retain the ability to differentiate throughout their lives.
Explain the importance of cell differentiation.
Microscopy
Practical 1: Use a light microscope to observe, draw and label a selection of plant and animal cells, including a magnification scale.
Understand:
- How microscopy techniques have developed over time.
- Differences in magnification and resolution for a light and electron microscope.
Explain how:
- Electron microscopy has increased understanding of sub-cellular structures because it has a much greater magnification and resolution than a light microscope which can view study cells in much finer detail.
Calculate:
- Magnification, real size and image size of a microscope image/drawing using the ‘I AM’ formula (including expressing answers in standard form).
- Ability to use the prefixes centi, milli, micro, nano.
Culturing Microorganisms
Practical 2: Investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zones of inhibition.
Understand that:
- Bacteria multiply by binary fission (simple cell division).
- This can be once every 20 minutes if sufficient nutrients and temperature.
- Scientists can grown bacteria either in a nutrient broth solution or as colonies on an agar gel plate.
- Uncontaminated cultures of microorganisms are used to investigate the action of disinfectant and antibiotics.
Calculate:
- The number of bacteria in a population after a given period of time using the mean division time (using standard form, when appropriate).
- The cross-selection areas of colonies or clear areas around colonies using π r².
Describe how to prepare an uncontaminated culture using aseptic techniques.
Explain why:
- Petri dishes and culture media must be sterilised before use.
- Inoculating loops must be passed through a flame to sterilise before transfering microorganisms to the media.
- The lid of the Petri dish is secured with adhesive tape and stored upside down
- Cultures are incubated at 25°C in schools.
Cell Division
Understand that:
- The nucleus of a cell contains chromosomes made of DNA molecules
- Each chromosome carries a large number of genes
- Chromosomes in body cells are usually found as pairs.
Mitosis and the cell cycle
Understand that:
- Cells divide in a series of stages in the cell cycle which results in two identical cells.
- Cell division by mitosis is important for the growth and development of multicellular organisms
Describe the stages of the cell cycle, including mitosis:
- 1 – Genetic material (DNA) is doubled to form two copies of each chromosome and the number of sub-cellular structures (inc. ribosomes, mitochondria) are increased.
- 2 – Mitosis – the nucleus divided and one set of chromosomes pulled to each end of the cell.
- 3 – Cytoplasm and cell membranes divide, forming two identical cells.
Recognise and describe mitosis occurring in a given context.
Stem Cells
Understand that:
- A stem cell is a undifferentiated cell of an organism capable of giving rise to many more cells of the same type, or other cell types from differentiation.
- Treatment with stem cells may have use in diabetes and paralysis treatment.
- Therapeutic cloning is a medical treatment method in which an embryo is produced with the same genes as the patient so the stem cells are not rejected by the patient’s body.
- The use of stem cells have potential risks including transfer of viral infection.
- Some people have ethical or religious objections
- Stem cells from meristem tissue in plants can be used to produce clones of plants quickly and economically, including those with special features like disease resistance for farmers or to clone rare plants to protect from extinction.
Describe the function of stem cells in:
- Embryos – human embryo stem cells cloned and made to differentiate into most different types of human cells.
- Adults – adult bone marrow stem cells can form many types of cells, including blood cells.
- Plants – meristem tissue in plants can differentiate into any type of plant cell, throughout the plants life.
Evaluate the social and ethical issues, as well as practical risks and benefits, of the use of stem cells in medical research and treatments.
Diffusion
Understand that:
- Diffusion is the spreading out of particles of any substance in solution, or particles of a gas, resulting in the net movement from an area of higher concentration to an area of lower concentration.
- Oxygen and carbon dioxide move into and out of cells across cell membranes in gas exchange via diffusion.
- The waste product urea diffuses from cells into blood plasma for excretion in the kidney.
Explain:
- How the following factors affect the rate of diffusion:
- Concentration gradient (difference in concentration)
- Temperature
- Surface area (including how single-celled organisms have a relatively large surface area to volume).
- How the relatively large surface area to volume ratio of single celled organisms means diffusion is sufficient for the transport of molecules to meet demands.
- The need for exchange surfaces and transport systems in multi-cellular organisms, with reference to surface to volume ratio.
- How the following are adapted for exchanging materials:
- Small intestine and lungs in mammals
- Gills in fish
- Roots and leaves in plants.
Describe how surfaces and organ systems in multicellular organisms are specialised for exchanging sufficient molecules/materials into and out of cells to meet needs, including:
- A large surface area
- A thin membrane (short diffusion pathway)
- Animals – efficient blood supply
- Animals – ventilation (for gaseous exchange)
Osmosis
Practical 3: Investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissues.
Understand that:
- Osmosis is the net diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
- Water may move across cell membranes via osmosis.
Calculate (based on practical):
- The rate of water uptake, using simple compound measures
- Percentage gain and loss of mass of plant tissue.
Recognise, draw and interpret diagrams that model organisms.
Graph skills: Plot, draw and interpret graphs.
Active Transport
Understand that:
- Active transport is movement of substances from a more dilute solution to a more concentration solution, against a concentration gradient, requiring energy from respiration.
- Active transport allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration to be used by cells for respiration.
- Active transport allows mineral ions, required for healthy growth, to be absorbed into plant root hairs from very dilute solutions in the soil.
Describe how substances are transported into and out of cells by diffusion, osmosis and active transport.
Explain the differences between diffusion, osmosis and active transport.
B2 – Organisation
Average marks available per series: 45.3
Principles of Organisation
Understand:
- Cells are the basic building blocks of all living organisms.
- A tissue is a group of cells with similar structure and function.
- Organs are aggregations of tissues performing specific functions.
- Organs are organised into organ systems, working together to form organisms.
- Size and scale in relation to cells, tissues, organs and organ systems.
Human Digestive System
Practical 4: Use qualitative reagents to test for a range of carbohydrates, lipids and proteins: Benedict’s test for sugars, iodine test for starch, Biuret reagent for protein.
Practical 5: Investigate the rate of pH on the rate of reaction of amylase enzyme using a continuous sampling technique.
Understand that:
- The digestive system is an organ system where several organs work together to digest and absorb food.
- Digestive systems are adapted to break large food molecules into smaller ones which can travel in the blood to cells and are used for life processes.
- Enzymes are substances that speed up the chemical reactions for digestion by converting food into small soluble molecules that can be absorbed into the bloodstream.
- Carbohydrases break down carbohydrates to simple sugars (including glucose).
- Amylase is the carbohydrase which breaks down starch.
- Proteases break down proteins to amino acids.
- Products of digestion are used to build new carbohydrates, lipids and proteins in the body and some glucose is used in respiration.
- Bile is alkaline to neutralise hydrochloric acid from the stomach and emulsify fats to form small droplets to increase surface area of fats. It is made in the liver and stored in the gall bladder.
Describe:
- The nature of enzyme molecules as biological catalysts which catalyse specific reactions in living organisms due to the shape of their active site.
- The effect of temperature and pH changes on enzyme activity.
Explain:
- The nature of enzyme molecules as biological catalysts which catalyse specific reactions in living organisms due to the shape of their active site.
- The ‘lock and key theory’ as a simplified model to explain enzyme action.
- The role of enzymes in relation to metabolism (link to Respiration topic).
- How bile creates the alkaline conditions and larger surface area which increases the rate of fat breakdown by lipase.
The heart and blood vessels
Understand that:
- The heart is an organ that pumps blood around the body in a double circulatory system.
- The right ventricle pumps blood to the lungs where gas exchange takes place.
- The left ventricle pumps blood around the rest of the body.
- The lungs are adapted for gaseous exchange.
- Natural resting heart rate is controlled by a group of cells which act as a pacemaker. These are in the right atrium.
- Artificial pacemakers are electrical devices used to correct irregularities in the heart rate.
- Arteries, veins and capillaries are the three different types of blood vessels.
Recall:
- The structure and function the human heart.
- The structure of the lungs, including trachea, bronchi, alveoli and capillary network surrounding alveoli.
- The following blood vessels associated with the heart:
- The aorta
- Vena cava
- Pulmonary vein and pulmonary artery
- Coronary arteries.
Explain the structure of arteries, veins and capillaries and how this relates to their function.
Calculate rate of blood flow using simple compounds measures.
Blood
Understand that blood is a tissue consisting of plasma, in which the red blood cells, white blood cells and platelets are suspended.
Describe the function of each component of blood.
Explain how each type of blood cell is adapted to its function.
Recognise types of blood cells in a photograph or diagram.
Observe and draw blood cells seen under a microscope.
Evaluate risks related to the use of blood products.
Coronary heart disease
Understand:
- The cause of coronary heart disease (see describe).
- Treatment for coronary heart disease includes stents to keep coronary arteries open.
- Statins are commonly used to reduce blood cholesterol levels and slow the rate of fatty material deposit.
- The consequences of faulty valves which prevent the valve opening fully or cause a leak to develop.
- Biological or mechanical valves can replace faulty heart valves.
- Treatments for heart failure include:
- Heart transport (donor heart)
- Artificial hearts (intermediate whilst waiting for a donor heart)
- Allow heart to rest (aids recovery).
Describe coronary heart disease, including:
- Layers of fatty materials build up inside coronary arteries, narrowing them.
- Reduces flow of blood through coronary arteries, resulting in a lack of oxygen for the heart muscle.
Evaluate methods of treatment, accounting for benefits and risks of each treatment.
Health issues
Understand:
- That health is the state of physical and mental well-being.
- That communicable and non-communicable diseases are major causes of health issues.
- That diet, stress and life situations effect health.
- The principles of sampling, applied to epidemiological data.
Explain the interaction between different diseases:
- Defects in the immune system make an individual more susceptible to infectious diseases.
- Viruses in living cells can trigger cancerous tumours to grow.
- Immune reactions initially caused by a pathogen can trigger allergies (e.g. skin rash) and asthma.
- Severe physical ill health can lead to depression and other mental illness.
Data handling skills:
- Translate disease incidence information between graphical and numerical forms.
- Construct and interpret frequency tables and diagrams, bar charts and histograms.
- Identify a correlation between two variables using a scatter diagram.
The effect of lifestyle on some non-communicable diseases
Understand:
- Risk factors are linked to increased rate of a disease
- Risk factors can be aspects of an individual’s lifestyle or a substance in the body or environment.
- Many diseases are caused by many factors interacting.
- The principles of sampling, applied to data on risk factors.
Explain:
- The effect of lifestyle on the incidence of non-communicable diseases at local, national and global levels.
- The causal mechanism which have been some between risk factors and disease:
- Diet, smoking and exercise – Cardiovascular disease
- Obesity – Type 2 diabetes
- Alcohol – Impaired liver and brain function
- Smoking – Lung disease and lung cancer
- Smoking and alcohol – Growth and development issues in unborn babies
- Carcinogens (including ionising radiation) – Cancer.
Discuss:
- The human and financial cost of non-communicable diseases:
- For an individual
- For a local community
- For a nation
- Globally
Data handling skills:
- Translate disease incidence information between graphical and numerical forms.
- Construct and interpret frequency tables and diagrams, bar charts and histograms.
- Identify a correlation between two variables (including a risk factor) using a scatter diagram.
Cancer
Describe cancer as a result of changes in cells that lead to uncontrolled growth and division.
Understand:
- Benign tumours are growths of abnormal cells, contained in one area, usually within a membrane and do not invade other parts of the body.
- Malignant tumour cells are cancerous because they invade neighbouring tissues and spread to different parts of the body in the blood (forming secondary tumours).
- Scientists have identified lifestyle and genetic risk factors for some types of cancer.
Plant tissues
Understand and explain how structures of plant tissues relate to their function:
- Epidermal tissue
- Palisade mesophyll
- Spongy mesophyll
- Xylem and phloem
- Meristem tissue.
Recall the structure of a leaf (as a plant organ) including:
- Epidermis
- Palisade & spongy mesophyll
- Xylem and phloem
- Guard cells and stomata.
Observe and draw the transverse section of a leaf.
Plant organ system
Explain:
- How the structure of the following organs make them adapted for their function:
- Xylem
- Phloem
- Root hair cells
- Explain the effect of changing temperature, humidity, air movement and light intensity on the rate of transpiration.
Explanations will include descriptions of:
- Transpiration and translocation including the structure of stomata.
- The role of guard cells and stomata in gas exchange and water loss.
- Root hair cells adaptation for the efficient uptake of water by osmosis and mineral ions by active transport:
- Large surface area
- Lots of mitochondria.
- Xylem adaptations for the transpiration of water and transport mineral ions from the roots to the stems and leaves:
- Hollow tubes strengthened by lignin.
- Phloem tissue is adapted for translocation, the transportation of dissolved sugars from the leaves to the rest of the plant for storage or immediate use:
- Elongated cells
- Pores in the end walls for cell sap to move through.
Calculate rate of transpiration using simple compound measures.
Graph skills:
- Translate information between graphical and numerical form.
- Plot and draw graphs, selecting appropriate scales for axes.
- Extract and interpret information from graphs, charts and tables.
Investigations:
- Rate of transpiration by measuring the uptake of water.
- The distribution of guard cells and stomata.
B3 – Infection and Response
Average marks available per series: 26.3
Communicable (infectious) diseases
Understand that:
- Pathogens are microorganisms that cause infectious disease.
- Pathogens may be viruses, bacteria, protists or fungi.
- Pathogens can be spread by direct contact, water or air to infect plants or animals.
Explain:
- How diseases caused by viruses, bacteria, protists and fungi are spread in animals and plants.
- How spread of diseases can be reduced or prevented. of the scale and size of cells to make order of magnitude calculations (requires standard form).
- Ability to use the prefixes centi, milli, micro, nano.
Viral Diseases
Understand that:
- Viruses live and reproduce rapidly inside cells, causing cell damage
Measles:
- Symptoms: fever and red skin rash.
- Transmission: inhaling droplets from sneezes and coughs.
- Most young children get vaccinated against measles.
- Serious illness which can be fatal if complications arise.
HIV:
- Symptoms: initially a flu-like illness, but then can symptomless until late stage HIB, or AIDs when the body immune system is so severely damaged, they cannot deal with other infections or cancerous tumours.
- Transmission: sexual contact or exchange of bodily fluids (e.g. blood in shared needles)
Tobacco Mosaic Virus (TMV):
- Symptoms: ‘mosaic’ pattern of discoluration on the leaves
- Widespread affecting plants, including tomatoes.
- Affects growth due to lack of photosynthesis.
Bacterial Diseases
Understand that:
- Bacteria reproduce rapidly inside the body.
- Bacteria may produce poisons (toxins) that damage tissue and make us feel ill.
Salmonella
- A type of food poisoning caused by the bacteria Salmonella and the toxins they secrete.
- Symptoms: cramps, vomiting and diarrhoea.
- Transmission: bacteria ingested in food or food prepared in unhygienic conditions.
- Poultry in the UK vaccinated against Salmonella to control the spread.
Gonorrhoea
- A sexually transmitted disease (STD) caused by a bacterium.
- Symptoms: thick yellow or green discharge from the vagina or penis, pain when urinating.
- Transmission: sexual contact.
- Treatment: it was easily treated with antibiotic penicillin until many resistant strains appeared.
- Treatment with antibiotics and barrier methods of contraception control the spread.
Fungal Diseases
Rose Black spot:
- Plant fungal disease which affects the growth of the plant as photosynthesis is reduced.
- Symptoms: purple or black spots develop on leaves, often turning yellow and drop early than expected.
- Transmission: water or wind in the environment.
- Treatment: Fungicides and/or removing and destroying the affected leaves.
Protist Diseases
Malarial protists:
- The mosquito is part of the malarial protist life cycle. It is spread to humans through mosquitos, which are the vector by the disease.
- Symptoms: recurrent episodes of fever, can be fatal.
- Transmission: vector, mosquitos
- Controlled by preventing mosquitos from breeding and using mosquito nets to avoid being bitten.
Human Defence Systems
Describe:
- Non-specific defence systems of the human body against pathogens, including:
- Skin
- Nose
- Trachea
- Bronchi
Explain:
- The role of the immune system in the defence against disease by trying to destroy pathogens.
- How white blood cells defend against pathogens by:
- Phagocytosis
- Antibody production
- Antitoxin production.
Vaccination
Describe how vaccinations work:
- Introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies.
- If the same pathogen re-enters the body, white blood cells respond quickly to produce the correct antibodies, preventing infection.
Explain:
- How vaccination will prevent illness in an individual.
- How the spread of pathogens can be reduced by immunising a large proportion of the population.
Antibodies and painkillers
Understand that:
- Antibiotics are medicines that kill infective bacteria inside the body, curing bacterial diseases.
- Penicillin is an example of an antibiotic.
- The use of antibiotics have reduced the deaths from infectious bacterial diseases greatly.
- The emergence of antibiotic resistant bacteria is a great concern.
- Antibiotics cannot kill viral pathogens.
- Painkillers and other medicines can treat symptoms, but do not kill bacterial pathogens.
Explain
- The use of antibiotics and other medicines to treat disease. A type of food poisoning caused by the bacteria Salmonella and the toxins they secrete.
- It is difficult to develop drugs that skill viruses without also damaging body tissues because they live inside cells.
Discovery and development of drugs
Understand:
- Traditionally drugs were extracted from plants and microorganisms.
- Most drugs developed in the pharmaceutical industry today are synthesised by chemists from chemicals, the starting point of which could be extraction from a plant.
- Medical drugs are tested and trialled before use to check their safety and effectiveness.
- Preclinical testing is done in a laboratory using cells, tissues and live animals before clinical trials are done with healthy volunteers and patients.
Describe:
- The process of discovery and development of potential new medicines, including preclinical and clinical testing.
- How new drugs are tested for toxicity, efficacy and dose.
- The steps in a clinical trial:
- Very low doses of the drug are given at the start.
- If determined to be safe, further clinical trials are carried out to find the optimum drug.
- In double blind trials, some patients are given a placebo.
Recall the following examples of traditional drugs extracted from plants and microorganisms:
- Heart drug – digitalis – originates from foxgloves.
- Painkiller – aspirin – originates from willow.
- Penicillin – discovered by Alexander Fleming from the Pencillium mould.
Producing monoclonal antibodies
Understand that:
- Monoclonal antibodies are specific to one binding site, on one protein antigen. Therefore, they can target a specific chemical or cell in the body.
- Hybridoma cells divide and make the antibody.
Describe how the monoclonal antibodies are produced:
- Produced from a single clone of cells.
- Scientists stimulate mouse lymphocytes to make a particularly antibody.
- The lymphocytes are combined with a particular kind of tumour cell to make a hybridoma cell.
- A single hybridoma cell is cloned to produced many identical cells which all produce the same antibody.
- A large amount of the antibody is collected and purified.
Uses of monoclonal antibodies
Understand examples of ways in which monoclonal antibodies can be used:
- Diagnosis – pregnancy tests
- Measure chemical levels – hormones in the blood
- Detect pathogens in the blood
- Locate or identify specific molecules in a cell or tissue – bind/tag the antibodies with a fluorescent dye
- Treat cancer – monoclonal antibody bound to a radioactive substance, a toxic drug, or chemical to stop the cancer cells growing and dividing without harming other cells in the body.
Evaluate the advantages and disadvantages of monoclonal antibodies, including:
- Their power and medical potential
- They create more side effects that was expected
- Their use is not currently as widespread as originally hoped.
- Ethical issues.
Detection and identification of plant diseases
Understand that:
- The ability to detect and identify plant disease is essential in agriculture.
- Plants can be infected by viral, bacterial and fungal pathogens and insects.
- Tobacco mosaic virus is a viral disease.
- Black spot is a fungal disease.
- Aphids are insects which infect plants.
- Plant diseases symptoms include:
- Stunted growth
- Spots on leaves
- Areas of decay (rot)
- Growths
- Malformed stems or leaves
- Discolouration
- Pest presence
- Diseases can be identified/diagnosed by:
- Using a testing kit with monoclonal antibodies
- Testing plant in a laboratory to identify a pathogen
- Reference a gardening manual or website.
- Ion deficiency conditions can damage plants:
- Nitrate is needed for protein synthesis and growth, therefore deficiency causes stunted growth.
- Magnesium is needed to make chlorophyll, therefore deficiency causes chlorosis.
- Different species need different levels of ions, therefore horticulturists need to understand ion deficiencies to provide optimum conditions.
Plant Defence Responses
Describe plant defence responses:
- Physical (resist invasion of microorganisms):
- Cellulose cell wall
- Tough waxy cuticle on leaves
- Layers of dead cells around stems (bark on trees) which fall off
- Chemical:
- Antibacterial chemicals
- Poisons (deter herbivores)
- Mechanical
- Thorns and hairs (deter animals)
- Leaves droop or curl when touched
- Mimicry (trick animals)
B4 – Bioenergetics
Average marks available per series: 31.3
Photosynthetic reaction
Describe photosynthesis:
- An endothermic reaction
- Energy is transferred from the environment to the chloroplasts by light,
Recall the equation for photosynthesis:
Recognise the chemical symbols:
- CO₂ (carbon dioxide)
- H₂O (water)
- O₂ (oxygen)
- C₆H₁₂O₆ (glucose)
Rate of photosynthesis
Practical 6: Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed.
Explain the effects of the following factors on the rate of photosynthesis
- Temperature
- Light intensity
- Carbon dioxide concentration
- Amount of chlorophyll
Understand that:
- Factors interact and any one of them may be the limiting factor.
- Limiting factors are important in the greenhouses to gain the maximum rate of photosynthesis while still maintaining profit.
Graph skills:
- Extract and interpret graphs of photosynthesis rate involving one limiting factor,
- Plot and draw appropriate graphs, selecting appropriate scales for axes.
- Translate information between graphical and numerical form.
- Explain graphs of photosynthesis rate involving two or three factors and decide which is the limiting factor.
Maths skills:
- Measure and calculate rate of photosynthesis
- Understand and use inverse proportion – the inverse square law and light intensity (in context of photosynthesis)
- Use data to relate limiting factors to the cost effectiveness of adding heat, light or carbon dioxide to greenhouses
Uses of glucose from photosynthesis
Recall the ways in which glucose produced in photosynthesis may be used:
- For respiration
- Converted into insoluble starch (for storage)
- Produce fat or oil (for storage)
- Produce cellulose (strengthens cell wall of cells)
- Produce amino acids (for protein synthesis)
Understand that:
- Plants also need nitrate ions absorbed from the soil to produce proteins.
Use qualitative reagents to identify starch, glucose and proteins.
Aerobic and anaerobic respiration
Understand that:
- Organisms need energy for:
- Chemical reactions to build larger molecules
- Movement
- Keeping warm
- Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy.
- Anaerobic respiration in yeast cells is called fermentation – it has economic importance in the manufacture of bread and alcoholic drinks.
Describe cellular respiration:
- An exothermic reaction continuously happening in living cells.
Compare the processes of aerobic and anaerobic respiration in relation to:
- Need for oxygen
- Differing products
- Relative amounts of energy transferred.
- The oxidation of glucose is incomplete in anaerobic respiration, so much less energy is transferred compared to aerobic.
Recall the equation for aerobic respiration:
Recall the equation for anaerobic respiration in muscles:
Recall the equation for anaerobic respiration in plant and yeast cells:
Recognise the chemical symbols:
- CO₂ (carbon dioxide)
- H₂O (water)
- O₂ (oxygen)
- C₆H₁₂O₆ (glucose)
Metabolism
Understand that:
- Metabolism is the sum of all reactions in a cell or the body.
- The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules.
Explain:
- The importance of the following molecules in the synthesis and breakdown of carbohydrates, proteins and lipids:
- Sugars
- Amino acids
- Fatty acids
- Glycerol
Recall the following components of metabolism (linked to other topics):
- Conversion of glucose to starch, glycogen and cellulose.
- The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids.
- The use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins.
- Respiration
- Breakdown of excess proteins to form urea for excretion.
Paper 2
B5 – Homeostasis
Average marks available per series: 30.6
Homeostasis
Define homeostasis as:
- The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external conditions
Understand that:
- Homeostasis maintains optimal conditions for enzyme action and cellular functions, including:
- Blood glucose concentration
- Body temperature
- Water levels.
- These are controlled by automatic control systems, which may involved nervous and chemical responses.
- All control systems include:
- Receptors – cells which detect stimuli.
- Coordination centres – receive and process information from receptors (such as the brain, spinal cord and pancreas).
- Effectors, muscles or glands – bring about responses to restore optimum levels.
Human Nervous System
Understand that:
- The human nervous system enables humans to react to surroundings and coordinate behaviour accordingly.
- Reflex actions are automatic and rapid (meaning they do not involve the conscious part of the brain).
- Reflex actions are important in preventing injuries.
Recall the path of information along the nervous system:
- Stimulus – Receptor – Coordinator – Effector – Responses
- Information from the stimulus is sent from receptors along sensory neurones (cells) as electrical impulses to the central nervous system (CNS), which is the coordinator (brain or spinal cord) of the response. The information for the response is sent along motors neurones to effectors (muscles contracting, glands secreting) to initiate the response.
Graphs and tables skills:
- Extract and interpret data from graphs
- Extract and interpret data from tables
Maths skills:
- Translate information about reaction times between numerical and graphical forms.
Practical 7 – Plan and carry out an investigation into the effect of a factor on human reaction time.
The Brain
Understand that:
- The brain controls complex behaviour.
- It is comprised of billions of interconnected neurones.
- Different regions carry out different functions.
Identify and describe the function of the:
- Cerebral cortex
- Cerebellum
- Medulla
Explain:
- Challenges of investigating brain function and treating brain damage, disorders and disease, including the complexity and delicacy of the brain.
- That neuroscientists have mapped regions of the brain to particular functions by:
- Studying patients with brain damage,
- Electrically stimulating different parts of the brain,
- Using MRI scanning techniques.
Evaluate benefits and risks of procedures carried out on the brain and nervous system.
The Eye
Understand that:
- The eye is a sense organ.
- It contains receptors sensitive to light intensity and colour.
- Accommodation is the process of changing the shape of the lens to focus on near or distant objects.
Identify and describe the function of the:
- Retina
- Optic nerve
- Sclera
- Cornea
- Iris
- Ciliary muscles
- Suspensory ligaments
Explain:
- Accommodation to focus on near objects:
- Ciliary muscles contract and suspensory ligaments loosen so the lens is thicker and refracts light rays strongly.
- Accommodation to focus on distant objects:
- Cilitary muscles relax and suspensory ligaments are pulled tight, so the lens is pulled think and only slight refract light rays.
Describe
- The following defects of the eye where rays do not focus on the retina:
- Myopia (short sightedness)
- Hyperopia (long sightedness)
- The treatment of these defects with spectacle lenses which refract light rays so they do focus on the retina.
- New technologies, including:
- Hard and soft contact lenses,
- Laser surgery (changes the shape of the cornea)
- Replacement lenses.
Control of Body Temperature
Understand that:
- Body temperature is monitored and controlled by the thermoregulatory centre in the brain.
- The centre contains receptors sensitive to temperature of the blood.
- The skin contains temperature receptors which send nervous impulses to the thermoregulatory centre.
- Mechanisms to reduce body temperature cause a transfer of energy from the skin to the environment.
Describe the mechanisms for when body temperature is:
- Too high – blood vessels dilate (vasodilation), sweat produced from sweat glands.
- Too low – blood vessels contract (vasoconstriction), sweating stops, skeletal muscles contract (shivering).
Explain:
- How the mechanisms lower or raise body temperature in a given context.
The Human Endocrine System
Describe:
- The principles of hormonal coordination
- The control of this by the human endocrine system
Understand that:
- A variety of glands in the body comprise the endocrine systems.
- Glands secrete hormones (chemicals) directly into the bloodstream in which it is carried to a target organ where it will produce an effect.
- Effects are slower, but act for longer compared to the nervous system effects.
Explain:
- That the pituitary gland in the brain is the ‘master gland’ as it secretes several hormones directly into the bloodstream which in turn act on other glands to stimulate other hormones to bring about effects, in response to body conditions.
Identify the position of the following glands on a human body diagram:
- Pituitary gland
- Pancreas
- Thyroid
- Adrenal gland
- Ovary
- Testes
Maths skills:
- Translate information about reaction times between numerical and graphical forms.
Control of Blood Glucose
Understand that:
- Blood glucose concentration is monitored and controlled by the pancreas.
Explain:
- What happens when blood glucose concentration is too high and how insulin control blood glucose levels in the body:
- The pancreas produces the insulin which causes glucose to move from the blood into the cells.
- In muscle and liver cells, excess glucose is converted to glycogen for storage.
- What happens when blood glucose concentration is too low:
- The pancreas produces glucagon which causes glycogen to be converted into glucose and released into the blood.
- How glucogen interacts with insulin in a negative feedback cycle to control blood glucose levels in the body.
Compare type 1 and type 2 diabetes and explain how they can be treated.
- Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin.
- Uncontrolled high blood glucose levels
- Treated with insulin injections.
- Type 2 diabetes is a disorder where the body no longer responds to insulin produced by the pancreas.
- Usually treated with a carbohydrate controlled diet and exercise regime.
- Obesity is a risk factor.
Graph skills
- Extract and interpret data from graphs to show the effect of insulin on blood glucose levels in people with and without diabetes.
Evaluate information about the relationship between obesity and diabetes to make recommendations which account for social and ethical issues.
Maintaining Water and Nitrogen Balance
Explain the effect on cells of osmotic changes in body fluids:
- There is no control over water loss via:
- Exhalation – water leaves the body via the lungs.
- Skin in sweat – water, ions and urea lost.
- If body cells lose of gain too much water by osmosis, they do not function efficiently.
Understand that:
- Excess water, ions and urea are removed via kidneys in the urine.
- Digesting proteins from the diet results in excess amino acids which need to be excreted safely. This is done by forming urea, which is produced deaminating amino acids in the liver to form ammonia, which is toxic so it is immediately converted to urea for safe excretion.
- People who suffer from kidney failure may be treated by organ transplant or kidney dialysis. Know the basic principles of dialysis.
Describe:
- The function of the kidneys in maintaining the water balance of the body.
- The production of urine by the kidneys:
- Filtration of the blood
- Selective reabsorption of useful substances such as glucose, some ions and water.
- The effect of ADH on the permeability of kidney tubules (an example of negative feedback):
- The hormone ADH controls water level in the body by acting on the kidney tubules.
- ADH is released by the pituitary gland when the blood is too concentrated and causes more water to be reabsorbed back into the blood from the kidney tubules.
- How kidney dialysis works
Evaluate the advantages and disadvantages of treating organ failure by mechanical device or transplant.
Negative Feedback
Understand that:
- Blood glucose concentration is monitored and controlled by the pancreas.
Explain:
- The role of thyroxine and adrenaline in the body
- Adrenaline – produced by adrenal gland in times of fear or stress
- Increases heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, prearing the body for ‘flight or fight’.
- Thyroxine – stimulates basal metabolic rate
- Important role in growth and development.
- Levels controlled by negative feedback.
Interpret and explain simple negative feedback control diagrams.
Hormones in Human Reproduction
Understand that:
- During puberty, reproductive hormones cause secondary sex characteristics to develop.
- Oestrogen is the main female reproductive hormone produced in the ovary.
- Ovulation begins during puberty, It is where eggs begin to mature and one is released approximately every 28 days.
- Testosterone is the main male reproductive hormone produced by the testes and stimulates sperm production.
- Several hormones are involved in the menstrual cycle of a woman.
Describe:
- The roles of hormones in human reproduction, including the menstrual cycle.
- Follicle stimulating hormone (FSH) – maturation of an egg in the ovary.
- Luteinising hormone (LH) – stimulates the release of an egg
- Oestrogen and progesterone – maintaining the uterus lining.
Extract and interpret data from graphs showing hormones during the menstrual cycle.
Contraception
Evaluate the different hormonal and non-hormonal methods of contraception to demonstrate how contraception cannot be answered by science alone.
Explain everyday and technological applications of science; evaluate associated personal, social, economic and environmental implications; and make decisions based on the evaluation of evidence and argument.
Understand and describe the following hormonal and non-hormonal methods of contraception to control fertility:
- Oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature
- Injection, implant or skin patch of slow release progesterone to inhibit the maturation and release of eggs for a number of months or years
- Barrier methods such as condoms and diaphragms which prevent the sperm reaching an egg
- Intrauterine devices which prevent the implantation of an embryo or release a hormone
- Spermicidal agents which kill or disable sperm
- Abstaining from intercourse when an egg may be in the oviduct
- Surgical methods of male and female sterilisation.
Use of hormones to treat infertility
Explain:
- The use of hormones in modern reproductive technologies to treat infertility.
- The ‘fertility drug‘ gives a woman FSH and LH who may then become pregnant without other interventions.
- Personal, medical , ethical and social issues associated with IVF treatments including:
- It is very emotionally and physically stressful
- Success rates are not high
- It can lead to multiple births, which are a risk to both babies and the mother.
Describe the process of In Vitro Fertilisation (IVF) treatment
- Mother given FSH and LH to stimulate the maturation of several eggs.
- The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.
- Fertilised eggs develops into embryos.
- At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb).
Plant Hormones
Understand that:
- Plant hormones coordinate and control growth and responses to light (phototropism) and gravity (gravitropism or geotropism).
- It is the unequal distribution of auxin which causes the unequal growth rates in plants roots and shoots, causing the directional growth.
- Gibberellins – important in initiating seed germination.
- Ethene – controls cell division and ripening of fruits.
Practical 8 – Investigate the effect of light or gravity on the growth of newly germinating seedlings.
Use of plant hormones
Describe:
- The effects of some plant hormones which relate to the way people can use them to control plant growth.
- The use of plant growth hormones in agriculture and horticulture:
- Auxin:
- As weed killers
- As rooting powders
- Promoting growth in tissue culture.
- Ethene
- Used in the food industry to control ripening of fruit during storage and transport.
- Gibberellins
- End seed dormancy
- Promote flowering
- Increase fruit size
Understand how the everyday use of hormones as weed killers impacts biodiversity.
B6 – Inheritance, Variation and Evolution
Average marks available per series: 31.6
Reproduction
Understand that:
- Meiosis leads to non-identical cells being formed.
- Mitosis leads to identical cells being formed.
- Sexual reproduction involves the fusion of male and female gametes:
- Sperm and egg cells in animals.
- Pollen and egg cells in flowering plants.
- Asexual reproduction involves one parent (no fusion of gametes).
Explain that:
- The formation of gametes involves meiosis.
- In sexual reproduction the gametes mix genetic information, leading to variety in offspring, with characteristics inherited from the mother and father.
- Asexual reproduction only involves mitosis.
- In asexual reproduction, there is no mixing of genetic information, leading to genetically identical offspring (clones).
Meiosis
Understand and explain that:
- Cells in reproductive organs divide by meiosis to form gametes.
- Gametes join at fertilisation restore the full number of chromosomes.
- The new cell developed by fertilisation divides by mitosis to increase the number of cells,
- Cells differentiate as the embryo develops.
Describe what happens when a cell divides to form gametes:
- Copies of genetic information made.
- Cell divides twice to form four gametes, each with a single set of chromosomes.
- All gametes are genetically different to each other.
Advantages and disadvantages of sexual and asexual reproduction
Understand:
- Advantages of sexual reproduction:
- Variation in offspring produced.
- Natural selection – variation provides a survival advantage if the environment changes.
- Humans can speed up natural selection by selectively breeding livestock and agriculture, to increase food production.
- Advantages of asexual reproduction:
- Only one parent needed.
- Faster than sexual reproduction.
- Produces many identical offspring when conditions are favourable.
- No need to find a mate, so it is more time and energy efficient.
- That some organisms can reproduce by both asexual and sexual reproduction, depending on circumstances.
- Malarial parasites – reproduce asexually in human hosts, but sexually in mosquitos.
- The historical developments of understanding causes and prevention of malaria.
- Fungi – reproduce asexually by spores, but sexually to give variation.
- Plants – many produce seeds sexually, but asexually by runners.
- Runners of strawberry plants.
- Bulb division in daffodils.
- Malarial parasites – reproduce asexually in human hosts, but sexually in mosquitos.
Explain advantages and disadvantages of sexual and asexual reproduction for any organism, if given appropriate information.
DNA and the Genome
Define:
- Genome – the entire genetic material of an organism.
- Gene – a small section of DNA on a chromosome which codes for a particular sequence of amino acids, to make a specific protein.
Describe:
- The structure of the chemical DNA
- A polymer made up of two strands, forming a double helix.
- Contained in chromosomes.
Understand that:
- The whole human genome has been studied, which will be very important for future medicine.
Discuss the importance of understanding the human genome:
- Search for genes linked to different types of disease
- Understanding and treatment for inherited disorders.
- Tracing human migration patterns from the past.
DNA Structure
Interpret a diagram of DNA structure.
Describe:
- DNA as a polymer made from four different nucleotides: A, C, G and T.
- The structure of nucleotides:
- Each nucleotide consists of a common sugar, a phosphate group with one of four different bases attached to the sugar.
Understand that:
- A sequence of three bases is the code for a particular amino acids.
- The order of the bases control the order in which amino acids are assembled to produce a particular protein.
- Not all parts of DNA code for a protein.
- Non-coding parts of DNA switch genes on and off, so variations in these areas may affect how genes are expressed.
Simply describe protein synthesis and explain how DNA affects the proteins made, including:
- The gene is copied by a molecule to form a template.
- In the complementary strands, C – G and A – T are always linked on the opposite strands to each other.
- Proteins are synthesised on ribosomes, according to a template copied from the gene.
- Carrier molecules bring specific amino acids to add to the growing protein chain in the correct order.
- When the protein chain is complete, it folds up to form an unique shape, which enables the proteins to do to their role as an enzyme, hormone, or forming body structures such as collagen.
Explain how:
- A change in DNA structure may result in the wrong protein synthesised by a gene.
- A few mutations code for an altered protein with a different shape.
- For an enzyme, it means it no longer fits the substrate binding or a structural protein may lose its strength.
- Most mutations do not alter the protein, or only slightly so that the appearance or function of the protein does not change.
Model insertions and deletions in chromosomes to illustrate mutations.
Genetic Inheritance
Define and explain:
- Gamete – reproductive cells of sexually reproducing organisms.
- Chromosomes – the structures formed by DNA molecules in the nucleus of a cell.
- Gene – the sequence of bases which codes for a particular protein.
- Allele – different forms of a particular gene.
- Dominant – describes an allele that is always expressed, even if there is only one copy present.
- Recessive – describes an allele that is only expressed if two copies are present.
- Homozygous – if the two alleles present are the same.
- Heterozygous – if the the two alleles present are different.
- Genotype – the collection of genes an individual has.
- Phenotype – physical characteristics of an individual, an expression of the genotype.
Understand that:
- Some characteristics are controlled by a single gene, including:
- Fur colour in mice
- Red-green colour blindness in humans.
- Most characteristics are the result of multiple genes interacting.
Discuss the importance of understanding the human genome:
- Search for genes linked to different types of disease
- Understanding and treatment for inherited disorders.
- Tracing human migration patterns from the past.
Genetic Crosses
Understand:
- The concept of probability in predicting the results of a single gene cross.
Math skills:
- Use direct proportion and simple ratios to express the outcome of a genetic cross.
- Complete a Punnett square diagram and extract and interpret information from genetic crosses and family trees.
Construct a genetic cross by Punnett square diagram and use it to make predictions using the theory of probability.
Inherited Disorders
Understand that:
- Inherited disorders are caused by the inheritance of certain alleles.
- Polydactyly (extra fingers and toes) is caused by a dominant allele.
- Cystic fibrosis (disorder of cell members) is caused by a recessive allele.
- Embryo screening and gene therapy can alleviate suffering, but consider ethical issues which arise.
Make judgements about:
- The economic, social and ethical issues regarding embryo screening.
Sex Determination
Understand:
- Normal body cells contain 23 pairs of chromosomes.
- 22 pairs are autosomes – they control characteristics only.
- 1 pair carries genes that determine sex.
- In females, sex chromosomes are the same (XX).
- In males, sex chromosomes are different (XY). he concept of probability in predicting the results of a single gene cross.
Perform a genetic cross to show sex inheritance.
Math skills – use direct proportion and simple ratios to express the outcomes of a genetic cross.
Variation
Describe:
- How the genome and its interaction with the environment influences the development of the phenotype of an organism.
Understand that:
- Variation is the differences in characteristics of individuals in a population.
- There is usually extensive genetic variation within a population of a species.
- Variation can have:
- Genetic causes (genes inherited)
- Environmental causes (conditions during development)
- A mix of both causes.
- All genetic variation arise from mutations, which occur continuously.
- Some have no effect on the phenotype,
- Some influence phenotype
- Very few determine phenotype.
- Mutations occur continuously but rarely lead to a new phenotype. However, when it does, if the new phenotype is suited to an environmental change, it can lead to a relatively rapid change in the species.
Evolution
Describe evolution as:
- 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. The concept of probability in predicting the results of a single gene cross.
Explain that:
- The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
- Evolution occurs through natural selection of variants that give rise to phenotypes best suited to their environment.
- If two populations of one species become so different in a phenotype that they can no longer interbreed to produce fertile offspring, they have formed two new species.
Selective Breeding
Understand that:
- Selective breeding – the process by which humans breed plants and animals for particular characteristics.
- Humans have selectively bred food crops from wild plants and domesticated animals for thousands of years.
- Characteristics can be chosen for usefulness or appearance:
- Disease resistance in food crops.
- Animals which produce more meat and milk.
- Domestic dogs with a gentle nature.
- Large or unusual flowers.
Describe the process of selective breeding:
- Breed parents with desired characteristics from a mixed population together.
- From this offspring, those with desired characteristics are bred together.
- This process is repeated over many generations until all offspring have the desired characteristics.
Explain:
- The impact of selective breeding of food plants and domesticated animals.
- The benefits and risks of selective breeding given appropriate information and consider related ethical issues.
Genetic Engineering
Describe:
- Genetic engineering – a process involving the modification of the genome of an organism by introducing a gene from another organism to give a desired characteristic.
- Genes from the chromosome of humans and other organisms can be ‘cut out’ and transferred to the cells of other organisms.
- Main steps:
- Enzymes isolate the required gene
- The gene is inserted into a vector (bacterial plasmid or virus).
- The vector inserts the gene into the required cells.
- Genes transferred into cells of animals, plants or microorganisms at an early stage of development.
Understand that:
- Genetically Modified (GM) crops are plant crops that have been genetically engineered.
- Resistance to diseases
- Resistance to insects or herbicides
- Produce bigger fruits.
- Bacterial cells have been genetically engineered to produce useful substances, such as human insulin to treat disease.
- Modern medical research is exploring how genetic modification could overcome some inherited disorders.
Explain:
- Potential benefits and risks of genetic engineering in agriculture and medicine.
- Benefits – resistance to disease, insects or herbicides, increase yields.
- Concern/risks – Effects of wild populations of flowers and insects. Lack of exploration into the effects of eating GM crops on human health.
- Some people have objections.
Interpret information about genetic engineering techniques to make informed judgements about issues concerning cloning and genetic engineering.
Cloning
Describe current cloning methods:
- Tissue cultures – a small group of cells from part of plant to grow identical new plants.
- Preserves rare plant species
- Used commercially in nurseries.
- Cuttings – used by parents to produce many identical new plants from a parent plant.
- Older, but simple method.
- Embryo transplants – split apart cells from a developing animals embryos before they become specialised then transplanting identical embryos into hosting mothers.
- Adult cell cloning:
- The nucleus is removed from an unfertilised egg cell.
- The nucleus from an adult body cell, such as skin cell, is inserted into the egg cell.
- An electric shock stimulates the egg cell to divide to form an embryo.
- These embryo cells contain the same genetic information as the adult skin cell.
- When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue developing.
Explain:
- The potential benefits and risks of cloning in agriculture and in medicine.
- That some people have ethical objections.
Evolution and Speciation
Understand and appreciate that the theory of evolution by natural selection developed overtime and from information gathered by many scientists:
- Charles Darwin proposed the Theory of Evolution by Natural Selection in his publication, On the the Origin of Species (1859).
- His theory was developed following observations on a world expedition and subsequent years of experimentation and discussion to link developing knowledge of geology and fossils.
- His observations included:
- Individual organisms within a particular species show a wide range of variation for a characteristic.
- Individual with characteristics most suited to their environment are more likely to survive and breed successfully.
- Those characteristics are passed onto the next generation.
- There was many controversies surrounding his ideas because:
- The theory challenged the idea that God made all animals and plants that live on Earth: Creationism.
- Insufficient evidence was published to satisfy many scientists.
- Mechanisms of inheritance and variation was not known for another 50 years after publication.
- Jean-Baptiste Lamarck’s theory of acquired characteristics was based on the idea that characteristics can change during an organisms lifetime.
- We now know the vast majority of this type of inheritance cannot occur.
- Alfred Russel Wallace independently proposed the theory of evolution by natural selection.
- Worked worldwide gathering evidence for evolutionary theory.
- Warning colouration in animals
- Theory of speciation – much of the pioneering work which has been built on with more evidence over time.
- Wallace and Darwin published joint writings in 1858, prompting Darwin to publish On the Origins of Species (1859) the following year.
Understanding of genetics
Describe the:
- Work of Mendel in the development of our understanding of genetics.
- In the mid-19th century, Gregor Mendel performed breeding experiment on pea plants and observed that the inheritance of each characteristic was determined by ‘units‘ passed on to descendants unchanged.
- Scientific work by many scientists leading to the gene theory being developed overtime:
- Late 19th century – behaviour of chromosomes during cell division observed.
- Early 20th century – observed that chromosomes and Mendel’s ‘units’ behave in similar ways, leading to the idea that ‘units’, now genes, were on chromosomes.
- Late 20th century – structure of DNA and mechanism of gene function worked out.
- Early 20th century – observed that chromosomes and Mendel’s ‘units’ behave in similar ways, leading to the idea that ‘units’, now genes, were on chromosomes.
- Late 19th century – behaviour of chromosomes during cell division observed.
Understand:
- Why the importance of Mendel’s discovery was not recognised until after his death (see above for our developing understanding).
Evidence for evolution
Understand that:
- The theory of evolution by natural selection is now widely accepted.
- It has been shown that characteristics are passed on to offspring in genes.
Describe the evidence for evolution, including:
- The Fossil Record
- How antibiotic resistance evolves in bacteria
Fossils
Describe:
- Fossils – the ‘remains’ of organisms from millions of years ago.
- The ways in which fossils may form:
- From parts of organisms that did not decay as a result of one or more conditions for decay being absent.
- Parts of the organisms replaced by minerals during decay.
- Preserved traces of organisms, including footprints, burrows and rootlet traces.
Understand that:
- Scientific methods and theories develop overtime.
- The fossil record is incomplete.
- Many early life forms were soft bodied so they leave few traces and many of these have been destroyed by geological activity.
- The fossil record available shows us how much or little different organisms changed as life developed on Earth.
Extract and interpret information from charts, graphs and tables such as evolutionary trees.
Extinction
Define extinction – occurs when there are no remaining individuals of a species still alive.
Describe factors which may contribute to the extinction of a species.
Resistant bacteria
Understand that:
- Bacteria can evolve rapidly because they reproduce at a fast rate.
- Mutations of bacterial pathogens produce new strains. If this new strains are resistant to antibiotics, they will not be killed.
- They survive and reproduce, so the population of the resistant strain increases.
- Resistant strain will spread because people are not immune to it and there is no effective treatment.
- MRSA is an example of a bacteria resistant to most antibiotics.
- Development of new antibiotics does not keep up with the emergence of new resistant strains due to cost and time it takes for research, development and testing.
Explain how the rate of antibiotic resistant strain development can be reduced:
- Doctors should not prescribe antibiotics inappropriately (non-serious or viral infections).
- Patients complete course of antibiotics so all bacteria are killed. avoiding survivors from mutating and developing resistance.
- Restrict use of antibiotics in agriculture.
Classification of living organisms
Understand that:
- Carl Linnaeus developed the classification system used to classify living things depending on their structure and characteristics.
- The Linnaean system classifies living things into:
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
- Organisms are named using the binomial system, which uses the genus and species name.
- Evolutionary trees are a method used by scientists to show how their theories of how organisms are related.
- Based on current classification data for living organisms and fossil data for extinct organisms.
- Scientific methods and theories develop over time and this can be very rapid in evolutionary biology.
Describe:
- The impact of developments in biology on classification systems which creates new models for classification, including:
- Evidence for internal structures more developed through microscope advancements.
- Understanding of biochemical processes improved.
Explain:
- That chemical analysis led to Carl Woese developing the ‘three-domain system’ which divides organisms into:
- Archaea (primitive bacteria, usually living in extreme environments)
- Bacteria (true bacteria)
- Eukaryota (includes protists, fungi, plants and animals).
Extract and interpret information to show understanding of the Linnaean system.
B7 – Ecology
Average marks available per series: 40.6
Communities, Interpretation and Competition
Understand that:
- An ecocsystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of the environment.
- Organisms require materials from their surroundings and other organisms living there to survive and reproduce.
- Interdependence is the idea that within a community, each species depends on others for food, shelter, pollination, seed dispersal and more, so if one species is removed, it can affect the whole community.
- Plants often compete for:
- Light
- Space
- Water from the soil
- Mineral ions from the soil-
- Animals often compete for:
- Food
- Mates
- Territory
- Stable community – where all species and environmental factors are in balance and populations remain fairly constant.
Extract and interpret information from charts, graphs and tables relating to the interactions of organisms within a community.
Abiotic factors
Explain how a change in one of the following abiotic factors would affect a community given appropriate information, data, or context:
- Light intensity
- Temperature
- Soil pH and mineral content
- Moisture levels
- Wind intensity and direction
- Carbon dioxide levels (plants)
- Oxygen levels (aquatic animals)
Biotic factors
Explain how a change in one of the following biotic factors would affect a community given appropriate information, data, or context:
- Food availability
- Arrival of new predators
- New pathogens
- Population of one species becoming too low for breeding due to being outcompeted by another species.
Extract and interpret information from charts, graphs and tables relating to:
- The interactions of organisms within a community.
- The effect of abiotic factors on organisms within a community.
- The effect of biotic factors on organisms within a community.
Adaptations
Understand that:
- Adaptations are features that enable species to survive in the conditions they normally live.
- Adaptations can be structural, behavioural or functional.
- Extremophiles are organisms that live in very extreme environments, including to high temperature, pressure or salt concentration.
- Example: Bacteria living in deep sea vents.
Levels of Organisation
Understand that:
- Photosynthetic organisms are producers of biomass for life on Earth.
- Feeding relationships in communities are represented by food chains.
- Start with a producer – synthesises molecules. E.g. Green plant, alga make glucose by photosynthesis
- Producers are eaten by primary consumers,
- Primary consumers might be eaten by secondary consumers,
- Then tertiary consumers.
- Photosynthetic organisms are producers of biomass for life on Earth.
- Predators – consumers that kill and eat other animals.
- In a stable community, the number of predators and prey fall in cycles.
- Transects and quadrats are use in experiment methods to determine the distribution and abundance of species in an ecosystem.
Maths skills:
- Understand mean, median and mode.
- Calculate arithmetic means.
Graph skills:
- Plot and draw appropriate graphs, selecting appropriate scales for axes,
- Interpret graphs that model the predator-prey population cycles.
Practical 9 – 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 cycles
Explain:
- The importance of carbon and water cycles to living organisms,
- The role of microorganisms in cycling materials through an ecosystem by returning carbon dioxide to the atmosphere as carbon dioxide and mineral ions to the soil.
Understand that:
- Many different materials cycle through the abiotic and biotic components of an ecosystem,
- All materials in the living world are recycled to provide the building blocks for future organisms.
- The carbon cycle returns carbon from organisms to the atmosphere, which carbon dioxide to be used by the plants in photosynthesis.
- The water cycle provides fresh water for plant and animals on land before draining into the seas which is continuously evaporated and precipitated.
Decomposition
Explain:
- How temperature, water and availability of oxygen affect the rate of decay of biological material.
- How gardeners and farmers aim to provide optimal conditions for rapid decay of waste biological materials in order to produce compost to use as a natural fertiliser for growing plants or crops.
Understand that:
- Anaerobic decay produces methane gas.
- Biogas generators can be used to produce methane gas as a fuel.
Maths skills:
- Calculate rate changes in the decay of biological materials.
Graph skills:
- Translate information between numerical and graphical form.
- Plot and draw appropriate graphs selecting appropriate scales for the axes.
Practical 10 – Investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change.
Impact of environmental change
Explain:
- How the following environmental changes affect the distribution of species in an ecosystem seasonally, geographically or as a result of human interaction:
- Temperature
- Availability of water
- Composition of atmospheric gases
Evaluate:
- The impact of environmental changes on the distribution of species in an ecosystem (given appropriate information).
Biodiversity
Understand that:
- Biodiversity is the variety of all the different species of organisms on earth, or within an ecosystem.
- Many human activities reduce biodiversity.
- Measures to mitigate reduction in biodiversity by human actions is only recent.
- The future of human species on Earth depends on maintaining a good level of biodiversity.
Explain:
- High biodiversity ensures a stable ecosystem because it reduces the dependence of one species on another for food, shelter and the physical environment maintenance.
- How waste, deforestation and global warming have an impact on biodiversity.
Waste management
Understand that:
- Pollution kills plants and animals which can reduce biodiversity.
- Increasingly more resources are used and more waste is produced due to rapid human population growth and increases in the standard of living.
Explain:
- How pollution can occurs:
- In water: sewage, fertiliser or toxic chemicals
- In air: smoke and acidic gases
- On land: landfill, toxic chemicals
Land Use
Understand that:
- Humans reduce the amount of land available for other animals and plants by:
- Building
- Quarrying
- Farming
- Dumping waste
- Decay or burning of peat released carbon dioxide into the atmosphere.
- Peat bogs are destroyed to produce garden compost.
- The destruction of peat bogs reduces the habitat area and therefore biodiversity:
- There is conflict between the need for cheap compost to increase food production and the feed to conserve peat bogs and peatlands as habitats for biodiversity and reduce carbon dioxide emissions.
Deforestation
Understand that:
- Large-scale deforestation in tropical areas has occurred to provide land for:
- Grow crops for biofuel
- Provide land for cattle and rice fields.
Evaluate:
- The environmental implications of deforestations.
Global Warming
Describe:
- Some of the biological consequences of global warming.
Understand that:
- Levels of carbon dioxide and methane in the atmosphere are increasing and contribute to ‘global warming’.
- Global consensus about global warming and climate change is based on systematic reviews of 1000s of peer reviewed publications.
Explain:
- Why evidence is uncertain or incomplete in a complex context.
Maintaining biodiversity
Describe:
- Positive and negative human interactions in an ecosystem and explain their impact on biodiversity,
Understand that:
- Scientists and concerned citizens have put in place programmes to reduce the negative effects of humans on ecosystems and biodiversity, including:
- Breeding programmes for endangered species
- Protection and regeneration of rare habitats
- Reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of crop
- Reduction of deforestation and carbon dioxide emissions by some governments
- Recycling resources rather than dumping waste in landfill
Evaluate:
- Given information about methods that can be used to tackle problems caused by human impacts on the environment.
- Conflicting pressures on maintaining biodiversity given appropriate information.
Trophic Levels
Describe:
- The differences between the trophic levels of organisms within an ecosystem.
- Trophic levels as represented by numbers, starting at level 1 to level 4, according to how far the organism is along the food chain:
- Level 1: Producers – plants and algae make their own food.
- Level 2: Primary consumers – herbivores eat plants/algae.
- Level 3: Secondary consumers – carnivores eat herbivores.
- Level 4: Tertiary consumers/Apex predators – carnivores that eat other carnivores and have no predators.
- Decomposers as microorganisms which break down plant and animal matter by secreting enzymes into the environment, which create to small soluble food molecules which diffuse into the microorganism.
Pyramids of Biomass
Understand that:
- Pyramids of biomass can be constructed to represent the relative
amount of biomass in each level of a food chain. - Trophic level 1 is at the
bottom of the pyramid.
Construct:
- Accurate pyramids of biomass from appropriate data.
Transfer of biomass
Describe:
- Pyramids of biomass
- That producers transfer about 1% of incident energy from light for photosynthesis.
- Only 10% of biomass from each trophic level is transferred to the level about it.
Explain:
- How biomass is lost between different trophic levels:
- Not all ingested material is absorbed, some is egested as faeces.
- Some absorbed material is lost as waste
- Carbon dioxide and water in respiration.
- Water and urea in urine
- Large amount of glucose used in respiration.
Calculate:
- Efficiency of biomass transfers between trophic levels by percentages or fractions of mass.
- Explain how this affects the number of organisms at each trophic level.
Factors affecting food security
Understand that:
- Food security is having enough food to feed a population.
- Sustainble methods must be found to feed all people on earth.
Describe:
- Some biological factors affecting and threatening levels of food security:
- Increasing birth rate has threatened food security in some countries
- Changing diets in developed countries means scarce food resources are transported around the world
- New pests and pathogens that affect farming
- Environmental changes that affect food production, such as widespread famine occurring in some countries if rains fail
- The cost of agricultural inputs
- Conflicts that have arisen in some parts of the world which affect the availability of water or food.
Interpret population and food statistics to evaluate food security.
Farming Techniques
Understand that:
- The efficiency of food production can be improved by restricting energy transfer from food animals to the environment by limiting their movement and control surrounding temperatures.
- Some animals are fed high protein foods to increase growth.
- Some people have ethical objections to modern intensive farming techniques.
Evaluate:
- Advantages and disadvantages of modern farming techniques.
Sustainable fisheries
Understand that:
- Fish stocks in the oceans are declining.
- Fish stocks need to remain at a level where breeding can continue to avoid loss of species in some areas.
- Control of net sizes and fishing quotas are important for conserving fish stocks at a sustainable level.
- The application of different fishing techniques promotes recovery of fish stocks.
Role of Biotechnology
Describe and explain:
- Some possible biotechnical and agricultural solutions to the demands of the growing human population:
- Genetic modification
- Large quantities of microorganisms to be cultured for food by modern biotechnology.
- Fusarium – a fungus useful for producing mycoprotein (protein-rich food suitable for vegetarians).
- Grown on glucose syrup in aerobic conditions and the biomass produced is harvested and purified.
- A genetically modified bacterium produces human insulin which is harvested and purified to treat diabetes.
- GM crops – increased food yields or food with improved nutritional value (e.g. golden rice).
- Fusarium – a fungus useful for producing mycoprotein (protein-rich food suitable for vegetarians).
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