Edexcel International A Level Biology (YBI11)

Video lessons · International A Level Biology revision notes · International A Level Biology past papers

Every topic of Edexcel International A Level Biology (YBI11), all six units, in short video lessons with diagrams, clear revision notes and past papers with mark schemes.

The first 5 lessons of every chapter are free.

1 Chemistry for biologists

• Water: the dipole and why it dissolves things
• Monosaccharides and disaccharides
• Starch and glycogen: storing energy
• Core practical 1: estimating sugar and starch concentrations
• Lipids: triglycerides, saturated and unsaturated
• Amino acids and peptide bonds
• Primary to quaternary structure
• Globular and fibrous: haemoglobin and collagen

2 Mammalian transport systems

• Why many animals need a heart and circulation
• Blood and haemoglobin: carrying oxygen and carbon dioxide
• The oxygen dissociation curve
• The Bohr effect and fetal haemoglobin
• Arteries, veins and capillaries
• The structure of the mammalian heart
• The cardiac cycle and the pressure graph
• Dissecting a mammalian heart
• How atherosclerosis develops
• Blood clotting and its role in CVD

3 Cardiovascular health and risk

• Risk, correlation and cause
• Reading illness and mortality data
• Evaluating studies of health risk
• Risk factors for cardiovascular disease
• Energy balance, BMI and waist-to-hip ratio
• Blood cholesterol, HDLs and LDLs
• Dietary antioxidants and CVD
• Core practical 2: vitamin C content of food and drink
• Treatments for CVD: benefits and risks

4 Membranes and transport

• The fluid mosaic model
• Core practical 3: beetroot and membrane permeability
• Diffusion and facilitated diffusion
• Active transport, endocytosis and exocytosis
• Osmosis and water potential
• Finding the water potential of plant tissue
• Gas exchange surfaces and Fick's law
• How the lung is adapted for gas exchange

5 Proteins and DNA

• Enzymes: biological catalysts
• Active sites, specificity and induced fit
• Core practical 4: measuring the initial rate of an enzyme reaction
• Temperature, pH, enzyme and substrate concentration
• Nucleotides, DNA and RNA
• Semi-conservative DNA replication
• Meselson and Stahl: proving semi-conservative replication
• The genetic code
• Transcription: DNA to mRNA
• Translation: mRNA to polypeptide

6 Gene expression and genetics

• Gene mutations: substitution, insertion, deletion
• Genetic terms and monohybrid crosses
• Codominance and pedigree diagrams
• Sex linkage and red-green colour blindness
• Cystic fibrosis
• Genetic screening: carriers, PGD and prenatal tests
• The ethics of genetic screening

7 Cell structure

• Light and electron microscopes: magnification and resolution
• Magnification calculations and units
• Core practical 5: the graticule and drawing animal cells
• The ultrastructure of an animal cell
• What each organelle does
• Recognising organelles in electron micrographs
• Protein transport: rough ER to Golgi to the outside
• Prokaryotic cells
• From cells to organ systems

8 Mitosis, meiosis and reproduction

• The cell cycle
• The stages of mitosis
• Core practical 6: the root tip squash
• Calculating the mitotic index
• Meiosis: two divisions, four haploid cells
• Independent assortment and crossing over
• Loci and linked genes
• Sperm and egg: specialised gametes
• Fertilisation in mammals
• Fertilisation in flowering plants
• Investigating pollen tube growth

9 Development of organisms

• How cells become specialised
• Phenotype: genotype plus environment
• Epigenetics: methylation and histones
• Multiple alleles, polygenic inheritance and continuous variation
• One gene, more than one protein
• Stem cells: totipotent and pluripotent
• Using stem cells: society and decisions

10 Plant structure and function

• Cellulose and the plant cell wall
• Plant cell ultrastructure
• Xylem, phloem and sclerenchyma
• Plant fibres, starch and sustainability
• Core practical 7: plan diagrams of roots, stems and leaves
• Water, nitrate, calcium and magnesium
• Investigating plant mineral deficiencies
• Core practical 8: tensile strength of plant fibres
• Conditions for bacterial growth and plant antimicrobials
• Core practical 9: antimicrobial plants and aseptic technique
• From digitalis soup to three-phase trials

11 Classification

• Classifying living things
• What is a species?
• The three-domain system

12 Biodiversity and conservation

• Biodiversity and endemism
• Species richness and the heterozygosity index
• The index of diversity
• Niches and adaptations
• The Hardy-Weinberg equation
• Changing allele frequencies: mutation and natural selection
• Reproductive isolation and new species
• Conservation: zoos and seed banks

13 Practical Skills in Biology I

• Variables, controls and a fair test
• Planning an experiment for Unit 3
• Accuracy, precision, validity and repeatability
• Significant figures, units and results tables
• Evaluating results and suggesting improvements
• Drawing and reading graphs
• Percentage change, ratios and rates
• Mean, range, standard deviation and error bars

14 Photosynthesis

• Photosynthesis: the overall reaction
• ATP: the immediate energy supply
• Chloroplast structure and function
• Absorption and action spectra
• Separating leaf pigments by chromatography
• The light-dependent reactions
• Cyclic and non-cyclic photophosphorylation
• The Calvin cycle
• What the plant makes from GALP
• Core practical 10: measuring the rate of photosynthesis
• Limiting factors: light, carbon dioxide, temperature and wavelength

15 Ecology

• Population, community, habitat and ecosystem
• Succession: from colonisation to climax
• Abiotic factors and population size
• Biotic factors: predation, competition and disease
• How the niche explains distribution and abundance
• Core practical 11: random sampling with quadrats
• Core practical 11: transects and abiotic measurements
• Null hypotheses and choosing a statistical test
• Spearman's rank correlation coefficient
• Student's t-test
• The chi-squared test

16 Environment and climate change

• Energy transfer between trophic levels
• Gross and net primary productivity
• The carbon cycle
• Using the carbon cycle to reduce atmospheric CO₂
• The greenhouse effect and anthropogenic climate change
• Evidence for climate change: CO2 and temperature records
• Evidence for climate change: pollen in peat bogs and dendrochronology
• The climate debate: correlation, causation and who concludes
• Extrapolating data: climate models and their limitations
• How climate change affects plants and animals
• Temperature, enzymes and Q10
• Core practical 12: temperature and the development of organisms
• Evolution: a change in allele frequency
• Allopatric and sympatric speciation

17 Microbiology

• Bacteria and viruses compared
• Lytic and latent infections
• The bacterial growth curve
• Calculating exponential growth and the growth rate constant
• Culturing microorganisms with aseptic technique
• Measuring growth: cell counts and dilution plating
• Measuring growth: turbidity and mass
• Core practical 13: growth of microorganisms in liquid culture
• How pathogens enter and how the body keeps them out
• Tuberculosis: how Mycobacterium tuberculosis causes disease
• HIV: how the virus infects and leads to AIDS

18 Immunity

• Non-specific responses: inflammation, lysozyme and interferon
• Phagocytosis
• Antigens, antibodies and antigen-presenting cells
• The specific response: B cells and antibodies
• The specific response: T helper, T killer and T memory cells
• Natural, artificial, active and passive immunity
• The evolutionary race between pathogens and hosts
• Antibiotics: bacteriostatic and bactericidal
• Core practical 14: the effect of antibiotics on bacteria
• Antibiotic resistance and hospital-acquired infections

19 Decomposition and forensics

• Microorganisms, decomposition and the carbon cycle
• Time of death: body temperature and rigor mortis
• Time of death: decomposition, succession and forensic entomology
• The polymerase chain reaction (PCR)
• Gel electrophoresis
• DNA profiling: identification and relationships

20 Cellular respiration

• Aerobic respiration: the overall reaction
• Glycolysis
• Anaerobic respiration and what happens to lactate
• The link reaction and the Krebs cycle
• Oxidative phosphorylation and chemiosmosis
• The respiratory quotient (RQ)
• Core practical 15: a redox indicator and respiration in yeast
• Core practical 16: the respirometer and RQ

21 Muscles, movement and the heart

• How muscles, tendons, ligaments and the skeleton produce movement
• The structure of a skeletal muscle fibre
• Fast and slow twitch muscle fibres
• The sliding filament theory
• The myogenic heartbeat: SAN, AVN, bundle of His
• Reading ECGs
• Negative and positive feedback
• Cardiac output
• Controlling heart rate: the cardiovascular control centre
• Controlling breathing: the ventilation centre
• Core practical 17: spirometer traces and exercise

22 Control of the internal environment

• How hormones switch genes on and off
• The gross and microscopic structure of the kidney
• Urea production and ultrafiltration
• Selective reabsorption in the proximal tubule
• The loop of Henle as a countercurrent multiplier
• ADH and the control of plasma concentration
• Homeostasis and thermoregulation during exercise

23 The nervous system and neurones

• Sensory, relay and motor neurones
• From stimulus to response
• The spinal reflex arc
• The resting potential
• The action potential
• How an impulse travels: local circuits and saltatory conduction
• How a synapse works
• How the pupil dilates and contracts
• How drugs affect nerve transmission
• How rods detect light
• Habituation

24 Coordination in animals and plants

• The regions of the human brain
• Nervous and hormonal coordination
• Imaging the brain: MRI, fMRI, PET and CT
• Brain chemicals: dopamine, serotonin and new drugs
• Plant responses: auxin and gibberellins
• Phytochrome and flowering
• Phytochrome, transcription and plant responses
• Core practical 18: amylase production in germinating cereal grains

25 Gene technology

• Producing recombinant DNA
• Getting recombinant DNA into cells
• Drugs from genetically modified organisms
• Microarrays and bioinformatics
• Genetically modified organisms: risks and benefits

26 Practical Skills in Biology II

• Planning an investigation for Unit 6
• Controlling variables: saying exactly how
• Recording and analysing data: tables, logs and tests
• Limitations, improvements and extensions
• The Unit 5 pre-release article