Overview
This lecture reviews the main topics from Edexcel GCSE Biology Paper 1, including key concepts in cells, genetics, natural selection, and disease, focusing on content for foundation and higher tier students.
Cells and Microscopy
- All life is made of cells, visible with light microscopes but not detailed structures.
- Electron microscopes provide higher resolution and can reveal organelles.
- Magnification = image size ÷ object size; actual size can be calculated from this.
- Eukaryotic cells (plants/animals) have a nucleus; prokaryotic cells (bacteria) do not.
- Key structures: cell membrane (semi-permeable), cell wall (plants/bacteria), cytoplasm, mitochondria, ribosomes, chloroplasts (plants), vacuole (plants).
Enzymes and Digestion
- Enzymes are biological catalysts that speed up reactions, e.g., amylase breaks starch into glucose.
- Enzymes are specific; they use a lock-and-key mechanism for substrates.
- Enzyme activity increases with temperature until optimum; then denaturation occurs.
- Enzyme activity also depends on pH with an optimum range.
- Food tests: iodine for starch, Benedict’s for sugars, Biuret for protein, ethanol for lipids.
Transport in Cells
- Diffusion: movement from high to low concentration, passive, across membranes.
- Osmosis: diffusion of water across a semi-permeable membrane.
- Active transport: uses energy to move substances against the concentration gradient via carrier proteins.
- Practical: potato osmosis experiment measures percentage mass change.
Genetics and Cell Division
- DNA is stored in chromosomes in the nucleus; humans have 23 pairs (diploid).
- Gametes have 23 single chromosomes (haploid).
- Mitosis produces two identical cells; meiosis produces four genetically varied gametes.
- Stem cells are unspecialized and can develop into various cell types.
- Cloning and stem cell therapy raise ethical issues.
Nervous System and Response
- CNS (brain/spine) and PNS (nerves) control body response.
- Neurons transmit signals; reflex arcs bypass the brain for faster reactions.
- Brain regions: cortex (higher functions), cerebellum (movement), medulla (basic functions).
- Investigate reaction time with ruler drop test.
Eye Structure and Function
- Accommodation: lens changes shape to focus on near/far objects.
- Retina contains rods (light intensity) and cones (color).
- Myopia (short-sighted) and hyperopia (long-sighted) corrected with lenses or surgery.
Variation, Inheritance, and Evolution
- Sexual reproduction increases variation; asexual creates identical offspring.
- Genes code for proteins; alleles are different forms of a gene.
- Dominant alleles mask recessive ones; use Punnett squares to predict outcomes.
- Sex determined by XX (female) and XY (male).
- Evolution: natural selection favors better-adapted organisms; antibiotic resistance as evidence.
- Selective breeding and genetic modification can alter traits quickly.
Disease and Immunity
- Non-communicable diseases: CVD, diabetes, cancer.
- Communicable diseases caused by pathogens: viruses, bacteria, fungi, protists.
- Immune system: skin/mucus barriers, white blood cells, antibodies, antitoxins.
- Vaccines stimulate immunity using dead/inactive pathogens or mRNA technology.
Medicines and Treatment
- Antibiotics kill bacteria, not viruses; resistance can develop.
- Drug discovery: lab, animal, then human (blind/double blind) trials.
- Monoclonal antibodies (triple only): lab-made for treatment/diagnosis, but may have side effects.
Key Terms & Definitions
- Eukaryotic cell — cell with a nucleus.
- Prokaryotic cell — cell without a nucleus.
- Enzyme — biological catalyst speeding up reactions.
- Diffusion — passive movement from high to low concentration.
- Osmosis — diffusion of water across a membrane.
- Active transport — energy-requiring movement against concentration gradient.
- Allele — alternative form of a gene.
- Punnett square — tool to predict genetic crosses.
- Antigen — molecule on a pathogen that triggers immune response.
- Antibody — protein that binds specifically to an antigen.
Action Items / Next Steps
- Review key concepts and terms from lecture.
- Practice calculating magnification, percentage change, and using Punnett squares.
- Complete any assigned practicals or textbook readings on cell structure, genetics, and immunity.