GCSE Biology (UK)
UK GCSE Biology (Years 10-11, ages 14-16) aligned with AQA/Edexcel/OCR/WJEC common core: cell biology, organisation, infection and response, bioenergetics, homeostasis, inheritance, ecology, and required practicals.
Ämne: Biologi · Nivå: Högstadium (13–15) · 442 kort
Innehåll
- Eukaryotic cells have a nucleus enclosed in a membrane. Animal, plant, fungal and protist cells are all eukaryotic.
- Prokaryotic cells (bacteria) have no nucleus. Their DNA sits free in the cytoplasm as a single loop, with extra small rings called plasmids.
- Sub-cellular structures found in both animal and plant cells: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes.
- Plant cells contain extra structures animal cells lack: a cellulose cell wall, chloroplasts (for photosynthesis) and a permanent vacuole filled with cell sap.
- The nucleus contains the genetic material (DNA arranged as chromosomes) and controls the activities of the cell.
- Mitochondria are the site of aerobic respiration, releasing energy from glucose. Cells with high energy demand (muscle, liver, sperm) have many mitochondria.
- Ribosomes are the sites of protein synthesis. They are present in all cells, including prokaryotes (though prokaryotic ribosomes are smaller).
- Chloroplasts contain chlorophyll, a green pigment that absorbs light energy for photosynthesis. They are found in plant cells and algae but not in animal cells.
- The cell wall in plants is made of cellulose. It is rigid and gives the cell strength and shape; bacterial cell walls are different and made mainly of peptidoglycan.
- Bacterial plasmids are small loops of DNA carrying extra genes (e.g. antibiotic resistance). They can be transferred between bacteria and are widely used in genetic engineering.
- Magnification = image size ÷ actual size. The same equation rearranges to find actual size or image size when two of the three are known.
- Light microscopes use light and have lower resolution (~200 nm); electron microscopes use electron beams and resolve down to ~0.2 nm, revealing detailed sub-cellular structures.
- Useful unit conversions in microscopy: 1 mm = 1000 µm; 1 µm = 1000 nm. Convert all measurements to the same unit before calculating magnification.
- Specialised animal cells include: sperm cells (long tail, many mitochondria, enzymes in head), nerve cells (long axon, branched dendrites, myelin), muscle cells (proteins that contract, many mitochondria).
- Specialised plant cells include: root hair cells (large surface area for water/mineral uptake), xylem (hollow dead cells with lignin for water transport), phloem (sieve tubes with companion cells for sugar transport).
- Stem cells are undifferentiated cells that can divide and become specialised. Embryonic stem cells can form any cell type; adult stem cells (e.g. in bone marrow) are more limited.
- Plant meristem tissue contains stem cells that can produce any plant cell type throughout the plant's life. Found in root and shoot tips, used for tissue culture and cloning.
- Therapeutic cloning produces stem cells with the same genes as the patient, reducing the risk of rejection when used to treat conditions such as diabetes or paralysis.
- The cell cycle has three main stages: growth and DNA replication (interphase), mitosis (nuclear division), and cytokinesis (cytoplasm division). It results in two genetically identical daughter cells.
- Mitosis produces two diploid daughter cells genetically identical to the parent. It is used for growth, repair and asexual reproduction.
- Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It is passive (no energy from respiration needed).
- Factors affecting rate of diffusion: concentration gradient (steeper = faster), temperature (higher = faster), surface area (larger = faster), and diffusion distance (shorter = faster).
- Osmosis is the diffusion of water molecules through a partially permeable membrane, from a dilute solution (high water concentration) to a more concentrated solution (low water concentration).
- Active transport moves substances against a concentration gradient, from a lower to a higher concentration. It requires energy from respiration (ATP) and is used by root hair cells and the small intestine.
- Required practical: investigating osmosis in potato cylinders. Mass change (%) is plotted against sucrose concentration. The line crosses 0% change at the concentration equal to the cell sap.
- Levels of organisation: cells → tissues → organs → organ systems → organism. A tissue is a group of cells with similar structure and function.
- The digestive system is an organ system that breaks down food. Main organs: mouth, oesophagus, stomach, small intestine, large intestine, pancreas, liver, and gall bladder.
- Digestive enzymes: amylase digests starch → maltose (in mouth and pancreas); proteases digest proteins → amino acids (stomach, pancreas); lipases digest lipids → fatty acids + glycerol (pancreas, small intestine).
- Bile is made by the liver and stored in the gall bladder. It is alkaline (neutralises stomach acid) and emulsifies fat into small droplets, giving a larger surface area for lipase.
- Enzymes are biological catalysts. The active site has a specific shape that fits one substrate — the 'lock and key' model. Higher Tier specification also includes the 'induced fit' model where the active site flexes around the substrate.
- Enzymes are denatured (active site permanently changes shape) by high temperature or wrong pH. They can no longer bind substrate, so the reaction stops.
- Most human enzymes work best near 37 °C (body temperature). Optimum pH varies: pepsin (stomach) ~2; amylase ~7; lipase in small intestine ~8.
- Food tests: Benedict's reagent + heat — brick-red precipitate indicates reducing sugars; iodine solution — blue-black indicates starch; biuret solution — purple indicates protein; ethanol emulsion — cloudy white indicates lipids.
- The heart has four chambers: two atria (top) receive blood; two ventricles (bottom) pump it out. The right side handles deoxygenated blood; the left side handles oxygenated blood.
- The left ventricle has a thicker, more muscular wall than the right ventricle because it pumps oxygenated blood at higher pressure around the whole body.
- The heart's natural pacemaker is a group of cells in the right atrium called the sino-atrial node (SAN). Artificial pacemakers correct an irregular heart rhythm.
- Blood vessels: arteries carry blood away from the heart at high pressure (thick muscular walls, narrow lumen); veins return blood to the heart (thinner walls, wider lumen, have valves); capillaries are one cell thick for exchange.
- Blood is a tissue made of four components: red blood cells (carry oxygen), white blood cells (defence), platelets (clotting), and plasma (a straw-coloured liquid that transports nutrients, CO₂, urea, hormones).
- Red blood cells (erythrocytes) have a biconcave disc shape (large surface area), no nucleus (more room for haemoglobin) and contain haemoglobin which binds oxygen reversibly as oxyhaemoglobin.
- Coronary heart disease (CHD): fatty deposits build up in the coronary arteries narrowing them, reducing blood flow to the heart muscle. Treatments include statins, stents and bypass surgery.
- Gas exchange in the lungs occurs in alveoli. They are adapted by: a huge surface area, walls one cell thick, a moist lining, and a rich blood supply giving short diffusion distances and steep gradients.
- Plant tissues include: epidermis (covers plant), palisade mesophyll (most photosynthesis), spongy mesophyll (gas exchange), xylem (transports water), phloem (transports sugars), and meristem (growth).
- Transpiration is the loss of water vapour from the leaves of a plant, mainly through stomata in the lower epidermis. The transpiration stream pulls water up the xylem from the roots.
- Factors that increase transpiration rate: higher light intensity (opens stomata), higher temperature, lower humidity, and more air movement (wind).
- Translocation is the movement of dissolved sugars (mainly sucrose) and amino acids around the plant through phloem tissue, from source (e.g. leaves) to sink (e.g. roots, fruits).
- Stomata are tiny pores in the leaf epidermis surrounded by guard cells. They open in the light to allow CO₂ in for photosynthesis but also release water vapour.
- Non-communicable diseases include cardiovascular disease, type 2 diabetes, many cancers, and lung disease. They cannot be passed between people and are linked to genetics and lifestyle.
- Cancer is uncontrolled cell division producing tumours. Benign tumours stay in one place; malignant tumours invade neighbouring tissues and can spread via the blood (metastasis).
- Risk factors for cancer include smoking (lung), UV exposure (skin), ionising radiation, viral infection (e.g. HPV → cervical), some chemicals, and genetic risk factors (e.g. BRCA1/2 mutations).
- BMI = mass (kg) ÷ (height (m))². A BMI over 30 is classed as obese. High BMI is a risk factor for type 2 diabetes and cardiovascular disease.