IB Biology SL
Comprehensive flashcards for the IB Biology Standard Level (2025 syllabus). Covers all four themes (A: Unity and diversity, B: Form and function, C: Interaction and interdependence, D: Continuity and change) at SL depth.
Ämne: Biologi · Nivå: Gymnasium (16–19) · 492 kort
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- Water is a polar molecule because the oxygen atom is more electronegative than hydrogen, creating partial negative (δ−) charge on O and partial positive (δ+) on H.
- Hydrogen bonds form between water molecules when δ+ hydrogens are attracted to δ− oxygens of neighbouring molecules. They are individually weak but collectively strong.
- Cohesion is attraction between water molecules; adhesion is attraction between water and other polar surfaces. Both enable capillary action and water transport in xylem.
- Water has high specific heat capacity (~4.18 J/g/°C), high heat of vaporisation, and a wide liquid range — properties that buffer temperature in cells and aquatic habitats.
- A solvent is the dissolving medium; a solute is what dissolves. Water dissolves polar and ionic solutes (hydrophilic) but not nonpolar molecules (hydrophobic).
- The Goldilocks hypothesis suggests life requires liquid water; Earth lies in the Sun's habitable zone where surface temperature allows water to remain liquid.
- Carbohydrates have the general formula (CH₂O)ₙ. Monosaccharides include glucose, fructose, galactose; disaccharides include maltose, sucrose, lactose.
- Polysaccharides include starch (plant storage, α-glucose), glycogen (animal storage, α-glucose, more branched), and cellulose (plant cell walls, β-glucose).
- Lipids are nonpolar biomolecules. Triglycerides = glycerol + 3 fatty acids; phospholipids = glycerol + 2 fatty acids + phosphate group (amphipathic).
- Saturated fatty acids have no C=C double bonds and are solid at room temperature; unsaturated fatty acids have one or more C=C bonds, causing kinks, and are typically liquid.
- Proteins are polymers of amino acids joined by peptide bonds. There are 20 standard amino acids, each with a unique R-group that determines properties.
- Protein structure: primary (amino acid sequence), secondary (α-helix/β-sheet via H-bonds), tertiary (3D folding), quaternary (multiple polypeptide subunits).
- Denaturation is loss of a protein's 3D shape due to heat, pH change, or harsh chemicals. The primary structure is preserved but function is lost.
- DNA nucleotides consist of deoxyribose sugar, a phosphate group, and one of four bases: adenine (A), thymine (T), cytosine (C), guanine (G).
- RNA differs from DNA by containing ribose (not deoxyribose), uracil instead of thymine, and being typically single-stranded.
- Chargaff's rules: in DNA, %A = %T and %C = %G. Base pairing is A–T (2 hydrogen bonds) and C–G (3 hydrogen bonds).
- DNA's double helix has antiparallel strands: one runs 5' to 3' and the complementary strand runs 3' to 5'. The sugar-phosphate backbone is on the outside.
- Watson and Crick proposed the DNA double-helix model in 1953 based on Rosalind Franklin's X-ray diffraction images, especially Photo 51.
- The cell theory states: (1) all living organisms are composed of cells, (2) the cell is the basic unit of life, (3) all cells arise from pre-existing cells.
- Prokaryotic cells (bacteria, archaea) lack membrane-bound organelles and a nucleus. DNA is found in a nucleoid region; ribosomes are 70S.
- Eukaryotic cells have a nucleus and membrane-bound organelles. Ribosomes are 80S in the cytoplasm but 70S in mitochondria and chloroplasts.
- The nucleus contains chromatin (DNA + histones), is bounded by a double membrane (nuclear envelope) with pores, and houses the nucleolus where ribosomes are assembled.
- Mitochondria are the site of aerobic respiration. They have a double membrane; the inner membrane is folded into cristae increasing surface area for the electron transport chain.
- Chloroplasts perform photosynthesis. They have a double membrane and contain thylakoids (stacked into grana) and stroma, with chlorophyll embedded in thylakoid membranes.
- Rough endoplasmic reticulum is studded with ribosomes and synthesises proteins for export. Smooth ER lacks ribosomes and synthesises lipids and detoxifies compounds.
- The Golgi apparatus modifies, sorts, and packages proteins received from the ER into vesicles for secretion or delivery to other organelles.
- Lysosomes contain hydrolytic enzymes (~pH 5) that digest worn-out organelles, foreign materials, or, during apoptosis, the cell itself.
- Plant cells have a cellulose cell wall, large central vacuole, and chloroplasts — features absent in animal cells. Animal cells have centrioles, which plant cells lack.
- The endosymbiotic theory proposes mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotic cells. Evidence: own circular DNA, 70S ribosomes, double membrane.
- The fluid mosaic model describes the plasma membrane as a phospholipid bilayer with proteins embedded (integral) or attached to its surface (peripheral). The membrane is fluid at body temperature.
- Cholesterol in animal cell membranes regulates fluidity: at high temperatures it reduces fluidity; at low temperatures it prevents the membrane from solidifying.
- Glycoproteins and glycolipids on the outer membrane surface act as cell-identity markers and receptors for hormones or signalling molecules.
- Simple diffusion is the passive movement of small nonpolar molecules (O₂, CO₂) directly through the phospholipid bilayer, down their concentration gradient.
- Facilitated diffusion uses channel or carrier proteins to move polar/large molecules down their gradient. It is passive (no ATP needed) but selective.
- Osmosis is the net movement of water across a partially permeable membrane from a region of higher water potential to lower water potential.
- Active transport moves substances against their concentration gradient using carrier proteins (pumps) and ATP. Example: Na⁺/K⁺ pump exchanges 3 Na⁺ out for 2 K⁺ in.
- Endocytosis brings material into the cell by membrane invagination (phagocytosis = solids, pinocytosis = liquids). Exocytosis releases material via vesicle fusion with the membrane.
- Enzymes are biological catalysts (usually proteins) that lower activation energy and speed up reactions without being consumed.
- The induced-fit model: when substrate binds the active site, the enzyme changes shape slightly to fit more snugly, stressing substrate bonds and lowering activation energy.
- Competitive inhibitors resemble the substrate and bind to the active site; non-competitive inhibitors bind elsewhere (allosteric site) and change the enzyme's shape.
- Enzyme activity is affected by temperature (rate doubles per ~10°C until denaturation), pH (each enzyme has an optimum), and substrate concentration (rate plateaus at V_max).
- ATP (adenosine triphosphate) is the universal energy currency of cells. Hydrolysis of its terminal phosphate releases ~30.5 kJ/mol and yields ADP + Pi.
- Cell respiration overall equation: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ~30 ATP per glucose (aerobic).
- Glycolysis occurs in the cytoplasm and splits one glucose (6C) into two pyruvate (3C) with net yield of 2 ATP and 2 NADH. It does not require oxygen.
- In anaerobic respiration, pyruvate is converted to lactate (animals) or to ethanol + CO₂ (yeast), regenerating NAD⁺ so glycolysis can continue without oxygen.
- Aerobic respiration occurs in mitochondria: link reaction and Krebs cycle in the matrix, electron transport chain on the inner membrane. Yields ~30 ATP per glucose total.
- Photosynthesis overall equation: 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂ (light energy required). Glucose stores chemical energy and O₂ is a by-product.
- Light-dependent reactions occur on thylakoid membranes: chlorophyll absorbs light, water is split (photolysis) releasing O₂, and ATP + NADPH are produced.
- Light-independent reactions (Calvin cycle) occur in the stroma: CO₂ is fixed onto RuBP by the enzyme rubisco, and ATP + NADPH from the light reactions drive sugar production.
- Limiting factors for photosynthesis are light intensity, CO₂ concentration, and temperature. The factor in shortest supply limits the rate.