Biology (US High School)
NGSS-aligned high school biology covering cell structure, biomolecules, photosynthesis and cellular respiration, DNA/RNA and protein synthesis, cell division, genetics, evolution, ecology, human body systems, biotechnology, and biodiversity.
Ämne: Biologi · Nivå: Gymnasium (16–19) · 471 kort
Innehåll
- All living organisms are composed of one or more cells, and the cell is the basic unit of structure and function in life. This is the central idea of the cell theory.
- Prokaryotic cells lack a membrane-bound nucleus and other membrane-bound organelles. Bacteria and Archaea are the two domains of prokaryotes.
- Eukaryotic cells have a true membrane-bound nucleus that contains the genetic material, plus various membrane-bound organelles such as mitochondria, ER, and Golgi.
- The nucleus is the control center of the eukaryotic cell. It contains DNA organized into chromosomes and is enclosed by a double membrane called the nuclear envelope.
- Mitochondria are the powerhouses of the cell. They generate ATP through aerobic cellular respiration and have their own circular DNA, supporting endosymbiotic theory.
- Chloroplasts are organelles found in plant and algal cells that carry out photosynthesis. They contain chlorophyll and, like mitochondria, have their own DNA.
- The rough endoplasmic reticulum (RER) is studded with ribosomes and synthesizes proteins destined for membranes, secretion, or lysosomes.
- The smooth endoplasmic reticulum (SER) synthesizes lipids, metabolizes carbohydrates, detoxifies drugs, and stores calcium ions.
- The Golgi apparatus modifies, sorts, and packages proteins and lipids received from the ER, then ships them to their destinations in vesicles.
- Lysosomes contain hydrolytic enzymes that digest macromolecules, worn-out organelles, and engulfed material. Their interior is acidic (pH ≈ 5).
- Ribosomes are the sites of protein synthesis. They are composed of rRNA and proteins, and can be free in the cytoplasm or bound to the rough ER.
- The cell membrane (plasma membrane) is a phospholipid bilayer with embedded proteins. It is selectively permeable and controls what enters and leaves the cell.
- The fluid mosaic model describes the cell membrane as a fluid phospholipid bilayer with a mosaic of embedded proteins, cholesterol, and carbohydrate chains.
- Plant cells have a rigid cell wall made primarily of cellulose, a large central vacuole, and chloroplasts. Animal cells lack these structures.
- The cytoskeleton is a network of microfilaments, intermediate filaments, and microtubules that gives the cell shape, supports organelles, and enables movement.
- Cilia are short, numerous hair-like projections that move fluids past cells (as in the trachea), while flagella are longer and propel cells (as in sperm).
- Diffusion is the net movement of particles from an area of higher concentration to lower concentration. It is passive and requires no energy input.
- Osmosis is the diffusion of water across a selectively permeable membrane, from a region of lower solute concentration to higher solute concentration.
- Active transport moves substances against their concentration gradient, requiring ATP. The sodium-potassium pump is a classic example in animal cells.
- In a hypertonic solution a cell loses water and shrinks (crenates). In a hypotonic solution a cell gains water and may burst (lyse). Isotonic = no net change.
- The four major classes of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids. All are built from smaller monomers.
- Carbohydrates contain C, H, and O in a roughly 1:2:1 ratio. Their monomers are monosaccharides like glucose, fructose, and galactose.
- Starch and glycogen are polysaccharides used for energy storage in plants and animals respectively. Cellulose and chitin are structural polysaccharides.
- Lipids are nonpolar, hydrophobic molecules that include fats (triglycerides), phospholipids, steroids, and waxes. They store energy and form membranes.
- Saturated fatty acids have no C=C double bonds and are solid at room temperature. Unsaturated fatty acids have one or more double bonds and tend to be liquid.
- Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails. They spontaneously form bilayers in water — the basis of cell membranes.
- Proteins are polymers of amino acids linked by peptide bonds. There are 20 standard amino acids, each with a unique R group (side chain) that gives it properties.
- Protein structure has four levels: primary (amino acid sequence), secondary (alpha helix or beta sheet), tertiary (3D folding), and quaternary (multi-subunit).
- Denaturation is the loss of a protein's three-dimensional shape due to heat, pH change, or chemical agents. A denatured protein loses its function.
- Enzymes are biological catalysts (almost always proteins) that lower the activation energy of reactions, speeding them up without being consumed.
- The induced-fit model says that an enzyme's active site changes shape slightly when its substrate binds, optimizing the fit and catalyzing the reaction.
- Nucleic acids (DNA and RNA) are polymers of nucleotides. Each nucleotide has a sugar, a phosphate, and a nitrogenous base.
- ATP (adenosine triphosphate) is the cell's main energy currency. Energy is released when the bond between the second and third phosphate is hydrolyzed to form ADP.
- Photosynthesis converts light energy, CO₂, and H₂O into glucose and O₂. Overall: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂.
- The light-dependent reactions occur in the thylakoid membranes of chloroplasts. They split water, release O₂, and produce ATP and NADPH.
- The Calvin cycle (light-independent reactions) occurs in the stroma. It uses ATP and NADPH from the light reactions to fix CO₂ into glucose (G3P).
- Chlorophyll a is the main photosynthetic pigment, absorbing mainly red and blue light and reflecting green, which is why plants appear green.
- Cellular respiration breaks down glucose to release energy as ATP. Overall: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~30–38 ATP.
- Glycolysis splits one glucose into two pyruvate molecules in the cytoplasm. Net yield: 2 ATP and 2 NADH. It does not require oxygen.
- The Krebs cycle (citric acid cycle) occurs in the mitochondrial matrix. Each turn yields 3 NADH, 1 FADH₂, 1 ATP, and 2 CO₂.
- The electron transport chain is on the inner mitochondrial membrane. It uses NADH and FADH₂ to pump H⁺, producing ATP via chemiosmosis with O₂ as final acceptor.
- Fermentation regenerates NAD⁺ from NADH so glycolysis can continue without oxygen. Lactic acid fermentation (muscles) and alcoholic fermentation (yeast) are two types.
- Photosynthesis and cellular respiration are essentially reverse processes. Photosynthesis stores energy in glucose; respiration releases that energy as ATP.
- DNA is a double helix made of two antiparallel strands. The four bases are adenine (A), thymine (T), guanine (G), and cytosine (C).
- In DNA, A pairs with T (two hydrogen bonds) and G pairs with C (three hydrogen bonds). This complementary base pairing is the basis of replication.
- The DNA double helix was described by Watson and Crick in 1953, using Rosalind Franklin's X-ray diffraction data (Photo 51) and Chargaff's base ratios.
- DNA replication is semiconservative: each new double helix contains one old strand and one newly synthesized strand. This was proven by Meselson and Stahl.
- DNA polymerase synthesizes new DNA strands in the 5′ to 3′ direction. It requires a primer and proofreads as it goes.
- Helicase unwinds the DNA double helix at the replication fork. The leading strand is synthesized continuously; the lagging strand is built as Okazaki fragments.
- RNA differs from DNA: it is usually single-stranded, has the sugar ribose (not deoxyribose), and contains uracil (U) instead of thymine (T).