China 高一 Biology
Chapters: 12
1. Comp.1 Ch.1 Approaching cells
Cells as basic units; cell theory · Diversity and unity; prokaryotes vs eukaryotes
- Cell: The Unit of Life – Every living thing is made of cells, and every new cell comes from an old cell. Prokaryotic cells (bacteria) have no nuclear envelope and no membrane-bound organelles; eukaryotic cells have a true nucleus and many organelles. The membrane is a fluid mosaic of lipids and proteins; plants add a cellulose wall. ER, Golgi, lysosomes and vacuoles form the endomembrane system. Mitochondria and plastids make energy and food, ribosomes make proteins, the cytoskeleton, cilia, flagella and centrioles give shape and movement, and the nucleus holds the DNA.
2. Comp.1 Ch.2 Molecules of cells
Elements and compounds; water and salts · Carbohydrates and lipids · Proteins · Nucleic acids
- Biomolecules – A cell is mostly water, plus four big families of carbon compounds: proteins, carbohydrates, lipids and nucleic acids. Grinding tissue in acid separates small molecules (acid-soluble pool) from big ones – proteins, polysaccharides and nucleic acids (acid-insoluble pool). Proteins are chains of amino acids folded into four levels of structure. Polysaccharides are chains of sugars; lipids are fatty acids on glycerol; nucleic acids are chains of nucleotides. Enzymes are protein catalysts that bind a substrate at the active site, lower the activation energy, and are affected by temperature, pH, substrate level and inhibitors.
3. Comp.1 Ch.3 Cell structure
Cell membrane · Organelles and cooperation · Nucleus
- Cell: The Unit of Life – Every living thing is made of cells, and every new cell comes from an old cell. Prokaryotic cells (bacteria) have no nuclear envelope and no membrane-bound organelles; eukaryotic cells have a true nucleus and many organelles. The membrane is a fluid mosaic of lipids and proteins; plants add a cellulose wall. ER, Golgi, lysosomes and vacuoles form the endomembrane system. Mitochondria and plastids make energy and food, ribosomes make proteins, the cytoskeleton, cilia, flagella and centrioles give shape and movement, and the nucleus holds the DNA.
4. Comp.1 Ch.4 Transport
Passive transport; osmosis · Active transport; endo/exocytosis
- Membrane Transport: How Things Get In and Out of a Cell – The cell membrane is a thin double layer of fat-like molecules with proteins in it. It lets some substances through and stops others (selectively permeable). Diffusion moves particles from high to low concentration with no energy. Facilitated diffusion does the same through protein channels. Osmosis is the diffusion of water through a partially permeable membrane. Active transport uses ATP and a protein pump to move particles from low to high concentration. Very large things enter and leave in bubbles (endocytosis and exocytosis).
5. Comp.1 Ch.5 Energy
Enzymes · ATP · Cellular respiration · Photosynthesis
- Biomolecules – A cell is mostly water, plus four big families of carbon compounds: proteins, carbohydrates, lipids and nucleic acids. Grinding tissue in acid separates small molecules (acid-soluble pool) from big ones – proteins, polysaccharides and nucleic acids (acid-insoluble pool). Proteins are chains of amino acids folded into four levels of structure. Polysaccharides are chains of sugars; lipids are fatty acids on glycerol; nucleic acids are chains of nucleotides. Enzymes are protein catalysts that bind a substrate at the active site, lower the activation energy, and are affected by temperature, pH, substrate level and inhibitors.
- ATP: The Energy Currency of the Cell – ATP (adenosine triphosphate) is a nucleotide made of the base adenine, the sugar ribose and three phosphate groups. The enzyme ATP hydrolase splits off the last phosphate using water (hydrolysis): ATP + H₂O → ADP + Pi, releasing about 30 kJ per mole in small, usable amounts. ATP synthase joins ADP and Pi back together by a condensation reaction during respiration and photosynthesis. Cells make and use ATP constantly instead of storing it. One glucose gives roughly 30–32 ATP in aerobic respiration but only 2 in anaerobic respiration.
- Respiration in Plants – Respiration breaks food like glucose to release energy stored as ATP. Plants take in O₂ through stomata and lenticels. Glycolysis in the cytoplasm splits glucose into two pyruvates. Without O₂, pyruvate is fermented to ethanol or lactic acid. With O₂, pyruvate enters the mitochondrion, runs the Krebs cycle, and the electron transport system uses O₂ to make most of the ATP: up to 38 per glucose. The same path also builds molecules (amphibolic). RQ = CO₂ given out ÷ O₂ taken in.
- Photosynthesis in Higher Plants – Green plants make sugar from carbon dioxide and water using light. It happens in chloroplasts. The light reaction in the thylakoids splits water, gives out oxygen and makes ATP and NADPH. The Calvin cycle in the stroma uses that ATP and NADPH to fix CO₂ into sugar. C₄ plants add a CO₂ pump that stops the wasteful photorespiration. The slowest factor, such as light, CO₂ or temperature, sets the rate.
6. Comp.1 Ch.6 Cell life cycle
Mitosis · Differentiation; stem cells · Ageing and death; apoptosis
- Cell Cycle and Cell Division – A cell grows, copies its DNA and splits in a fixed order called the cell cycle: interphase (G1, S, G2) and M phase. In S phase the DNA doubles (2C → 4C) but the chromosome number stays the same. Mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis give two cells identical to the parent – it is an equational division used for growth and repair. Meiosis has two divisions; in meiosis I homologous chromosomes pair, cross over and separate, halving the chromosome number (2n → n). It makes four haploid cells for gametes and creates variation.
- Cell Differentiation and Stem Cells – Your body has more than 200 kinds of cells, but all of them come from one cell, the zygote. Every cell carries the same DNA. Differentiation happens when a cell switches some genes ON and others OFF, so it grows into a special shape with a special job. Cells that can still divide and become many types are called stem cells.
- Ageing and Death of Cells: Apoptosis – Cells do not live forever. As a cell ages it gets smaller, works slower and collects waste. A cell can die in two ways. In apoptosis the cell dies by a planned programme: it shrinks, breaks into sealed packets and neighbours eat them, so nothing leaks. In necrosis an injury makes the cell swell and burst, and the leaking contents cause swelling. Apoptosis shapes the body (for example it removes the webbing between fingers) and removes damaged cells that could become cancer.
7. Comp.2 Ch.1 Mendel
Segregation · Independent assortment
- Heredity and Mendel's Laws – Heredity is the passing of traits from parents to children through genes. Each parent gives one copy of every gene. A dominant copy hides a recessive one, which is why Mendel saw 3:1 in a monohybrid cross and 9:3:3:1 in a dihybrid cross. Genes are pieces of DNA that make proteins, and proteins build the trait.
8. Comp.2 Ch.2 Genes and chromosomes
Meiosis and fertilisation · Genes on chromosomes · Sex-linked inheritance
- Cell Cycle and Cell Division – A cell grows, copies its DNA and splits in a fixed order called the cell cycle: interphase (G1, S, G2) and M phase. In S phase the DNA doubles (2C → 4C) but the chromosome number stays the same. Mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis give two cells identical to the parent – it is an equational division used for growth and repair. Meiosis has two divisions; in meiosis I homologous chromosomes pair, cross over and separate, halving the chromosome number (2n → n). It makes four haploid cells for gametes and creates variation.
- Chromosomes: Where Your Genes Live – A chromosome is a thread-like packet of DNA inside the nucleus. Genes are short pieces of that DNA, lined up one after another. A human body cell has 46 chromosomes in 23 pairs: one chromosome of each pair from the mother and one from the father. Egg and sperm carry only 23 each, so a baby gets 46 again. Sutton saw that chromosomes behave like Mendel's factors, and Morgan showed that genes sit on them in a line.
- Sex-Linked Inheritance – Some genes sit on the X chromosome and have no partner on the short Y chromosome. Such X-linked genes pass from parents to children in a special pattern. A man (XY) has only one X, so one faulty recessive allele shows up in him. A woman (XX) needs two faulty copies; with one she is a healthy carrier. Red-green colour blindness and haemophilia follow this X-linked recessive pattern.
9. Comp.2 Ch.3 Nature of genes
DNA as genetic material · DNA structure · Semi-conservative replication · Genes as functional DNA segments
- DNA as the Genetic Material: The Experiments – Genes are the instructions of life, but what are they made of? In 1928 Griffith saw that a substance from dead disease-causing bacteria could change harmless bacteria into harmful ones. In 1944 Avery and his team showed that this substance is DNA, because only a DNA-destroying enzyme stopped the change. In 1952 Hershey and Chase labelled virus DNA with radioactive phosphorus and virus protein with radioactive sulphur, and found that only the DNA entered the bacteria. So in most living things DNA is the genetic material. Some viruses use RNA instead.
- DNA Structure: The Double Helix – DNA is a twisted ladder called a double helix. Each side rail is a strand made of nucleotides; a nucleotide is a phosphate, a sugar and one base (A, T, G or C). The rungs are base pairs: a big base always pairs with a small one, A with T (2 hydrogen bonds) and G with C (3 hydrogen bonds). The two strands run in opposite directions. The helix turns once every 10 base pairs (3.4 nm) and is 2 nm wide. Because of the pairing rule, A = T and G = C in any double-stranded DNA (Chargaff's rule).
- DNA Replication: How a Cell Copies Its DNA – Before a cell divides, it makes an exact copy of its DNA so each new cell gets a full set of instructions. Helicase unzips the double helix. Each old strand is a template. DNA polymerase adds matching bases (A with T, G with C). The result is two DNA molecules, each with one old and one new strand (semi-conservative). Polymerase checks its work, so mistakes are very rare; a mistake that stays is a mutation.
- Gene Structure: What Is Inside a Gene? – A gene is a stretch of DNA that carries the instructions to make a functional product, usually a protein (sometimes an RNA). A typical gene has a promoter (where RNA polymerase binds and transcription starts), a coding region (the message) and a terminator (where transcription stops). The template strand is read; the coding strand has the same sequence as the mRNA (with T instead of U). In prokaryotes, genes are continuous (no introns) and related genes are often grouped in an operon under one promoter, making one polycistronic mRNA. In eukaryotes, genes are split: coding exons are separated by non-coding introns. The whole gene is copied into pre-mRNA; then introns are removed and exons joined (splicing), a cap and a poly-A tail are added, and the mature mRNA leaves the nucleus. Alternative splicing lets one gene make several proteins. The genome is all the DNA of an organism; in humans only about 1–2% codes for protein.
10. Comp.2 Ch.4 Gene expression
Transcription and translation · Gene expression and traits; epigenetics
- Protein Synthesis: From Gene to Protein – A gene is a stretch of DNA that holds the recipe for one protein. In transcription, the cell copies the gene into messenger RNA (mRNA) inside the nucleus; U replaces T. The mRNA goes to a ribosome in the cytoplasm. In translation, the ribosome reads the mRNA three bases at a time (a codon). Each codon matches one amino acid, carried in by a transfer RNA (tRNA). The amino acids join into a chain that folds into a protein. A change in the DNA (a mutation) can change the protein.
- Molecular Basis of Inheritance – DNA is the genetic material in most living things (some viruses use RNA). It is a double helix: two antiparallel strands of nucleotides, A pairs with T by 2 hydrogen bonds and G with C by 3. Long DNA is packed on histones into nucleosomes and then chromatin. DNA copies itself semi-conservatively (Meselson–Stahl). The central dogma says DNA → RNA → protein. Transcription makes RNA from one strand; in eukaryotes the hnRNA is capped, tailed and spliced. The genetic code is a triplet, has 64 codons (61 for amino acids, 3 stops), starts with AUG, is nearly universal and degenerate. Ribosomes translate mRNA into protein with tRNA adaptors. Genes are switched on and off; the lac operon is the classic example. The Human and Rice Genome Projects read whole genomes, and DNA fingerprinting uses repeat DNA (VNTRs) to identify people.
11. Comp.2 Ch.5 Mutation and variation
Gene mutation and recombination; cancer · Chromosome variation · Human genetic disease
- Mutations – A mutation is a sudden, lasting change in the DNA. Gene (point) mutations change one or a few bases: substitution, insertion or deletion. Insertions and deletions shift the reading frame. Chromosome mutations change big pieces or the number of chromosomes. Mutations happen by chance or because of mutagens such as UV light, X-rays and some chemicals. They can be harmful, neutral or useful, and they are the first source of all genetic variation.
- Genetic Disorders – A genetic disorder is a health problem caused by a change in a gene or in the number or shape of chromosomes. Single-gene disorders can be recessive (cystic fibrosis, sickle cell anaemia: you need two faulty copies), dominant (Huntington disease: one faulty copy is enough) or X-linked (haemophilia, colour blindness: mostly boys). Chromosome disorders such as Down syndrome (an extra chromosome 21) come from a mistake when egg or sperm cells form. Punnett squares predict the chance of each outcome, and genetic testing, counselling and gene therapy help families.
12. Comp.2 Ch.6 Evolution
Evidence for common ancestry · Natural selection and adaptation · Gene pools and speciation · Coevolution and biodiversity
- Evolution: How New Kinds of Living Things Arise – Variations arise during reproduction. Nature selects those that help survival, so over many generations populations change: this is evolution. Only inherited (DNA) changes pass on; acquired changes do not. Separated populations can become new species. Homologous organs, analogous organs and fossils help us trace who is related to whom, and complex organs evolved step by step.
- Population Genetics: Gene Pools, Hardy–Weinberg and New Species – Population genetics studies how allele frequencies change in a population. The gene pool is all alleles of all individuals. For one gene with alleles A and a, p + q = 1. If a population is large, mates randomly, and has no migration, mutation or selection, the Hardy–Weinberg principle says frequencies stay the same and genotypes are p² (AA) + 2pq (Aa) + q² (aa) = 1. Any change from this means evolution is happening, caused by genetic drift (bottleneck, founder effect), gene flow, mutation, natural selection or non-random mating. A species, in the biological species concept, is a group whose members can interbreed: a shared gene pool. New species form when gene pools are cut off by reproductive isolation: allopatric (geographic barrier) or sympatric (same area, e.g. polyploidy, habitat or behaviour). One ancestor can split into many forms (adaptive radiation, divergence), while unrelated groups can evolve similar shapes (convergence).
- Coevolution and the Formation of Biodiversity – Coevolution happens when two or more kinds of living things change each other through natural selection over many generations. A flower with a deep tube and a moth with a long tongue, a fast hunter and fast prey, a parasite and its host are classic pairs. Each partner is a part of the other's environment, so a change in one favours a matching change in the other. Along with isolation, mutation and natural selection in different habitats, coevolution builds new species and tight partnerships, and the result is the great variety of life called biodiversity (genes, species and ecosystems).