Myanmar Matriculation Biology cheat sheet

Prokaryotic cells lack a membrane-bound nucleus and membranous organelles; they have 70S ribosomes, a single circular DNA molecule, and a peptidoglycan wall in bacteria.

Eukaryotic organelles: mitochondria (aerobic respiration, own DNA, 70S ribosomes), chloroplasts (photosynthesis, own DNA), rough ER (protein synthesis for export), smooth ER (lipid synthesis, detoxification), Golgi (modification and packaging), lysosome (hydrolytic enzymes, acidic pH).

Fluid mosaic model: phospholipid bilayer with embedded proteins, cholesterol, and glycolipids; membrane is selectively permeable and proteins may be integral (transmembrane) or peripheral.

Diffusion moves solute down a concentration gradient without energy; osmosis is water movement across a semipermeable membrane from low to high solute concentration; both are passive.

Active transport uses ATP and carrier proteins against a gradient (e.g., Na+/K+ pump, root hair ion uptake); facilitated diffusion uses channel or carrier proteins but no ATP.

Mitosis stages: prophase (chromosomes condense, spindle forms, nuclear envelope breaks down), metaphase (chromosomes align at equator), anaphase (sister chromatids separate to poles), telophase (nuclei reform), followed by cytokinesis.

Meiosis I is reductional (homologous chromosomes separate; crossing over in prophase I); meiosis II is equational (sister chromatids separate); result is four haploid cells with genetic variation.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces gametes and halving of chromosome number from 2n to n.

Cell cycle: interphase (G1 growth, S DNA replication, G2 preparation) occupies most of the cycle; mitosis is the shortest phase; checkpoints control progression.

Carbohydrates: monosaccharides (glucose C6H12O6, fructose), disaccharides (sucrose = glucose + fructose, maltose = glucose + glucose, lactose = glucose + galactose), polysaccharides (starch, glycogen, cellulose).

Proteins are polymers of amino acids joined by peptide bonds; primary structure is sequence, secondary is alpha-helix or beta-pleated sheet, tertiary is 3D folding, quaternary is multiple polypeptide chains.

Lipids: triglycerides = glycerol + three fatty acids (ester bonds); saturated fatty acids have no C=C double bonds and are solid; unsaturated have C=C bonds and are liquid; phospholipids are amphipathic.

Nucleic acids: DNA is double-stranded with deoxyribose and bases A, T, G, C; RNA is usually single-stranded with ribose and uracil replacing thymine.

Tests: Benedict's test (reducing sugar, brick-red precipitate on heating), iodine (starch, blue-black), Biuret (protein, violet), emulsion test (lipid, white emulsion).

Enzymes are biological catalysts, usually globular proteins, that lower activation energy; they are specific because the active site is complementary to the substrate.

Enzyme rate factors: temperature (optimum then denaturation above it), pH (optimum; extreme pH denatures), substrate concentration (rate rises then plateaus at Vmax), enzyme concentration.

Competitive inhibitors resemble the substrate and bind the active site (effect reduced by more substrate); non-competitive inhibitors bind elsewhere and change active site shape (effect not reversed by substrate).

Denaturation destroys the tertiary structure and active site shape; the enzyme is inactivated but peptide bonds are not broken by heat alone.

Gene = a length of DNA coding for a polypeptide; allele = alternative form of a gene at the same locus; genotype = allele combination; phenotype = observable characteristic.

Mendel's law of segregation: two alleles of a gene separate during meiosis so each gamete receives one; law of independent assortment applies to genes on different chromosomes.

Monohybrid cross Aa x Aa gives phenotypic ratio 3:1 and genotypic ratio 1:2:1; test cross with homozygous recessive distinguishes AA from Aa.

Dihybrid cross AaBb x AaBb gives 9:3:3:1 phenotype ratio when genes assort independently; linked genes deviate from this.

Codominance: both alleles expressed equally (e.g., AB blood group); incomplete dominance: heterozygote shows intermediate phenotype.

Multiple alleles: ABO blood group has IA, IB, and i alleles; IA and IB are codominant and both dominant to i.

Sex-linked traits: genes on the X chromosome; affected males inherit from carrier mothers; X-linked recessive disorders appear more often in males (e.g., haemophilia, colour blindness).

Sex determination in humans: XX female, XY male; the father's sperm determines the sex of the offspring.

Mutations: gene mutation (substitution, insertion, deletion causing frameshift) and chromosome mutation (deletion, duplication, inversion, translocation); sickle-cell anaemia is a substitution mutation.

Pedigree rules: unaffected parents with affected child indicates recessive; affected father passing X-linked trait to all daughters indicates X-linked dominant pattern consideration.

DNA structure: two antiparallel strands wound into a right-handed double helix; adenine pairs with thymine by two hydrogen bonds, guanine with cytosine by three; sugar-phosphate backbone joined by phosphodiester bonds.

Semi-conservative replication: helicase unwinds, DNA polymerase adds nucleotides 5' to 3', each new molecule has one parental and one new strand.

Transcription: RNA polymerase makes mRNA from the template strand in the nucleus; mRNA processing removes introns and splices exons in eukaryotes.

Translation: mRNA codons are read by tRNA anticodons at the ribosome; start codon AUG codes methionine; stop codons UAA, UAG, UGA terminate translation.

Genetic code features: triplet, degenerate (several codons per amino acid), non-overlapping, and nearly universal.

Protein synthesis occurs on ribosomes; mRNA carries the message, tRNA transfers amino acids, rRNA forms part of the ribosome.

Lac operon: lactose acts as inducer, repressor released from operator, structural genes transcribed; glucose absence raises cAMP and CAP binding, increasing expression.

Gene mutation effects: silent (no amino acid change), missense (different amino acid), nonsense (premature stop codon), frameshift (insertion or deletion not in multiples of three).

PCR: denaturation (~95°C), annealing of primers (~55°C), extension by Taq polymerase (~72°C); used to amplify DNA for analysis.

Five-kingdom classification: Monera (prokaryotes), Protista (unicellular eukaryotes), Fungi (chitin walls, heterotrophic absorption), Plantae, Animalia; viruses are acellular and not in the five kingdoms.

Binomial nomenclature: genus name capitalised, species name lower case, both italicised or underlined (e.g., Homo sapiens).

Evidence for evolution: fossil record, homologous structures (same origin, different function), analogous structures (different origin, same function), vestigial organs, biochemical and embryological similarities.

Darwin's natural selection: heritable variation exists, more offspring are produced than survive, competition for resources, differential survival and reproduction of favourable variations.

Lamarckism proposes inheritance of acquired characteristics; it is rejected because somatic changes are not passed to gametes.

Speciation: geographic isolation leads to reproductive isolation and accumulation of genetic differences; allopatric speciation is the commonest model.

Hardy-Weinberg equilibrium: p + q = 1 and p^2 + 2pq + q^2 = 1; allele frequencies stay constant in a large random-mating population without selection, mutation, or migration.

Antibiotic resistance illustrates directional selection: resistant bacteria survive treatment and reproduce, increasing the frequency of resistance alleles.

Adaptive features: xerophytes reduce water loss (thick cuticle, sunken stomata, reduced leaves), hydrophytes have air spaces and little cuticle.

Root: epidermis with root hairs for absorption, cortex for storage, endodermis with Casparian strip, pericycle, xylem and phloem in the stele.

Monocot stem has scattered vascular bundles and no secondary growth; dicot stem has vascular bundles in a ring with cambium enabling secondary thickening.

Xylem transports water and mineral ions upward; vessels and tracheids are dead, lignified, and rely on transpiration pull, cohesion, and adhesion.

Phloem transports sucrose and amino acids bidirectionally by translocation; sieve tube elements are living and companion cells supply ATP.

Transpiration is water loss as vapour through stomata; affected by light, temperature, humidity, wind, and stomatal opening; guard cells open when turgid.

Photosynthesis: light-dependent reactions in thylakoids produce ATP and NADPH and split water (photolysis) releasing O2; Calvin cycle in the stroma fixes CO2 via RuBP and rubisco.

Limiting factors of photosynthesis: light intensity, CO2 concentration, and temperature; rate plateaus when another factor becomes limiting.

Mineral requirements: nitrogen for proteins and chlorophyll, phosphorus for ATP and nucleic acids, magnesium for chlorophyll, potassium for enzyme activation and stomatal function.

Plant hormones: auxin promotes cell elongation and phototropism, gibberellin promotes stem elongation and germination, abscisic acid closes stomata and induces dormancy.

Mammalian heart: right side pumps deoxygenated blood to lungs, left side pumps oxygenated blood to body; valves prevent backflow; SA node sets the heart rate.

Blood vessels: arteries carry blood away from the heart (thick muscular walls, elastic), veins return blood (valves, wide lumen), capillaries are one cell thick for exchange.

Gas exchange: alveoli provide a large surface area, thin walls, moist surface, and good blood supply; ventilation maintains a concentration gradient.

Digestion: amylase digests starch to maltose, protease digests protein to amino acids, lipase digests lipids to fatty acids and glycerol; bile emulsifies fats and neutralises stomach acid.

Absorption in the small intestine occurs through villi with a large surface area, thin epithelium, and a rich blood supply; glucose and amino acids enter blood, fats enter lacteals.

Nephron function: filtration in the glomerulus, selective reabsorption of glucose, amino acids, and most water in the proximal tubule, and water reabsorption controlled by ADH in the collecting duct.

Nervous system: neurone impulse is electrical along the axon and chemical across synapses via neurotransmitters; reflex arc involves receptor, sensory neurone, relay, motor neurone, effector.

Homeostasis: negative feedback maintains body temperature, blood glucose, and water balance; insulin lowers blood glucose, glucagon raises it.

Immunity: phagocytes carry out non-specific phagocytosis; lymphocytes provide specific immunity, B cells produce antibodies, T cells kill infected cells; vaccination produces memory cells.

Asexual reproduction produces genetically identical offspring by mitosis (binary fission, budding, vegetative propagation); sexual reproduction involves meiosis and fertilisation and generates variation.

Human male reproductive system: testes produce sperm and testosterone; sperm formed by spermatogenesis in seminiferous tubules; epididymis stores and matures sperm.

Human female reproductive system: ovaries produce oocytes and oestrogen and progesterone; oviduct is the site of fertilisation; uterus supports implantation.

Menstrual cycle: FSH stimulates follicle development, oestrogen thickens the endometrium, LH surge triggers ovulation around day 14, progesterone maintains the endometrium.

Fertilisation: a single sperm penetrates the ovum and the zona pellucida hardens to prevent polyspermy; the zygote divides by mitosis to form a blastocyst.

Developmental stages: zygote, morula, blastocyst, implantation, gastrulation forming three germ layers, then organogenesis; the placenta exchanges nutrients, gases, and wastes.

Contraception and fertility: barrier methods prevent gamete contact, hormonal methods inhibit ovulation, IVF involves fertilisation outside the body followed by embryo transfer.

Plant reproduction: pollination transfers pollen to the stigma, pollen tube grows to the ovule, double fertilisation forms zygote and endosperm; seeds disperse by wind, water, or animals.

Growth and development are controlled by genes and hormones; metamorphosis in insects and amphibians is hormonally regulated (ecdysone, thyroxine).

Levels of organisation: organism, population, community, ecosystem, biosphere; habitat is where an organism lives, niche is its role including resource use.

Food chains begin with producers; energy transfer between trophic levels is about 10%, so food chains are short and energy pyramids are always upright.

Trophic levels: producers, primary consumers, secondary consumers, decomposers; decomposers recycle nutrients such as carbon and nitrogen.

Carbon cycle: photosynthesis removes CO2, respiration and combustion release it; nitrogen cycle involves nitrogen fixation, nitrification, assimilation, and denitrification.

Population growth: exponential growth occurs with unlimited resources; logistic growth levels off at carrying capacity K due to limiting factors.

Symbiosis: mutualism benefits both species, commensalism benefits one without harming the other, parasitism benefits one and harms the host.

Ecological succession: pioneer species colonise bare ground, then intermediate species replace them, ending in a stable climax community.

Human impacts: greenhouse gases (CO2, methane) cause global warming; eutrophication from fertiliser runoff causes algal blooms and oxygen depletion.

Conservation: in situ (national parks, reserves) and ex situ (zoos, seed banks) methods; biodiversity is measured by species richness and evenness.

Genetic engineering steps: isolate the gene of interest, cut DNA with restriction enzymes, insert into a vector (plasmid) with DNA ligase, transform host cells, select and culture them.

Restriction enzymes cut DNA at specific recognition sequences, often producing sticky ends; DNA ligase joins sugar-phosphate backbones.

GM crops: Bt cotton carries a bacterial gene for pest resistance; golden rice is engineered to produce beta-carotene; concerns include gene flow and effects on non-target species.

Cloning: somatic cell nuclear transfer transfers a diploid nucleus into an enucleated egg; Dolly the sheep was the first mammal cloned this way.

Stem cells are undifferentiated cells able to divide and differentiate; embryonic stem cells are pluripotent, adult stem cells are usually multipotent.

Tissue culture and micropropagation use meristem tissue on sterile nutrient medium with auxin and cytokinin to produce many identical plants quickly.

Fermentation: yeast carries out anaerobic respiration producing ethanol and CO2 (bread, beer); bacteria produce acids in yoghurt and cheese.

Biogas and antibiotics: anaerobic digestion of organic waste produces methane; Penicillium mould produces penicillin, an antibiotic.

Biotechnology in medicine: insulin produced by recombinant bacteria, gene therapy delivers functional genes, and vaccines use antigens or mRNA to trigger immunity.