Angola 12th Grade Biology National Exam cheat sheet

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells have both.

Mitochondria carry out aerobic respiration; the inner membrane folds (cristae) increase surface area for ATP production.

Ribosomes are the site of protein synthesis; free ribosomes make cytosolic proteins, bound ribosomes make secreted or membrane proteins.

Chloroplasts contain chlorophyll and perform photosynthesis; thylakoid membranes host the light reactions, the stroma hosts the Calvin cycle.

The cell membrane is a phospholipid bilayer with embedded proteins (fluid-mosaic model); small nonpolar molecules diffuse freely, ions and large polar molecules need channels or carriers.

Osmosis is net water movement across a semipermeable membrane from low to high solute concentration; cells shrink in hypertonic and swell in hypotonic solutions.

Enzymes lower activation energy; activity peaks at an optimum pH and temperature and falls when the active site denatures.

Mitosis produces two genetically identical diploid cells; meiosis produces four genetically distinct haploid cells.

Mendel's law of segregation: the two alleles of a gene separate during gamete formation, so each gamete carries one allele.

Law of independent assortment applies to genes on different chromosomes or far apart on the same chromosome.

A monohybrid cross of two heterozygotes (Aa × Aa) gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio.

A dihybrid cross of two double heterozygotes (AaBb × AaBb) gives a 9:3:3:1 phenotype ratio when genes assort independently.

A test cross (cross with a homozygous recessive) reveals whether a dominant-phenotype individual is homozygous or heterozygous.

Codominance: both alleles are expressed in the phenotype (e.g. AB blood type). Incomplete dominance: the heterozygote shows an intermediate phenotype.

Sex-linked traits carried on the X chromosome appear more often in males, who have only one X.

A carrier is heterozygous for a recessive allele and shows the dominant phenotype; two carriers have a 25% chance per child of an affected child.

DNA is a double helix of nucleotides; adenine pairs with thymine (2 hydrogen bonds), guanine with cytosine (3 hydrogen bonds).

DNA replication is semi-conservative: each new molecule keeps one parental strand and one new strand.

Transcription copies DNA into mRNA in the nucleus; translation builds a polypeptide at the ribosome using mRNA codons and tRNA anticodons.

The genetic code is a triplet code read in non-overlapping groups of three bases; the start codon is AUG.

Restriction enzymes cut DNA at specific recognition sequences, producing sticky ends used to insert genes into plasmids.

Gel electrophoresis separates DNA fragments by size; smaller fragments migrate farther toward the positive electrode.

PCR amplifies DNA through repeated cycles of denaturation, primer annealing and extension by a heat-stable DNA polymerase.

Genetic engineering steps: isolate the gene, cut with restriction enzymes, insert into a vector, transform host cells, then select and clone.

Blood flows through the heart: right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta.

Arteries carry blood away from the heart under high pressure; veins return blood to the heart and contain valves.

Gas exchange occurs in the alveoli, which have thin walls and a large surface area richly supplied with capillaries.

The nephron is the functional unit of the kidney; filtration occurs in the glomerulus and reabsorption in the tubules.

Insulin lowers blood glucose and glucagon raises it; both are secreted by the pancreas.

Neurons transmit impulses as electrical signals along the axon and as chemical neurotransmitters across synapses.

Mechanical digestion begins in the mouth; most chemical digestion and absorption of nutrients occurs in the small intestine.

Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in tissues; white blood cells defend against pathogens.

Spermatogenesis produces four haploid sperm from one primary spermatocyte; oogenesis produces one ovum and polar bodies.

Fertilisation normally occurs in the fallopian tube; the zygote is diploid, formed by fusion of two haploid gametes.

Cleavage produces a morula, then a blastocyst, which implants in the uterus about one week after fertilisation.

The placenta exchanges nutrients, oxygen and wastes between mother and fetus and secretes hormones such as progesterone.

The menstrual cycle is controlled by FSH, LH, oestrogen and progesterone; ovulation occurs around day 14 of a 28-day cycle.

HIV is transmitted by unprotected sexual contact, contaminated blood and from mother to child; it is not spread by casual contact.

Malaria is caused by Plasmodium and transmitted by the bite of an infected female Anopheles mosquito.

Vaccination induces immunity by exposing the body to weakened or inactivated antigens, prompting antibody production and memory cells.

Natural selection requires heritable variation, competition for limited resources and differential reproductive success.

Fossils, homologous structures, embryology and molecular (DNA) comparisons provide evidence for evolution.

Homologous structures share a common origin but may differ in function; analogous structures have similar function but different origins.

A species is a group of organisms that can interbreed to produce fertile offspring.

Speciation occurs when populations become reproductively isolated, often after geographic separation.

Binomial nomenclature gives each species a two-part name: genus (capitalised) followed by species (lowercase).

Classification hierarchy: domain, kingdom, phylum, class, order, family, genus, species.

Antibiotic resistance spreads because resistant bacteria survive treatment and reproduce, increasing the proportion of resistant individuals.

A food chain shows one-way energy flow; a food web shows interconnected chains and is more realistic.

Energy transfer between trophic levels is about 10%, so higher trophic levels support fewer organisms.

Producers convert light energy to chemical energy; consumers obtain energy by eating other organisms; decomposers recycle nutrients.

Photosynthesis equation: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2.

Carbon returns to the atmosphere through respiration, combustion and decomposition; it is removed by photosynthesis.

Nitrogen-fixing bacteria convert atmospheric N2 into usable compounds; decomposers return nitrogen to the soil.

Carrying capacity is the maximum population an environment can sustain; limiting factors include food, water, space and disease.

Bioaccumulation is the build-up of non-degradable pollutants along a food chain, reaching highest concentrations in top predators.

Steps of investigation: observation, hypothesis, prediction, experiment, data analysis, conclusion.

The independent variable is manipulated by the researcher; the dependent variable is measured; controlled variables are kept constant.

A control group receives no treatment or a standard treatment and provides a baseline for comparison.

A hypothesis must be testable and falsifiable; a single experiment cannot prove a hypothesis, only support or reject it.

Reliability increases with repeated trials and larger sample sizes; validity requires that the experiment measure what it claims to measure.

Correlation between two variables does not establish causation.

A conclusion must be based on the data collected and should state whether the hypothesis was supported.

Random sampling reduces bias when selecting subjects or quadrats.

Use a microscope: start on low power, focus with the coarse knob, then switch to high power and use the fine knob only.

Total magnification = eyepiece magnification × objective magnification.

Always place a coverslip at an angle to avoid air bubbles when preparing a wet mount.

Biological drawings should be in pencil, large, with clear labels and a stated magnification.

Read a graph by identifying axes, units, trend direction, and key points such as peaks, plateaus and intersections.

Calculate a mean by summing values and dividing by the number of values; the range is the highest minus the lowest value.

When using a colorimeter or balance, read at eye level and record to the precision of the instrument.

Handle chemicals with goggles and gloves, never pipette by mouth, and dispose of biological waste as instructed.