NSSCO Biology 6116 cheat sheet

Independent variable = factor changed by the investigator; dependent variable = factor measured; controlled variables are kept constant; a control group receives no treatment.

Accuracy is closeness to the true value; precision is how close repeated readings are to one another; random error reduces precision, systematic error reduces accuracy.

Mean = sum of all values ÷ number of values; range = highest value − lowest value; median = middle value of data ordered by size; mode = most frequent value.

Magnification = image size ÷ actual size; actual size = image size ÷ magnification; 1 mm = 1000 µm = 1 000 000 nm, so convert to the same unit before dividing.

Rate = change in quantity ÷ time, e.g. rate of photosynthesis = number of bubbles per minute or volume of oxygen released per minute.

Line graph for continuous variables; bar chart for categorical or discontinuous data; scatter graph to show correlation between two continuous variables.

Reliability improves with repeats, rejection of anomalies and calculation of a mean; validity depends on controlling variables so the method tests what it claims to test.

Common measurement errors: parallax when reading a meniscus (read at eye level), human reaction time with a stopwatch, heat loss from apparatus, uncalibrated thermometer or balance.

Nucleus stores DNA; cytoplasm is the site of most reactions; cell membrane controls entry and exit; mitochondria carry out aerobic respiration; ribosomes synthesise proteins.

Plant cells have a cellulose cell wall, chloroplasts and a large permanent sap vacuole; animal cells lack these and are irregular in shape.

Prokaryotic cells have no nucleus and no membrane-bound organelles, with circular DNA and plasmids; eukaryotic cells have a nucleus and membrane-bound organelles.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four haploid gametes and generates genetic variation.

Diffusion is net movement of particles from high to low concentration (passive); rate increases with a steeper gradient, higher temperature, larger surface area and shorter diffusion distance.

Osmosis is the movement of water across a partially permeable membrane from high water potential (dilute solution) to low water potential (concentrated solution).

Active transport moves substances against a concentration gradient using carrier proteins and energy from ATP, e.g. mineral ions into root hair cells.

Plant cell in pure water becomes turgid; in concentrated sugar solution it plasmolyses. Animal cell in pure water may burst; in concentrated solution it shrinks.

Photosynthesis: carbon dioxide + water → glucose + oxygen, using light energy and chlorophyll; balanced equation 6CO2 + 6H2O → C6H12O6 + 6O2.

Limiting factors of photosynthesis are light intensity, carbon dioxide concentration and temperature; a graph plateaus when another factor becomes limiting.

Chlorophyll absorbs mainly red and blue light and reflects green; the rate of photosynthesis is measured by oxygen production or carbon dioxide uptake.

Plant minerals: nitrates for amino acids and proteins; phosphates for DNA and ATP; potassium for enzyme action and stomatal function; magnesium for chlorophyll; calcium for cell walls.

Deficiency symptoms: nitrate - stunted growth with yellowing older leaves; magnesium - chlorosis between the veins; potassium - yellow leaf edges and weak stems.

Balanced diet needs carbohydrates, proteins, lipids, vitamins, minerals, fibre and water; deficiencies include scurvy (vitamin C), rickets (vitamin D) and anaemia (iron).

Digestion: amylase converts starch to maltose; protease converts protein to amino acids; lipase converts fat to fatty acids and glycerol; bile emulsifies fat and neutralises stomach acid.

Absorption occurs in the small intestine: villi give a large surface area, thin epithelium, dense capillary network and lacteals; most water is absorbed in the large intestine.

Aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy; it occurs mainly in the mitochondria.

Anaerobic respiration in humans: glucose → lactic acid + small amount of energy; in yeast: glucose → ethanol + carbon dioxide + energy (fermentation).

Energy released by respiration powers muscle contraction, active transport, protein synthesis, growth and heat production.

Alveoli are adapted for gas exchange by a large total surface area, thin one-cell walls, a moist surface, a dense capillary network and a short diffusion distance.

Inhalation: the diaphragm contracts and flattens, external intercostal muscles raise the ribs, thorax volume increases and pressure falls, so air enters.

Exhalation: the diaphragm relaxes and domes, ribs fall, thorax volume decreases and pressure rises, so air leaves; this is passive at rest.

Exercise increases breathing rate and depth and heart rate; anaerobic respiration causes lactic acid build-up and an oxygen debt.

Plants exchange gases through stomata and lenticels; stomata close in darkness or drought, reducing both gas exchange and transpiration.

Water enters root hair cells by osmosis; mineral ions are absorbed by active transport; root hairs increase the surface area for uptake.

Transpiration is the loss of water vapour mainly through stomata; it creates the transpiration pull that draws water up the xylem.

Transpiration rate increases with higher temperature, lower humidity, higher wind speed and brighter light (which opens stomata).

Xylem: dead, hollow, lignified tubes carrying water and dissolved minerals upwards. Phloem: living sieve tubes and companion cells carrying sucrose and amino acids in both directions.

Blood: plasma transports dissolved substances; red blood cells carry oxygen using haemoglobin; white blood cells defend against pathogens; platelets cause clotting.

Circulation route: right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta; the left ventricle wall is thickest.

Arteries have thick muscular elastic walls, carry blood away from the heart at high pressure; veins have valves and low pressure; capillaries are one cell thick for exchange.

Cardiac output = heart rate × stroke volume; in double circulation blood passes through the heart twice per complete circuit (pulmonary then systemic).

Homeostasis maintains a stable internal environment by negative feedback: a change is detected and a response reverses that change.

Kidney: filtration occurs in the glomerulus and Bowman's capsule; selective reabsorption of glucose, amino acids, water and ions occurs in the tubule; urine contains urea, excess salts and water.

ADH from the pituitary gland increases water reabsorption in the collecting ducts when blood is too concentrated; low ADH produces a large volume of dilute urine.

Dialysis removes urea by diffusion but does not reabsorb glucose or amino acids; patients need a controlled diet and regular dialysis sessions.

Too hot: vasodilation, sweating, body hair lies flat, reduced shivering. Too cold: vasoconstriction, shivering, hair erector muscles contract, less sweat.

Core body temperature is about 37 °C; enzymes denature above about 40 °C; the hypothalamus coordinates temperature regulation.

Blood glucose: insulin from the pancreas lowers glucose by converting it to glycogen; glucagon raises it; uncontrolled diabetes causes persistently high blood glucose.

Excretion is removal of metabolic waste such as carbon dioxide and urea; egestion is removal of undigested food and is not excretion.

The CNS is the brain and spinal cord; sensory neurones carry impulses to the CNS, motor neurones carry impulses to effectors, relay neurones connect them.

Reflex arc: receptor → sensory neurone → relay neurone (spinal cord) → motor neurone → effector; reflexes are rapid, automatic and protective.

At a synapse, a neurotransmitter diffuses across the gap; the impulse travels electrically along the neurone and chemically across the synapse.

The myelin sheath insulates the axon and speeds up the impulse; dendrites receive impulses; axon terminals release neurotransmitter.

Eye in bright light: circular muscles of the iris contract, radial muscles relax and the pupil constricts; rods detect dim light, cones detect colour.

Hormones are chemical messengers carried in the blood; their responses are slower and longer-lasting than nervous responses.

Adrenaline from the adrenal glands raises heart rate, breathing rate and blood glucose, preparing the body for fight or flight.

Auxin from shoot tips accumulates on the shaded side and causes cell elongation, producing positive phototropism; in roots auxin inhibits elongation, giving positive geotropism.

Flower structure: sepals protect, petals attract pollinators, stamens (anther and filament) are male, the carpel (stigma, style, ovary, ovule) is female.

Pollination is the transfer of pollen to a stigma; fertilisation is the fusion of a male gamete with the egg; ovule → seed, ovary → fruit, zygote → embryo.

Seed germination requires water, oxygen and a suitable temperature; most seeds do not need light to germinate.

Male: testes produce sperm and testosterone. Female: ovaries produce eggs, oestrogen and progesterone.

Menstrual cycle: FSH matures a follicle, oestrogen thickens the uterus lining, LH triggers ovulation around day 14, progesterone maintains the lining.

Fertilisation occurs in the oviduct; implantation occurs in the uterus lining; the placenta exchanges oxygen, nutrients, antibodies and waste; amniotic fluid protects the fetus.

Contraception: barrier methods (condoms also reduce STI risk), hormonal pills that inhibit ovulation, IUDs, sterilisation; only condoms give significant protection against STIs.

STIs include HIV, gonorrhoea, chlamydia and syphilis; bacterial infections are treated with antibiotics, HIV is managed with antiretroviral drugs and has no cure.

Plant growth occurs by cell division in meristems followed by cell elongation; human growth is controlled by growth hormone and monitored using height charts.

A gene is a section of DNA coding for a protein; an allele is a different version of a gene; humans are diploid with 46 chromosomes (23 pairs).

Dominant alleles are expressed when present; recessive alleles are expressed only when homozygous; genotype = alleles present, phenotype = observable characteristic.

Monohybrid cross Bb × Bb gives genotype ratio 1 BB : 2 Bb : 1 bb and phenotype ratio 3 dominant : 1 recessive.

Sex chromosomes: XX is female, XY is male; the father's sperm determines the sex of the offspring.

Variation is genetic (mutation, meiosis, random fertilisation) or environmental; continuous variation forms a normal distribution, discontinuous variation falls into distinct groups.

Natural selection: inherited variation → competition → better-adapted individuals survive and reproduce → favourable alleles increase in frequency over generations.

Selective breeding by humans increases desired traits but reduces genetic variation and can increase inherited disorders.

Genetic engineering transfers a gene into a vector such as a plasmid; human insulin is produced by genetically modified bacteria.

Ecosystem = community + physical environment; population = one species in an area; habitat = where an organism lives; niche = its role in the community.

Food chains begin with a producer; arrows show the direction of energy flow; only about 10 % of energy passes to the next trophic level.

Energy is lost through respiration, heat, excretion and uneaten parts, so pyramids of energy are always widest at the producer level.

Carbon cycle: photosynthesis removes carbon dioxide; respiration, combustion and decomposition release carbon dioxide.

Nitrogen cycle: nitrogen fixation (Rhizobium bacteria and lightning) → nitrification → assimilation by plants → decomposition → denitrification.

Eutrophication: nitrate and phosphate run-off → algal bloom → decomposition uses up oxygen → fish die; caused by fertilisers and sewage.

Human impacts: deforestation, burning fossil fuels (carbon dioxide; acid rain from sulfur dioxide and nitrogen oxides), pesticides (bioaccumulation), plastic pollution and global warming.

Conservation measures: protected areas, captive breeding, seed banks, recycling, renewable energy and sustainable forestry.

Mark-recapture population estimate (Lincoln index) = (number marked in first sample × total in second sample) ÷ number recaptured that were marked.