MSCE Biology cheat sheet

Prokaryotic cells lack membrane-bound organelles and a nucleus; eukaryotic cells have a true nucleus, mitochondria, and (in plants) chloroplasts and a cellulose cell wall.

Magnification = image size ÷ actual size; use the same units on both sides before dividing.

Surface area : volume ratio falls as a cell enlarges, so large cells need transport systems or a flattened/elongated shape to keep diffusion adequate.

Mitochondria: site of aerobic respiration; inner membrane folds (cristae) increase surface area for the electron transport chain and ATP synthesis.

Chloroplast structure: thylakoid membranes stacked into grana carry chlorophyll for the light-dependent reactions; the stroma carries the light-independent (Calvin) reactions.

Enzymes are proteins that lower activation energy; they are denatured by high temperature or extreme pH because the active site shape changes.

Diffusion moves particles down a concentration gradient passively; osmosis is water movement across a partially permeable membrane from higher to lower water potential.

Active transport uses ATP and carrier proteins to move substances against a concentration gradient, e.g. mineral ions into root hair cells.

Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2, catalysed in chloroplasts using light energy trapped by chlorophyll.

Limiting factors of photosynthesis: light intensity, CO2 concentration, and temperature; the rate rises until another factor becomes limiting.

Leaf adaptations: large surface area, thin lamina for short diffusion distance, stomata for gas exchange, and palisade mesophyll packed with chloroplasts.

Essential plant mineral ions: nitrate for amino acids and proteins, magnesium for chlorophyll, phosphate for ATP and DNA, potassium for enzyme and stomatal function.

Deficiency signs: nitrate lack gives stunted growth and yellowing older leaves; magnesium lack gives yellowing between veins (chlorosis).

Balanced diet components: carbohydrates and lipids for energy, proteins for growth and repair, vitamins and minerals for health, fibre for gut function, water for transport.

Energy in food is measured in kilojoules; calorimetry burns a known food mass to heat a known water mass, using energy = mass of water × 4.2 × temperature rise.

Malnutrition includes both deficiency (e.g. kwashiorkor from protein lack) and excess (obesity from energy intake above expenditure).

Mammalian heart route: vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta.

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

The left ventricle wall is thicker than the right because it pumps blood around the whole body rather than only to the lungs.

Aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy; anaerobic in muscle gives lactic acid, and in yeast gives ethanol and CO2.

Alveoli maximise gas exchange: large total surface area, thin walls, moist surface, and a steep concentration gradient maintained by blood flow and ventilation.

Transpiration is water loss as vapour through stomata; rate rises with temperature, wind, light and low humidity, and falls when stomata close.

Xylem carries water and mineral ions upward in dead lignified vessels; phloem carries sucrose and amino acids in both directions in living sieve tubes with companion cells.

Smoking damages cilia and alveoli, increasing mucus, infection risk and reducing surface area as in emphysema.

The nephron sequence: glomerulus filtration → proximal tubule reabsorption of glucose and most water → loop of Henle → distal tubule → collecting duct under ADH control.

ADH from the pituitary increases collecting-duct water permeability, producing small concentrated urine when blood water potential is low.

Negative feedback: a receptor detects a change, a coordination centre compares it to a set point, and an effector reverses the change (e.g. insulin lowering blood glucose).

Insulin lowers blood glucose by promoting uptake and glycogen storage; glucagon raises it by glycogen breakdown; failure of this control causes diabetes mellitus.

Thermoregulation: vasodilation and sweating cool the body; vasoconstriction, shivering and hair erection conserve heat.

A reflex arc: stimulus → receptor → sensory neurone → relay neurone in spinal cord → motor neurone → effector, giving a rapid involuntary response.

Synaptic transmission: an impulse releases neurotransmitter across the cleft to receptors on the next neurone, ensuring one-way transmission.

Hormones travel in blood and act on target cells with specific receptors; nerves act faster and more locally than hormones.

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

Meiosis halves chromosome number and creates variation by crossing over in prophase I and independent assortment of homologous chromosomes.

Human gametes: sperm (haploid, motile, many mitochondria) and egg (haploid, large food store); fertilisation restores the diploid number.

Menstrual cycle: FSH stimulates follicle development, oestrogen thickens the uterus lining, LH triggers ovulation, and progesterone maintains the lining.

Contraceptive hormones work by inhibiting FSH and LH release, preventing follicle maturation and ovulation.

Plant sexual reproduction: pollination → pollen tube growth → fertilisation → seed and fruit formation; seeds disperse and germinate with water, oxygen and warmth.

Asexual reproduction (e.g. runners, tubers, cuttings) gives genetically identical offspring rapidly but no variation for adaptation.

Growth is measured by length, mass or cell number; growth curves show a rapid juvenile phase, a slower plateau at maturity, and different allometric rates between organs.

Genotype is the allele combination; phenotype is the observable characteristic resulting from genotype and environment.

Monohybrid cross 3:1 ratio arises from heterozygous × heterozygous parents; a test cross with a homozygous recessive identifies unknown genotypes.

Codominance and multiple alleles (e.g. ABO blood groups) produce phenotype ratios that differ from simple dominance ratios.

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

Mutations are random changes in DNA sequence and are the source of new alleles; most are neutral or harmful, some are beneficial.

Natural selection: heritable variation exists, selection pressures favour some phenotypes, survivors reproduce, and allele frequencies change over generations.

Evidence for evolution includes fossils, homologous structures, and molecular (DNA and protein) sequence comparisons.

Hardy–Weinberg: p + q = 1 and p² + 2pq + q² = 1, where p and q are allele frequencies and q² is the frequency of homozygous recessives.

Food chain energy flow: producers capture light, consumers transfer about 10% between trophic levels, so pyramids of energy are always upright.

Pyramids of numbers can be inverted (e.g. many insects on one tree); pyramids of biomass are usually upright but can invert seasonally.

Population size is affected by birth rate, death rate, immigration and emigration; carrying capacity is set by limiting resources.

The carbon cycle: photosynthesis fixes CO2, respiration and combustion release it, and decomposers return carbon from dead matter.

The nitrogen cycle: nitrogen fixation, nitrification, assimilation, ammonification and denitrification convert nitrogen between atmosphere, soil and organisms.

Eutrophication: nutrient runoff causes algal blooms, decomposers deplete oxygen, and aquatic animals die from hypoxia.

Conservation strategies include protected areas, captive breeding, seed banks, habitat corridors and sustainable resource quotas.

Indicator species and lichen diversity reveal pollution levels; dissolved oxygen and pH are direct measures of water quality.

Pathogens include bacteria, viruses, fungi and protoctists; viruses are not living cells and need a host to replicate.

Body defences: skin and mucus as barriers, phagocytes for non-specific engulfment, lymphocytes for antibody production and specific immunity.

Vaccination introduces antigens (weakened or inactive pathogen) so memory cells form, giving a faster, stronger secondary response.

Antibiotics target bacterial structures such as cell walls and ribosomes; they are ineffective against viruses.

Antibiotic resistance spreads by natural selection of resistant bacteria, worsened by overuse and incomplete courses.

Monoclonal antibodies are identical antibodies from a single clone of cells, used in diagnosis and targeted treatment.

Biotechnology applications: fermentation with yeast for bread and alcohol, bacteria for insulin production, and enzymes in detergents and food processing.

Disease risk factors include diet, smoking, alcohol, inactivity and genetic predisposition; correlation in epidemiological data does not prove causation.

Diffusion rate increases with steeper concentration gradient, higher temperature, larger surface area and shorter diffusion distance.

Facilitated diffusion uses channel or carrier proteins down a gradient without ATP; active transport uses carrier proteins and ATP against a gradient.

Osmosis in animal cells: in pure water cells swell and may lyse; in concentrated solution they shrink (crenate). Plant cells become turgid or plasmolysed.

Water potential is highest in pure water (0 kPa) and becomes more negative as solute concentration rises.

The cell cycle: interphase (G1, S, DNA replication, G2) precedes mitosis, which has prophase, metaphase, anaphase and telophase.

In mitosis, chromosomes line up at the equator in metaphase and sister chromatids separate to opposite poles in anaphase.

Uncontrolled mitosis caused by mutations in genes controlling cell division leads to tumour formation and cancer.

Root hair cells and villi increase surface area for absorption by diffusion, osmosis and active transport.

Enzymes in digestion: amylase (starch to maltose), protease (proteins to amino acids), lipase (lipids to fatty acids and glycerol); bile emulsifies fats.

Villi in the small intestine have thin walls, rich blood supply and a large surface area for absorption of digested nutrients.

Blood glucose control: pancreatic islets detect glucose, insulin promotes uptake and storage, glucagon promotes release from liver glycogen.

Lung volumes: tidal volume is air moved per breath, vital capacity is maximum exhaled after maximum inhalation, residual volume remains after full exhalation.

Practical controls: independent variable changed, dependent variable measured, and all other variables kept constant to make results valid.

Reliability improves with repeats and mean calculation; accuracy improves with calibrated instruments and correct technique.

Aseptic technique in microbiology: sterilise equipment, work near a flame, and seal plates to prevent contamination.

Rates calculated as change ÷ time; graphs must label axes with quantity and unit, and conclusions must reference the data trend.