MATSEC SEC Biology cheat sheet

Cell theory: all living organisms are made of cells, the cell is the basic unit of life, and new cells arise from pre-existing cells by division.

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells have a true nucleus and organelles such as mitochondria, chloroplasts and the Golgi apparatus.

Diffusion moves particles down a concentration gradient without energy input; osmosis is the diffusion of water across a partially permeable membrane from high to low water potential.

Active transport moves substances against a concentration gradient using carrier proteins and ATP; it occurs in root hair cells and the gut lining.

Photosynthesis: carbon dioxide + water → glucose + oxygen, in the presence of chlorophyll and light; the balanced equation is 6CO2 + 6H2O → C6H12O6 + 6O2.

Aerobic respiration releases more energy per glucose molecule than anaerobic respiration; anaerobic respiration in muscle produces lactic acid, and in yeast produces ethanol and carbon dioxide.

Enzymes are biological catalysts made of protein; they are denatured by high temperature or extremes of pH because the active site shape changes.

The nitrogen cycle depends on decomposers, nitrifying bacteria and nitrogen-fixing bacteria converting atmospheric nitrogen into usable nitrates.

Food chains transfer energy between trophic levels; only about 10 percent of energy passes to the next level, the rest is lost as heat and through excretion.

DNA carries genetic information in a double helix; a gene is a section of DNA that codes for a protein, and chromosomes are found in the nucleus.

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

In a monohybrid cross, a dominant allele is expressed when present; a recessive phenotype appears only when both alleles are recessive.

Sex determination in humans: XX gives a female and XY gives a male; the father determines the sex of the offspring.

Homeostasis maintains a constant internal environment; negative feedback reverses a change, as in temperature regulation and blood glucose control by insulin and glucagon.

Insulin lowers blood glucose by promoting uptake by cells and storage as glycogen; glucagon raises blood glucose by converting glycogen to glucose in the liver.

Natural selection: individuals with advantageous variations are more likely to survive, reproduce and pass on their alleles, so the population changes over generations.

Ecological terms: a population is one species in an area, a community is all populations, and an ecosystem includes the community and its physical environment.

Human impact: deforestation reduces carbon dioxide absorption, and burning fossil fuels releases carbon dioxide and sulfur dioxide, contributing to global warming and acid rain.