Angola 12th Grade Biology National Exam key terms

The smallest structural and functional unit of a living organism, bounded by a membrane and containing cytoplasm and genetic material. All organisms are made of one or more cells.

A thin, flexible barrier of lipids and proteins surrounding the cell that controls which substances enter and leave, keeping the internal environment stable.

The membrane-bound organelle in eukaryotic cells that stores DNA and directs most cellular activities, including growth, metabolism and division.

An organelle with a folded inner membrane where aerobic respiration takes place, releasing energy from glucose as ATP for the cell's activities.

A green organelle found in plant cells containing chlorophyll, where photosynthesis converts light energy into chemical energy stored in glucose.

A tiny structure, free in the cytoplasm or attached to membranes, where amino acids are joined together to build proteins according to instructions from mRNA.

The net movement of particles from a region of higher concentration to a region of lower concentration, caused by random motion and requiring no energy input.

The diffusion of water across a semi-permeable membrane from a dilute solution to a more concentrated one, moving toward the side with lower water potential.

A type of cell division producing two genetically identical daughter cells with the same chromosome number, used for growth, repair and asexual reproduction.

A reduction division producing four daughter cells, each with half the chromosome number of the parent, forming gametes and creating genetic variation.

A thread-like structure of DNA and protein found in the nucleus, carrying genes in a linear order. Humans have 46 chromosomes in body cells.

A section of DNA that carries the instructions for making a particular protein or trait, and which is passed from parents to offspring.

One of the alternative versions of a gene that can occupy the same position on a chromosome, such as the versions producing brown or blue eyes.

The particular combination of alleles an organism carries for a gene or set of genes, written as letters such as AA, Aa or aa.

The observable characteristics of an organism, such as eye colour or blood group, resulting from its genotype interacting with the environment.

An allele whose effect appears in the phenotype even when only one copy is present, masking the effect of a recessive allele paired with it.

An allele whose effect on the phenotype appears only when two copies are present, because it is masked by a dominant allele in heterozygotes.

Describing an organism that carries two identical alleles for a particular gene, for example AA or aa, so it breeds true for that trait.

Describing an organism that carries two different alleles for a particular gene, for example Aa, so the dominant allele determines the visible trait.

Deoxyribonucleic acid, a double-stranded molecule shaped like a twisted ladder that stores the genetic instructions for building and operating living organisms.

The basic building block of DNA and RNA, made of a phosphate group, a sugar and a nitrogenous base such as adenine, thymine, guanine or cytosine.

The rule that in DNA adenine always pairs with thymine and guanine with cytosine, held together by hydrogen bonds between the two strands.

The process by which a DNA molecule makes an exact copy of itself before cell division, so each daughter cell receives a complete set of genetic instructions.

The first step of gene expression, in which a strand of messenger RNA is built from a DNA template inside the nucleus.

The stage of protein synthesis in which ribosomes read the sequence of messenger RNA and assemble the matching chain of amino acids.

A permanent change in the sequence of bases in DNA, which may alter a protein, have no effect, or produce a new characteristic in the organism.

The process by which green plants use light energy, carbon dioxide and water to make glucose and release oxygen, with chlorophyll as the trapping pigment.

The series of chemical reactions in cells that break down glucose to release energy for life processes, using oxygen in aerobic respiration and producing carbon dioxide and water.

A protein that speeds up a specific chemical reaction in living things by lowering the energy needed, without being used up itself.

The breakdown of large food molecules into smaller soluble ones that can be absorbed into the blood, carried out by mechanical action and enzymes.

One of the millions of tiny air sacs in the lungs where oxygen enters the blood and carbon dioxide leaves it, through a very thin, moist surface.

The red iron-containing protein in red blood cells that binds oxygen in the lungs and releases it to tissues that need it.

The microscopic filtering unit of the kidney that removes wastes such as urea from the blood and reabsorbs useful substances like water and glucose.

The maintenance of a stable internal environment, such as constant body temperature and blood glucose, despite changes in the surroundings.

A chemical messenger released by an endocrine gland into the blood, which travels to a target organ and alters its activity, such as insulin lowering blood glucose.

A nerve cell specialised to carry electrical impulses quickly through the body, consisting of a cell body, dendrites and a long axon.

A rapid, automatic response to a stimulus that does not involve conscious thought, protecting the body from harm, such as pulling the hand from a hot object.

A reproductive cell such as a sperm or egg cell that carries half the normal chromosome number and fuses with another at fertilisation.

The fusion of a male gamete nucleus with a female gamete nucleus to form a zygote with the full chromosome number.

The single cell formed when a sperm and egg fuse at fertilisation, which then divides repeatedly by mitosis to develop into an embryo.

The organ formed in the uterus during pregnancy through which the embryo receives oxygen and nutrients from the mother's blood and passes out wastes.

Any method or device used to prevent pregnancy, for example condoms, contraceptive pills or intrauterine devices, some of which also reduce risk of sexually transmitted infections.

The process by which individuals with characteristics better suited to their environment survive and reproduce more, so those features become more common in later generations.

A feature or behaviour of an organism that improves its chance of surviving and reproducing in its particular habitat, such as a camel's water storage.

The gradual change in the inherited characteristics of a population over many generations, leading to new species and to the diversity of living things.

A group of organisms with similar features that can breed together to produce fertile offspring, but cannot do so with members of other groups.

The variety of living things in an area, including the number of different species, the genetic differences within them and the range of habitats they occupy.

A community of living organisms interacting with each other and with the non-living parts of their surroundings, such as light, water, soil and temperature.

A sequence showing how energy passes from one organism to another through feeding, beginning with a producer and ending with a top predator.

An organism, usually a green plant or alga, that makes its own food by photosynthesis and so forms the base of every food chain.

An organism such as a bacterium or fungus that breaks down dead organisms and waste, recycling nutrients such as carbon and nitrogen back into the soil.

The largest population of a species that an environment can support sustainably, limited by food, water, space and other resources.

A testable, clear statement predicting a relationship between variables, which an experiment is designed to support or reject with evidence.

The factor that the experimenter deliberately changes in an investigation, so its effect on the measured outcome can be observed.

The factor that is measured or observed in an experiment, which is expected to change in response to the independent variable.

A standard setup in an experiment in which the variable being tested is absent or unchanged, allowing a fair comparison with the experimental setup.

An instrument that uses lenses to magnify small objects so their structure can be observed, essential for studying cells and microorganisms.

The number of times an image is enlarged compared with the real object, calculated as image size divided by actual size.

The measurements, observations or counts collected during an investigation, which are analysed to draw conclusions or identify patterns.

The extent to which repeated measurements give consistent results, improved by repeating readings and calculating a mean.