ILEARN Biology ECA key terms

A thin, flexible barrier of lipids and proteins that surrounds a cell and controls which substances enter or leave, helping the cell maintain a stable internal environment.

An organelle in eukaryotic cells that releases usable energy by breaking down sugars during cellular respiration; cells with high energy demands, such as muscle cells, contain many of them.

A green organelle found in plant cells and algae where photosynthesis takes place; it contains chlorophyll, the pigment that captures light energy used to build sugars from carbon dioxide and water.

A protein that speeds up one specific chemical reaction in living things by lowering the energy needed to start it, working best at particular temperatures and pH levels.

The process in which plants, algae, and some bacteria use light energy to combine carbon dioxide and water into sugars, releasing oxygen as a byproduct.

The set of chemical reactions in cells that break down glucose, with or without oxygen, to release energy stored in ATP while producing carbon dioxide and water.

A small molecule that acts as the cell's main energy currency; energy released when its phosphate bonds are broken powers many cell processes, including active transport and building proteins.

The ability of an organism to keep internal conditions, such as temperature, water balance, and blood sugar, within narrow limits even when conditions outside the body change.

The movement of particles from an area where they are crowded to an area where they are less crowded, without added energy, until the particles are spread evenly.

The diffusion of water across a membrane that lets water pass but blocks some dissolved materials, so water moves toward the side with more dissolved material.

Movement of substances across a membrane from a region of lower concentration to one of higher concentration, which requires energy from the cell and usually carrier proteins.

A long, double-stranded molecule that stores instructions for building proteins and for passing traits to offspring; its sequence of bases is copied before a cell divides.

A section of DNA that carries the instructions for making a protein or for controlling a trait; offspring inherit genes from their parents.

One of the different versions of a gene; for example, a gene for flower color may have a purple allele and a white allele.

A structure made of DNA coiled tightly around proteins that carries many genes in a line; human body cells contain 46 chromosomes arranged in 23 pairs.

An allele whose trait appears in an organism whenever at least one copy is inherited, because it masks the effect of the recessive allele paired with it.

An allele whose trait appears only when two copies are inherited, because its effect is hidden whenever a dominant allele is also present.

The combination of alleles an organism carries for a particular gene, which may be two identical alleles or two different ones and is usually written with letters.

The observable traits of an organism, such as eye color or plant height, which result from its genotype interacting with the environment.

A grid used to predict the possible allele combinations and the chance of each offspring genotype from a cross between two parents with known genotypes.

A type of cell division that halves the chromosome number and produces genetically varied sex cells, such as sperm and eggs, used in sexual reproduction.

A change in the DNA sequence of a gene or chromosome that may have no effect, may change a protein, or may be passed to offspring and add new variation.

The process by which individuals with inherited traits that help them survive and reproduce in their environment leave more offspring, so those traits become more common over generations.

An inherited feature or behavior that improves an organism's chance of surviving and reproducing in its environment, such as thick fur in a cold climate.

Differences in traits among individuals of the same species, often caused by different combinations of genes and by mutations; it provides the raw material on which natural selection acts.

The formation of a new species, usually when populations become separated and build up so many genetic differences that their members can no longer interbreed.

Body parts in different species that share a similar underlying structure because they were inherited from a common ancestor, such as the forelimbs of humans, whales, and bats.

The collected fossils and their positions in rock layers, which give evidence about the order in which organisms lived and how they changed over long periods.

A random change in allele frequencies within a small population, caused by chance events rather than by natural selection; it can remove helpful alleles or make harmful ones common.

How well an organism survives and reproduces in its environment, measured by how many offspring it contributes to the next generation.

All the living organisms in an area together with the nonliving parts of their surroundings, such as water, soil, sunlight, and temperature, interacting as one system.

A nonliving part of an environment, such as temperature, water, or sunlight, that affects which organisms can survive and how many can live there.

A model showing several connected food chains and the many feeding relationships among producers, consumers, and decomposers in an ecosystem.

An organism, such as a plant or alga, that makes its own food using energy from sunlight or from chemical reactions and forms the base of a food chain.

An organism such as a fungus or bacterium that breaks down dead organisms and wastes, releasing nutrients back into the soil and water for other organisms to use.

The largest population of a species that an ecosystem can support over a long period without damaging the resources that the population depends on.

A feeding position in a food chain, such as producer, primary consumer, or secondary consumer, where only a small share of the energy passes to each higher level.

A close, long-term relationship between two different species in which both may benefit, one may benefit and the other be harmed, or one may benefit with no effect on the other.

The variety of living things in an area, measured by the number of species present and by the genetic differences among individuals within those species.