MCAS Biology key terms

The thin outer boundary of a cell that controls what enters and leaves. It is selectively permeable, letting some substances pass while blocking others.

A rigid outer layer found in plant cells, fungi, and many bacteria that supports and protects the cell. It lies outside the cell membrane and is mostly cellulose in plants.

A green organelle in plant cells where photosynthesis takes place. It contains chlorophyll, which captures light energy used to make glucose from carbon dioxide and water.

An organelle that releases usable energy from food through cellular respiration. It produces ATP, the molecule cells use to power most of their work.

The organelle that holds a eukaryotic cell's DNA and directs its activities. It is surrounded by a membrane and contains chromosomes made of DNA and protein.

A small structure that builds proteins by linking amino acids in the order specified by messenger RNA. Ribosomes are found in the cytoplasm and on the rough endoplasmic reticulum.

An organism whose cells lack a membrane-bound nucleus and other membrane-bound organelles. Bacteria are prokaryotes; their DNA sits in the cytoplasm rather than inside a nucleus.

An organism whose cells contain a membrane-bound nucleus and other organelles. Plants, animals, fungi, and protists are eukaryotes.

The net movement of particles from an area of higher concentration to an area of lower concentration, driven by random motion. It requires no energy input from the cell.

The diffusion of water across a selectively permeable membrane from an area of higher water concentration to lower water concentration. It moves water into or out of cells.

The molecule that stores genetic information in the sequence of its bases. It is double-stranded, and its sequence determines the proteins an organism can make.

A segment of DNA that carries the instructions for making a protein or for controlling a trait. Genes are passed from parents to offspring.

The process in which a cell reads the instructions in DNA and builds a protein from amino acids. It involves transcription into mRNA and translation at the ribosome.

A protein that speeds up a chemical reaction in a cell without being used up. Each enzyme acts on specific molecules, and its shape determines its function.

The loss of a protein's shape and function caused by heat, extreme pH, or other harsh conditions. Because enzymes depend on shape, denatured enzymes cannot catalyze their reactions.

The process by which plants, algae, and some bacteria use light energy to make glucose from carbon dioxide and water, releasing oxygen. It stores energy in chemical bonds.

The process by which cells break down glucose to release energy, producing ATP, carbon dioxide, and water. It can occur with oxygen or without it.

A molecule that stores and transfers energy in cells. When its phosphate bond is broken, energy is released to power cell activities.

The division of a cell's nucleus that produces two genetically identical daughter cells. It is used for growth, repair, and replacement of body cells.

The cell division that produces gametes with half the usual number of chromosomes. It creates genetic variation through crossing over and independent assortment.

A structure made of DNA and protein that carries genes. Human body cells normally contain 46 chromosomes, arranged as 23 pairs.

One of the alternative forms of a gene. An organism inherits two alleles for each gene, one from each parent, and these can be dominant or recessive.

A trait that appears when at least one dominant allele is present. A recessive allele is masked unless an organism carries two copies of it.

A trait that appears only when an organism carries two copies of the recessive allele. It is masked when a dominant allele for the same gene is present.

The combination of alleles an organism carries for a particular gene. It can be homozygous, with two identical alleles, or heterozygous, with two different alleles.

The observable traits of an organism, such as eye color or plant height. It results from the organism's genotype interacting with its environment.

A diagram used to predict the possible genotypes of offspring from two parents. It shows all combinations of the parents' alleles in a grid.

A change in the DNA sequence of a gene or chromosome. Mutations can be harmful, helpful, or neutral, and they are a source of new genetic variation.

The process by which organisms with traits better suited to their environment tend to survive and reproduce more, passing those traits to offspring. It drives evolutionary change.

A trait that helps an organism survive and reproduce in its environment. Adaptations arise over generations through natural selection.

The change in the inherited traits of a population over many generations. It is driven by mechanisms such as natural selection, mutation, and gene flow.

A community of organisms together with the nonliving parts of their environment, such as water, soil, and sunlight. Organisms in an ecosystem interact and exchange energy and matter.

An organism that makes its own food, usually through photosynthesis, and forms the base of a food chain. Plants and algae are examples.

An organism that obtains energy by eating other organisms. Herbivores, carnivores, and omnivores are all consumers.

A diagram showing how energy moves through an ecosystem as organisms eat one another. It links several food chains and shows feeding relationships among many species.

The ability of an organism to keep internal conditions, such as temperature and water balance, within a stable range. It helps cells keep working properly.

A process for investigating questions through observation, hypothesis formation, controlled experiments, and analysis of data. Conclusions are revised when new evidence appears.

The part of an experiment that is treated the same as the experimental group but does not receive the tested treatment. It provides a baseline for comparison.

A factor in an experiment that can change. A controlled experiment changes one independent variable while keeping other variables constant.