The movement of chemical substances, usually across the cell membrane, against a concentration gradient; requires cells to use energy.
single-celled organisms that lack a nucleus; prokaryotes
A change in the characteristics of a population from one generation to the next; the gradual development of organisms from other organisms since the beginnings of life.
The smallest unit that can perform all life processes; cells are covered by a membrane and have a nucleus and cytoplasm.
A phospholipid layer that covers a cell's surface and acts as a barrier between the inside of a cell and the cell's environment.
In a eukaryotic cell, biology, a membrane-bound organelle that contains the cell's DNA and that has a role in processes such as growth, metabolism, and reproduction.
One of the small bodies that are found in the cytoplasm of a cell and that are specialized to perform a specific function.
A rigid structure that surrounds the cell membrane and provides support to the cell.
An organelle found in plant and algae cells where photosynthesis occurs.
In a eukaryotic cell, one of the structures in the nucleus that are made up of DNA and protein; in a prokaryotic cell, the main ring of DNA.
The region of the cell within the membrane that includes the fluid, the cytoskeleton, and all of the organelles except the nucleus.
The movement of particles from regions of higher density to regions of lower density.
Deoxyribonucleic acid, the material that contains the information that determines inherited characteristics.
An organism made up of cells that have a nucleus enclosed by a membrane, multiple chromosomes, and a mitotic cycle; eukaryotes include animals, plants, and fungi but not bacteria or cyanobacteria.
Cell organelle that helps make and package materials to be transported out of the cell.
In eukaryotic cells, the cell organelle that is surrounded by two membranes and that is the site of cellular respiration, which produces ATP.
An organism that consists of a single cell that does not have a nucleus or cell organelles;an example is a bacterium.
An organic compound that is made up of one or more chains of amino acids and that is a principal component of all cells.
A cell organelle composed of RNA and protein; the site of protein synthesis.
cell organelle that stores materials such as water, salts, proteins, and carbohydrates
A nonliving, infectious particle composed of a nucleic acid and a protein coat; it can invade and destroy a cell.