A collection of organs whose primary function is to take in oxygen and expel carbon dioxide; the organs of this system include the lungs, the throat, and the passageways that lead to the lungs.

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, 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 smallest bodies that are found in the cytoplasm of a cell and that are specialized to perform a specific function

An organism that consists of a single cell

A molecule that is made up of amino acids and that is needed to build and repair body structures and to regulate processes in the body.

In biology, the smallest unit that can perform all life processes.

The ability to store and recall past experience.

A haploid reproductive cell that unites with another haploid reproductive cell to form a zygote

In eukaryotic cells, the organelle that is the site of cellular respiration, which releases energy for use by the cell

In a eukaryotic cell, a membrane-bound organelle that contains the cell's DNA and has a role in processes such as growth, metabolism, and reproduction

A new organism that results from sexual or asexual reproduction.

A plant structure that provides support and transports nutrients.