Cells

Nucleolus

Small, dark structure within the nucleus of a cell; thought to make r-RNA to construct the ribosomes.

Vacuole

A cell storage body that increases in size with age; included within, but not a part of the cytoplasm; often stores water and poisonous by-products of cell activities.

Eukaryote

A cell that has a membrane-bound nucleus and/or organelles as its major characteristic.

Prokaryote

A cell whose nucleus is not bound by a membrane.

Golgi body

A flattened sac within the cytoplasm of the cell; an extension of the endoplasmic reticulum; involved in producing and packaging secretions.

Chlorophyll

A green pigment in plants that serves to trap the Sun's energy for photosynthesis.

Tissue

A group of cells working together to perform a particular task.

System

A group of organs working together for a common purpose.

Organ

A group of tissues working together as a unit for a particular purpose in the body.

Membrane

A protein and fat structure serving as a covering and enclosure for cells.

Enzyme

A protein molecule that is specialized to speed up a specific chemical reaction in biological systems.

Centriole

A rod-shaped structure on the side of an animal cell nucleus; thought to play a role in the formation of the spindle during cell division.

Endoplasmic reticulum

A series of tubes in the cytoplasm of a cell that are believed to be used as channels for transporting molecules within the cell.

Organelle

A small structure within the cell that serves specialized functions.

Mitochondria

Structures within the cell cytoplasm responsible for the production of energy and the storage of energy in ATP.

Specialization

Limiting a cell to a specific function.

Lysosome

Packets within the cell cytoplasm that contain digestive enzymes.

Peroxisome

Packets within the cell cytoplasm that contain powerful enzymes.

Cytoskeleton

Protein fibers that provide support and shape for the cell.

Vesicle

Sacs containing protein produced by the endoplasmic reticulum.

Resolving power

The ability to clearly distinguish between two objects.

Cell

The basic building block of all forms of life.

Osmosis

The diffusion of water across a semipermeable membrane.

Spindle

The fibers that direct the even distribution of chromosomes to each daughter cell during nuclear division.

Cell theory

The idea of Schleiden and Schwann that the basic unit of life is the cell and that all living organisms are composed of cells.

Cytoplasm

The living substance of a cell, excluding the nucleus.

Protoplasm

The organic substance making up the cells of all living things.

Cytokinesis

The part of the cell division that causes the separation of the cytoplasm.

Nucleus (pl. nuclei)

The protoplasmic substance separate from the cytoplasm; the cell headquarters or information center; location of DNA and RNA; contains chromosomes and the nucleolus.

Cell wall

The rigid wall that surrounds the cell membrane of plant cells.

Plasma membrane

The semipermeable membrane surrounding human and animal cells; made of phospholipids and proteins.

Chloroplast

The tiny body that contains chlorophyll; part of the cell in which photosynthesis takes place.

Choloroplast

The tiny body that contains chlorophyll; part of the cell in which photosynthesis takes place.

Organismal theory

Theory that states that the basic unit of life is the organism itself, which may be divided into cells for efficiency.

Plastid

Tiny sacs in the cell that may either contain starch or oils as stored food or a plant pigment.

Ribosome

Tiny, dot-like bodies in the cytoplasm or on the endoplasmic reticulum; important in protein synthesis.

Flagella

Whip-like cell extensions that give the cell motility.