Chapter 4

Cell Wall

A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists; protects the cell and helpsl maintain its shape.

Ribosomes

A cell structure consisting of RNA and protein organized into two subunits and functioning as the site of protein synthesis in the cytoplasm. The ribosomal subunits are constructed in the nucleolus.

Lysosome

A digestive organelle in eukaryotic cells; contains hydrolytic enzymes that digest the cell's food and wastes.

Nuclear Envelope

A double membrane, perforated with pores, that encloses the nucleus and separates it from the rest of the eukaryotic cell.

Vacuole

A membrane-enclosed sac that is part of the endomembrane system of a eukaryotic cell, having diverse functions.

Organelles

A membrane-enclosed structure with a specialized function within a cell.

Transmission Electron Microscope (TEM)

A microscope that uses an electron beam to study the internal structure of thinly sectioned specimens.

Scanning Electron Microscope (SEM)

A microscope that uses an electron beam to study the surface architecture of a cell or other specimen.

Rough ER (Endoplasmic Reticulum)

A network of interconnected membranous sacs in a eukaryotic cell's cytoplasm. The membranes of this are studded with ribosomes that make membrane proteins and secretory proteins.

Smooth ER (Endoplasmic Reticulum)

A network of interconnected membranous tubules in a eukaryotic cell's cytoplasm, This lacks ribosomes.

Endomembrane System

A network of membranes inside and around a eukaryotic cell related either through direct physical contact or by the transfer of membrane vesicles.

Cytoskeleton

A network of protein fibers in the cytoplasm of a eukaryotic cell; includes microfilaments, intermediate filaments, and microtubules.

Vesicles

A sac made of membrane in the cytoplasm of a eukaryotic cell.

Cilia

A short cellular appendage specialized for locomotion formed from a core of nine outer doublet microtubules and two single microtubules covered by the cell's plasma membrane.

Nucleolus

A structure within the nucleus of a eukaryotic cell where ribosomal RNA is made from the cytoplasm to make ribosomal subunits.

Chromosomes

A threadlike, gene-carrying structure found in the nucleus of a eukaryotic cell and is most visible during mitosis and meiosis; also, the main gene-carrying structure of a prokaryotic cell. These consist of chromatin, a combination of DNA and protein.

Transport Vesicle

A tiny membranou scas in a cell's cytoplasm carrying molecules produced by the cell. This buds from the endoplasmic reticulum or Golgi apparatus and eventually fuses with another membranous organelle or the plasma membrane, releasing its contents.

Prokaryotic Cells

A type of cell lacking a membrane-enclosed nucleus and other membrane-enclosed organelles; found only in the domains Bacteria and Archaea.

Eukaryotic Cells

A type of cell that has a membrane-enclosed nucleus and other membrane-enclosed organelles. All other organisms except bacteria and archaea are composed of eukaryotic cells.

Endoplasmic Reticulum (ER)

An extensive membranous network in a eukaryotic cell, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.

Electron Microscope (EM)

An instrument that focuses an electron beam through, or onto the surface of a specimen. This instrument achieves a hunredfold greater resolution than a light microscope.

Intermediate Filaments

An intermediate-sized protein fiber that is one of the three main kinds of fibers making up the cytoskeleton of eukaryotic cells. These are ropelike, made of fibrous proteins.

Plasmodesmata

An open channel in a plant cell wall through which strands of cytoplasm connect from adjacent cells.

Light Microscope

An optical instrument with lenses that refract (bend) light to magnify images and project them into a viewers eye or onto a photographic film.

Peroxisome

An organelle containing enzymes that transfer hyrdogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.

Chloroplast

An organelle found in plants and photosynthetic protists that absorb sunlight and uses it to drive the synthesis of organic molecules (sugars) from carbon dioxide and water.

Mitochondria

An organelle in eukaryotic cells where cellular respiration occur. Enclosed by two concentric membranes, it is where most of the cell's ATP is made.

Golgi Apparatus

An organelle in eykaryotic cells consisting of stacks of membranous sacs that modify, store, and ship products of the endoplasmic reticulum.

Cytoplasm

Everything inside a cell between the plasma membrane and the nucleus; consists of a semifluid medium and organelles.

Chromatin

The complex of DNA and proteins that constitutes eukaryotic chromosomes; often used to refer to the diffuse, very extended form taken by chromosomes when a cell is not dividing.

Nucleus

The genetic control center of a eukaryotic cell.

Plasma Membrane

The membrane that sets a cell off from its surroundings and acts as a selective barrier to the passage of ions and molecules into and out of the cell; consists of a phospholipid bilayer in which are embedded molecules of protein and cholesterol.

Microtubules

The thickest of the three main kinds of fibers making up the cytoskeleton of a eukaryotic cell; a straight, hollow tube made up of globular proteins called tubulins. This forms the basis of the structure and movement of cillia and flagella.

Microfilaments

The thinnest of the three main kinds of protein fibers making up the cytoskeleton of a eukaryotic cell; a solid, helical rod composed of the globular protein actin.