AQA A-Level Biology Keywords - Cells

Magnification

the number of times bigger the image/drawing is compared to the object/real size

Resolution

the minimum distance needed to differentiate between 2 adjacent objects

Micrometer

1x10-6 m

Nanometer

1x10-9 m

Light Microscope

A type of microscope which has a condenser, objective lens and eyepiece lens and light is passed through the thin specimen an up through the objective and eyepiece lenses to the eye.

Electron microscope

Beams of electrons are used to visualize structures in a vacuum. Electrons have a smaller wavelength than light so electron microscopes have a higher resolution than light microscopes.

Scanning Electron Microscope (SEM)

A type of electron microscope which bounces beams of electrons off the surface of an object to develop a 3D image of the specimen (no need therefore for thin sections).

Transmission electron microscope (TEM)

A type of electron microscope which asses a beam of electrons through a very thin section of specimen (which often has been stained with heavy metals to show up the fine internal structures).

Cell fractionation

The process where cells are broken up and the different organelles they contain are separated out.

Homogenation

The first stage of cell fractionation when cells are broken up by a homogeniser (blender) and organelles are released from the cell.

Ultracentrifugation

The second stage of cell fractionation when the fragments in filtered homogenate are separated in a machine called a centrifuge.

Graticule

A series of lines on a microscope which can be used to calculate the size of objects.

Eukaryote

A cell that has a membrane-bound nucleus and chromosomes. The cell also possesses a variety of other membrane-bound organelles, such as mitochondria and endoplasmic reticulum.

Organelle

A part of a cell.

Nucleus

Organelle which contains the hereditary material (DNA) which codes for she synthesis of proteins in cytoplasm.

Mitochondria

Organelle where energy is released in aerobic respiration

Chloroplast

Organelle that is the site of photosynthesis

Rough endoplasmic reticulum (RER)

Organelle which provides a large surface area for the synthesis of proteins and glycoproteins and where proteins are transported that are synthesised on ribosomes.

Smooth endoplasmic reticulum (SER)

Organelle where lipids and carbohydrates are synthesized, stored and transported.

Golgi

Organelle that contains a stack of membranes that make up flattened sacs (cisternae) where glycoproteins are synthesized, lipids are transported, modified and stores, proteins are packaged and lysosomes are formed.

Lysosome

Organelle formed when the vesicles produced by the Golgi apparatus contain enzymes. They are where unwanted materials & worn-out organelles are digested.

Ribosome

Organelle made of rRNA and protein where protein synthesis occurs.

Cell Wall

Organelle which provides mechanical strength to prevent the cell bursting under the pressure created by the osmotic entry of water, to give mechanical strength. Made of cellulose in plants and chitin in fungi.

Vacuole

Organelle which contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anthocyanins. They support herbaceous plants by making cells turgid, may provide a temporary food store and if they contain pigments they may colour petals to attract pollinating insects.

Tissue

A collection of similar cells that perform a specific function.

Organ

A combination of different tissues that are coordinated to perform a variety of functions.

Organ system

Many organs work together in an organ system to perform a particular function.

Prokaryote

A cell of an organism belonging to the kingdom Prokaryote that is characterized by lacking a nucleus and membrane-bound organelles. E.g. bacteria

Bacteria

A prokaryote.

Plasmid

Small circular loops of DNA which contain genes that bacteria can have.

Flagellum

Part of a bacterial cell which helps the bacteria to move.

Virus

Acellular, non-living particles that are smaller than bacteria. They contain DNA or RNA but can only multiply inside living host cells.

Capsid

A protein coat which encloses the nucleic acid in a virus.

Attachment Protein

The capsid can have these which are essential to allow the virus to identify and attach to a host cell.