Definitions Flashcards
Magnification
The degree to which the size of an image is larger than the object itself. Numerically, it is the image size divided by the actual size measured in the same units.
Resolution
The degree to which it is possible to distinguish between two objects that are very close together. The higher the resolution, the greater the detail that can be seen.
Staining
Any process that helps to reveal or distinguish different features. In light microscopy, stains may be coloured or fluorescent dyes. In electron microscopy, they are heavy metal salts.
Cytoskeleton
Network of protein fibres found within cells that gives structure and shape to the cell, and also moves organelles around inside cells.
Organelle
A particular structure of a cell that has a specialised function. Some organelles are membrane-bound, others are not. All perform a particular role in the life processes of the cell.
Division of labour
Any system where different parts perform specialised functions, each contributing to the functioning of the whole.
Phospholipid bilayer
The basic structural component of plasma membranes (cell surface membranes). It consists of two layers of phospholipid molecules. Proteins are embedded in this layer.
Fluid mosaic model
The model of cell membrane structure. The lipid molecules give fluidity and proteins in the membrane give it a mosaic (patchwork) appearance. The molecules can move about.
Cell signalling
Cells communicate with one another by signals. Many molecules act as signals - some signal during processes taking place inside cells; others signal from one cell to another. Cytokines are an example of cell signals.
Diffusion
The passive net movement of molecules from a region of higher concentration to a region of lower concentration down a potential gradient.
Active transport
The movement of molecules or ions across membranes, which uses ATP to drive protein ‘pumps’ within the membrane.
Hypertonic
A solution with a lower water potential (higher solute concentration) compared to the cell.
Hypotonic
A solution with a higher water potential (lower solute concentration) compared to the cell.
Isotonic
A solution with the same water potential (same solute concentration) compared to the cell.
Osmosis
Passive net movement of water across a partially permeable membrane from an area of higher water potential to an area of lower water potential, down the water potential gradient.
Cell cycle
The events that take place as one parent cell divides to produce 2 daughter cells which then grow to full size. For single-celled organisms, the cell cycle is the life cycle, and each daughter cell is an offspring.
Mitosis
The process of nuclear division where 2 genetically identical nuclei are formed from 1 parent cell nucleus, producing 2 daughter cells that are genetically identical.
Meiosis
The process of nuclear division where 4 genetically different nuclei are formed from 1 parent cell nucleus, producing 4 daughter cells that are genetically different.
Homologous pair
Chromosomes that have different versions of the same genes at the same loci (alleles). All chromosomes in a diploid organism come in pairs and those produced by sexual reproduction have one from the father and one from the mother, creating variation.
Clones
Cells and organisms that are genetically identical to the parent.
Differentiation
The changes that occur in cells of a multicellular organism so that each different type of cell becomes specialised to perform a specific function.
Stem cells
Undifferentiated cells that are capable of becoming differentiated to a number of possible cell types.
Tissue
A group of similar cells that perform a particular function.
Organ
A collection of tissues that work together to perform a specific overall function or set of functions within a multicellular organism.
