OCR A-level Biology: Module 2

Light microscope

An instrument that uses visible light and glass lenses to enable the user to objects magnified many times

Compound light microscope

A light microscope which uses two lenses to magnify an object; the objective lens, which is placed near to the specimen and an eyepiece lens, through which the specimen is viewed

Differential staining

Using specific stains to distinguish different types of cell

Counterstain

Application of second stain with a contrasting colour to sample for microscopy

Electron microscopy

Microscopy using a microscope that employs a beam of electrons to illuminate the specimen. As electrons have a much smaller wavelength than light they produce images with higher resolutions than light microscopes

Ultrastructure

The ultrastructure of a cell is those features which can be seen by using an electron microscope

Artefacts

Objects or structures seen through a microscope that have been created during the processing of the specimen

Transmission electron microscope

An electron microscope in which a beam of electrons is transmitted through a specimen and focused to produce an image

Scanning electron microscope

An electron microscope in which a beam of electrons is sent across the surface of a specimen and the reflected electrons are focused to produce a three-dimensional image of the specimen surface

Laser scanning confocal microscope

A microscope that employs a beam of fluorescence and a pin-hole aperture to produce an image with a very high resolution

Prokaryotic cell

Cells with no membrane-bound nucleus or organelles

Eukaryotic cell

Cells with a nucleus and other membrane-bound organelles

Magnification

How many times larger the image is than the actual size of the object being viewed

Resolution

The ability to see individual objects as separate entities

Cytoplasm

Internal fluid of cells, composed of cytosol (water, salts, organic molecules) , organelles and cytoskeleton

Metabolism

All of the chemical reactions that occur within an organism

Organelles

Membrane-bound compartments with varying functions inside eukaryotic cells

Nucleus

A part of the cell containing DNA and RNA and responsible for growth and reproduction

Histones

Proteins that form a complex with DNA called chromatin

Chromatin

Uncondensed DNA in a complex with histones

Chromosomes

Structures of condensed and coiled DNA in the form of chromatin. Chromosomes become visible under the light microscope when cells are preparing to divide

Mitochondria

An organelle found in large numbers in most cells, in which the biochemical processes of respiration and energy production occur

Cristae

Highly folded structures within the mitochondria inner membrane

Matrix

The fluid interior in the inner membrane of a mitochondria

Mitochondrial DNA

DNA present within the matrix of the mitochondria

Vesicles

Small membrane sacs that specialize in moving products into, out of, and within a cell

Lyosomes

Specialised vesicles containing hydrolytic enzymes for the breakdown of waste materials within a cell

Cytoskeleton

A network of fibres in the cytoplasm of a eukaryotic cell

Microfilament

Contractile protein actin fibres responsible for cell movement and cell contraction when the cytoplasm of a single eukaryotic cell divides to two daughter cells

Microtubules

Tubes used to from a scaffold like structure to determine the shape of the cell. Also act as tracks for the movement of organelles and vesicles around the cell. Makes up spindle fibres

Intermediate fibres

Fibres that give mechanical strength to cells and maintain their integrity

Centrioles

Component of the cytoskeleton of most eukaryotic cells, composed of microtubules

Secretion

A process by which substances are produced and discharged from a cell, gland, or organ for a particular function in the organism or for excretion.

Endoplasmic reticulum

A network of membranes enclosing flattened sacs called cisterne

Rough endoplasmic reticulum

Ribosomes are bound to the surface and is responsible for the synthesis and transport of proteins

Smooth endoplasmic reticulum

Responsible for lipid and carbohydrate synthesis and storage

Ribosomes

Constructed of RNA molecules and are the site of protein synthesis

Golgi apparatus

Organelle in most eukaryotic cells formed from an interconnected network of flattened, membrane-enclosed sacs, or cisternae. Play a role in modifying and packaging proteins into vesicles.

Tonoplast

Membrane forming a vacuole in a plant cell

Cell wall

A strong but flexible layer that surrounds some cell-types

Vacuole

Membranous sacs used to transport materials in the cell

Chloroplast

Organelles that are responsible for photosynthesis in plant cells. Contain chlorophyll pigments, which are the site of the light reactions of photosynthesis

Stroma

The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water

Granum

A structure inside chloroplasts composed of a stack of several thylakoids. Contains chlorophyll pigments, where light reactions occur during photosynthesis

Endosymbiosis

The widely-accepted theoretical process by which eukaryotic cells evolved from prokaryotic cells

Elements

A molecule composed of one kind of atom; cannot be broken into simpler units by chemical reactions

Ion

A positively or negatively charged atom or group of atoms where the number of electrons is different from the number of protons

Polymers

Long-chain molecules composed of bonded multiple individual molecules (monomers) in a repeating pattern

Monomers

Individual molecules that make up a polymer

Covalent bonding

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Ionic bonding

The electrostatic attraction between positive and negative ions

Polar molecules

A molecule with an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule

Capillary action

A proccess powered by adhesion that causes water molecules to move upward through a narrow tube such as the stem of a plant

Carbohydrates

Organic polymers composed of the elements carbon, hydrogen and oxygen in the ratio Cx(H2O)y

Monosaccharide

A single sugar molecule

Polysaccharide

A polymer made up of many sugar monomers

Glucose

A monosaccharide with the chemical formula C6H12O6. One of the main products in photosynthesis in plants

Hexose Monosaccharide

A monosaccharide composed of six carbons

Glycosidic bond

A covalent bond between two monosaccharides

Condensation reaction

A reaction between two molecules resulting in the formation of a larger molecule and the release of a water molecule

Maltose

Two glucose molecules linked by a 1-4 glycosidic bond

Disaccharide

A molecule comprising two monosaccharides, joined together by a glycosidic bond

Sucrose

A disaccharide made up of a fructose and glucose monosaccharides

Lactose

A disaccharide made up of a galactose and glucose monosaccharide

Pentose monosaccharide

A monosaccharide composed of five carbons

Ribose

The pentose monosaccharide present in RNA molecules

Starch

A polysaccharide formed from alpha glucose molecules either joined to form amylose or amylopectin

Beta pleated sheet

Sheet-like secondary structure of proteins

Glycogen

A branched polysaccharide formed from alpha glucose molecules. A chemical energy store in animal cells

Hydrolysis reaction

The breakdown of a molecule into two smaller molecules requiring the addition of a water molecule

Cellulose

A polysaccharide formed from beta glucose molecules where alternate beta glucose molecules are turned upside down. Unable to coil or branch but makes hydrogen bonds with other cellulose molecules to produce strong and insoluble fibres.

Reducing sugars

Saccharides that donate electrons resulting in the reduction (gain of electrons) of another molecule

Benedict's reagent

An alkaline solution of copper(II) sulphate used in the chemical tests for reducing sugars and non-reducing sugars. A brick red precipitate indicates a positive result.

Iodine test

A chemical test for the presence of starch using a potassium iodide solution. A colour change to purple/black indicates a positive result

Colorimetry

The use of a spectrophotometer to determine the absorption of various wavelengths of visible light by a given solution

Lipids

Non-polar macromolecules containing the elements carbon, hydrogen, and oxygen. Commonly known as fats and oils

Macromolecules

Large complex molecules with a large molecular weight

Triglyceride

A lipid composed of one glycerol molecule and three fatty acids

Tertiary structure

Further folding of the secondary structure of proteins involving interactions between R-groups

Glycerol

Alcohol found in triglycerides

Fatty acids

Long chain carboxylic acids used in the formation of triglycerides

Saturated

Containing the greatest possible number of hydrogen atoms, without carbon-carbon double or triple bonds

Unsaturated

Having carbon-carbon double or triple bonds and therefore not containing the greatest possible number of hydrogen atoms

Phospholipids

Modified triglycerides, where one fatty acid has been replaced with a phosphate group

Hydrophobic

The physical property of a molecule that is repelled by water

Hydrophilic

The physical property of a molecule that is attracted to water

Surfactants

Compounds that lower the surface tension of water

Sterols

Type of lipid; Carbons arranged in rings; Cholesterol is most well-know

Emulsion test

Laboratory test for lipids using ethanol; white emulsion indicates the presence of a lipid

Peptides

Chains of two or more amini acid molecules

Proteins

One or more polypeptides arranged as a complex macromolecule

Peptide bond

Bond formed between two amino acids

Polypeptide

Chains of three or more amino acids

Prosthetic group

Non protein component of a conjugated protein

Protease

Enzymes that catalyse the breakdown of proteins and peptides into amino acids

Plasma membrane

All the membranes of cells, which have the same basic structure described by the fluid mosaic model

Phospholipid bilayer

Arrangement of phospholipids found in cell membranes; the hydrophilic phosphate heads form both the inner and outer surface sandwiching the fatty acid tails to form a hydrophobic core

Receptors

Extrinsic glycoproteins that bind chemical signals, triggering a response by the cell

Passive transport

Transport that is a passive process (doesn't require