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OCR Biology AS Level (Definitions)
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Typed up definition for all of 1st year Biology as level(yr12)
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Chapter 2: Key definitionsCentrioles: Structures found in the cytoplasm made of microtubules that produce the spindle fibres during mitosis.
Chloroplasts: Organelles found in plants and algae that are the site of photosynthesis.
Cilia: Small hair-like structures that project from the surface of cells.
Confocal microscopy: A type of microscopy that uses lasers to scan a specimen point by point to produce an image.
Cytoskeleton: A mesh of protein fibres found in the cytoplasm of eukaryotic cells used for structural support and
intracellular transport.
Differential staining: Using multiple different stains to distinguish different parts of a specimen.
Eukaryotic cell: A type of cell that contains a nucleus along with membrane bound organelles.
Flagella: A whip-like structure found on bacterial cells that is used for cell movement.
Golgi apparatus: An organelle found in eukaryotic cells that is involved in the modification and packaging of proteins.
Light microscope: A type of microscope that uses a series of lenses to magnify the visible light reflecting off a
specimen.
Lysosomes: Membrane-bound vesicles found in the cytoplasm that contain a hydrolytic enzyme called lysozyme.
Magnification: How much bigger an image appears compared to the original object
Mitochondrion: An organelle found in eukaryotic cells that is the site of aerobic respiration.
Nuclear envelope: A double membrane that surrounds the nucleus.
Nucleolus: A structure found inside the nucleus that contains proteins and RNA and is involved in synthesizing new
ribosomes.
Nucleus: An organelle found in eukaryotic cells that stores the genetic information of the cell as chromosomes and is
surrounded by a membrane called the nuclear envelope.
Plasma membrane: A semipermeable lipid bilayer studded with proteins that surrounds the cell and many
organelles.
Prokaryotic cell: A type of cell that does not contain any membrane bound organelles or a nucleus.
Resolution: The ability to distinguish two different points in a specimen.
Ribosomes: Organelles found either free in the cytoplasm or membrane bound that are involved in the synthesis of
proteins.
Rough endoplasmic reticulum (RER): A membrane-bound organelle that is involved in the synthesis and packaging of
proteins.
Scanning electron microscope (SEM): A type of microscope that passes a beam of electrons over the surface of a
specimen to produce an image.
Smooth endoplasmic reticulum (SER): A membrane-bound organelle involved in lipid synthesis.
Transmission electron microscope (TEM): A type of microscope that passes a beam of electrons through a sample to
produce an image.
Chapter 3: Key definitions
Adhesion: A property of water molecules that creates an attraction between them and surfaces that they are in
contact with.
,Amino acid: The monomers containing an amino group (NH2), a carboxyl group (COOH) and a variable R group that
make up proteins.
Amylopectin: A branched polysaccharide made up of alpha glucose monomers joined by α-1,6 glycosidic bonds that
makes up starch along with amylose.
Amylose: An unbranched polysaccharide made up of alpha glucose monomers joined by α-1,4 glycosidic bonds that
makes up starch along with amylopectin. Anions: An ion with a negative charge.
Benedict’s test: A biochemical test used to detect the presence of a reducing sugar in a solution and distinguish
between solutions of different reducing sugar concentrations.
Biuret test: A biochemical test that produces a purple colour when it is added to a solution containing protein.
Cations: An ion with a positive charge.
Cellulose: A linear polysaccharide that is the main component of the cell wall in plants and is made up of many beta
glucose molecules joined by β-1,4 glycosidic bonds.
Chromatography: A technique used to separate different molecules in a solution by their different properties.
Cohesion: A property of water molecules that creates an attraction between them which causes them to stick
together.
Collagen: A type of fibrous protein that provides strength to many different cell types and makes up connective
tissues.
Condensation reaction: A type of reaction that joins two molecules together with the formation of a chemical bond
involving the elimination of a molecule of water.
Conjugated protein: A protein with a prosthetic group bound to it.
Elastin: A type of fibrous protein that allows tissues and structures like blood vessels to stretch and return to their
original shape.
Fibrous protein: A class of long chain proteins that are generally insoluble in water and typically have structural roles.
Globular protein: A class of spherical shaped proteins that are generally water soluble and typically have metabolic
roles.
Glucose: A hexose monosaccharide that is the main respiratory substrate in eukaryotes.
Glycogen: A highly branched polysaccharide that is used as the main energy storage molecule in animals and is made
up of alpha glucose monomers joined by α-1,4 glycosidic bonds.
Haemoglobin: A type of conjugated globular protein used to transport oxygen that is made up of four polypeptide
chains each containing a haem prosthetic group.
Hexose monosaccharide: A simple sugar that contains 6 carbon atoms.
Hydrogen bond: A type of weak bond formed between an electropositive hydrogen and an electronegative atom like
oxygen or nitrogen.
Hydrolysis: Breaking a chemical bond between two molecules involving the use of a water molecule.
Insulin: A globular protein hormone that is made in the pancreas in response to detection of high glucose levels in
the blood.
Iodine test: A biochemical test that produces a blue/black colour when it is added to a solution containing starch.
Keratin: A type of fibrous protein that provides strength to hair and nails.
Lactose: A disaccharide made of a molecule glucose and galactose joined by a glycosidic bond.
, Lipid emulsion test: A biochemical test that produces a cloudy emulsion when performed on lipids.
Maltose: A disaccharide made of two molecules of glucose joined by a glycosidic bond.
Monomer: An individual unit that can be bonded to other identical monomers to make a polymer.
Monomers: The smaller units from which larger molecules are made.
Pentose monosaccharide: A simple sugar that contains 5 carbon atoms.
Phospholipid: A type of amphipathic lipid made from a molecule of glycerol bonded to two fatty acid molecules and
a phosphate group.
Polymer: A molecule made from many repeating monomers joined together.
Polymers: Molecules made from a large number of monomers joined together.
Primary structure: The individual sequence of amino acids in a protein.
Quaternary structure: A structure only applicable to proteins with multiple polypeptide chains that describes the
interactions of the different chains.
Ribose: A pentose monosaccharide which composes the backbone of RNA.
Saturated fatty acid: A type of fatty acid molecule containing only single bonds between the carbon atoms.
Secondary structure: The local interactions of the amino acids in the polypeptide chain.
Solvent: A liquid that solutes can dissolve in to form a solution.
Starch: A polysaccharide used for energy storage in plants that is made up of alpha glucose joined together in the
forms of amylose and amylopectin.
Sucrose: A disaccharide made of a molecule glucose and fructose joined by a glycosidic bond.
Tertiary structure: The way that the whole protein folds to make a three-dimensional structure.
Triglyceride: A type of lipid formed from a molecule of glycerol joined by ester bonds to three fatty acid molecules.
Unsaturated fatty acid: A type of fatty acid molecule containing at least one double bond in the carbon chain.
Adenosine triphosphate (ATP): A nucleotide consisting of a molecule of ribose joined to the nitrogenous base
adenine and three phosphate groups.
Degenerate (genetic code): A term used to describe the fact that some amino acids can be coded for by multiple
different codons.
Deoxyribonucleic acid (DNA): A double stranded polynucleotide that contains the genetic material of an organism
and is made up of deoxyribonucleotide monomers joined together by phosphodiester bonds.
DNA nucleotide: The monomer that makes up DNA and consists of deoxyribose, a nitrogenous base and a phosphate
group.
DNA polymerase: An enzyme that catalyses the formation of phosphodiester bonds between nucleotides during the
synthesis of a new DNA strand.
RNA polymerase: An enzyme that catalyses the formation of phosphodiester bonds between nucleotides during the
synthesis of a new RNA strand.
Helicase: An enzyme that catalyses the unwinding and unzipping of DNA in many processes like replication and
transcription.
Messenger RNA (mRNA): A type of RNA that carries genetic information from the DNA in the nucleus to the
ribosomes for translation.
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