Biology A-Level

abiotic factors

non-living conditions in a habitat

activation energy

the energy required to initiate a reaction.

active site

area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind a substrate with specificity.

active transport

movement of particles across a plasma membrane against a concentration gradient. Energy is required. (ATP)

adenosine diphosphate (ADP)

a nucleotide composed of a nitrogenous base (adenine), a

pentose sugar and two phosphate groups. Formed by the hydrolysis of ATP, releasing a phosphate ion and energy.

adenosine triphosphate (ATP)

a nucleotide composed of a nitrogenous base (adenine), a

pentose sugar and three phosphate groups. The universal energy currency for cells.

agglutinins

chemicals (antibodies) that cause pathogens to clump together so they are easier for phagocytes to engulf and digest.(caused by cross linking by antibodies that have a number of binding sites)

alleles

different versions of the same gene.

amino acids

monomer used to build polypeptides and thus proteins

anabolism (anabolic)

reactions of metabolism that construct molecules from smaller units. These reactions require energy from the hydrolysis of ATP.

analogous structures

structures that have adapted to perform the same function but have a different origin.

anaphase

third stage of mitosis when chromatids are separated to opposite poles of the cell.

antibiotic-resistant bacteria

bacteria that undergo mutation to become resistant to an antibiotic and then survive to increase in number.

antibiotics

a chemical or compound that kills or inhibits the growth of bacteria

antibodies

Y-shaped glycoproteins made by B cells of the immune system in response to the

presence of an antigen.

antigen

identifying chemical on the surface of a cell that triggers an immune response

antigen−antibody complex

the complex formed when an antibody binds to an antigen.

antigen-presenting cell (APC)

a cell that displays foreign antigens complexed with major histocompatibility complexes on their surface plasma membranes, so it can be recognised by other cells

antisense strand 'lagging strand'

the strand of DNA that runs 3' to 5' and is complementary to the sense strand. It acts as a template strand during transcription.

anti-toxins

chemicals (antibodies) that bind to toxins produced by pathogens so they no longer have an effect.

apoplast

the cell walls and intercellular spaces of plant cells.

apoplast route

movement of substances through the cell walls and cell spaces by diffusion and into cytoplasm by active transport.

arrhythmia

an abnormal rhythm of the heart.

artefacts

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

artificial active immunity

immunity which results from exposure to a safe form of a pathogen, for example, by vaccination.

artificial passive immunity

immunity which results from the administration of antibodies from

another animal against a dangerous pathogen.

asexual reproduction

the production of genetically identical offspring from a single parent.

assimilates

the products of photosynthesis that are transported around a plant, e.g., sucrose

atrial fibrillation

an abnormal rhythm of the heart when the atria beat very fast and incompletely.

atrio-ventricular node (AVN)

stimulates the ventricles to contract after imposing a slight delay to ensure atrial contraction is complete.

autoimmune disease

a condition or illness resulting from an autoimmune response.

autoimmune response

response when the immune system acts against its own cells and destroys healthy tissue in the body.

autotrophic

organisms that acquire nutrients by photosynthesis.

B effector cells

B lymphocytes that divide to form plasma cell clones

B lymphocytes (B cells)

lymphocytes which mature in the bone marrow and that are involved in the production of antibodies

B memory cells

B lymphocytes that live a long time and provide immunological memory of the

antibody needed against a specific antigen.

belt transect

two parallel lines are marked along the ground and samples are taken of the area

at specified points.

Benedict's reagent

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

beta pleated sheet

sheet-like secondary structure of proteins

binomial nomenclature

the scientific naming of a species with a Latin name made of two parts − the first indicating the genus and the second the species.

biodiversity

the variety of living organisms present in an area

biuret test

the chemical test for proteins; peptide bonds form violet coloured complexes with

copper ions in alkaline solutions.

Bohr effect

the effect of carbon dioxide concentration on the uptake and release of oxygen by

haemoglobin

bradycardia

a slow heart rhythm of below 60 beats per minute

breathing rate

the number of breaths (inhalation and exhalation) taken per minute.

bulk transport

a form of active transport where large molecules or whole bacterial cells are

moved into or out of a cell by endocytosis or exocytosis

bundle of his

conducting tissue composed of purkyne fibres that passes through the septum of

the heart

alpha-glucose

glucose in which the hydrogen atom on carbon no.1 projects above the plane of the ring

ab initio protein modelling

a model is built based on the physical and electrical properties of the atoms in each amino acid in the sequence

accuracy

how close a measured or calculated value is to the true value

active immunity

where the immune system is activated and manufactures its own antibodies

adaption

a characteristic that enhances survival in the habitat

adhesion

the attraction between water molecules and the walls of the xylem vessels

affinity

a strong attraction

alveoli

tiny folds of the lung epithelium to increase the surface area

amphiphilic

attracted to both water and fat - containing hydrophobic and hydrophilic parts

amylopectin molecule

a molecule of polysaccharide with glycosidic bonds between carbon 1 and 4, and branches formed by glycosidic bonds between 1 and 6. It is a constituent of starch

amylose molecule

a molecule of polysaccharide with long straight chains of between 100 and 1000 alpha glucose molecules. It is a constituent of starch. Like maltose, it has glycosidic bonds between carbon 1 and 4

anatomical adaptations

structural features

anatomy

a branch of science that concerns the studying of the structure of living organisms

angina pectoris

a condition marked by severe pain in the chest, resulting from an inadequate blood supply, and therefore a lack of oxygen to the heart muscle that causes the coronary arteries to spasm

anion

a negatively charged ion

anomaly

result that does not fit the expected trend nor pattern

aorta

the main artery of the body in mammals

apoptosis

the death of cells which happens as a normal part of an organism's growth and development

archaea

prokaryotic microorganisms of similar size to bacteria but have some differences of metabolism

arteries

vessels that carry blood away from the heart

arterioles

small blood vessels that distribute the blood from an artery to the capillaries

artificial classification

a classification based on just one or a few characteristics

artificial immunity

immunity that is achieved as a result of medical intervention

artificial insemination

the medical procedure of injecting semen into the uterus of a female of the same species

asymptomatic

having no symptoms

atria

thin walled chambers of the heart that receive the blood from the veins and then pass it to the ventricles

atrio-ventricular valves

valves between the atria and the ventricles, which ensure that the blood flows in the correct direction

callose

a polysaccharide containing β 1-3 linkages and β 1-6 linkages between the glucose monomers that is important in the plant response to infection.

carbaminohaemoglobin

the compound formed when carbon dioxide combines with haemoglobin.

carbohydrates

organic polymers composed of the elements carbon, hydrogen and oxygen in the ratio Cx(H2O)y. Also known as saccharides or sugars.

carbonic anhydrase

enzyme which catalyses the reversible reaction between carbon dioxide and water to form carbonic acid.

cardiac cycle

the events of a single heartbeat, composed of diastole and systole.

carrier proteins

membrane proteins that play a part in the transport of substances through a membrane.

cartilage

strong, flexible connective tissue found in many areas of the bodies of humans and other animals

catabolism (catabolic)

reactions of metabolism that break molecules down into smaller units. These reactions release energy.

catalase

an enzyme that catalyses the breakdown of hydrogen peroxide.

cell cycle

the highly ordered sequence of events that takes place in a cell, resulting in division of

the nucleus and the formation of two genetically identical daughter cells

cell signalling

a complex system of intercellular communication.

cellulose

a polysaccharide formed from beta glucose molecules where alternate beta glucose molecules are turned upside down. It is unable to coil or form branches but makes hydrogen bonds with other cellulose molecules to produce strong and insoluble fibres. Major component of plant cell walls.

cell wall

a strong but flexible layer that surrounds some cell-types.

centrioles

component of the cytoskeleton of most eukaryotic cells, composed of microtubules.

centromere

region at which two chromatids are held together

channel proteins

membrane proteins that provide a hydrophilic channel through a membrane.

checkpoints

control mechanisms of the cell cycle.

chiasmata

sections of DNA, which became entangled during crossing over, break and rejoin

during anaphase 1 of meiosis sometimes resulting in an exchange of DNA between bivalent chromosomes, forming recombinant chromatids and providing genetic variation.

chloride shift

the movement of chloride ions into the red blood cells as hydrogen ions move out

to maintain the electrochemical equilibrium.

chloroplasts

organelles that are responsible for photosynthesis in plant cells. Contain

chlorophyll pigments, which are the site of the light reactions of photosynthesis

chromatids

two identical copies of DNA (a chromosome) held together at a centromere.

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.

circulatory system

the transport system of an animal.

clonal expansion

the mass proliferation of antibody-producing cells by clonal selection.

clonal selection

the theory that exposure to a specific antigen selectively stimulates the

proliferation of the cell with the appropriate antibody to form numerous clones of these specific antibody-forming cells (clonal expansion).