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Biology A-level > Definitions > Flashcards

Definitions Flashcards

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1
Q

activation energy

A

the energy that must be provided to make a reaction take place; enzymes reduce the activation energy required for a substrate to change into a product

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2
Q

active site

A

an area on an enzyme molecule where the substrate can bind

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3
Q

active transport

A

the movement of molecules or ions through transport proteins across a cell membrane, against their concentration gradient, using energy from ATP

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4
Q

allele

A

a particular variety of a gene

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5
Q

amylopectin

A

a polymer of alpha-glucose monomers linked by both 1,4 and 1,6 linkages, forming a branched chain; amylopectin is a constituent of starch

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6
Q

amylose

A

a polymer of alpha glucose monomers linked by 1,4 linkages, forming a curving chain; amylose is a constituent of starch

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7
Q

anticodon

A

sequence of three unpaired bases on a tRNA molecule that binds with a codon on mRNA

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8
Q

antigen

A

a substance that is foreign to the body and stimulates an immune response

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9
Q

arteriole

A

a small blood vessel that carries blood from arteries to capillaries; arterioles determine how much vlood flows through capillaries

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10
Q

artery

A

a blood vessel that carries blood AWAY from the heart; it has a relatively thick wall and contains large amounts of elastic fibres

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11
Q

atrioventricular node

A

a patch of tissue in the septum of the heart, through which the wave of electrical excitation is passed from the atria to the Purkyne tissue

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12
Q

autosomes

A

all the chromosomes except the X and Y chromosomes

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13
Q

Bohr effect

A

the decrease in affinity of haemoglobin for oxygen that occurs when carbon dioxide is present

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14
Q

capillary

A

the smallest type of blood vessel, whose function is to facilitate exchange of substances between the blood and the tissues

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15
Q

cardiac cycle

A

the sequence of events taking place during one heart beat

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16
Q

carrier

A

someone who is infected with a pathogen but does not show any symptoms of the disease

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17
Q

carrier protein

A

a type of membrane protein which changes shape to allow the passage into or out of the cell of specific ions or molecules by facilitated diffusion or active transport

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18
Q

channel protein

A

a membrane protein of fixed shape which has a water-filled pore through which selected hydrophilic ions or molecules can pass

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19
Q

chiasma

A

the visible effects of crossing over

20
Q

chi-squared test

A

a statistical test that can be used to determine whether any difference between observed results and expected results is significant or is due to chance

21
Q

chromatid

A

one of two identical parts of a chromosome, held together by a centromere, formed during interphase during the replication of the DNA strand

22
Q

chromatin

A

the loosely coiled form of chromosomes during interphase of the cell cycle; chromatin is made of DNA and proteins and is visible as loosely distributed patches or fibres within the nucleus when stained

23
Q

chromosome

A

a structure made of DNA and histones, found in the nucleus of a eukaryotic cell; the term bacterial chromosome is now commonly used for the circular strand of DNA present in a prokaryotic cell

24
Q

chromosome mutation

A

a random and unpredictable change in the structure or number of chromosomes in a cell

25
Q

codominant

A

two alleles are said to be codominant when both alleles have an effect on the phenotype of a heterozygous organism

26
Q

codon

A

sequence of three bases on an mRNA molecule that codes for a specific amino acid or for a stop signal

27
Q

competitive inhibition

A

when a substance reduces the rate of activity of an enzyme by competing with the substrate molecules for the enzyme’s active site; increasing the concentration of the substrate reduces the degree of inhibition

28
Q

crossing over

A

an event that occurs during meiosis 1, when chromatids of two homologous chromosomes break and rejoin so that a part of one chromatid swaps places with the same part of the other

29
Q

diffusion

A

the net moement of molecules or ions from a region of higher concentration to a region of lower concentration down a gradient, as a result of the random movements of particles

30
Q

dihybrid cross

A

a genetic cross in which two different genes are considered

31
Q

diploid cell

A

one that possesses two complete sets of chromosomes

32
Q

disaccharide

A

a suger molecule consisting of two monosaccharides joined together by a glycosidic bond

33
Q

dominant

A

an allele is said to be dominant when its effect on the phenotype of a heterozygote is identical to its effect in a homozygote

34
Q

double circulation

A

a circulatory system in which the blood travels twice through the heart on one complete circuit of the body; the pathway from heart to lungs and back to the heart is known as the pulmonary circulation, and that from the heart to the rest of the body and back to the heart as the systemic circulation

35
Q

enzyme

A

a protein produced by a living organism that acts as a catalyst in a specific reaction by reducing activation energy

36
Q

facilitated diffusion

A

the diffusion of a substance through transport proteins in a cell membrane; the proteins provide the hydrophilic areas that allow the molecules or ions to pass through the membrane which would otherwise be less permeable to them

37
Q

fluid mosaic model

A

protein molecules are free to move about in a fluid bilayer of phospholipid molecules

38
Q

gamete

A

a haploid cell specialised for fertilisation

39
Q

gene

A

a length of DNA that codes for a particular protein or polypeptide

40
Q

gene mutation

A

a change in the base sequence in part of a DNA molecule

41
Q

globular protein

A

a protein whose molecules are folded into a relatively spherical shape, which is often water-soluble and metabolically active

42
Q

glycogen

A

a polysaccharide made of many glucose molecules linked together, that acts as a glucose store in liver and muscle cells

43
Q

haploid cell

A

one that possesses one complete set of chromosomes

44
Q

heterozygous

A

having two different alleles of a gene

45
Q

homologous chromosomes

A

a pair of chromosomes in a diploid cell that have the same structure, with the same genes at the same loci, and that pair together to form a bivalent furing the first division of meiosis

46
Q

homozygous

A

having two identical alleles of a gene

Biology A-level (18 decks)

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