AQA BIOLOGY ALEVEL definitions, ALevel AQA Biology, AQA ALEVEL BIOLOGY (copy)

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Biology

427 Terms

1

Species

A group of similar organisms that can reproduce to give fertile offspring

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2

Population

A group of organisms of the same species living in a particular area at a particular time

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3

Gene pool

The complete range of all the alleles of all the genes of all the individuals present within a population at a given time

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4

Allele frequency

How often / how many times an allele occurs in a population

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5

Variation

The differences that exist between individuals

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6

Selection Pressure

Anything that affects an organisms chance of survival and reproduction

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7

Evolution

A change in allele frequencies over time

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8

Stabilising selection

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce

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9

Directional selection

Where individuals with alleles for characteristics towards one end of the range are more likely to survive and reproduce

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10

Disruptive selection

Where individuals with alleles for characteristics towards both ends of the range are more likely to survive and reproduce

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11

Speciation

The development of a new species from an existing species

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12

Geographical isolation

Individuals are completely separated by a physical barrier

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13

Allopatric speciation

Speciation due to geographical isolation

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14

Sympatric isolation

Speciation that does not require geographical isolation

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15

Reproductive isolation

Individuals from different populations have changed so much that they can no longer breed with one another to give fertile offspring

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16

Genetic drift

When chance rather than environmental factors dictate which individuals survive breed and pass on their genes

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17

Gene

A sequence of bases on a DNA molecule that codes for a polypeptide

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18

Allele

A different version of a gene

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19

Genotype

The alleles an organism possesses

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20

Phenotype

The expression of the genotype of an organism - an organisms characteristics

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21

Dominant

An allele whose characteristic is expressed in the phenotype even if there is only one copy

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22

Recessive

An allele whose characteristic only appears in the phenotype if there are two copies present

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23

Codominant

Two dominant alleles that are both expressed in the phenotype

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24

Locus

The fixed position of a gene on a chromosome

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25

Carrier

A person carrying an allele which is not expressed in their phenotype but can be passed onto offspring

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26

Sex-linked genes

Genes carried on the sex chromosomes

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27

Autosome

Any chromosome that isnt a sex chromosome

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28

Epistasis

One gene affects / masks the expression of another gene

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29

Chi-squared test

A statistical test used to see if the results of an experiment support a theory

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30

Habitat

The place where an organism lives

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31

Population

All the organisms of one species in a habitat

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32

Community

Populations of different species in a habitat

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33

Ecosystem

A community and all the abiotic conditions in the area which it lives

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34

Abiotic

The non living features of an ecosystem

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35

Biotic

The living features of an ecosystem

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36

Niche

The role of a species within its habitat, such as what it its and when and where it feeds

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37

Adaptation

A feature that members of a species have that increase their chances of survival and reproduction

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38

Physiological adaptations

Adaptations that change the physical processes inside an organisms body

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39

Behavioural adaptaions

Adaptations that change the way an organism acts

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40

Anatomical adaptations

Adaptations that change the structural features of an organisms body

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41

Population size

The total number of organisms of one species in a habitat

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42

Carrying capacity

The maximum stable population size of a species that an ecosystem can support

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43

Interspecific competition

Competition between different species for the same resources

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44

Intraspecific competition

Competition within a species for the same resources

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45

Predation

Where an organism kills and eats another organism

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46

Dynamic

Constantly changing

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47

Primary succession

Occurs on land thats been newly formed or exposed, starts when a new species colonise a new land surface

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48

Secondary succession

Happens on land thats been cleared of all the plants but where soil remains - happens in the same was as primary succession but starts at a later stage, with larger plants as there is already a soil layer

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49

Climatic climax

The climax community for a particular climate

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50

Plagioclimax

The climax community when succession is stopped artificially

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51

Conservation

The protection and management of ecosystems in a sustainable way

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52

Sustainable

Enough resources are taken to meet the needs of people today, without reducing the ability of people in the future to meet their own needs

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53

Succession

The process by which the structure of a biological community evolves over time

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54

Mutation

Any change to the base sequence of DNA

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55

Substitution

One or more bases swapped for another

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56

Deletion

One or more bases are removed

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57

Addition

One or more bases are added

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58

Duplication

One or more bases are deleted

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59

Inversion

A sequence of bases is reversed

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60

Translocation

A sequence of bases is moved from one location in the genome to another. This could be movement within the same chromosome or movement to a different chromosome

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61

Hereditary mutations

Mutations passed from parents to the offspring via gametes

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Frame shift

A shift in the bases that follow after a mutation, could be to the left or right

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Downstream

The base triplets that follow on after a mutation

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64

Mutagenic agennts

Things that can increase the rate of mutation

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65

Acquired mutations

Mutations that occur in an individual after fertilisation

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66

Cancerous tumours

A mass of abnormal cells that form a tumour which grows rapidly and invades and destroys surrounding tissue. Cells can break off and form tumours elsewhere in the body

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67

Benign tumours

Non-cancerous tumours that grow slowly and are covered in fibrous tissue that stops cells invading other tissues. They are harmless but can cause blockages and put pressure on organs

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68

Genetic factor

A factor that is linked to the alleles an individual has

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69

Environmental factor

A factor not linked to the alleles an individual has

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70

Proto-oncogenes

Genes that stimulate cell division by producing proteins that make cells divide

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71

Oncogene

A mutated proto-oncogene

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72

Tumour suppressor genes

Genes which slow cell division by producing proteins that stop cells dividing or causes them to self destruct

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73

Stem cells

Unspecialised cells which can develop into other types of cell

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Totipotent

Stem cells that can mature into any type of body cell, including those of the placenta. They are only present in the first few cell divisions of an embryo

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Pluripotent

Embryonic stem cells which have lost the ability to become cells that make up the placenta, but can still become any other body cell

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Multipotent

Stem cells which are able to differentiate into a few different cell types, eg cells that are found in the bone marrow can become red or white blood cells

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Unipotent

Stem cells that can only differentiate into one type of cell

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78

Cardiomyocytes

Heart muscle cells that make up a lot of the tissue found in hearts

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79

Adult stem cells

Stem cells which are obtained from the body tissues of an adult

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80

Embryonic stem cells

Stem cells which are obtained from embryos at an early stage of development

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81

iPS cells

Stem cells that are made by reprogramming already specialised adult body cells by making them express genes associated with pluripotency

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82

Genome

The entire set of DNA including all the genes in an organism

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83

Human genome project

A 2003 project which mapped the whole sequence of the human genome for the first time

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84

Proteome

All the proteins produced by an organism

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85

Regulatory genes

Genes that determine when other genes that code for particular proteins should be switched on and off

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86

Transgenic organisms

Organisms that contain transferred DNA

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87

Recombinant DNA technology

Transferring a fragment or DNA from one organism to another

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88

Target gene

The gene you are interested in when making DNA fragments

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89

cDNA

The complimentary DNA produced when making the DNA fragments using reverse transcriptase

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90

Palindromic sequence

Sequences of DNA which consist of antiparallel base pairs, that are read the same in opposite directions

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91

Recognition sequences

Another name for palindromic sequences

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92

Sticky ends

Small tails of unpaired bases at each end of a DNA fragment

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93

Gene machine

A machine that synthesises DNA fragments from scratch without the need for a preexisting template

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94

Protecting groups

Groups that make sure nucleotides are joined at the right points in a gene machine to prevent unwanted branching

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95

why is a membrane structure model called a fluid mosaic?

Phospholipids and proteins are abks to move. And embedded proteins vary in structure and size.

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96

phospholipid bilayer

a double layer of phospholipid molecules that form membranes in cells. Hydrophilic head and hydrophobic tail forms a hydrophobic region.

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97

Golgi apparatus

modifies and packages proteins for export by the cell

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98

Why is cholesterol important?

Reduces membrane fluidity and permeability (binds hydrocarbon tails together reducing spaces for diffusion).

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99

Unsaturated membrane

A more liquid membrane as they have kinks in tails so are more loosely packed.

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100

Saturated membrane

A more solid membrane as they are long and straight so more tightly packed.

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