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

Species

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

Population

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

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

Allele frequency

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

Variation

The differences that exist between individuals

Selection Pressure

Anything that affects an organisms chance of survival and reproduction

Evolution

A change in allele frequencies over time

Stabilising selection

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

Directional selection

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

Disruptive selection

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

Speciation

The development of a new species from an existing species

Geographical isolation

Individuals are completely separated by a physical barrier

Allopatric speciation

Speciation due to geographical isolation

Sympatric isolation

Speciation that does not require geographical isolation

Reproductive isolation

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

Genetic drift

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

Gene

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

Allele

A different version of a gene

Genotype

The alleles an organism possesses

Phenotype

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

Dominant

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

Recessive

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

Codominant

Two dominant alleles that are both expressed in the phenotype

Locus

The fixed position of a gene on a chromosome

Carrier

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

Sex-linked genes

Genes carried on the sex chromosomes

Autosome

Any chromosome that isnt a sex chromosome

Epistasis

One gene affects / masks the expression of another gene

Chi-squared test

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

Habitat

The place where an organism lives

Population

All the organisms of one species in a habitat

Community

Populations of different species in a habitat

Ecosystem

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

Abiotic

The non living features of an ecosystem

Biotic

The living features of an ecosystem

Niche

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

Adaptation

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

Physiological adaptations

Adaptations that change the physical processes inside an organisms body

Behavioural adaptaions

Adaptations that change the way an organism acts

Anatomical adaptations

Adaptations that change the structural features of an organisms body

Population size

The total number of organisms of one species in a habitat

Carrying capacity

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

Interspecific competition

Competition between different species for the same resources

Intraspecific competition

Competition within a species for the same resources

Predation

Where an organism kills and eats another organism

Dynamic

Constantly changing

Primary succession

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

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

Climatic climax

The climax community for a particular climate

Plagioclimax

The climax community when succession is stopped artificially

Conservation

The protection and management of ecosystems in a sustainable way

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

Succession

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

Mutation

Any change to the base sequence of DNA

Substitution

One or more bases swapped for another

Deletion

One or more bases are removed

Addition

One or more bases are added

Duplication

One or more bases are deleted

Inversion

A sequence of bases is reversed

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

Hereditary mutations

Mutations passed from parents to the offspring via gametes

Frame shift

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

Downstream

The base triplets that follow on after a mutation

Mutagenic agennts

Things that can increase the rate of mutation

Acquired mutations

Mutations that occur in an individual after fertilisation

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

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

Genetic factor

A factor that is linked to the alleles an individual has

Environmental factor

A factor not linked to the alleles an individual has

Proto-oncogenes

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

Oncogene

A mutated proto-oncogene

Tumour suppressor genes

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

Stem cells

Unspecialised cells which can develop into other types of cell

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

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

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

Unipotent

Stem cells that can only differentiate into one type of cell

Cardiomyocytes

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

Adult stem cells

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

Embryonic stem cells

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

iPS cells

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

Genome

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

Human genome project

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

Proteome

All the proteins produced by an organism

Regulatory genes

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

Transgenic organisms

Organisms that contain transferred DNA

Recombinant DNA technology

Transferring a fragment or DNA from one organism to another

Target gene

The gene you are interested in when making DNA fragments

cDNA

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

Palindromic sequence

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

Recognition sequences

Another name for palindromic sequences

Sticky ends

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

Gene machine

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

Protecting groups

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

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.

phospholipid bilayer

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

Golgi apparatus

modifies and packages proteins for export by the cell

Why is cholesterol important?

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

Unsaturated membrane

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

Saturated membrane

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