Summary of Biology Definitions

Summary of Biology Definitions


2.4.4 – Define diffusion and osmosis

Diffusion – the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis – the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.


3.2.1 – Distinguish between organic and inorganic compounds

Organic compounds are based on carbon and can be found in living things. Exceptions CO. These are classed as non-organic carbon. Three types of organic compounds widely found in living organisms are lipids, proteins and carbohydrates.

Inorganic compounds are any compounds that do not fall into the category of organic compounds.


3.6.1 – Define enzyme and active site

Enzyme – A biological catalyst made of globular protein

Active Site -The region of an enzyme molecule surface where the substrate molecule binds and catalysis occurs


3.6.4 – Define denaturation

A structural change in a protein that alters its shape and results in a loss of biological properties. This can be caused by pH or temperature.


3.7.1 – Define cell respiration

Cell respiration is the controlled release of energy from organic compounds in cells in the form of ATP


4.1.2 – Define gene, allele and genome

Gene – A gene is a heritable factor that controls a specific characteristic

Allele – An allele is a specific form of a gene, differing for other alleles by one or a few bases only. They occupy the same gene locus as the other alleles on the gene

Genome – The whole of the genetic information of an organism


4.1.3 – Define gene mutation

A gene mutation is a change in the base sequence of an allele


4.2.2 – Define homologous chromosomes

Chromosomes in a diploid cell which contain the same sequence of genes, but are derived from different parents.


4.3.1 – Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross

Genotype – The alleles of an organism

Phenotype – The characteristics of an organism

Dominant Allele – An allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state

Recessive Allele – An allele that only has an effect on the phenotype when present in the homozygous state

Codominant Alleles – Pairs of alleles that both affect the phenotype when present in a heterozygote

Locus – The particular position on homologous chromosomes of a gene

Homozygous – Having two identical alleles of a gene

Heterozygous – Having two different alleles of a gene

Carrier – An individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele

Test Cross – Testing a suspected heterozygote by crossing it with a known homozygous recessive

4.3.7 – Define sex linkage

Genes carried on only one of the sex chromosomes and which therefore show a different pattern of inheritance in crosses where the male carries the gene from where the female carries the gene

4.4.11 – Define clone

A group of genetically identical organisms or a group of cells derived from a single parent cell

5.1.1 – Define species, habitat, population, community, ecosystem and ecology

Species – A group of organisms that can interbreed and produce fertile offspring.

Habitat – The environment in which a species normally lives or the location of a living organism.

Population – A group of organisms of the same species who live in the same area at the same time.

Community – A group of populations living and interacting with each other in the same area.

Ecosystem – A community and its abiotic environment.

Ecology – The study of relationships between living organisms and their environment

5.1.2 – Distinguish between autotroph and heterotroph

Autotroph – An organism that synthesizes its organic molecules from simple inorganic substances

Heterotroph – An organism that obtains organic molecules from other organisms

5.1.3 – Distinguish between consumers, detritivores and saprotrophs

Consumers – An organism that ingests other organic matter that is living or recently killed

Detritivore – An organism that ingests non-living organic matter, also known as a decomposer.

Saprotroph – An organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion

5.1.6 – Define trophic level

The trophic level of an organism defines the feeding relationship of that organism to other organisms in a food chain. In a food web, a consumer can occupy a number of different trophic levels, depending on which organism is the prey.

5.4.1 – Define evolution

Evolution is the cumulative change in the heritable characteristics of a population.

6.1.6 – Distinguish between absorption and assimilation

Absorption – Soluble products of digestion are absorbed into the blood circulation system, or the lymphatic system if they are fats droplets.

Assimilation – Products of digestion are absorbed into the cells from the blood to be stored or used within the tissues.

6.3.1 – Define pathogen

An organism or virus that causes a disease or sickness. These are usually microorganisms.

6.3.5 – Distinguish between antigen and antibodies

Antigen – A foreign substance that stimulates the production of antibodies. It is recognised by the immune system, triggering this immune response.

Antibodies – Proteins, immunoglobin, that recognise and bind to specific antigens. These have a T or Y shape made from polypeptide chains.

6.4.1 – Distinguish between ventilation, gas exchange and cell respiration 

Ventilation – The pumping mechanism that moves air in and out of the lungs efficiently, thereby maintaining the concentration gradient for diffusion.

Gas Exchange – The exchange of gases between an organism and its surroundings, including the uptake of oxygen and the release of carbon dioxide in animals and plants.

Cell Respiration – The controlled release of energy in the form of ATP from organic compounds in cells. It is a continuous process in all cells.

6.5.4 – Define resting potential and action potential (depolarisation and repolarisation)

Resting Potential – An electrical potential across a cell membrane when not conducting an impulse

Action Potential – The localised reversal, or depolarisation, and then restoration, or repolarisation, of electrical potential between the inside and outside of a neuron as the impulse moves along it

7.3.2 – Distinguish between the sense and antisense strands of DNA

Sense strand – The coding strand that carries the promoter sequence of bases to which RNA polymerase binds and begins transcription. It has the same base sequence as mRNA, except with uracil instead of thymine. It also carries the terminator sequence of bases at the end of each gene, causing RNA polymerase to stop transcription

Antisense strand – The template strand for transcription by complementary base pairing. It has the same base sequence as tRNA with uracil instead of thymine.

9.2.5 – Define transpiration

Transpiration is the loss of water vapour from the leaves and stems of plants

9.3.2 – Distinguish between pollination, fertilisation and seed dispersal

Pollination – The transfer of pollen grains from the mature anther to the receptive stigma

Fertilisation – The fusion of the male gamete with the female gamete to form a zygote

Seed Dispersal – Seeds are moved away moved away from the vicinity of the parental plant before germination to reduce competition for limited resources. Mechanisms for this include fruits, winds, water and animals.

10.2.2 – Distinguish between autosomes and sex chromosomes

Autosome – A chromosome that is not a sex-chromosome. They do not vary depending on gender

Sex Chromosome – A chromosome which determines sex rather than other body (soma) characteristics

10.3.1 – Define polygenic inheritance

Inheritance of phenotypic characters (such as height, eye colour in humans) that are determined by the collective effects of several genes – a single characteristic that is controlled by two or more genes

11.3.1 – Define excretion

The removal of the waste products of metabolic pathways from the body

11.3.5 – Define osmoregulation

The control of the water balance of the blood, tissue or cytoplasm of a living organism.