Biology - Definitions

Movement

an action by an organism or part of an organism causing a change of position or place

Respiration

the chemical reactions in cells that break down nutrient molecules and release energy for metabolism

Sensitivity

the ability to detect and respond to changes in the internal or external environment

Growth

a permanent increase in size and dry mass

Reproduction

the processes that make more of the same kind of organism

Excretion

the removal of the waste products of metabolism and substances in excess of requirements

Nutrition

the taking in of materials for energy, growth and development

Cell

The smallest unit of life that can function independently

Tissue

a group of cells with similar structures that work together to perform

Organ

a structure made of two or more tissues that work together to perform a specific function

Organ System

A group of organs that work together to perform a major function or meet physiological needs of the body

Diffusion

the net movement of particles from a region of their higher concentration to a region of their lower concentration as a result of their random movement

Osmosis

the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement

Active transport

as the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

Catalyst

a substance that increases the rate of a chemical reaction and is not changed by the reaction

Enzyme

proteins that are involved in all metabolic reactions, where they function as biological catalysts

Photosynthesis

the process by which plants synthesize carbohydrates from raw materials using energy from light

Ingestion

taking in of substances into the body

Chemical digestion

Breakdown of large insoluble molecules to small soluble molecules using chemical means, such as enzymes.

Mechanical Digestion

Breakdown of large insoluble molecules to small soluble molecules using physical means, such as teeth

Absorption

the movement of nutrients from the intestines into the blood

Assimilation

uptake and use of nutrients by cells

Egestion

the removal of undigested food from the body as faeces

Emulsification

the process of breaking down fat globules into smaller droplets, for an increased surface area for chemical digestion

Peristalsis

wave like contraction and relaxation of the muscles in the alimentary canal to move food through the digestive system

Hormone

chemical/ substance, produced by a gland transported in the blood and alters the activity of one or more specific target

Transpiration

loss of water vapour from leaves

Translocation

the movement of sucrose and amino acids in phloem from sources to sinks

Pathogen

a disease-causing organism

Transmissible Disease

a disease in which the pathogen can be passed from one host to another

Antibody

proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for destruction by phagocytes

Active immunity

as defence against a pathogen by antibody production in the body

Passive Immunity

short-term defences against a pathogen by antibodies acquired from another individual.

Aerobic respiration

chemical reactions in cells that use oxygen to break down nutrient molecules to release energy

Anaerobic respiration

the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen

deamination

removal of the nitrogen-containing part of amino acids to form urea

Reflex action

a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors

synapse

a junction between two neurones

sense organs

groups of receptor cells responding to specific stimuli

homeostasis

maintenance of a constant internal environment

gravitropism

response in which parts of a plant grow towards or away from gravity

phototropism

response in which parts of a plant grow towards or away from the direction of the light source

drug

any substance taken into the body that modifies or affects chemical reactions in the body

drug

any substance taken into the body that modifies or affects chemical reactions in the body

asexual reproduction

a process resulting in the production of genetically identical offspring from one parent

sexual reproduction

process involving the fusion of the nuclei of two gametes to form a zygote and the production of offspring that are genetically different from each other

fertilisation

fusion of the nuclei of gametes

pollination

the transfer of pollen grains from an anther to a stigma

self-pollination

the transfer of pollen grains from the anther of a flower to the stigma of the same flower

cross-pollination

transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species

sexually transmitted infection

an infection that is transmitted through sexual contact

Gene

a length of DNA that codes for a protein

Allele

an alternative form of a gene

Haploid nucleus

nucleus containing a single set of chromosomes

Dipoid nucleus

nucleus containing two sets of chromosomes

Mitosis

nuclear division giving rise to genetically identical cells

Stem Cells

unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions

meiosis

reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells

inheritance

transmission of genetic information from generation to generation

genotype

genetic make-up of an organism and in terms of the alleles present

phenotype

observable features of an organism

homozygous

having two identical alleles of a particular gene

heterozygous

having two different alleles of a particular gene

dominant allele

allele that is expressed if it is present in the genotype

recessive allele

allele that is only expressed when there is no dominant allele of the gene present in the genotype

codominance

situation in which both alleles in heterozygous organisms contribute to the phenotype

sex-linked characteristic

a feature in which the gene responsible is located on a sex chromosome

variation

differences between individuals of the same species

continuous variation

a range of phenotypes between two extremes

discontinuous variation

a limited number of phenotypes with no intermediates

mutation

genetic change

gene mutation

random change in the base sequence of DNA

adaptive feature

an inherited feature that helps an organism to survive and reproduce in its environment

food chain

the transfer of energy from one organism to the next, beginning with a producer

producer

organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis

consumer

organism that gets its energy by feeding on other organisms

herbivore

animal that gets its energy by eating plants

carnivore

animal that gets its energy by eating other animals

decomposer

organism that gets its energy from dead or waste organic material

trophic level

the position of an organism in a food chain, food web or ecological pyramid

population

a group of organisms of one species, living in the same area, at the same time

community

all of the populations of different species in an ecosystem

ecosystem

unit containing the community of organisms and their environment, interacting together

biodiversity

the number of different species that live in an area

sustainable resource

resource which is produced as rapidly as it is removed from the environment so that it does not run out

genetic modification

changing the genetic material of an organism by removing, changing or inserting individual genes