Glossary

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abiotic

A term used to describe a non-living factor that may affect organisms in an ecosystem. Examples include light intensity, water availability, soil pH, temperature, wind speed, humidity, etc.

abiotic

Non-living factors that affect ecosystems, eg rainfall, pH, soil type, light intensity, temperature, etc.

active site

The place on an enzyme to which the substrate molecule becomes attached during the reaction.122

aerobic respiration

Chemical process by which energy is released from glucose using oxygen.

It can be represented by the following word equation:

              glucose + oxygen = Energy + carbon dioxide + water 

Alleles

Alternative forms of a gene that are responsible for different expressions of an inherited characteristic.

amino acid

Building blocks of protein molecules and the end products of protein digestion.

Definition for senior students:

The building blocks of proteins. There are approximately 20 different amino acids all of which have the same basic structure cantaining an acidic carboxyl group and an amino group, both bonded to the same central carbon atom.

ammonium compound

A chemical containing nitrogen  that is produced by bacteria during the decomposition of nitrgen containing compounds.

Amoeba

Unicellular pond animal lacking definite shape.

antibiotic

General name for a chemical produced by one micro-organism (eg a fungus) that prevents the growth of some other micro-organism (eg a bacterium).

Asexual Reproduction

Production of identical offspring by one parent without the involvement of sex cells.

Axon

Fibre that carries a nerve impulse away from the cell body of a neurone.158

backcross

A testcross where an organism is crossed with a homozygous recessive organism. By doing this it can help determine the genotype of an unknow individual.

bioaccumulation

Where materials from the environment accumulate within an individual through a variety of biological processes usually associated with feeding or respiration.

Also known as bioconcentration.

bioconcentration

Where materials from the environment accumulate within an individual through a variety of biological processes usually associated with feeding or respiration.

Also known as bioaccumulation.

biodegradable

Any substance that is capable of being decomposed by decay micro-organisms.

biological control

Where human beings deliberately introduce a natural predator or a disease into an area in an attempt to control a pest species, eg ladybirds are released into greenhouses to control aphids.

biology

The study of living things.

biomagnification

The process whereby the concentration of a pollutant within living tissues increases at each link in the food chain.

biome

Large areas of the Earth which have similar climatic conditions, particularly in terms of temperature and rainfall, and because of this have similar communities of flora (plants) and fauna (animals).

Biomes can be grouped into 5 main types: aquatic, deserts, forests, grasslands and tundra.

 

 

biome

Large areas of the Earth that have similar climatic conditions, particularly in terms of temperature and rainfall, and because of this have similar communities of flora (plants) and fauna (animals).

Biomes can be grouped into 5 main types: aquatic, deserts, forests, grasslands and tundra.

biotic

A term used to describe living factors that may affect organisms in an ecosystem. Examples include food availability, number of predators, diseases present, compeition.

biotic

Living factors that affect ecosystems, eg food availability, predation, competition, disease, grazing.

biotransformation

The change in the form of chemicals by biological processes, eg nitrates into proteins by primary producers.

body cell

A cell in an organism's body that contains two sets of chromosomes.

Brain

Mass of nerve tissue inside the skull that is the controlling and co-ordinating centre of the nervous system.159

carbohydrate

High energy compound, (eg sugar, starch) containing the elements carbon, hydrogen and oxygen.

carbon dioxide

Produced as a waste product during respiration.

Need as a raw material for photosynthesis.

carnivore

Any animal that feeds on other animals only, eg lion.

catalase

An enzyme found in plant and animal cells that speeds up the breakdown (degradation) of hydrogen peroxide into water and oxygen.

catalyst

A chemical that increases the rate of chemical reactions. The catalyst itself does not change during the reaction.

cell

The structural, functional and biological unit of all organisms.

cell division

Process by which a cell divides to form two identical daughter cells.

cell membrane

Boundary surrounding a cell that controls entry and exit of small materials, eg glucose, oxygen, carbon dioxide. It is selectively (or semi-) permeable.

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Advanced definition for senior students:

See 'plasma membrane'

cell sap

Solution of salts and sugars found in the vacuole of cells.

cell wall

Boundary round a plant cell that is slightly flexible but maintains the cell's shape. It is made of cellulose and allows substances to pass through.

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Advanced definition for senior students:

Structure present in plant and bacterial, but not animal cells. In plant cells it consists of a matrix of polysaccharide and protein with cellulose fibres embedded in it. The cell wall is freely permeable.

cellulose

A type of carbohydrate made up of many glucose molecules linked to form branching chains that make up plant cell walls.

Central Nervous System

Part of the body composed of the brain and spinal cord.

centromere

Structure that holds together two identical chromatids.

 

Cerebellum

Region of the brain responsible for the control of balance and muscular co-ordination.

Cerebrum

Region of the brain responsible for memory, reasoning and imagination.

chemical energy

Form of energy present in food.

chlorophyll

Green pigment found in the chloroplasts of plants. It traps light energy during photosynthesis.

chloroplast

Structure containing chlorophyll found in some types of plant cells. It is the site of photosynthesis.112

chromatid

One of two identical copies of a chromosome.

 

Chromosome

Thread-like structure found inside the nucleus of a cell. 157

chromosome complement

The normal number of chromosomes found in a cell that is characteristic of the species, eg there are normal chromosome complement for human beings is 46 chromosomes.

community

All the plants, animals and micro-organisms that live together in an ecosystem.

competition

There will be competition if organisms use the same resources which are in short supply.

Animals may compete for food, water, mates, nesting sites, etc if they are in short supply.

Plants may compete for light, water, nutrients, space if they are in short supply .

 

competition

Where plants or animals compete with each other for resources that are in short supply.

concentration gradient

The difference in concentration that exists between two regions.

consumer

An organism that cannot make it's own food and needs to feed on plants or other animals.

continuous

Type of variation that cannot be put into discrete groups, eg height, weight, hand span.

contractile vacuole

119 Found in unicellular organisms and is a structure that expels excess water to prevent it from bursting.

control

Copy of an experiment in which all the factors are kept constant except the one being investigated in the original experiment.

copulation

Sexual intercourse.

copulation

Sexual intercourse.

cytoplasm

Transparent material found in cells. It is the site of chemical reactions.114

daughter cell

The new cells produced at the end of mitosis. Each are identical to each other and to the original cell in terms of the number of chromosomes and the genetic information carried on them.

DDT

A pesticide that was used to kill insect pests. It was found to be very polluting in food chains and caused harm to many other organisms. It is now banned in the UK and many other countries.

Further information for senior students.

DDT is short for dichlorodiphenyltrichloroethane (if you must know!!).

It is a stable compound which accumulates in the soil and becomes concentrated up a food chain. It is soluble in lipids and therefore builds up in fatty tissues of carnivores, eg fish-eating birds. It can cause shell thinning in these birds which ulitmately results in breeding failure.

decay

The process by which dead organisms and organic waste are broken down by micro-organisms.

decomposer

Simple definition:

Any organism that breaks down dead organic matter to obtain energy. the organisms involved are mainly bacteria and fungi.

More detailed definition for senior students:

Organisms, usually bacteria and fungi  that are capable of breaking down the complex structural molecules of organic debris. This is achieved by the bacteria and fungi releasing enzymes externally.

degradation

The breaking down of large, complex molecules into simpler ones, eg the breakdown of a large starch molecule into glucose.

denatured

Describes the state of an enzyme that has been permanently destroyed by being heated to a temperature of 50 degrees C or above.

denitrification

The process by which soil bacteria (eg Pseudomonas dentirificans) breaks down nitrate in the soil solution releasing nitrogen gas.

Further information for senior students:

This process usually takes place in waterlogged soil and represents a loss of nitrate form the soil solution. This may impact on plant growth.

detritivore

Organisms, usually invertebrates that feed on detritus to obtain nutrients and energy.  This results in the production of humus, the partly decayed organic part of the soil. Decomposers can then utilise the humus.

diffusion

The process by which molecules move from a region of high concentration to a region of low concentration until they are evenly spread (at equilibrium).

digestion

Chemical breakdown of large complex molecules to simpler ones.

discontinuous

Type of variation that can be put into discrete groups, eg rolling or non rolling tongue, blood groups, attached or unattached ear lobes.

Dominant

Describing the member of a pair of alleles that always shows in effect and masks the presence of the recessive allele.

ecosystem

A natural biological unit made up of living organisms and the non-living surroundings with which the organisms interact.

You might also see it  described as a word equation:

community + habitat = ecosystem

Examples of ecosystems include heather moorland, Caledonian forest, coral reefs, etc.

 

ecosystem

A natural biological unit made up of living and non-living parts. Examples include: heather moorland, coniferous forest, coral reef, tropical rainforest, etc.

Effector

Muscle or gland that responds to a nerve impulse by making a response.

egg

Female sex cell (gamete). Also known as ovum (pl, ova)

egg tube

See entry for oviduct.

embryo

The stage of animals and plants that immediately follows fertilisation.

Embryo

Multicellular structure that develops from a zygote following cell division.

end product

Substance formed as a result of an enzyme acting on its substrate, eg water and oxygen are the end products of the breakdown of hydrogen peroxide by the enxyme catalase.

enzyme

Produced by cells that act as biological catalysts to speed up chemical reactions in the cell. Enzymes are made of protein.

Examples of enzymes include catalase, amylase, phosphorylase, pepsin, lipase.

equator

Central region of the cell where chromosomes line up during mitosis.

eutrophication

The process of pollution of a waterway due to excessive quantities of sewage or fertilisers. The excess nitrate and phosphate causes rapid growth of algae which use up the oxygen in the water, especially during the hours of darkness when the algae is not photosynthesising. This can cause the death of other plants and animals in the ecosystem.

Even when the algae die back in the winter months oxygen is still depleted because of the high level of decomposition of the dead algae by bacteria.

external fertilisation

The process by which a sperm fuses (joins together) with an egg outside the female's body. It usually takes place in water.

F1

See 'First filial generation'

F2

See 'Second filial generation'

Fallopian tube

See entry for oviduct.

Family Tree

Branched diagram showing how the members of several generations of human beings are related to one another.

fat

Energy rich food composed of fatty acids and glycerol. Examples of fat rich food include olive oil, butter.

fatty acid

Type of building block of fat molecules and an end product of fat digestion.

fertilisation

The process by which the nucleus of the sperm fuses (joins together) with the nucleus of the egg. The cell that is formed is called a zygote.

fertiliser

A substance added to soil to replace the nutrients that have been removed by plants. Fertilisers may be natural (sometimes known as organic), eg farmyard manure, or synthetic (sometimes known as inorganic), ie made by humans.

first filial generation

The first generation of a cross. Usually shortened to F1.

flaccid

116 Describes the appearance of a cell that has lost water by the process of osmosis. The vacuole has shrunk and the cell loses shape.

See also the definition for plasmolysed.

foetus

The name given to the embryo at a later stage of development. The species can be identified by the appearance of the embryo.

food chain

A diagram to show the direction of energy flow between orgnisms living in an ecosystem. Food chains always start with a producer. The arrows show the direction of energy flow.

An example of a food chain is:103

food web

104 A diagram made up of several food chains to show the feeding relationship between organisms in an ecosystem.

This is an example of a food web.

freely permeable

Term used to describe a structure (eg plant cell wall) that allows all molecules in solution to pass through it.

fungicide

A group of chemicals that can be used to kill disease causing fungi.

gamete

 A reproductive cell or sex cell that contains the haploid set of chromosomes

gamete

The general name for the sex cells involved in reproduction. In animals they are the sperm and egg, in plants pollen and egg.

Gene

Basic unit of inheritance many of which make up a chromosome; each controls an inherited characteristic.

genetic information

Information which determines hair colour, tongue rolling ability and many other chraracteristics, and is passed on from one generation to the next in genes.

genetic modification

The process where enzymes are used to cut pieces of DNA from one organism and join them into a gap in the DNA of another organism. This means that the new organism with the inserted genes has the information for one or more new characteristics.One example is the insertion of the gene for human insulin is added to the the DNA of a bacteria (E. coli). The genetically altered bacteria can produce human insulin. This human insulin can be used to treat diabetics.

genotype

The set of genes an organism possesses; usually written as a formula, eg Tt, TT or tt.

gestation

The length of time the embryo takes to develop inside the mother's body.

glucose

Simple sugar produced by plants during photosynthesis.

glycerol

Type of building block for fat molecules and an end product of fat digestion.

habitat

The place where an organism lives.

Note - do not say the 'home' of an organism.

haploid

The structural, functional and biological unit of all organisms.

herbicide

A group of chemicals that can be used to kill weeds which compete with crop plants.

herbivore

An animal that feeds on plants only, eg sheep.

heterozygous

An individual that possesses two different forms of a gene, eg Tt.

Heterozygous

Describing a genotype that contains two differet alleles of a particular gene.

homozygous

An individual that possesses two identical forms of a gene, eg TT or tt.

Means the same as the term tru-breeding.

Homozygous

Describing a genotype that contains two identical alleles of a particular gene.

humus

Material that makes up the organic part of soil. It consists of decayed plant and animal remains.

impermeable

Term used to refer to a structure that does not allow molecules in solution to pass through it.

indicator species

Type of living organism that only thrives well under certain environmental conditions and whose presence indicates that those conditions are present.

An example of an indicator species is mayfly larvae which will only survive if the oxygen content of the water is high, therefore if mayfly larvae are observed in a pond or river their presence indicates that the water contains plenty of oxygen.

inherited

Characteristics which are passed on from one generation to the next.

insulin

Hormone made by the pancreas that controls blood sugar level.

inter-specific competition

Where plants or animals of different species compete for resources that are in short supply.

internal fertilisation

The process by which the nucleus of the sperm fuses (joins together) with the nucleus of the egg inside the female's body.

Internal Fertilisation

Process by which a sperm fuses with an egg inside the female's body.

intra-specific competition

Where plants or animals of the same species compete for resources that are in short supply.

iodine

A red brown liquid used to test for starch. The iodine goes black when starch is present.

Iodine can also be used to stain cells so that they are easier when viewing them under a microscope.

joint

Where two bones meet.

key

A way to identify unknown organisms using a branched diagram (a branching key) or a series of numbered paired statements (a paired statement key). Keys use characteristics that can be seen, eg colour of fur, spot pattern, etc.

ligament

Tough, slightly elastic material that holds bones together.

light energy

The form of energy taken in by green plants during photosynthesis and converted to chemical energy.

light meter

A piece of equipment used to measure the light intensity.

light meter

Instrument used to measure the light intensity.

limiting factor

Any factor that holds up a process when that factor is in short supply, eg when it is dark light intensity is a limiting factor for the process of photosynthesis.

lock and key theory

The idea that the substrate and enzyme molecules fit together in a precise and specific way.

Medulla

Region of the brain responsible for the control of rate of breathing and heart beat

mitosis

A type of cell division that results in the production of two identical daughter cells. It is the type of cell division that occurs during growth and the reproduction of unicellular organisms.

moisture meter

A oiece of equipment used to measure soil moisture.

moisture meter

An instrument used to measure soil moisture.

monohybrid

A cross between two parents which have only one difference, eg tall or dwarf plants.

Monohybrid Cross

Breeding experiment involving two different alleles of one gene.

Motor Nerve

Branch of nervous system that carries nerve impulses from the CNS to muscles and glands.

multicellular

Describes an organism that consists of more than one cell, eg human being, daffodil, etc.

Multicellular Organism

Term used to describe an organism that consists of more than one cell.

mutagenic agent

Any factor that increases the mutation rate in organisms. Examples include radiation, UV light, some chemicals such as colchicine.

mutant

An individual whose phenotype shows a mutation.

mutation

The general term for a change in an organism's genetic material.

natural selection

The process by which evolutionary changes occur in organisms over a long period of time. Organisms that are well adapted to their environment will survive to produce offspring, whereas organisms that are not so well adaoted will not. As the better adapted organisms pass their genes from one generation to the next, these are the organisms that are 'selected' to survive.

niche

The role that an organism plays within its community. It includes the use it makes of the resources available including light, temperature and nutrient availability, and its interactions with other organisms including competition, parasitism and predation.

 

niche

The role that an organism plays within its community. It includes the use it makes of the resources available including light, temperature and nutrient availability, and its interactions with other organisms including competition, parasitism and predation.

nitrate

A compound containing nitrogen that is absorbed from the soil solution by plant roots.

nitrification

The process by which bacteria in soil convert ammonium compounds to nitrite and nitrite to nitrate.

Further information for senior pupils

Examples of bacteria which carry out this process are:

Nitrosomonas and Nitrococcus species convert ammonia to nitrite.

Nitrobacter converts nitrite to nitrate.

nitrifying bacteria

Bacteria that are capable of carrying out the process of nitrification.

nitrite

A compound containing nitrogen that is converted to nitrate in the soil solution by bacteria.

Nitrobacter

A bacteria found in the soil that is capable of oxidising nitrite to nitrate releasing energy in the process.

Nitrococcus

A bacteria that lives in the soil that is capable of converting ammonia to nitrite.

nitrogen

A chemical needed by all living things to make protein.

nitrogen cycle

The circulation of the chemical element nitrogen between the atmosphere, the soil or aquatic environment and the living organisms in an ecosystem.151

nitrogen fixation

The process by which certain bacteria absorb nitrogen gas and convert it to nitrogen containing compounds for use by plants to make protein.

Further information for senior students:

This process requires the enzyme nitrogenase which only works in the absence of oxygen and the input of enrgy. Examples of bacteria that can carry out this reaction include a few few species of prokaryotic bacteria, cyanobacteria and Rhizobium bacteria.

nitrogenase

The enzyme that speeds up the reaction involved in nitrogen fixation. It requires anaerobic conditions to work.

Nitrosomonas

A bacteria which is capable of converting ammonia to nitrite.

nucleus

Structure in the cell that contains chromosomes and controls the cell's activities.

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Advanced definition for senior students:

Organelle found in the cytoplasm of plant and animal cells (eukaryotes) but not bacteria. It contains DNA. The nucleus is surrounded by a double membrane which have many nuclear pores to allow the movement of material between the nucleus and the cytoplasm.

  

 

 

 

 

 

 

 

omnivore

Any animal that eats both plants and other animals, eg human, fox, badger.

optimum

Describes the particular conditions at which an enzyme is most active, eg the optimum temperature of the enzyme amylase is 37 degrees C because this is the temperature at which amylase is most active.

organism

Any living thing, eg cat, oak tree, bacterium, fungus, etc

osmosis

The movement of water molecules from a region of high water concentration to a region of lower water concentration through a selectively permeable membrane.

ovary

Part of the female reproductive system that produces eggs.

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Ovary

Part of female reproductive system that produces eggs.

oviduct

The tube leading from the ovary to the uterus in the female body. The egg passes along this tube. Fertilisation takes place in the oviduct. The oviduct is also known as the egg tube or the Fallopian tube.

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Oviduct

Tube along which eggs pass from an ovary to the uterus in a female's body. The oviduct is the site of fertilisation.

oxygen

Needed for aerobic respiration by organisms.

Produced as a by-product during photosynthesis.

P

Short for parents in a genetic cross.

parasite

An organism that obtains its food from the body of another living organism that is harmed as a result.

penis

Male organ connected to testis. Used during sexual intercourse to introduce sperm into the female body.

Penis

Male organ containing tube connected to testis; used to introduce sperm into female.

pepsin

An enzyme made by the stomach that speeds up the breakdown of proteins into amino acids.

pesticide

Any chemical that is used to kill pests but which may pollute food chains if used in excess.

phenotype

The outward appearance of an organism.

Phenotype

Physical appearance of an organism

Phenotypic Ratio

The relative sizes of two groups expressed as a proportion (e.g. 3 black: 1 white).

phosphorylase

An enzyme that speeds up the synthesis (build-up) of starch from glucose-1-phosphate molecules. This reaction is seen to take place in potatoes.

Note - glucose-1-phosphate is the reactive form of glucose.

photosynthesis

Process by which a green plant converts light energy to chemical energy.

It can be represented by the following word equation:121

pitfall trap

101 A piece of equipment used to catch small organisms living in leaf litter. It consists of a simple pot buried up to the rim in soil and the open top camouflaged with a stone or branches and leaves.

pitfall trap

A piece of equipment used to sample organisms active on the soil surface.152

placenta

Organ that allows exchange of materials, eg glucose, oxygen, carbon dioxide between the blodd supplys of the mother and developing foetus.144

plasmolysed

Describes a plant cell whose contents have shrunk due to loss of water by osmosis. It describes a greater water loss than plant cells that are flaccid.117

pole

The regions at either end of the cell where the chromosomes move towards during cell division.

pollution

Contamination of the environment by a harmful substance.

population

A group of organisms of one species living together in an ecosystem.

primary consumer

Any animal that eats plants only. Means the same as 'herbivore'.

producer

Any organism that can produce it's own food, usually a green plant.

protein

Type of food needed for growth and repair. Proteins are made up of amino acids and contain the elements carbon, hydrogen, oxygen and nitrogen.

Definition for advanced students:

A group of organic compounds containing carbon, hydrogen, oxygen, nitrogen and usually sulphur which are built up of amino acids in long polypetide chains. There are two main types of protein:

Globular - include enzymes, antibodies and some hormones.

Fibrous - include proteins in muscle, and connective tissue.

Pseudomonnas denitrificans

The soil living bacteria that can carry out the process of denitrification.

pyramid of biomass

A diagram that represents the total dry mass of the organisms at each link in a food chain. 149

pyramid of energy

A diagram that represents the total energy produced at each link in a food chain. It is always a pyramid shaped diagram.150

pyramid of numbers

A diagram that represents the number of organisms at each link in a food chain.148

quadrat

102 A square shaped piece of equipment used to sample the number of plants in an area. It can also be used to sample non-moving, or very slow moving animals, eg mussels on a rock.

quadrat

A square shaped sampling unit of a known area that is used to sample plants or very slow moving or staionary animals (eg mussels on a rock)

random

Term used to describe the use of a quadrat where the user does not choose where to lay the quadrat down.

random

No pre-arranged pattern.

recessive

The form of a gene which is masked by the dominant form. The recessive gene is only expressed in the phenotype when the dominant gene is absent, eg tt.

Recessive

Describing the member of a pair of alleles that is always masked by dominant alleles.

Reflex Action

A rapid automatic involuntary response to a stimulus.

Reflex Arc

Arrangement of three different types of neurone through which an impulse passes resulting in a reflex action.

Relay Neurone

Intermediate nerve cell in a reflex arc that transmits a nerve impulse triggered by a stimulus.

reproduction

The production of new individuals.

reproduction

The production of new members of a species.

Reproduction

Production of new members of a species

Rhizobium bacteria

A bacteria which lives in a mutualistic relationship with leguminous plants (eg peas, beans, lupins, clover). It is found in the root nodules of these plants and carries out the process of nitrogen fixation.

second filial generation

The second generation of a cross. Usually shortened to F2.

secondary consumer

Any animal that feeds on other animals only. Means the same as carnivore.

selectively permeable membrane

A structure that allows small molecules (eg oxygen, glucose, carbon dioxide, water) but not larger molecules (eg starch) to pass through it.

Means the same as semi permeable.

semi permeable membrane

A structure that allows small molecules, (eg oxygen, glucose, carbon dioxide, water) but not large molecules (eg starch) to pass through it.

Means the same as selectively permeable. 

Sensory Neurone

Nerve cell in a reflex arc that transmits a nerve impulse from the receptor to the relay neurone.

Sexual Reproduction

Reproduction involving two parents and the fusion of a male and female sex cell.

source of error

Any limitation in experiments that produces unreliable results.

speciation

The process by which new species are created.

species

A group of organisms that can breed together to produce fertile offspring.

specific

Used to describe the unique relationship between an enzyme and its substrate where the enzyme is only able to act on that one type of substrate and their molecules fit together like a lock and key.

For example catalase only fits on to the substrate hydrogen peroxide and no other substrate.

sperm

The male gamete (sex cell).

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sperm duct

The tube leading from the testes to the penis through which sperm pass.

Spinal Cord

Thick nerve protected by the vertebral collumn; connects with the brain.

spindle fibre

Thread-like structure that attaches to the centromere of a chromosome and pulls it to the pole during cell division.

starch

A carbohydrate formed when many glucose molecules link together in a chain. Plants convert glucose produced during photosynthesis to starch. Starch is a store of chemical energy.

It can be found in many food stuffs, eg potatoes, bread, pasta. 

sterile

Term used to describe an organism that is unable to reproduce.

survival of the fittest

The idea that only the organisms with the best characteristics to survive in a given habitat will breed to pass their genes on to the next generation.

Synapse

Tiny space between the axon ending of one neurone and the dendrite of the next.

synthesis

The building up of large complex molecules from simpler ones by an enzyme controlled reaction, eg starch is synthesised from glucose-1-phosphate by the enzyme phosphorylase.

Note - glucose-1-phosphate is the reactive form of glucose.

tendon

Tough, inelastic material that attaches muscles to bones.

testis

The part of the male reproductive system that produces sperm.

true-breeding

Means the same as homozygous, where an individual possesses two identical forms of a gene, eg TT or tt.

True-breeding

Describing an organism that on being crossed with a member of the same strain always produces more organisms of exactly the same strain. They are homozygous.

Tullgren funnel

A piece of equipment used to trap tiny organisms that live in the soil. It works by heating and lighting  the soil so that the organisms move down through the soil and into a trap.100

turgid

Describes a plant cell swollen with water taken in by osmosis.115

umbilical cord

The tube containing blood vessels that connect the foetus to the placenta in mammals.146

unicellular

Describes an organism that consists of one cell, eg Paramecium as shown here.118

Unicellular Organism

Term used to describe an organism that consists of one cell.

uterus

The part of the female reproductive organ where the foetus develops. Also known as the womb.

Uterus

Hollow muscular organ of female mammal within which the embryo develops.

vacuole

Found in some plant cells and contains cell sap.113

vagina

Part of the female reproductive system that leads to the uterus. The penis enters the vagina during copulation.

variation

Differences due to inherited and environmental factors that exist between species.

virus

Tiny disease-causing organism that shows living and non-living characteristics.

visking tubing

A synthetic material containing tiny pores that act as a selectively (or semi-) permeable membrane used to demonstrate osmosis and diffusion.

womb

See entry for uterus.

working range

The limits of a particular variable factor (eg temperature, pH) within which an enzyme can work on its substrate.

yolk sac

Seen in young fish. It is a bag containing a yolky food store.

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zygote

The name given to the egg when it is first fertilised. It is the first cell of a new individual.

Zygote

Cell formed when a female gamete is fertilised by a male gamete.