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 Dictionary :: biologist 


Shorthand version denoting adenine.

A Band

The dark band of the muscle sarcomere that corresponds to the thick myosin (protein) filaments.

The "A Band" is situated on either side of the "H Zone" of a muscle sarcomere, that is the area where contraction and relaxation of the muscle occurs, where sarcomeres overlap during muscle movements.

A Chromosomes

The normal amount of chromosomes for an organism, for instance, 46 being the standard number of chromosomes in the typical human chromosome set. Extra chromosomes, which can bring about new species or medical complications are deemed B Chromosomes.


Shorthand for antibody.


Pertaining to a leaf surface that is facing away from the stem.


The part of the body that contains many of the major organs in many vertebrates. In vertebrates such as ourselves, the abdomen contains many of our major organs, including the intestines (small Intestine and large Intestine in humans), liver, kidney and stomach, and is seperated by the diaphragm which provides a wall between these organs and the respiratory organs.

Abducens Nerve

The cranial nerve in vertebrate species that controls the rectus muscle of the eye. This nerve is mainly "motor" in function, meaning that the information transmitted through this nerve is a response deriving from interneurones based in the CNS (Central Nervous System)


Muscles which are designed to move limbs away from the body. Muscles that do the opposite (move limbs closer to the body) are deemed adductors

Abiotic Factor

Pertaining to factors that are non-biological but still play an important role in an organisms environment. Examples are soil pH, cloud cover and forest fires. Abiotic factors are varied and are essentially the consequences of organisms' effect on the environment and natural changes in the equilibrium of the plant itself (like natural global warming). Abiotic factors are further investigated in the freshwater ecology tutorial.

Abiotic Stress

Abiotic Factors that have a negative impact on organisms in a given environment. An example of abiotic stress is acid rain caused by pollution, where pollution reduces a species capacity to survive in the environment due to its harmful nature.


The ending of milk production in mammals (organisms that have mammary glands, organs that are capable of producing milk).


Damage and removal to part of an organism either in part or in whole. Ablation can be promoted by an organisms internal functions, and sometimes this is done for the greater safety of the organism. In plants, a natural defence mechanism is to remove infected areas of the plant via abscission, which can be promoted in the presence of abscisic acid.

ABO Blood Group

Classification of blood types in humans, A, B, AB and O. Blood transfusions of blood type O are suitable to transfer to all other blood groups. Blood groups tend to change in proportion in differing races, usually as a result of the geographical location in which the group has previously existed and consequently the ancestors who had such a blood group.


Part of the ruminant stomach designed for digestion via secreting enzymes to breakdown food.


Pertaining to away from the mouth in organisms with no distinct front or back sides. An example of such an aboral organism is an earthworm.


Spontaneous (naturally occurring) or artificially induced expulsion of a foetus before natural live birth can occur.

Abrupt Speciation

The creation of a new species over a relatively short time span. This is in accordance with Charles Darwin's work on adaptive radiation and natural selection.


An inflamed tissue or organ which is damaged, resulting in swelling and collection of pus (dead organic matter). In plants, this can lead to abscission, where the safety of the plant as a whole supercedes the damaged area, and thus, the damaged part is removed to preserve the fuller organism.

Abscisic Acid

Partly responsible for leaf abscission in aging or diseased plants and also responsible for promoting dormancy in buds and seeds, abscisic acid is a plant growth substance which is also involved in the induction of dormant buds and seeds.


A plant process that initiates the removal or part of the plant in cases of aging or infection. This process is controlled primarily by 3 compounds, namely auxin, ethylene and abscisic acid. Human medicine incorporates the idea of abscission in the form of an amputation, where a badly infected area of the body is amputated to prevent infection spreading towards more vital and uninfected areas of the body.

A behavioural occurrence where the parents of offspring leave the offspring to 'fend for themselves'. The parent may occasionally return to provide some support and check up on their vulnerable offspring. This is done so that the young can adapt quickly to their harsh environment and learn to support themselves, exceeding the support provided by these less than accommodating parents.

Absolute Refractory Period

An occurrence after a neuron has fired an impulse where the neurone cannot fire another pulse for a short time directly after, due to the nervous systems inability to work at an even faster rate (the absolute refractory period is fractions of a second).

Absolute Zero

Thought to be the coldest possible temperature that any substance can exist at, -273 degrees Celsius. At this temperature atoms contain no heat energy.


A degree of measurement used to measure the amount of light absorbed by a particular substance at a particular wavelength.


Where substances either actively or passively enter another mass, such as in photosynthesis where light energy is actively absorbed into chlorophyll to make chemical energy.

Absorption Spectrum

The spectrum used to measure absorption where various wavelengths of light represent different colours of light.

Abundance mRNA

Pertains the the amount of freely available mRNA within a cell. Depending on the function of the cell and the genes in expression (which genes are on) will affect the amount of abundance mRNA in a particular cell.


Pertaining to areas of water deeper than one kilometre.


The ocean floor area, also known as the benthic region.


The region in the abyssal zone known as the pelagic region.


Pertaining to a spiky appearance, such as the acanthus genus who have such a phenotype.


Relating to plants that do not bear fruit, or organisms that are sterile.

Acceptor Molecule

Molecules that have a capacity to accept electrons, as is the case of a Redox Reaction. Such acceptor molecules are used in respiration and photosynthesis and are catalysed by relevant enzymes such as dehydrogenase.

Accessory Chromosome

Also known as B chromosomes, these chromosomes are excess chromosomes resulting from unsuccessful meiotic divisions where resultant cells have extra chromosomes. A common reason for this happening is Non-Disjunction, where the split of chromosomes into daughter haploid cells is uneven in number.


Acclimatisation is where an organism is subject to sudden changes of environments, where it must adapt physiologically so that the organism can continue to operate normally in the new environment.


Parts of a flower that becomes enlarged after flowering.


Any plants that contribute nutrients to an ecosystem. As plants are the primary producers on the whole, this is usually the case; their decaying organic matter will breakdown into detritus by both herbivores and detrivores which can accummulate the energy contained within the plants that was gained from photosynthesis during the plants' lifetime.


Also known as unicellular, this term pertains to single cells, as in the case of unicellular organisms (organisms that are only one cell in mass).

Acentric Chromosome

A resultant chromosome that is the product of 2 broken chromosomes joining together after an unsuccessful meiotic division. This chromosome is useless and is discarded at the next division.


Pertaining to organisms without a head.


A socket found in the  femur of mammals that assists in joint movement.

Acetic Acid

A transparent liquid that is part of vinegar, that gives it its characteristic smell.


Pertaining to a flower that lacks petals.


An organism or substance that lacks chlorophyll.


A substance that is either colourless or is resistant to staining agents.


Substances that have a pH of lower than 7 (neutral) that can dissolve in water.

Acid Rain

Biologically harmful precipitation, mostly caused by pollutants released by human activity. The pollutants are released into the atmosphere and then return to ground level within the rain droplets, dramatically altering the pH of the land on which it falls upon.

This is an example of an abiotic factor at work, where the dramatic change in pH can have a dramatic effect on some species within the area, which can in turn have a knock on effect on the rest of the ecosystem.


Pertaining to substances that have a pH lower than 7 (neutral).


The resultant effect where the kidney fails to regulate acidic materials present in the body, resulting in excessive acidity in the body.


Pertaining to the hearing capabilities of animals.

Acquired Immune Deficiency Syndrome

Caused by the Human Immuno-Deficiency Virus which attacks the central nervous system. The virus causes the amount of T cells that are used to fight infection to drop to dangerously low levels. In someone who has acquired AIDS, it is not the disease that actually kills them, it is the fact that their immune system is degenerated by the virus leaving them prey to opportunistic infections like influenza.


Pertaining to the centromere of a chromosome. If the centromere is not positioned in the middle of a chromosome, i.e. one end is longer than the other then the chromosome; it is deemed acrocentric.

Acrocentric Chromosome

An adjective describing a chromosome where the centromere is situated some distance from the middle of it.


A condition in humans caused by over-production of growth hormone during adolescence. The resultant phenotype includes large un-proportional limbs and head in relation to the body.


Found at the head of a sperm gamete, the acrosome is an enzyme filled sac that assists in breaking down the wall of the egg mother cell so that the sperm can fertilise the egg.


A protein found in the muscles of organisms that is initiated by ATP to allow contraction of a muscle.

Actinomycin D

This substance is sometimes used as an antibiotic, as it has the capability of inhibiting the transcription of mRNA from DNA. This means that in the case of viral attack, actinomycin D could inhibit the replication of a virus by stopping protein synthesis (the food supply it needs) in the very cells the virus is trying to affect.

Action Spectrum

The action spectrum is an indicator of which wavelength of light can be used by a plant to allow photosynthesis. Also see absorption spectrum.

Activation Energy

Activation energy is the energy required to initiate a reaction, such at the 2 ATP required to breakdown glucose into pyruvic acid in respiration. In this case, the process results in a net gain of energy.

Active Absorption

See active transport.

Active Immunity

When a foreign agent such as a virus or bacteria enters the body, the defensive mechanism starts coding for relevant antibodies to remove such foreign agents. This is known as active immunity, as opposed to passive immunity.

Active Ingredient

The chemically active part of a chemical compound.

Active Site

A structural element of protein that determines whether the protein is functional when undergoing a reaction from an enzyme. This structural element will be accordingly shaped to the structure of the enzyme at work on it.

Active Transport

Active transport is the movement of a substance against a concentration gradient, as opposed to diffusion and osmosis where a substance moves along a concentration gradient. This process requires ATP to occur.


A type of protein involved in muscle contraction.


Pertaining to the focus of the eye, acuity is the measurement of sharpness that the eye can focus with.


Pertaining to organisms incapable of cyanogenesis.


Behavioural, physiological or anatomical changes in an organism over time to become more suited to their environment, as a result of adaptive radiation via natural selection.


Pertaining to the ability to modify behavioural, physiological or anatomical patterns in the gene pool (and consequently phenotype) of species in order to ensure survival in an ever changing external environment.

Adaptive Radiation

The evident effects of natural selection on organisms results in them diversifying over time, as illustrated in the genetics tutorial looking at natural selection and Darwin's finches.

In essence, the gene pool of a species undergoes a frameshift, where the best suited genes become more frequent in the species' population, depending on the environment of each organism. Over time the same species can diversify into other species; each trying to be as adaptive as possible in their environment. This is known as adaptive radiation, and was investigated in much detail by Charles Darwin.


Additive Genes

Additive genes are more than one gene that genetically code for the same function. This function will usually have a wide range of possible phenotypes, such as eye colour, because the wide range of genes and possible permutations of genetic coding allows for a wide range of results.


A muscle that is responsible for bringing a part of the body closer to the main bulk of the body, such as the biceps in the arm that pull the arm closer to the torso of the body. See abductor.


Adenine is one of the bases that form part of a nucleotide, the structures that are present in DNA chains. Adenine is always paired with thymine in a DNA chain though in mRNA and tRNA it is complimented with uracil. Adenine is also present in DNA, hence the name of the substance aden-os-ine.


Lymphatic tissue that can be found at the top of the pharynx near the nasal cavity.


Adenosine is found in nucleic acids (DNA, mRNA etc) and also forms part of ATP.

Adenosine Diphosphate (ADP)

Adenosine Diphosphate consists of one adenosine molecule and 2 inorganic phosphate molecules. The bonds that connect the phosphate molecules have a high potential energy state, and therefore is ideal to be used in biological processes. See ATP.

Adenosine Monophosphate (AMP)

AMP is the acronym for Adenosine monophosphate, consisting of one adenosine molecule attached to an inorganic phosphate molecule via a low level energy bond. See ADP and ATP.

Adenosine Triphosphate

ATP is ADP in its high energy state, where one of the high energy bonds connecting the phosphate molecules can be broken down releasing energy and forming ADP in the process. ATP consists of 1 adenosine molecule and 3 inorganic phosphate molecules. ATP is the biological energy used to execute biological processes in organisms.


Viruses that are often found in the lymphatic tissue deemed the adenoids. These viruses target the respiratory system.


Common acronym standing for anti-diuretic hormone which is used for osmoregulation in animals. High concentrations of ADH promote the re-absorption of water (and other compounds) in the kidney, via making the kidney tubules more permeable to water.


The attraction of two molecules that are unlike, i.e. water in a thin glass water column creates a meniscus at the top (a dimpled surface where the water is higher at the edges closest to the glass). This is advantageous in plants when transporting water upwards in the plant.


A modified substance that is intended to produce a desirable response. Adjuvants are implanted in viruses to weaken or kill them so that they can be used in immunisation so that the body can code for the respective antibodies in case of future infection.


Pertaining to part of a structure of an organ that connects itself to a completely different organ.


The stage of life in humans where hormonal changes dramatically change the physiology of a growing child into a mature adult.


Describing which side of an animal the mouth is situated on.

Adrenal Gland

Part of the endocrine system which is usually divided into to distinct parts, which secrete different hormones into the bloodstream. One of these hormones is adrenaline, which is secreted in 'fight or flight' circumstances.


This is a hormone secreted by an animal in 'fight or flight' circumstances, which basically means when the organism has to exert higher than average thinking and movement in a particular situation, usually in danger. Adrenaline increases heart rate, and in general makes the organism more alert to their external environment.


These cells are mostly found in mesophytes that possess evolutionary adaptations to assist them in floating in an aquatic environment, and as a means of gaseous exchange in the organism. Aerenchyma cells are characterised by their cork like structure and a large air filled cavity where gaseous exchange can occur.

Aerial Respiration

Humans amongst a wide range of other species undergo this type of respiration. Aerial respiration involves attaining water from the atmosphere (or dissolved oxygen in water) which is used in the organisms respiratory system. For the oxygen to be absorbed, a water layer is required so that their is a regulatory control (via a concentration gradient) on the exchange of gases.


Organisms that can only survive in the presence of oxygen. See Aerobic Respiration.

Aerobic Respiration

A cellular process in which one molecule of glucose is broken down via a number of steps to produce a total of 38 ATP. This ATP is the biological energy to power cellular processes via the energy made available from the breakdown of it into ADP.


A type of plankton that exists above ground level, these animals move subject the the air currents in their environment.


Aerotropism is a behavioural response in a plant that results in it growing towards the presence of air. Negative aerotropism has the opposite effect, where the plant grows away from the presence of oxygen.


Aestivation in animals is a state of dormancy usually to assist in water regulation, where minimal activity results in retaining more water during the hottest parts of the day. These animals will find a shaded/underground area to do this.

Afferent Neurone

Part of the nervous system, the afferent neurones are nerve fibres that carry impulses towards the central nervous system. This is opposed to an efferent neurone.


Pertaining to the remaining placenta and umbilical cord that are expelled from the internal environment of some mammals directly after birth.


Asexual reproduction - Where a female gamete can successfully develop offspring without fertilisation from a male gamete.


Species that do not require fertilisation of male and female gametes to produce offspring. See agamogenesis.


Reproduction that produces an embryo without the need of a male gamete via fertilisation.


Agar is a biological substance obtained from marine algae and has many properties which make it a valuable tool to scientists in scientific experiments.


Agglutin is an antibody that causes agglutination, a situation where cells become more compact to prevent foreign agents entering the high concentrated and more rigid cell structure.


Agglutination is an allergic reaction type occurrence where cells become more compact together to prevent foreign materials entering them. This is usually the result of an antigen in the vicinity of the cells.


Aggressins are found in bacteria and are designed to break down the tissue of organisms that the bacteria infect. An example of this is pectinase used to break down the pectin structure of a cell wall in plants.


A behavioural occurrence that is used to defend organisms in light of attack or simulate a threat display in order to fend off the attacker.


Substances that are responsible for inducing a cellular reaction such as hormones initiating a response at their target tissue.


A type of white blood cell produced in bone marrow that form two distinct types of leucocytes, being lymphocytes and monocytes.


Agriculture is the process by which man harnesses the nutrients of the soil to house various species in which the want to grow. This may range from a grassy field to feed cattle to a botanical garden for conservation purposes.


The study of agricultural practices and methods to improve its effectiveness and efficiency.


See Acquired Immune Deficiency Syndrome.

Air Pollution

An abiotic factor, air pollution is any substance that has a negative effect on living organisms in the environment, such as excessive concentrations of CO2 that can result in global warming, thus changing temperature which is a factor in many biological processes.

Air Space

Air spaces are present in some cells for a variety of reasons. Sometimes air spaces are present in hydrophytes (aquatic plants) that assist in buoyancy.

Airborne Pathogen

Any organism that causes disease that spreads throughout the environment via the air.


Short hand version of Alanine, an amino acid.


Alanine is one of twenty amino acids that form a polypeptide chain (proteins).


A condition related to the production of melanin in the body, which controls colouring in areas such as the skin, eyes and hair. A lack of melanin usually results in characteristics such as pale skin, white hair and red eyes, a phenotype which is inherited as a result of a genotype that possesses an inborn error of metabolism where tyrosine (an amino acid) cannot be broken down within a biochemical pathway involved with melanin.


A phenotypical occurrence defined by non-pigmented skin, eyes and hair in an organism due to the lack of melanin.


Also know as egg white, albumen is used inside an egg as a food source, as it consists of protein, which can be used by the embryo.


A protein found in albumen.


Alcohol is used as a recreational drug in most societies, and is created via fermentation with yeast undergoing anaerobic respiration creating alcohol from ethane, a hydrocarbon. Excessive consumpt.

Alcoholic Fermentation

Alcoholic fermentation is a type of cellular respiration which does not require oxygen (anaerobic respiration), and involves the breaking down of glucose to pyruvic acid and then finally ethanol.


Aldosterone is a hormone that is involved in regulating sodium and potassium concentration in the body, and is excreted by the adrenal gland. It promotes the re-absorption of sodium back into the body and removes excess potassium.

Aleurone Layer

A layer found in some plant seeds that excretes enzymes used to promote embryonic growth. Gibberellin, a family of growth hormones, enters the aleurone layer which induces the release of these enzymes. These promote the breakdown of starch into sugar that can be used by the embryo as energy.


A collection of plant species that thrive in wet conditions, many algae are primitive unicellular organisms.


An organism that is not thought to have occurred naturally in a particular ecosystem, therefore artificially introduced by man.

Alimentary Canal

Pertaining to the digestive system, beginning at the mouth and ending at the anus. Its primary function is the intake and breakdown of food to be stored and used as energy, though the latter stages of the alimentary canal involves the re-absorption of substances from the large intestine. Any excess material is then excreted out the body via the anus.


A bone in the central part of the skull in mammals.


A substance that has a pH higher than 7.


A law stating that stimuli either produce a reaction or no reaction at all in particular circumstances, no matter how much or how little or the inducing factor is present (stimuli). Compare this to digital and analogue transmissions, digital can either be 1 or 0, ON or OFF.


Pertaining to the DNA expression of a gene in a chromosome for a particular characteristic.

Allele Frequency

This is a measurement that determines how frequent the allele expression of a particular gene arises in a population. The result should be in close correlation with the laws of natural selection, where more favourable alleles should become dominant in a species over time, or are present due to a niche environment where a particular allele would prove advantageous.

Allelopathic Substances

A particular substance secreted by organisms that has an inhibiting effect on others, such as the excretion by skunks to evade predators.

Allen's Rule

A rule of thumb law devised by the biologist J.A.Allen that states structures in endotherms such as limbs (which are more prone to heat loss) are reduced in size by means of natural selection over time in cooler climates. This is a favourable circumstance with the intention to reduce heat loss.


Pertaining to antigens that induce an allergic response in an organism.


An allergy is an antigen that causes an allergic reaction as the result of foreign agents present inside the body which antibodies attempt to break down and destroy.


Pertaining to organic material that is foreign to a particular environment, i.e. it has arrived from elsewhere.

Allometric Growth

Unequal growth in part of an organism in relation to its whole.


Allopolyploids are hybrids that have a chromosome number double that off their parents. Some of these are created via selective breeding to produce new varieties of plants from previously sterile species.

Allosteric Enzyme

An enzyme that can be in two states, active and inactive, in the first instance, the process is relatively normal, where the enzyme binds to its binding site and carries out its reaction. In the second instance, the enzyme is unable to attach itself to the binding site. This is due to a modulator molecule which alters the shape of the binding site, making it inactive.

Allosteric Inhibitors

See allosteric enzyme. Inhibitors act as 'modulators' in enzyme execution as they can attach themselves to a molecule that will alter the binding site for the enzyme, rendering it unusable and therefore rendering the enzyme inactive.

Allosteric Protein

A protein that has underwent a fundamental structural change after reacting in the presence of another molecule. This will alter its ability to react with that particular type of molecule in the future.

Allosteric Transition

The transitional stage of a changing of structure in a protein.


An allotetraploid is a hybrid that has a chromosome set 4 times that of a haploid organism. Allotetraploids are created as a result of both chromosome sets of each parents being present in gametes.

Alluvial Soil

Fertile soil that can be found in aquatic communities.


Thought to be in response to stress, this condition results in hair loss in humans.

Alternation of Generations

A unique occurrence where one generation reproduces sexually then the next reproduces asexually.


Pertaining to offspring that require supervision and care from their parents after birth, where they are supplied with shelter, food and protection.

Alzheimer's Disease

A disease of the central nervous system, with symptoms including memory loss which increases over time until the body is no longer able to function due to the bodies inability to process the electrical signals via the degrading nervous system.


Pertaining to the surrounding environment or prevailing conditions.

Amino Acid

Amino acids are transcribed from DNA and form proteins when connected in chains. 20 of these amino acids are common in proteins.

Amino Acid Sequence

Pertaining to the sequencing of amino acids that create the protein they are coded for.


A colourless gas, chemical formula NH3.


The amnion is a fluid filled sac that forms around a foetus and its main function is to provide protection to the foetus.


An animal that possesses an amnion. See amnion.

Amniotic Cavity

The space found between the amnion in an amniote.


A drug that stimulates the central nervous system , and can both physically and psychologically addictive when overused. This drug is abused recreationally.


Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.


Sexual reproduction.

Amphivasal Bundle

A vascular bundle where the xylem tissue of the plant covers the circumference of the phloem.


Amylase is an enzyme that can break down starch, a polysaccharide into more simple and readily usable sugars. The enzyme is present in the saliva of mouth to begin breakdown of foodstuff, though most of its activity is in the stomach in mammals. In plants, amylase is commonly used in seeds, where amylase breaks down starch into a sugar which can be used by the embryo to induce growth.


A state of suspended animation.


An energy requiring type of metabolism where complex molecules are synthesised from more simple ones, such as in photosynthesis where light energy is used in the process to a more usable energy form by the plant.


Pertaining to animals that live their lives in the sea and migrate to a freshwater river to spawn.


A condition of the blood where red blood cells are in some way not operating to their required optimum level, maybe due to a lack in number or their haemoglobin content, which supports their function in absorbing blood and transporting it through the body.


Organisms that can undergo anaerobic respiration as a means of survival (without oxygen). When oxygen is present, some of these organisms undergo aerobic respiration where energy production from the substrate can be more effective.

Anaerobic Respiration

Anaerobic respiration is effectively respiration without the presence of oxygen. This involves step 1 of respiration, glycolysis, but after this the oxygen requiring stages cannot be executed and only a small net gain of ATP is produced.


Substances (particularly used in medicine) that reduce pain without the unwanted side effect of unconsciousness.

Analogous Structures

Structures found in various species that may have the same function, but have originated from somewhere different on the evolutionary chain. See convergent evolution.


Pertaining to plants lacking stamens.


An allergic reaction in response to the return of a particular antigen in the body of the organism.


Opposite of cell specialisation, cells retire from their specialised form into a more simplistic, unspecialised cell.


Pertaining to looping structures such as the Loops of Henle in the kidney.


The biological science that focuses on the structure of organisms.


Any type of male hormone that is involved in expressing secondary male characteristics that would not occur in a female.


The development of secondary male characteristics (deepening of voice, more body hair etc.) via androgen hormones.


Anemophily is the cross pollination between plants as a result of male gametes fertilising a plant via the wind. Adaptations in plants that undergo anemophily as a means of fertilisation are apparent in their physical appearance, where structures are present as a means of catching the pollen.


Organisms that possess that lack 1 or possess 1 extra chromosome in their chromosome set, such as Down's Syndrome sufferers who possess 47 chromosomes (46 being the norm in humans), 1 more than the species chromosome number.


Pertaining to the arterial walls, which become dilated perhaps due to weakening of the artery wall itself. The dilation can be a result of the force brought about by blood pressure.


Pertaining to plants that contain seeds enclosed in the ovary.


An old unit of measurement, 1 angstrom equalling ten thousandths of a micron.


Any organism under the animal kingdom classification of taxonomy.

Animal Kingdom

All animals on Earth are found in the animal kingdom taxonomic classification. Animals are divided into various subcategories to further define them, namely division, class, order, family, genus and species. Each classification matches similar organisms related physically, anatomically or behaviourally in some way. The similarities are closer as you move down the divisions, classes etc until unique species are defined in their own right.


A condition where joints in an animal such as the elbow or knee that are unable to operate to their potential, as a result of a wearing down of the joint surfaces.

Annotated Diagram

A diagram with a series of explanatory notes.

Annual Plants

Annual plants circadian rhythms are all positioned round them living their lifecycle in the space of a year, mostly Summer, and produces new seeds for the next generation for the next year.

Annual Rings

Internal circles within a tree marking the circumference of the tree (and therefore its size) each successive year. This is due to anatomical reasons within a tree involving the transports of nutrients and water up and down the plant.

Annular Thickening

Annular thickening occurs in tree and particularly the xylem tissue devoted to transporting water. The thickening of these cells provide stability within the structure of the plant.


A description of a cell lacking in oxygen. See anoxygenic.


A producer of oxygen


Opposing forces/factors which inhibit or cancel out the effect of another factor/force.

Antagonistic Muscle

A muscle that acts as the opposing force in contraction or relaxing of a muscle. An example of this is the the contraction of the biceps, where the triceps would be the antagonistic muscles. See antagonism.


In most organisms the antennae is a structure found on the head performing a sensory function such as touch or sight.


The part of a plant that produces the male gametes used in reproduction. Pollen grains develop by meiosis providing half the genetic information required to produce the offspring.


Pertaining to the evolution of humans.


Genes that are capable of cancelling out the lethal consequences of a tumour being malignant.


A chemical substance that inhibits the effects of auxins found in plants.


Antibiotics are used in medicine due to their capability of inhibiting or neutralising alien agents that enter the human body. Antibiotics are naturally produced by organisms as a means of defense and hence survival. Through natural selection, organisms that fall prey to antibiotics begin to develop a resistance, and the effects of the antibiotics diminish over time until the organisms are immune to its effect.


Antibodies are produced as a means of secondary defense against foreign agents entering the body. They consist of a protein and are structured and coded to react to a specific antigen. Antibodies can either be produced by direct exposure to a new type of foreign agent (active immunity) or via passive immunity, such as when a mammal sibling receives antibodies via the milk from its mother.

Anticoding Strand

The DNA sequence responsible for the coding of a particular mRNA sequence, such as the sequence for a particular protein.


See tRNA

Antidiuretic Hormone

More commonly known as ADH.


Antigens are considered to be foreign agents within an organism, and therefore must be removed so that the body can continue with its normal cellular processes without hindrance. These antigens produce an immune response by the organism in response to their presence.

Antigenic Drift

An occurrence where the surface of antigens is altered, possibly as a means of overcoming immune responses in organisms that they live in. This results in the coding of antibodies to combat the antigens must be altered to accommodate for the change in surface (which the antibody would bind to at the receptor site).


Substances that inhibit the effect of gibberellins.


One of the main arteries involved in carrying oxygenated blood around the body. It supplies many of the main organs in the torso of the body, and branches off into tributary arteries that direct blood to more remote areas of the body.


Pertaining to plants that do not possess petals.


A type of brain damage affecting communication capabilities in the organism.


Pertaining to the aphotic zones and organisms within.

Aphotic Zone

An area in a depth of water where light cannot reach, resulting in a lack of light for photosynthetic activity and therefore autotrophic organisms.


Relating to plants that do not possess leaves.


In relation to the apex of a stem in plants (the shoot tip).

Apical Dominance

A condition where vertical growth supercedes lateral growth in a plant. This is controlled by auxins, where in high concentrations can inhibit growth but on the whole promote it. Removal of the apex can induce lateral growth.

Apical Growth

Growth promoted by the apical meristem region of plants (at the root and shoot tips).

Apical Meristem

Meristems are areas in plants where mitosis occurs, and due to this cell division, it is also where growth occurs. Lateral Meristems can be found at the tip of lateral growths in the plant while the apical meristems responsible for vertical growth can be found at the root and shoot (apex) tips.

Apical Region

Pertaining to the meristems in the root and shoot tips.


A result where an organ fails to develop completely or not at all.


Pertaining to organisms that lack legs.


An organ important to herbivores as it is responsible for the breaking down of cellulose which composes the cell wall. Over time, the appendix has become redundant in animals such as humans and are no longer an essential organ in our daily functions.

Aquatic Respiration

Respiration occurring in aquatic communities by organisms that are adapted to do so. These organisms most usually have their respiratory organisms in direct contact with the environment to ensure that sufficient oxygen is up taken to be used in cellular processes.

Aqueous Habitat

Pertaining to water environments.

Arable Farming

An occurrence where man has harnessed the power of land to produce crops as a means of food.


Viruses that are transmitted via the arthropod taxonomic classification of animals.


A Kingdom taxon that belongs under the Superkingdom Procaryota. Organisms that belong to this taxon possess cell walls and a single chromosome, and are of unicellular nature. Archaebacteria are some of the most primitive organisms to have existed on Earth, and are found far back on the evolutionary chain.


Shorthand for arginine, a common amino acid found in proteins.


An amino acid that is a common part of many proteins.


A Greek philosopher who was one of the first to seriously approach taxonomy, and classed species on their habitat and their general appearance.


Arterioles are responsible for carrying oxygenated blood from the heart to all over the body. These arterioles get progressively smaller the more distanced they are from the heart, as most of the blood supply is required by the major organs positioned close to the heart and is provided by the arteries.


An artery carries large volumes of oxygenated blood to the major organs of the body. These arteries eventually branch off into smaller arterioles which transport blood to more remote areas in the body.


A condition that results in inflammation of the joints causing pain when moved.


Connection by means of a joint.

Artificial Selection

More commonly known as selective breeding, where professionals study the genotype and phenotype of parent organisms in the hope of producing a hybrid that possesses many of the desirable characteristics found in their parents.

Ascorbic Acid

More commonly known as Vitamin C which is found in citrus fruits and some green vegetables. Lack of this vitamin can result in scurvy.

Asexual Reproduction

Asexual reproduction results in the creation of offspring without the need for specialised gametes (male and female) to fuse into a zygote. This means that a species which undergoes asexual reproduction may be isolated in an environment but still capable of reproducing. On the other hand, producing offspring from its own DNA results in a clone of itself, and therefore does not increase genetic variation in the species as a whole.


Shorthand for asparagine, a common amino acid found in proteins.


Shorthand for aspartate, a common amino acid found in proteins.


An amino acid that is a common part of many proteins.


A type of amino acid, also referred to as aspartic acid.


Pertaining to the direction in which an object is facing, most commonly used to describe which part of an environment receives sunlight due to the face of the landscape.


Suffocation, due to a lack of oxygen.

Assortative Mating

Describing the occurrence where organisms of similar phenotypes reproduce.


A respiratory condition that is aggravated by small particles entering the lungs. The effects that an asthmatic sufferer feels is due to the narrowing of tubes in their respiratory system which make breathing harder, though this effect can be relaxed with particular drugs that relax the muscles involved.


An emergence of a characteristic in a blood line that has been absent for some generation and then re-appears.


Relating to the condition of arteries and arterioles, atheroma is the degeneration of the lining of these tissues.


A piece of apparatus most commonly used to measure transpiration.

Atomic Weight

A way of measuring atoms and molecules at the atomic level, where hydrogen, the lightest element in the periodic table has an atomic weight of 1.


See Adenosine Triphosphate.


A chamber found in the heart that receives deoxygenated blood from the body.


The reduction in size of tissue or organ, possibly after disease. For example when breaking an arm, the arm is temporarily put in a cast for the bone to heal in position. In light of this, many of the muscles in the arm lay unused for a period of time, and begin to waste away due to their redundancy.

Auditory Canal

The canal that leads from the outer ear to the ear drum, carrying wavelengths of sound that can be amplified by the ear drum and interpreted by the brain.

Auditory Nerve

The nerve responsible for carrying messages from the ear to the brain, where sounds can be interpreted by the brain.


The study of the environment in relation to one species as opposed to the study of the environment affecting species in the area as a whole.


An occurrence where naturally occurring substances in an organism are mistaken as foreign agents and therefore are subject to attack from antibodies.

Autonomic Nervous System

Also known as the involuntary nervous system, this part of the system executes actions unconsciously in the organism. See sympathetic and parasympathetic nervo.


An occurrence where both sets of chromosomes in parents have been duplicated in the offspring, sometimes resulting in the formation of a new species.

Autosomal Gene

A gene present on an autosome.

Autosomal Inheritance

Phenotypical characteristics that are inherited via the autosomes from parents regardless of parents sex.

Autosomal Set

Pertaining to all the chromosomes of an organisms genome bar the sex chromosomes.


Autosomes are all the chromosomes found in an organism barring its sex chromosomes. These autosomes carry a bulk of the genetic information required to create a fully functioning organism.


Autotrophic organisms are capable of synthesising organic materials from inorganic material, such as a plants who obtain their energy from the sun to fund this reaction. These organisms are essential in ecosystems as they are the main contributors of the net energy in a particular system.


Pertaining to autotrophs


An auxin is a growth regulating substance that can be found in the meristems of plants. The concentration of auxin has the deciding effect on how much (and where) growth occurs in a plant.

Avoidance Behaviour

Animals are capable of behaving in particular ways to a stimulus. If a particular aspect of the external environment possesses a threat, the organism in question will exhibit avoidance behaviour to avoid any potential escalation in the situation at hand. This typically involves a retreat, which will either physically remove the organism from the situation (running away) or exhibiting characteristics to illustrate the animals intentions. Behaviour is unique to each animal, for instance, batesian mimicry by butterflies (colourful, dangerous like wings) is used to initiate such avoidance behaviour in organisms that would otherwise be a danger to the butterfly. Also see habituation.


Part of the nerve cell that conducts electrical impulses.

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