Biology Book 2

abiotic factors

the non-living elements of the habitat of an organism

absolute refractory period

• first millisecond or so after the action potential

• it is impossible to re-stimulate the fibre

• sodium ion channels are completely blocked

• resting potential has not been restored

absorption spectrum

a graph showing the amount of light absorbed by a pigment against the wavelength of light

abundance

the relative representation of a species in a particular ecosystem

acetyl coenzyme A (acetyl CoA)

• 2C compound

• produced in the link reaction which feeds directly into Krebs cycle

• combines with a 4C organic acid to form a 6-carbon compound

acetylcholine (ACh)

neurotransmitter in:

• parasympathetic nervous system

• synapses of motor neurones

• cholinergic synapses in brain

acetylcholinesterase

• enzyme found within post-synaptic membrane of cholinergic nerves

• triggers a post-synaptic potential

• then breaks down acetylcholine in the synapses

ACFOR scale

a simple scale used to describe the abundance of a species in a given area

acquired immunodeficiency syndrome (AIDS)

• disease which results from the destruction of the T helper cells

• is a result of infection with HIV

actin

one of the proteins which form the contracting mechanism of muscle cells

action potential

when the potential difference across the membrane is

• briefly reversed to about +40 mV on the inside with respect to the outside

• for about 1 millisecond

action spectrum

a graph demonstrating the rate of photosynthesis against the wavelength of light

actomyosin

the chemical produced when cross-bridges form between actin and myosin during muscle contraction

adenosine diphosphate (ADP)

a nucleotide formed when a phosphate group is removed from ATP in a hydrolysis reaction, providing energy to drive reactions in the cell

adenosine triphosphate (ATP)

• a nucleotide that acts as the universal energy supply in cells

• made of the base adenine, the pentose sugar ribose, and three phosphate groups

adrenaline

hormone produced by the adrenal glands which stimulates the fight or flight response

adrenergic nerves

nerves using noradrenaline as their synaptic neurotransmitter

aerobic respiration

the form of cellular respiration that occurs in the mitochondria in the presence of oxygen

agglutination

the grouping together of cells caused when antibodies bind to the antigens on pathogens

agranulocytes

leucocytes:

• with round nuclei

• without granules in their cytoplasm

• involved in the specific immune response to infection

allopatric speciation

an evolutionary process that occurs when populations become physically or geographically isolated

amplified

the process by which DNA is replicated repeatedly (using the polymerase chain reaction) to produce a much bigger sample

anaerobic respiration

the form of cellular respiration that occurs in the cytoplasm when there is no oxygen present

antagonistic pairs

• muscles which work in opposition to each other

• pull in opposite directions