definitions for biology 2011!!

8/6/2019 Definitions for Biology 2011!!

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Word Definition

Tropism The growth or movement of a plant in response to a certain stimulus.

Phototropism The growth or movement of a plant in response to light.

Geotropism The growth or movement of a plant in response to gravity.

Chemotropism The growth or movement of a plant in response to a chemical.

Thigmotropism The growth or movement of a plant in response to touch.

Growth The permanent increase in body size by cell division or cell elongation.

Meristems Undifferentiated plant tissue consisting of actively growing and dividing cells.

Cell division The process by which a cell divides to produce 2 genetically identical

daughter cells.

Cell assimilation The absorption and incorporation of nutritive elements by plants

Cell elongation The lengthening of a cell

Red light. 580-600nm causes germination

Far red light 700-730nm inhibits germination

Phytochromes A cytoplasmic pigment that absorbs light and regulates dormancy, germinate

and growth.

Short-day plants A plant that requires long periods of darkness to initiate flowering.

Long day plants Plants which require short periods of darkness to initiate floweringDay-neutral plants Plants which will flowering in any periods of light and darkness

Critical day length The period of day light that appears to initiate or inhibit flowering of a

species.

Etiolation Paleness resulting from light deprivation

Unilateral light Light that only hits one side of a plant

Positively

phototropic

The movement or growth will be towards the light

Negatively

phototropic

The movement or growth of the plant will be away from the light

Auxin A plant hormone produced to promote longitudal growth and controls bud

formation, root formation and leaf abscission.

IAA A type of auxin C10H9NO2Allelopathy The inhibition of growth in one plant caused by chemicals released by

another.

Photoperiodism The response of an organism to changes in its photoperiod.

Vernalisation The subjection of seeds to low temperatures to hasten plant development.

Apical dominance The inhibition of the growth of lateral buds by the terminal bud of a plant

shoot

Gibberellins Plant hormones that stimulate growth in the stem and leaves, trigger seed

germination and breaking of bud dormancy.

Pheromone A chemical produced by an animal and released into the external

envorinment where it will affect the physiology or behaviour of members of

the same species.

Neurones Cells specialised for the rapid transmission fo electrical impulses from the

receptor cells to effector cells

Receptor cells Cells which detect changes in the internal or external environment.

Effector cells Cells which bring about the appropriate response to an impulse

Sensory organs Groups of receptor cells working together

Sensory neurones Carry impulses from the sensory organs to the CNS

Motor neurones Carry impulses from the CNA to effector cells

CNS Made up of the brain and spinal cord


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Axons Fibres which carry impulses away from the nerve cell body

Dendrons Fibres which transmit impulses towards the cell body

Dendrites Finger like extensions which receive impulses

Schwann cells Specialised cells which wrap themselves around the axon and Dendron

forming a myelinated sheath

Myelin sheath A nerve fibre which has been insulated by a layer of Schwann cells increasing

the speed of transmission of impulses.Nodes of ranvier The spaces between the Schwann cells in a myelinated sheath which allow

the faster transmission of the impulses by salutatory conduction.

Resting potential. The electrical potential across a nerve cell membrane before it is stimulated

to release the charge. The resting potential for a neurone is -70 mV.

Depolarisation The electrical charge change in the nerve cell from -70 mV to +35mV caused

by the influx of sodium ions, creating a positive charge inside the cell.

Repolarisation The electrical charge change in the nerve cell from +35mV to a negative value

as the potassium channels open and the potassium ions rush out of the cells.

Hyperpolarisation The over-negative shoot of the repolarisation caused by a delay in the closing

of the potassium channels.

Action potential An impulse along a nerve cell created by the depolarisation and then

repolarisation of a section of the nerve cell, followed by the next section.Threshold The level at which the depolarisation must reach for an action potneital to be

created.

Absolute refractory

period.

The period immediately following the firing of a nerve fiber when it

cannot be stimulated no matter how great a stimulus is applied

Relative refractory

period.

The period shortly after the firing of a nerve fibre when partial repolarisation

has occurred and so a secondary action potential can be generated upon the

stimulation of a stronger than normal stimulus.

Synapse. The junction between two nerve cells made up of the synaptic cleft and the

pre and post synaptic membrane.

Saltatory conduction The leaping of the action potential between the nodes of ranvier of a

myelinated nerve.

Synaptic cleft The gap between the post and pre synaptic membranes.

Acetyl choline The most abundant neurotransmitter in humans

Cholinergic nerves Nerves which have acetyl choline as a neurotransmitter

Excitatory post

synaptic potential

The partial deporlaisation of the post-synaptic membrane caused by the

influx of sodium ions caused by the uptake of neurotransmitter across the

synaptic cleft

Inhibitory post

synaptic potential.

The influx of negatively charged ions into the post synaptic membrane

caused by the uptake of neurotransmitter, leading to a more negative

potential.

Spatial summation When 2 or more pre-synaptic neurones come toagther at a synapse to

generate an action potneital in the post synaptic membrane

Temporal

summation

When 2 or more impulses from the pre synaptic neurone come together at a

synapse to generate an action potential in the post synaptic membrane.

Facilitation. In temporal summation, when the first impulse makes it easier for the

second impulse to generate an action potential as the two are added

together.

Accommodation. When over time the same stimulus will decrease its effect on the synapse in

terms of the amount of neurotransmitter released as the neurones become

fatigued.

Primary receptor A receptor made up of only neurones with a dendrite sensitive to a paryicular


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stimulus.

Secondary receptor A receptor made up of a specialised cell attached to a sensory neurone

whicih then transmits the impulse to the CNS.

Exteroceptors. Receptors which detect changes in the outside environment.

Interoceptors Receptors which detect change in the inside environment.

Proprioceptors. Sensitive to the relative positions of the skeleton and degrees of muscle

contraction.Chemoreceptors. Sensitive to chanemucal shanges eg pH of blood

mechanoreceptors Sneitive to mechanical stimuli such as pressure, movement and gravity

Photoreceptors Sensitive to electromagnetic stimuli light

Thermoreceptors. Respond to heat stimuli.


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definitions for biology 2011!!

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