A2 biology key terms

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  • Created on: 11-12-12 16:46
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Module 1
A stimulus is any change in the environment that causes a response.
A response is a change in behaviour or physiology as a result of a change in the environment.
Homeostasis is the maintenance of the internal environment in a constant state despite external
Negative Feedback is a process that brings about a reversal of any change in conditions. It ensures
that an optimum steady state can be maintained, as the internal environment is returned to its
original set of conditions after any change.
Positive Feedback is a process that increases any change detected by the receptors. It tends to be
harmful and does not lead to homeostasis.
An ectotherm is an organism that relies on external sources of heat to regulate its body
An endotherm is an organism that can use internal sources of heat, such as heat generated from
metabolism in the liver, to maintain its body temperature.
A polarised membrane is one that has a potential difference across it. This is the resting potential.
Depolarisation is the loss of polarisation across the membrane. It refers to the period when sodium
ions are entering the cell making the inside less negative with respect to the outside.
The resting potential is the potential difference or voltage across the neurone cell membrane while
the neurone is at rest. It is about -60mV inside the cell compared with the outside. Other cells may
also maintain a resting potential that might change under certain circumstances.
Voltage-gated channels are channels in the cell membrane that allow the passage of charged
particles or ions. They have a mechanism called a gate which can open and close the channel. In these
channels the gates respond to changes in the potential difference across the membrane.
The threshold potential is a potential difference across the membrane of about -50mV. If the
depolarisation of the membrane does not reach threshold potential then no action potential is
created. If the depolarisation reaches the threshold potential then an action potential is created.
The action potential is a depolarisation of the cell membrane so that the inside is more positive that
the outside, with a potential difference across the membrane of +40mV. This can be transmitted
along the axon or dendron plasma membrane.

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Local currents are the movements of ions along the neurone. The flow of ions is caused by an
increase in concentration at one point, which causes diffusion away from the region of higher
Saltatory conduction means `jumping conduction'. It refers to the way that the action potential
appears to jump from one node of Ranvier to the next.
A neurotransmitter is a chemical that diffuses across the cleft of the synapse to transmit a signal to
the postsynaptic neurone.…read more

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Hyperglycaemia is the state in which the blood glucose concentration is too high.
Hypoglycaemia is the state in which the blood glucose levels are too low.
Genetically engineered bacteria re those in which the DNA has been altered. In this case a gene
coding form human insulin has been inserted into the DNA of the bacteria.
Stem cells are unspecialised cells that have the potential to develop into any type of cell.…read more

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Module 2
Excretion is the removal of metabolic waste from the body.
Metabolic waste consists of waste substances that may be toxic or are produced in excess by the
reactions inside cells
Egestion is the removal of undigested food by the process of defecation.
Deamination is the removal of the amine group from an amino acid to produce ammonia.
The hepatic portal vein is an unusual blood vessel that has capillaries at both ends- it carries blood
from the digestive system to the liver.…read more

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Detoxification is the conversion of toxic molecules to less toxic or non-toxic molecules.
The nephron is the functional unit of the kidney. It is a microscopic tubule that receives fluid from the
blood capillaries in the cortex and converts this to urine, which drains into the ureter.
The glomerulus is a fine network of capillaries that increases the local blood pressure to squeeze
fluid out of the blood.…read more

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The hypothalamus is a part of the brain that contains neurosecretory cells and various receptors
that monitor the blood.
Neurosecretory cells are specialised cells that act like nerve cells but release a hormone into the
blood. ADH is manufactured in the cell body and passes down the axon to be stored in the terminal
bulb. If an action potential passes down the axon then ADH is released from the terminal bulb.…read more


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