The Refractory Period Very shortly (about 1 ms)?after an action potential?has been generated in a section of the axon membrane, all the?sodium ion voltage-gated channel proteins in this section?clo...
Speed of Conduction of Impulses The?speed of conduction?of an impulse refers to?how quickly the impulse is transmitted?along a neurone It is determined by two main factors: the?presence or absence ...
Transmission of Nerve Impulses Neurones?transmit?electrical impulses, which travel extremely quickly along the neurone?cell surface membrane?from one end of the neurone to the other Unlike a normal...
Sequence of Events Resulting in an Action Potential The?surface?of the?tongue?is covered in many small bumps known as?papillae The surface of each papilla is covered in many?taste buds Each taste b...
Sensory Receptor Cells A cell that?responds?to a?stimulus?is called a?receptor cell Receptor cells are?transducers?– they?convert energy?in one form (such as light, heat or sound) into energy in an...
Neurones Neurones have a?long fibre?known as an?axon The axon is?insulated?by a?fatty sheath?with small uninsulated sections along its length (called?nodes of Ranvier) The sheath is made of?myelin,...
The Nervous System The human nervous system consists of the: Central nervous system?(CNS) – the brain and the spinal cord Peripheral nervous system?(PNS) – all of the nerves in the body It allows u...
The Endocrine System A?hormone?is a?chemical substance?produced by an?endocrine gland?and carried by the?blood They are chemicals which?transmit information from one part of the organism to another...
Abscisic Acid & Stomatal Closure During times of?water stress,?the hormone?abscisic acid?(ABA) is produced by plants to?stimulate the closing of their stomata Certain environmental conditions c...
Guard Cells Structure of guard cells Each stoma is surrounded by?two guard cells Guard cells have the following features: Thick?cell walls facing the air outside the leaf and the?stoma Thin?cell wa...
Stomata Plants carry out?homeostasis?– just like animals they need to maintain a?constant internal environment For example, mesophyll cells in leaves require a?constant supply of carbon dioxide?for...
Test Strips & Biosensors Measuring urine glucose concentration People with?diabetes?cannot?control?their blood glucose concentration so that it remains within normal, safe limits The presence o...
