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...
The Control of Blood Glucose If the concentration of glucose in the blood decreases below a certain level, cells may not have enough glucose for respiration and may not be able to function normally...
