OCR A Level Biology -The Need For Homeostasis.

OCR A Level Biology -The Need For Homeostasis. OCR A Level Biology Revision Notes 5.1 Communication & Homeostasis YOUR NOTES ⬇ © Save My Exams Ltd OCR A Level Biology Resources REVISION NOTES TOPIC QUESTIONS PAST PAPERS Page 1 CONTENTS 5.1.1 The Need for Homeostasis 5.1.2 The Principles of Homeostasis 5.1.3 Cell Signalling 5.1.4 Thermoregulation 5.1.1 THE NEED FOR HOMEOSTASIS The Need for Communication Systems in Organisms Animals and plants need to be able to respond to changes in their internal and external environment and to coordinate the activities of their different organs In order to function properly and efficiently, organisms have different control and communication systems that ensure their internal conditions are kept relatively constant Physiological control systems maintain the internal environment within restricted limits through a process known as homeostasis Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function Examples of physiological factors that are controlled by homeostasis in mammals include: Core body temperature Metabolic waste (eg. carbon dioxide and urea) Blood pH Concentration of glucose in the blood Water potential of the blood Concentration of respiratory gases (carbon dioxide and oxygen) in the blood Homeostatic mechanisms in mammals require information to be transferred between different parts of the body There are two communication systems in mammals that do this: The nervous system The endocrine system OCR A Level Biology Revision Notes 5.1 Communication & Homeostasis YOUR NOTES ⬇ © Save My Exams Ltd OCR A Level Biology Resources REVISION NOTES TOPIC QUESTIONS PAST PAPERS Page 2 The nervous system The human nervous system consists of: The central nervous system (CNS) – the brain and the spinal cord The peripheral nervous system (PNS) – all of the nerves in the body It allows us to make sense of our surroundings and respond to them and coordinate and regulate body functions Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones A bundle of neurones is known as a nerve Neurones coordinate the activities of sensory receptors (eg. those in the eye), decisionmaking centres in the central nervous system, and effectors such as muscles and glands OCR A Level Biology Revision Notes 5.1 Communication & Homeostasis YOUR NOTES ⬇ © Save My Exams Ltd OCR A Level Biology Resources REVISION NOTES TOPIC QUESTIONS PAST PAPERS Page 3 The human nervous system OCR A Level Biology Revision Notes 5.1 Communication & Homeostasis YOUR NOTES ⬇ © Save My Exams Ltd OCR A Level Biology Resources REVISION NOTES TOPIC QUESTIONS PAST PAPERS Page 4 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 and bring about a change They alter the activity of one or more specific target organs Hormones are used to control functions that do not need instant responses The endocrine glands that produce hormones in animals are known collectively as the endocrine system.