ORC_A Level Biology; Homeostasis Summary Notes
5.1 Communication & Homeostasis
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
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,5.1 Communication & Homeostasis
The human nervous system
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, 5.1 Communication & Homeostasis
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), decision-
making centres in the central nervous system, and effectors such as muscles and
glands
Page 2
5.1 Communication & Homeostasis
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
Page 1
,5.1 Communication & Homeostasis
The human nervous system
Page 3
, 5.1 Communication & Homeostasis
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), decision-
making centres in the central nervous system, and effectors such as muscles and
glands
Page 2
