Biology Spec Led Revision
Chapter 16 - Communication and Homeostasis
(c) The principles of homeostasis
Responding to their Environment Helps Organisms Survive
• Animals increase their chance of SURVIVAL by responding the CHANGES in their EXTERNAL
ENVIRONMENT
• hey also respond to changes in their INTERNAL ENVIRONMENT to make sure the conditions
are always OPTIMAL for their METABOLISM
• Any change in the internal or external environment is called a STIMULI
Receptors can Detect Stimuli and Effectors Produce a Response
• Receptors detect stimuli
• Receptors are SPECIFIC - only detect a specific type of stimulus
• There are many different types of receptors which each detect a different type of stimulus
• Some receptors are CELLS e.g. Photoreceptors and receptor cells of the nervous system
• Some receptors are PROTEINS on Cell Surface Membranes e.g. Glucose receptors are proteins
on membranes of pancreatic cells
• EFFECTORS are cells that bring about a RESPONSE to a STIMULUS to produce an EFFECT
• EFFECTORS include MUSCLE CELLS and cells found inside GLANDS
Communication Can Occur Between Adjacent and Distant Cells
To produce a response, receptors need to COMMUNICATE with EFFECTORS and effectors may
need to, in turn communicate with other cells
This happens via CELL SIGNALLING
Cell signalling can occur between ADJACENT cells or between DISTANT cells
Cells in the nervous system communicate by SECRETING NEUROTRANSMITTERS
The hormonal system communicate by secreting HORMONES
CELL SURFACE RECEPTORS allow cells to RECOGNISE the chemicals involved in cell signalling
Homeostasis is the Maintenance of a Constant Internal Environment
• Homeostasis involves CONTROL SYSTEMS which keep your INTERNAL ENVIRONMENT
constant
• Keeping the internal environment constant is vital for maintaining cell function
• It is particularly important to maintain the correct CORE TEMPERATURE as this can affect
ENZYME CONTROLLED reactions within the body, and the rate of metabolic reactions etc
• It is also important to maintain the correct level of GLUCOSE in the body to ensure there is
enough in the body, available for RESPIRATION
Homeostatic Systems Detect a Change and Respond by Negative Feedback
• Involves RECEPTORS, COMMUNICATION SYSTEMS and EFFECTORS
• Receptors detect when a level is TOO HIGH or TOO LOW and information is communicated via
the NERVOUS SYSTEM or the HORMONAL SYSTEM to EFFECTORS
• The effectors COUNTERACT the change
• The mechanisms RESTORES the level to NORMAL is called a NEGATIVE FEEDBACK
mechanism
• Negative feedback can only work within LIMITS if the change is too big then EFFECTORS may
not be able to counteract it
Chapter 16 - Communication and Homeostasis
(c) The principles of homeostasis
Responding to their Environment Helps Organisms Survive
• Animals increase their chance of SURVIVAL by responding the CHANGES in their EXTERNAL
ENVIRONMENT
• hey also respond to changes in their INTERNAL ENVIRONMENT to make sure the conditions
are always OPTIMAL for their METABOLISM
• Any change in the internal or external environment is called a STIMULI
Receptors can Detect Stimuli and Effectors Produce a Response
• Receptors detect stimuli
• Receptors are SPECIFIC - only detect a specific type of stimulus
• There are many different types of receptors which each detect a different type of stimulus
• Some receptors are CELLS e.g. Photoreceptors and receptor cells of the nervous system
• Some receptors are PROTEINS on Cell Surface Membranes e.g. Glucose receptors are proteins
on membranes of pancreatic cells
• EFFECTORS are cells that bring about a RESPONSE to a STIMULUS to produce an EFFECT
• EFFECTORS include MUSCLE CELLS and cells found inside GLANDS
Communication Can Occur Between Adjacent and Distant Cells
To produce a response, receptors need to COMMUNICATE with EFFECTORS and effectors may
need to, in turn communicate with other cells
This happens via CELL SIGNALLING
Cell signalling can occur between ADJACENT cells or between DISTANT cells
Cells in the nervous system communicate by SECRETING NEUROTRANSMITTERS
The hormonal system communicate by secreting HORMONES
CELL SURFACE RECEPTORS allow cells to RECOGNISE the chemicals involved in cell signalling
Homeostasis is the Maintenance of a Constant Internal Environment
• Homeostasis involves CONTROL SYSTEMS which keep your INTERNAL ENVIRONMENT
constant
• Keeping the internal environment constant is vital for maintaining cell function
• It is particularly important to maintain the correct CORE TEMPERATURE as this can affect
ENZYME CONTROLLED reactions within the body, and the rate of metabolic reactions etc
• It is also important to maintain the correct level of GLUCOSE in the body to ensure there is
enough in the body, available for RESPIRATION
Homeostatic Systems Detect a Change and Respond by Negative Feedback
• Involves RECEPTORS, COMMUNICATION SYSTEMS and EFFECTORS
• Receptors detect when a level is TOO HIGH or TOO LOW and information is communicated via
the NERVOUS SYSTEM or the HORMONAL SYSTEM to EFFECTORS
• The effectors COUNTERACT the change
• The mechanisms RESTORES the level to NORMAL is called a NEGATIVE FEEDBACK
mechanism
• Negative feedback can only work within LIMITS if the change is too big then EFFECTORS may
not be able to counteract it
