Give two examples of external stimuli
Temperature Oxygen concentration Sunlight level Water availability Nutrient levels Predation Competition
Give two examples of internal stimuli
CO2 levels O2 levels Blood glucose Temperature Water levels Salt levels
What are the two methods of cell signalling
The Nervous System
The endocrine system
What is the nervous system?
Interconnected neurones which signal to each other across synapse junctions
What is the endocrine system
Secretes hormones directly into the blood
The maintenance of internal environmental conditions despite external fluctuations
Define negative feedback
The process which brings about a reversal in the change of internal conditions
Define positive feedback
The process which increases any change detected by the receptors
e.g. Oxytocin and birth
An animal that is dependent on external sources of body heat
An animal that is dependent of the internal generation of heat
Give one example of both a physiological and behavioural response of an ectotherm
Physiological- lizards open their frills to absorb more heat from the sun
Behavioural- snakes bask on hot rocks
Give one example of both a physiological and behavioural response of an endotherm
Physiological- •sweat glands •panting •hairs on skin •vasodilation •skeletal muscle Behavioural- •move to shade or into sunlight
Why do organisms need to respond to changes in their environment?
Explain the difference between positive and negative feedback
Negative feedback monitors a change and initiates a process to reverse the change whereas positive feedback will increase the change.
Why is it important to maintain a constant body temperature?
If body temp is too low, enzyme activity falls and the rate of metabolism drops. High temp. denatures proteins such as channel proteins in the membranes.
Explain how basking can help regulate body temperature
If an ectotherm is too cool it can absorb heat from the rock and direct from the sun. This will warm up the skin and the blood flowing near the surface which will warm muscles.
Explain how vasoconstriction helps reduce heat loss.
It reduces blood flow through the skin, blood flows through vessels deeper in the body. Heat is less easily radiated out from the body.