1. Metabolism and Survival
Key Area 5a
Metabolism and Surviving Adverse Conditions

2. By the end of this topic you should be able to:
Explain the meaning of dormancy and give an example of organisms who use this as a means of survival
Explain the difference between predicted and consequential dormancy
Give examples of hibernation in animals and aestivation in organisms and how these help their survival in adverse conditions
Say what is meant by daily torpor and why it is important for some organisms

3. Adverse conditions
In some environments there exists extreme conditions:
Extreme heat or cold
Drought
Lack of food
These conditions can change, be cyclic or be unpredictable depending on the country and time of year. Therefore, many environments vary beyond the tolerable limits for normal metabolic activity for particular organisms.
Homeostatic control would break down as it would no longer be able to produce enough energy to bring about its corrective mechanisms to return its internal environment to the norm and so could prove fatal
In order to survive, organisms have adapted to survive or avoid these conditions

4. Surviving Adverse Conditions
Organisms can have adaptations to help them survive adverse conditions. These can be:
Structural e.g. body size, appendages, insulation, colour
Physiological e.g. dormant states such as hibernation (‘winter sleep’); aestivation (‘summer sleep’); daily torpor (small period of reduced activity)
Behavioural e.g. collective den, snow roost

5. Surviving Adverse Conditions

6. Surviving adverse conditions
When an organism finds itself in adverse conditions it will reduce its metabolic rate as it would use too much energy trying to maintain normal activity.
For instance, it would spend too much energy trying to keep warm in extreme cold conditions (or vice versa)
One way of achieving this is by entering a period of dormancy

7. Dormancy
Dormancy is part of some organisms life cycle where it temporarily reduces its growth and development by reducing its metabolic rate, heart rate, breathing rate and body temperature to the minimum required for cells to survive.
Dormancy can be predictive or consequential

8. Predictive Dormancy
An organism enters a dormant phase before the onset of adverse conditions and it is usually genetically programmed
Many trees respond to decreasing photoperiod (day length) and temperature in autumn by shedding their leaves and entering their dormant stage before winter

9. Consequential Dormancy
An organism enters a dormant phase after the onset of adverse conditions and it is usually a response by organisms living in unpredictable environments
There are advantages and disadvantages to this:
Advantage – can remain active for longer and exploit environmental resources
Disadvantage – sudden, severe change in environmental condition may kill organism before they have a chance to become dormant

10. Dormancy Examples of dormancy in animals include:
Hibernation (eg bear, dormouse)
Aestivation (snails, lungfish)
Daily Torpor (birds, mammals)

11. Hibernation
Hibernation is often defined in terms of mammals and is usually brought about to survive the adverse conditions of winter/low temperatures.
Hibernation is usually a predictive response to shortening day-length and can last weeks or months.
The mammal tends to eat extra food before hibernating which becomes a store of fat.

12. Hibernation
During hibernation the mammals metabolic rate is reduced resulting in a decrease in:
Body temperature
Herat rate
Breathing rate
General activity
This allows the mammal (bear, doormouse) to survive the period of adverse conditions

13. Aestivation
This form of dormancy allows some animals to survive periods of high temperature or drought during the summer
Aestivation is not just due to a lack of food but the conditions are too hot and dry for the animal to survive.

14. Aestivation
The process usually involves burrowing into the ground where the temperature is cooler and reducing metabolic activity in a similar manner to hibernation
Examples include:
snails seeking high branches (safer), retreating into its shell and sealing the opening with dried mucus (except a small hole for gas exchange)
Lungfish burying itself in the mud of a dried lake and surrounding itself with a layer of dried mucus until the rainy season returns (can survive like this for up to 3 years)

15. Daily Torpor
Daily torpor is a period (within 24 hours) of reduced activity in an organism which has a high metabolic rate (birds and mammals)
The physiological state changes so it is similar to short-term hibernation:
Heart rate reduces
Breathing rate reduces
Body temperature decreases
These all increase an organisms chance of survival by reducing the energy required to maintain a high metabolic rate

16. Daily Torpor
Some birds (hummingbirds) feed during the day and exhibit torpor at night whilst others (bats) feed at night and exhibit torpor during the day
These birds have a relatively large surface area through which they can lose heat. If endotherms, this means they need to have a high metabolic rate to maintain an optimum body temperature
This daily period of torpor helps reduce the level of energy consumption at times of the day when they have little chance of obtaining food or are at risk from predators