Practical: Temperature & Development of Organisms
- Evidence from the natural world indicates that global warming affects the development of living organisms
- It is possible to investigate the effect of temperature change on development in the laboratory
- This enables the elimination of other factors that might influence development e.g. light intensity or food availability
- It is possible to investigate the effect of temperature on
- Seedling growth rate
- Rate of hatching in brine shrimp
Temperature and seedling growth rate
- Plant seeds of the same plant variety in several pots or trays of compost
- Ensure that all seeds are kept in identical conditions at this stage
- Allow the seeds to germinate and produce some initial days of growth
- Measure the initial height of every seedling
- Place each pot or tray into an incubator at a different temperature for the same amount of time e.g. 5 days
- During this time ensure that all factors other than temperature are kept the same e.g. soil moisture, soil pH, light intensity
- After the allotted time remove the seedlings from the incubators and record the final height of every seedling
- Use the measurements and the following formula to calculate the average growth rate of seedlings in each incubator per day
average growth rate = average change in seedling height for incubator days of incubation
Seedling growth rate increases as temperature increases up to 25 °C, after which growth rate decreases. This could be due to cellular enzymes denaturing at high temperatures.
Temperature and brine shrimp hatching
- Place an equal number e.g. 40 brine shrimp eggs into a series of water baths at different temperatures
- Water baths should contain non-chlorinated water with 2 g of salt added per 100 cm3
- A magnifying lens may be needed to count the eggs
- A wet piece of paper can be used to pick up and transfer the eggs to the water bath
- Ensure that all factors other than temperature are kept the same between water baths e.g. age of shrimp eggs, water pH, water volume, dissolved oxygen concentration
- Observe and record the number of brine shrimps that hatch at set time intervals e.g. every 12 hours
- A bright lamp can be used to illuminate the water bath and count the hatchlings
- Use the number of eggs hatched to calculate the hatching rate per hour
hatching rate = number of hatched shrimp eggs hours in water bath
Shrimp hatch rate increases as temperature increases up to a temperature of 25 °C, after which hatch rate decreases
- Note that brine shrimps are living organisms and so welfare considerations should be taken into account when using them for experimental purposes
- Hatched shrimps should be returned to a suitable environment that replicates their natural habitat at the end of the experiment
- Any handling and transfer of hatched shrimps should be carried out gently and quickly
- Dangerously high temperatures should not be used
- Any bright lamp used for observation should be switched off when not in use