Core Practical 12: Effect of Temperature on Development (Edexcel International A Level Biology)

• 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 shrimps

Temperature and seedling growth rate

1. 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
2. Allow the seeds to germinate and produce some initial days of growth
3. Measure the initial height of every seedling
4. 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
5. After the allotted time remove the seedlings from the incubators and record the final height of every seedling
6. 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

1. Place an equal number, e.g. 40, of 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
2. 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
3. Use the number of eggs hatched to calculate the hatching rate per hour 

hatching rate = number of hatched shrimp eggs  hours in water bath

• 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

Shrimp hatch rate increases as temperature increases up to a temperature of  25 °C, after which hatch rate decreases