9.2 Applications and skills

9.2.3 Lab: Factors affecting germination

When certain conditions are met, germination occurs in a stereotyped sequence, as described on Page 9.1.3. Germination converts energy in the seed to produce the first roots and shoots of a plant. In this activity, you will investigate how temperature affects the rate of respiration in germinating seeds, using an apparatus called a respirometer.

Activity

This activity will take at least two classes to perform. Work in pairs.

Materials

  • Plastic beads
  • Dried peas or beans
  • Calibrated glass tubing (pipette)
  • Shallow tray
  • Glass vial and fitted rubber stopper (hole for pipette)
  • Cottonwool (absorbent)
  • Nylon wool (non-absorbent)
  • Concentrated koh solution (15%)
  • Pasteur pipette
  • Food colouring
  • Thermometer

 Instructions

  1. Soak some dried peas for 48 hours in water. Make sure the volume of water is at least twice the volume of peas to allow for imbibation.
  2. Dampen a measured mass of cottonwool in 15% KOH solution and place the damp cotton at the bottom of each glass vial. Cover the cotton with nylon. Then add a measured volume of soaked peas atop the nylon. Place the bung on the vial and place the pipette through the hole in the bung. You may need to seal the bungs with parafilm or petroleum jelly. These vials will become your test respirometers.
  3. Using a second set of glass vials, repeat step 2, but replace the soaked (germinating) peas with dry (non-germinating) peas.
  4. In a third set of vials, place a mixture of dried peas and plastic beads. Sets two and three are your controls. 

    respirometers

    Figure 9.2.3a – Respirometers
    Make sure to control the volume of the contents in each vial.
  5. Fill the shallow trays with water of varying temperatures. Submerge the respirometers in water, leaving the pipette tips on the edge of the trays. Let the gas in the respirometers equilibrate for 10 minutes.
  6. Using a Pasteur pipette, add a drop of food colouring into the tapered end of the pipette. Gently lower the glass tube into the water bath, being careful to keep the tubes horizontal. You may need to use a piece of tape to keep the pipette tips level. You may also need to weigh down the respirometers to keep them from floating around in the water.
  7. As oxygen is consumed, the coloured water is drawn into the tube. Measure the volume of oxygen consumed every 30 seconds.

lab set-up

Figure 9.2.3b – Lab set-up
This diagram shows only one experimental trial (germinating peas). You should have more than one in order to have more reliable results. 

Conclusion and discussion

When you have finished collecting your data, answer the following questions:

  • At which temperature is the rate of oxygen consumption highest? Lowest?
  • What is the relationship between rate of respiration and temperature?

Discuss the relevance of the following steps in the procedure:

  • Adding KOH to each of the vials.
  • Using two types of control (dried peas/dried peas and beads).

In the lab

  • How does changing the soaking conditions (duration, temperature and quality of water) affect the rate of respiration? Design an experiment to find out.
  • Make sure the temperatures you choose are biologically appropriate. Too high or too low temperatures will de-activate the enzymes involved in respiration.