A student investigated the effect of temperature on the rate of respiration in yeast cells. When yeast cells respire they release carbon dioxide gas. The student used this method: Step 1 Fill a syringe with $$\(15 \mathrm{~cm}^{3}\)$$ of yeast suspension. Step 2 Gently lower the syringe into the measuring cylinder, as shown in Fig. 1.1. Step 3 Fill the measuring cylinder with hot water. Ensure that the water level in the measuring cylinder is above the syringe nozzle. Step 4 Measure the temperature of the water in the measuring cylinder. Step 5 Start the stop-clock and wait for two minutes. Step 6 After two minutes, reset the stop-clock to zero. Step 7 Start the stop-clock again and count the number of bubbles produced by the yeast suspension in three minutes. Step 8 Pour the hot water in the measuring cylinder into the waste container. The syringe containing the yeast suspension should remain in the measuring cylinder. Step 9 Fill the measuring cylinder with cold water. Ensure that the water level in the measuring cylinder is above the syringe nozzle. Step 10 Repeat steps 4 to 7. Fig. 1.2 shows the thermometer during step 4 and step 10. Fig. 1.3 shows the number of bubbles the student counted in three minutes in step 7 and step 10 Bread is made from flour, water and yeast which are mixed to form a dough. Fig. 1.5 shows a person making bread. The carbon dioxide gas produced by yeast causes the volume of the dough to increase. Sodium chloride (salt) is often added to dough when making bread. The sodium chloride affects the rate at which the yeast respire. Plan an investigation to determine the effect of the mass of sodium chloride on the volume of dough.

Answer:

Knowledge points:

Solution: