Science 7 · Unit 7: Microorganisms in the environment · Cambridge Lower Secondary Science Stage 7

Questions

1. 1. Which of these is a microorganism?

   • an ant
   • an earthworm
   • a bacterium
   • a snail
   Check

2. 2. Marcus compares microorganisms in the air of two classrooms. What should he collect first?

   • an empty test tube
   • a dish containing sterile agar jelly
   • a jar of soil
   • a dish of tap water
   Check

3. 3. Why must the agar jelly be sterile at the start?

   • so the only microorganisms that grow come from the classroom air
   • so the jelly sets faster
   • so the dish is easier to label
   • so the jelly is a nicer colour
   Check

4. 4. Why does Marcus label the base of the dish, not the lid?

   • Pens do not write on plastic lids.
   • The lid is too small to write on.
   • The lid could get swapped with another dish.
   • The label would block the light.
   Check

5. 5. Marcus has labelled the base of his dish with the classroom number. What is the next instruction?

   • Place the dish in the classroom and take off the lid.
   • Collect a dish of sterile agar jelly.
   • Tape the lid onto the base.
   • Put the dish upside down in the laboratory.
   Check

6. 6. What does Marcus do after taking the lid off in the classroom?

   • He pours water on the jelly.
   • He puts the lid back on after five minutes.
   • He leaves the lid off for five days.
   • He touches the jelly with his finger.
   Check

7. 7. Why does Marcus tape the lid onto the dish?

   • so it is not opened, as some microorganisms may be harmful
   • so more air can get in
   • so the jelly does not melt
   • so the dish looks neat
   Check

8. 8. Why does Marcus put the dish upside down in a safe place?

   • so the microorganisms fall out
   • so water drops do not fall onto the jelly
   • so the light can reach the jelly
   • so the label is on top
   Check

9. 9. Which variable does Marcus change in his experiment?

   • the room where he puts the dish
   • the length of time the lid is off
   • the type of jelly in the dish
   • the type of pen he uses
   Check

10. 10. Which variable should Marcus keep the same?

    • the colour of his shirt
    • the length of time he leaves the lid off
    • the room where he puts the dish
    • the type of pen he uses
    Check

11. 11. Which other variable should Marcus keep the same?

    • the room where he puts the dish
    • the name on the label
    • the type of pen he uses to label the dish
    • the type of jelly in the dish
    Check

12. 12. Why doesn't the type of pen matter?

    • The label is on the lid.
    • Pens kill microorganisms.
    • It does not affect how many microorganisms grow.
    • All pens are the same.
    Check

13. 13. After five days, the Classroom 203 dish has many more spots (colonies) than the Classroom 204 dish. What can Marcus conclude?

    • There are more microorganisms in the air in Classroom 203.
    • There are more microorganisms in the air in Classroom 204.
    • Both rooms have the same microorganisms.
    • The jelly in 203 was not sterile.
    Check

14. 14. Which hypothesis could Marcus test with Petri dishes and agar jelly?

    • Bacteria grow faster at 30 °C than at 10 °C.
    • Bacterial cells are smaller than yeast cells.
    • All bacteria are single-celled.
    Check

15. 15. How could Marcus test whether bacteria grow faster at 30 °C than at 10 °C?

    • Put identical dishes at 30 °C and 10 °C, and compare the colonies after the same time.
    • Put one dish at 30 °C and look at it after one minute.
    • Put dishes at different temperatures for different times.
    • Use different types of jelly at each temperature.
    Check