Practicals

Question 1

Experiment to determine energy content of a sample (seed for example here) (6)

Answer 1

• ignited sample (seed)
• use calorimeter
• complete combustion
• measure mass / volume of water
• measure temperature increase
• repeat

Question 2

Experiment to show the phototropic response of plant stems to light

Answer 2

• (one shoot) with light from one side
• (other shoot) with light from the other side
• leave both plants for 5 days
• look at the bending of the plants

Question 3

Using hydrogen-carbonate indicator to investigate the effect of light intensity on net gas

Answer 3

• (vary light intensity by): move lamp / cover a leaf (/ leaves) with foil
• leaf in test tube with bung (to prevent gas exchange)
• (look for color change after) same time
• same species of leaf / plant
• same temperature / same volume of indicator
• yellow with increased CO2 in dark OR
• red with reduced CO2 in light

WHAT COLOURS MEAN:

• if yellow:
• means that CO2 was released from respiration only
• so high CO2 levels
• so leaf was in the dark
• (since only respiration)
• if red:
• means CO2 was used up in photosynthesis
• so low CO2 levels
• so leaf was in the light
• (since you need light energy for photosynthesis)

Question 4

What results of light intensity + gas exchange hydrogen carbonate indicator practical mean

Answer 4

• if yellow:
• means that CO2 was released from respiration only
• so high CO2 levels
• so leaf was in the dark
• (since only respiration)
• if red:
• means CO2 was used up in photosynthesis
• so low CO2 levels
• so leaf was in the light
• (since you need light energy for photosynthesis)

Question 5

How to use: a boiling tube; mounted needle; (plant) food sample; thermometer; Bunsen burner for calorimetry experiment

Answer 5

• fill boiling tube with 50cm3 of water
• (burn plant / sample with Bunsen burner) and hold the sample beneath the water
• allow sample to burn completely (relight if needed)
• measure temperature before and after
• do: Q = mc ΔT
• measure mass of sample
• repeat + calculate average

Question 6

Use of controls in practicals

Answer 6

• controls
• comparison

Question 7

Practical for how light intensity affects photosynthesis

Answer 7

• leaves in light + dark
• (measure) glucose
• using Benedict’s solution
• control species

Question 8

Investigating the effect of pH on enzyme activity practical

Answer 8

1. Add one drop of iodine to each well of dimple tray
2. Use syringe and 1cm’ of amylase to 1cm’ of pH solution
3. Add 1cm of Starch solution to the amylase test tube
4. Press the start button on the timer
5. Every 20s add a drop of amylase solution to a well
6. If it stays blue/black, starch still present
7. After 20s another drop of amylase solution to a well
8. If iodine stays yellow, all starch has been broken down
9. Record the time it took, and repeat for another pH