QUESTIONS

1. The roots of two groups of pea plants were placed in solutions containing radioactive potassium ions. For the experimental plants a respiratory inhibitor was added to the solution. At regular intervals the solutions surrounding the roots were tested for radioactive potassium ions. The table shows the results of this investigation.

Time from placing roots in solution / minutes

Concentration of radioactive potassium ions in the solutions surrounding the roots / arbitrary units

Experimental plants

Control plants

0

7.5

7.5

15

6.6

3.3

30

6.4

2.9

60

6.3

2.4

120

6.3

1.2

240

6.3

0.6

(a)

(i)

The rate of uptake of potassium by the experimental plants in the first 15 minutes was 0.06 units per minute. Calculate the rate of uptake of potassium by the control plants over the same time period. 
 

 

 

 

(1)

(ii)

Suggest an explanation for the difference between the rates of uptake of the experimental and control plants in the first 15 minutes.
 

 

 

(2)

(iii)

The rate of potassium ion uptake in the control plants in the first hour was faster than in the second hour. Suggest why.
 

(2)

(b)  At the end of the investigation sections were cut across the stems of the pea plants and the amount of radioactivity measured. The diagram shows a section across the stem of a pea plant.

(i) Give one feature by which this section can be recognised as a stem.
 

(1)

(ii) Using a guideline, label and name the tissue in which you would expect to find the greatest amount of radioactivity.
 

(1)

NEAB 1999