K.C.S.E Biology Q & A - MODEL 2014PP2QN06

K.C.S.E Biology Q & A - MODEL 2014PP2QN06

An experiment was done to determine the uptake of nitrogen from the soil by broad bean seedlings. The experiment was done with one set of seedlings M grown in the atmosphere enriched with carbon (IV) oxide and another set up of seedlings N grown in the normal atmosphere.
The amount of nitrogen in each seedling was measured in milligrams at intervals often days.
The table below shows the results obtained.

​(a) Using the same axis draw line graphs of nitrogen uptake by the two (M and N) sets of broad bean seedlings against time. 
(b) Determine the rate of uptake of nitrogen in Set M between 65 and 85 days. 
(c) (i) What is the relationship between carbon (IV) oxide concentration in the air and nitrogen uptake? 
(ii) Account for the relationship in (c)(i) above. 
(d) (i) What would happen to the concentration of nitrogen in the seedlings in set M, if after 75 days the seedlings are transferred to a normal atmosphere. 
(ii) Explain your answer in (d)(i) above. 
(e) State three ways in which nitrogen fixation occurs.

answers

(c) (i) The higher the carbon UV) oxide content in air, the higher the nitrogen uptake and vice versa;
(ii) More Carbon (IV) oxide in the air makes the seedlings to photosynthesize more; hence more amino acids/protein; are formed in the dark stage; formation of amino acids/protein requires nitrogen; 
(d) (i) The concentration of nitrogen would remain constant; 
(ii) Despite decline in CO,; the nitrogen already absorbed/taken up by the plant will still remain: 
(iii) Lightning;
By free-living bacteria/micro organisms;
By Rhizobium (in root nodules of legumes);