Question

(a) A scientist compares the relative concentrations of bacteria and dissolved oxygen in a river before and after fertiliser is added.
Fig. 4.1 is a graph of the results.

Complete the sentences to describe and explain the changes seen in Fig. 4.1.
Fertilisers entering the water contain ………………………………….. ions.
An increase in the availability of these ions enables an increase in the ………………………………
of producers on the surface of the water.
Producers underneath the water are unable to ………………………………….. due to a lack of light  and they die.
The population of bacteria increases as they ………………………………….. the dead material.
The concentration of dissolved oxygen decreases because the bacteria need oxygen for the 
process of ………………………………….. ………………………………….. .
This entire process is called ………………………………….. .
(b) Bacteria reproduce by a type of asexual reproduction.
(i) State the type of cell division used in asexual reproduction.

…………………………………………………………………………………………………..
(ii) Describe two ways that asexual reproduction is different from sexual reproduction.
1 ……………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
(iii) State the name of one type of cell adapted for sexual reproduction in humans.
…………………………………………………………………………………………………………………….