The graph below represents the increase in the number of yeast cells over a period of 48 minute:

K.C.S.E Biology Q & A - MODEL 1995PP1QN15

25/5/2020

(a)
Name the type of curve shown (1 mk)
(b)
Determine the number of yeast cells after 26 minutes (1 mk)
(c)
Work out the rate of cell division between 24 and 28 minutes (2 mks)
(d)
After how long was the population of yeast cells 128? (1 mk)
(e)
Name the phase of the curve labeled
- (i) A to B
- (ii) B to C
(f)
Give reasons for the shape of the graph between points C and D (3 mks)
(g)
State five factors, which would cause human population growth to assume the shape of the graph curve between points B and C (5 mks)
(h)
Describe how the quadrant method can be used to estimate the population of various species of plants in a given habitat (5 mks)

KNEC ANSWERS

(g)

Low death rate/ low mortality; [Rej. Decrease in death rate/ reduced death rate]
High birth rate/ high fertility acc. Increased birth rate
Improved medical services: Acc. Increased medical facilities
Enough food/ availability of food
Absence of war/ political stability/ peace
Improved standard of living

(h)

Measure the total area of the habitat, throw or mark out the quardrat in the area for the study; at random. Identify label the various species of the plants in the quardrat; count plants of each species; record the numbers, repeat the process (owtte) work out the average per quardrat for each species in the area/ calculate the population for the total area in Nairobi.