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

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

• (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)

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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.