Sexual reproduction in plantsEdexcel A-Level Biology B: Subtopic test

1. 1
   A student investigated the effect of sucrose concentration on pollen germination. She placed pollen grains from one flower in sucrose solutions of 0%, 5%, 10% and 20% on cavity slides and kept them at 25 °C for 30 minutes. She then counted 100 grains in each solution and recorded the percentage that had produced a pollen tube: 8%, 52%, 81% and 23% respectively.

   (a)

   Which change would make the results of this investigation more reliable?

   [1 mark]

   • AUse a single pollen grain at each concentration
   • BTest only 0% and 20% sucrose
   • CUse several slides at each concentration and calculate a mean percentage germination
   • DUse pollen from a different plant for each concentration

   (b)

   The percentage germination fell at 20% sucrose. What is the most likely explanation?

   [1 mark]

   • AThe sucrose solution is toxic to the generative nucleus
   • BThe enzymes in the pollen tube are denatured at 20% sucrose
   • CWater entered the pollen grains by osmosis so they burst
   • DWater left the pollen grains by osmosis because the solution had a lower water potential

   (c)

   Suggest why only 8% of the pollen grains germinated in the 0% sucrose solution.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a lily flower, pollen grains form in the anthers from pollen mother cells. In the ovules, the embryo sac forms from a megaspore mother cell. Both types of mother cell are diploid.

   (a)

   How many pollen grains can form from one pollen mother cell?

   [1 mark]

   • A4
   • B2
   • C8
   • D1

   (b)

   How many haploid nuclei are present in a mature embryo sac?

   [1 mark]

   • A4
   • B8
   • C7
   • D16

   (c)

   Explain why the pollen mother cell divides by meiosis.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In flowering plants the male gametes cannot swim to the egg, which lies deep inside the ovule. Each pollen grain contains a generative nucleus and a tube nucleus. After a pollen grain lands on the stigma of a compatible flower, it germinates.

   (a)

   Explain how the pollen tube grows through the style to reach the ovule.

   [3 marks]

   (b)

   Describe how the generative nucleus gives rise to male nuclei and how these reach the embryo sac.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A pea seed consists of an embryo, a food store and a protective coat. All of these structures develop from an ovule after pollen grains from the anthers of another flower have reached the stigma.

   (a)

   Describe how a pollen grain is formed in the anther and how an embryo sac is formed in the ovule.

   [6 marks]

   (b)

   Explain what happens in double fertilisation and discuss why it is an advantage to the plant.

   [6 marks]

   Total for question 4: 12 marks

End of questions