Sexual reproduction in plants

• One fertilisation involves a male gamete nucleus fusing with the egg cell

  nucleus. Give two functions of this fertilisation.

  to produce a {zygote / eq} ;

  2. to produce {original / full} complement of {DNA / chromosomes / genetic material } / diploid / 2n number / eq ;

  3. to allow mixing of {genes / genetic material } / ref to { genetic variation / eq } ;
• In the second fertilisation, the other male gamete nucleus fuses with two

  polar nuclei forming a triploid structure. Name the triploid structure formed.

  (triploid) endosperm nucleus ;
• Describe the process of double fertilisation in flowering plants.

  one male nucleus fuses with two polar nuclei

  to form 3n nucleus

  one male nucleus fuses with the egg cell cell

  to form 2n zygote
• Devise an investigation to determine the effect of pH on the rate of growth of pollen tubes.

  5 different ph values

  sucrose solution added

  suitable time before measured

  measure using stage micrometer and graticule

  calculation of rate of growth

  method of control

  repeat
• Nuclei of the following:

  Zygote 2n

  Endosperm nucleus 3n

  Pollen tube nucleus n
• In which part of the plant are pollen grains made?

  anther
• The styles of some plants secrete RNAase enzymes when pollen from the same flower germinates on the stigma.

  Explain how these RNAase enzymes affect the growth of the pollen tube.

  enzymes hydrolysed the mRNA

  this prevents translation

  which prevents pollen tube reaching ovule/ prevents self pollination/ digestion of style/pollen tube growth
• Describe the role of enzymes in the growth of the pollen tube.

  enzymes hydrolyse the tissue of the style

  provides energy for pollen tube growth

  clears path for pollen tube growth/ allows pollen tube to enter ovule
• Explain the role of double fertilisation in flowering plants.

  one male nucleus fuses with two polar nuclei

  which produces 3n nucleus endosperm

  which provides nutrients for germination

  one male nucleus fuses with female gamete nucleus

  forms diploid 2n zygote
• Explain how the pollen tubes grow through the style of the flower.

  1. idea of enzymes being {produced / released / secreted /

  eq} ;

  2. idea of these enzymes being used to {digest / break down / eq} (tissues of style) ;

  3. idea of forming a pathway ;
• The tip of the pollen tube breaks through the micropyle to enter the

  embryo sac
• During fertilisation, nuclei from the pollen tube fuse with

  the egg cell and the polar nuclei
• During fertilisation, the following structures are produced

  diploid zygote and triploid endosperm
• Describe how the structure of a pollen grain differs from that of a sperm cell.

  1. pollen grain does not possess flagellum / eq

  2. pollen grain does not have an acrosome ;

  3. idea of {more / 2 / 3} nuclei in pollen grain ;

  4. idea of difference in outer boundary e.g. exine in pollen

  grains ;
• Describe the process of fertilisation that takes place in flowering plants.

  1. idea that generative nucleus divides to form two male gametes ;

  2. by mitosis ;

  3. pollen tube fuses with embryo sac /

  eq ;

  4. reference to double fertilisation ;

  5. (one) male { gamete / nucleus } fuses with egg (cell) nucleus ;

  6. to produce diploid zygote;

  7. other male nucleus fuses with two polar nuclei ;

  8. to produce triploid endosperm ;
• Describe the role of each of the male nuclei in the process of fertilisation in flowering plants.

  1. reference to double fertilisation ;

  2. idea that one (haploid) male {gamete / nucleus } fuses with (haploid) {egg cell / egg nucleus / female gamete / female nucleus} ;

  3. to produce a {diploid / 2n} {zygote / embryo} ;

  4. idea that one (haploid) male {gamete / nucleus} fuses with { polar nuclei / diploid endosperm nucleus / fusion

  nucleus} ;

  5. to produce a {triploid / 3n} endosperm (nucleus) ;
• Suggest why pollen in peat bogs is preserved for many years.

  1. idea of {lack of / very slow} decomposition ;

  2. due to lack of {microorganisms / bacteria / fungi / named decomposer} (involved in decomposition) / eq ;

  3. as a result there are fewer enzymes / eq ;

  4. low pH {reduces enzyme activity / kills microorganisms

  /eq} ;

  5. low oxygen affects respiration (of microorganisms) / eq ;

  6. idea that bacteria cannot produce enzymes to breakdown sporopollenin ;
• Give three roles of water in a plant other than for pollen tube growth.

  1. photosynthesis ;

  2. {component / eq} of {cytoplasm / sap} ;

  3. water as a solvent /eq ;

  4. water as a transport medium /eq ;

  5. involved in thermoregulation / eq ;

  6. reference to role in structural support ;

  7. reference to involvement in hydrolysis ;

  8. reference to turgor changes ;
• The tip of the growing pollen tube releases digestive enzymes into the style. Suggest the role of these digestive enzymes in the growth of the pollen tube.


  idea of {breakdown / digestion / eq} of style ;

  2. (breaks down) protein / pectin / middle

  lamella ;

  3. reference to hydrolysis / eq ;

  4. easier for pollen tube to grow / reduced resistance

  5. supplies {nutrients / named nutrient / energy} for (pollen tube) growth / eq ;
• The pollen tube grows from the pollen grain to the micropyle. Suggest one stimulus, other than water, that causes the pollen tube to grow towards the micropyle.

  reference to {chemical / air / gravity / light / eq}
• Suggest the advantages to flowering plants of increased pollen tube growth

  more likely to reach the ovule /eq ;

  2. fertilisation more likely to occur /eq ;

  3. idea of fertilisation in shorter time period