IGCSE Biology Paper-3: Specimen Questions with Answers 291 - 293 of 358

Passage

Fig. is a diagram showing the events from pollination to fertilization in a species of flowering plant.

Structure of Plant

Question 291 (1 of 6 Based on Passage)

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Name structure Q shown in Fig. and state its function.

Explanation

Q: Pollen Tube

Pistil and pollen chemical secretions determine the compatibility of pollen grains. If incompatible is there, then either germination of pollen grain is inhibited or pollen tube abort in style, but if compatible pollen tube reaches the style it causes fertilization.

L. S. Of Pistill Showing Path

Question 292 (2 of 6 Based on Passage)

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In Fig. pollen is transferred from one plant to another.

State the name for this type of pollination.

Explanation

Cross Pollination

  • Cross pollination involves the transfer of pollen grains from the flower of one plant to the stigma of the flower of another plant. It is also called xenogamy.
  • Example: Apple, Pumpkin, Daffodils etc.

  • It is performed with the help of external agency that may be abiotic or biotic.

Pollen Transfer between Flowers

Question 293 (3 of 6 Based on Passage)

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Fertilization occurs at R as shown in Fig.

Describe what happens at fertilization in flowering plants.

Explanation

Doule Fertilization
  • The pollen tube enters the embryo sac only from the micropylar end irrespective of its mode of entry into the ovule. The pollen tube either passes between a synergid and the egg cell or enters one of the synergids through filiform apparatus. The synergids direct the growth of pollen tube by secreting some chemical substances (chemotropic secretion) . The tip of pollen tube enters one synergid. The penetrated synergid starts degenerating.
  • After penetration, the tip of pollen tube enlarges and ruptures releasing most of its contents including the two male gametes and the vegetative nucleus into the synergid. The nuclei of both the male gametes are released in the embryo sac. One male gamete fuse with the egg to form the diploid zygote (2n) . The process is called syngamy or generative fertilization.

  • The diploid zygote finally develops into embryo. The other male gamete fuses with the

  • two polar nuclei (or secondary nucleus) to form the triploid primary endosperm nucleus (3n) . The process is called triple fusion or vegetative fertilization. These two acts of fertilizations constitute the process of double fertilization.