15 March 2014

#110 Seed dispersal

Nutmeg is dispersed by birds.
Photo credit: r
ussolab.unl.edu
The flowers produce seeds which can be dispersed by the wind or other animals, providing a means of colonising new areas.













1. Wind-dispersed seeds
  • Fruits contain seeds, and usually have a parachute or a wing to help them be carried away from the parent plant by the wind.
  • Examples: dandelion, sycamore


The dandelion fruit has a group of fine hairs called a pappus, which catches the wind and acts like a parachute. The fruit counterbalances the pappus.


The sycamore has a wing with a large surface area. When the fruit drops off the tree it spins, slowing down in descent. If caught by the wind the seed will be carried away from the parent plant, reducing competition for nutrients, water and light.



2. Animal-dispersed seeds

There are 2 main modification of fruits for animal dispersal: succulent fruits and hooked fruits.

Succulent fruits attract animals because they are brightly coloured, juicy and nutritious. When eaten, the seed pass through animal’s faeces, which may be a long way from the parent plant. The faeces provides nutrients when the seeds germinate.


Hooked fruits catch on to an animal’s fur as it brushes past the parent plant. Eventually the seeds drops off, or the animal grooms itself to remove them. This disperses the seeds away from the parent plant. 






Try this

Figure below shows a section through a bean seed.



1. i) Name the parts labeled AB and C.                                        [3 marks]
    ii) Copy the diagram and label with an the part that contains the seed’s food reserves.                                                                                 [1 mark]

2. Seeds and fruits are dispersed away from the parents plant.
   i)Sketch a seed or fruit that is adapted for dispersal by wind. Label with a Y the special feature of the seed or fruit that helps in wind dispersal. [1 mark]  
  ii) Suggest how this feature helps in wind dispersal.  [2 marks]

  iii) Suggest another way in which wind assist in the reproduction of plants.  [1 mark]


Answer

1. i) A plumule; B cotyledon, testa (seed coat)
    ii) X on any part of the cotyledon.

2. i) Sketch of dandelion, sycamore…
      Y on the part that catches the wind (parachute, wing…).
ii) Two points from:
- description of how the feature catches the wind
- and slows down the descent of the seed or fruit
- so the seed or fruit is carried away from the parent plant.
iii) Wind pollination


Video: Seeds - An amazing video taken from BBC's The Private Life of Plants documentary series (MUST SEE). 




2 comments:

  1. This has been removed from the IGCSE syllabus :)

    ReplyDelete
    Replies
    1. But it is included in the O level syllabus :)

      Delete