Seed Dispersal

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Seed Dispersal
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Reproduction in plants getting the flowers
pollinated

• Plants have adaptations to help them in
  pollination.
• Flowers that are pollinated by animals are
  usually large and colourful.
• They also have nectar and a fragrance so that the
  animals are attracted to them.

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Reproduction in plants getting the flowers
pollinated

• Plants have adaptations to help them in
  pollination.
• Flowers that are pollinated by wind are usually
  small, plain and without fragrance because they
  do not need to attract animals.

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From Flower to Fruit

• When all the ovules in a flower have been
  fertilized, the petals, stamens, stigma and style
  are no longer needed.
• They will usually wither and fall, leaving an
  ovary in which the ovules are developing into
  seeds.
• The fruit protects the seeds.
• What is so important about seeds such that they
  need protection?

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Flower to Fruit
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Pea fruit from flowers
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The Fruit and the Seeds

• Seeds will grow into new plants and ensure the
  continual existence of that type of plant.
• However, seeds cannot grow too close to their
  parent plant. Why?
• OVERCROWDING
• Overcrowding leads to competition for
• Water
• Space
• Nutrients
• Light
• Get to grow in new habitats where conditions may
  be even better.

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Before we look at dispersal

• Take note of the THREE points
• Dispersal method of the fruit and the dispersal
  agent.
• Characteristics of the fruit that supports
  dispersal.
• Dispersal pattern of the fruit.

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AGENTS OF DISPERSAL

• Seeds and fruits are modified in different ways
  to be dispersed using one or two of the agents of
  dispersal.
• Which parts get modified?

The testa and pericarp are often modified to help
in dispersal
An ovule which has been fertilised and become
mature. Its wall is the testa.
Seed
A mature ovary which contains fertilised seeds.
Its wall is the pericarp
Fruit
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Reproduction in plants getting the seeds
dispersed

• Flowering plants have different adaptations to
  enable their seeds to be dispersed as far away as
  possible.
• The different methods of seed dispersal are
• by wind
• by animals
• by water
• by splitting open forcefully

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Reproduction in plants getting the seeds
dispersed
What are the adaptations that help
thesefruits/seeds to be dispersed?

• Dispersal by wind
• small
• light
• dry
• wing-like

shorea
angsana
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Dispersal by Wind

• Plants which depend on the wind for the dispersal
  of seeds usually have
• light seeds or
• wings or
• a parachute of fine hairs or
• feathery hairs that act like many little
  parachutes
• to help keep them floating in the air

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Dispersal Pattern - Wind
Parent
Wind direction
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Reproduction in plants getting the seeds
dispersed
What are the adaptations that help
thesefruits/seeds to be dispersed?

• Dispersal by animals (eaten)
• bright colours
• sweet
• juicy

• Dispersal by animals (carried)
• small
• hooks stiff hairs

tomato
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Dispersal by Animals

• Three ways
• First way
• The seeds or fruits have hooks or sticky hair
  that catch onto the fur of animals or clothing of
  human beings
• Second way
• Fruits get eaten by animals and seeds are thrown
  onto the ground as they are too big to be eaten
  by animals or
• Fruits and seeds get eaten by animals but the
  seeds are too hard to be digested by animals and
  are passed out in the droppings
• Third way
• Animals collect the fruits and seeds and take
  them to their burrows.

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Dispersal Pattern - Animals
Parent
Wind direction
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Reproduction in plants ? getting the seeds
dispersed
What are the adaptations that help
thesefruits/seeds to be dispersed?

• Dispersal by water
• buoyant
• waterproof
• air spaces

• Dispersal by splitting open
• dry and hard fruit wall

coconut
saga
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Dispersal by Water

• Plants which depend on the water for the
  dispersal of seeds usually have
• Some feature that will allow it to float
• Some protective covering to protect it during its
  long water journey.

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Pong Pong
Coconut
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Nipah Fruit
Lotus Fruit Pod
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Dispersal Pattern - Water
Parent
Downstream
Wind direction
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Dispersal by Explosive Mechanism or Splitting of
the Fruit
The fruit wall suddenly breaks into several parts
and the movement causes the seeds to be shot out.
This is caused by the unequal drying up of the
fruit wall. The wall may split in one, two or
many places along the line/lines of dehiscence
(lines of splitting).
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Unripe
Ripe
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Ripe and unripe Kapok fruits
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Dispersal Pattern Splitting Action or Explosive
Mechanism Only
Parent
Wind direction
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Dispersal Pattern Splitting Action WITH Wind
Parent
Wind direction
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At a glance
Adaptations for reproduction
plants