The World of Plants

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The World of Plants

• Growing Plants

G Davidson
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Structure of a seed

• In order to reproduce flowering plants produce
  seeds.
• Seeds contain nearly everything required to start
  the growth of a new plant.
• A seed is made up of the embryo a food supply
  (endosperm) both enclosed in a tough seed coat
  (testa).

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Germination

• Seeds can survive for many years in the ground.
• They appear to be dead.
• When conditions are suitable they burst into life
  and start the growth of a new plant.
• This is called germination.

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Germination
What is needed for germination to be successful
How do we find out
Investigate!!
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Investigation

• When setting up an investigation we need to
  change something and this is called a variable
• We start by setting up the basic apparatus
• In this case it will look like this

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Investigation

• Our variables will be
• Water
• Light
• Heat
• Oxygen
• So we now want our investigation to be 5 boiling
  tubes
• 1. No light
• 2. No water
• 3. No heat
• 4. No oxygen
• 5. Everything (the control)

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Germination

• So just what do seeds need for germination
• Water
• Oxygen
• Minimum temperature

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Structure of a Flower

• Sexual reproduction occurs in plants as well as
  animals.
• The FLOWER contains the reproductive organs of a
  plant.
• Flowers of different plants may not be exactly
  alike but they are built to the same basic plan.

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Structure of a Flower
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Structure of a Flower
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Structure of a flower

• Pollen is made inside the anthers.
• When they ripen the pollen is released.
• Pollen grains are like specks of dust.
• They contain the MALE sex cell.
• This has to reach the egg cell (ovule) in the
  ovary.

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Pollination

• Pollination is the transfer of pollen from the
  anthers of one plant to the stigma of another.

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Pollination

• Most flowers rely on either the wind or insects
  to transfer their pollen
• It is often easy to tell the method of
  pollination used by a flower by its appearance.
• Insect pollinated flowers use animals such as
  bees butterflies birds bats.
• Wind pollinated flowers have structures which
  make use of the wind.

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Methods of Pollination
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Insect pollination
e.g. Passion flower
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Wind Pollination
e.g. Sedge
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Fertilisation

• Once the pollen has landed on the stigma the male
  sex cell inside has to get to the female sex
  cell.
• To do this it has to grow a pollen tube down
  through the style.
• The stigma produces a sugary fluid to feed the
  growing pollen tube.

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Fruit Formation

• After fertilisation the fertilised ovule becomes
  the seed
• The ovary develops into the fruit
• The fruits can help in seed dispersal depending
  on what kind of fruit they are.
• There are 2 kinds

• Dry fruits e.g. poppy lupin dandelion
  sycamore etc
• Flesh fruits e.g. tomatoes plums
  gooseberries etc

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Seed Dispersal

• Once fertilisation has taken place the flower
  withers and a seed and fruit are formed from the
  ovary.
• The seeds must be scattered as far away from the
  parent plant as possible.
• This avoids the new plants competing with the
  parent for vital resources.
• This seed dispersal is achieved in a variety of
  ways.

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Animal (external)

• Seeds can be dispersed by animals.
• The seed has hooks which catch onto animals fur
  and are transported by the animal until they fall
  off and hopefully germinate elsewhere.
• E.g. Burdock

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Animal (internal)

• Seeds can also be eaten by animals along with the
  fruit.
• The seeds pass through the animal and are
  deposited in the droppings elsewhere
• E.g. bramble

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Wind Dispersal

• Plants can also use the wind to scatter their
  seeds and they use different mechanisms to
  achieve this.
• E.g. the poppy uses the pepper pot method

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Wind Dispersal

• Ragwort dandelions cotton etc. use the
  parachute method.
• Each seed has a number of small feather-like
  structures to help it float in the wind.

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Wind Dispersal

• Some seeds have wings to help them fly in the
  wind.
• E.g. sycamore ash etc..

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Explosive

• Some plants such as peas and gorse use pods which
  explode to fire the seeds away from the parent.
• As a pod dries tensions are set up in the wall
  of the pod eventually causing it to split along
  two lines of weakness.

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Plant Life Cycle
SEED
POLLINATION
GERMINATION
FLOWERS
STEMS ROOTS
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Plant Life Cycles

• All stages involved in plant reproduction take
  place continually year after year.
• Some plants can reproduce WITHOUT forming seeds.
• This is another form of reproduction
• It only involves one parent
• No sex cells are involved
• It is called ASEXUAL reproduction

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Plant Life Cycles

• During asexual reproduction the parent plant
  produces new cells which eventually separate and
  become new independent plants.
• E.g. strawberry spider plant etc..

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Plant Life Cycles
The Mexican Hat Plant produces plantlets around
the edge of the leaves. These eventually fall
off and develop into new independent plants.
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Asexual Reproduction

• Asexual reproduction is quite common in plants
• It produces new plants with the same
  characteristics as the parent.
• There is no variation
• If the plant is resistant to a particular
  disease then so will the offspring.

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Asexual Reproduction

• Plants produced in this way are often found
  growing in clumps to reduce competition from
  other plants.
• Growth occurs very quickly because of available
  food store.
• It is successful as it does not involve the
  vulnerable stages of germination and early
  seedling growth.
• Plants which are all identical formed in this
  way are called a CLONE

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Sexual Asexual Reproduction
There are some important differences between
these 2 methods of reproduction. Each method has
advantages and disadvantages.
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Artificial Propagation

• Gardeners make use of a plants ability to
  reproduce asexually by using a method known as
  artificial propagation.
• Instead of growing seeds they take a small
  section of stem root or leaf and under the right
  conditions these will grow into a full plant.

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Taking Cuttings
Take a piece 100-150 mm long by snipping (a tip
cutting - a) or by tearing off a side shoot (a
heel cutting - b).
Remove all flowers and buds and all leaves
to about half way up the stem.
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Taking Cuttings
Slice a small sliver of bark off the bottom 5 mm
of tip cuttings (a) or carefully trim the end
of heel cuttings (b).
Make holes with a pencil or knitting needle in
damp potting mix in a small clean pot. A
suitable mix is a mixture of 75 washed river
sand and 25 sieved peat moss (or preferably an
environmentally-friendly peat alternative such as
Coco Peat).
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Taking Cuttings
Dip the prepared end of the cutting into a root
-promoting hormone powder blow off the excess
place in the hole in the damp sand to about half
its length and press the sand firmly around the
cutting. Root-promoting hormones should be kept
in a refrigerator when not being used and are
also available as liquids or gels.
Place the pot of cuttings into a plastic
ice-cream container (or similar) with a little
damp sand or peat-moss in the bottom cover with
a plastic bag and seal with an elastic band or
sticky tape.
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Grafting
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Grafting
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Layering