World of Plants

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World of Plants

• Revision

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Uses of plants
RAW MATERIALS
MEDICINES
Foxglove
Periwinkle
Rubber
Pine
Cotton
Seaweed
Poppy
Cabbage
Wheat
Sunflower
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Structure of a seed
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Germination

• Germination is the growth of a plant embryo into
  a new plant
• For germination seeds need the following
• Water
• Oxygen
• Suitable temperature
• Remember seeds do NOT need LIGHT (think about
  where seeds are usually planted)

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Structure of a flower
Petals
Nectary
Sepals
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The male and female parts of a flower
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Pollination
Pollen is produced in the anthers
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Pollination 2
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Animal and wind pollination

• Most flowers have the same basic structure, but
  many flowers are ADAPTED to increase their
  chances of pollination (either by wind or by
  animals).

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Growth of a pollen tube

• Once pollen land on the stigma it uses sugar on
  the stigma for energy to form a pollen tube
• The male nucleus of the pollen grain travels down
  the pollen tube to the ovary where it meets and
  fuses with the female nucleus in the ovule
• Following fertilisation, the ovule becomes a SEED
  and the ovary becomes the FRUIT

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Seed Dispersal

• If seeds are well dispersed the chance of
  survival is greater because competition is
  reduced
• There are 3 seed dispersal mechanisms
• Wind e.g. sycamore seed. These seeds are very
  light so they can be carried easily
• Animal internal e.g. cherry. These seeds are
  bright coloured and juicy to entice an animal
• Animal external e.g. burdock. These seeds can
  have hooks which attach to an animals fur

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Asexual reproduction

• Plants can also reproduce asexually
• This means that sex cells and fertilisation are
  not involved
• Plants that are produced in this way are CLONES
  which means they are genetically identical to
  each other
• Asexual reproduction can occur NATURALLY or
  ARTIFIALLY

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Natural Methods

• Runners these are side shoots that grow out
  from the parent plant. At the end of the runner a
  new plantlet will grow which will form roots when
  it comes into contact with the ground
• Tubers this is a swollen region of a stem or
  root which is a food storage organ

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Artificial Methods

• Humans can reproduce plants artificially in 2
  ways
• Cuttings a piece of stem or leaf is cut and
  placed in compost where it will form roots
• Grafting a bud or shoot of a valuable plant is
  taken and joined to a plant that already has a
  root system

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Which is best sexual or asexual reproduction?
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Making Food Transport systems

• Plants need both water and dissolved food in all
  parts of the plant
• Therefore, they need transport systems to move
  these substances around the plant
• XYLEM and PHLOEM are the 2 main transport systems

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Features of xylem and phloem
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Xylem and Phloem

• Together, xylem and phloem form the VASCULAR
  BUNDLES

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Leaf Structure
(transparent to let light through)
Palisade mesophyll cells (contains many
chloroplasts. These cells are where most
photosynthesis occurs)
Spongy mesophyll cells (have air spaces between
them to allow easy gas exchange
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Stomata

• Stomata are tiny pores on the surface of leaves
  that allow gases in and out
• Carbon dioxide enters a leaf from the air
• Oxygen is produced during photosynthesis and this
  passes out of the leaf through stomata
• Stomata are open during the day and closed at
  night to prevent water being lost
• http//www.bbc.co.uk/schools/gcsebitesize/biology/
  greenplantsasorganisms/1watertransportrev3.shtml

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Photosynthesis

• Green plants use LIGHT to combine CO2 and H2O
  together to make GLUCOSE and OXYGEN
• CHLOROPHYLL is the green chemical found in plants
  and it is essential for photosynthesis

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The fate of food

• The food that the plants make is a carbohydrate
• The simplest carbohydrate is glucose which can
  have different fates
• It can be used straight away as an energy source
• It can be converted to starch which can be stored
  until it is needed

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Limiting Factors

• A limiting factor is something which slows down
  or stops a process from happening
• Photosynthesis can be limited if certain things
  are in short supply
• The most common limiting factors in
  photosynthesis are low LIGHT, lack of CO2 or low
  temperatures