Transcript The World of Plants - Oronsay Bed & Breakfast

The World of Plants
Growing Plants
G Davidson
Structure of a seed
• In order to reproduce,
flowering plants
produce seeds.
Embryo
• Seeds contain nearly
everything required to
start the growth of a
Plumule
new plant.
• A seed is made up of Radicle
the embryo, a food
supply (endosperm),
both enclosed in a
tough seed coat (testa).
Testa
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.
Germination
What is needed for germination to be successful?
Light??
Heat??
Germination
Oxygen??
How do we find out??
Soil??
Water??
Investigate!!
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:
Boiling
tube
Seeds
Cotton wool
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”)
Germination
• So, just what do
seeds need for
germination?
• Water
• Oxygen
• Minimum
temperature
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.
Structure of a Flower
Structure of a Flower
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.
Pollination
• Pollination is the “transfer”
of pollen from the anthers
of one plant to the stigma
of another.
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.
Methods of Pollination
Insect pollination
Have a scent
Wind pollination
No scent
Sticky, spiky pollen
Large amounts of light
pollen
Sticky stigma inside
Feathery stigmas hang
flower
outside the flower
Stamens surrounded by Large stamens hang outside
petals
flower
Produce nectar
Don’t produce nectar
Petals large & bright
Petals small & dull
Insect pollination
e.g.
Passion
flower
Wind Pollination
e.g. Sedge
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.
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:
1. Dry fruits – e.g. poppy, lupin, dandelion,
sycamore, etc…
2. Flesh fruits – e.g. tomatoes, plums,
gooseberries, etc…
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.
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
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
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
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.
Wind Dispersal
• Some seeds have
wings to help them fly
in the wind.
• E.g. sycamore, ash,
etc..
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.
Plant Life Cycle
SEED
POLLINATION
GERMINATION
FLOWERS
STEMS & ROOTS
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
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..
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.
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.
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
Sexual & Asexual Reproduction
There are some important differences between
these 2 methods of reproduction. Each method
has advantages and disadvantages.
Asexual
Sexual
Advantages
Early quick growth
Variety
Reduced competition Seeds dispersed
Disadvantages
Overcrowding
Quality doesn’t
improve &
weaknesses passed on
Gametes
required
Limited food
store in seeds
Artificial Propagation
• Gardeners make use of a plant’s 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.
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.
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").
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 icecream 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.
Grafting
Grafting
Layering