Transcript Lesson 8- Vegetative vs Artificial propagation

Lesson Starter
•What 3 things to seeds need in order to
germinate?
•What does germination mean?
•What are the 3 parts of the seed and their
function?
Propagating and
growing plants
Learning intention
• To Investigate germination
Seed Dormancy
• Seeds are prevented from
germinating when the
environment is unsuitable (and
their chances of survival is low)
• They remain DORMANT until
the conditions are favourable
What we know..
• Seeds need water, oxygen
and warmth to GERMINATE
• Germination is when the
seed starts to grow into the
plant
Investigation
1. Will seeds germinate in the absence of
WATER?
2.Will seeds germinate in the absence of
WARMTH?
Plan
• Using seeds, cotton wool, petri dishes and
water- how could we carry out the two
investigations?
• With the person next to you write a plan for
what you are going to do
• REMEMBER YOU MUST HAVE A CONTROL
Without water
• Collect two petri dishes, cotton wool and seeds
• Line each of the petri dishes with cotton wool
• Into each dish place 10 seeds- spread them out as
evenly as possible
• Water the seeds in ONE OF THE DISHES
• Place both dishes along the window
Without warmth
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Collect two petri dishes, cotton wool and seeds
Line each of the dishes with cotton wool
Place 10 seeds in each dish- spread out evenly
Water both dishes- place one at the window and
give one to me to go in the fridge
Predictions
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10 seeds
Cotton wool
Light (heat)
Water
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10 seeds
Cotton wool
Light (heat)
No water
10 seeds
Cotton wool
Water
Light (heat)
• 10 seeds
• Cotton wool
• No heat
(fridge)
• Water
Learning Intention
• Vegetative Propagation
Vegatative propagation
• Vegetative propagation is a form
of asexual reproduction used by
plants which produce cloned
offspring.
• There are many methods of
vegetative propagation.
Copy and complete as we go
Structures produced by vegetative
propagation
Description of the
structure
Example of plants
produced
Bulbs
• Bulbs store food.
• They have buds which produce flowers or
daughter bulbs.
• As bulbs are produced from one parent, this
is a method of vegetative propagation.
• The food store allows bulbs to withstand
winter conditions and to grow early in the
spring before seeds germinate.
• Examples of plants grown from bulbs include
daffodils, tulips and onions
Tubers
• Tubers are another example of a food storage
organ e.g. potato and dahlias
Attached Offspring
• Some plants produce
miniature plants called
plantlets attached to the
parent.
• The plantlets obtain food
from the parent plant until
they have produced roots
and can absorb water and
minerals from the soil.
Attached Offspring
• Plants such as Mother of Thousands produce plantlets at the
ends of their leaves.
• These plantlets drop off naturally and take root, if the conditions
are suitable.
• The plantlets will then grow into new plants, all of which are
identical to the parent
Production of Plantlets from Runners
• Spider Plants form plantlets at the end of
a runner (a horizontal stem).
• The plantlet can be 'pegged down' into a
small pot of compost using wire.
• When roots are established, the runner is
cut close to the new plant and the wire
removed.
• Strawberry plants can also be propagated
by this method.
Offsets
• Some plants, for example
Mother-in-Law’s Tongue,
produce offsets.
• Offsets are small plantlets
produced as side shoots at the
base of the parent plant.
• These can be detached from the
parent plant and grown
separately.
Learning Intention
•Artificial Propagation
Artificial Propagation
• A new plant can be grown from part of the original plant.
• Artificial propagation means that part of a plant, for example
a stem or leaf, is cut off from its parent and treated so that it
grows into a new plant.
• This method is quicker than waiting for the parent plant to
produce seeds and all new plants will be exactly like the
parent plant e.g. same colour of flower and leaves.
Nodes
• Nodes are points on a plant's
stem where
new growth occurs.
• When a plant stem is wounded
the stem produces roots.
• Rooting powder can be used to
speed up root growth.
Roots untreated
Roots treated
Using Propagators
• Propagators have electrical cables that supply heat to
the cuttings.
• This also encourages root growth.
However, if too much heat is supplied, the plant will wilt
as it loses too much water.
• This can be prevented by
– reducing the leaf surface area by removing some of the
lower leaves
– increasing the humidity by placing the cutting in a
propagator
– covering it with a polythene bag.
Taking Cuttings
• Step 1 A diagonal cut is made
in the stem below a node
(where leaf joins the stem)
• Step 2 The lower leaves are
removed to reduce water loss.
• Step 3 The cut end of the
stem is dipped into rooting
powder to encourage the
growth of roots
• Step 4 The cutting is placed into a
hole in the centre of compost in a
plant pot.
• Step 5 The compost is watered
• Step 6 The potted cutting is placed
in a propagator with a lid to increase
humidity and reduce water loss
from the cutting.
Layering
• Layering is a method of propagating plants
which have long flexible stems.
• When the stem is still attached to the
parent plant, it is 'pegged down' into a pot
of rooting compost or into the soil if it is
an outdoor plant.
• Often the stem is wounded by cutting
below a node and dusted with rooting
powder to encourage root growth.
• When roots develop, the stem is cut to
separate the new plant from the parent
plant.
Advantage of Layering
• The advantage of 'layering' is that
the new plant is supplied with water,
food and minerals from the parent
plant.
• This means that many plants,
difficult to raise from cuttings, can
be propagated by this method.
• The plants produced are also larger.
Questions: Answer in sentences
• Give two examples of how artificial methods
can be used to grow plants
• Give two methods used to encourage the
growth of roots in new plants
• Give an advantage of layering as a means of
propagating plants
Learning Intention
•Cultivating plants
Protected Cultivation
• This includes the use of
glass, plastic and floating
fleece.
• Greenhouses and
polythene tunnels protect
plants from cold, wind,
rain and frost.
Greenhouse
Polythene tunnel
Heating Greenhouses
• To control the temperature in a greenhouse, the
electricity supply is connected to a thermostat.
When the temperature falls below a fixed
temperature, the thermostat switches the heating
on and switches it off when a fixed upper
temperature is reached.
• The advantage of heating is that it prevents frost
damage and encourages plant growth.
• The disadvantage is that the plant may lose too
much water and wilt.
Ventilation of Greenhouses
• Ventilation means providing fresh air. Stale moist air
provides ideal conditions for the spread of disease for
example grey mould (mildew).
• Ventilation is also important in controlling temperature
and humidity (how much moisture is in the air).
• To provide the best conditions for plant growth,
automatic ventilation is essential. Automatic systems
work without anyone being there to operate them.
The are two main automatic systems for controlling
ventilation are automatic window openers and
thermostatically controlled electric fans.
Floating Fleece and Cloches
• Floating fleece and cloches also protect plants from
the weather.
• Cloches are tent-like structures made from glass,
plastic or polythene.
• Plastic or polythene cloches are the most common
type nowadays being cheaper and less likely to
break than glass.
• Floating fleece is a light material which allows the
plants to grow under it, protecting the plants from
frost while still allowing water and light to pass
through.
Limiting factors in photosynthesis
 A limiting factor is a factor which slows down (or limits) a process if it is
in short supply.
 In photosynthesis there are three main limiting factors:
Light Intensity
Carbon Dioxide Concentration
Temperature
Limiting factor- Light Intensity
• Between points A and B on the graph,
light is the limiting factor since as the
light intensity increases so does the
rate of photosynthesis.
• Between points B and C, light is no
longer the limiting factor since
increasing the light intensity does not
increase the rate of photosynthesis
 A shortage of carbon dioxide is now
the limiting factor and the rate of
the reaction can only be increased by
adding more carbon dioxide.
Carbon Dioxide as a Limiting Factor
• Between points A and B, the
carbon dioxide concentration is
the limiting factor
• Between points B and C,
temperature or light intensity is
now the limiting factor.
Effect of Temperature
Temperature is a limiting
factor because it affects
the activity of the
enzymes which control
photosynthesis.
Questions
1. Name two different structures used for
protected cultivation
2. What is the effect on plant growth of adding
additional carbon dioxide?
3. How can a gardener control heat in a
greenhouse?