Transcript Plants

Growing Plants from Seeds
All seeds contain an embryo plant with a
root and shoot.
The seed also contains a starchy food store
which the embryo uses as energy to grow. (
germinate )
The seed coat protects the embryo from
damage by micro-organisms that live in the
• Germination is the growth of a plant
embryo into a plant with green leaves.
• The embryo uses the food store for
• A seed needs three things to grow
– Warmth
– Water
– oxygen
Test Tube
1 (warmth ,air,
Number of
seeds growing
2 ( no water)
3 ( no air )
4 (no light )
5 ( cold )
Plants make food by a process called
All green parts of the plant make food but
most food is made in the leaves.
Plants need light to make the food starch.
This food is then used by plants for
Testing leaves for Starch
When leaves are tested for starch, they
need to be boiled first
to open the cells.
Alcohol is used to remove the green colour.
Finally, iodine is added.
Iodine turns blue/black when starch is
Testing for Photosynthesis
• Glucose manufactured in the process of photosynthesis can be stored as
starched. We can test for starch using iodine solution following the steps
outlined below.
Sowing Seeds
When planting seeds, the way they are
planted depends on the seed size.
Fine seeds should be mixed with silver sand
to space the seeds out. This stops them
fighting with each other for water, root
space and light.
Medium size seeds can be scattered over
the surface of the compost ( soil ).
Large seeds can be sown individually in seed
trays or pots.
Pelleted seeds
• A pelleted seed is coated in layers of
material such as clay before it is planted.
• This can make irregularly shaped seeds
round and smooth to stop them sticking
• Useful chemicals such as fungicides,
pesticides or nutrients can be added to the
• Pelleting makes small seeds easier to
Many seed will not germinate after they are
Even although they have been given ideal
These seeds are dormant and need a long
cold period before they grow.
This stops them growing during a warm
winter spell.
• Pre-germinating or chitting a seed
means making it start to germinate
before it has been planted.
• This can be done by soaking the seeds
in water for a few days.
• If the seed coat is very tough and will
not allow water to enter, it can be slit
open using a sharp knife.
• This is best done at the opposite side
from the embryo to avoid damage.
• If the seed is very big, a nail file can
be used instead to file away part of
the seed coat.
• Very small seeds can be rolled in
between sheets of sand paper.
Vegetative propagation
• Propagation is a way a grower can increase
their supply of plants.
• Vegetative propagation is a way of growing
plants without using seeds.
• This involves structures such as bulbs and
cuttings and all new plants formed are
identical to the original parent plant.
• Vegetative propagation produces new
plants faster than using seeds.
Natural vegetative propagation
• Bulbs
– A bulb is a natural plant
propagation structure. It
is made up of several leaf
bases (layers) which
contain stored food
(starch) and has a short,
thick stem.
– Buds can be found among
the leaf bases and grow
into new daughter bulbs.
– Tulips and daffodils grow
from bulbs.
• Tubers
– A tuber is a large food store
found on a root or stem.
– A potato is an example of a
– Tubers can grow into whole
new plants
– In summer, potato plants
grow many tubers and each
tuber has ‘eyes’ which are
really tiny buds. When
planted, shoots grow from
the bud and turn into new
potato plants.
• Plantlets
• A plantlet is a tiny plant
attached to a parent plant.
These plantlets eventually
separate from the parent
and grow on their own.
• The Mexican hat plant
grows plantlets on the
edges of its leaves.
• The Piggyback plant grows
plantlets at the base of
each leaf.
Mexican hat plant
Piggyback plant
• Runners
– Some plants grow
plantlets at the end of
horizontal stems called
– Spider plants grow
– Strawberries grow
plantlets on runners.
– If runners are pegged to
the ground, the plantlets
grow roots and the
runner can then be cut.
• Offsets
– An offset is a plantlet
which grows as a side
shoot at the base of
the parent plant..
– Sometimes lots of
offsets grow and form
a clump.
– Mother-in-law’s tongue
is a plant which grows
Plant production
Artificial Propagation
Artificial propagation is when part of a
plant is cut from the parent and used to
make a new plant.
This is quicker then waiting for the
parent plant to make seeds and all the
new plants will be identical to the
A cutting is a piece of plant stem with
leaves which is cut, dipped in rooting
hormone ( encourages roots to be made )
and planted .
Layering is another method of artificial
A long stem is nicked, dusted with rooting
hormone and pegged to a pot of compost.
When the roots grow, the new plant can
be cut from the parent.
This makes bigger new plants and the
parent supplies it with water and minerals
while they are attached.
Using heat during
• A propagator is an electric device for
providing cuttings and new plants
with heat. Propagators are often
used inside greenhouses.
• Propagators keep the soil at a
siutable temperature 24 hors a day.
• This encourages roots to grow
• Propagators are mot useful during
winter to protect young plants from
frost damage.
• Gardeners must be careful not to
make the temperature too high for
young plants as they will lose too
much water and wilt.
• Some propagators have thermostats
which control the temperature. This
allows the temperature to be set by
the gardener and it will stay constant.
For plants to be healthy, the soil ( loam) must be
right for the plant.
The soil must have :
1. Air
2. Good drainage
3. Minerals
4. Free of most bacteria or fungus
There are 2 kinds of compost : loam based and
Loam based soils contain mainly loam.
Loamless soils contain a 1:1 ratio of peat to sand
Loamless soils do not need to be sterilised but can
dry out more easily.
• Rooting Composts: Sometimes called a
cutting compost,this is a mixture of peat
and sand in a 1:1 ratio (half and half). Water
drains better from this compost because it
has more sand and this prevents roots from
rotting. Perlite or vermiculite can be used
instead of sand.
• Potting Composts: This is a mixture of peat
and sand in a 3:1 ratio so for example, 6L of
peat would be mixed with 2L of sand.
Fertiliser is also added to supply the
growing plant with enough minerals to keep
it healthy.
Sand or perlite
Loam (soil)
Plants need minerals for healthy growth.
The 3 main minerals :
1. Nitrogen : leaf growth
2. Phosphorous : root growth
3. Potassium : flower and fruit growth
Plants also need some other minerals in tiny
amounts. These are called trace elements and
an example is iron.
Fertiliser is used if a soil does not have enough of the
right minerals.
Different plants need varying amounts of each of the
3 main minerals.
For example grass needs nitrogen as the main
element of fertiliser whereas, growing tomatoes
would need high potassium ( potash).
The proportion or ratio of the 3 main minerals is
listed on fertiliser containers in the following order
Nitrogen (N) : phosphorous (P) : potassum (K)
Applying Fertilisers
Fertilisers come in 2 forms , as liquids or granules (
small pellets)
Liquid fertilisers are quick acting but drain away
from soil quickly
Granules release minerals slowly and are longer
Some liquid fertilisers can be absorbed by the
leaves as well as the roots ex Miracle Grow .
Man made or natural fertilisers (organic) can be
used. An example of an organic fertiliser would be
manure but they can be bought from shops also.
Watering house plants
• Some plants should be watered from above.
A watering can can be used to pour water
into the plant pot. Water is added until a
small amount appears in the drainage saucer
• Some plants should be watered from below.
The pot or tray should be placed in shallow
water for about 15 mins to allow the roots to
absorb as much water as they need. African
violets and young seedlings should be
watered in this way
Watering Systems
Automatic watering systems allow plants to be
watered without anyone having to do the job.
What are the advantages of this ?
There are several different types :
1. Trickle irrigation
Plastic hose connects a tank of water with several
pots. Water “trickles “ continuously between
the pots.
2. Capillary Bench
Capillary matting is a material that will suck up water and
stay moist. If one end of the water is placed in a water
trough , it will absorb water along its length , and plant pots
can be placed on top.
3. Water Retentive Gels
These are chemicals that can absorb and hold a great deal
of water. If mixed with soil , they can last many seasons
holding water for plants. This is useful for hard to reach
plants ex. Hanging baskets
Temperature is measured in degrees
Centigrade (ºC )
Different types of plants grow best at
different temperatures. For example a
spider plant grows well between 10 and
30°C. At temperatures outside this range
the plant does not grow well and may die.
People who grow plants must find ways of
growing them at the correct temperature.
Greenhouses are often used or polythene
tunnels which are plastic sheets draped over
metal poles, almost like a tent for plants!
• The temperature inside greenhouses
or polythene tunnels can be controlled
using an electric heater.
• The grower sets the thermostat at a
certain temperature and when the
greenhouse is warm enough the
thermostat switches the heater off.
• When the greenhouse begins to cool
down the thermostat switches the
heater back on.
Growers can check the range of temperatures
their plants have been exposed to in the
previous 24hours using a maximum and
minimum thermometer.
This is u-shaped. One arm records the
maximum temperature that occurred in the
previous 24 hours and the other arm records
the minimum temperature that occurred in the
previous 24hours.
As liquid in the thermometer moves up or
down it pushes metal markers. These show
the max and min temperatures.
• Both arms also show the present
temperature. The position of the
liquid inside the thermometer
shows this.
This is the amount of water vapour in
the air.
Plants lose water from their leaf
surfaces. This has a cooling effect
similar to sweating in humans.
If the air is very humid, hardly any
water will evapourate from the plant. If
the air is very dry, the plant may lose
too much water and could die.
Different levels of humidity suit
different types of plants.
Relative humidity is the percentage of
water vapour the air is holding.
The higher the percentage, the more
humid the air.
100% humidity means the air can hold no
more water vapour and is saturated
• A wet and dry hygrometer is used to
measure relative humidity
• It is made up of two ordinary
thermometers but one bulb is
wrapped in wet muslin and will show a
lower temp.
• Relative humidity is worked out as
– Read dry bulb temp
– Read wet bulb temp
– Subtract wet reading from dry reading.
Refer to table of relative humidities and
find value
This is providing fresh air. Stale moist air means
mould and mildew will grow and kill plants.
Automatic vent openers are cylinders full of wax.
The wax expands when the temperature gets too
high and this pushes the window open. As the
green house cools down the wax contracts and the
window closes.
Extractor fans can also be used to cool green
houses. These are switched on and off by
Potting On
If a plant grows too large for the pot it is in,it will
not have enough space for the roots to grow. We
say it has become pot-bound. You will recognise
such a plant by the following features:
~ slow growth rate
~ compost dries quickly
~ roots growing out holes in bottom of pot
Potting on means re-potting the plant in a larger
Pricking Out
When seeds are planted in a seed tray, they
eventually start to fight for light and root space.
They are now ready to transplant into pots and this
process is called pricking out . This means
transferring them to a new location where they will
have more room to grow.
Seedlings are ready to prick out when their first set
of leaves open out.
Dead Heading
• Normally a plant produces a set of flowers which
die after making seeds. If the heads of dead
flowers are removed regularly the plant may
produce more flowers.
• This removal of dead flower heads to encourage
the plant to continue flowering is called dead
• Dead heading allows the plant to direct energy to
dormant flower buds instead of fruit production.
Types of Plants
House plants can be divided into 4 groups :
Flowering Plants : we grow these for their
attractive flowers. Some varieties flower year
after year (geranium) and some only once.
Foliage Plants : we grow these for the shape
and colour of their leaves.
Succulent Plants : these have fleshy leaves or
stems that store water eg. Cacti. Some may have
sharp spines and sometimes produce flowers.
Native to dry enviroments such as desert or
• Ferns: Non-flowering plants native to
damp woodlands that are not brightly
lit. Will not survive in dry, hot
Pests and disease
• A pest is an animal which causes damage to
a plant. An example in an aphid (greenfly).
Greenfly suck the plants sugary sap using
their sharp, syringe-like mouthparts.
• The greenfly usually attack young parts of
the plant like the flower buds. The plant
cannot grow properly because it is not
getting a full supply of energy
• Disease is caused by a micro-organism that
can damage the plant. An example is grey
mould which is a fungus.
• This disease causes a fuzzy grey fungal
growth on the leaves . Infected leaves
quickly rot and die and infection can spread
to the rest of the plant.
• This disease thrives in damp, poorly
ventilated conditions.
Control of Aphids
• A pesticide is a chemical that kills insects
and other pests. An insecticide is a type of
pesticide especially for insects.
• Plants can be sprayed with insecticide and
so any aphid which tries to feed on its sap
will die.
• Aphids can also be controlled by biological
methods. This means introducing one of its
natural predators (ladybirds) which will eat
them before they can destroy the plants.
Control of grey mould
• We can prevent this disease by making sure
plants are well spaced out and given good
ventilation. Any infected plants should be
removed and burned immediately to prevent
spread of the disease to other plants.
• Plants can also be sprayed with a chemical
called a fungicide which kills fungi such as
grey mould.
Protected cultivation
• Plants can be damaged by wind, rain, low
temperatures and in particular, frost.
• We can protect plants from damage by
protective cultivation. This also allows
farmers to plant seeds earlier and therefore
sell their crops early and receive a higher
Methods of protection
• Glass (ex.greenhouse or cloche)
Lets light through
Retains heat
Not damaged by wind
• Plastic (cloche)
– Light and easy so handle
– Less easily broken than glass
– cheap
• Polytunnels
– Good for large areas
– Made of transparent plastic stretched over wire
hoops like a tent.
– Can be raised at either end for ventilation
• Floating fleece
– Sheet of woven man-made fibres
– Place over crops and is gradually lifted up by
plants as they grow.
– Helps keep soil warm and protects against pests
– Water and air can still get through