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1 of 48 © Boardworks Ltd 2007
3 of 48 © Boardworks Ltd 2007
How are plants adapted to growth?
Different parts of a plant are adapted to assist its growth
and survival.
Flowers are adapted
to enable reproduction.
Stems support the plant
and transport nutrients.
Leaves are adapted for
photosynthesis, which makes
materials for growth.
Roots anchor the plant to the
ground. They also take up water
and minerals from the soil.
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How tall can plants grow?
The tallest known plants are
the Coast Redwoods, found in
the USA. These grow to over
100 metres tall. That’s twice the height of Nelson’s column!
The tallest native European
tree is the Caucasian Fir,
which can reach a height of
68 metres.
Eucalyptus trees imported
from Australia to Spain have
been known to grow to a
height of 80 metres.
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How big can plants grow?
The Giant Sequoia, Sequoiadendron giganteum, does not
grow as tall as the Coast Redwood but it has a larger volume.
The largest, General Sherman, has a volume of almost
1,500m3, about half the volume of an Olympic swimming pool.
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What is the oldest plant in the world?
Bristlecone pines, found in the
USA, are the oldest-known plants.
They can live for over 4,000 years.
Unlike animal cells, there is no
limit to the number of times plant
cells can divide and multiply.
It is common for trees to live for
100 years but rare for animals to
live this long. Why?
Plant cells can differentiate to
form specific cells throughout the
plant’s life. Animal cells lose this ability early in their life cycle.
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What do plants need to grow?
This plant hasn’t been looked after very well. What do plants
need to grow healthily?
sunlight and an air supply
water
mineral nutrients.
If a plant cannot get these from
its environment, can it move to
somewhere else?
Plants are rooted to one place.
However, they can control their
direction of growth.
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What controls plant growth?
Plants grow in response to
their environment.
The shoots of these tulips
grow upwards and the
roots grow downwards.
To what environmental
factors do plants respond
to make sure they grow
properly?
If a plant was unable to do
this it might not be able to
get enough water or sunlight
from its environment.
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What do plants respond to?
Plants are very sensitive and their growth is affected by
their environmental conditions.
Any condition that affects plant growth is called a stimulus.
light water gravity
Which stimulus will have the
strongest effect on the plant?
What are three types of stimuli that plants respond to?
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A tropism is a growth movement in response to a stimulus.
Plants grow towards or away from stimuli.
A growth movement towards a stimulus
is called a positive tropism.
A growth movement away from a
stimulus is called a negative tropism.
What is a tropism?
Will all the parts of a plant respond
to a stimulus in the same way?
What is growth away from
a stimulus called?
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Plant responses to stimuli are given specific names:
What do the names of each tropism mean?
water gravitylight
hydrotropism geotropismphototropism
Which parts of a plant respond to these different stimuli?
Are there different types of tropisms?
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How do tropisms affect growth?
This plant does not have a
very straight stem. What
might have caused this?
The shoots of plants grow
towards sunlight.
The plant was placed on a
window sill and received light
from one direction only.
What is the name of this
type of plant response?
The response to sunlight
is called phototropism.
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Do plants have hormones too?
The growth of shoots and roots is
controlled by a group of hormones
called auxins. These chemicals are
produced in the tips of the shoots
and roots.
Like humans, plants use hormones,
(chemical messengers)
to control their development.
Hormones produced by plants
control growth, flowering and
fruit ripening.
What environmental stimuli might
cause a plant to produce auxins?
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Which way up?
How do plants always grow the right way up?
Plants respond to gravity to grow in the right direction.
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Roots always grow towards water, which is a positive
tropism.
Roots will grow sideways, or even upwards, towards water.
Roots always have a stronger response to water than
gravity to ensure that a plant gets the water it needs.
How do roots respond to water?
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How do roots and shoots respond to stimuli?
Shoots grow towards sunlight.
They are positively phototropic.
Plant stimuli affect certain parts of the plant in different ways.
Shoots grow away from gravity.
They are negatively geotropic.
Roots grow away from sunlight.
They are negatively phototropic.
Roots grow towards gravity.
They are positively geotropic.
What experiments can be used to test these ideas?
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growing cuttings
killing weeds.
ripening fruit
Why are these purposes useful for gardeners and farmers?
Plant hormones are naturally-occurring chemicals but they
can also be produced synthetically for use in gardening and
agriculture such as:
How can plant hormones be used?
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A cutting is a part of plant that is removed from the main
shoot. Do cuttings have everything they need to grow?
How are cuttings grown?
A cutting does not have roots and so has no supply of water
or minerals.
To stimulate root growth,
cuttings are dipped into
rooting powder. This
contains plant growth
hormones.
Cuttings are genetically
identical to the parent
plant. This allows growers
to copy successful plants.
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Weeds are unwelcome plants that compete with the plants
being grown by gardeners and farmers.
How do plant hormones kill weeds?
Plant hormones can be used
instead to make weedkillers
that only affect certain plants.
However, many chemicals that are potential weedkillers are
toxic to animals and humans, as well as plants.
Most weeds have broad
leaves. Cereals, which have
narrow leaves, can be
protected from weeds by using
weedkillers that only effect the
growth of broadleaved plants.
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Fruit often has to
travels thousands of
miles from where it is
picked to where it is
sold in the shops.
How are hormones used to ripen fruit?
When the fruit reaches its destination, it can then be sprayed
with artificial plant hormones to encourage ripening.
Fruit is often picked before it is fully ripe. Why might this
help keep the fruit edible?
Unripe fruit is harder and
less likely to bruise than
ripe fruit when transported.
Why might it be a good idea to wash fruit before eating it?
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Which hormone makes fruit ripen?
Using artificial ethylene to ripen
fruit is not just a modern practice.
Ancient Egyptians exposed figs to
natural gas, which contains
ethylene, to encourage ripening.
Ethylene is a plant hormone that controls fruit ripening.
It can be sprayed on unripe fruit to speed up ripening.
Why might it be important to keep fruit
away from coal-burning engines during
transportation?
Some fruit, such as bananas, actually
produce a large amount of ethylene, which
can cause other nearby fruits to ripen.
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What do plants need for a balanced diet?
Plants need carbon dioxide and water for photosynthesis.
Do they need any other nutrients to keep healthy?
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What minerals do plants need?
Plants also need mineral ions for healthy growth.
Some of the most important minerals needed by plants are:
The mineral ions are found in salts, dissolved in water.
Plants obtain minerals when they absorb water from the soil.
How do plants obtain these minerals?
nitrogen
potassium ions
phosphorus
potassium
magnesium magnesium ions
phosphates
nitrates
What type of salt are each of these elements found in?
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Mineral ions are used by plants for growth and to build new
cells.
making proteins for growth
respiration and making roots
respiration and photosynthesis
making chlorophyll
Mineral element How mineral is used in plants
nitrogen (N)
phosphorus (P)
potassium (K)
magnesium (Mg)
What are minerals used for?
Plants need a variety of minerals because they are used
by the plant in different ways.
How are the four key mineral ions used by plants?
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How do minerals affect cell formation?
nitrogen is needed to make
amino acids and proteins
phosphorus is needed to make
DNA and cell membranes
potassium helps enzymes
work during photosynthesis
magnesium is needed to
make chlorophyll.
Minerals form the building
blocks of vital cell components:
What would happen to the plant if it
was not able to get these nutrients?
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Plants do not grow properly and begin to look unhealthy
if they are deprived of minerals.
If a plant does not get enough of a mineral it is said to
have a mineral deficiency.
What happens when plants do not get minerals?
Do all mineral deficiencies affect a plant in the same way?
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Where do minerals come from?
Rocks. The minerals in rocks are
slowly dissolved by rainwater,
which is slightly acidic. These
minerals are washed into the soil.
What are the sources of minerals in the soil?
Why might farmers need to add fertilizers to their soil?
Natural fertilizers. Animal
faeces and the decay of dead
plants and animals return
minerals to the soil.
Artificial fertilizers. These
contain a ready-made mixture of
the minerals needed by plants.
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30% phosphorus
15% nitrogen
What are NPK values?
Fertilizers will often show NPK values on their labels.
What do you think these letters stand for?
NPK stands for nitrogen (N), phosphorus (P), and potassium
(K). Fertilizers contain these elements because plants need
these nutrients in higher quantities than other minerals.
What percentage of each mineral is in a
fertilizer with the NPK value 20–10–5?
The numbers show the percentage of each
mineral element. This fertilizer contains:
15% potassium.
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Glossary (1/2)
auxins – Plant hormones that control the rate of growth.
cutting – Part of a plant that has been removed from the
main shoot and does not have roots.
ethylene – A plant hormone used to ripen fruit.
geotropism – A growth movement in response to gravity.
hydrotropism – A growth movement in response to water.
mineral deficiency – A condition that occurs when a plant
is missing one or more of the minerals needed for growth.
mineral ions – Naturally-occurring or synthetic chemicals
needed for healthy plant growth.
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Glossary (2/2)
mineral salts – Compounds containing essential plant
minerals.
negative tropism – A growth movement away from a
stimulus.
NPK value – The percentage of nitrogen, phosphorus and
potassium available in a fertilizer.
phototropism – A growth movement in response to light.
positive tropism – A growth movement towards a
stimulus.
tropism – Any growth movement in response to a
stimulus.