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Biology
Contents
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Plant Processes
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◦ Leaf structure
◦ Photosynthesis
◦ Biomass
 Pyramid of Numbers
 Pyramid of Biomass
 Limiting Factors
 Uses of Glucose
◦ Intensive Farming and
Organic Farming
◦ Plants and Water
 Osmosis
 Osmosis in Different Cells
 Pesticides
 Fertilisers
 Eutrophication
◦ Transpiration
◦ Plant Growth and
Fertilisers
 Plant Senses and their
Commercial Uses
 Response to Water
 Response to Gravity
 Response to Light
Biomass, Farming and
Decay
◦ Decay and Food
Preservation
◦ Recycling of Carbon and
Nitrogen
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Key Words
Back to Contents
Leaf structure
Photosynthesis
Limiting Factors
Uses of Glucose
Plants and Water
Osmosis
Osmosis in Different Cells
Transpiration
Plant Growth and Fertilisers
Plant Senses and their Commercial Uses
Response to Water
Response to Gravity
Response to Light
PLANT PROCESSES
The Leaf Structure
The Leaf
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It is the organ of photosynthesis
the guard cells become flaccid and less
curved. This closes the stomata to save
The waxy cuticle is a waterproof layer
on water
that cuts down the loss of water by
evaporation
 When there is a lot of water the guard
cells become turgid and curved. The
The epidermis allows sunlight to pass
stomata are open and allows the water
through to the palisade cells where
to escape
most of photosynthesis takes place
It contains lots of chloroplasts which  For maximum efficiency, the plant:
◦ Leaves are flat with a large surface area to
contains chlorophyll to absorb sunlight
absorb as much sunlight as possible
The spongy layer contains rounded
◦ They are thin to allow carbon dioxide to
cells with lots of air spaces to allow
reach the inner cells easily
carbon dioxide to circulate and reach
◦ They have plenty of stomata in the lower
the palisade cells
skin
The leaf vein contains xylem and
◦ They have plenty of veins to support the
phloem tubes which supply water and
leaf and carry substances around the plant
glucose throughout the plant
At the bottom are stomata which
open and close to let carbon dioxide
in and water vapour and oxygen out
Guard cells surround the stomata and
control their opening and closing
When there is a short supply of water
Leaves and Photosynthesis
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A leaf has an upper and lower epidermis covered with a waxy cuticle
The spongy mesophyll and palisade cells contain chloroplasts
Guard cells surround the stomata
Leaves are adapted for efficient photosynthesis by having a large surface
area, being thin and having veins
Photosynthesis occurs mainly in the leaves
Water enters the root hairs by osmosis
Carbon dioxide enters and oxygen leaves by diffusion through stomata
The leaf is very efficient in photosynthesising because it has a large
internal surface area, internal air spaces and many chloroplasts in the
palisade layer
There are three main limiting factors that affect the rate of
photosynthesis. They are:
◦ Light
◦ Carbon dioxide
◦ Temperature
Limiting Factors
Light
Rate of Photosynthesis
Temperature
• If the light intensity is increased,
photosynthesis will increase
steadily, but only up to a certain
point
• After this point, increasing the
amount of light will not make
any difference as it will be either
the amount of CO₂ or
temperature that is the limiting
factor
Amount of Light
Rate of Photosynthesis
• If carbon dioxide
concentration is increased,
photosynthesis will increase
to a certain point
• Beyond this point, light or
temperature become the
limiting factor
Rate of Photosynthesis
Carbon Dioxide
• You can increase light and CO₂ as much as
possible, but the temperature must not get
too cold or too hot
• A temperature of about 45°C destroys the
enzymes in chloroplasts
• Usually the rate of photosynthesis is limited
by the temperature being too low, as is the
case for plants not normally grown in
Britain
• Greenhouses help maintain a high enough
temperature for optimum growth
conditions
Carbon Dioxide Concentration
Temperature
45°C
Uses of Glucose
Some glucose is used in respiration to obtain
energy
 Other uses include converting it to:
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◦ Insoluble starch stored in the roots, particularly in the
winter. In this form it does not cause too much water
to move into the cells by osmosis, as it doesn’t
contribute to the concentration inside the cells
◦ Cellulose, needed for cell walls
◦ Lipids and oils are formed from glucose and stored in
seeds
◦ Glucose can also be combined with other substances,
such as nitrates obtained from the oil and turned into
proteins
Plants and Water
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Plant cells are supported by their cell walls and turgor pressure in
the cell sap
Water enters the root hairs by osmosis
Osmosis is the movement of water from a high concentration to a
low concentration through semi-permeable membrane
A semi-permeable membrane only allows the movement of small
molecules
Water moves both in and out of the root to try to even the
concentrations. Therefore we use the net movement of water
Osmosis is a type of diffusion
A plant must balance its water uptake and water loss
Water is needed for photosynthesis, cooling and transport
A leaf is adapted to reduce water loss
Leaves lose water because a leaf is adapted for photosynthesis
Osmosis
Root hairs take in water by osmosis
 Water moves along the cells of the
root and up the xylem to the leaf
 All the time the water is moving to
areas of lower water concentration
 Osmosis makes plant cells swell up
 The water moves into the plant cell
vacuole and pushes against the cell
wall making it turgid
 It is useful as it gives the stem
support
 When there is little water the cells
become flaccid as water has moved
out of the cell
 If a lot of water leaves the cell, the
cytoplasm started to peel away from
the cell wall which is called
plasmolysis
 The cell will behave differently in an
animal cell because there is no cell
wall to prevent the cell from
bursting (haemolysis)
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In an Animal
In a Plant
Too Much Water
Normal
Too Little Water
Osmosis in Different Cells
Transpiration
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Water loss from a plant is called transpiration
The water evaporates and exits the leaves by diffusion
Water travels from the roots, through the stem to the leaves in xylem cells
Dissolved food travels downwards in phloem cells
The rate of transpiration is speeded up by a higher temperature, more wind, a
low humidity and more light
More light will increase the transpiration rate because the stomata will be
open
A higher temperature will increase the transpiration rate by increasing the
diffusion rate
A low humidity will allow more water vapour to diffuse out of the leaves
Xylem cells are dead because they have extra lignin thickening
The flow of water up the xylem to the leaves is called the transpiration
stream
The transpiration stream also draws minerals into the plant as well as water
As water is lost, the transpiration stream replaces it so there is a constant
flow
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Fertilisers and Plant Growth
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Plants need minerals in fertilisers such as nitrates, phosphates,
potassium and magnesium compounds
Minerals are needed only in small quantities
Nitrates are needed to make proteins for growth
Phosphates are needed for root growth
Potassium is needed for flower formation
Magnesium is needed to make chlorophyll
If minerals are missing from the soil water, the plant shows that it
is mineral-deficient
Minerals are taken up from the soil water by active transport
Minerals are taken up against a concentration gradient
Active transport uses energy
An NPK fertiliser contains nitrogen (N), phosphorus (P) and
potassium (K)
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Plant Senses
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Plants respond to their
surroundings to give them a
better chance of survival
Plant responses are called
tropisms and are controlled
by a hormone
Plants respond to light,
gravity and water
Remember: unequal
distribution of auxin speeds
up growth in shoots and
slows down growth in
roots
Commercial Uses
Growing Cuttings
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Rooting powder contains synthetic auxins
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A cutting is taken from a plant and dipped in
this powder. This stimulates the roots to
grow quickly and enables gardeners to grow
lots of exact copies of a particular plant
Killing Weeds
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Synthetic auxins are used as selective weedkillers
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They only affect the broad-leaved weeds;
narrow-leaved grasses and cereals are not
affected
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They kill the weed by making the weed grow
to quickly
Seedless Fruits
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Synthetic auxins are sprayed on unpollinated
flowers
Fruits form without fertilisation and thus
form without pips
Early Ripening
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Plant hormones can also be used to ripen
fruit in transport
Plant Senses and Commercial Uses
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Response to Water
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A plant’s response to water is
called hydrotropism
Roots always grow to a certain
extent towards water, even if it
means ignoring the pull of gravity
and growing sideways
An uneven amount of moisture
will cause more auxin to appear
on the side with more water
This inhibits the growth of cells
on this side
The root cells on the outside will
grow quicker and will bend
towards the moisture
Response to Gravity
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A plant’s response to gravity is
called geotropism
Even if you plant a seed the
wrong way up, the shoot always
grows up, away from gravity and
the root grows down towards
gravity
If a plant is put on its side, auxin
gathers on the lower half of the
shoot and root
Auxin slows down the growth of
root cells, so the root curves
downwards
Auxin speeds up the growth of
the shoot cells so the shoot
curves up
Responses to Water and Gravity
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Response to Light
A plant’s response to light is called phototropism
 Plants need light for photosynthesis and thus grow
towards the light
 Normally light shines from above. Auxin is spread evenly
and the shoot grows upwards
 If light comes from one side, auxin accumulates down the
shaded side. Auxin makes these cells grow faster
 The result is that the shoot bends towards the light
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Biomass
Pyramid of Numbers
Pyramid of Biomass
Intensive Farming and Organic Farming
Pesticides
Fertilisers
Eutrophication
Decay and Food Preservation
Recycling of Carbon
Recycling of Nitrogen
BIOMASS, FARMING
AND DECAY
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Biomass
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Energy enters food chains in photosynthesis
Plants are producers because they produce food
Animals are consumers
A pyramid of numbers show the number of organisms in
each link (trophic level) in a food chain
A pyramid of biomass shows the mass of living material in
each link (trophic level) in a food chain
Energy is transferred along a food chain or food web
Some energy is transferred into less useful forms such as
hear or body waste
Biomass fuels are wood (by burning), alcohol (by
fermentation) and biogas (from decay)
Biomass fuels are renewable, produce less pollution and are
energy self-reliant
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Pyramids of Numbers
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A pyramid of numbers tells us how many
organisms are involved at each stage in the
food chain
At each trophic level the number of
organisms get less
However, sometimes a pyramid of numbers
doesn’t look like a pyramid at all because it
doesn’t take into account the size of the
organisms
◦ E.g. There are many fleas on a single fox which
would make the pyramid ‘top heavy’
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Pyramids of Biomass
A biomass pyramid takes into account the
size of an organism at each level unlike
the pyramid of numbers
 It looks at the mass of the organism
 You can take the information from the
pyramid of numbers and multiply it by the
organism’s mass which will achieve the
pyramid shape again
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Intensive and Organic Farming
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Intensive farming uses pesticides (insecticide and fungicide)
to kill pests and herbicides to kill weeds
Intensive farming produces more food but also causes
problems such as pesticides accumulation in food chains
Fish farming, glasshouses, hydroponics and battery farming
are all examples of intensive farming
Organic farming does not use artificial fertilisers, herbicides
or pesticides
Organic farming uses animal manure, crop rotation, handweeding and biological control of pests
Intensive farming improves the efficiency of energy transfer
in food chains
Hydroponics gives better control of fertilisers and diseases
Intensive Farming
 Intensive
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farming can produce
more food because it is designed
to provide more food for the given
land
 Many people regard intensive
farming of animals as cruel
 In order to produce more food
from the land, fertilisers and
pesticides are needed
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Pesticides
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Pesticides are used to kill insects that
damage crops
They also kill harmless insects, then insecteating birds have a shortage of food
The pesticides can get washed into rivers
and lake which can then get into our food
chains
This was the case in the 60s when a
pesticide, DDT, got into the food chain and
threatened populations of animals
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Fertilisers
Plants need nutrients from the soil to grow
Artificial fertilisers are used to replace the
nutrients in the soil because there isn’t
enough because of intensive farming
 Fertilisers enable farmers to crop more
crops in a smaller space.
 Less countryside will be lost for farming
but eutrophication is caused because of
fertilisers
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Eutrophication
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If too much fertiliser is used and it rains, it goes into
rivers and lakes
The water plants grow quicker as a result of this and
they quickly cover the surface of the water
There is then more competition for light and some
plants die
Microbes break down the dead plants and use the
oxygen for respiration
The amount of oxygen in the water is then reduced
and animals die through suffocation
Untreated sewage can also cause eutrophication
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Organic Farming
People need to limit their needs
Intensive farming produces quality food and
enough to supply people’s needs in Europe but
has its problems – alternative is organic farming
 Organic farming produces less food per area of
land but is kinder to the environment
 Organic farming uses manure as a fertiliser and
has land for wild plants and animals to flourish.
 Biological control of pests are also used where
animals eat the pests, it’s not as effective but it
isn’t harmful
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Decay and Food Preservation
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Decomposers such as fungi and bacteria cause decay
Decay breaks down sewage and compost
Decay is affected by temperature and the amount of oxygen
and water
Detritivores are animals that feed on dead and decaying
material
Earthworms, maggots and woodlice are Detritivores
Saprophytes are plants that live on dead and decaying
material
Food can be preserved by stopping or reducing decay
Food preservation methods include canning, freezing, drying
and adding salt, sugar or vinegar
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Recycling of Nitrogen and Carbon
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When plants and animals die, their chemicals, such as nitrogen and carbon,
are recycled
Plants remove carbon fro the air by photosynthesis
Respiration and the burning of fossil fuels releases carbon in the form of
carbon dioxide
Carbon is recycled through marine shells, limestone and eventual
weathering
There is 78% nitrogen in the atmosphere but it is unreactive
Plants take in nitrogen as nitrates
Dead bodies decay, releasing nitrates
Decomposers convert proteins and urea into ammonia
Ammonia is converted into nitrates by nitrifying bacteria
Some nitrates are converted into nitrogen by denitrifying bacteria
Nitrogen-fixing bacteria in the soil and root nodules fix atmospheric
nitrogen
(This is further explained on the next few slides...)
THE CARBON
CYCLE
The atmosphere
Photosynthesis
Death and Decay
Decomposers
Death but no decay
Feeding
Respiration
Burning and
Combustion
Fossil Fuels
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THE CARBON CYCLE IN
DETAIL
Added Notes:
In the atmosphere, carbon
dioxide is a rare gas, making up
only 0.03% of the atmosphere.
The amount should stay that
same because plants absorb the
carbon that is realised.
Plants absorb carbon dioxide
during photosynthesis. They
use the carbon to make
carbohydrates, proteins and fats
using the Sun for energy.
Animals eat the plants and so
they absorb the carbon. However,
the animals also respire.
Carbon is realised into the soil
because the animals and plants
die and produce waste through
death and decay.
However, sometimes the plants
and animals die but do not
decay. The heat and pressure
then produce fossil fuels over
millions of years.
Bacteria and fungi in the soil
break down the dead matter,
urine and faeces – all of which
contain carbon. The
decomposers realise carbon
dioxide when they respire.
Fossil fuels are produced,
making coal from plants as well
as oil and gas from animals. The
fossil fuels then realise carbon
dioxide when they are burnt in
the industry.
All plants, animals and
decomposers respire.
Respiration then realises
carbon dioxide into the
atmosphere again.
Decomposition
•Decomposers
are bacteria and fungi
which break down dead material
•They help recycle carbon into the
atmosphere and recycle nutrients
into the soil
•Plants use this nutrients dissolved in
water during photosynthesis.
•Animals eat plants, and both animals
and plants die, making the cycle start
from the beginning again
•Decomposition happens everywhere
in nature, in compost heaps and even
sewage works
•The perfect conditions are:
• Warm
• Moist
• Plenty of oxygen
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THE NITROGEN CYCLE
Nitrates into
Nitrogen
• Denitrifying
bacteria
• Plants and dissolved
in water
Nitrogen into
Nitrates
• Lightening
• Artificial fertilisers
• Nitrogen-fixing
bacteria
• Nitrifying bacteria
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THE NITROGEN CYCLE
1. Nitrogen is in the air
8. Animals and plants produce
waste.
9. Animals and plants die and
their bodies decay.
2. Lightening causes
nitrogen oxides by combining
oxygen and nitrogen.
Dissolved in the rain, they are
washed into the soil and form
nitrates.
7. Animals eat the plants
and the protein becomes part
of the animals’ proteins.
10. Detritivores, e.g.
worms, feed on the decaying
material which make it easier
for decomposers to break
down.
3. Nitrogen-fixing bacteria
in the soil convert nitrogen in
the air into nitrates.
6. Plants take the nitrates
and convert them into
proteins.
11. Decomposers, e.g.
Bacteria, turn this material
into ammonium
compounds – which contain
nitrogen.
14. Denitrifying bacteria
live in waterlogged soils and
change nitrates back into
ammonia which returns
nitrogen into that
atmosphere again
4. Nitrogen-fixing bacteria
are in the roots of some
plants, e.g. Beans. The
bacteria form root nodules
which improves the nitrate
content of the soil.
5. Fertilisers generated
from the Haber process
can be added to the soil to
improve the nitrate content.
12. Nitrifying bacteria in
the soil change ammonia
into nitrates.
13. Nitrates can be washed
out of the soil before they
are used. This is called
leaching and can have
serious consequences for
rivers and streams.
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THE NITROGEN CYCLE
ADDED NOTES
•The
atmosphere contains 78%
nitrogen gas
•Nitrogen is needed to make
protein
•Plants and animals cannot use
nitrogen as a gas – it has to be
converted into nitrates
•Animals get protein by eating
plants which plants make from
nitrates
•It is a continuous cycle
•There are four ways that nitrogen
is converted into nitrates and only
two ways that nitrogen is taken out
of the soil
•There are three different types of
bacteria involved in this cycle:
• Nitrifying bacteria
• Nitrogen-fixing bacteria
• Denitrifying bacteria
Proteins in
Plants
Proteins in
Animals
Death and
Decay
Fertilisers
Nitrogen in
the air
Soil
Nitrates
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Photosynthesis
Respiration
Combustion
Carbon
Fossil fuels
Decomposers/decompositi
on
Nutrients
Warmth
Moisture
Oxygen
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Lightening
Nitrates
Nitrogen
Nitrogen-fixing bacteria
Root nodules
Protein
Detritivores
Decomposers
Nitrifying bacteria
Leaching
Denitrifying bacteria
Key/ Scientific Words
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More Key/ Scientific Words...
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Xylem
Phloem
Transpiration
Starch
Vascular bundle
Nitrates
Phosphates
Potassium
Magnesium
Iron
Osmosis
Large surface area
Transpiration stream
Cuticle
Stomata
Guard cells
Light
Temperature
Humidity
Flaccid
Turgid
Carbon dioxide
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Water
Glucose
Oxygen
Photosynthesis
Cellulose
Lipids
Proteins
Enzymes
Epidermis
Palisade cells
Leaf vein
Spongy layer/ mesophyll
Chloroplasts
Chlorophyll
Active transport
Diffusion
Semi-permeable
Net movement
Plasmolysis
Haemolysis
Limiting factors
Lignin
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Concentration gradient
Biomass
Pyramid of numbers
Trophic level
Biogas
Fermentation
Pesticides
Intensive farming
Organic farming
Fertilisers
Eutrophication
Hydroponics
Decomposers
Detritivores
Saprophytes
Tropisms
Auxin
Hydrotropism
Geotropism
Phototropism