Sustainability and
interdependence
Key areas:
1. Food supply, plant growth and productivity
2. Plant and animal breeding by manipulation of
heredity
3. Crop protection
4. Animal welfare and behavioural indicators of
poor welfare
5. Symbiosis
6. Social behaviour
7. Mass extinction, regaining biodiversity and
measuring biodiversity
8. Threats to biodiversity
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Sustainability
and
interdependence
Key area 1: Food supply, plant
growth and productivity
Food supply
LI:
1. Describe the problems arising from an
increasing human population in terms
of food supply.
2. Describe how agriculture can be used
to control plant growth.
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Food supply
The human population in currently
growing.
The present human population is:
http://www.census.gov/popclock/
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United
Nations
estimate of
how the
human
population
could
increase.
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Feeding over 7 billion people requires a
sufficient and sustainable supply of
food.
This makes food security a massively
important subject for the future of the
human race.
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Food security
Food security is defined as:
Sufficient
food must be
available at
all times
Quantity
Quality
Food
security
Access
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Food is
sufficiently
nutritious
and varied to
provide a
balanced diet
People have
economic
means to
Sustainability
and
obtain the available
interdependence
food
Food security: The challenge
Watch these videos Feeding the future and Food
security
Get a copy of this article from Science (a highly
respected science publication) on Food Security.
Divide into small groups. Divide the article up and
each read a separate section.
After reading discuss each section. Come up with a
list of the main challenges in assuring food
security in the future.
How can biological science contribute to solving
these challenges?
Produce a A4 summary of the challenges and
solutions to be photocopied for each group
Sustainability
member.
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and
interdependence
Agricultural production
The earth possesses 75,000 edible plant
species, yet we depend on a few to
produce 95% of what we eat.
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Main crop species
Cereals
Maize
Legumes
Root crops
Rice
Potato
Cassava
Soya bean
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Improving yields
As the area of land suitable for growing
crops is limited, agriculture can:
1. Add minerals (fertiliser) or water
(irrigation systems) to remove factors
which may be limiting plant growth.
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2. Replace existing strains of crops with a
higher-yielding cultivar (cultured
variety).
3. Protect crops from pests (e.g. insects),
diseases (e.g. fungi), and competition
(from weeds) by using pesticides,
fungicides and herbicides.
4. Develop pest-resistant crop plants.
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Productivity of arable land
Think back to National 5: What were the three
ways that energy is lost from a food chain?
Energy is lost from food chains in the
following ways:
Undigested
food and waste
Only 10% is
incorporated into
body tissues
Movement
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Maintaining body
temperature
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As you move a long a food chain, energy is
lost between each trophic level and the
next.
90% energy lost
Cereal plant
Farm animal
10% energy
passed on
90% energy lost
Human
10% energy
passed on
As a result of this loss of energy livestock
production generates far less food per
area of land than plant production.
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Shorter food chains have much less loss of
energy:
90% energy lost
Cereal plant
10,000 kJ
90% energy lost
Farm animal
10% energy
passed on
1,000 kJ
Human
10% energy
passed on
100 kJ
90% energy lost
Cereal plant
10,000 kJ
Human
10% energy
passed on
1,000 kJ
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Therefore arable land planted with crops
produces far more food than the same
land planted with grass to feed
livestock.
However, not all land can be
planted with crops. In this
case it is more efficient to
use them for livestock.
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Plant growth and productivity
LI:
1. Describe the processes underlying
photosynthesis.
2. Explain the links between
photosynthesis and plant productivity.
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Plant growth: Photosynthesis
Reminder of photosynthesis from National 5:
Take a piece of blank paper – discuss the
following:
• Write the summary word equation for
photosynthesis
• Name the two stages.
• Describe what happens in each stage.
Pass the sheet to the next group. Tick the
correct bits and add any corrections.
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What is light?
Light is a form of electromagnetic
radiation which travels in waves.
Wavelength
Light
wave
The distance between two crests on a wave
is called the wavelength and is measured
in nanometres (nm). (1 nm = 10-9 m)
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Visible light is made up of a spectrum of
different colours.
Each colour of light has
a different wavelength.
400 nm
500 nm
600 nm
700 nm
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Colour in a copy
of the visible
light spectrum in
your jotters.
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and
interdependence
The fate of light when it hits a
leaf
White
light
hitting a
leaf (or
any
surface)
will be
either:
Reflected
Absorbed
Transmitted
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Light absorption by leaf pigments
Leaves contain several coloured pigments
of which chlorophyll is the most
important.
These pigments absorb light energy.
These pigments absorb different
wavelengths of light.
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Which wavelengths of light are
used by plants
Your teacher will explain how to extract
leaf pigments from nettles.
Place the leaf pigments solution in front
of a spectroscope. This will show which
colours are absorbed by the leaf
pigments.
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•
•
•
•
•
Collect a leaf and cut into small pieces.
Add some propanone and sand into a
mortar and pestle.
Grind this up, until the propanone turns
green.
Filter the mixture into a test tube.
Hold the spectroscope up towards the
test tube and look towards the light.
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violet
blue
green
yellow
orange red
Colour in the normal spectrum. Then colour
in a second copy of the spectrum viewed
through the leaf pigments:
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Spectrum viewed through Chlorophyll
violet
blue
green
yellow
orange red
The blue and violet are no longer visible and
only some of the red is still seen. These
have been absorbed by the leaf pigments.
These are most important wavelengths for
a plant in photosynthesis.
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Separation of leaf pigments by
thin-layer chromatography
Follow the instructions for the separation
of leaf pigments by chromatography
practical.
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Absorption and Action Spectra
A leaf contains several pigments which
can be separated by chromatography.
The main pigments are:
1. Chlorophyll a (blue-green*)
2. Chlorophyll b (yellow-green*)
3. Carotene (yellow*)
4. Xanthophyll (yellow*)
* This is the colour of the spot on the chromatography paper
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An absorption spectrum shows the
absorption of light of each wavelength
by each pigment.
An action spectrum shows the rate of
photosynthesis at each light wavelength.
Comparison of absorption and action
spectra reveals a close match – this is
good evidence for the importance of leaf
pigments in photosynthesis. Sustainability
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Absorption
spectrum
Action
spectrum
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Accessory pigments
The xanthophyll and carotene allow the
plant to carry out photosynthesis is a
wider range of light wavelengths.
They are known as accessory pigments as
they pass the energy they capture onto
chlorophyll a and b.
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The chloroplast
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The photosynthetic pigments are
contained with in the grana. Therefore
this is where absorption of light energy
and photosynthesis take place.
Carbon fixation occurs with in the stroma
of the chloroplast.
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Capture of energy and photolysis
In the chloroplast, when light energy is
absorbed by Chlorophyll a, its electrons
become excited and are raised to a
higher energy state.
High energy electrons are captured by
the primary energy acceptor.
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The electrons are then transferred along
an electron transport chain releasing
energy.
This energy is used by the enzyme ATP
synthase to generate ATP.
Some of the energy is also used to split
water into hydrogen – which is picked by
by the hydrogen acceptor NADP to
make NADPH – and oxygen.
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1. Light energy is Primary electron + H+ H+
acceptor H
absorbed by the
chlorophyll creating
high-energy electrons
Chlorophyll
3. Energy also
used to split water Oxygen
Water
2. Electron
+ H+ H+
H
passed along
transport chain, H+ H+ H+
pumping H+ into
grana.
5. Hydrogen ions
used by ATP
synthase to make
ATP for carbon
fixation (calvin
cycle).
H+
ADP + Pi
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Hydrogen
NADP
NADPH
H+
ATP
4. Hydrogen picked by
NADP to make NADPH
for carbon fixation
(calvin cycle).
ATP synthase
enzyme
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Calvin Cycle (Carbon fixation)
At the end of the first stage of
photosynthesis (the light dependent
stage), the hydrogen (in the form of
NADPH) and the ATP are essential for
the second stage – known as the Calvin
cycle.
This takes place in the stroma of the
chloroplast.
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RuBisCO
3-phosphoglycerate
3-phosphoglycerate
Glyceraldehyde-3phosphate
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1. Carbon dioxide enters the cycle and
becomes attached to RuBP (ribulose
bisphosphate). This reaction is
controlled by the enzyme RuBisCO
(ribulose bisphosphate
carboxylase/oxygenase).
2. The Carbon dioxide and RuBP combine
to make 3-phosphoglycerate.
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3. The 3-phosphoglycerate then joins with
the hydrogen from NADPH and is
phosphorylated by the addition of inorganic
phosphate (Pi) from ATP which supplies the
energy.
4. This process produces glyceraldehyde-3phosphate (G3P).
5. Some G3P is then used to regenerate
RuBP (to continue the process). The
remainder is used to synthesis sugars.
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Uses of sugar
The sugar formed during photosynthesis
goes onto the following uses:
Glucose
Respiration
Starch
(Storage
carbohydrate)
Cellulose
(Structural
carbohydrate
e.g. cell wall)
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Biosynthesis
pathways
Fats and
oils
Nucleic
acids
Proteins
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Plant productivity
The biomass of a population of plants is
its total mass. This is normally measured
as dry mass – as the water content of
living organisms varies greatly through
out the year.
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Assimilation
The conversion of the glucose produced
by photosynthesis into complex
components of the plant cell is called
assimilation. This process causes an
increase in the plants biomass.
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Net assimilation
As some of the sugar produced in
photosynthesis is used up during
respiration, therefore:
Gain in dry
Net assimilation =
mass by
photosynthesis
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+
Loss in mass
caused by
respiration
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Plant productivity
Productivity is the rate at which plants in
an ecosystem generate new biomass.
It is measured as “units of biomass per
unit area per unit time” e.g. grams per
square metre per yer.
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Factors affecting plant
productivity
The rate of photosynthesis (and
productivity) is affected by several
environmental factors known as limiting
factors.
These include: temperature, light
intensity and carbon dioxide
concentration.
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The rate at which photosynthesis
proceeds to limited by which ever one of
these factors is in short supply.
e.g. Light intensity would be the limiting
factor on a dull summer day.
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Assessing productivity
In order to grow crops efficiently to
ensure the maximum yield,
farmers/scientists/policy makers need to
be able to assess the growing potential of
the area.
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The biological yield of an area is the total
biomass of plant produced this is useful
because tells you the total producing
power of the land.
The economic yield of an area is the mass
of the desired product (e.g. mass of just
the barley grains from a barley field)
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The harvest index is calculated using this
formula:
dry mass of economic yield
dry mass of biological yield
This gives a useful estimate of what is
wasted during the growth of a crop.
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