Sustainability and interdependence. CFE Higher Biology Sustainability and interdependence Key areas:...

Sustainability and interdependence

CFE Higher BiologySustainability

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Key areas:1. Food supply, plant growth and

productivity2. Plant and animal breeding by

manipulation of heredity3. Crop protection4. Animal welfare and behavioural

indicators of poor welfare5. Symbiosis6. Social behaviour7. Mass extinction, regaining biodiversity

and measuring biodiversity8. Threats to biodiversity

Key area 1: Food supply, plant growth and productivity


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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 securityFood security is defined as:

Food security

Quantity Quality

Access

Sufficient food must be available at all times

Food is sufficiently nutritious and varied to provide a balanced diet

People have economic means to obtain the available food


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Food security: The challengeWatch these videos Feeding the future and

Food securityGet 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 member.


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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 speciesCereals Root

crops

Legumes

Maize 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 landThink 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:

Movement

Maintaining body temperature

Undigested food and

waste

Only 10% is incorporated into

body tissues


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As you move a long a food chain, energy is lost between each trophic level and the next.

Cereal plant Farm animal Human

As a result of this loss of energy livestock production generates far less food per area of land than plant production.

90% energy lost 90% energy lost

10% energy passed on



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Shorter food chains have much less loss of energy:

Cereal plant Farm animal Human

Cereal plant Human

90% energy lost 90% energy lost



90% energy lost


10,000 kJ 1,000 kJ 100 kJ

10,000 kJ 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.

The distance between two crests on a wave is called the wavelength and is measured in nanometres (nm). (1 nm = 10-9 m)

Light wave

Wavelength


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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

Colour in a copy of the visible light spectrum in your jotters.


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The fate of light when it hits a leaf

White

light

Absorbed

Reflected

Transmitted

White light hitting a leaf (or any surface) will be either:


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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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violet blue green yellow orange

red

Spectrum viewed through Chlorophyll

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 SpectraA 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.


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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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Chlorophyll

1. Light energy is absorbed by the chlorophyll creating high-energy electrons

ADP + Pi ATP

Primary electron acceptor H+H+ H+

H+H+ H+

Water

Oxygen

Hydrogen

NADPH

NADPH+H+ H+

H+H+

2. Electron passed along

transport chain, pumping H+ into

grana.

3. Energy also used to split water

4. Hydrogen picked by NADP to make NADPH for carbon fixation (calvin cycle).

5. Hydrogen ions used by ATP synthase to make ATP 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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3-phosphoglycerate

3-phosphoglycerate

Glyceraldehyde-3-phosphate

RuBisCO


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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-3-phosphate (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 sugarThe sugar formed during photosynthesis goes onto the following uses: Glucose

Respiration

Starch Cellulose

Biosynthesis pathways

Fats and oils

Proteins

Nucleic acids(Structural

carbohydrate e.g. cell wall)

(Storage carbohydrate

)


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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:

Net assimilationGain in dry

mass by photosynthesi

s

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 yielddry mass of biological yield

This gives a useful estimate of what is wasted during the growth of a crop.

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