1. Plant nutrition and Photosynthesis
18 May 2019
Plant nutrition and Photosynthesis
Define photosynthesis as the process by which plants manufacture carbohydrates from raw materials using energy from light

2. Advanced preparation
In a future lesson you will look at the process of translocation. Measure and record the mass of a potato tuber and then plant it. You will observe the growth of the tuber over the next few weeks.
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3. Learning objectives Define autotroph Define photosynthesis
State a word and chemical equation for photosynthesis
State the role of chlorophyll
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4. Autotrophs
An autotroph is an organism that is able to make its own food through the process of photosynthesis
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5. Plants make starch
Plants can make glucose and store it in their cells as starch!
This incredible process is called photosynthesis.
Inside the plant cells are chloroplasts which contain a pigment called chlorophyll to absorb the sunlight.
What is the word equation for photosynthesis
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6. How does a plant make starch?
Starch is made of long chains of glucose.
Glucose is made by a process called photosynthesis.
sunlight + +
Carbon dioxide
Water
Glucose
Oxygen
chlorophyll
sunlight + +
CO2
H2O
C6H12O6 O2
chlorophyll
Can you balance this equation?
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7. How does a plant make starch?
Starch is made of long chains of glucose.
Glucose is made by a process called photosynthesis.
sunlight + +
Carbon dioxide
Water
Glucose
Oxygen
chlorophyll
sunlight + +
CO2
H2O
C6H12O6 O2
chlorophyll
Can you balance this equation?
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8. Balancing the equation
Its easy to balance the photosynthesis equation.
Just remember that everything has a 6 before it except the glucose. + +
6CO2
6H2O
C6H12O6
6O2
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9. Test a leaf for starch
You can test a leaf with iodine to show it contains starch.
Test leaves for their starch content by firstly removing their chlorophyll
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10. Test a leaf for starch First remove a leaf from the plant.
First remove the green pigment called chlorophyll from the leaf so you can see the results clearly.
First remove a leaf from the plant.
Place it in a beaker of boiling water for 30 seconds to soften it.
3. Then place it in a boiling tube of ethanol, inside the beaker of boiling water, and make sure the Bunsen flame is switched off.
4. Remove the leaf after a minute using forceps and rinse with cold water under the tap.
5. Spread it out on a white tile and drip iodine over it.
6. Iodine will turn blue black if starch is present.
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11. Test a leaf for starch
This leaf contains starch as it has gone blue black
This leaf contains no starch
This is because the leaf has been destarched.
It has been left in a dark cupboard for a few days, the plant has not been able to photosynthesise and has therefore used up its store of starch for energy instead.
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12. Is chlorophyll needed
Plan and carry out an investigation to determine of chlorophyll is needed for photosynthesis
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13. Starch and light
What happens when we block out the light on part of the leaf? Can you get a plant to write your name with starch?
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14. Learning objectives Identify the different layers of a leaf
Explain how different parts of the leaf are linked to photosynthesis and gas exchange
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15. The structure of a leaf Cuticle Chloroplasts Upper epidermis Palisade
Mesophyll
Spongy
Lower epidermis
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Guard cell
Stoma
Air space

16. The Leaf 10
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17. The Leaf Waxy Cuticle Chloroplast Upper Epidermis Palisade Mesophyll
Spongy
Lower Epidermis
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Guard Cell
Air Space
Stoma

18. The leaf- an alternative viewB C
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19. Adaptations of the leaf
The palisade layer is packed with chloroplasts for photosynthesis.
The leaf has a transparent upper epidermis to let light through to the palisade layer.
The leaf has a broad shape to catch more light.
The leaf is thin to allow rapid diffusion for gaseous exchange.
The leaf has air spaces in the spongy layer to allow for gaseous exchange.
The leaf has lots of stomata to allow for gaseous exchange.
The leaf has guard cells to control if the stomata or open or closed.
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20. Observing the air spaces and stomata
Dip different leaves in to biolong water and look for any air bubbles on the underside of the leaf These air bubbles indicate the presence of air spaces and stomata
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21. Observing stomata
Paint a 1cm2 of clear nail varnish on the under and upper side of a leaf
Allow the nail varnish to dry- carefully remove it from the leaf
Observe the stomata frequency
Repeat the procedure for a second plant and compare the two samples
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22. A Chlorophyll chromatogram
Extension task - Produce a chromatogram of the extracted pigment
Break a leaf up in to small pieces and place in to a mortar
Add a small amount of propanone
Grind the mixture with a pestle to release the chlorophyll
Draw a pencil mark 1 cm from the bottom of a piece of chromatography paper
Using a capillary tube place one tiny drop of the mixture on the pencil line and allow it to dry
Add a second drop and allow it to dry also
Repeat until you have added 5 drops
Place a small amount of propanone in to a beaker and then place the chromatography paper in to the beaker
Observe what happens

23. Learning objectives
Identify the uses and storage of the products of photosynthesis
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24. Do all leaves from the same plant photosynthesize at the same rate?
Plan and investigation to find an answer to this question.
You should first propose a hypothesis
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25. Do all leaves from the same plant photosynthesize at the same rate?
Plan and investigation to find an answer to this question.
You should first propose a hypothesis
AIM- To find out if the leaves at the top of a plant photosynthesise more than leaves at the bottom of the plant
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26. Testing a leaf for glucose
Remove a leaf from the upper part of the plant
Break the leaf in to small pieces and place in a mortar
Add water to the mortar and grind the leaf using the pestle
After a few minutes, remove the water from the mortar and place into a test-tube
Add Benedicts solution to the test-tube and heat at 80oc for a few minutes
Repeat the procedure the a leaf from the bottom of a plant
Record your observations
How can you make the investigation a fair test?
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27. Learning objectives
Compare the rate of respiration and photosynthesis taking place in a plant
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28. What happens to the glucose?
Stored as starch
Used in respiration to release energy
Stored in fruit as sucrose
Turned into cellulose to make cell walls
Turned into proteins with the addition of nitrogen so the plant can grow
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29. Gaseous Exchange in plants
Gaseous exchange in plants occurs through the stomata in the leaves.
The gases move by diffusion
Carbon Dioxide
Respiration
Photosynthesis
Oxygen
During photosynthesis, carbon dioxide enters the leaf and oxygen exits the leaf.
During respiration, oxygen enters the leaf and carbon dioxide exits the leaf.
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30. The Leaf- explain the path taken by O2 and CO2 as they enter and leave the cell
Waxy Cuticle
Chloroplast
Upper Epidermis
Palisade
Mesophyll
Spongy
Lower Epidermis
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Guard Cell
Air Space
Stoma

31. Gaseous Exchange in plants
Respiration occurs in plants 24 hours a day.
However photosynthesis only occurs when sunlight is available.
Therefore the net exchange of gasses depends on how much light is available.
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32. How can you measure gas exchange in plants?
There is an indicator which is used to measure the amount of carbon dioxide.
It is called Hydrogencarbonate indicator.
It is red in equilibrium with atmospheric air.
It becomes more orange/yellow with increased carbon dioxide levels.
It changes from red through magenta to deep purple as carbon dioxide is removed.
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33. How can you measure gas exchange in plants?
This is an aquatic plant placed and hydrogencarbonate indicator
The indictor has had carbon dioxide bubbled through it which has turned it yellow
CO2 Level
It is placed under a light and as it uses up the available carbon dioxide the indictaor turns to purple
How will the results differ if we placed the pond weed into the dark?
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34. Possible method
Take a sample of pondweed and place in to a boiling tube
Cover the pond weed with hydrogen carbonate indicator
Shine the light from a lamp on to the boiling tube and leave for 30 minutes
Repeat the procedure but this time cover the tube with card and a further tube with tissue paper
Record your observations
Aim- to observe the effect of light on photosynthesis and respiration
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35. Discussion of results Which had the most and the least carbon dioxide?
Why was this?
What can you say about respiration and photosynthesis in relation to light intensity?
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36. Learning objectives
Describe the effects of chlorophyll, carbon dioxide and light on photosynthesis
Discuss limiting factors
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37. How fast can a plant grow?
The rate of photosynthesis relies on three things.
Temperature
Amount of CO2
Light intensity
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38. Temperature
As the temperature rises, the rate of photosynthesis increases – provided there is plenty of carbon dioxide and light. This is because the temperature affects the enzymes controlling photosynthesis.
However, at a certain point the higher temperature causes the enzymes to denature and photosynthesis slows down and stops.
Rate of photosynthesis
Temperature
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39. Amount of CO2
The higher the carbon dioxide level, the faster the rate of photosynthesis – again, provided there is plenty of light and a suitable temperature.
At a certain point it wont matter how much more CO2 you give the plant the rate is at its maximum or one of the factors is in short supply. That is why the graph plateaus.
Rate of photosynthesis
CO2
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40. Light intensity
The higher the light intensity, the faster the rate of photosynthesis – provided that there is lots of carbon dioxide and the temperature is warm enough.
At a certain point it wont matter how much more light you give the plant the rate is at its maximum or one of the factors is in short supply. That is why the graph plateaus.
Rate of photosynthesis
Light Intensity
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41. Limiting Factors
The factor that is at the lowest level will be the factor which limits the rate of reaction. This factor is called the limiting factor.
If the limiting factor is increased, the rate of photosynthesis will increase until one of the other factors becomes limiting.
Light intensity
Amount of CO2
Temperature
What conditions are needed for maximum output in a greenhouse?
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42. Photosynthesis Experiments
You can use an aquatic plant such as Elodea to measure the rate of photosynthesis under various conditions.
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43. Photosynthesis Experiments
As the plant photosynthesises it produces oxygen gas as bubbles.
You can measure the volume produced in a given time to calculate the rate.
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44. Photosynthesis Experiments
One variable at a time can be changed to then investigate their effect on the rate.
For example the lamp can be moved. Or sodium hydrogencarbonate can be added to increase the CO2 in the water, or the temperature of the water could be changed.
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45. Photosynthesis Experiments
Remember only to change one variable (light intensity, temp or CO2), this will be your independent variable for the investigation.
All the other variables in the investigation must stay controlled.
The variable measured which will be the number of bubbles of oxygen is the dependent variable.
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46. Plan an investigation to see the effect of different CO2 concentrations on plant growth
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47. Learning objectives Discuss the effect of minerals on plant growth
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48. Plant minerals
As we know the plant makes it’s food by the process of photosynthesis in the leaves.
However it needs various mineral ions and water from the soil in order to stay healthy.
Two of these are nitrates and magnesium.
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49. Magnesium Used to make chlorophyll for the plant.
Deficiency turns the leaves yellow
Used to make chlorophyll for the plant.
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50. Nitrates
Used to make DNA, proteins and many other molecules for the plant.
Deficiency causes stunted growth and yellow leaves
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51. Phosphorous Needed for good root and shoot growth
Deficiency purple leaves
Needed for good root and shoot growth
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52. Potassium Used to promote good general growth
Deficiency dead spots on leaves
Used to promote good general growth
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53. Plan an investigation in to the growth of plants with different fertilizers
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