2. Plant Nutrition
In this topic you will learn:
Photosynthesis is the fundamental process by
which plants manufacture simple sugars from raw
materials.
3. Starter Question
A tree is planted in a
meadow. After 20
years it has grown into a
big tree, weighing 250kg
more than when it was
planted.
Where do the extra
250kg come from?
Explain your answer as
fully as you can.
4. Learning Outcomes
Define photosynthesis and state the equation
for the production of simple sugars and
oxygen in words.
State the equation for photosynthesis in
symbols
5. Plant Nutrition
Photosynthesis is the process in which light
energy, trapped by chlorophyll, is used to
convert carbon dioxide and water into glucose
and oxygen.
Word Equation
Light energy
Carbon dioxide + water glucose + oxygen
Chlorophyll
6. Photosynthesis
Word equation
Light energy
Carbon dioxide + water glucose + oxygen
chlorophyll
Balanced Symbol Equation
Light energy
6CO2 + 6H2O C6H12O6 + 6O2
chlorophyll
7. Learning Outcome
Describe the intake of raw materials, the
trapping and storing of energy (conversion of
light energy into chemical energy), the
formation of food substances and their
subsequent storage.
8. THINK!!
What are the raw materials in
photosynthesis?
Where does the plant get them from?
What are the products of photosynthesis?
What happens to them?
9. Process of photosynthesis
Carbon dioxide diffuses into the leaves of
green plants
Water is absorbed by osmosis through plant’s
roots and transported to the leaf through
xylem vessels
Chloroplasts, containing chlorophyll, are
responsible for trapping light energy (energy
is used to break up water molecules and then
bond hydrogen and carbon dioxide to form
glucose)
10. Process of photosynthesis
Glucose is usually changed to sucrose for
transport around the plant, or to starch for
storage
Oxygen is released as a waste product.
11. Leaves – a factory for
photosynthesis
Leaves are adapted to make them very
efficient for photosynthesis
Network of veins
carry water and
minerals to the
leaf and food
away from it.
Leaf is green, as it contains
chlorophyll to absorb light
Leaf is broad to give a
large surface area to
absorb light
Petiole holds the
leaf at an angle
so it faces the sun
and absorbs as
much light as
possible
Leaf is thin to allow
substances to move
quickly between
and into cells
(diffusion)
12. Testing a leaf for starch
Dip a leaf into boiling water for
about a minute to soften it.
Turn off the Bunsen burner.
Put the leaf into a test-tube of
ethanol.
Stand the test-tube in a beaker of
hot water for about 10 minutes.
Wash the leaf in cold water
Spread the leaf out flat on a petri
dish and cover it with iodine
solution.
If the leaf goes blue-black, starch
is present.
13. Is light needed for photosynthesis?
Take a de-starched geranium plant.
Cover part of a leaf with some tin foil (this
prevents light getting through).
Leave the plant in sunlight for a few hours
Test the leaf for starch.
14. Is light needed for photosynthesis?
Questions:
Which parts of the leaf went blue black?
Why do parts that were not covered contain
starch?
16. Is carbon dioxide needed for
photosynthesis?
Take a de starched
geranium plant
Enclose it in a plastic bag
with a chemical that
absorbs carbon dioxide. (e.g.
soda lime or sodium
hydroxide pellets).
Leave the plant in sunlight
for a couple of hours
Test the leaf for starch.
17. Is carbon dioxide needed for
photosynthesis?
Questions:
Does the leaf contain starch? Why not?
Has the plant carried out photosynthesis?
What would be your control plant?
(Hint: a control plant should have everything it needs for
photosynthesis including carbon dioxide).
18. Learning Outcomes
Define the term limiting factor and interpret
(as limiting factors that affect
photosynthesis) the effects of light and
carbon dioxide concentration.
19. Limiting Factors
The factors which if increased will increase
the rate of photosynthesis.
The process of photosynthesis depends on:
Availability of light
Presence of a pigment to absorb the light
Supply of carbon dioxide and water
A temperature suitable for enzyme activity
20. Limiting factors
If any of these factors are in short supply
the rate of photosynthesis will be less then
its maximum possible rate
The factor furthest from it’s optimum level is
controlling the overall rate of photosynthesis!
21. The effect of light on the rate of
photosynthesis
Graph
As light intensity increase, so does the rate
of photosynthesis, until a point where another
factor becomes limiting
If the limiting factor in the graph was carbon
dioxide concentration and the plants were
given more carbon dioxide the graph would
level off at a higher rate of photosynthesis.
22. The effects of carbon dioxide on
the rate of photosynthesis
graph
23. Effect of temperature on the
rate of photosynthesis
Temperature affects the enzymes that
control the rates of the chemical reactions of
photosynthesis.
Graph
Compare this graph to the graphs showing the
effect of temperature on enzyme activity.
24. Learning Outcome
Explain the use of carbon dioxide enrichment,
optimum light and optimum temperatures in
greenhouse systems
25. Optimum conditions in
greenhouse systems
Greenhouses are used to control the
conditions for plant growth
The atmospheric conditions can be controlled
and the glass traps heat inside
26. Carbon dioxide enrichment
0.04% carbon dioxide in the air, so it can
easily limit the rate of photosynthesis
Carbon dioxide concentration in a greenhouse
can be increased by:
Burning fossil fuels
Releasing pure carbon dioxide from a gas cylinder
27. Optimum light and temperature
Optimum light
Light conditions for growth can be improved by
using artificial lights
Optimum temperature
Can be raised by using a heating system
28. Learning outcomes
Identify the cellular and tissue structure if a
dicotyledonous leaf, as seen in cross section
29. Leaf Structure
Revision:
How external features if a leaf design it to be a
factory for photosynthesis
Activity – Bioviewers
Observe and draw a cross section of a
dicotyledonous leaf
30. Internal Structure of a leaf
Use the words below to
label your diagram of a
leaf
Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Lower epidermis
Guard cell
Stoma
Phloem
xylem
31. Functions of structures
Pupil Activity
Cut out the internal structures and functions of a
leaf
Match up the structure to the function
32. Functions
Structure Function
Waxy cuticle Prevents water loss from the leaf
Upper epidermis Transparent, Allows light to travel to cells within
the leaf
Palisade mesophyll Cells tightly packed together, Main region of
photosynthesis, Cells packed with chloroplasts
Spongy mesophyll Cells spherical and loosely packed, air spaces
between cells allow for gas exchange
Vascular bundle Contains the xylem (transports water and minerals
to the leaf) and phloem (translocation)
Lower epidermis Acts as a protective layer
stomata Regulates water loss (transpiration)
Site of gaseous exchange in the leaf
Guard cells Control the opening and closing of stomata
33. Annotating a diagram
Using the information you have already been
provided with
Label the diagram
Write a statement for each structure that you
have labelled.
34. Learning Outcomes
Describe the importance of nitrate ions for
protein synthesis and magnesium ions for
chlorophyll synthesis
Explain the effects of nitrate ions and
magnesium ion deficiency on plant growth
Describe the uses and the dangers of overuse
of nitrogen fertilisers
35. Nitrate ions
Importance
Needed for
synthesising amino
acids
Amino acids form
long chains to make
proteins
Deficiency
Plant growth is
stunted
Weak stem
Yellow, dying lower
leaves
Upper leaves turn
pale green
36. Magnesium ions
Importance
Forms part of
chlorophyll molecules
Plants need
chlorophyll to trap
light to provide
energy for
photosynthesis
Deficiency
Chlorosis
Leaves turn yellow
Lack of
photosynthesis limits
plant growth
37. Nitrogen fertilisers
Nitrogen fertilisers can be used
To increase crop yields
To replace the nitrate ions removed by intensive
farming
Nitrate can also be replaced by
Applying animal manure
Crop rotation
Grow leguminous plants in the field every 2/3 years
38. Dangers of overuse of fertilisers
Too much nitrogen fertiliser can cause plant
roots to lose water by osmosis
The plant wilts and dies
Eutrophication
Fertilisers are soluble in rainwater and are washed
out of the soil
This is known as leaching
40. Stages of Eutrophication
Fertilisers used by farmers may be washed into lakes
and rivers
Rapid growth of water plants cause by the fertilisers
Death of some of these plants due to lack of light
from overcrowding
Microbes which feed on the dead organisms now
increase in number
Oxygen is used up quickly by the microbes
Suffocation of fish and other aquatic animals due to
the lack of oxygen in the water.
41. Pupil Activity
Using the 5 main stages of eutrophication
leaching
Rapid algal growth
Death of algae
Decay by bacteria
Death of aquatic animals
Design a cartoon strip that summarises the
process of Eutrophication
42. Progress Question – easy ones
1. Plants need a supply of nitrate ions. State
the use made of nitrate ions in plants. [1]
2. Many farmers regularly add nitrate
fertilisers to their fields. Explain why this
is necessary. [2]
43. Progress Question – difficult one
3. A farmer spreads a nitrate-rich fertiliser
over his fields. Each time he does this, he
washes out his spreading equipment in a farm
pond.
Suggest and explain what the likely effects
of such pollution will be on the plants and
animals in the pond. [5]
