The document discusses photosynthesis and the factors that affect its rate. It explains that the three limiting factors of photosynthesis are light intensity, carbon dioxide concentration, and temperature. Graphs show how the rate levels off or declines when these factors become limited. Horticulture can help reduce these limiting effects by providing extra lighting to greenhouses, increasing temperature which also releases more carbon dioxide, and allowing for increased and earlier crop yields under more controlled conditions.

1. Learning Intentions
• I can contribute to a discussion
highlighting the importance of
photosynthesis.
• I can state and describe the
photosynthesis equation.

2. • 3, 000, 000, 000  9,200, 000, 000
• experts estimate that the last remaining
rainforests could be consumed in less than
40 years.
• An area of a rainforest the size of a
football field is being destroyed each
second"
• Greenhouse effect
http://www.worldometers.info/population/

3. • 250,000 extra people in the world every
day that’s more than 8 times the
population of Motherwell
• That’s an extra 2.9 people per second,
9,396 in this period alone!!!!!!

4. 90.20kg
soil
How do plants get their food ?
The soil was watered but nothing else was added. After 5 years, the
tree had gained 74kg in weight but the soil had lost only 52g.
van Helmont concluded that the tree had made 74kg of new growth
from water alone
2
90.72kg soil
In the 17th Century, A Belgian physician, van Helmont, set up an
experiment in which he planted a willow sapling in a weighed
amount of soil.

5. • van Helmont’s experiment was effective in
showing that the plant’s food did not come
from the soil.
• But he had overlooked the fact that air was
available to the plant as well as water.
• Could it be that the plant made 74kg of
material from just air and water?
• This might seem unlikely but we now know
that plants do indeed make their food from
carbon dioxide from the air and water from
the soil.
3

6. Photosynthesis
• Photosynthesis is the process in which
GREEN plants manufacture food
(glucose) in the presence of LIGHT
• Photosynthesis is a biochemical reaction
that occurs in the structures within
plant cells called CHLOROPLASTS

7. Learning Intentions
• I understand the photosynthesis equation.
• I can describe the 2 stages (photolysis and
carbon fixation) that make it up.

8. Carbon dioxide + Water
sunlight
chlorophyll
Glucose + Oxygen
CO2 H2O C6H12O6 O2
Raw Materials Essentials Waste
Product
PRODUCT
Photosynthesis
Light To make (food)

9. sunlight
(energy)
waterwater
carbon
dioxide
9

10. Sunlight energySunlight energy
Raw materials
from the
environment
Raw materials
from the
environment
Green plants
make
carbohydrate
Green plants
make
carbohydrate
Animals eat
plants which
contain
carbohydrate
Animals eat
plants which
contain
carbohydrate
Producers = green plants that make
their own food
Producers = green plants that make
their own food

12. The chemistry of…
• The chemistry of photosynthesis can be
divided into two stages:
• Photolysis (light dependant)
• Carbon fixation (light independent)
Light Splitting

13. PHOTOLYSIS…..
• Is the process by which energy from
sunlight is used to split water molecules
into hydrogen and oxygen.

14. PHOTOLYSIS
• During photolysis, light energy from the
sun is captured by chlorophyll and
converted to chemical energy. Some of
this chemical energy is used to split the
raw materials water into hydrogen and
oxygen. The hydrogen formed in the
reaction is carried away for use in the
second stage of photosynthesis. Oxygen
is given off as a waste product.

15. Photolysis
• Some of the energy captured by the
chlorophyll is also transferred and
stored as chemical energy in the form
of ATP. This ATP is made from ADP and
Pi. The ATP formed is then passed for
use in the second stage of
photosynthesis.

18. Photolysis Questions
1. What is the source of energy for the first
stage of photosynthesis?
2. What happens to water molecules during
photolysis?
3. After photolysis, how is the hydrogen used?
4. What happens to the oxygen produced by
photolysis?
5. In what two ways is energy required in the
first stage of photosynthesis

19. Stage 1Stage 1
Photolysis

20. Carbon Fixation
Stage 2Stage 2

21. Reaction XReaction X

22. CARBON FIXATION
• The carbon from CO2 combines with
hydrogen from photolysis to form
GLUCOSE in a series of enzyme
controlled reactions which occur in a
cycle.

25. Inside the CHLOROPLAST

26. CONVERSATION OF GLUCOSE INTO
COMPLEX CARBOHYDRATE

27. CARBOHYDRATE PRODUCTION
• Plants are able to produce carbohydrate in 3
different forms:
Glucose – used for respiration
Starch- used for storage
Cellulose- used for structure (cell wall)

28. Carbon Fixation questions
1. Where does the carbon dioxide come from that is
needed in this stage of the photosynthesis process?
2. In what substance is the carbon from carbon dioxide
found after carbon fixation has taken place?
3. Where does the hydrogen for the carbon fixation
stage come from?
4. Where does the energy come from that is needed for
the carbon fixation?
5. What controls the reactions involved in CF?
6. What will happen to the carbon fixation process if
photolysis is unable to take place, eg when it is too
dark? Why?

29. 01/27/15 17:14 Mr D Campbell 29
Step 1- Place
leaf in water
and allow to
boil (5
minutes)
Step 2-
Place leaf
in test
tube with
ethanol (3
minutes)
Step 3- rinse
leaf in water
then test for
starch with
iodine
ethanol
water

30. Elodea bubbler experiment (2)

31. Learning Intentions
• I can state the 3 factors that affect
the rate of photosynthesis .
• I can explain how horticulture reduces
the effects of limiting factors (in some
situations).

32. Factors affecting photosynthetic rate
• Several environmental factors affect the rate of
photosynthesis. These include light intensity,
carbon dioxide concentration and temperature.
• The rate of photosynthesis can be estimated by
measuring one of the following:
• Evolution of oxygen (per unit time)
• Uptake of carbon dioxide (per unit time)
• Production of carbohydrate (as increase in dry
weight ) per unit time

33. Elodea
Filter
funnel
Dilute sodium bicarbonate
….
Lamp
Heat shield

34. Elodea bubbler experiment

35. Limiting Factors
• A limiting factor is a factor that is in
shortage and holds up a process.
• 3 limiting factors of photosynthesis are:
• Light intensity
• CO2 concentration
• Temperature

36. LIMITING FACTORS
Units of light
RateofPhotosynthesis

37. Light Intensity
• As we can see from the graph, the line
levels off indicating that further
increases in light intensity will not
increase the rate of photosynthesis.
• Some other limiting factor must be
taking effect at this stage.

38. LIMITING FACTORS
RateofPhotosynthesis
CO2 Concentration

39. Temperature
• Why does increasing the temperature,
whilst keeping everything else the same,
increase the rate of reaction?
• Photosynthesis is an enzyme controlled
reaction. So what happens to the rate
of reaction after 40C?
• Above 40o
C enzymes start to denature

40. LIMITING FACTORS- TEMPERATURE
RateofPhotosynthesis
Temperature

41. Temperature
• We can see from the graph that as the
temperature increases, so does the rate of
photosynthesis.
• This happens until it reaches the optimum
temperature, when photosynthesis cannot
happen any quicker.
• After this, the rate of photosynthesis
slows down as the enzymes which control it
are denatured.

43. Horticulture
• If we can reduce the limiting factors in
photosynthesis, then we may be able to
increase the yield of plants.
• Obviously this can’t be done by a farmer
in his fields, but it can be done in
controlled environments such as
greenhouses.

44. Horticulture
• Extra lighting can be supplied to
greenhouses to extend the number of
daylight hours.
• The temperature in winter and spring is
often increased using paraffin heaters,
and these have the added bonus of
releasing extra carbon dioxide which may
also be limiting photosynthesis.
• This also allows, not only an increased
yield, but earlier crops.

46. Success Criteria
• The 3 factors that affect photosynthesis and
that may become limiting are……
• Horticulture reduces limiting factors by…….