Outcome Statements
Photosynthesis
IB Biology Core 3.8
Photosynthesis Song!
http://www.youtube.com/watch?v=wj8TGhcCnxs
Photosynthesis
Light from the sun
Light from the sun is normally referred to as white light
but it is composed of a wide range of wavelengths
including red, green, and blue.
3.8 Photosynthesis
3.8.1 State that photosynthesis involves the conversion of light energy into
chemical energy.
3.8.2 State that light from the Sun is composed of a range of wavelengths
(colours).
3.8.3 State that chlorophyll is the main photosynthetic pigment.
3.8.4 Outline the differences in absorption of red, blue and green light by
chlorophyll.
3.8.5 State that light energy is used to produce ATP, and to split water
molecules (photolysis) to form oxygen and hydrogen.
3.8.6 State that ATP and hydrogen (derived from the photolysis of water)
are used to fix carbon dioxide to make organic molecules.
3.8.7 Explain that the rate of photosynthesis can be measured directly by
the production of oxygen or the uptake of carbon dioxide, or indirectly by
an increase in biomass.
3.8.8 Outline the effects of temperature, light intensity and carbon dioxide
concentration on the rate of photosynthesis.
is a process that involves the conversion of energy.
Light energy, usually in the form of sunlight is converted
into chemical energy.
Chlorophyll
Chlorophyll is a substance (pigment) which can absorb
light and is the main photosynthetic pigment.
Absorption by Chlorophyll
Due to the structure of chlorophyll, it absorbs red and
blue light better than green. Green light is reflected
which makes chlorophyll and as a result plants and
chloroplasts appear green.
Pigments are substances which absorb light and some
pigments can absorb more colors or wavelengths than
others.
The colors they absorb depend on their structure.
A pigment that absorbs all colors appears as black and a
pigment that absorbs all colors except blue appears blue
due to the fact that this part of the sunlight is not being
absorbed.
In other words, the remaining colors that are not
absorbed are reflected and the color is perceived by the
brain of the observer.
Water splitting
A process called photolysis of water (splitting water
molecules) is driven by energy absorbed through
chlorophyll.
This results in the formation of hydrogen and oxygen, a
waste product which is released.
Some light energy absorbed by chlorophyll is used to
produce ATP.
Light energy is used to produce ATP, and
to split water molecules (photolysis) to
form oxygen and hydrogen
Carbon Fixation
Carbon fixation is a process which involves the
conversion of carbon in a gas to carbon in solid
compounds.
In order for carbon fixation to occur, energy in the form
of ATP and hydrogen (from photolysis) are needed.
The carbon can now be used to make organic
compounds.
Photosynthesis is the conversion of energy
Photosynthesis Overall
Rate of Photosynthesis
Oxygen
Collection of Oxygen as a measure of
Photosynthesis
Some aquatic plants such as Myriophyllum which carry out
photosynthesis will release bubbles of oxygen.
These bubbles can be
collected and the
volume measured to
determine the plants
rate of photosynthesis.
Biomass
The process of photosynthesis involves the production of
oxygen, an increase in biomass, and the absorption of
carbon dioxide.
Any of the three processes can be used to measure the
rate of photosynthesis:
Harvesting batches of plants at various intervals and
measuring the rate of increase in biomass can result in an
indirect measurement of the rate of photosynthesis in the
plant.
Carbon Dioxide
It is difficult to measure the amount of CO2 taken in by a
plant from the air.
However, if the CO2 is absorbed from water the pH of
the water rises and this can be measured giving an
indication of the rate of photosynthesis.
Effects on rate of photosynthesis
When the intensity of light ranges from low to medium,
the rate of photosynthesis is directly proportional to the
intensity of light.
Once the intensity of
light is high there is
a plateau in the rate
of photosynthesis.
Temperature
There is an optimum temperature for photosynthesis.
The rate of photosynthesis increases rapidly with an
increase in temperature.
Once the optimum
temperature is
exceeded the rate
of photosynthesis
falls rapidly.
Something fun for last!
Learn about plants!
http://www.youtube.com/watch?v=1gLa5EWn9OI
Photosynthesis!
http://www.youtube.com/watch?v=pdgkuT12e14&feature
=related
Low Carbon Dioxide
There is no photosynthesis at very low CO2
concentrations.
Between low and high concentrations of CO2 the rate of
photosynthesis is positively correlated with
the rate of CO2.
If the rate of CO2
reaches very high
concentrations there
is a plateau in the
rate of photosynthesis.
Practice Question: