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Photosynthesis

Biology SL Topic 2.9 absorption of light, stages of photosynthesis, ra...
Subject

Biology SL

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IB

Academic year: 2016/2017
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Photosynthesis Topic 2 Biology SL

➢ Plants convert sun energy to glucose through photosynthesis ○ Occurs in chloroplasts ○ Plants need carbon dioxide, water and light ➢ When plants evolved, oxygen became an important gasin the atmosphere ○ It could react with dissolved iron in the oceans forming solid iron oxide as a rock deposition on the seafloor ➢ Photosynthesiscan be described as a series of reactions in which carbon dioxide and water are fixed into glucose and oxygen is produced as a by-product

Absorption of light ➢ The only green structures in a leaf are chloroplasts ➢ There are many pigments in the chloroplasts ○ The photosynthetic pigment is the moleculechlorophyllin most plant species ➢ Plants use the same part of the spectrum that we are able to see ○ 400-700 nm ➢ Chlorophyll is a green pigment and this means that it reflects green light and absorbs the other wavelengths of visible light ○ The red and blue wavelengths are absorbed and used for photosynthesis ○ Almost all the energy of the green wavelength is reflected

Stages of photosynthesis ➢ Photosynthesis occurs in 2 stages ○ The light dependent reactions ○ The light independent reactions ➢ First step ○ Chlorophyll and other photosynthetic pigments absorb light energy and convert it to a form of chemical energy, ATP ○ Light energy is also used to protolyse water ■ Protolysisof water is when a water molecule is split into its component elements ○ The oxygen produced by protolysis is released from the cell as a waste product ○ ATP and hydrogen are the only useful products for the plant ○ It occurs in the chloroplasts ➢ Second step

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Photosynthesis Topic 2 Biology SL

○ Takes place in the chloroplasts ○ ATP and hydrogen are used as forms of chemical energy to convert carbon dioxide and water into useful organic molecules forthe plant ○ Glucose is an organic molecule made out of 6 inorganic carbon dioxide molecules ■ The conversion of an inorganic form of any element to an organic form is known asfixation 6CO 2 + 6H 2 O ⇒ C 6 H 12 O 6 + 6O 2

Rate of photosynthesis ➢ Photosynthesis is the reverse reaction of cell respiration ➢ A plant has a fairly consistent and low rate of cell respiration at any given time, day and night ➢ Low need of ATP ➢ The photosynthetic rate is highly dependent on manyenvironmental factors ➢ The glucose and some of the oxygen produced in photosynthesis is used by the plant itself ➢ When no light is available, the plant must rely on produced glucose and take in oxygen through the stomata from the air ➢ Measuring the oxygen production or carbon dioxide intake is a direct measurement of photosynthetic rate ➢ We can also keep track of the change in biomass of experimental plants ○ Indirect reflection of photosynthetic rate, as biomass can be aected by other factors

Environmental limiting factors ➢ Rate of photosynthesis will increase, as the light intensity increases ○ Until enzymes start working at maximum rate ➢ Rate of photosynthesis will increase, as the temperature increases ○ Until enzymes and proteins become denatured ➢ Rate of photosynthesis will increase, as carbon dioxide increases ○ Rate reaches a plateau unless light and temperaturealso increase ➢ Light and temperature are limiting factors

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Photosynthesis

Subject: Biology SL

695 Documents
Students shared 695 documents in this course
Level:

IB

Was this document helpful?
Photosynthesis Topic 2.9 Biology SL
➢Plants convert sun energy to glucose through photosynthesis
○Occurs in chloroplasts
○Plants need carbon dioxide, water and light
➢When plants evolved, oxygen became an important gas in the atmosphere
○It could react with dissolved iron in the oceans forming solid iron oxide as a
rock deposition on the seafloor
➢
Photosynthesis
can be described as a series of reactions in which carbon dioxide
and water are fixed into glucose and oxygen is produced as a by-product
Absorption of light
➢The only green structures in a leaf are chloroplasts
➢There are many pigments in the chloroplasts
○The photosynthetic pigment is the molecule
chlorophyll
in most plant
species
➢Plants use the same part of the spectrum that we are able to see
○400-700 nm
➢Chlorophyll is a green pigment and this means that it reflects green light and
absorbs the other wavelengths of visible light
○The red and blue wavelengths are absorbed and used for photosynthesis
○Almost all the energy of the green wavelength is reflected
Stages of photosynthesis
➢Photosynthesis occurs in 2 stages
○The light dependent reactions
○The light independent reactions
➢First step
○Chlorophyll and other photosynthetic pigments absorb light energy and
convert it to a form of chemical energy, ATP
○Light energy is also used to protolyse water
■
Protolysis
of water is when a water molecule is split into its
component elements
○The oxygen produced by protolysis is released from the cell as a waste
product
○ATP and hydrogen are the only useful products for the plant
○It occurs in the chloroplasts
➢Second step
1

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