U3 Photosynthesis Flashcards
What is dependent ultimately upon photosynthesis?
all food production
What is photosynthesis?
A process in which green plants trap sunlight energy to produce carbohydrates (food)
Chloroplast structure
lamella (links between grana)
stroma (fluid)
outer membrane
inner membrane
thylakoids (make up a granum)
granum (stack of thylakoids (plural=grana))
DNA
What are the 3 fates of white light when it hits a leaf?
-most of it is absorbed by pigments in the leaf
light energy not absorbed can either be:
-transmitted through the leaf
-or reflected off the surface
what do leaves contain?
several coloured pigments of which chlorophyll is the most important
What do different pigments do differently?
absorb different wavelengths (colours) of light
What does an action spectrum graph show?
the rate of photosynthesis at different wavelengths of light
what does an absorption spectrum graph show?
the ability of each pigment to absorb different wavelengths of light
what are accessory pigments?
Pigments that extend the range of wavelengths absorbed in photosynthesis
AND they pass the energy they capture onto chlorophyll
Example of an accessory pigment
carotenoids
what is stage 1 of photosynthesis?
the light reactions/photolysis
where do the light reactions take place?
grana of the chloroplast
what happens during the light reactions?
in the chloroplast, when light energy is absorbed by pigments, electrons in the pigment become excited and are raised to a higher energy stage
the electrons are then transferred along an electric transports chain, releasing energy
this energy is used to generate atp by atp synthesis (used later in carbon fixation)
energy is also used for photolysis in which water is split into oxygen and hydrogen
What happens to the oxygen produced during the light reactions?
it is evolved (released) from the cell/leaf
it is a by-product of
what happens to the hydrogen produced during the light reactions?
it is transferred to the coenzyme (hydrogen acceptor) NADP to make NADPH
The NADPH is used later in carbon fixation
what is the second stage of photosynthesis?
carbon fixation where glucose is made
a series of enzyme-controlled reactions
Steps of carbon fixation
1-Carbon dioxide enters the cycle and becomes attached to RuBP. This reaction is controlled by the enzyme RuBisCO
2-The carbon dioxide and RuBP combine to make 3PG
3-3PG then joins with the hydrogen from NADPH and is phosphorylated by the addition of phosphate (Pi) from ATP which supplies the energy
4-This process produces G3P
5-Some G3P is then used to regenerate RuBP (to continue the process). The remainder is used to synthesise glucose
Fates of glucose after photosynthesis
Respiration (respiratory substrate)
Starch (storage carbohydrate)
Cellulose (structural carbohydrate eg cell wall)
Biosynthesis pathways-fats and oils, proteins, nucleic acids (DNA, RNA)
