2. photosynthesis
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where does photosynthesis take place
in the chloroplasts of plant cells
where does photosynthesis take place
in the chloroplasts of plant cells
chloroplasts are
flattened organelles surrounded by a double membrane
thylakoids (fluid-filled sacs) are
stacked up in the chloroplast into structures called grana (singular=granum)
grana are linked together by
bits of thykaloid membrane called lamellae (singular=lamella)
e.g. of photosynthetic pigments in chlorplasts
Chlorophyll A chlorophyll B carotene
photosynthetic pigments are
coloured substances that absorb light energy needed for photosynthesis
photosynthetic pigments are found
in thykloid membrane attached to proteins
photosynthetic pigment attached to protein is called a
photosystem
contained within the membrane of the chloroplast and surrounding the thykloids is a
gel-like substance called the stroma
what does the stroma contain
enzymes, sugars and organic acids
carbohydrates produced by photosynthesis are not used straight away. they are
stored as starch grains in the stroma
non-cyclic photophosphorylation 1. Light energy excites the electrons in the chlorophyll
• light energy is absorbed by photosystem • excites electrons in chlorophyll • electrons move to higher energy level (they have more energy) • released from chlorophyll and move down electron transport chain
non-cyclic photophosphorylation 2. photolysis of water produces protons (H+ ions) , electrons and O2
• as excited electrons from chlorophyll leave Photosystem and move down electron transport chain must be replaced • light energy splits water into protons (H+ ions), electrons and O2 (photolysis) • the reaction is H2O -> 2H+ + 1/2O2
non- cyclic photophosphorylation 3. energy from the excited electrons make ATP
• excited electrons loose energy as they move down the electron transport chain • energy is used to transport protons into the thylakoid. thylakoid has higher concentration of protons in stroma. = proton gradient across thylakoid membrane • protons move down concentration gradient into stroma via enzyme ATP synthase (in thylakoid membrane) energy from movement combines ADP and inorganic phosphate to from ATP
non-cyclic photophosphorylation 4. and generated reduced NADP
• electrons are transferred to NADP along with a proton (H+ ion) from the stroma to form reduced NADP
the light dependent reaction some of the energy from released electrons is used
• to add a phosphate group to ADP forming ATP (which transfers energy) • to reduce NADP to form reduced NADP (which transfers hydrogen to the light-independent reaction)
the light dependent reaction during the process, H2O is
oxidised to O2
the light independent reaction is also called the
Calvin cycle
the light independent reaction it doesn’t use
light energy directly but it relys on the products of the light dependent reaction
the light independent reaction it takes place in the
stroma of the chloroplast
the light independent reaction what happens in the stroma of the chloroplast
ATP and reduced NADP from light dependent reaction supply energy and hydrogen to make simple sugars from CO2
phostosystems in the thylakoid membranes are linked by
electron carriers
electron carriers are
proteins that transfer electrons