Chapter 8: Photosynthesis Flashcards
Which organisms use photosynthesis?
Plants, algae and cyanobacteria
photoautotroph
organism that use sunlight to make their own food
heterotroph
organism that relies on other organisms for food
chemoautrotroph
organism that uses energy from inorganic chemical compounds to make their own food
GA3P
glyceraldehyde-3-phosphate
What is the general equation for photosynthesis?
Carbon dioxide + water -light-> sugar + oxygen
What is the general equation for photosynthesis using chemical symbols?
6CO2 + 6H2O -light-> C6H12O6 + 6O2
mesophyll
middle layer of cells in a lead where photosynthesis occurs
stoma
small regulated openings on a leaf’s underside that exchanges oxygen and carbon dioxide
Why are stomata on the undersides of leaves?
To prevent water loss from high temperatures created by the sun
What are stomata surrounded by?
Guard cells
What is the role of guard cells around stomata?
They swell or shrink in size to regulate the opening and closing of stomata
chloroplast
organelle where photosynthesis occurs
What is the structure of a chloroplast?
It has an outer and inner membrane
Where are chloroplasts thought to have come from?
They were derived from photosynthetic cyanobacteria
thylakoid
disc-shaped structure in a chloroplast
pigment
molecule that absorbs light
chlorophyll
pigment in a chloroplast that is responsible for the initial interaction between light and a plant
What is embedded in the thylakoid membrane?
Chlorophyll and proteins that make up the electron transport chain
thylakoid lumen
space that the thylakoid membrane surrounds
granum
stack of thylakoids
stroma
liquid that fills the space in the inner membrane of a chloroplast
What are the two parts of photosynthesis?
The light-dependent and light-independent reactions
light-dependent reactions
energy from the sun is harvested and stored as chemical energy
light-independent reactions
chemical energy harvested from light-dependent reactions is used to assemble sugar molecules
What wavelengths of light can humans see?
700nm to 400nm
What wavelengths of light can plants absorb?
700nm to 400nm
Why do organic pigments have such a narrow range of light they can absorb?
Energy levels lower than red light aren’t energetic enough and energy levels higher than blue light will tear molecules apart
photobleaching
when molecules are damaged or torn apart due to absorbing light with too much energy
What are the two main types of photosynthetic pigments found in plants and algae?
Chlorophylls and carotenoids
What are the five main types of chlorophyll?
Chlorophylls a, b, c, d and bacteriochlorophyll
carotenoid
pigment that is effective at disposing excess energy
Why are carotenoids useful in plants?
Since light-dependent reactions process a lot of energy, energy not processed can be harmful
absorption spectrum
range of wavelengths that can be absorbed by a substance
Which wavelengths do carotenoids reflect?
Yellow-orange-red wavelengths
What are the structural differences between chlorophyll a and b?
Chlorophyll b has an extra double bound oxygen and single bound hydrogen
spectrophotometer
instrument used to measure reflected light and determine which wavelengths a substance can absorb
photosystem
group of proteins and pigments that are used in light-dependent reactions
What are the two types of photosystems?
Photosystem I and photosystem II
What is the difference between photosystem I and II?
PSII gains its electrons from splitting water, and PSI gains its electrons from the electron transport chain
What wavelengths of light can humans see?
700nm to 400nm
What wavelengths of light can plants absorb?
700nm to 400nm
Why do organic pigments have such a narrow range of light they can absorb?
Energy levels lower than red light aren’t energetic enough and energy levels higher than blue light will tear molecules apart
photobleaching
when molecules are damaged or torn apart due to absorbing light with too much energy
What is the reaction centre composed of?
A complex of organic molecules which surround a pair of special chlorophylls and a primary electron acceptor
What are the five main types of chlorophyll?
Chlorophylls a, b, c, d and bacteriochlorophyll
carotenoid
pigment that is effective at disposing excess energy
Why are carotenoids useful in plants?
Since light-dependent reactions process a lot of energy, energy not processed can be harmful
absorption spectrum
range of wavelengths that can be absorbed by a substance
Which wavelengths do carotenoids reflect?
Yellow-orange-red wavelengths
What are the structural differences between chlorophyll a and b?
Chlorophyll b has an extra double bound oxygen and single bound hydrogen
spectrophotometer
instrument used to measure reflected light and determine which wavelengths a substance can absorb
photosystem
group of proteins and pigments that are used in light-dependent reactions
What are the two types of photosystems?
Photosystem I and photosystem II
plastocyanin
copper protein that transfers electrons from the cytochrome complex to photosystem I
antenna protein
proteins to which chlorophyll is bound to and surrounds the reaction centre
reaction centre
area in a photosystem where the photochemistry occurs
light-harvesting complex
passes harvested energy from the sun to the reaction centre
What is the light-harvesting complex made of?
Multiple antenna proteins that contain many pigments
P700
the reaction centre in photosystem I
photoact
ejection of an electron from the reaction centre using energy absorbed from light
P680
reaction centre of photosystem II
primary electron acceptor
molecule that accepts an electron from the reaction centre
How is an electron passed on to the primary electron acceptor from a photosystem?
Photons absorbed are passed on to the chlorophyll pair in the reaction centre, which excites an electron into a higher energy level, which is passed on to the primary electron acceptor
What is water split into by photosystem II?
Water is split into two electrons, two hydrogens and one oxygen
What happens to the oxygen in water split by photosystem II?
About ten percent is used in oxidative phosphorylation and the rest is released into the atmosphere as a byproduct
What happens to the hydrogen in water split by photosystem II?
It accumulates in the thylakoid lumen to be used later
cytochrome complex
enzyme that transfers electrons from plastoquinone to plastocyanin
plastoquinone
electron carrier molecule that delivers electrons to the cytochrome complex
plastocyanin
protein that transfers electrons from the cytochrome complex to photosystem I
plastoquinol
the oxidised form of plastoquinone
What happens to electrons as they pass through the cytochrome complex?
Their energy is used to pump hydrogen ions into the thylakoid lumen
Why is the reaction centre in photosystem II called P680?
It absorbs light with a wavelength of 680nm
Why is the reaction centre in photosystem I called P700?
It absorbs light with a wavelength of 700nm
P700
the reaction centre in photosystem I
ferredoxin
iron-sulphur protein that transports electrons from photosystem I to NADP+ reductase
What are the two pathways of electron transport in PSI?
Noncyclic electron transport and cyclic electron transport
What happens in noncyclic electron transport?
Electrons from PSI are transferred to ferredoxin and then to NADP+ reductase to produce NADPH
What happens in cyclic electron transport?
Electrons from PSI are transferred to ferredoxin then to the cytochrome complex pump via plastoquinone, then back to PSI via plastocyanin
How is the amount of ATP and NADPH controlled?
By alternating between cyclic and noncyclic electron transport
How is ATP produced during light-dependent reactions?
The accumulated protons in the thylakoid lumen diffuse through ATP synthase to the stroma
Calvin cycle
light-independent reactions that convert CO2 into sugars using ATP and NADPH
What happens in the regeneration stage of the Calvin cycle?
One G3P out of six produced is used to contribute to making sugars, and the rest are regenerated into RuBP
What are the three components that start the Calvin cycle?
Carbon dioxide, RuBisCO and RuBP
RuBisCO
enzyme that catalyses the reaction between CO2 and RuBP
RuBP
ribulose bisphosphate
What is created when CO2 and RuBP react with each other?
3-phospho glyceric acid
3-PGA
3-phospho glyceric acid
What is the general structure of RuBP?
It has a five carbon backbone and is flanked by two phosphates
How many carbon dioxides and RuBPs are needed to start the Calvin cycle?
One CO2 and one RuBP
How much 3-PGA is produced from one CO2 and one RuBP?
Two molecules of 3-PGA
carbon fixation
process of converting inorganic carbon dioxide into organic molecules
What happens in the fixation stage of the Calvin cycle?
Carbon dioxide and RuBP are converted to 3-PGA
What happens in the reduction stage of the Calvin cycle?
3-PGA is converted to G3P using ATP and NADPH
G3P
glyceraldehyde-3-phosphate
How is 3-PGA converted to G3P?
3-PGA is reduced to G3P using ATP and NADPH
How much ATP and NADHP is used in the reduction stage of the Calvin cycle?
Six ATP and six NADPH
What happens in the regeneration stage of the Calvin cycle?
One G3P out of six produced is used to contribute to making sugars, and the rest are regenerated into RuBP
How many turns of the Calvin cycle does it take to export one G3P?
Three turns creates six G3Ps, which is enough to export one G3P
How is G3P regenerated into RuBP?
ATP is used to turn G3P into RuBP
How much ATP is used in the regeneration stage of the Calvin cycle?
Three ATP
