Chapter 10 Flashcards
What is photosynthesis?
conversion of sunlight to chemical energy in sugars and other organic molecules
How did photosynthesis originate?
Originates in a group of bacteria that had infolded regions of the plasma membrane
What are autotrophs? (2)
AKA producers produce their organic molecules from CO2
sustain themselves without eating anything derived from other living beings
what are photoautotrophs?
organisms that use light to synthesize organic substances
what are heterotrophs? (2)
aka consumers, includes decomposers
obtain organic material through compounds produced by other animals
what is the endosymbiont theory for chloroplast?
original chloroplast was a photosynthetic prokaryote that lived inside an ancestor of eukaryotes
where does photosynthesis take place?
in the mesophyll
What is mesophyll? (3)
tissue of the interior leaf
where chloroplasts are found
30-40 chloroplasts between 2-4 um by 4-7 um
what is the stomata? (2)
microscopic pores in leaves
where CO2 enters and O2 leaves
what is the stroma?
a dense fluid surrounding the envelope of two membranes in a chloroplasts
what are thylakoids?
sacs that segregate the stroma from the thylakoid space in the stroma
what is granum?
stacks of thylakoids
what is chlorophyll? (2)
green pigment in the thylakoid
absorbs light energy
how does photosynthesis work? (3)
plants produce organic compounds and oxygen from carbon dioxide and water in the presence of light
produces a three C sugar used to make glucose
chloroplast splits water into oxygen and excess water, while CO2 is used to form sugar
Photosynthesis vs Cellular Respiration (4)
both are redox
photosynthesis reverses direction of electron flow
splits water, and electrons are transferred with H+ to reduce sugar
photosynthesis is endergonic, requiring energy in the form of light
what are the stages of photosynthesis?
Light reaction and Calvin cycle
What is the light reaction? (2)
steps that convert solar energy to chemical energy
occurs in the thylakoids
What occurs during the light reaction? (4)
Water is split
O2 is given off as a by-product
light drives e- and H+ to an acceptor called NADP+
generated ATP using chemiosmosis
What occurs during the calvin cycle? (4)
synthesis of sugar
occurs in the stroma
incorperates CO2 from the air into organic molecules in the chloroplast (carbon fixation)
reduces fixed carbon using NADPH to carbohydrates by adding electrons using ATP
what is electromagnetic energy?
energy traveling in waves
What are wavelengths?
distance between crests of electromagnetic waves
What is visible light?
radiation in the band of 380 nanometers to 750 nanometers
What are photons? (2)
discrete particles consisting of light
Shorter the wavelength, the higher the energy of the photon
What are pigments? (5)
substances that absorb visible light
Different pigments absorb different wavelengths
White light- wavelength is reflected
If all wavelengths is absorbed, pigment is black
Color is whatever that is reflected
What is a spectrophotometer?
instrument that measures how a pigment absorbs light
what is an absorption spectrum?
pigment’s light absorption vs wavelength
what is chlorophyll alpha? (3)
key light-capturing pigment in the chloroplast that participate in the light reactions
Violet blue and red light works best
Green is the least effective
what is chlorophyll beta? (3)
hydrocarbons that are shades of yellow and orange
Broadens the action spectrum
photoprotection absorbs and dissipates excessive light energy that would damage chlorophyll
what is an action spectrum?
profiles relative effectiveness of different wavelengths of radiation in driving a process
What happens after the light is absorbed?
the electrons in the molecule are elevated to an orbital with more potential energy
pigment molecules are excited
energy transferred from pigment to pigment within a light-harvesting complex, until it is passed to a reaction center complex
what is a photosystem? (2)
composed of a reaction center surrounded by several light-harvesting complexes (organized association of proteins holding chlorophyll alpha molecules)
thylakoid consists of two photosystems
what is a light-harvesting complex?
consists of various pigment molecules bound to a protein
What happens in the reaction complex?
contains a molecule capable of accepting e- and becoming reduced
electron is transferred from the reaction-center chlorophyll alpha to said molecule
What is Photosystem 2? (2)
reaction center complex aka P680
Absorbs wavelengths of 680 and 700 nanometers
what is the linear electron flow?
Flow of electrons through the two photosystems which synthesizes ATP
What are the first four steps of the linear electron flow?
- photon strikes pigment molecules in PS2. chain of pigments excited until it reaches the P680 pair of chlorophyll alpha
- electron is then transferred to the primary electron acceptor
- enzyme splits water int two electrons. these are supplied to the P680. H+ is released into the thylakoid. Photoezcited e- is passed through an ETC to PS1
What are the last four steps in the LEF?
- fall of electrons provide energy for ATP synthesis. the electron si passed through the cytochrome complex
- light energy is transferred to the PS1 to excite an electron of the P700 pair of chlorophyll alpha, which is then passed to a primary electron acceptor.
- electron is passed in a series of redoc reactions to a second ETC
the enzyme NADP+ reductase catalyzes electrons transfer to NADP+ to form NADPH
what is the cyclin electron flow? (4)
An alternate path for photoexcited electrons
Uses PS1 only
Does not produce NADPH or oxygen
Generates ATP
what is chemiosmosis in chloroplast? (4)
In chloroplast, the e- dropped down the transport chain come from water
Chloroplast do not need molecules from food to make ATP
I
n light, the pH of the thylakoid space is about 5
pH of the stroma is 8 in light
what occurs in the calvin cycle? (5)
anabolic reaction, building carbohydrates from smaller molecules using energy
carbon eters the cycle through CO2 and leaves as sugar
spends ATP and consumes NADPH
provides glyceraldeyhyde 3 Phosphate (G3P)
for one G3P, it takes 3 cycles and fixes 3 CO2
Phase 1 of the calvin cycle (3)
aka carbon fixation
incorporates each CO2 one at a time, attaching to a 5 C sugar called RuBP (catalyzed by Rubisco)
product splits in half to form 2 molecules of 3-phosphoglycerate
Phase two of the Calvin cycle (6)
aka reduction phase
each molecule of 3-phosphoglycerate receives an additional P group from ATP and becomes 1,3-bisphosphoglycerate
the electron from NADPH reduces the above molecule
above molecule loses its p group and becomes G3P
the carboxyl group gets reduced to an aldehyde group
for every 3 CO2, 3 G3P is formed, but 5 G3P is used during the process
Phase 3 of the Calvin cycle (3)
aka regeneration of RuBP
Carbon skeleton of five molecules of G3P are rearranged in the last steps into three RuBP
spends three more molecules of ATP
What are C3 plants? (2)
plants that fix carbon using rubisco to add CO2 to RuBP
during hot temperatures, stomata closes and prevents CO2 intake
what is Photorespiration (6)
when plants bind using O2 instead of CO2
results with a 2C being released, where peroxisomes and mitochondria rearrange it to release as CO2
Uses ATP
Produces no sugar
decreases photosynthetic output
prevent damage due to excessive light
Where did photorespiration originate?
ancient times having much less O2 in the atmosphere, so excluding O2 in the cycle made little difference
What are C4 plants?(5)
during carbon fixations, produces a four-carbon compound as its first product
contains two types of photosynthetic cells- bundle-sheath and mesophyll
Calvin cycle is confined to the chloroplasts in bundle-sheath cells
Preceded by incorporation of CO2 into mesophyll cells
contains only PS1
what are bundle-sheath cells?
bundles around veins of leaves
What are mesophyll cells?
found between bundle-sheath cells and leaf surfaces
Calvin cycle in C4 plants part 1 (4)
Carried out by PEP carboxylase found in mesophyll cells
Adds CO2 to PEP forming 4C product oxaloacetate
PEP has no affinity for O2
PEP carboxylase is more efficient than rubisco because it cannot fix O2
Calvin cycle in C4 Plants part 2
The C4 product is exported to bundle sheath cells through plasmodesmata
4C compounds release CO2 which is reassimilated into organic material by rubisco
regenerates pyruvate, transported to mesophyll
ATP is used to convert pyruvate to PEP
How is ATP regenerated in C4 cells?
bundle-sheath cells carry out cyclic electron flow
How do rising CO2 levels affect plants? (3)
Advantages to C3 plants as it prevents photorespiration
- Temperatures rise as well though, so it can induce an opposite effect
C4 plant remain unaffected
