Photosynthesis Flashcards
Photosynthesis
The process that converts solar energy into chemical energy
Autotrophs
Substain themselves without eating anything derived from other organisms
Autotrophs (Consumers or Producers)
Producers, produce organic molecules from CO2 , other inorganic molecules and sunlight
What are plants classified as??
Photo-Autotrophs
Heterotrophs contain their organic material from?
Other Organisms
What are Heterotrophs considered to be?
Consumers of the biosphere
What do Heterotrophs depend on?
Photo-Autotrophs for food and O2
Chloroplasts structurally similar and likely evolved from?
Photo Synthetic Bacteria (Endosymbiotic Theory)
Major Location of Photosynthesis?
Leaves
Where are Chloroplasts found?
Mainly in cells of the mesophyll, the interior tissue of the leaf
How many chloroplasts in each mesophyll?
30-40 Chloroplasts
What is the purpose of the Stomata?
CO2 enters and O2 exits the leaf through microscopic pores
What is a Stroma?
In a chloroplast, there is an envelope of two membranes surrounding a dense fluid, which is called stroma
Thylakoids Definition
Are connectd sacs in the chloroplast which compose a third membrane system
Grana Definition
Thylakoids may be stacked in columns, are called this
Where does Chlorophyll Reside?
The pigment, which gives leaves their green color, resides in the thylakoid membrane
Photosynthesis Equation
6CO2 + 12H20 + Solar Energy –> C6H12O6 (starch) + 6O2 + 6H2O
Overall chemical change during photosynthesis is the ___ of the one that occurs during cellular respiration
Reverse
What becomes reduced in Photosynthesis?
CO2
What becomes oxidized in Photosynthesis?
H20
Photosynthesis ___ the direction of electron flow compared to respiration
Reverses
What kind of Process is Photosynthesis?
Endergonic Process, the energy boost is provided by light
What are the two stages of Photosynthesis?
Light reactions (The photo part) and the Calvin Cycle (The synthesis part/light independent/ “dark”)
Light reactions definition
Convert solar energy to the chemical energy of ATP and NADPH
Four Steps in Light Reactions
Light splits H20 into H2 and O2
Release O2
Reduce NADP+ to NADPH
Generate ATP from ADP
Products from Light Reactions?
O2 + NADPH + ATP
What does the Calvin Cycle in the Stroma produce?
Forms sugar from CO2, using ATP and NADPH from light reaction
Calvin cycle begins with..
carbon fixation, incorporating CO2 into organic molecules
Sunlight is a form of ..
Electromagnetic Energy
Sunlight travels in..
Rhythmic Waves
Distance between the crests of two adjacent waves is called
a wavelength
Wavelength determines..
the type of electromagnetic energy
Electromagnetic Spectrum is..
The entire range of electromagnetic energy from very short (gamma rays) to very long (radio waveS)
Visible light..
is the fraction of the spectrum that our eyes see as different colors
Sunlight consists of
Discrete packets of energy, called photons
Pigments are..
Substances that absorb visible light
Why do leaves green appear green?
Because chlorophyll reflects and transmits green light
What is the absorption spectrum?
A graph plotting a pigments light absorption versus wavelength
What is best absorbed in Chlorophyll?
Violet-Blue and Red Light are absorbed, and work best for Photosynthesis
Action Spectrum..
Profiles the relative effectiveness of different wavelengths of radiation in driving a process
Chlorophyll A…
is the main photosynthetic pigment
Chloropyll b..
Broaden the spectrum used for photosynthesis
What is the difference between a and b
Difference in the absorption spectrum between a and b due to slight structural difference between the pigment molecules
Accessory pigments called carotenoids
Absorb excessive light that would damage chlorophyll
Structure in Chlorophyll a?
CH3
Structure in Chlorophyll b?
CHO
Porphyrin Ring
Light-Absorbing “head” of molecule; note magnesium atom at center
Hydrocarbon Tail in Chlorophyll
Interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown
What happens when pigment absorbs light
The pigments electrons gains energy, goes from a ground state to a excited state
How stable is the excited state?
Highly unstable. Electrons lose their energy and fall back to the ground state releasing energy in the form of heat or light or flurescence
The two types of Photosystems?
Photosystem II and Photosystem I
Photosystem II (PS II)
Functions first (Numbers reflect the order of discovery) and is best at absorbing a wavelength of 680 nm. The reaction-center chlorophyll of a PSII is called P680
Photosystem I (PSI)
Best at absorbing a wavelength of 700 nm.
Reaction center chlorophyll of a PS I is called P700
What are the two possible routes for electron flow in a light reaction?
Cyclic and Linear
Linear Electron Flow:
The primary pathway, involves both photosystems and produces ATP, NADPH & O2 using light energy
How many steps are there in a linear electron flow?
8 Steps
Step 1 in Linear Electron Flow
Photon hits a pigment and its energy is passed among pigment molecules until it excites P680 ( a pair of chlorophylls)
Linear Electron Flow; Step 2
An excited electron from P680 is transferred to the primary electron acceptor (now called P680+)
Linear Electron Flow; Step 3
H20 is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680
What is the strongest known biological oxidizing agent?
P680+
What is released in Step 3?
O2 is released as a by-product of this reaction
Linear Electron Flow; Step 4
Each electron “falls” down an electron transport chain fro the primary electron acceptor of PSII to PSI
Linear Electron Flow; Step 5
Energy is released by the electron fall drives the creation of a proton gradient across the thylakoid membrane.
What drives ATP synthesis in Step 5?
The diffusion of H+ (protons) across the membrane
Linear Electron Flow; Step 6
In PS I (like PS II), transferred light energy excites P700, which loses an electron to an electron acceptor
More details for Step 6 of Linear Electron Flow (P700+)
P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the ETC.
Linear Electron Flow; Step 7
Each electron “falls” down ETC from the primary electron acceptor of PS I to the protein Ferredoxin (Fd)
Linear Electron Flow; Step 8
Electrons are then transferred to NADP+ and reduces it to NADPH. Electrons here available for reactions of Calvin Cycle. Removes H+ from Stroma too
Linear Electron Flow; Summary
Light reactions generate ATP and increase the potential energy of electrons by moving them from H20 to NADPH.
Cyclic Electron Flow
Electrons cycle back from Fd to the PS I reaction center. Cyclic electron flow uses only photosystem I and produced ATP, not NADPH. No oxygen released
What came first, Cyclic or Linear?
Cyclic electron flow is thought to have evolved before linear electron flow
How does Cyclic Electron protect?
It may protect cells from light-induced damage
Chemiosmosis in Mitochondria
Protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
Chemiosmosis in Chloroplasts
Protons are pumped into the thylakoid space and drives ATP synthesis as they diffuse back into the stroma
Why does the Calvin cycle use chemical energy?
Uses energy of ATP and NADPH to reduce CO2 to sugar
Calvin cycle builds sugars from smaller molecules by using..
ATP and the reducing power of electrons carried by NADPH
Carbon enters the Calvin Cycle as ..
CO2
Carbon leaves the Calvin Cycle as
A sugar named Glyceraldehyde 3-Phosphate (G3P)
The Calvin cycle regenerates what?
Regenerates its starting material (RuBP) after molecules enter and leave the cycle
Calvin Cycle has three phases
Carbon Fixation
Reduction
Regeneration of the CO2 accept RuBP
Carbon Fixation Info
Catalyzed by rubisco, ribulose bisphosphate carboxylase. The most enzyme on this Earth
Reduction Info
Formation of G3P (glyceraldehyde 3 phosphate)
RuBP name
Ribulose Biphosphate
How and which energy rich molecule is made during the Calvin Cycle using Carbon?
Using Carbon from CO2, eenrgy from ATP and high energy electrons from NADPH, constuct a energy right sugar molecule called G3P
What is G3P called?
Glyceraldehyde-3-Phosphate
How many molecules have to enter in order to get a net output of 1 G3P
3 molecules of CO2 have to enter the cycle
What is G3P?
A raw material for making glucose, cellulose, and starch
What is the remaining G3P used for?
TO regenerate RuBP
Light Reactions Summary
Carried out by molecules in thylakoid membrane
Convert light energy to chemical energy of ATP and NADPH
Split H2O and release O2
Calvin Cycle Summary
Take place in stroma
Use ATP and NADPH to convert CO2 to G3P
Return ADP, and NADP+ to the light reactions
Problems with Photorespiration
Consumes O2 and Organic Fuel & releases CO2 without producing ATP or Sugar
If PS CO2 is taken in..
these processes can work against each other
Photorespiration in a plant under temperature stress
It can drain as much as 50% of the carbon fixed by the Calvin cycle
Result of Photorespiration
PR lowers production of sugars, and limits plant growth
What plants cannot grow well in hot areas as rubisco?
C3 Plants cannot. Adds more oxygen into RuBP as temperature rises
Why may Photorespiration be an evolutionary relic?
Because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2
Photorespiration limits what?
Damaging products of light reactions that build up in the absence of the Calvin Cycle
C4 and CAM PLants have what adaptations?
ALlows them to survive in hot and dry areas and they can out compete C3 Plants
Some examples of C4 plants?
Sugarcane, Maize
How do C4 plants minimize cost of photorespiration?
By incorporating CO2 ino 4-Carbon Compounds
Two distinct types of cells in the leaves of C4 pants
Bundle-Sheath Cells
Mesophyll Cells
What are Bundle-Sheeth Cells
They’re arranged in tightly packed sheaths around the veins of the leaf
What are Mesophyll Cells
They’re loosely packed between the bundle sheath and the leaf surface
The 4-Carbon compounds are exported to..
bundle-sheath cells
With the bundle-sheath cells, the 4-c compounds..
release CO2 that is then used in the Calvin cycle
How do some plants, including succulents, fix carbon?
They use Crassulacean Acid Metabolism (CAM)
When do CAM plants open their Stomata?
At night, incorporating CO2 into organic acids
When does Stomata close and what happens?
Closes during the day, and CO2 is released from organic acids and used in the Calvin Cycle
Energy entering chloroplasts as sunlight gets stored as what?
As chemical energy in organic compounds
Plants store excess sugar as?
Starch in structures such as roots, tubers, seeds, and fruits
Sugar made in the chloroplasts supply what and to do what?
Chemical Energy and Carbon skeletons to synthesize the organic molecules of cells
The cluster of pigment molecules function as what?
As a light gathering antenna
What happens when a photon strikes one of the pigment molecules?
The energy jumps from one molecule to molecule until it arrives at the reaction center of the photosystem
The reaction center consists of chlorophyll a molecule that sits next to what?
A primary electron acceptor
What is a primary electron acceptor?
Traps light excited electron from the chlorophyll a in the reaction center and is reduced as a result
What is one of the first steps of the light reactions?
Solor-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor
The team of molecules built in the thylakoid membrane do what?
Uses the trapped energy to make ATP and NADPH
