Chapter 10 - Photosynthesis Flashcards
Autotrophs
Self-feeders
Sustain themselves without eating anything derived from other living beings
Produce organic molecules from CO2 and other inorganic raw materials from the environment (producers)
Photoautotrophs - use light to make food
How does an organism acquire the organic compounds it uses for energy?
Either by creating its own food (being an autotroph), or consuming it (heterotroph)
Photosynthesis is the foundation of this process
Heterotrophs
Biosphere’s consumers because they consume compounds produced by other organisms
Decomposers (bacteria) that feed on carcasses and waste, are also heterotrophs
Depend on Photoautotrophs for both food and oxygen
Where does most photosynthesis occur?
The leaves of a plant , more specifically he Mesophyll - which occurs mainly in the chloroplasts
30-40 chloroplasts per Mesophyll cell
Mesophyll
The tissue in the interior of the leaf where most chloroplasts are found
30–40 chloroplasts per Mesophyll cell
Stomata
Pores that allows carbon dioxide in and oxygen out.
Also allows water to come out
Stroma
An envelope with two membranes surrounding a dense fluid of the chloroplasts
Thylakoids
Third membrane system that includes sacs which segregates the Stroma from the thylakoid space inside the sacs
Granum
Stacked thylakoid stacks in columns
Chlorophyll
Green pigment that gives leaves their color inside thylakoid membrane of the chloroplast
What happens when a plant is exposed to light?
The green parts of the plant produce organic compounds and oxygen from carbon dioxide and water
Photosynthesis chemical equation
6CO2 + 12 H2O + light energy —-> C6H12O6 + 6 O2 + 6H2O
The reverse equation of cellular respiration
Where does O2 come from in photosynthesis?
H2O; not carbon dioxide like most people think
The chloroplast splits water into hydrogen and oxygen
They incorporate the electrons of hydrogen into sugar molecules and then release oxygen as a byproduct
Photosynthesis
Chloroplasts capture light energy and converts it to chemical energy that is stored in sugar and other molecules
It’s a redox reaction in which H2O is oxidized (loses an electron) to become 6O2 and CO2 is reduced (gains an electron) to become C6H12O6
It’s endergonic because it uses light to aid the process.
Explain van niel’s discovery about photosynthesis
He studied photosynthesis in bacteria. They make their carbohydrate from CO2, but don’t release O2.
Concluded that co2 isn’t split to make carbon and oxygen; it split its hydrogen sulfide instead. He reasoned that plants are more likely to split their h2o and use the hydrogen electrons releasing O2 as a byproduct
Photosynthesis is reverse of cellular respiration
It reverses the electron flow.
Water is split and electrons are transferred along with hydrogen ions from water to co2, reducing it to sugar.
It’s endergonic because the electrons increase in potential energy as they move from water to sugar
Light provides this energy boost.
What are the two cycles of photosynthesis
Light reactions (photo part)
Calvin cycle (synthesis part)
Light reactions
Covert solar energy to chemical energy
Water is split providing a source of electrons and protons (H+) ions giving off O2 as a byproduct
Light absorbed by chlorophyll drives a transfer of electrons and hydrogen ions from water to NADP+ where they’re temporarily stored
Light uses solar energy to NADP+ to NADPH by adding a pair of electrons along with H+
The light reactions also generate ATP using chemiosmosis to power the additional phosphate group to ADP using phosphophorylation
Phosphorylation
Using chemiosmosis to add a phosphate to ADP
Which two compounds are converted to chemical energy in the first stage of photosynthesis?
NADPH and ATP
NADPH
A source of electrons that reduce power that can be passed along to an electron acceptor
Calvin cycle
Carbon fixation
Then reduces the fixed carbon to carbohydrate by the addition of electrons (done via NADPH)
Uses ATP convert CO2 to carbohydrate which is generated by light reactions
Referred to as dark reactions, or light independent reactions because they don’t require light directly.
How is light used to covert solar energy into chemical energy?
Because chloroplasts are solar powered chemical factories…
Use thylakoids to transform lights energy into chemical energy of ATP and NADPH
Light
A form of electromagnetic energy/radiation
Occurs in rhythmic waves
Wavelength
Involves the distance between crests of the waves
It determines the type of electromagnetic energy
Electromagnetic spectrum
The entire range of electromagnetic energy or radiation
Visible light
Involves all the wavelengths we can physically see
Includes light waves for photosynthesis
This is how we see color
380 nm - 750 nm
Photons
Lights ability to function as particles as well.
Particles of light
Photosynthetic pigments
Pigments that Absorb light
Different pigments absorb different wavelengths
Wavelengths that are not absorbed are transmitted or reflected
Leaves appear green because chlorophyll reflects/transmits green light
Spectrophotometer
Measures a pigment’s ability to absorb various wavelengths
It sends light through the pigments and measures the fraction of light transmitted at each wavelength
Absorption spectrum
A graph that documents pigment’s light absorption versus wavelength
Chlorophyll a which is violet-blue and red work best for photosynthesis
400-500 nm?
Engelmann experiments
Used aerobic algae to test which wavelengths were the most suitable for photosynthesis
The wavelengths that were suitable to photosynthesis caused the algae to expel excess O2 and then the aerobic bacteria would congregate around it.
What is the main pigment of photosynthesis?
Chlorophyll a
What are accessory pigments?
Chlorophyll b and carotenoids
Carotenoids
They are responsible for photoprotection.
They absorb excess light that would damage chlorophyll
What happens when light hits chlorophyll?
When a pigment absorbs light, its electrons get excited and jump from one shell to one that’s unstable.
When the electrons fall back to their ground state, they release photons called fluorescence
It gives off light and heat.
Photosystem
Consists of a reaction center complex (a type of protein complex) surrounded by light harvesting complexes
Light harvesting complex
Pigment molecules bound to proteins
Transfer the energy of photons to the reaction center
Primary electron acceptor
Exists in the reaction center and accepts excited electrons and is reduced as a result
What are the two types of photosystems in the thylakoid membrane?
Photosystems 2 is the first and its chlorophyll best absorbs wavelengths that are 680 nm long
Its reaction center is called P680
Photosystems 1 is best at absorbing wavelengths that are 700 nm long and its reaction center is called P700
What are the two possible pathways during the light systems reaction?
Cyclical and linear
Linear electron flow is the primary pathway and it involves both photosystems creates both ATP and NADPH using light energy
What are the 8 steps in linear electron flow?
- Photon hits the pigment and the energy is passed from pigment molecules until it excites P680
- An excited electron from P680 is transferred via the primary electron transport (P680+)
- H2O is split by enzymes and the electrons are transferred from the hydrogen atoms to P680+ thus reducing it to P680 (O2 is released as a byproduct)
- Each electron “falls” down an electron transport chain to from the primary electron acceptor of PS 2 to PS 1
- Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane (diffusion of H+ across the membrane drives ATP synthesis)
- In PS 1 transferred light energy excites P700 which loses an electron (P700+ accepts an electron passed down from PS 2 through the transport chain)
- Each electron falls down the chain from the primary electron acceptor in PS1 to ferredoxin (fd)
- The electrons are then transferred to NADP+ and reduced to NADPH
NADPH is then available for the Calvin cycle
This also removed H+ from the Stroma
Cyclic electron flow
Electrons cycle back from Fd to PS1 reaction center
Uses only PS 1 and produces ATP, but no NADPH
Don’t release O2
Ie purple bacteria which have PS1 but not PS2
Evolved before linear flow and may protect the plant from light damage
Chemiosmosis in chloroplasts vs mitochondria
Both generate ATP via chemiosmosis
Mitochondria use food, chloroplasts use light
Mitochondria pump protons into the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
In chloroplasts protons are pumped into the thylakoid space and they generate ATP as they diffuse back into the Stroma
Calvin cycle
Similar to the citric acid cycle because it regenerates its starting material after molecules enter and leave the molecule
It builds sugar from smaller molecules using ATP and reducing the power of electrons via NADPH
Carbon enters as CO2 and releases as glyceralhyde three phosphate G3P (has to go through Calvin cycle three times for this to occur
Three Phases of the Calvin Cycle
- Carbon fixation (catalyze do by the protein rubisco)
- Reduction
- Regeneration of CO2 acceptor by RuBP
Photosynthesis in hot climates
Plants close stomatas on hot days, which keeps H20 in, but also limits photosynthesis
Closed stomatas reduces access to CO2 and causes a buildup of O2
Photorespiration
rubisco adds O2 instead of
CO2 in the Calvin cycle, producing a two-carbon
compound
consumes O2 and organic fuel
and releases CO2 without producing ATP or sugar
In many plants, photorespiration is a problem
because on a hot, dry day it can drain as much
as 50% of the carbon fixed by the Calvin cycle
C3 plants
most plants
initial fixation of CO2,
via rubisco, forms a three-carbon compound
3-phosphoglycerate
C4 plants
minimize the cost of photorespiration by
incorporating CO2 into four-carbon compounds
two distinct types of cells in the leaves
of C4 plants:
Bundle-sheath cells
mesophyll cells
Bundle-sheath cells
arranged in tightly packed
sheaths around the veins of the leaf
mesophyll cells
loosely packed between the
bundle sheath and the leaf surface
Three steps for Sugar production in C4 plants
- The production of the four carbon precursors is
catalyzed by the enzyme PEP carboxylase in
the mesophyll cells
PEP carboxylase has a higher affinity for CO2
than rubisco does; it can fix CO2 even when CO2
concentrations are low - These four-carbon compounds are exported to
bundle-sheath cells - Within the bundle-sheath cells, they release CO2
that is then used in the Calvin cycle
crassulacean acid metabolism (CAM)
what succulent plants use to fix carbon
open their stomata at night,
incorporating CO2 into organic acids
Stomata close during the day, and CO2 is released
from organic acids and used in the Calvin cycle
LIGHT REACTIONS
• Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere
Calvin cycle
Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions
