Chapter 10: Photosynthesis Flashcards
What are autotrophs?
the producers of the biosphere
what are heterotrophs?
the consumers of the biosphere
What are photoautotrophs?
organisms that use light energy to make organic substances
What are the 5 different types of photoautotrophs?
- plants
- cyanobacteria
- purple sulfer bacteria
- unicellular bacteria
- multicellular algae
What stage of photosynthesis captures solar energy and transforms it into chemical energy?
The light reactions
what stage of photosynthesis uses that chemical energy to make the organic molecules of food?
the Calvin cycle
How would you identify which parts of the plant have chloroplasts?
they are green
For most plants, what part of their anatomy is a major site of photosynthesis?
their leaves
What is the mesophyll?
the tissue in the interior of the leaf where chloroplasts can be found
What is the stomata?
tiny pores in the leaf where CO2 enters and oxygen exists
How many chloroplasts does a typical mesophyll cell have?
30-40
What is the stroma?
a dense fluid inside the chloroplast surrounded by two membranes.
What are thakaloids?
sacs inside the stroma
What is the inside of a thakaloid called?
the thakaloid space
When thakaloids are stacked what are they called?
grana
What is chlorophyll
the green pigment that gives leaves their color
Where is chlorophyll located?
in the membrane of the thakaloid
What drives the synthesis of organic molecules in the chloroplast?
light energy absorbed by chlorophyll
What is the most complete equation for photosynthesis?
6 CO2 + 12 H2O + Light Energy –> C6H12O6 + 6 O2 and 6 H2O
What is the equation for photosynthesis that shows the net consumption of water?
6 CO2 + 6H2O + Light Energy —> C6H12O6 + 6 O2
What is the empirical formula for photosynthesis?
CO2 + H2O –> [CH2O] + O2
What reactant is reduced in photosynthesis? What is its product?
CO2 turns into C6H12O6
What reactant is oxidized in photosynthesis? What is its product?
H2O turns into O2 (remember all the non sense about the scientist)
What happens to the potential energy of the electrons as the move from water to sugar?
They increase in potential energy
What is required to increase potential energy of electrons?
An input of energy
Is the process of moving electrons from water to sugar exergonic or endergonic?
endergonic
What are the two stages of photosynthesis?
The light reactions and the Calvin Cycle
When water is split in photosynthesis what does it provide?
Electrons
Hydrogen ions (H+)
and a bi-product of O2
Light absorbed by chlorophyll drives the transfer of electrons and hydrogen ions from water to an acceptor. What is this acceptor called?
NADP+
What is the difference between NAD+ and NADP+
NADP+ has an extra phosphate group
What is the reduced form of NAD+ ?
NADPH
What is photophosphorylation?
When light reactions create ATP by using chemiosmosis to add a P to an ADP
Light reactions produce sugar. T or F?
F
What is carbon fixation?
The initial step of the Calvin cycle in which CO2 is incorporated into present organic compounds
The Calvin cycle reduces fixed carbons into what?
Carbohydrates
Where does the reducing power come from to reduce fixed carbons into carbohydrates?
NADHP
Where did NADHP in the Calvin cycle get its electrons
From the light reactions cycle
What are the CELLULAR inputs and outputs of the light reactions stage?
Input: light energy and H2O
Output: O2
What are the CELLULAR inputs and outputs of the Calvin cycle?
Input: CO2
Output: CH2O (sugar)
Where does the Calvin cycle take place?
The stroma
Where does the light reactions cycle take place?
The thakaloid membrane
What does the light reactions stage of photosynthesis provide for the Calvin cycle?
ATP and NADPH
What does the Calvin cycle of photosynthesis provide for the light reactions?
ADP and Phosphate groups
NADP+
What does the Calvin cycle require to convert CO2 into carbohydrates?
chemical energy in the form of ATP
Does the Calvin cycle require light directly?
no
Where do NADP+ and ADP pick up electrons and phosphate?
On the outside of the thakaloids
Light is a form of energy known as _______________
electromagnetic energy
Dropping a pebble in a pond is to disturbances of a material medium as electromagnetic waves are to disturbances of?
electric and magnetic fields
What is the distance between the crests of electromagnetic waves called?
Wavelength
What is the electromagnetic spectrum?
the entire range of radiation
What is the range of visible light?
380nm to 750 nm in wavelength
What are photons?
photons are not tangible particles but they act like objects in that each of them has a fixed amount of energy
What happens to the energy of a photon as wavelength increases?
it decreases
List the colors by order of wavelength
Purple Blue Green Yellow Orange Red
Which has a higher energy level purple or red?
purple
What radiation drives photosynthesis?
visible light
What are the three outcomes of light meeting matter?
1, absorbed
- reflected
- trasmitted
What are pigments?
substances that absorb visual light
Pigments are specific to _____
wavelength
What colors does chlorophyll absorb?
violet-blue and red
Why does chlorophyll appear green?
it is being transmitted/reflected
What is chlorophyll a
the key light-capturing pigments that participates directly in the light reactions
What is chlorophyll b
the accessory pigment
What are the three different pigments in chloroplasts and which of the two are accessory?
- chlorophyll a
- chlorophyll b
- carotenoids
What light works best for photosynthesis? and what are their ranges?
violet light blue (450 ish)
red (700-750)
What us an action spectrum?
the way we test which wavelengths of radiation are most effective
the action spectrum for photosynthesis is much broader than the absorption spectrum for chlorophyl a. Why?
With the help of the accessory pigments, chlorophyl b and carotenoids, the light than can be absorbed become less restricted
What is the structural difference between chlorophyl a and b
chlorophyl b includes CHO where chlorophyll a includes CH3
What colors do carotenoids absorb?
violet and blue green light
What color are carotenoids?
various shades of yellow and orange
What color are chlorophyl b?
olive
What type of molecule are carotenoids
hydrocarbons
Besides aiding in broadening the spectrum of light used in photosynthesis, what else do carotenoids do?
They protect the cell from excessive light that would possibly damage the cell and react with oxygen
What happens when a molecule absorbs a photon of light?
It excites and electron out to a higher orbital increasing its potential energy
What must be the case for a photon to be absorbed by a compound?
The energy of the photon must be exactly the same as the difference in energy between the excited and ground state of that specific electron
An electron cannot stay excited for long, meaning that in a billionth a second the electron will drop back down to ground state. What will this produce?
heat
What causes light energy to be changed into heat?
light energy excited an electron pushing it to a higher potential energy state and then the electron drops back down releasing this gained energy as heat
What are the components of photosystems?
chlorophyll molecules, organic molecules, and proteins
Where are photosystems located?
in the thakaloid membrane
What is the central complex of a photosystem?
a reaction center complex
What several smaller complexes surround the reaction center complex of a photosystem?
light-harvesting complexes
What are the two critical components of a reaction center complex of a photosystem?
special pair of chlorophyll a molecules
primary electron acceptor
What holds together the reaction center complex of a photosystem?
proteins
What are light harvesting complexes in photosystems made of?
chlorophyll a, b, and carotenoids bound to proteins
What a pigment molecule absorbs a photon in the light harvesting complex what happens?
The electron pops out, then on its way back to a ground state it releases energy that excites the pigment molecule next to it until it passes to the special pair of chlorophyll a molecules in the reaction center
Why are their of chlorophyll a molecules special?
They can use the energy to boost one of their electrons but they can also transfer it to a different molecule
Where is the excited electron of the special chlorophyl molecules transferred?
To the primary electron acceptor
What is the primary electron acceptor?
a molecule capable of accepting electrons and becoming reduced
Why is the potential energy represented by the excited electron not dissipated as light and heat?
There is a primary electron acceptor readily available to be reduced
What are the two types of photosystems in the thakaloid membrane?
Photosystem I and Photosystem II
Which photosystem functions first in light reactions?
PSII
What is the reaction center chlorophyll a of PS II known as?
P680 (red)
What is the reaction center chlorophyll a of PS I known as?
P700 (far red)
What causes the difference between P680 and P700?
Their relationship with the proteins around them
What is the linear electron flow?
the flow of electron through he photosystems and other molecular components built into the thakaloid membranes
Where does linear electron flow occur?
In light reactions of photosynthesis
What is the first step of linear electron flow?
A photon excites the pigment molecules in the light harvesting complex of PS II which causes a chain reaction of excited pigment molecules leading all the way to the P680
What is step 2 of the linear electron flow?
P680 loses its electron instantly to the primary electron acceptor
What its step 3 of the linear electron flow?
An enzyme catalyzes the splitting of a H2O
Where does the oxygen go in step 3 of the electron flow?
binds with another oxygen to form O2
Where do the two electrons go in step 3 of the electron flow
The electrons are supplied back to P680
Where do the hydrogen atoms go in step 3 of the electron flow?
they are released into the thakaloid space
What is step 4 of the linear electron flow?
Photoexcited electrons are passes from PSII to PSI via an electron transport chain
What are the three components of the electron transport chain from PSII to PSI
- PQ (plastoquinone)
- A Cytochrome complex
- PC (plastocyanin)
What happens as electrons work heir way down the electron transport chain?
free energy is released that is used to pump H+ ions into the thakaloid space
How is ATP produced in light reactions?
through chemiosmosis
What is step 5 of the linear electron flow?
The potential energy stored in the pH gradient is used to produce ATP
What is step 6 of the linear electron flow?
The electron being moved down the electron chain replace the electron of P700 that was recently excited by light harvesting complex pigments in PSI
What is step 7 of the linear electron flow?
Photoexcited electrons in PSI are passed down a second electron chain
What makes up the second electron chain of photosynthesis?
Fd (Ferradoxin)
and the enzyme NADP+ reductase
Does the second electron chain produce add to the electrochemical gradient?
no
What is step 8 of the linear electron flow
The enzyme NADP+reductase uses the electrons being passes to it by Ferrodoxin to turn into NADHP
Why is it beneficial for the electrons to be held in NADHP?
They are at a higher energy level then they were in water
What is a cyclic electron flow?
A flow of electrons that utilizes photosystem I but not photosystem II
Where is the starting point of cyclic electron flow?
The cytochrome complex of the first electron transport chain
What is different about the products of cyclic electron flow compared to linear electron flow?
cyclic electron flow does not produce oxygen or NADPH, but does produce ATP
Electron transport chains transform redox reaction to what?
proton-motive force
Where do the high-energy electrons dropped down the electron transport chain come from in chloroplasts?
water
What happens to the pH of the thylakoid space when chloroplasts are illuminated?
the pH in the thylakoid drops to about 5 (increases in H+ ion)
What happens to the pH in the stroma when the chloroplasts are illuminated?
the pH in the stroma increases to about 8 (decrease in H+ ions)
Is the Calvin cycle catabolic or anabolic?
anabolic
How does carbon enter and leave the Calvin cycle?
enters as CO2
leaves as sugar
What is the sugar produced by the Calvin cycle/ the starting point of the carbon cycle?
G3P (glyceraldehyde 3-phosphate)
For the net synthesis of one molecule of G3P, how many times must the cycle take place?
3
How many molecules of CO2 must be used in order to produce 1 net G3P?
3
What are the three phases of the Calvin cycle?
- carbon fixation
- reduction
- regeneration
What does the term carbon fixation refer to?
the initial incorporation of CO2 into an organic molecule
What are the steps of phase 1 (carbon fixation) of photosynthesis?
CO2 is attached to RuBP with the help of the enzyme rubisco to produce a six carbon intermediate that almost instantly turns into 2 separate 3 carbon structures
What are the 3 carbon structures produced in the phase of carbon fixation?
3-phosphoglycerate
What is the first step of phase 2 (reduction) of photosynthesis?
3-phosphoglycerate receives an additional phosphate group and becomes 1, 3-biphosphoglycerate.
What is the second step of phase 2 (reduction) of photosynthesis?
1, 3-biphosphoglycerate is reduced by NADHP into glyceral-dehyde 3-phosphate (G3P)
In the second step of phase 2 of photosynthesis what looses electrons?
Both 1, 3-biphosphoglycerate and NADHP loose their electrons
How do the electrons from NADHP effect the carboyxl group on 1,3-biphosphoglycerate
It reduces into the aldehyde group of G3P
Does aldehyde or carboxyl have higher potential energy?
the aldehyde group
For every three molecules of CO2 that enter the cycle there are ____ molecules of G3P formed.
6
How many carbons start the cycle?
15
How many carbons end phase 2 (reduction)?
18
What is the last phase of the Calvin cycle?
regeneration
What happens in the last phase of the Calvin cycle?
G3P is rearranged into RuBP
How many molecules of G3P are at the start of regeneration?
5
How many molecules of RuBP are produced by 5 molecules of G3P?
3
How many molecules of ATP and NADPH are produced by the net synthesis of one G3P?
9 ATP
6 NADPH
What is the input of the Calvin cycle?
CO2
What is the output of the Calvin cycle?
1 G3P molecule
