Chapter 10 Flashcards
Autotroph
Self feeders
Sustain themselves without eating anything derived from other living things
Heterotrophs
Other feeders
Live on compounds produced by other organisms
Thylakoids
Sacs suspended within the stroma
Third membrane system
Mesophyll
Where chloroplasts are mainly found, tissue of the interior leaf
Stroma
Dense fluid, surrounded by an envelope of 2 membranes
Thylakoid space
Space inside the sacs that thylakoids segregate the stroma from
Plants are
Photoautotrophs
Decomposers
An organism whose function is to recycle nutrients by decomposition as it feeds on decaying organisms
__ enters the leaf, __ exits the leaf, by way of microscopic pores called the __
CO2
O2
Stomata
Chlorophyll
Green pigment, gives leaves color
Resides in thylakoid membranes of the chloroplast
Light energy absorbed from chlorophyll drives the synthesis of
Organic molecules in the chloroplast
Reactants of photosynthesis
Carbon dioxide Water Light energy 6 CO2 6 H2O
Products of photosynthesis
Glucose Oxygen Water C6H12O6 6 O2 6 H2O
Where does the oxygen come from?
Oxygen given off by plants is derived from the water and not from the carbon dioxide. The chloroplast splits H2O into H and O. Plants split H2O as a source of electrons from H atoms, releasing O2 as a by product
Photosynthesis is an __ and a __ reaction
Endergonic
Redox
Electrons __ in potential energy as they move from H2O to sugar
Increase
Process requires energy
Endergonic reaction provided by light
Water is split and electrons are transferred with H ions from the H2O to the CO2…
Reducing it to sugar
A photosystem is composed of a protein complex called
A reaction-center complex surrounded by several light-harvesting complexes
Reaction-center complex
Organized association of proteins holding a special pair of chlorophyll a molecules
Light-harvesting complexes
Consists of various pigment molecules bound to proteins
Primary electron acceptor
Molecule capable of accepting electrons and becoming reduced
Each photosystem (a reaction center complex surrounded by light-harvesting complexes) …
Functions in the chloroplast as a unit
Photosystem II (PS II)
Functions first in the light reactions
Light reactions convert
Solar energy to chemical energy
Light reactions and dark reactions
Light reactions require light to function
Dark reactions don’t require light
Light reactions
Water is split and provided a source of electrons and protons, gives off O2 as a by-product
Light absorbed by chlorophyll drives a transfer of the electrons and hydrogen ions from H2O to an acceptor: NADP+, where they are temporarily stored
Light reactions use
Solar energy to reduce NADP+ to NADPH by adding a pair of electrons along with an H+
Light reactions generate
ATP, using chemiosmosis to power the addition of a phosphate group to ADP, which is a process called photophosphorylation
Light energy is initially converted into…
Chemical energy in the form of two compounds: NADPH and ATP
NADPH is a…
Source of electrons, and acts as “reducing power” that can be passed along to an electron acceptor, reducing it
ATP is the
Energy currency of cells
Calvin cycle produces
Sugar
Light reactions store chemical energy in __ and __, which shuttle the energy to the carbohydrate-producing __ cycle
ATP
NADH
Calvin
Calvin cycle begins
Incorporates CO2 from the air into organic molecules already present in the chloroplast
Carbon fixation
Initial incorporation of carbon into organic compounds
Calvin cycle reduces
The fixed carbons to carbohydrate by the addition of electrons
Reducing power provided by NADPH
To convert CO2 to CH2O, the Calvin cycle requires
Chemical energy in the form of ATP, also generated by the light reactions
The Calvin Cycle can only make sugar with the help of
NADPH and ATP, produced by the light reactions
Calvin cycle does not require what directly?
Light
But can happen in light
Thylakoids are the site of
The light reactions
Calvin cycle occurs in the
Stroma
On outside of thylakoids, molecules of NADP+ and ADP pick up
Electrons and phosphate, then ATP and NADPH are then released to the stroma
Thylakoid has two type of photosystems that cooperate in the light reactions:
Photosystem II
Photosystem I
Linear electron flow
Flow of electrons through the photosystems and other molecular components built into the thylakoid membrane
Occurs during the light reactions
In some cases, photoexcited electrons can take an alternative path
Cyclic electron flow
Uses PS I, but not PS II
No production of NADPH and ATP and no release of O2
Chloroplasts and mitochondria generate ATP by the same basic mechanism
Chemiosmosis
Chemiosmosis
Step 1
Electron transport chain pumps protons (H+) across a membrane as electrons are passed through a series of carriers that are progressively more electronegative
Chemiosmosis
Step 2
Transform redox energy to a proton-motive force, potential energy stored in the form of an H+ gradient across a membrane
Chemiosmosis
Step 3
An ATP synthase complex in the same membrane couples the diffusion of H ions down their gradient to the phosphorylation of ADP to ATP
Differences between cellular respiration and photosynthesis
Chloroplast
Phosphorylation
High energy electrons dropped down from the transport chain come from water
Mitochondria
Oxidative phosphorylation
High energy electrons are extracted from organic molecules, which are then oxidized
Differences continued
Chloroplast
Do not need molecules from food to make ATP, their photosystems capture light energy and use it to drive the electrons from water to the top of the chain
Transforms light energy into chemical energy in ATP
Mitochondria
Uses food to make ATP
Uses chemiosmosis to transfer chemical energy from food molecules to ATP
Differences overview
Spatial organization differs slightly
Similarities overview
Electron carriers and ATP synthase complexes are very similar
Similarities between cellular respiration and photosynthesis
Chloroplasts
Thylakoid membrane pumps protons from stroma into the thylakoid space (interior of thylakoid), which serves as reservoir of H ions
Mitochondria
Inner membrane pumps protons from matrix out to the intermembrane space, which serves as reservoir of H ions
Similarities continued
Chloroplast ATP is synthesized as the H ions diffuse from the thylakoid space back to the stroma through ATP synthase complexes Cycle is anabolic Photosynthesis is endergonic Mitochondria Protons diffuse down their concentration gradient from the intermembrane space through ATP synthase to the matrix, driving ATP synthase Cycle is catabolic Respiration is exergonic
Calvin cycle is anabolic
Because it builds carbohydrates from smaller molecules and consumes energy
Carbon enters the cycle in the form of __ and leaves in the form of __
CO2
Sugar
Cycle spends ATP as an energy source and consumes
NADPH as reducing power for adding high-energy electrons to make sugar
3 Phases of Calvin Cycle
- Carbon fixation
- Reduction
- Regeneration of the CO2 acceptor
Photosynthesis
Process that converts solar energy into chemical energy
Directly and indirectly nourishes almost entire living world
Organic
From CO2
Plants take hydrogen out of
H2O
Chemiosmosis
Chloroplasts split
H2O into H and O2, using the electrons of H into sugar molecules and release O2 as a by-product
Photosynthesis reverses the direction of electron flow compared to
Cellular respiration
H2O is __ and CO2 is __
Oxidized
Reduced
Calvin cycle puts
CO2 into photosynthesis
Light reactions (in thylakoids)
Split H2O
Release O2
Reduce the electron acceptor NADP+ to NADPH
Generate ATP from ADP by photophosphorylation
Calvin Cycle (in the stroma)
Forms sugar from CO2 using ATP and NADPH
Begins with carbon fixation
Thylakoids transform
Light energy into the chemical energy of ATP and NADPH
Electromagnetic spectrum
Entire range of electromagnetic energy, or radiation
Different pigments absorb
Different wavelengths
Spectrophotometer
Measures a pigment’s ability to absorb various wavelengths
An absorption spectrum
A graph plotting a pigment’s light absorption versus wavelength
Carotenoids
Accessory pigments
Chloroplasts and mitochondria generate ATP by
Chemiosmosis but use different sources of energy
Mitochondria transfer chemical energy from food to ATP; chloroplasts
Transform light energy into the chemical energy of ATP
Spatial organization of chemiosmosis differs between chloroplasts and mitochondria, but
Also shows similarities
In mitochondria, protons (hydrogen ions) are pumped…
In chloroplasts, protons are pumped…
To the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
Into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma
Calvin scale builds sugars from
Smaller molecules by using ATP and NADPH
Carbon enters and leaves as G3P
On dry days, plants close stomata, which conserves
H2O, but limits photosynthesis
Closing of stomata reduces
Access to CO2 and causes O2 to build up
Wasteful process called photorespiration
Photosystems consist of
Chlorophyll molecules
Primary electron acceptor
Light harvesting complexes
Reaction center complex
Why are most autotrophs referred to as the producers of the biosphere?
They are the ultimate sources of organic compounds for all nonautotrophic organisms
G3P is used in what?
Production of cellulose, glucose, sucrose, starch, and the production of the cell walls in growing plants
Where do the electrons entering photosystem II come first?
Water, comes from the splitting of water molecules
The two photosystems work together in using light energy to generate
ATP and NADPH
The most important role of pigments in photosynthesis is to
Capture light energy
Pigments
Substances that absorb visible light
When chloroplast pigments absorb light
Their electrons become excited
The energy used to produce ATP in the light reactions of photosynthesis comes from
The movement of H+ through a membrane
Chemiosmosis
The light reactions of photosynthesis use chemiosmosis to produce ATP that will be used in the Calvin cycle. The electrochemical gradient that drives chemiosmosis is formed across which structure?
Thylakoid membrane
The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a 5-C sugar named
ribulose bisphosphate
What process is the most similar to photophosphorylation?
Oxidative phosphorylation in cellular respiration
During what process if molecular oxygen produced in photosynthesis?
The light reactions by linear electron flow
What is the difference in carbon fixation between C3 and C4 plants?
The first product of carbon fixation in C4 plants is a 4 Carbon compound instead of a 3 Carbon compound
Light reactions generate high energy electrons which end up in NADPH. The reactions also produce
ATP and Oxygen
Calvin cycle occurs
In the stroma
What occurs during the second phase (reduction phase) of the Calvin cycle?
G3P production
When chloroplast pigments absorb light
Their electrons become excited
Chlorophyll molecules are where?
In the thylakoid membrane
Water is __, CO2 is __
Oxidized
Reduced
