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Biology Ch 8 Photosynthesis Study Guide
Prentice Hall Chapter 8 Vocabulary & Review
Terms in this set (96)
organisms such as plants or mushrooms, which make their own food from sunlight or chemicals
organisms, such as animals, that obtain energy from the foods they consume
Where do plants get the energy they need to produce food?
Plants and some other types of organisms are able to use light energy from the sun to produce food.
What is the role of ATP (adenosine triphosphate) in cellular activities?
ATP is used by all types of cells as their basic energy source.
process by which plants and some other organisms use light energy to convert water and carbon dioxide into oxygen and high-energy carbohydrates such as sugars and starches
What did the experiments of van Helmont, Priestly, and Ingenhousz reveal about how plants grow?
In the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen.
What is the role of light and chlorophyll in photosynthesis?
Light is a form of energy and chlorophyll absorbs light and the energy from the light.
principal pigment of plants and other photosynthetic organisms; captures light energy
Plants gather the sun's energy with light-absorbing molecules are called...
What happens in the light-dependent reactions?
... use energy from sunlight to produce ATP, NADPH, and oxygen. It takes place within the thylakoid membranes of chloroplasts.
What is the Calvin cycle?
... uses ATP and NADPH from the light-dependent reations to produce high-energy sugars. It takes place in the stroma of chloroplasts and does NOT require light.
Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters known as...
the region outside the thylakoid membranes in chloroplasts
(nicotinamide adenine dinucleotide phosphate) one of the carrier molecules that transfers high-energy electrons from chlorophyll to other molecules.
reactions of photosynthesis that use energy from light to produce ATP and NADPH
large protein that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP
One of the principal chemical compounds that living things use to store energy is...
Which scientist concluded that most of a growing plant's mass comes from water?
In addition to light and chlorophyll, photosynthesis requires...
water and carbon dioxide
The leaves of a plant appear green because chlorophyll...
reflects green light
The products of photosynthesis are...
sugars and oxygen
The first process in the light-dependent reactions of photosynthesis is...
Which substances from the light-dependent reactions of photosynthesis is a source of energy for the Calvin cycle?
ATP & NADPH
The light independent reactions of photosynthesis are also known as the...
How do heterotrophs and autotrophs differ in the way they obtain energy?
heterotrophs obtain energy from the food they eat.
autotrophs obtain energy from the sunlight
Describe the three parts of an ATP molecule.
3 Phosphate groups
Use the analogy of battery to explain how energy is stored in and released from ATP.
ATP can be compared to a fully charged battery because both contain stored energy.
Compare the amounts of energy stored by ATP and glucose. Which compound is used by the cell as an immediate source of energy.
- A single molecule of the sugar glucose stores more than 90 times the chemical energy of a molecule of ATP.
- ATP is used as an immediate source of energy.
How were Priestley's and Ingenhousz's discoveries about photosynthesis related?
They both showed that light was necessary for plants to produce oxygen.
Write the basic equation for photosynthesis using the names of the starting and final substances of the process.
6CO2 + 6H20 —> C6H12O6 + 6O2
carbon dioxide + water —> sugars + oxygen
(NOTE: —> is light)
What role do plant pigments plan in the process of photosynthesis?
They gather the sun's energy
Explain the role of NADP+ as an energy carrier in photosynthesis.
It transfers high-energy electrons from chlorophyll to other molecules.
What is the role of ATP synthase? How does it work?
they provide the energy to build energy - containing sugars from low - energy compounds.
It allows hydrogen ions out of the thylakoid
Summarize what happens during the Calvin cycle.
plants use the energy that ATP and NADPH contain to build high-energy compounds that can be stored for a long time.
How do the events in the Calvin cycle depend on the light-dependent reactions?
The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars.
Describe three factors that affect the rate at which photosynthesis occurs.
- intensity of light
Autotrophs are plants and some other types of organisms are able to use ________ from the sun to produce _________.
- light energy
Energy comes in many different forms. Give examples.
- chemical compounds
ADP + phosphate —>(energy)—> ATP
Sodium (Na) Potassium (K) pump maintaining ions on both sides of the cell
Cells only keeps a small amount of _____ .
- ATP does not store easily
________ stores 90 times more chemical energy than a molecule of ATP.
Jan Baptista van Helmont (1580-1644)
Demonstrated that the substance of the plant was not produced only from the soil
Living vegetation adds something to the air
proposed that the green parts of the plant carry
out a process that uses sunlight to split carbon dioxide into
carbon and oxygen
scientist who proposed plants convert light energy into chemical energy
scientist who traces chemical path that carbon follows to form glucose (Calvin cycle)
scientist who describes the process of electron transfer from molecule to electron transport chain
- Reactants —> Products
- Carbon Dioxide + water in the presence of light yields sugars & oxygen
In addition to water and carbon dioxide, photosynthesis requires ________ and _________, a molecule in chloroplasts.
light and chlorophyll
Light is in ___________ form and creates a spectrum from ________ to ______.
- wavelength form
- violet to red
light absorbing molecules in plants
2 main types of chlorophyll:
chlorophyll a & chlorophyll b
__________ (green) absorbs the blue-violet and red ends of the spectrum and transfers it to the electrons. While other pigments like __________ absorb the other color.
Chloroplasts contain tiny sacs like photosynthetic membranes called...
Thylakoids are arranged in stacks known as ...
Pigments are arranged into clusters known as ...
What are the 2 Photosystems reactions?
- (1) light dependent (takes place in the thylakoids)
- (2) light independent or Calvin cycle (takes place in the stroma - the region outside the thylakoid membranes)
Sunlight excites the electrons in ________.
The excited electrons and their energy must be transported by an electron carrier, like _______. This electron carrier can hold ______ electrons and an ion of _________. It is converted into _________ which is trapping sunlight energy into _______ energy. This is the electron ________ _______.
- 2 electrons
- hydrogen (H+)
- chemical energy
- electron transport chain
3 factors that affect photosynthesis:
- water supply
- intensity of light
Oxygenic photosynthesis is carried out by
7 groups of algae
All land plants - chloroplasts
Pigments clustered into ____________
- connect grana
- semiliquid surrounding thylakoid membranes
Capture energy from sunlight
Make ATP and reduce NADP+ to NADPH
Carbon fixation reactions or light-independent reactions
Does not require light
Use ATP and NADPH to synthesize organic molecules from CO2
photosynthesis is in fact a multistage process, only one portion of which uses light directly
Light versus dark reactions
C. B. van Niel (1897-1985)
Found purple sulfur bacteria do not release O2 but accumulate sulfur
Proposed general formula for photosynthesis
CO2 + 2 H2A + light energy → (CH2O) + H2O + 2 A
Later researchers found O2 produced comes from water
Robin Hill (1899-1991)
Demonstrated Niel was right that light energy could be harvested and used in a reduction reaction
Photon - particle of light
Acts as a discrete bundle of energy
Energy content of a photon is inversely proportional to the wavelength of the light
- removal of an electron from a molecule by light
- range and efficiency of photons molecule is capable of absorbing
When a photon strikes a molecule, its energy is either
Lost as heat
Absorbed by the electrons of the molecule
Boosts electrons into higher energy level
Organisms have evolved a variety of different pigments
Only two general types are used in green plant photosynthesis
Main pigment in plants and cyanobacteria
Only pigment that can act directly to convert light energy to chemical energy
Absorbs violet-blue and red light
Accessory pigment or secondary pigment absorbing light wavelengths that chlorophyll a does not absorb
Structure of chlorophyll
Complex ring structure with alternating double and single bonds
Magnesium ion at the center of the ring
Photons excite electrons in the ring
Electrons are shuttled away from the ring
Hundreds of accessory pigment molecules
Gather photons and feed the captured light energy to the reaction center
Also called light-harvesting complex
Captures photons from sunlight and channels them to the reaction center chlorophylls
In chloroplasts, light-harvesting complexes consist of a web of chlorophyll molecules linked together and held tightly in the thylakoid membrane by a matrix of proteins
1 or more chlorophyll a molecules
Passes excited electrons out of the photosystem
Transmembrane protein-pigment complex
When a chlorophyll in the reaction center absorbs a photon of light, an electron is excited to a higher energy level
Light-energized electron can be transferred to the primary electron acceptor, reducing it
Oxidized chlorophyll then fills its electron "hole" by oxidizing a donor molecule
Light dependent reactions steps
*Capture of light energy
Photon of light is captured by a pigment molecule
Energy is transferred to the reaction center; an excited electron is transferred to an acceptor molecule
Electrons move through carriers to reduce NADP+
In sulfur bacteria, only one photosystem is used
Generates ATP via electron transport
Excited electron passed to electron transport chain
Generates a proton gradient for ATP synthesis
Chloroplasts have two connected photosystems
-Photosystem I (P700)
Functions like sulfur bacteria
-Photosystem II (P680)
Can generate an oxidation potential high enough to oxidize water
Working together, the two photosystems carry out a noncyclic transfer of electrons that is used to generate both ATP and NADPH
Plants use photosystems II and I in series to produce both ATP and NADPH
Path of electrons not a circle
Photosystems replenished with electrons obtained by splitting water
Resembles the reaction center of purple bacteria
-Core of 10 transmembrane protein subunits with electron transfer components and two P680 chlorophyll molecules
-Reaction center differs from purple bacteria in that it also contains four manganese atoms
-Essential for the oxidation of water
Proton pump embedded in thylakoid membrane
Reaction center consists of a core transmembrane complex consisting of 12 to 14 protein subunits with two bound P700 chlorophyll molecules
Photosystem I accepts an electron from plastocyanin into the "hole" created by the exit of a light-energized electron
Passes electrons to NADP+ to form NADPH
Electrochemical gradient can be used to synthesize ATP
Chloroplast has ATP synthase enzymes in the thylakoid membrane
Allows protons back into stroma
Stroma also contains enzymes that catalyze the reactions of carbon fixation - the Calvin cycle reactions
Production of additional ATP
-Noncyclic photophosphorylation generates
-Building organic molecules takes more energy than that alone
-Cyclic photophosphorylation used to produce additional ATP
-Short-circuit photosystem I to make a larger proton gradient to make more ATP
Carbon Fixation - Calvin Cycle
-To build carbohydrates cells use Energy ATP from light-dependent reactions
-Cyclic and noncyclic photophosphorylation
-Drives endergonic reaction
-NADPH from photosystem I
SouNamed after Melvin Calvin (1911-1997)
-Also called C3 photosynthesis
-Key step is attachment of CO2 to RuBP to form PGA
-Uses enzyme ribulose bisphosphate carboxylase/oxygenase or rubiscorce of protons and energetic electrons
Calvin Cycle 3 stages
RuBP + CO2 → PGA
PGA is reduced to G3P
Regeneration of RuBP
PGA is used to regenerate RuBP
3 turns incorporate enough carbon to produce a new G3P
6 turns incorporate enough carbon for 1 glucose
Output of Calvin cycle
Glucose is not a direct product of the Calvin cycle
G3P is a 3 carbon sugar
Used to form sucrose
Major transport sugar in plants
Disaccharide made of fructose and glucose
Used to make starch
Insoluble glucose polymer
Stored for later use
Rubisco has 2 enzymatic activities
Addition of CO2 to RuBP
Favored under normal conditions
Oxidation of RuBP by the addition of O2
Favored when stoma are closed in hot conditions
Creates low-CO2 and high-O2
CO2 and O2 compete for the active site on RuBP
**O2 is incorporated into RuBP, which undergoes
additional reactions that actually release CO2. Hence, photorespiration releases CO2, essentially undoing carbon fixation.
Types of photosynthesis
Plants that fix carbon using only C3 photosynthesis (the Calvin cycle)
-C4 and CAM
Add CO2 to PEP to form 4 carbon molecule
Use PEP carboxylase
Greater affinity for CO2, no oxidase activity
C4 - spatial solution
CAM - temporal solution
-Corn, sugarcane, sorghum, and a number of other grasses
-Initially fix carbon using PEP carboxylase in mesophyll cells
-Produces oxaloacetate, converted to malate, transported to bundle-sheath cells
-Within the bundle-sheath cells, malate is decarboxylated to produce pyruvate and CO2
-Carbon fixation then by rubisco and the Calvin cycle
-C4 pathway, although it overcomes the problems of photorespiration, does have a cost
-To produce a single glucose requires 12 additional ATP compared with the Calvin cycle alone
-C4 photosynthesis is advantageous in hot dry climates where photorespiration would remove more than half of the carbon fixed by the usual C3 pathway alone
***the capture of CO2 occurs in one cell and the decarboxylation occurs in an adjacent cell. This represents a spatial solution to the problem of photorespiration
-Many succulent (water-storing) plants, such as cacti, pineapples, and some members of about two dozen other plant groups
-Stomata open during the night and close during the day
Reverse of that in most plants
-Fix CO2 using PEP carboxylase during the night and store in vacuole
-When stomata closed during the day, organic acids are decarboxylated to yield high levels of CO2
-High levels of CO2 drive the Calvin cycle and minimize photorespiration
**perform both reactions in the same cell, but
capture CO2 using PEP carboxylase at night, then decarboxylate during the day. CAM stands for crassulacean acid metabolism, after the plant family Crassulaceae
Compare C4 and CAM
Both use both C3 and C4 pathways
C4 - two pathways occur in different cells
CAM - C4 pathway at night and the C3 pathway during the day
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