Photosynthesis Flashcards

All information on photosynthesis!

How do living organism recieve energy?

From the sun

How to photosynthetic organisms capture energy?

plants, algae, bacteria, protists: capture light energy and use it to convert carbon dioxide into organic carbon sugars

What is not required for photosynthesis?

oxygen

Where does the light energy from the sun go?

it becomes stored energy in molecules of simple sugars

What is the equation of photosynthesis?

6CO2 + 6H2O + Light energy → \[CH2O\]n +6O2

How does water enter plants?

through the roots

How is water tranposted to the leaves?

through the veins

How does carbon dioxide enter?

through stomata openings in leaves

After CO2 and water diffuse into cells, where do they go?

into the chloroplasts

Where does photosynthesis take place?

in the chloroplast

What is a thylakoid?

A membrane system within the chloroplast which forms interconnected disks that look like flattened sacs

What are a stack of thylakoid called?

grana

Why are thylakoids central to photosynthesis?

the molecules the absorb the solar energy are embedded in their membranes

What fluid surrounds the grana in the chloroplasts?

stroma

What is the role of the enzymes in the stroma?

to catalyze the conversion of CO2 and water into carbohydrates

What two sets of reactions make up photosynthesis?

1. Light-dependent reactions
2. Light-independent reactions

What occurs in the light-dependent reactions?

light energy is trapped and used to generate two high-energy compounds: ATP and NADPH

What occurs in the light-independent reactions?

the energy of ATP and the reducing power of NADPH are used to make high-energy organic molecules (sugars)

What is a light-dependent reaction?

* involves a series of reactions that are energized by light

Where do the light-dependent reactions take place?

in the thylakoid membranes of the chloroplasts

After the ligh-dependent reaction, where does the energy go?

the energy absorbed by the thylakoid is transferred to carbohydrate molecules

What are the two main functions of light-dependent reactions?

1. the capturing of light energy
2. using the light energy to make ATP and reduce NADP+

Where do the light-independent reactions occur?

in the stroma

What is carbon fixation?

the incorporation of the carbon of CO2 into organic compounds, like glucose that can be used by the plant

What do light-dependent reactions require?

ATP and NADPH (from light reactions)

What is the Calvin cycle?

where carbon fixation occurs during a sequence of enzyme catalyzed reactions

What is a photon?

light behaves as if it were composed of “units” or “packets” of energy that travels in waves

How are photons characterized?

by a wavelength that is inversely porportional to their energy

Photons with short wavelengths…

have high energy

Photons with long wavelengths…

have low energy

What does the wavelnegth of light determine?

colour

What is the wavelength for red light?

700 nm

What is the wavelength of bue light?

470 nm

What is pigment?

a compound that absorbs certain wavelengths of visible light

What is a photosynthetic pigment?

a compound that traps light energy and passes it on to other compounds

What happends to pigment when sunlight is available?

pigments embedded in the thylakoid membranes absorb light energy, initiating light-dependent reactions

What is the main type of photosynthetic pigment in plants?

Chorophyll

What are the two types of chlorophyll which chloroplasts contain?

1. Chlorophyll a
2. Chlorophyll b

What light does chlorophyll a absorb?

blue-green, and red light

Which type of light is reflected by chlorophyll a?

green light

What are accessory pigments?

pigments that absorb slightly different wavelengths of light. These pigments can pass on their energy to chlorophyll a

What type of light does chlorophyll b absorb?

blue-green light

What type of light does chlorophyll b reflect?

yellow-green light

What type of light do carotenoids absorb?

blue-green light

What type of light do carotenoids reflect?

yellow-orange light

Do pigments absorb light independently?

NO

What is a photosystem?

Light is absorbed by chlorophyll or accessory pigment molecules that are associated with these proteins in clusters

Where are photosystems located?

embedded in thylakoid membranes

What does a photosystem consist of?

antenna complex, and reaction center

What is the antenna complex?

a web of chlorophyll and accesory pigment molecules embedded in the thylakoid membrane

What is the purpose of the antenna complex?

is absorbs a photon and transfers the energy from pigment to pigment until it reaches chlorophyll a

What is the reaction center?

the chlorophyll a molecule

What happends when the chlorophyll a absorbs energy?

an electron becomes excited and jumped to a higher energy level

Where does the excited electron go?

is transferred to the primary electron acceptor

What type of reactions occur within photosystems?

redox reactions

What is being oxidized in photosystem redox reactions?

chlorophyll

What is being reduced in photosystem redox reactions?

the primary electron acceptor

What are the two types of photosystems in the thylakoid membrane?

1. Photosystem I
2. Photosystem II

What light wavelength can be absorbed in Photosystem I?

* contains chlorophyll a (in reaction center)
* aborbs 700 nm (red light)

What light wavelength can be absorbed in Photosystem II?

* contains chlorophyll a (in reaction center)
* absorbs 680 nm (red light)

What are the roles of the photosystems?

they work together as part of the light-dependent reactions

What is the goal of light-dependent reactions?

to transfer energy of light to ATP and NADPH

What is photoexcitation?

the absorbance of a photon by an electron of chlorophyll in photosystem II

* jumping into a higher energy level

What is the ground state of an electron?

before a photon of light strikes a chlorophyll molecule, the chlorophyll electrons are in the lowest possible energy level

What happeneds when a photon is aborbed by a chlorophyll molecule?

the electron gains energy and jumps to a higher energy level

When energy is given to the electron, what happeneds?

the electron can break free from an atom of the chlorophyll molecule

What does chlorophyll do during photoexcitation?

donate an electron

How does this lost electron get replaced in the chlorophyll?

a molecule of water is split

What does the splitting of water do?

* releases a pair electrons
* can replace two donated electrons


* results in formation of oxygen and H+ ions in the thylakoid space

After replacing the electron, what happends?

chlorophyll is able to respond to another photon

What is a bydroduct made by the splitting of water?

* oxygen
* this makes its way into the surrounding environment
* H+ ions
* play a role in proton gradient

What is the electron transport chain (ETC)?

When photosystem II transfers the free electron over to a series of proteins inside the thylakoid membrane

As electrons pass along these proteins, what does the energy from the electrons fuel?

the b6-f complex (membrane pump)

* actively moves H+ ions against their concentration gradient from:

STROMA →THYLAKOID SPACE

What is created due to the pumping of H+ into thylakoid space?

electrochemical gradient

What occurs as electrons move to photosystem I?

the electron from the ETC arrives and is regenerized by another photon captured by chlorophyll

What does the energy from photosystem I drive?

the energy from this electron drives the formation of NADPH (from NADP+) and a H+

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What enzyme is used to turn NADP+ to NADPH during ETC?

NADP reductase

Where is solar energy stored?

in the electron carriers

* later used to make sugar molecules

Is the ETC cyclic or noncyclic?

noncyclic because an electron is lost by a reaction center chlorophyll within the photosystem

* does not return back to the system
* flow of electrons is unidirectional

How many times must the ETC occur?

* NADP+ requires 2 electrons to reduce to NADPH
* entire process happends TWICE per NADP+ reduced

What is photophosphorylation?

the use of proteins of light to drive the phosphorylation of ADP to produce ATP via chemiosmosis

What is cyclic photophosphorylation?

* excited electrons only use photosystem I
* Excited electrons leave photosystem I and are passed to an electron acceptor
* They are then passed to the b6-f complex and back to photosystem I

What does the cyclic pathway generate?

a proton gradient for chemiosmosis ATP synthe

What is NOT produced in cyclic pathway?

NADPH nor oxygen

Which pathway is the plant going to use, cyclic or noncyclic?

the activities of these two photophosphorylation pathways vary depending on the amount of ATP and NADPH required in the stroma

What is chemiosmosis?

* the net movement of protons through ATP synthase to drive the phosphorylation of ADP to ATP
* the protons that accumulate in the thylakoid space contribute to an electrochemical gradent that drives the process
* light energy is required to create the proton gradient so the process is called: photophosphorylation

What is produced in the light-dependent reactions?

NADPH and ATP

What do all chloroplast plants contain?

enzymes in the stroma that, with the energy supplied by ATP and NADPH, convert CO2 to carbohydrates

What did light-independent reactions used to be called?

“dark” reactions

Why is “dark” reactions an inaccurate name?

these reactions can take place in the presence or absence of light

What is the purpose of the light-independent reactions?

Carbon fixation

What are the 3 stages of the Calvin cycle?

1. Carbon Fixation
2. Reduction Reactions
3. Regeneration of RuBP

What is the key to Carbon fixation?

the chemical bonding of the carbon atom in CO2 to a pre-existing molecule in the stroma (RuBP)

How many molecules of CO2 are added to how many molecules of RuBP?

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6 molecules of CO2 + 6 molecules of RuBP

What molecule is used to CO2 to RuBP?

Rubisco

How many carbon atoms are in RuBP?

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5 carbon sugar

What is formed when 6 CO2 molecules combine with 6 RuBP molecules?

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6 unstable six-carbon intermediates are formed

What happends after the intermediates are formed?

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they are instantly split, and their molecules are reorganized to form 12 molecules of PGA

(3-phosphoglycerate)

How many carbons are in PGA?

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3 carbons each

What is the Calvin cycle also known as?

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C3 photosynthesis because the first compound produced (PGA)

* Plants that use this method of photosynthesis are C3 plants