Photosynthesis Flashcards

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1
Q

Where does LDR take place?

A

Thylakoid membranes of the chloroplast

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2
Q

What is LDR and LIR?

A

LDR is the first stage of photosynthesis and requires light to start

LIR is the second stage and doesn’t require light but needs the products produced in LDR

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3
Q

How do electrons get to the PSI?

A

Light is absorbed by PSII

Light excites electrons in PSII and causes them to move to higher energy state

electrons passed onto electron carriers in the transport chain to PSI

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4
Q

How are lost electrons replaced?

A

Electrons lost from PSII need to be replaced

Done through photolysis of water

light energy causes water molecule to split and release hydrogen ions, electrons and oxygen

electrons from water replace the electrons lost from PSII

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5
Q

How is a proton gradient formed?

A

Electrons move along the transport chain form an area of high to low energy

Energy lost by electrons is used to pump hydrogen ions from stroma into the thylakoids

Proton gradient generated across thylakoid memebrane

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6
Q

What is chemiosmosis?

A

protons flow down concentration gradient through ATP synthase

Energy from movement of protons is used for photophosphorylation

ADP -> ATP

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7
Q

What is non-cyclic photophosphorylation?

A

Light absorbed by PSI causes another electron to become excited and passed along the rest of electron transport chain

electron is passed onto NADP to form reduced NADP

reduced NADP is an electron carrier which transfers electrons between molecules

ATP and reduced NADP move into stroma for next stage of photosynthesis

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8
Q

explain cyclic photophosphorylation

A

Electrons leave PSI

instead of being accepted by NADP they flow down to first electron acceptor

ATP is produced but no reduced NADP

may happen when reduced NADP is in plentiful supply

more common in plants with high ATP demands

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9
Q

What is the Calvin cycle?

A

Takes place in stroma and uses products of LDR

Reactions can be divided into carbon fixation, reduction and regeneration

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10
Q

What is carbon fixation?

A

Carbon dioxide is fixed by adding a 5-carbon molecule called ribulose biphosphate (RuBP)

catalysed by Rubisco

The 6C molecule is unstable and breaks down to form two 3C compounds called glycerate-3-phosphate (GP)

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11
Q

What is reduction?

A

an isomerisation reaction which converts GP into another 3C compound called glyceraldehyde-3-phosphate (GALP)

this reaction requires energy so ATP is hydrolysed into ADP

reaction requires electrons form reduced NADP which transfers electrons to GP to produce GALP

some GALP is converted to organic molecules

some used to regenerat RuBP

for every 6 GALP:
- 5 for RuBP regeneration
- 1 for organic molecules

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12
Q

What is regeneration?

A

GALP is coverted back into RuBP - requires energy from hydrolyses of ATP

The cycle is completed and carbon fixation can happen again

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