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Biology > 8.3 Photosynthesis > Flashcards

8.3 Photosynthesis Flashcards

1
Q

Where does the light-dependent reactions take place?

A

in the intermembrane space of thylakoids and across the thylakoid membranes

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2
Q

What two reactions make up photosynthesis?

A

light dependent reactions
light independent reactions

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3
Q

Why does the light independent reaction only carry on in darkness for a few seconds?

A

Because they depend on substances produced by the light-dependent reactions which rapidly run out

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4
Q

What is within the thylakoid?

A

a compartment called the thylakoid space

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5
Q

What are the products of the light-dependent reactions?

A

Reduced NADP and ATP

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6
Q

What is light converted to in the light dependent reaction?

A

into chemical energy in the form of ATP and reduced NADP

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7
Q

What do ATP and reduced NADP serve as for the light-independent reactions?

A

as energy sources

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8
Q

What is the stroma?

A

a compartment enclosed by the inner membrane of the chloroplast

  • a thick protein-rich medium containing enzymes for use in the light-independent reactions (Calvin cycle)
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9
Q

What kind of pathway is the calvin cycle?

A

an anabolic pathway that requires endergonic reactions to be coupled to the hydrolysis of ATP and the oxidation of reduced NADP

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10
Q

What are the events that occur in both the light and dependent and independent reactions?

image

A
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11
Q

What are the reactions that occur in light-independent? (6)

A
  • photolysis
  • photoactivation
  • electron transport
  • chemiosmosis
  • ATP synthesis
  • reduction of NADP
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12
Q

What are the reactions that occur in light independent? (6)

A
  • carbon fixation
  • carboxylation of RuBP
  • production of triose phosphate
  • ATP and NADPH as energy sources
  • ATP used to regenerate RuBP
  • ATP used to produce carbohydrates
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13
Q

What are photosystems?

A

Chllorophyll and the accessory pigments grouped together in a light-harvesting array

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14
Q

Where are photosystems located?

A

in the thylakoids, an arrangement of membranes inside the chloroplast

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15
Q

What are the two types of photosystems?

A

Photosystem I and photosystem II

Photosystem II begins the light dependent reactions

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16
Q

What do the photosystems do?

A
  1. contain special chlorophyll molecules
  2. absorb energy froma photon of light
  3. an electron within the molecule becomes excited
  4. the chlorophyll is then photoactivated
  5. the chlorophylls at the reaction centre donates the excited electrons to an electon acceptor
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17
Q

What is the elctron acceptor for photosystem II?

A

plastoquinone

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18
Q

What does plastoquinone do?

A

collects two excited electrons from photosystem II and then moves away to another position in the membrane

it is hydrophobic, so although it is not in a fixed position, it remains within the membrane

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19
Q

What is plastoquinone called after it has recieved two electrons from photosystem II?

A

reduced plastoquinone

20
Q

What does the reaction center at photosystem II become after reducing plastoquinone?

A

it becomes a powerful oxidizing agent and cause the water molecules nearest to split and give up its electrons to replace those that is lost

21
Q

What is photolysis?

A

the splitting of water

oxygen is the waste product and diffuses away

22
Q

What is photophosphorylation?

A

the production of ATP, using energy derived from light

carried out by thylakoids

23
Q

What are thylakoids? What structure do their membrane contain?

A

regular “stacks” of membranes, with very small fluid filled spaces inside

The thylakoid membranes contain:
* Photosystem II
* ATP synthase
* A chain of electron carriers
* Photosystem I

24
Q

Where does plastoquinone carry the excite par of electrons to?

A

from the reaction centre of photosystem II to the start of the chain of electron carriers

25
What happens as plastoquinone transfers it electrons and then are passed from carrier to carrier?
as the electron pass, eneegy is released, which is used to pump protons across the thylakoid membrane into the space inside the thylakoids a concentration gradient of protons develops across the thylakoid membrane, which is a store of potential energy.
26
What two reactions contribute to the proton gradient?
* electrons passing from carrier to carrier and energy released is used to pump protons * Photolysis
27
What happens in chemiosmosis?
* Protons accumulated inside the thylakoid travel back across the membrane, down the concentration gradient, by passing through the enzyme ATP synthase * Energy is released by the passage of protons down their conecntration gradient * energy released is used to make ATP from ADP and inorganic phosphate
28
What is use from the light dependent reactions in the light independent reactions?
Reduced NADP
29
What is the role of reduced NADP in photosynthesis?
it carries a pair of electrons that can be used to carry out reduction reactions
30
What do chlorophyll molecules within photosystem I do?
* absorb light energy and pass it to the special two chlorophyll molecules in the reaction centre * This raises an electorn in one of the chlorophylls to a high energy level (photoactivation occurs again like in photosystem II)
31
Where is the excited electron from photoactivation at photosystem I passed along?
passed along a chian of carriers at the end of which is passed to feredoxin
32
What is ferrodoxin?
a protein in the fluid outside the thylakoid
33
What are two molecules of reduced ferredoxin the used for?
to reduce NADP to form reduced NADP
34
What is the electron that photosystem I donated to the chain of electron carriers replaced by?
an electron carried by plastocyanin
35
How are photosystem I and II linked?
electrons excited in photosysm II are passed along the chain of carriers to plastocyanin, which transfers them to photosystemI.
36
What is the process of cyclic photophosphorylation?
When supply of NADP runs out * electrons return to the ETC that links the two photosystems, rather than being passed to NADP * Asthe electron flow back along the ETC to photosystem I, they cause pumping of proton, which allows ATP production
37
What is carbon fixation?
the reaction in which carbon dioxide converted into another carbon compound
38
Where does carbon fixation occur?
stroma - the lfuid that surrounds the thylakoids in the chloroplast
39
What is the process of carbon fixation?
* enzyme ribulose bisphosphate carboxylase (rubisco) catalyse reaction between carbon dioxide with ribulose bisphosphate, RuBP (5C) * Produces 2 molecules of glycerate 3-phosphate
40
How does the stroma maximize carbon fixation?
by having a large amount of rubisco in the stroma
41
What occurs in the reduction of glycerate 3 phosphase?
* from the light-dependent reactions, ATP provides energy neded to perform the reduction and reduced NADP provides the hydrogen atoms * glycerate 3 phosphate is reduced to triose phosphate (3C)
42
What occurs in the regeneration of RuBP?
the conversion of 3C sugars to 5C sugars + regenerate RuBP used * 3 RuBP molecules are used * 6 triose phosphates are produced * 5 of the triose phosphates are needed to regenerate * 1 triose phosphate is left for the conversion to hexose, starch or other products of photosynthesis * cycle begins again overal: 6 turns of the calvin cycle = one molecule of glucose
43
What is the calvins lollipop apparatus?
* radioactive carbon-14 is added to a 'lollipop' apparatys congtaining freen algae (chlorella) * light is shone on the apparatus to induce photosynthesis (which will incorporate the carbon-14 into organic compounds) * after different periods of time, the algae is killed by running it into a solution of ehated alcohol (stops cell metabolism) * dead algal samples are analysed using 2D chromatography, which separates out the different carbon compounds * Any radioactive carbon compounds on the chromatogram were then identified using autoradiography (X ray film exposure) * by comparing difference periods of light exposure, the order by which carbon compounds are generated was determined * calvin used this information to propose a sequence of events known as the calvin cycle (light indeendent reactoins)
44
Adaptations of a chloroplast to its functions
* **large area of thylakoid membranes** containing photosystems carry out light absorption and has a **large light-absorbing capacity**. Thylakoids are often arranged in stacks called **grana** and leaves are brightly illuminated typically have chloroplasts with deep grana, which allow more light to be absorbed * The **volume of fluid inside the thylakoids is very small**, so when protons are pumped in, a proton gradient develops after relatively few photons of light have been absorbed, allowing ATP synthesis to begin. Now chloroplasts **can produce ATP by photophosphorylation** -> **develops proton gradient quickly** * **Stroma** contains **concentrations of enzymes and substrates** that speed up the whole calvin cycle and there are **ATP and reduced NADP** inthe stroma. Are **easily available for many chemical reactions** since they are distrubuted throughout the stroma.
45
What are 5 features of a chloroplast?
* a **double membrane** forming the outer chloroplast envelope * an extensive system of internal membranes called **thylakoids**, which are an intense green colour * **small fluid-filled spaces** inside the thylakoids * a colourless fluid around the thylakoids called **stroma** that contains many different enzymes * in most chloroplasts there are stacks of thylakoids, called **grana**. if a chloroplast has been photosynthesizing rapidly then there may be **starch grains** or **lipid droplets** in the stroma

Biology (57 decks)

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