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Biology - Year 13 > Photosynthesis - Chapter 11 > Flashcards

Photosynthesis - Chapter 11 Flashcards

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1
Q

What is photosynthesis carried out by, and what organisms are they ?

A

Carried out by plants + algae, they are autotrophic

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2
Q

Organisms such as animals cannot photosynthesis, where do they get their nutrients from, and what type of organism is an animal ?

A

They get their nutrients by eating plants or other animals

Animals are heterotrophic organisms

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3
Q

What is the reaction for photosynthesis and where does it take place?

A

6CO2 + 6H20 ~> C6H12O6 + 6O2

~> = energy from light

Reaction takes place in the chloroplasts

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4
Q

Where do light dependent reactions take place, and what light dependent reactions involve?

A

On the thylakoid membrane.

They can only happen in the presence of light
In light-dependent reactions, light energy is harvested and used to produce ATP + a reduced hydrogen carrier (NADPH)
It also involves water splitting , forming oxygen

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5
Q

Where do light independent reactions take place ?

A

In the stroma , they do not require light to function

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6
Q

What do the light independent reactions use from the light dependent reactions?

A

They use the ATP and reduced NADP produced in the light dependent reactions.

In the light independent reactions, glucose is produced from CO2.

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7
Q

What happens to the light dependent and light independent reactions if light is not present ?

A

If light is not present, the light dependent reactions stop, the levels of ATP and NADPH then fall, causing the light independent reactions to stop.

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8
Q

What do thylakoid membranes contain?

A

Light-harvesting pigments such as chlorophyll + and range of proteins needed for the light dependent reactions .

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9
Q

What is chlorophyll and the different forms ?

A

Chlorophyll is a pigment which absorbs visible light
Several different forms : chlorophyll a, chlorophyll b

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10
Q

What is chlorophyll a ?

A

The central molecule in the light dependent reactions.
Primary pigment.
Chlorophyll a works with a range of proteins/ other molecules : reaction centre

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11
Q

What is a photo-system ?

A

Together the reaction centre + light harvesting system

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12
Q

What are the wavelengths of both photo systems ?

A

Photosystem 1 : absorbs light with 700nm wavelength
Photosystem 2: absorbs light with 680nm wavelength

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13
Q

How many photosystems are involved in light-dependent reactions?

A

2: PSI, PSII

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14
Q

Explain the light dependent reaction process

A

-light energy is absorbed by chlorophyll. Electrons in the chlorophyll are excited to a higher energy level.
- electrons are lost from the chlorophyll molecule in PSII, (and passed to electron carries in the thylakoid membrane)
-electrons are passed between carriers in ETC
- energy released during transfer of electrons is used to produce ATP by chemiosmosis

[Photosystem II has lost a pair of electrons. To replace the electron pair, an enzyme in PSII splits a molecule of water/photolysis of water using light energy. Photolysis of water produces 2 electrons, 2 H+ ions, and 2 O2 molecules.
The electrons from H20 replace the electrons lost from the chlorophyll molecule, PSII to the ETC.
O2 from the splitting of H20 is lost as a waste product. ]

  • light energy is now absorbed by photosystem I and the pair of electrons is excited again.
  • the electrons make now make their way through ETC again, generating ATP by chemiosomis
    -NADP is reduced by the addition of electrons along the ETC, and H+ ions
    -oxygen from the splitting of water (photolysis) is lost as a waste product
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15
Q

What is phosphorylation ?

A

Making ATP from ADP+Pi

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16
Q

What is photo phosphorylation?

A

The energy from light has been used to produce ATP

17
Q

What is non-cyclic phosphorylation ?

A

The pair of electrons that have left photosystem II have not returned to photosystem II

18
Q

What is cyclic phosphorylation ?

A

Light energy is absorbed by PSI. This causes a pair of electrons on PSI to be excited. These electrons pass through the ETC, generating ATP.
At the end, the electron pair returns back to PSI - cyclic phosphorylation

19
Q

What is cyclic and non cycle photo phosphorylation in relation to ATP?

A

Cyclic photo phosphorylation takes place when the chloroplast requires an increased amount of ATP.

Both non-cyclic and cyclic photo phosphorylation produces ATP, a key part of this involves the electron transport chain.

20
Q

What is the chemiosmosis theory ?

A

-the excited electrons lose energy as they move along the ETC (lower energy level each time)
- this energy is used to transport protons into the thylakoid so that the thylakoid has a higher concentration of protons than in the stroma, forming a proton gradient across the membrane.
- protons diffuse down their concentration gradient, into the stroma (by diffusion), via ATP synthase channels.
- the energy from this movement combines ADP+Pi to form ATP.

Chemiosmosis is the name of the process where the movement of H+ ions across a membrane generates ATP

21
Q

Light energy is absorbed by photosystems and used for what 3 things?

A
  1. Making ATP from ADP + Pi (phosphorylation)
  2. Making reduced NADP from NADP
  3. Splitting water into H+ ions, electrons + O2 (photolysis)
22
Q

What is photoionisation ?

A

Light energy is absorbed by chlorophyll. Electrons in the chlorophyll are excited to a higher energy level.
Electrons are lost from the chlorophyll molecule (and passed to electron carriers in the thylakoid membrane).

23
Q

What is the cycle in light independent reactions ?

A

The Calvin Cycle

24
Q

What are the stages in the Calvin cycle?

A

Fixation, reduction, regeneration

25
Q

Explain the Calvin cycle.

A
  1. Fixation - in this stage, the 5C molecule ribulose bisphosphate (RuBP) reacts with CO2. This reaction is catalysed by the enzyme ribulose bisphosphate carboxylate (RuBisCO). From this reaction, we make 2X glycerate 3-phosphate (GP).
    Each molecule of GP has 3 carbon atoms.
  2. Reduction - in this stage, each molecule of GP is reduced forming triose phosphate (TP). This reaction uses reduced NADP and ATP from the light-dependent reactions.
    ~> The reduced NADP provides the hydrogen needed for reduction
    ~> The ATP provides energy.

Some of the TP is removed from the cycle and used by the plant cell to make glucose and other molecules : amino acids

  1. Regeneration - in this stage, the RuBP is regenerated using ATP. This stage is really important as this allows the cycle to continue.
26
Q

What is a limiting factor, and what are the limiting factors for photosynthesis?

A

Any factor that reduces the rate of photosynthesis.
These could be temperature, CO2 concentration, or light intensity

27
Q

For max photosynthesis, how do farmers remove limiting factors?

A

For max photosynthesis, and therefore plant growth, common agricultural practices incorporate techniques to remove limiting factors :

~> these range from growing plants under artificial lighting to max. light intensity
~> heating a greenhouse to increase temperature
~> burning more fuel such as paraffin burners, to release more carbon dioxide

28
Q

What happens to the rate of photosynthesis if we increase light intensity ?

A
  1. When light intensity is low, rate of photosynthesis is low. That’s because the light intensity will be too low for the light-dependent reactions to function at their maximum rate
    ~> levels of ATP + NADPH will also be low, so light-independent reactions will also be running slowly
  2. As we increase light intensity, the rate of photosynthesis increases. That’s because the light dependent reactions have increased in rate, producing more ATP + NADPH. Because of this, the light-independent reactions are also running at a faster rate.
29
Q

How can we see if limiting factor is CO2 concentration ?

A

Repeat experiment with a higher CO2 concentration

30
Q

What is the effect of temperature on the rate of photosynthesis?

A

-if the temperature is too low, then RuBisCo will not be functioning at a fast rate. So, this will limit the rate of light-independent reactions, and the overall rate of photosynthesis.

-[ However, if the light intensity is low, then the overall rate of photosynthesis is less effected by temperature. At low light intensity, the overall rate of photosynthesis is limited by the rate of light-dependent reactions, which are less dependent on enzymes, and so are less effected by temperature. So at low light intensity, temperature has less of an effect on the overall rate of photosynthesis.]

31
Q

What is the effect of light intensity in the Calvin cycle?

A

At low light intensity, the light-dependent reactions are slow, and the concentrations of ATP +NADPH fall, less GP can now be converted to TP.
So the concentration of GP increases and the concentration of TP decreases.

As RuBP is made from TP, the concentration of RuBP also decreases.

32
Q

What is the effect of CO2 concentration in the Calvin cycle?

A

If the concentration of CO2 falls, then less GP can be formed. This means that less TP will also be formed.
However, the concentration of RuBP will increase as less RuBP is reacting with CO2.

Biology - Year 13 (3 decks)

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