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Biology A-Level > Chapter 11: Photosynthesis > Flashcards

Chapter 11: Photosynthesis Flashcards

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1
Q

There are 3 main sequences in photosynthesis. What are they?

A

The absorption of light energy by the chlorophyll molecules in a plant cell

The light-dependent stage where light energy is directly used to form oxygen, ATP and reduced NADP (NADPH)

The light-independent stage where the products of the light-dependent stage are used to form triose-phosphate (TP) which goes on to form the products of photosynthesis (lipids, glucose)

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2
Q

What do plants need energy for?

A
  • Photosynthesis
  • Active transport (uptake of minerals from soil via roots)
  • DNA replication
  • Cell division
  • Protein synthesis
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3
Q

What do animals need energy for?

A

Muscle contraction

Maintain a constant body temperature

Active transport (e.g. absorption of glucose)

DNA replication

Cell division

Protein synthesis

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4
Q

Where is the site of photosynthesis?

A

The site of photosynthesis is the leaves of a plant. The leaf is the main photosynthetic structure in eukaryotic plants, while the chloroplasts are the cellular organelles where photosynthesis actually occurs.

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5
Q

How is a leaf adaptated for effective photosynthesis?

A
  1. A large surface area for absorbing sunlight
  2. A thin structure so that diffusion pathways are short and because light is absorbed in the first few micrometres of the leaf
  3. A transparent epidermis and waxy cuticle that lessens water loss through evaporation and lets sunlight through to the mesophyll cells
  4. Long narrow upper mesophyll cells so that more of them can fit at the top of the leaf and packed with chloroplasts to absorb sunlight
  5. Stomata are able to open and close depending on light intensity, which helps reduce water loss when the plant is not photosynthesising
  6. Lots of air spaces in the lower mesophyll layer that allow quick diffusion of gases

Extras

  1. Many stomata for gaseous exchange so that no mesophyll cell is too far away from one (short diffusion pathway)
  2. A special arrangement of leaves makes leaves non-overlapping and stops leaves been overshadowed by each other
  3. A network of xylem vessels that transport water to leaf cells and a network of phloem vessels that carry away the sugars produced during photosynthesis
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6
Q

The raw materials for photosynthesis are…

A

Carbon dioxide

  • colourless gas
  • 0.04% of atmosphere
  • enters microscopic pores/stomata in leaves

Water

  • root hairs absorb water passively - no energy needed
  • keeps plant tissue turgid
  • maximising SA for light
  • source of electrons
  • solvent - all chemical reactions must occur in solution

Light

  • catalyses the reaction
  • absorbed by chloryphyll
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7
Q

The products of photosynthesis are:

A

Glucose

  • used to make other substances such as fats and proteins

Oxygen

  • may be used in respiration
  • may diffuse out of plant via stomata

NADPH

  • gives hydrogen to independent stage

ATP

  • gives energy to independent stage
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8
Q

What is the chemical formula for photosynthesis?

A

6CO2 + 6H2O (+ energy) —- C6H12O6 + 6O2

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9
Q

What is reduction?

A

Reduction is when:

  • a molecule gains electrons (e-) or hydrogen (which is essentially an electron and a proton)
  • a molecule loses oxygen
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10
Q

What is oxidisation?

A

Oxidisation is when

  • a molecule loses electrons (e-) or hydrogen
  • a molecule gains oxygen
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11
Q

What is the mnemonic for oxdiation and reduction?

A

Oxygen

Is

Loss… of electrons

Reduction

Is

Gain… of electrons

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12
Q

Chlorophyll absorbs light energy from which part of the electromagnetic spectrum.

A

Chlorophyll absorbs light energy from the visible part of the electromagnetic spectrum

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13
Q

Why do plants have different pigments?

A

Each pigment absorbs a different wavelength of light so that the total amount of light absorbed is greater than if just one pigment was used

Having more than one type of pigment increases the range of wavelengths of light that a plant can absorb

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14
Q

Why do leaves appear green?

A

Only certain wavelengths of light are used for photosynthesis: 60nm and 700nm

The photosynthetic pigments chlorophyl a, chlorophyll b and carotene can only absorb red and blue light

Other wavelengths/green light is mostly reflected back, which is why plants look green.

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15
Q

Facts: Light dependent stage

A

First stage of photosynthesis

Needs light energy

Site: thylakoid membrane

Products:

  • ATP
  • NADPH
  • oxygen
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16
Q

Facts: Light independent stage/Calvin cycle

A

Does not need light directly

Needs the products of light dependent stage

Products of light-dependent used to reduce/fix CO2 into carbohydrate

Site: stroma of chloroplast

Simple sugars formed from CO2

ATP supplies energy

NADPH supplies hydrogen/protons

6 cycles needed to form 1 hexose 6C sugar

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17
Q

Describe what happens in the light-dependent stage of photosynthesis

A

Light energy is absorbed by chlorophyll in photosystem II

  • Chlorophyll becomes photoionised
  • An electron is excited to a higher energy level and released from the chlorophyll molecule
  • Electron passed down electron transport chain
  • Energy released as it moves down
  • Energy used to:

make ATP – photophosphorylation

ATP provides energy for light independent stage

reduce NADP – form reduced NADP or NADPH

NADPH carries hydrogen to light independent stage/has reducing power

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18
Q

Reduced NADP (NADPH)

A

Coenzyme/electron carrier used in photosynthesis

Main product of light dependent reaction

Protons produced from photolysis of water

Pass through ATP synthase channel

Into thylakoid space

Protons taken up by NADP

NADP is reduced when it picks up the protons

Has gained OILRIG

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19
Q

What is a coenzyme?

A

A coenzyme is a molecule that aids the functioning of an enzyme by transferring a chemical group from one molecule to another, i.e. it is a carrier

20
Q

What is photolysis?

A

Photolysis is the splitting of a molecule using light energy.

Water H2O is split into

  • oxygen O2
  • protons H+
  • electron e-

Replaces the electrons lost from chlorophyll

21
Q

Describe the chemiosmotic theory…

A

The process of electrons flowing down the electron transport chain, creating a proton gradient across the thylakoid membrane to drive ATP synthesis

22
Q

How is ATP made in the light dependent stage of photosynthesis?

A

Energy released from electrons passing down the electron transport chain is used to create an electrochemical/proton gradient across the thylakoid membrane

Protons transported/pumped into thylakoid

Protons build up in the thylakoid and move down their concentration gradient back into the stroma

Thylakoid membrane impermeable to protons

Have to pass through the ATP synthase enzyme embedded in the thylakoid membrane

The energy from this movement combines ADP and Pi to form ATP

This process of making ATP is photophoshorylation

23
Q

What is cyclic photophosphorylation?

A

Cyclic photophosphorylation is a type of photosynthesis that occurs in bacteria.

It only involves PSI

The electrons released from chrolophyll return to PSI via an electron transport chain/electron carriers

The energy released when the electron passes down the transport chain is used to make small amounts of ATP

No oxygen or reducing power in the form of reduced NADP is formed

24
Q

What happens to the rate of photosynthesis at different light intensities:

A

At high light intensity:

more light energy for the light-dependent stage meaning there is more light energy for ATP production and the production of reduced NADP

This means that the light-independent reaction can happen much more quickly as the products needed for it are being quickly supplied

As a result more sugars are produced that can be used for respiration

And as respiration increases, there is more energy for growth and there is a faster synthesis of new organic substance

25
Q

What is the importance of reduced NADP in photosynthesis?

A

Reduced NADP is needed for biosynthesis

26
Q

What is non-cyclic photophosphorylation?

A

Non-cyclic photophosphorylation is a type of photosynthesis that occurs in plants and cyanobacteria.

Two photosystems are involved: PSI and PSII

An electron from PSII is boosted to a higher energy level, released/emitted/ejected and passed down an electron transport chain to PSI and this electron transport chain generates a proton force used to make ATP

The electrons lost are replaced by the photolysis of water (releasing oxygen) and does not return to PSII

Hence this way of making ATP is called non-cyclic

Light energy is absorbed by PSI and an electron is excited and emitted, going towards making reduce NADP to NADPH

The ejected electron is replaced by an electron from PSII

27
Q

How is reduced NADP formed in the light dependent stage of photosysnthesis?

A

Reduced NADP/NADPH is formed when an electron released from PSI is transferred to NADP along with a proton/H+ ion from the stroma

28
Q

Describe what happens in the light independent stage of photosynthesis?

A

Carbon dioxide diffuses into the stroma from atmoshpere

  • CO2 combines with 5-carbon molecule RuBP ribulose biphosphate
  • reaction catalysed by enzyme rubisco
  • results in a 6-carbon molecule
  • very unstable so splits/breaks down quickly
  • to give 2x 3-carbon molecules of GP glycerate 3 phosphate

ATP and NADPH are used to convert GP to 3-carbon molecule TP triose phosphate

  • ATP is hydrolysed to provide energy to convert GP to TP
  • NADPH donates protons needed to reduce GP/for the reaction to happen

For every 1 molecule of CO2 2 TP molecules are produced

29
Q

How many cycles of the Calvin cycle are needed to produce 1 hexose sugar and why.

A

6 turns/cycles of the Calvin cycle are needed to produce 1 hexose sugar.

Because…

For every 1 cycle you get 2 molecules of TP

For 3 cycles you get 6 molecules of TP (2 x 3)

But for every 6 molecules of TP

5 are used to regenerate RUBP

Only 1 goes towards making a hexose sugar

ratio of 5:1

30
Q

Carbohydrates or hexose sugars are made by…

A

joining 2 molecules of TP triose phosphate molecules together

31
Q

Lipids are made using glycerol and fatty acids.

  • Glycerol is sysnthesised from…
  • Fatty acids are synthesised from…
A

Glycerol is sysnthesised from TP while fatty acids are synthesised from GP

32
Q

Some amino acids are synthesised from…

A

GP

33
Q

Name 3 photosynthetic pigments in the chloroplasts of plants.

A

chlorophyll a

chlorophyll b

carotene

34
Q

At what wavelength does photosystem I absorb light best?

A

Photosystem I absorb light best at a wavelength of 700 nm

35
Q

At what wavelength does photosystem II absorb light best?

A

Photosystem II absorbs light best at a wavelength of 680 nm

36
Q

What are photosynthetic pigments?

A

Photosynthetic pigments are coloured substances within chloroplasts that absorb light energy at different wavelengths

37
Q

Briefly explain how ribulose biphosphate RuBP is regenerated in the Calvin cycle. (2 marks)

A

For every 6 molecules of TP produced, 5 of them are used to regenerate RuBP

The rest of the ATP from the light-dependent stage is needed to convert TP to regenerate RuBP

38
Q

Why is the Clavin cycle important?

A

It produces TP and GP

TP and GP are converted into useful substances

Such as: glucose, sucrose, starch, lipids, proteins

That are needed for growth of the plant

39
Q

What are the optimum conditions for photosynthesis?

A

High light intensity

  • light provides energy for light dependent stage
  • higher light intensity = more energy

Temperature of 25 °C

  • enzymes denature at above 45 °C and become inactive at below 10 °C
  • stomata close to avoid losing water = less CO2

Carbon dioxide at 0.4%

  • higher % of carbon = higher rate of photsynthesis
  • hgher than 0.4% = stomata start to close

Constant supply of water

  • not enough = photosynthesis stops
  • too much = waterlogged cells
  • reducing uptake of minerals needed to make minerals fro making chlorophyll a
40
Q

What is the saturation point?

A

The saturation point is the point at which a factor is no longer the limiting the reaction

Something else has become the limiting factor

Increasing a variable makes no change to the dependent variable

?

41
Q

Describe what is going on in this graph. Light intensity is plotted against rate of photosynthesis.

A

At the start:

  1. Light is the limiting factor/the rate of photosynthesis is limited by the light intensity
  2. as light intensity increases the rate of photosynthesis increases
  3. the graph reaches saturation point
  4. increasing light intensity after this point makes no difference
  5. something else has become the limiting factor
  6. The graph levels off
42
Q

Describe what is going on in this graph. Temperature is plotted against rate of photosynthesis.

A
43
Q

Name 2 factors that can limit plant growth.

A
  • Temperature
  • Carbon dioxide
  • Light intensity
  • Water
44
Q

Why is it important that argicultural growers know about factors that limit photosynthesis?

A

They are able to use the information to create optimum environments/conditions with the right levels of everything that plants need

This increases growth

So increases yield

  • more to eat
  • more income
45
Q

How do managment techniques in glasshouses help growers to create optimum conditions?

A

CO2 is added to the air by burning small amounts of propane

Light gets through the glass while lamps provide light at night

Glasshouses trap heat energy which keeps the air warm

Heaters and coolers used to maintain a constant optimum temp

Air cirulation used so that temperature is even throughout

46
Q

Why would plants in a greenhouse with added CO2 grow faster on average and be larger than plants grown in a greenhouse with no added CO2?

A

CO2 is used by the plant for making glucose

glucose provides energy

the more CO2 the more glucose

more respiration

more energy/ATP

for cell division, DNA replication, protein synthesis

i.e. growth

47
Q

Desribe 2 ways in which conditions can controlled in glasshouses to increase yields. (2 marks)

A
  1. Burning
    2.

Biology A-Level (24 decks)

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