Photosynthesis Part 1 - (Week 3) Flashcards
- Define the terms autotroph and heterotroph - Define the term photosynthetic pigment and discuss its role in photosynthesis - Describe the fundamental processes in photosynthesis
Give 3 reasons why photosynthesis is a significant process
- Atmospheric O2 (the ‘ingredient’ to multicellular life)
- Global carbon cycle
- Food, fuel & medicine
What are autotrophs?
- ‘Self feeders’
- They are living organisms that sustain themselves without feeding/eating anything derived from other organisms
- Only need water, CO2 & minerals from soils
- Synthesise organic products/sugars
What are photoautotrophs?
They are organisms that get energy from the sun to produce organic compounds to feed on
What are heterotrophs?
They are organisms that rely either on:
- Compounds produced by other organisms (autotrophs are the ultimate source organic compounds for non-autotrophs)
- Other autotrophs or heterotrophs for energy
What is photosynthesis?
- The process of converting light energy to chemical energy
- It can be carried out by both uni/multicellular organisms
(Life on earth ultimately depends on the sun’s energy and this is the only process that can harvest this energy)
How are cells in a leaf arranged to maximise the products of photosynthesis?
Cells are packed closely together to increase CO2 absorption (apart from spongy layer - to allow CO2 & O2 to go in/out of leaf in respiration/photosynthesis)
What is the balanced equation for photosynthesis?
6 CO2 + 6 H20 -> 6 C6H12O6 + 6 O2
above arrow should be light energy
What is found in the stroma of chloroplasts?
Most enzymes for the kelvin cycle
What parts of photosynthesis take place in the thylakoid membrane?
- Electron Transport Chain (ETC)
- All of the ‘light reaction’
What happens in the thylakoid space that is important for photosynthesis?
Where electrochemical gradient is generated, required for the production of ATP
Why are there 2 parts to the process photosynthesis?
ATP & NADPH (energy carrier molecules) cannot be simply transported out of the chloroplasts so are channeled into the dark (carbon) reaction
Why is photosynthesis an endergonic process?
- Water is split & electrons are transferred
- H+ ions from water is transferred to CO2, reducing it to sugar
- Electrons increase in energy as they move from water to sugar
- This process requires energy from sunlight which is endergonic as energy is absorbed
Name the fundamental processes in photosynthesis
- Light harvesting
- Excitation of electrons
- Carbon fixation
- Kelvin cycle
Name the 3 key components of the light reactions
- Pigments
- Photosystems
- Electron Transport Chain (ETC)
What are photosynthetic pigments?
They are pigments that absorb the light that powers photosynthesis
Name the 5 types of pigment that can be found in photosynthetic organisms
- Bacteriochlorophyll a (usually in bacteria)
- Chlorophyll a
- Chlorophyll b
- Phytoerythrobilin (usually in cyanobacteria & algae)
- β-carotene
Which pigment causes the appearance of yellow leaves? Why? What is the reason???
β-carotene
- Lower temp. destroys chlorophyll so green fades & yellow of this pigment remains
(In plants usually when there is less sunlight & less chlorophyll produced)
Describe the role of chlorophyll in light reactions.
- Green pigment
- Absorbs light that powers photosynthesis through the excitation of electrons (in its porphyrin-like ring - electrons around ring will be excited by light)
- Makes up an antenna complex that is associated to a photochemical reaction centre, forming a photosystem
Describe the role of chlorophyll b in the light reactions
- It has the same structure & functions as chlorophyll a but the -CH3 is replaced by aldehyde group (-CHO)
- absorbs at 500-640nm (appears olive green)
Describe the role of carotenoids (β-carotene) in the light reactions
- Are yellow, orange, red or brown pigments
- Absorb strongly in the blue-violet range
- Pass absorbed light energy to chlorophyll A
- Provide photoprotection
What does photo protection do in carotenoids?
Absorbs & dissipate excessive light energy that would destroy chlorophyll a or react with O2 to form other O2 species (oxidative damage)
What type of pigment is chlorophyll a?
Primary photosynthetic pigment (& the most abundant pigment)
Define the term ‘accessory pigment’ and the two that are found in photosynthetic organisms
They are pigments that broaden the range of light absorbed
- Chlorophyll b
- Carotenoids
What is the antenna complex?
It is a part of the photosystem that is formed from the 3 pigments; carotenoids, chlorophyll a & b
In what order is light absorbed by the 3 pigments?
Carotenoids -> Chlorophyll b -> Chlorophyll a
How does the antenna complex act as a ‘funnel’?
- It funnels energy from sunlight to the reaction centre via excitation of electrons (through ‘resonance energy transfer’)
- Some energy is lost as heat/light (but is very quick to reduce/avoid energy lost)
What is resonance energy transfer?
When the sun hits the electrons & energy is transferred, electrons don’t move - the energy is transferred from electron to electron
Give the 3 possible fates of the energy absorbed by the pigments
- Converting extra energy to heat/combo. of heat & light
- Transferring energy from neighbouring chlorophyll molecules in antenna complex to reaction centre (via resonance energy transfer)
- When energy arrives in reaction centre, energy can power the movement of an electron (negatively charged high-energy electron) to another nearby molecule (electron acceptor)
