#5: Light Dependant Reactions Flashcards Preview

Bio 4U- Unit 2: Photosynthesis > #5: Light Dependant Reactions > Flashcards

Flashcards in #5: Light Dependant Reactions Deck (13)
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process used by plants to produce glucose

3 stages:
1. Capturing light energy
2. Using captured light energy to make ATP and NADPH
3. Using ATP and NADPH to make glucose from CO2


Photosynthesis Equation

6 CO2 + 6 H20 = glucose + 6 O2



site of photosynthesis in plant cells

consists of:
1. An inner and outer membrane
2. Thylakoids
3. Grana (stacks of thylakoids)
4. Stroma (a liquid-like substance)



a pigment is a compound that absorbs part of the spectra of visible light and reflects the rest

chlorophyll is a pigment


Chlorophyll a

absorbs light in the blue-violet and red spectra of visible light

chlorophyll a is the only pigment that can transfer light energy to the reactions of photosynthesis


Accessory pigments

accessory pigments must give the light-energy they have collected to chlorophyll a in order for the energy to be used in photosynthesis

Chlorophyll b
absorbs light in the blue-violet and red spectra of visible light

absorbs light in the blue-violet spectra of visible light


Capturing Light

Light must hit a cluster of proteins and pigments in the thylakoid membrane to begin process
Photon of light excites a single electron moving it to a higher energy state.
(3 Options)
Carotenoids/chlorophyll b transfer their energy to chlorophyll a (referred to as an antenna complex)
Energy hits chlorophyll a (reaction centre) and an electron is released to the electron transport chain


3 outcomes for an excited electron

1. Releases energy as thermal energy
2. Transfers energy to a different electron in neighbouring pigment molecule
3. Electron is accepted by an electron-accepting molecule


Stage 1 - Photoexcitation

absorption of light energy by photosystems
photosystems are clusters consisting of chlorophyll a, accessory pigments, and pr- in the membrane of thylakoids

- energy from photons of light are transferred through the photosystem until it reaches chlorophyll a
- chlorophyll a uses the energy to excite an e-
- the excited e - will then be passed on through the reactions of photosynthesis (redox reactions)


Two primary components of photosystems

1. Antenna Complex
- contains accessory pigments
- responsible for collecting light energy

2. Reaction Centre
- contains chlorophyll a
- responsible for transmitting light energy into the reactions of photosynthesis


Two types of photosystems used in photosynthesis

1. Photosystem I - contains chlorophyll a P700
2. Photosystem II - contains chlorophyll a P680


Stage 2 – e- Transport

excited e - from chlorophyll a are transferred through series of compounds that reduces NADP+ to NADPH and pumps H+ into the thylakoid space


Stage 3 – Chemiosmosis

H + gradient produced during e - transport is used to make ATP via ATP synthase