Photosynthesis Flashcards
Photosynthesis
The process that converts solar energy into chemical energy
Autotrophs
Sustain themselves without eating anything derived from other organisms (producers)
Heterotrophs
Obtains their organic material from other organisms (consumers)
Reactants
From air and soil (6CO2 + 6H2O + Light Energy)
Products
Used in cellular respiration to make ATP (6O2 + C6H12O6)
Chloroplasts
Structurally similar to photosynthetic bacteria- allows for the chemical reactions of photosynthesis
Chlorophyll
Green pigments within chloroplasts- creates green color in leaves
Mesophyll
The interior tissue of the leaf where most chloroplasts are found (cells contain 30-40 chloroplasts)
Stomata
Microscopic pores where CO2 enters and O2 exits
Thylakoids
Membrane (connected sacs in the chloroplast) where chlorophyll is in
Grana
Stacked columns of thylakoids
Stroma
A dense interior fluid contained in chloroplasts
The splitting of water
Chloroplasts split H2O into hydrogen and oxygen, releasing oxygen as a by-product
Oxidation
The substance that loses electrons is said to be oxidized (OIL)
Reduction
The substance that gains electrons is said to be reduced (RIG)
Light Reactions
- In the Thylakoids
- Split H2O -> release O2
- Reduce NADP+ to NADPH
- Generate ATP from ADP by photophosphorylation
Calvin cycle
- In the stroma
- Forms sugar from CO2 using ATP and NADPH
- Carbon fixation
Wavelength
The distance between crests of waves- determines the type of electromagnetic energy
Electromagnetic spectrum
The entire range of electromagnetic energy, or radiation
Visible light
Consists of wavelengths that produce colors we can see
Photons
Light also behaves as though it consists of discrete particles
Pigments
Substances that absorb visible light; Leaves appear green because chlorophyll reflects and transmits green light
Spectrophotometer
Measures a pigment’s ability to absorb various wavelengths
Absorption spectrum
A graph plotting a pigment’s light absorption verses wavelength
Action spectrum
Profiles the relative effectiveness of different wavelengths of radiation in driving process
Chlorophyll a
The main photosynthetic pigment
Chlorophyll b
Broaden the spectrum used for photosynthesis
Carotenoids
Absorb excessive light that would damage chlorophyll
Excited state
When a pigment absorbs light it goes from a ground state to an excited state which is unstable
Photosystem
Consists of a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes
Light-harvesting complexes
Pigment molecules bound to proteins; Transfers the energy of photons to the reaction center
Primary electron acceptor
In the reaction center; Accepts excited electrons and is reduced as a result
Photosystem II
Functions first and is best at absorbing a wavelength of 680 nm (reaction-center chlorophyll a is called P680)
Photosystem I
Best at absorbing a wavelength of 700 nm (reaction-center chlorophyll a is called P700)
Linear electron flow
The primary pathway; Involves both photosystems and produces ATP and NADPH using light energy
First step of the linear electron flow
A photon of light strikes a pigment molecule in a light-harvesting complex of PS II, boosting one of its electrons to a higher energy level (excited state). Energy is relayed to other pigment molecules until it reaches the P680 pair of chlorophyll a molecules in the reaction center complex
Second step of the linear electron flow
An electron from the excited P680 (now P680+) is transferred to the primary electron acceptor
Third step of the linear electron flow
P680+ is the strongest biological oxidizing agent; its electron “hole” must be filled -> An enzyme catalyzes the slitting of water molecule (2 electrons, 2 hydrogen ions (H+) -> released into the thylakoid lumen, an oxygen atom -> released in the form of O2)
Fourth step of the linear electron flow
Each photoexcited electron passes from the primary electron acceptor of PS II to PS I via an electron transport chain (ETC) made up of plastoquinone (Pq), a cytochrome complex, nd plastocyanin (Pc)
Fifth step of the linear electron flow
The exergonic “fall” of electrons to a lower energy level allows for the synthesis of ATP. As electrons pass through the cytochrome complex, H+ are pumped into the thylakoid lumen, contributing to the proton gradient that is used in chemiosmosis
Sixth step of the linear electron flow
Light harvesting complexes in PS I are excited by another photon and transfer energy. An electron of the P700 pair chlorophyll molecules is excited and passed to the PS I primary electron acceptor. Now that P700+ has an electron “hole”, it can act as an electron acceptor (PS I accepts the electron that reached the bottom of the ETC from PS II).
Cyclic electron flow
Uses only photosystem I and produces ATP, but not NADPH; generates surplus ATP
Chemiosmosis
The use of energy in a H+ gradient to drive cellular work; Protons build up in the thylakoid lumen -> can only diffuse through ATP synthase -> ATP is produced
First step of carbon cycle
Carbon fixation (CO2 catalysed by rubisco)
Second step of carbon cycle
Reduction (carbon molecules are reduced using ATP which is then turned into ADP & NADPH which is then turned into NADP+ + P until it creates a sugar named glyceraldehyde 3-phosphate (G3P))
Third step of carbon cycle
Regeneration of the CO2 acceptor (RuBP)
