C1.3 Photosynthesis Flashcards
Define Photosynthesis
- Conversion of light energy to chemical energy via the production of carbon compounds.
- This transfer is vital for most ecosystems
Chemical equation of Photosynthesis
6CO2 + 6H2O –> C6H12O6 + O2
Structure and their functions of Chloroplast
- Stroma: pores that open and close to release O2.
- Thylakoid: light dependent reaction occurs. They are sac-like vesicles.
- Granum: stacked columns of thylakoids
- Lamella.
- Double membrane.
Check slides.
Site where photosynthesis happens.
Chloroplasts. Chlorophyll are the pigments in the chloroplasts that absorb light energy.
Thin-layer Chromatography of chloroplasts
Experiment/method to separate the different chloroplasts. Stationary phase is usually silica gel, aluminium oxide or cellulose instead of paper. Thin-layer tends to give better result.
Limiting factors of Photosynthesis
- Temperature.
- (pH)
- Light intensity.
- CO2 concentration.
- Type of light
- Amount of water
Stages of Photosynthesis
Light dependent:
- Takes place in thylakoid
- Uses light to make ATP and reduced NADP
- Produces O2
Light independent:
- Takes place in the stroma
- Uses ATP and reduced NADP to form carbon compounds from CO2
Light dependent stage of photosynthesis
- Begins within photosystems: molecular arrays of chlorophyll and accessory pigments within protein complexes, located in membranes.
- Arrangement of pigments allows them to absorb light energy across a range of wavelengths
- Two types of photosystems in the thylakoid membrane: photosystem I and photosystem II
- Photosystem I is most sensitive to light wavelengths of 700nm
- Photosystem II is most sensitive to light wavelengths of 680nm
- When photons of light strike the pigment molecules in the photosystem, they excite the electrons within these molecules
- Excited electrons are transferred to reaction center chlorophyll molecules
- At the reaction center, they go through a photochemical reaction, resulting in the emission of an excited electron. This process is known as photoactivation
- Electron is released by photosystem II
Reason for having many different pigment molecules in the photosystem
- Only through use of a variety of pigment molecules can enough light energy be absorbed to photoactivate the central chlorophyll molecule
- This causes the excitation and release of the electrons that will provide the energy for the rest of the light-dependent phase of photosynthesis
What happens to the electrons released by photosystem II
- Passed along a series of proteins in the membrane (ETC)
- As they are passed from protein to protein, they drop in energy level and release that energy
- Energy is used to pump H+ from stroma into the intermembrane space of thylakoids
- This creates a concentration gradient across the thylakoid membrane
Define and Explain Photolysis
- Use of light energy to split water
- H2O –> (H+) + (e-) + O2
- Hydrogen required to convert CO2 into glucose
- Oxygen given off as byproduct
What do the photosynthetic organisms use to absorb light
Pigments. There are many different types
Method to separate the pigments
Paper chromatography
- Transfer plant pigments onto paper
- Allow paper to absorb the chromatography solvent upward
- Separate pigments, color
- Measure the distance that the solvent travelled and the distance each pigment travelled.
- Rf value = distance travelled by pigment/ distance travelled by solvent
Why do leaves look green
- They reflect green light and absorb other lights.
- All 3 pigments in the chloroplast (chlorophyll a, chlorophyll b and carotenoid) are poor absorbers of green light.
- Carotenoid good absorber at blue/purple.
- Chlorophyll a is a good absorber at orange/red and purple.
- Chlorophyll b is a good absorber at yellow and blue.
Differences between Absorption spectrum and Action spectrum
- Absorption spectrum: shows the wavelengths of light a pigment absorbs
- Action spectrum: photosynthesis rates at different wavelengths (% of max)
