T13 Processes and Key Points Flashcards
Thylakoid membrane
-Where light-dependent reactions occur
-Its membrane contains photosystems, inside which chlorophyll molecules are located
-It also has accessory pigment, ETC and ATP synthase
Grana
-Stacks of thylas koid membranes, increasing usrface are for light dependent reactions. Its memebrane:
-hols ATP synthase for chemiosmosis
-allows pigments to be arragned in light harvesting clusters )in funnel like structtures) for efficient light absorption
Stroma
-Contains enzymes for Calvin cycle (light independent reactions), 70S ribosomes, circular DNA, lipid droplets, starch grains
-Starch granule -> insolube storage carbohydate product of photosynthesis
Adaptation of palisade tissues
-Contain large numbers of chloroplasts
-Large vacuole helps in pushing chloroplast to edge of cell for max light absorption and short diffusion pathway
-Chloroplasts can move towards light and away from intense light to avoid damage
-Elongated & arranged to intercept maximum light
-Closely packed to absorb maximum light
-Large surface area for diffusion of gases
-Moist cell surfaces for diffusion of gases
-Thin cell walls for maximum light penetration and diffusion of gases
Light Dependent STage
Takes place in the thylakoid membranes
Photosystems are required to trap wavelengths of light (photons) to energize the electron found in the primary pigment (chlorophyll α)
Photoactivation: the excitation of an e- to a higher energy level, causing it to escape a chlorophyll molecule
Accessory pigments are arranged in light harvesting clusters that pass on absorbed energy to the primary pigment at reaction centre
Photosystem I absorbs wavelengths of 700nm
Photosystem II absorbs wavelengths of 680nm
Light Dependent STage
Takes place in the thylakoid membranes
Photosystems are required to trap wavelengths of light (photons) to energize the electron found in the primary pigment (chlorophyll α)
Photoactivation: the excitation of an e- to a higher energy level, causing it to escape a chlorophyll molecule
Accessory pigments are arranged in light harvesting clusters that pass on absorbed energy to the primary pigment at reaction centre
Photosystem I absorbs wavelengths of 700nm
Photosystem II absorbs wavelengths of 680nm
Non-Cylic Photophosphorylation
- Accessory pigments in PSII absorb photons of light. The energy is passed onto primary pigment,
exciting primary pigments e- to a higher energy level and causing them to escape the photosystem.
Photolysis: photosystem II contains a water splitting enzyme that catalyses the lysis of water in the presence of light
Oxygen diffuses out of the chloroplast and into the air
The protons build up in the thylakoid lumen causing a gradient to be formed
The electrons in water replace the electrons that have left the primary pigment
2.The energized electrons are taken up by electron
acceptors, and are passed down the ETC, which generates energy to pump protons from stroma to lumen. e- then travel to PS I, where more light is absorbed by the
chlorophyll molecules and the e- are reenergised.
Cyclic Photophosphorylation
Only involves Photosystem I
E- is photoactivated and is accepted by e- acceptor rather than falling back into the photosystem and giving out thermal energy
It is then passed on via a chain of electron carriers, during which, enough energy is released to synthesize ATP by chemiosmosis
ATP is then passed on to light independent reactions
Electron then returns to Photosystem I
Light Independent Stage
-Occurs in the stroma of chloroplast and is called the Calvin Cycle
-G3P is reduced and activated to form triose phosphate (TP or PGA). The ATP and NADPH from the light-dependent reactions is used in this step. The ADP and NADP return to the thylakoid membrane for recycling
Most of the triose phosphate regenerates the RuBP using ATP
Some of the triose phosphate molecules condense to hexose phosphates, to in turn form glucose, cellulose, sucrose and starch.
Others converted to amino acids, lipids, or acetyl coenzyme A (CoA).
Limiting Factors
Limiting factors: if a process is affected by more than one factor, the rate will be limited by the factor which is nearest its lowest value
Limiting factors of photosynthesis: light intensity, carbon dioxide concentration and temperature.
Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide.
At low light intensities, the limiting factor for rate of photosynthesis is the light intensity; as the intensities increase so does the rate. But at high light intensity, one or more other factors must be limiting, such as temperature or carbon dioxide supply.
The effects of limiting factors can be investigated using aquatic plants such as Elodea or Cabomba.
The number of bubbles produced in unit time can be counted in different conditions
A better method would be to calculate the volume of gas produced over time
Glasshouses
A better understanding of the environmental factors on rate of photosynthesis allows us to manage the growth of plants in protected fields increasing yield of crop.
Sensors monitor light intensity, humidity and concentration of CO2 and control optimum conditions
Plants are grown hydroponically- in nutrient soil solution where its contents vary depending on the plants stage of growth
Pests and fungal diseases are fewer, further improving yield
Pigments and the Absorption of Light
There are two groups of pigments
Chlorophylls (Primary Pigments)
Carotenoids (Accessory Pigments)
Pigments and the Absorption of Light
There are two groups of pigments
Chlorophylls (Primary Pigments)
Carotenoids (Accessory Pigments)
Absorption spectrum
: is the graph above and shows the absorbance at different wavelengths of light
A low absorption means that those wavelengths are not absorbed, but instead are reflected or transmitted \therefore∴ plants seem to be green as it is absorbed least
Carotenoids mainly absorb in the blue-violet region.
Action spectrum:
graph that shows rate of photosynthesis at different wavelengths of light
