Photosynthesis Flashcards
Why is energy needed
Active transport
Allows chemical reactions to take place
Build up or break down of molecules
What is the ultimate energy sources for living organisms
Sunlight
What is the evidence for there being two stages of photosynthesis
Temp has a clear effect on the rate of photosynthesis suggest that light levels may initially limit the rate but second step is controlled by temperature
A plant given alternative periods of light and dark forms more carbs than one in continuous light (periods of darkness ensure all product from first stage is converted into carbs before it builds up)
Describe the excitation of electrons
1) photon of light hits chlorophyll molecule
2) energy transferred to the electrons in the molecule
3) electrons raised to higher energy levels
4) if they are raised to a high enough level they will dissociate
5) electrons picked up by an electron acceptor
6) ATP is formed as the electrons is passed along an electron transport chain
What is an electron transport chain
Series of compounds that transfer electrons from electron donors to electron acceptor via redox (both reduction and oxidation occurring simultaneously) reactions
What is a proton gradient
A higher conc of protons (H+) on one side of a membrane than the other (e.g. Thylakoid lumen and stroma)
What is chemiosmosis
Movement of ions across a semi permeable membrane down their electrochemical gradient (more specifically to generate ATP)
What are the two stages of photosynthesis
Light dependant
Light independent
Where does the light dependant reaction take place
In the thylakoid membrane where photosystems facilitate the reduction of NADP and photophosphorylation resulting in the production of ATP
What are photosystems
PS1 and PS2 form distinct complexes, absorb a different wavelength of light dependant on its combination of chlorophyll
Describe the process of cyclic photophosphorylation
Only involves PS1 produces ATP
1) when a photo of light hits a chlorophyll molecule in PS1, an electron is boosted to a higher energy state and captured by an electron acceptor
2) then passed along the ELECTRON TRANSPORT CHAIN giving up energy at each stage, the energy given up drives PROTON PUMPS to move H+ ions
3) this causes a pH and electrochemical gradient
Chemiosmosis allows ATP Synthetase to convert ADP+Pi—-> ATP
electron is fed back to original chlorophyll
Describe the process of non-cyclic photophosphorylation
Involves PS1 and PS2 requires WATER
produces ATP and REDUCED NADP
1) When PS2 absorbs light, an electron excited to a higher level is captured by an ELECTRON ACCEPTOR
2) the oxidised chlorophyll is now an OXIDISING AGENT. A photolytic enzyme attached to PS2 extracts electrons from the OH- formed from the photolysis of water (H2O—->H+ + OH- + 1/2 O2 which replaces each lost electron (OXYGEN IS A WASTE PRODUCT)
3) H+ ions are used in the reduction of NADP
the high energy electron passed along an electron transport chain (producing ATP)
And is picked up my the acceptor NADP in PS1 - this reduces NADP
What happens in the light independent reaction
Uses the reducing power of NADP and the chemical energy in ATP
takes place in the stroma
CALVIN CYCLE:
1) carbon fixation
2) reduction
3) regeneration of RuBP
What is the process of carbon fixation
Molecules of CO2 combine with 5C RuBP
The CO2 molecules are now said to be FIXED
The enzyme RUBISCO acts as a catalyst to form an unstable 6C intermediate
3C glycerate 3 phosphate (GP) forms from the 6C intermediate
What is the process of reduction
The molecules of 3C GP are phosphorylated using ATP which destabilisers the molecule and provides energy required to reduce GP into glyceraldehye 3 phosphate (TP) using the reducing agent NADPH
NADPH oxidised back to NADP
What is the process of regenerating of RuBP
Most of 3C TP passes through steps to regenerate 5C RuBP using some ATP produced during light dependant reactions
some TP is converted into 6C glucose
What are the limiting factors of photosynthesis
Light
Temperature
CO2
Water
How does light affect photosynthesis
Light quality - plants can only use certain wavelengths
Light duration - day length affects available light
Light intensity - strength of light
At high light intensity chlorophyll can be damaged
What is the compensation point
When rate of photosynthesis = rate of respiration
What affect does temperature have
There are enzymes involved in the process of photosynthesis and so these will denature if it is too hot or not work efficiently if it is too cold
Between 10-35 degrees a 10 degree rise in temp doubles the rate of photosynthesis
What is the effect of CO2
Is the source of C atoms used to make the organic products of photosynthesis
Drops at end as when CO2 concentration exceeds 1.0% the stomata close preventing CO2 from entering
What is the effect of water
Affects lots of physiological processes in the plant
Affects rates of photosynthesis and is a limiting factor as low levels
How can farmers improve the overall growth of their crops
Have plants in glasshouses
As can control the CO2 conc the temperature and can add water
Can also get specific wavelength light lamps
How do plants create and use carbs
First hexose made is fructose phosphate. Can be converted to glucose and combined with glucose to make sucrose for transport around the plants
The alpha glucose molecules may be converted to starch (storage) or to beta glucose which is polymerised into cellulose for cells walls
