Chapter 17- Energy for biological processes Flashcards
(23 cards)
What is the importance of carbon-hydrogen bonds in trapping energy?
Organic molecules contain large number of carbon-hydrogen bonds, a non polar bond which doesn’t take a lot of energy to break
Where does the energy to build complex organic molecules come from?
The sun
What are two ways of exciting electrons?
Electrons present in pigment molecules are excited by absorbing light from the sun
High energy electrons are released when chemical bonds are broken in respiratory substrate molecules
What is the process that synthesises the large majority of ATP?
Chemisosmosis- the diffusion of protons form a region of high concentration to low concentration through a partially permeable membrane. The movement of these protons releases energy that is used to attach an inorganic phosphate to ADP
How do electron transport chains pump protons across a membrane?
As high energy electrons move across electron carriers of decreasing energy levels, they release energy which moves the protons across the membrane
Describe the structure of a chloroplast
Stacks of thylakoid membranes form grana (singular granum) which are interconnected by channels called lamellae.
Fluid is enclosed in chloroplasts called stroma
Why might leaves have different colours?
Different proportions of pigments (eg chlorophyll a or b, xanthophylls, carotenoids)
Define a photosystem
The light harvesting system (pigments) and the reaction centre collectively
What are the two stages of photosynthesis?
Light dependant stage and light independent stage
What are the two wavelengths absorbed mainly by each photosystem?
PS1- 700nm
PS11- 680nm
Describe the process of non cyclic phosphorylation
Energy from the sun excited electrons at PSII and travel down the ETC to produce ATP. These electrons enter the reaction centre at PSI. Electrons lost from this photosystem are replaced by photolysis. Electrons are re excited at PSI by the sun and go down a second ETC, where they are accepted with hydrogen by NADP.
Describe the process of photolysis
Using energy from the sun, water molecules are split into hydrogen ions, electrons and oxygen molecules. Oxygen is released and therefore a product
Summarise the reaction of photolysis
H20–> 2H + 2e + 1/2 O2
What occurs differently in cyclic phosphorylation compared to non cyclic phosphorylation?
Electrons leaving the ETC after PSI are returned to PSI, instead of forming NADPH
Describe the steps to the Calvin Cycle
- CO2 combines with ribulose bisphosphate
- Unstable six carbon intermediate
- Glycerate-3-phosphate
- Triose Phosphate (either forms the basis for complex molecules or is recycled into ribulose bisphosphate
What is the name of the enzyme needed to fix carbon dioxide and ribulose bisphosphate?
Ribulose bisphosphate Carboxylase (RuBisCo)
What is needed to covert glycerate 3 phosphate into triose phosphate?
A hydrogen atom supplied by reduced NADP and energy from ATP made from the light dependant reaction
How many turns of the Calvin cycle are needed to produce one glucose molecule?
Six CO2 molecules are needed, so six full turns of the cycle- this makes 12 TP molecules, 2 are used to produced glucose
The other 10 regenerate RuBP
What happens to cause photo respiration?
Stomata close to prevent water loss, CO2 can’t enter the plant, but photosynthesis still occurs, building up oxygen.
Oxygen acts as a competitive inhibitor to RuBisCo, producing phosphoglycolate and reducing GP production.
What are the four limiting factors to photosynthesis?
Light
Water availability
Temperature
Carbon dioxide concentration
What are the effects of reducing light intensity on the Calvin cycle?
Reducing light intensity reduces quantities of NADPH and ATP, meaning less GP can be converted to TP. This results in a build up of GP and a decrease in RuBP and TP
What kind of plants use C4 photosynthesis and why?
Plants adapted to high temperatures and limited water supply- they can fix CO2 more efficiently and do not need stomata to be open as long as C3 plants
What kind of plants use CAM photosynthesis and why?
Plants open their stomata at night and close them during the day- carbon dioxide is converted to an acid and stored during the night, and in the day the acid is broken back down. Dry environments eg cacti
