topic 5 (photosynthesis) Flashcards
what is photosynthesis?
the process where energy from light is used to make glucose from water and carbon dioxide
what is the word equation for photosynthesis?
carbon dioxide + water = glucose + oxygen
what is the chemical equation for photosynthesis?
6CO2+6H2O=C6H12O6+6O2
where does photosynthesis take place?
in the chloroplasts of plant cells
what is a chloroplast?
flattened organelle surrounded by a double membrane
what do thylakoid membranes stack to form?
grana
what are grana linked by?
lamellae
what photosynthetic pigments do chloroplasts contain?
chlorophyll a
chlorophyll b
carotene
what is a photosynthetic pigment?
coloured substances that absorb the light energy needed for photosynthesis
where are photosynthetic pigments found?
in the thylakoid membranes attached to proteins
what is a photosynthetic pigment attached to a protein called?
photosystem
what wavelength does photosystem I best absorb light at?
700nm
what wavelength does photosystem II best absorb light at?
680nm
what is the stroma?
gel like substance containing enzymes, sugars and organic acids
what happens to carbohydrates produced by photosynthesis that are not used straight away?
stored as starch grains in the stroma
what are the two stages of photosynthesis?
light dependent reaction
light independent reaction
where does the light dependent reaction occur?
in the thylakoid membranes
what is the energy in the light dependent reaction used by?
making ATP
making reduced NADP
photolysis
what are the two types of photophosphorylation in the light dependent reaction?
non cyclic and cyclic
what are the stages of non cyclic photophosphorylation?
light energy is absorbed by PSII
light energy excites electrons in chlorophyll
electrons move to a higher energy level
high energy electrons released from chlorophyll move down the electron transport chain to PSI
excited electrons from chlorophyll leave PSII to move down the electron transport chain (but these must be replaced)
light energy splits water into protons, electrons and oxygen during photolysis
excited electrons lose energy as they move down the electron transport chain
energy used to transport protons into the thylakoid so it has a higher concentration of protons than the stroma= proton gradient
protons move down their concentration gradient into the stroma via ATP synthase, which synthesises ATP
light energy absorbed by PSI excites the electrons to a higher energy level
electrons transferred to NADP with a proton from the stroma to produce reduced NADP
what happens in cyclic photophosphorylation?
only uses PSI
electrons from chlorophyll passed back to PSI by electron carriers
electrons recycled and repeatedly flow through PSI
produces small amounts of ATP
where does the light independent reaction occur?
in the stroma
what are the stages of the light independent reaction?
CO2 enters the leaf via the stomata and diffuses into the stroma
combined with ribulose bisphosphate, catalysed by the enzyme rubisco
produces unstable 6C compound- broken down into 2 3 carbon compounds= glycerate 3 phosphate
hydrolysis of ATP ,and H+ ions from reduced NADP, provides energy to change glycerate 3 phosphate into triose phosphate
some converted into useful organic compounds, some continues in the Calvin Cycle to regenerate ribulose biphosphate
what useful organic substances do triose phosphate and glycerate 3 phosphate make?
carbohydrates
lipids
amino acids
how is the Calvin Cycle used to make carbohydrates?
hexose sugars made by joining 2 triose phosphate molecules
larger carbohydrates made by joining hexose sugars together
how is the Calvin Cycle used to make lipids?
made using glycerol (which is synthesised by triose phosphate), and fatty acids (which are synthesised by glycerate 3 phosphate)
how is the Calvin Cycle used to make amino acids?
some amino acids are made from glycerate 3 phosphate
how many turns of the Calvin Cycle are needed to make 1 hexose sugar?
6
how many triose phosphate molecules are used to regenerate ribulose biphosphate?
5/6
how many triose phosphate molecules are needed to form 1 hexose sugar?
2
how many ATP do 6 turns of the Calvin Cycle need?
18
how many reduced NADP do 6 turns of the Calvin Cycle need?
12
what are the idea conditions for photosynthesis?
high light intensity of a certain wavelength
temperature around 25C
carbon dioxide at 0.4%
why is photosynthesis best at 25C?
if below 10C/above 45C, enzymes begin to denature
at high temperatures, stomata close to avoid losing too much water, which slows photosynthesis as less stomata can enter
what is usually the limiting factor for photosynthesis on a warm, sunny, windless day?
carbon dioxide
what is usually the limiting factor for photosynthesis at night?
light intensity
how can farmers manage carbon dioxide concentration in a greenhouse?
carbon dioxide added to the air, eg) by burning a small amount of propane in a CO2 generator
how can farmers manage light intensity in a greenhouse?
light can get in through the glass
lamps provide light at night time
how can farmers manage temperature in a greenhouse?
the glass traps heat energy from sunlight, which warms the air
heaters and cool systems keep a constant optimum temp
air circulation can be used to make sure the temperature is even throughout the greenhouse
