photosynthesis Flashcards
(33 cards)
What are autotrophs
- organisms that produce their own food from inorganic substances (e.g. CO2)
- harness light energy through photosynthesis, converting it into chemical energy
What are heterotrophs?
- cannot produce their own food
- need to ingest nutrition from other sources
What is photosynthesis/ what is its purpose
- biochemical pathway
- energy from sunlight cannot be directly used for cellular processes (cannot be transported, stored)
- photosynthesis transforms light energy into chemical energy in the form of glucose
Biochemical pathway of photosynthesis (balanced equation)
and word equation
6CO2 + 12H20 —-(light, chlorophyll) —- C6H12O6 +6O2 +6H20
carbon dioxide + water (light, chlorophyll) glucose + oxygen
word equation- where does each part come from/go
CO2: enters from atmosphere through stomata in the leaves
oxygen: released through stomata
water: taken up from roots, transported to leaves
light: sunlight hits the leaves and is absorbed by chlorophyll (not a reactant)
Stomata
- pores that allow the exhange of gases, and water to leave the plant
- surrounded by specialised cells (guard cells) which regulate opening and closing of pore
Light-dependent stage- where, and brief description
- in thylakoid membranes
involves:
- absorption of light energy by chlorophyll
- splitting of water
- production of NADPH and ATP
light-independent stage- what is it and purpose, when can it occur
- Calvin cycle
- occurs in stroma
- involves formation of glucose from carbon dioxide
- if NADPH and ATP are present, it can occur without light (although it cannot continue long after dark)
Chloroplast, what are they and structure
Chloroplast:
- membrane bound organelles
- site of photosynthesis
- green due to chlorophyll
Structure:
- outer and inner membrane
- thylakoids: membrane bound discs, contain chlorophyll, provide large surface area to capture sunlight
- thylakoid grouped into stacks called grana (singular- granum)
- enzymes in light-dependent stage located in thylakoid membranes
-stroma: fluid inside chloroplast, contains enzymes for calvin cycle
Photosynthetic pigments
- molecules that capture light energy
- many photosynthetic pigments- only need to know chlorophyll
- each photosynthetic pigment absorbs different wavelengths (colours) of light
Chlorophyll
- green photosynthetic pigment
- absorbs light energy
- found in thylakoid membrane
- absorbs violet wavelengths the best (then red, blue, yellow), reflects green
Light dependent stage
- Chlorophyll absorbs light energy from sun
- Energy trapped by chlorophyll is used to split water molecules into oxygen (O2), hydrogen ions (H+), high energy electrons
- Oxygen is a waste product- released into atmosphere via stomata.
- electron transport chain moves hydrogen ions from stroma into thylakoid to create a higher h+ concentration. - hydrogen ions pass through ATP synthase. This enzyme uses energy from H+ to synthesise a bond between ADP and Pi, creating ATP
- NADP+ accepts H+ that exit ATP synthase as well as electrons created by splitting of water, forming NADPH
Detailed process (don’t need to know everything)
- sunlight hits photosystem 2, energy is absorbed by chlorophyll which is used to excite electrons
- electrons become high energy
- when they have high energy, they have a tendency to lose energy to become less excited. they do this by being leaving photosytem 2 to an electron acceptor
- photosystem 2 has lost its electrons so it breaks the hydrogens off the oxygen (from H2o) and the electrons from H2O are released and go into photsystem 2, replacing electrons
- electrons release energy as they go, which is used to pump H+ into thylakoid
- electrons reach NADP+ reductase. negatively charged so attract H+ and NADP+, electrons go into NADP+ and hydrogen gets added to become NADPH
- higher H+ gradient inside membrane. facilitated diffusion through ATP synthase. releases energy, causing ATP synthase to rotate. as it rotates, it undergoes a conformational change so a phosphate ion and ADP can bind to form ATP
ATP and ADP +Pi
ATP:
- coenzyme
- transfers energy between reactions
- joining ADP and Pi requires energy which is stored in the bond created
ADP:
- the breakdown of ADP + Pi releases energy stored in the bond between 3rd phophate and ADP molecule
NADP+, NADPH
coenzyme
- transfer of electrons and protons between reactions, supporting anabolic reactions (e.g photosynthesis)
Inputs and outputs of light dependent stage
Inputs/reactants:
H20
NADP+
ADP + Pi
Outputs/products:
O2
NADPH
ATP
Light independent stage / calvin cycle
- Carbon fixation: (inorganic to organic)
Rubisco fixes CO2 from atmosphere to 5 carbon compound RuBP (inorganic carbon captured and attached to organic RuBP) This molecule is unstable and splits into 2 3 carbon molecules of PGA - Carbon reduction
- through multiple processes, PGA converted into glucose
- energy provided by breaking down ATP into ADP + Pi
- protons required donated by NADPH, which turns into NADP+ - Molecules not used in creation of glucose, used to regenerate RuBP (energy provided by ATP)
- H2O is also created from oxygen released from left over oxygen of CO2 with H+ provided by NADPH
2 cycles are required to make 1 glucose molecule
How can the rate of photosynthesis be measured?
- rate of CO2 consumption
- rate of O2 produced
- rate of glucose /starch produced
- rate of plant growth
How does light availability affect rate of photosynthesis?
- at low light intensity: photosynthetic rate is absent or slow
- with increasing light intensity, photosynthetic rate increases due to more light availablity for light dependent reactions and thus more loaded coenzymes are produced
- beyond optimal light intensity (where it first reaches greatest rate), rate plateaus.
- this point is the light saturation point
- another factor is limiting (e.g. enzymes involved in LD are saturated, availability of CO2, number of chloroplasts)
How does water availability affect rate of photosynthesis?
too little:
- soil dries out, rate declines then stops
- stomata close to prevent further water loss, preventing uptake of CO2 needed for calvin cycle
- prolonged period of water deficit can cause plant death
too much water: waterlogging
- rate declines then stops
- waterlogged soil prevents cells in roots from being able to respire
- this in turn stops the roots from taking up water, limiting its availablity as an input for LD reactions
How does temperature affect rate of photosynthesis?
low temp:
- rate is slow
- low collision rates between reactants and eznyme active sites
increasing temp:
- increased rate
- more collisions between reactants and active sites
- reaches optimal point
beyond opitmal:
- rate declines
- due to heat denaturing enzymes (altered shape of enzymes means active site is no longer complementary to substrate)
How does CO2 concentration affect rate of photosynthesis?
low co2:
- rate is slow
- less glucose can be created
increasing co2:
- rate increases as more glucose can be created
- reaches optimal
beyond optimal:
- plateaus
may be due to:
- enzymes involved in carbon fixation become saturated
- availability of coenzymes (e.g NADPH) become a limiting factor
Describe the role played by each of the coenzymes NADPH and ATP in photosynthesis.
- NADPH transfers hydrogen ions and electrons
- ATP transfers energy
what type of molecule is glucose?
monosaccharide (simple sugar)
comparing C3,C4 and CAM: temp, water availability, stomata open when, examples
C3:
temp: low to moderate (15-25 degrees)
water availability: plentiful water
stomata open: during day
majority of plants (rice, evergreen trees)
C4:
temp: warm/humid/tropical (30-40)
water availability: tropical (low water)
stomata open: during day
e.g corn, sugar cane
CAM:
temp: hot/arid (40+)
water availability: drought (low water)
stomata open during night
e.g cacti
