Photosynthesis Flashcards
Photosynthesis
Chemical process by which green plants use chlorophyll to convert CO2 and H2O to carbohydrates and O2 using sunlight
carbohydrates
composed C, H, O,
ratio 2H: 1O
Carbohydrates role
Turns light energy into chemical energy
Requirements for photosynthesis
- Light: Source sun
- CO2: Source atmosphere from combustion of fossil fuels and respiration. CO2 diffuses in through stomata
- Water: Source from soil through roots - brought up through xylem by transpiration stream
Chloroplast structure
- Photosynthesis occurs in the chloroplasts
- Chlorophyll traps the light energy
- Chloroplasts were derived from symbiotic bacteria because they have a double membrane, DNA and ribosomes
Adaptations of the leaf for photosynthesis
- Thin to make gaseous exchange efficient
2. Large surface area to collect maximum amount of light energy
functions of the leaf parts
DERMAL TISSUE
consists of upper and lower epidermis
role= protection water loss entry of pathogens
GROUND TISSUE
consists of mesophyll cells
role= photosynthetic tissue with chloroplast in the cells
VASCULAR TISSUE
consists of xylem and phloem transport tissue in plants
xylem transports water up stem as a reactant
phloem transports sugar produced as sucrose to other parts of the plants such as the meristems of the roots
leaf structure
diagram
- dermal tissue
- upper epidermis
- lower epidermis
- cuticles
- ground tissue
- vascular tissue
- xylem
- phloem
- air space
- spongy mesophyll
- stoma
- guard cell
- water vapor and o2 out
- co2 in
- palisade mesophyll
Chloroplast Locations
a) Palisade layer cells - most
b) Spongy layer cells - many
c) Guard cells – few
Chemical Equation of Photosynthesis
6 CO2 + 6 H2O = C6H12O6 +
6 O2
Human Intervention
To promote crop growth in greenhouses horticulturalists use
a) Heat: increased temperature increases the rate of chemical reactions
b) Artificial light: increased intensity increases rate and increased duration increases the amount
c) Carbon dioxide enrichment: Increased concentration the rate
chloroplast
diagram
- nonnuclear DNA
- starch grains
- outer membrane
- inner membrane
- ribosomes
- grana ( chlorophyll is here
- stroma ( enzyme here)
Light-Dependent Stage
grana
Products= Oxygen, NADPH and ATP.
Light energy is absorbed by the reaction center chlorophyll
Energized electrons are released from the chlorophyll and enter 2 pathways:
PATHWAY 1 - cyclic same electron returns
Electron is picked up by an acceptor
b. Then passed through carriers c. Energized electron loses its energy, which is captured by ADP to add a P and form d. Same electron‘ then returns to the reaction center chlorophyll’
PATHWAY 2- non cyclic not the same electron return
reaction center chlorophyll releases 2 energized electrons
captured by NADP+ to form NADP-
electron deficiency causes photolysis ( splitting of water using light energy)
release H , 2 energized electrons and oxygen
proton enters a pool
captured by NADP- to form NADPH
oxygen released into atmosphere
paired electron from water return to chlorophyll to replace those that left
Light-Independent Stage
dependent on products of light stage ATP and NADPH
stroma
product glucose
carbon dioxide is reduced to form glucose
supplies the carbon for the production of glucose
NADPH supplies necessary electrons and hydrogen ions
ATP supplies energy
ATP and NADPH break and ADP and NADP+ return to light stage to regenerate
To investigate the influence of light intensity on the ‘rate of photosynthesis’
vary light by placing lamp at different distance from elodea
keep temp constant using water bath at 25
keep CO2 level constant using saturated solution of sodium hydrogen carbonate
use spatula to add sodium hydrogen carbonate to distill water until it can no longer dissolve ( ensure constant solution of carbon dioxide)
place test tube in water bath 25 ( optimum temp )
PREPARE ELODEA ;
place fresh shot of elodea underwater use scalpel to cut stem at an angle ( elodea because grows underwater can easily see bubbles and count them )
remove any leaves at end ( stem cut at angle to allow bubbles escape easily)
add elodea to test tube secure with paper clip ( bottom of tube = easier for bubbles travel through column )
place apparatus in dark room lamp as only source ( fair test other source could alter results)
elodea kept 15cm allow time for elodea to adjust before counting bubbles ( precaution elodea must adjust)
control same set up no light ( used for comparison to provide a standard against which experiment can be judged)
measure rate counting bubbles produced per minute
repeat using same set up lamp different distance ( place lamp further decreasing light intensity
results - as light increases so does number of oxygen
bubbles produced per minute = rate of photo
certain light number of bubbles do not increase as light saturation reached
CO2 slows down rate
