BIOA02H3 Lecture 5: Photosynthesis
27 Apr 2018
School
Department
Course
Professor
BIO A02 ā Module 1 Notes Hassan Alibhai
Plant Form and Function Page 18
Photosynthesis
ā¢The conversion of carbon dioxide and water in the environment into
sugar and oxygen, with the assistance of light energy.
ā¦6 CO2 + 6 H2O => C6H12O6 + 6 O2
ā¢The main cells that contribute to this process are collenchyma, the
photosynthetic parenchyma cells.
ā¦Palisade Layer => positioned well to capture light from the sun
ā¦āSpongyā Mesophyll => photosynthesis zone, space to allow gas
exchange with stomata
Transpiration Compromise
ā¢Opening stomata allow the plant access to carbon dioxide, which it needs to photosynthesize.
However, that act also allows for transpiration, the loss of water due to excessive heat
ā¦Over 90 percent of the water in the xylem is lost to transpiration
ā¦If this water canāt be replaced through soil due to heat or drought, it presents a problem.
āŖEx. Sugar maples release about 200 liters per day into the environment through
transpiration, and it has to be replaced somehow
ā¢Goal of photosynthesis: more sugar per unit of transpired water.
SUGAR
The positioning of the
stomata at the bottom of the
leaf allows it to co-ordinate
gas exchange in the spongy
mesophyll.
Closed => water-stressed,
no gas exchange
Open => CO2 in, H2O and
O2 leave
BIO A02 ā Module 1 Notes Hassan Alibhai
Plant Form and Function Page 19
Calvin Cycle: A Review
ā¢The Calvin cycle the light independent part of photosynthesis, in that it is responsible for the
conversion of carbon dioxide into glucose
ā¦It does this by first allowing carbon dioxide to access RUBISCO, the protein that drives the
cycle, and eventually converting it to Glyceraldehyde 3-phosphate, the āstarting pointā for
eventual glucose synthesis.
C3 Plant Photosynthesis
ā¢Recall that stomata, at the bottom of leaf cells, control gas exchange inside leaf cells.
Open Stomata Closed Stomata
Weather ā¢Moist
ā¢Less sunny
ā¢Dry
ā¢Very sunny
Effect ā¢Gas exchange occurs,
O2, CO2, and H2O
free to leave and
enter
ā¢Gas equilibrium
ā¢No gas exchange
ā¢RUBISCO ends up using most of the
carbon for the calvin cycle
ā¦Concentration of O2 increases
āŖForced photorespiration
Illustration 7: Rubisco has a square around it above.
Illustration 6: An overview of
photosynthesis.
43
BIOA02H3 Full Course Notes
Verified Note
43 documents
