Transcript ppt - Coastalzone

Photosynthesis
Leaf Functions
Transpiration
• Most water loss occurs through stoma, as
gas exchange (necessary for phtosynthesis)
occurs through stoma water is lost through
evaporation
• Factors effecting transpiration rate - high
temperatures, bright light, low humidity all
increase rate
• Cools plant by shedding heat (remember
specific heat of water?)
Guttation
• Loss of liquid water
• occurs when water is available but
transpiration is low
• stoma close but plant continues to absorb
water (wet plants in morning)
Abscission
• Allows deciduous trees to survive drought
and winter
• low temperature and low moisture cause
plant metabolism to slow down. No need
for leaves…
• Plant reabsorbs sugars, starches from leaves
• Abscission zone (pg 535)
Tension-cohesion mechanism
• Water is pulled up the stem of a tree by the
suction caused by the evaporative loss of
water through the leaves
• Column of water is unbroken because of the
cohesive and adhesive tendencies of water
molecules
• page 550-551
Photosynthesis
• 1st Law of Thermodynamics ?
• 2nd Law of Thermodynamics?
• Entropy - the measure of disorder in a
system
• Free energy - the amount of energy avilable
to do work
Chemical Reactions
• Exergonic - release energy
• Endergonic - absorb energy, require energy
for reaction to occur
• some chemical reactions can be reversed!
• Dynamic equilibrium
Adenosine triphosphate (ATP)
• Modified nucleotide (related to DNA and
RNA) with 3 inorganic phosphate groups
attached at one end of molecule
• Phosphate groups are readily attached
(endergonic) or detached (exergonic) by
adding water.
Activation energy
• Is the energy required to initiate a reaction
• Enzymes are biological catalysts, that is, the
act to increase the rate of a chemical
reaction but are not consumed by it
• Enzymes are specific in that certain
enzymes work on certain reactions in a
certain order
Photosynthesis Links
• Enzymes act to increase the rate of a
reaction by lowering the activation energy
required.
• Visit http://khanda.unl.edu/~nikku/atp.html
for more info...
Photosynthesis
• Chlorophyll is a green pigment that absorbs
light in the first step in photosynthesis
• Pigments are located in sacks called
thylakoids within the chloroplasts of plant
cells. The thylakoids are stacked in groups
called grana
Light dependent reactions
• Chlorophyll absorbs light, energized
electrons flow from the chlorophyll
molecule
• energy is used by phosphorylate adenosine
diphosphate (ADP) to add a phospahte
group to form ATP
• some energy is used to split water molecule
Light Dependent Reactions
• Oxygen is released
• hydrogen combines with a molecule called
NADP+ that carries an extra electron to
form NADPH
• NADPH stores the sunlight as chemical
energy
• NADPH provides the energy to add the
phosphate group to ADP to form ATP
The Dark Reaction
• Carbon dioxide is not used in the light
dependent reactions and glucose is not
formed
• these are not light dependent activities
• Dark reactions = Calvin Cycle
• products of the light reactions are used to
form glucose
Photosynthesis and food
• All food comes from photosynthesis
• Plants allows us to harvest solar energy and
convert it into energy we can use
• Light energy is converted into chemical
energy which is converted into sugars and
starches
• oxygen is released
Energy
• Photosynthesis stores solar energy in the
forms of plants…wood….coal and
oil…ethanol…natural gas
Materials
• Solar energy converted into fibers…cotton,
wool… wood …paper…synthetic fibers
from petroleum….