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Photosynthesis and Plants
- What is photosynthesis?
- How are plants suitable for photosynthesis?
- Where, exactly, does it occur?
- How, roughly, does it happen?
- Why does it happen?
chapters 20-22, 30.2-.4, and 4.1-4.3 in text
What is photosynthesis?
Photosynthesis involves
the conversion of light energy into chemical energy.
The primary storage of this
chemical energy will be in
6 carbon sugars, usually glucose. →
6 H2O + 6 CO2 → C6H12O6 + 6 O2
So, we need water and carbon dioxide,
an input of energy,
(and to let out some oxygen):
Then energy will be stored in the bonds of the glucose.
- How are plants suitable for photosynthesis?
- root to obtain water and
minerals (and anchor plant)
- stem for transport and support
-buds where new growth
can occur (meristems)
- leaf to provide optimal situation
for photosynthesis,
including light exposure and
gas exchange.
Each has special tissues
to enable these specific uses.
(This is a dicotyledonous angiospermophyte)
Root
- epidermis covers the surfaces
- root hairs shown here ↓
- Minerals enter root
by active transport
- Water follows by osmosis
- Casparian strip:
tight junctions between
endodermis cells force
all materials to pass
through cytoplasmic
membranes before
entering xylem.
It also keeps water in the xylem,
building root pressure for water transport.
Stem
- phloem carries sugars
from leaves to rest of
plant.
- cambium is main site
of lateral (outward)
growth.
-Growth also builds
bark.
- Successive layers
of 2o xylem are the
“annular rings” or
heartwood.
- New length comes
from apical meristem.
- Capillary action is
the second step in
water transport.
Plant circulation vs mammal circulation
MAMMAL
Arterial and venous systems In one continuous circuit.
Powered by
cardiac contraction.
Circulatory system is closed.
Flow is one way,
ensured by valves in veins.
Flow rate impacted by water volume, heart
and vessel contraction, hormones….
Vessels have specialized tissue construction,
distinct from other tissues.
Provide for transport of water, essential nutrients, organics,
... and toxins.
http://www.phschool.com/science/biology_place/biocoach/images/cardio2/BlVesStr.jpg
http://ap-bio-patrick-steed.wikispaces.com/file/view/xylem__phloem.jpg/85280965/xylem__phloem.jpg
PLANT
Xylem and Phloem systems Two distinct pathways.
Powered by
transpiration or
mass water flow.
Xylem an open path, while
phloem a closed circuit.
Xylem is one way,
while phloem can reverse.
Flow rate dependant mostly
on water volume
http://www.inclinehs.org/smb/Sungirls/images/monocot%20leaf.JPG
http://www.sbs.utexas.edu/bio406d/images/pics/poa/Arundo%20donax%20leaf5.jpg
Leaf
- Primary site of photosynthesis
therefore,
- primary site of gas exchange
- Requires vascular tissue
to bring nutrients to leaf,
and carry products away.
Monocotyledonous angiosperms ↑
(like wheat, corn,... tulips)
have parallel veins.
←Dicotyledonous angiosperms
(like sunflowers, ivy.... tulip poplars)
have branched veins.
Leaf (cont.)
You should be able to
identify the following:
cuticle
upper epidermis
palisade mesophyll
(mostly photosynthesis)
spongy mesophyll
(mostly gas exchange)
vein, with
xylem (carries water)
phloem (carries sugars)
lower epidermis
stoma,
(port for gas exchange, and
for transpiration, the last step
in water transport)
bounded by
guard cells
http://kvhs.nbed.nb.ca/gallant/biology/leaf_structure.jpg
Where, exactly, does photosynthesis occur?
In chloroplasts within the mesophyllic leaf cells.
intermembrane space
inner membrane
outer membrane
granum
stroma site of
Calvin cycle, or light
independent
rxns.
thylakoid
site of lightdependent
reactions
lamella
lumen
What are the challenges of evolving from algae (aquatic protists) to plants on land?
1. Dehydration
While living in water there is still the problem of
water balance, but not like being surrounded by air.
2. Support
Aquatic algae are supported by the water.
3. Nutrient acquisition/gas exchange
These algae are surrounded by the nutrients they need,
suspended in the water itself.
4. Nutrient dispersal
Algae are generally small, or thin, and don’t have far
to move materials internally.
5. Dispersal of reproductive structures
Again, surrounded by water, reproductive cells are
hydrated and washed away, but on land…
These challenges were met in a step-wise progression,
reflected in modern examples.
Kingdom: Plantae
- photosynthetic
- cell walls
-complex multicellularity
-(In plants
these are “divisions”,
not “phyla”)
bryophyta
↓
Vascular
Roots
Leaves
Seeds
Flowers
No
No
No
No
No
gymnosperms
↓
Yes
Yes
Yes
No
No
↑
pteridophytes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
↑
angiosperms
6 H2O + 6 CO2 → C6H12O6 + 6 O2
We have brought water from the roots,
via the xylem,
through stems,
to the leaves.
Carbon dioxide is entering leaves through the stomata,
and oxygen, when it is released,
leaves leaves via stomata.
Glucose, once made,
will be actively transported into the phloem,
and water will osmose after it to carry it where needed.
Now all we need to do now is capture the sunlight…
Adenosine TriPhosphate
will be used as an intermediate
in this solar-to-carbohydrate energy transfer.
ATP will ultimately be re-charged from ADP
when energy is released from the carbs
in cellular respiration
when the cell has business to do.
NADPH2 is the other battery, ferrying energized electrons.
far red↑
- Visible light is one part of the electromagnetic spectrum.
- The strongest absorption is in blue-violet (400-500nm)
and near red (650-700).
- The middle of the spectrum – green – is NOT absorbed:
It is reflected. Hence, plants appear green.
http://www.uic.edu/classes/bios/bios100/lecturesf04am/absorption-spectrum.jpg
The absorption spectrum of selected plant pigments:
- How, actually,
does it happen?
- The chloroplast is the
site of photosynthesis
in eukaryotes.
- Two chief parts:
“photo-”
light-dependent reactions
in thylakoid
membranes,
“-synthesis”
light-independent reactions
(aka Calvin cycle)
in stroma.
- note ATP/ADP and
NADPH/NADP+ bridging the two
- note two photosystems
(II comes before I) for light energy capture.
- note electron transport chain
http://www.55a.net/firas/ar_photo/11/photosynthesis-overview.gif
-Light absorbed by
chlorophyll a in
photosystem II:
-An e- is energized,
and handed off to the
electron transport chain.
- Water split, providing
e- to replace them, with
O2 off as waste.
-ETC pumps protons into
the thylakoid lumen.
-Light absorbed by
chlorophyll a in
photosystem I
-e- are re-energized,
and handed off to NADP+,
which is reduced to NADPH
- The proton motive force powers ATP synthase, in
photophosphorylation.
http://cache.eb.com/eb/image?id=72207&rendTypeId=35
1. Light-dependent reactions
- Carbon fixation:
- CO2 is attached
to a 5C molecule
(H comes from
light-dependent
reactions.)
2. Light-independent reactions
- The intermediate
falls into two 3C units
which are reduced
by ATP and NADPH.
- every third time around
a 3C molecule is spun off,
which may become glucose
and other molecules.
- Another ATP is invested to replace
the original 5C molecule.
* “probably the most abundant protein on Earth”
How can we know if photosynthesis is taking place?
6 CO2 + 6 H2O → C6H12O6 + 6 O2
-------------------------------------------------------------------
Directly:
1. Measure the CO2 consumed.
2. Measure the O2 generated.
Indirectly
3. Determine the net increase in biomass.
4. Measure the reduction of NADP+ by providing a
colorimetric substitute for NADP+...(?)
What do you think would influence the rate of photosynthesis?
What would be the effect…, and why?
light? (intensity, duration)? temperature? pH? CO2 levels? ....
www.climateaudit.org/?p=884
http://www.marietta.edu/~spilatrs/biol103/photolab/rspCrve.gif
generalhorticulture.tamu.edu/.../light.html
Variations on a theme….
Oxygen actually binds to Rubisco more readily than does CO2,
so in low CO2 (like stomata closed to conserve water)
O2 is taken into the Calvin cycle, and CO2 is released:
Called photorespiration, but generates no ATP. Ouch.
Dry environments cause problems for photosynthesis:
Two specialized alternative photosynthetic adaptations
that you will want to know…
C4 pathway:
In arid climates is helps to be able to just crack the windows:
In order to increase the carbon locally available to the Rubisco
carbon is first fixed, more aggressively (to PEP by PEP carboxylase),
resulting in a 4-C molecule.
This is carried to bundle sheath cells around the leaf vein,
(which is where the Calvin cycle occurs in these plants)
and C is handed off into the Calvin cycle.
← Most commonly seen in corn,
sugar cane and other grasses.
www.steve.gb.com/science/photorespiration.html
CAM pathway:
Another route is to simply close the windows during the day:
By attaching the CO2 to some other organic molecule at night,
and then releasing it to Rubisco in the presence of light,
while the stomata are closed:
In both C4 and CAM carbon is first fixed by some other molecule:
- is C4 this is separated from Calvin by space (structural).
- in CAM they are separated by time.
Found in pineapples ↑
and cacti.
How do water, carbon, and
nitrogen enter a plant?
Trace energy’s path from sun to glucose.
Write the balanced equation for photosynthesis,
and describe where each component comes from
and/or goes to.
What are the structure and function
of the major plant parts.
How do you predict amount of light,
wavelength of light,
amount of CO2,
or temperature change
would influence rate of photosynthesis?
Benchmark SC.912.L.14.7
Relate the structure
of each of the major plant organs and tissues
to physiological processes.
Benchmark SC.912.L.14.36
Describe the factors
affecting blood flow
through the cardiovascular system.
Enduring Understandings
Organism development
facilitates efficient
metabolic processes. (?)
Essential Questions
How have the structures
and functions of plants
enabled them to survive?
Photosynthesis
capillary action
lumen
6 H2O + 6 CO2 → C6H12O6 + 6 O2
gas exchange
ATP
root
vascular tissue
ADP
stem
monocot
absorption spectrum
bud
dicot
pigment
meristem
cuticle
eukaryote
leaf
upper epidermis
light-dependent reactions
epidermis
palisade mesophyll
light-independent reactions
root hair
spongy mesophyll
Calvin cycle
active transport
vein
chlorophyll a
osmosis
lower epidermis
photosystem II:
Casparian strip
stoma
electron transport chain
endodermis
guard cell
photosystem I
xylem
chloroplast
NADPH
phloem
outer membrane
ATP synthase
cambium
stroma
photophosphorylation
bark
granum
carbon fixation
C4 pathway
heartwood
thylakoid
CAM pathway
stomata
guard cell
chemical reaction
reactants
products
conservation of mass
photosynthesis
chlorophyll
chloroplast
grana
stroma
thylakoid membrane
glucose