Photosynthesis
-energy producing process in AUTOTROPHS
-autotrophs are organisms that produce their own food
they are “self feeding”, ex: plants, algae, some bacteria
Making Your Own Food Requires:
-the intake of sunlight energy
-pigments (specifically Chlorophyll) found in cells of
autotrophs capture the light and use it to start the
photosynthesis reaction
-Chlorophyll is found in chloroplasts and is what makes the
plant green.
-Most chlorophyll is found in leaf material so most of the
photosynthesis that takes place happens in the leaf
The overall reaction for photosynthesis requires:
sunlight
water
carbon dioxide (you exhale during respiration)
And produces:
sugar
water
oxygen (you inhale during respiration)
Here’s how it all happens:
http://hosho.ees.hokudai.ac.jp/~tsuyu/figs/photosynthesis.gif
-white light colors are the colors of the
rainbow…red, orange, yellow, green, blue,
indigo and violet…ROYGBIV
-chlorophyll in plants absorbs the ends of
the spectrum better and reflects the green
in the middle. That is why we see plants
as being green…they reflect the green
wavelength
First step is called the LIGHT REACTION:
-as it’s name implies…it requires light!!
-not just any light will do…it has to be a specific wavelength
-notice how light in the
500 to 600 nm range is
not absorbed in any
great amount…WHY?
--green plant pigment
prefers light in the 400450 nm range and the
600-680 range.
http://1.bp.blogspot.com/_dB8l7L29Rvc/TTwNMD9gXeI/AAAAAAAAABg/RQt
motqGgDk/s1600/Chlorophyll-Absorption-Spectrum.jpg
Light reaction:
-uses sunlight to split water into H and O
-sunlight is captured by the chlorophyll in a chloroplast
-the energy in the light molecule is used to break apart
water molecules and releases some heat
-Oxygen that results from this split is given off as a
by-product that you use to breathe
-the Hydrogen is “captured” by an enzyme, NADP+ in the plant cell and
transported to the next step of the photosynthesis reaction as NADPH
-some ATP is made
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lightrxn.gif
The Dark Reaction (or Calvin Cycle) is the 2nd step in PS:
-NADPH comes from the
Light reaction to the
site of dark reaction to
“drop off” the hydrogen
collected
-CO2 from the air is used
to combine with the H
and produce a sugar
molecule (CH2O)n
-the NADP+ returns to
the light reaction to get
another H
-ATP is used to provide
some energy to make
the sugar
-If the Calvin Cycle does
not happen, no sugar is
made
http://2.bp.blogspot.com/_ADtjVgTw6Q/TSjL4DyUnhI/AAAAAAAAACs/xg261s8seQM/s1600/calvin_cycle.jpg
Just a few notes…
-the light reaction must have light to occur…this means
plants do not photosynthesize at night
-plants must have chlorophyll to photosynthesize…this
means that flowers, red, orange and yellow leaves, etc.
are not capable of making sugar
-the dark reaction can happen in the light…it just does
not need light to happen…it only needs the product of
the light reaction
-so…without light the dark reaction can only happen
for a short amount of time before the plant runs out
of H and cannot continue to make sugar
Application: When hay is harvested, it is always higher in
sugar content if harvested after lunch, rather than
before.
Explain…?
How do plants get gasses into and out of the cells for PS?
STOMATA (stoma singular)– small openings on the underside
of plant leaves that let air pass into and out of the plant. They
are controlled by GUARD CELLS that sense atmosphere
conditions which may cause water loss and close up the stoma
Why do you think the stoma are on the underside of the leaf?
Open
stomata
Guard
Cells are
cupped
Closed
stomata
Guard
cells are
stretched
out
Most plants we are familiar with use Carbon Dioxide directly from
The air. These are called C3 plants. Many are very important in
agriculture: soybeans, wheat, oats and rice.
In times of drought or extreme heat
These plants shut their stomata and
then do not make sugar. This in
return causes a low yield. Farmers
usually grow these under irrigated
conditions to insure they get a good
crop. How does irrigation help keep
the plant photosynthesizing?
Why can these plants not make
sugar after they shut their stomata?
What are the missing ingredients?
Some plants have adapted over the years (millions by evolution)
to drought…they
don’t rely on the C3 process to make sugar.
Instead they use different pathways and ingredients.
C4 plants have an enzyme that can find Carbon Dioxide inside
the leaf, even when the stomata are closed. This allows them
to continue making sugars even when conditions are hot and
dry and minimize water loss.
Examples: corn, sorghum, sugar cane…all tropical in origin and
important in agriculture.
http://cenblog.org/cleantechchemistry/files/2010/08/shutterstock57605581.jpg
CAM plants can close their stomata during the day and still
photosynthesize because they collect their Carbon Dioxide at
night and convert it to an acid. They store the acid and then use
the carbon molecules the next day for sugar making but don’t
have to worry about losing water.
CAM stands for Crassulacean Acid Metabolism, the acid that the
Carbon is stored in.
Most plants in this category are Succulents…they have thick,
leaves filled with a juicy tissue such as aloe, cacti and jade.
Agave also fits in this category. Do you know what agave is
used for??
Do any of
these
plants
have
leaves?
How does photosynthesis affect the environment??
-many fossil fuels give off Carbon products as they burn
-power plants
-auto exhaust
-fireplaces
-factories
Autotrophs act as a sink to soak up all the extra Carbon Dioxide in
the atmosphere so it doesn’t cause problems. When you
plant trees and grass and flowers, you are part of the
solution.
The lumber industry, urban growth, rainforest destruction all
remove autotrophs from the environment. If you take part
in or use products of these activities, you are part of the
pollution!!
Many species are also lost in the destruction. Some of these will
never recover and future generations will never see them.
In addition, many drugs come from plants. Species destruction
may keep us from finding a cure for disease someday.
The Greenhouse Effect is a large problem:
-rays from the sun reflect off the Earth and into space
-pollution in the air keeps many of these rays from reflecting
and they reradiate until they can escape
-this extra heat from the rays causes an increase in the
surface temperature of the Earth, which in turn causes
many different environmental problems
-CO2 has increased by about 30% in the atmosphere.
This has led to Global Warming:
-warming of the Earth’s surface and oceans
-causes some species to die out
-ice melting at the polar caps
-changing weather patterns
-increased number of tropical storms and ‘canes
-won’t know extent of damage for many years
DO SOMETHING GOOD...PLANT A TREE!!!
http://climatecommission.gov.au/wp-content/uploads/greenhouse_effect2.jpg