Download NOTES - Ch. 8 - Photosynthesis

All living things need energy.
Whether it’s the little
field mouse
or
The big ole owl
Energy is needed for all of life’s functions
for ALL forms of life.
Remember life functions?
Like reproduction, nutrition, transport,
respiration, regulation, excretion, growth …
Most cells have only a small amount of ATP, enough to last
for only a few seconds of activity.
Why is this?
Even though ATP is very efficient at transferring
energy, it is not very good for storing large amounts of
energy over the long term.
In fact, a single molecule of the sugar glucose stores
more than 90 times the chemical energy of a molecule
of ATP.
Therefore, it is more efficient for cells to keep only a
small supply of ATP on hand.
Cells can regenerate ATP from ADP as needed by
using the energy in carbohydrates like glucose.
But
where is that glucose coming
from?????
Some organisms are able to use a source of
energy, such as sunlight, to produce food
directly from simple inorganic molecules in the
environment.
These organisms are called:
AUTOTROPHS
There are:
photoautotrophs
Those that use the sunlight as their energy source
and
chemoautotrophs
Those that use inorganic chemicals for energy
PHOTOAUTOTROPHS
Let’s examine how sunlight is used as an energy
source.
“White Light” is a mixture of all of the different
wavelengths of light.
Remember the visible spectrum???
That’s made up of light visible to our eyes.
Like red, orange, yellow, green, blue, indigo and
violet.
The visible spectrum ranges from 380 nm (violet) to
700 nm (red)
Inside the plant, there are these structures called
CHLOROPLASTS
And inside the chloroplasts there are these colored
PIGMENTS
Which are colored substances that absorb or reflect
light.
The principal pigment of green plants is
Chlorophyll
Chlorophyll absorbs red and blue light but does not
absorb light in the in the middle region of the
spectrum
Chlorophyll a is the main photosynthetic pigment in
plants.
Thus….we see GREEN
Before we begin, we must discuss the structure where
photosynthesis occurs
The Chloroplast
Within each leaf there are many cells.
Within the cells are many oval shaped organelles
called chloroplasts.
Each chloroplast contains all the necessary
components needed for photosynthesis to take place.
Electron microgram of a chloroplast showing the
granum and the thylakoid membrane
The sun’s energy (light)
comes down on
photosynthetic
organisms, like plants
Although we always think of energy as waves, energy
also travels as particles called photons.
And, there are other pigments in plants besides
chlorophyll a
Like chlorophyll b and the carotenoids (the pigments
that give us the oranges and yellows of fall)
When photons of light strike pigments other than the
main pigment, chlorophyll a
They send that energy to chlorophyll a, the main
pigment.
By having other pigments, plants can use a broader
spectrum of light for photosynthesis
And now the process begins!
Photosynthesis is a two-step process.
Step one is called the light reactions or the light
dependent reactions.
The light reactions take place in the thylakoid
membrane of the chloroplast
In the light reaction the energy of sunlight is captured
and used to make energy-storing compounds.
The light reactions use water, ADP and NADP+ (an
electron carrier)
They produce O2 (which is of no help in photosynthesis
but is of great use to us)
and the energy-storing molecules ATP and NADPH.
The Light Reactions are so called because they require light to function.
1. Is absorbed
2. A water
molecule is
taken in and
then split
3. The oxygen
from splitting
water is released
4. High energy
molecules are formed
But
How is glucose formed?
Glucose is formed in the Dark Reactions (so
called because they do not require light)
from six molecules of carbon dioxide
The dark reactions are fueled by the high energy
molecules formed in the light reaction
ATP and NADPH
• The dark reactions take place in the stroma of the
chloroplast
Plants require carbohydrates or sugars for
survival and growth
The Calvin Cycle is a means of converting CO2,
energy rich molecules from the light reactions and
various intermediate molecules to produce these
needed sugars such as
GLUCOSE
CO2
ATP
Glucose
NADPH
Let’s look at an overview of the process of photosynthesis.
Let’s examine the chemical equation for photosynthesis.
What Factors Affect Photosynthesis
Because water is one of the raw materials of
photosynthesis, a shortage of water can slow or even
stop photosynthesis.
• Plants that live in dry conditions, such as desert plants
and conifers, have a waxy coating on their leaves that
reduces water loss
Temperature is also a factor.
• Photosynthesis depends on enzymes that function
best between 0°C and 35°C.
• Temperatures above or below this range may damage
the enzymes, slowing down the rate of
photosynthesis.
• At very low temperatures, photosynthesis may stop
entirely.
The conifers can carry out photosynthesis only on
sunny days
The intensity of light also affects the rate at which
photosynthesis occurs
As you might expect, increasing light intensity
increases the rate of photosynthesis.
After the light intensity reaches a certain level,
however, the plant reaches its maximum rate of
photosynthesis.
The level at which light intensity no longer affects
photosynthesis varies from plant type to plant type
Some Quick Plant Biology
Plant parts to remember for photosynthesis:
LEAVES:
Where photosynthesis takes place
STOMATA:
Located on the undersides of the leaves
Allows CO2 and O2 to diffuse into and out of the
leaf
GUARD CELLS:
Specialized cell in epidermis of plant that controls
the opening and closing of stomata by
responding to changes in water pressure
• VASCULAR TISSUES:
XYLEM: Carries water upward from the roots to
every part of a plant
PHLOEM: transports solutions of nutrients and
carbohydrates produced by photosynthesis.
Transport in Plants
• Root pressure forces water into the xylem, but
root pressure alone cannot account for the
movement of water and dissolved materials in
plants.
• ADHESION, COHESION AND CAPILLARITY.
• Water molecules are attracted to one another
by a force called COHESION.
• ADHESION is the interaction between
surfaces of DIFFERENT molecules
• The combination of cohesion and adhesion
explains the phenomenon known as
CAPILLARITY - the movement of water
upward in a small solid tube.
• TRANSPIRATION - Evaporation of water from
plant leaves
• Most evaporation/transpiration takes place
thru the STOMATES
SYMBIOTIC RELATIONSHIP
MYCORRHIZAE –
an association of roots and fungi
• The formation of mycorrhizae allows plants to
receive nutrients from the fungi, while the
fungi receive fixed carbon from the plant
roots.