Transcript Looking at leaf stomata and plant pigments

Looking at leaf stomata
and plant pigments
Bloody Chlorophyll
Sunlight is white light that is actually a mixture of different wavelengths of light
from the visible light spectrum. Photosynthetic plants gather energy from sunlight
through the use of light-absorbing pigments. The plants use this energy to power
the synthesis of organic molecules.
Chlorophyll is the green pigment in the chloroplasts of most plants. Chlorophyll
absorbs light very well in the red and blue-violet regions of the visible spectrum,
but it does not absorb green light very well. Green light is instead reflected, which
is why chlorophyll, and the leaves of plants where it is found, appear green.
When chlorophyll absorbs energy in the form of light, most of that energy transfers
directly to the electrons in the chlorophyll molecule. This raises the electrons to
higher energy levels. These high-energy electrons that do the work of
photosynthesis pass on to carrier molecules such as NADP+ to form NADPH in the
electron transport chain. Thus the light energy is trapped in a chemical form.
In this demonstration we remove chlorophyll from the chloroplasts of plant cells
and place it in a solution of ethanol. When we excite the electrons of the chlorophyll
molecules with the black light (ultraviolet light), in the absence of the electron
transport chain the electrons release their energy in the form of red light as they
return to their ground state.
Things to consider…
1. You can use chlorophyll fluorescence to measure
photosynthesis.
2. You can also use chlorophyll fluorescence to
measure plant stress, since these stresses typically
impact the plant’s metabolism and create an
imbalance between the amount of energy absorbed
by the chlorophyll and the use of this energy in
photosynthesis.
Are there other pigments in
plants besides chlorophyll?
Paper chromatography is a process that uses special
filter paper to separate and identify the different
substances in a mixture. Chromatography means “to
write with color.”
The substances in a mixture dissolve in alcohol and
move up the paper. Heavier substances move up the
paper more slowly, while lighter substances move up
the paper more quickly. Because of this, heavy and
light substances get separated from one another on the
paper.
From: http://www.biologyjunction.com/biology_projects.htm
Leaf Pigment
Chromatography
1. Obtain a strip of chromatography paper.
2. Use a ruler and draw a light PENCIL line 2 cm
above the bottom of the paper strip.
3. Wrap a leaf around a coin with the waxy side of the
leaf facing outward. Now rub the leaf along the
pencil line on the paper strip until you make a dark
green line. DO NOT RUB THE LEAF ABOVE OR
BELOW THE LINE!
Leaf Pigment
Chromatography
4. Wrap the top of the paper strip around a pencil so
that the end of the strip with the green line hangs
down. The pencil should be able to sit across the
top of the beaker with the bottom of the paper strip
just touching the bottom of the beaker. Cut off any
excess paper from the TOP of the strip if it is too
long. DO NOT CUT THE BOTTOM OF THE
STRIP WITH THE GREEN LINE!
5. Remove the pencil and paper strip from the beaker.
Leaf Pigment
Chromatography
6. Carefully add isopropyl alcohol to the beaker until
it reaches a depth of 1 cm in the beaker.
7. Lay the pencil across the top of the beaker with the
paper strip extending into the alcohol. MAKE
SURE THAT THE LEVEL OF ALCOHOL IS
BELOW THE GREEN LINE ON YOUR STRIP!
8. Observe as the alcohol gets absorbed and travels
up the paper. This may take up to 20 minutes. Do
not touch your experiment during this time.
Leaf Pigment Chromatography
Observations
Using colored pencils, draw your results in your
research notebook:
Before paper
chromatography
After paper
chromatography
Questions to consider…
1.
Why is paper chromatography an appropriate technique to
use to determine if different pigments are present in a leaf?
2.
How does paper chromatography work?
3.
Did the leaf you tested contain different pigments? How do
you know?
4.
Why do you think leaves tend to change color in the fall?
5.
Leaves in New England change color in the fall. However
leaves in Florida do not. Why do you think this happens?
6.
What are the names of other pigments that plants contain and
what color are they? (You might need to Google this one!)
What is the role of stomata
in leaves?
From:
http://www.biologyjunction.com/leaf_stomat
a_lab.htm
Plants have special pores called stomata to allow passage of
material. The stomata pores are surrounded on both sides by
jellybean shaped cells called guard cells. Unlike other plant
epidermal cells, the guard cells contain chlorophyll to do
photosynthesis. This allows the cells to expand/ contract to open
or close the stomata.
Guard cells also close when dehydrated. This keeps water in the
plant from escaping. The opening or closing of guard cells can be
viewed in a microscope by adding different water concentration
to the leaf tissue.
Most stomata are on the lower epidermis of the leaves on plants
(bottom of the leaf). The number of stomata on the epidermal
surface can tell you a lot about a plant. Usually, a high
concentration of stomata indicates fast growth and wet
climate. Lower concentrations of stomata indicate lower rates of
photosynthesis and growth or adaptations for dry weather.
Leaf Stomata
1. Obtain a spinach leaf.
2. Paint a thick patch that is about 1 square centimeter
of clear nail polish on the under side of the leaf
surface.
3. Allow the nail polish to dry completely.
Leaf Stomata
4. Tape a piece of clear tape to the dried nail polish
patch.
5. Gently peel the nail polish patch from the leaf by
pulling on a corner of the tape and “peeling” the
fingernail polish off the leaf. This is the leaf
impression you will examine.
6. Place your impression to a clean microscope slide.
7. Examine the leaf impression under a microscope at
high power.
Leaf Stomata Observations
1. Search for areas where there are numerous stomata, and
where there are no dirt, thumb prints, damaged areas,
or large leaf veins. Draw the leaf surface with stomata.
2. Count all the stomata in one microscopic field. Record
the number in a data table.
3. Repeat counts for at least three other distinct
microscopic fields. Record all the counts. Determine an
average number per microscopic field.
4. From the average number/400X microscopic field,
calculate the stomata per mm2 by multiplying by 8.
Questions to consider
1. Explain, in detail, how guard cells open and close
stomata?
2. At what time of day would stomata be closed and why?
3. Why does the lower epidermis have more stomata than
the upper epidermis of a leaf?
4. What is transpiration?
5. What two gases move in and out of the leaf stomata?
6. What does a larger number of leaf stomata indicate
about the growing climate of that plant?