Download slide 2: green leaf (350x)

PHOTOSYNTHESIS MICROVIEWER (SET 59)
Please DO NOT WRITE ON THIS SHEET!
INTRODUCTION:
Green plants are the source of all our food. They are autotrophic. This means they
can use energy from the Sun to create chemical energy through the process of
photosynthesis.
Plants are like a very efficient factory. They take in carbon dioxide from the air and
water from the soil. These are their raw materials. Then they use sunlight as fuel
and chloroplasts as their machines to make sugar. Sugar is the main product of the
factory and is usually stored until it is needed. Further, the factory creates a waste
product, Oxygen, which it releases as a gas.
We often sum up photosynthesis with the following equation:
In these slides we will examine how this remarkable food factory works.
SLIDE 1: GREEN LEAF (100X)
On this slide we have a cross-section view of the leaf of a Maple tree.
The leaf is protected by two unique structures. First, the cuticle is a waxy layer that
coats the leaf. This layer helps prevent water loss. Second, the epidermis is a
single layer of cells. Within the epidermis is the part of the leaf that plays the most
important part in the making of food. This layer is called the mesophyll layer.
Notice that this layer has many spaces (A) to allow for the circulation of air. Also
notice that within this layer is a bundle of dark green and red cells (B). This is a
vein (vascular bundle) that transports food and water through the leaf.
SLIDE 2: GREEN LEAF (350X)
Let us examine the leaf at a higher magnification using special stains to allow certain
parts of the leaf to stand out sharply for you.
PHOTOSYNTHESIS MICROVIEWER (SET 59)
As you look at the slide notice the upper epidermis (A) protects the leaf. The next
layer below is the mesophyll. This is divided into the palisade (B) and spongy (C)
layers, which have many dark red bodies. These dark red bodies are chloroplasts
(that have been dyed for better visibility.) Chloroplasts are special organelles
within the cell that contain chlorophyll. Chlorophyll is a pigment necessary for
photosynthesis. Chloroplasts also contain many special enzymes that catalyze the
reactions necessary for photosynthesis. Chloroplasts are unique in that they have the
ability to convert the energy in sunlight into chemical energy. They then use this
energy to turn carbon dioxide and water into sugar. Later, sugar can be further
converted into starch, fat, and protein.
As you continue to look at the slide notice that within the spongy mesophyll (C)
there are large clear spaces (D). These allow air to circulate. Remember that in a
leaf carbon dioxide comes in and oxygen leaves. Below the mesophyll layer is the
lower epidermis (E). The lower epidermis is basically the same as the upper one
except for one major difference. The lower epidermis has small pores called stomata
(S). The stomata allow air to move in and out of the leaf. Each stoma (singular for
stomata) is bordered by two guard cells that regulate when the stoma opens and
closes. As seen at (S), the guard cells have shrunk, closing the stoma. When the
guard cells swell with water, the stoma opens permitting air to enter or leave the leaf.
SLIDE 3: ROOT HAIR (35X)
This is the tip of a root of a plant, about 1/16 of an inch from the end. The fine hairlike extensions are root hairs. They help the root absorb water containing dissolved
minerals from the soil. Each root hair is part of a cell of the outer surface of the root
tip. They serve to give the root enormous surface for the absorption of water. In
transplanting a plant, careless handling destroys millions of these root hairs. Until it
develops new root hairs, the plant does not grow well.
SLIDE 4: VASCULAR BUNDLES (145X)
This is a cross-section of a corn stalk looking down into a bundle of tubular cells.
The bundle (A) is called a vascular bundle or vein. Its cells form continuous tubes
from the roots to the leaves.
PHOTOSYNTHESIS MICROVIEWER (SET 59)
The smaller cells (B) are called phloem, and their function is to carry food from one
place to another, usually down the leaf. The larger cells (C), called xylem,
specialize in carrying water from the soil upward. The minerals dissolved in the
water are necessary for life. Most of the corn stem is made up of cells (D) that store
food.
SLIDE 5: LEAF – WITH AND WITHOUT SUNLIGHT
This slide shows the results of an experiment. The objective of the experiment was
to determine the effect of sunlight on a green leaf.
In the experiment the entire leaf was placed in sunlight for three hours, however the
upper right half of the leaf was covered with a black cloth blocking out the sunlight.
Then, the leaf was treated and dyed with iodine. Iodine turns brownish black in the
presence of starch.
As you look at the slide notice that the upper right side is much lighter in color. This
is due to the fact that it was covered with black cloth. Therefore it was unable to
complete photosynthesis. Because it was unable to complete photosynthesis no
starch was made (remember that sugar is converted into starch for storage.)
This experiment proves that plants need sunlight to complete photosynthesis.
SLIDE 6: VARIEGATED LEAF (35X)
This slide looks very similar to slide #5, however it is quite different. This slide
shows the results of a different experiment. The objective of the experiment was to
determine whether chloroplasts are necessary for photosynthesis.
Variegated leaves are striped. You have probably seen them before. They are
mostly green with white stripes or spots. The green portion of the plant contains
chloroplasts while the white portion does not. As
you look at the slide the left half of the leaf was
green while the right half was white.
After three hours in bright sunlight the leaf was
treated and dyed with iodine. Iodine turns brownish
black in the presence of starch.
PHOTOSYNTHESIS MICROVIEWER (SET 59)
Look at the slide again. Did the green (left) or white (right) turn black? What does
this experiment prove?
SLIDE 7: STARCH GRAINS (135X)
Many of the foods we eat contain starch. Although plants make sugar during
photosynthesis they often convert it to starch, because it is stable and easily stored.
Shown on this slide are different starch grains from rice, wheat, barley, beans and
potatoes. These different starch grains reflect polarized light at different angles.
Notice how the polarized light creates different cross patterns in the various starch
grains.
Scientists often use polarized light to identify the type of plant, which made the
starch.
SLIDE 8: BEAN SEED (2X)
This is one half of a germinating bean seed. It is just beginning to form a new plant
and the developing embryo may be seen at (E). The lower part of the embryo will
form the root and stem of the plant. In the upper part, the design of the embryo leaf
is visible.
A large supply of food for the developing plant is stored in the entire dark mass – the
cotyledon. The cotyledon has been stained with iodine. Observe the color. What
does it indicate?
CONCLUSION
Throughout these slides you have been presented with the fundamental parts of a
plant. From the roots, which absorb water, to the stomata, which bring in carbon
dioxide, hopefully you have found that all of the parts of a plant are essential to
photosynthesis.
As you move forward through your studies the next step will be to examine the inner
workings of the leaf. To zoom into a mesophyll cell, hijack a chloroplast and start
exploring!