Leaves
Leaves are parts of plants. In most plants, leaves are the major sites of
photosynthesis, the conversion of energy from sunlight into chemical energy (food).
Leaves take in carbon dioxide from the air and produce oxygen through stomata (tiny
pores in the leaf). Leaves come in many sizes and shapes; they are often used to help
identify plants. Some leaves are flat and wide; others are spiky and thin. Plant spines
(like cactus spines) are actually modified leaves. Leaves are also responsible for
respiration and transpiration.
Leaves may be simple or compound. Simple leaves have a single blade, while
compound leaves have several leaflets. Leaves are attached to the stem of a plant
with a short stalk called the petiole. Label and color the stem and petiole light brown
on Figure 1. The axil is the angle between the upper side of the stem and a leaf or
petiole. Label the axil on Figure 1. The small, paired appendages (sometimes leaf-life)
that are found at the base of the petiole of leaves of many flowering plants are called
stipules. Label the stipules on Figure 1 and color them yellow. The blade is the wide
portion of the leaf and it is also called the lamina. Color and label the lamina light
green in Figure 1. The outer tip of the blade is called the apex. The midrib is the
central rib of a leaf. It is usually continuous with the petiole. Label the apex and
midrib on Figure 1. Veins are made of vascular tissue (xylem and phloem). Veins
provide supports for the leaf and transport both water and food through the leaf.
The leaf margin is the edge of a leaf. The edge or margin of a leaf can also be
used to help identify the leaf. Leaves with rounded teeth on the margin are said to be
crenate. Label and color the crenate leaf orange in Figure 2. When the edge of a leaf
is smooth and does not have teeth or lobes it is said to be entire. Label and color the
leaf with an entire margin light green. The margin of a leaf may be divided into
rounded or pointed sections or incisions (cuts) that go less than halfway to the midrib.
This type of leaf margin is said to be lobed. Label and color the lobed leaf red. Cleft
margins are between the irregular teeth go more than halfway to the midrib. Label
the leaf with a cleft margin and color it dark green. When a leaf has small, pointy
teeth that point toward the tip of the leaf, it is said to have a serrate or toothed
margin. Elm leaves have serrate margins. Label the leaf with a serrate margin and
color it light brown.
The whole leaf looks green to us, but most of the cells and cell material are
colorless or clear. The green color comes from the chlorophyll molecules in the
chloroplasts. The upper surface of a leaf is covered with a waxy cuticle to prevent
water loss. A single layer of specialized flattened epidermal cells makes up the upper
and lower surfaces of the leaf. Label the upper and lower epidermis in Figure 3 and
color the cells pink. Below the upper epidermis are two layers of photosynthetic cells
called mesophyll cells. The top layer of mesophyll cells look like bricks standing up on
their ends. They are called palisade mesophyll cells and are the site of
photosynthesis. Label and color the palisade mesophyll cells light green on Figure 3.
Below the palisade mesophyll cells are the spongy mesophyll cells. These cells are
irregular in shape and have spaces between them called intercellular spaces. These
spaces are filled with gases like oxygen that the leaf is producing and carbon dioxide,
which the leaf is using. Label the intercellular spaces on Figure 3, and color and label
the spongy mesophyll cells dark green. Running through the leaf are the veins made up
of vascular tissue in a bundle. Xylem (water carrying tubes) are at the top of the
vascular bundle, while the phloem (food carrying tubes) are below xylem in the vascular
bundle in cross section of the leaf. Label the xylem and color it light blue in Figure 3.
Color and label the phloem dark blue in Figure 3. On the lower epidermis of the leaf
are openings for gas exchange called stomata. Label a stoma on Figure 3. On either
side of the stomata are two cells called guard cells that help open and close the
stomata so the plant will not lose too much water in the heat of the day. Water loss
from leaves is called transpiration and causes the plant to wilt as it loses turgor
pressure and the cell membrane pulls away from the plant cell walls. Label and color
the guard cells violet in Figure 3.
The petiole of the leaf attaches to the stem at a place called the node. The
distance between one node (site of leaf attachment) and the next node on a stem is
called the internode. Label the node and internode on Figure 4. Above the node will be
a bud called the axillary bud. Axillary buds are found at the base of leaves, but not
leaflets in compound leaves. Label and color the axillary buds in Figure 4 yellow. When
a leaf falls off a tree in fall, the process is called abscission. The petiole leaves a
moon-shaped scar with small dots where the veins connected to the stem. This scar is
known as the leaf scar and is used in winter identification of leaves. Label and color
the leaf scars red on Figure 4. Leaves are modified in some plants to do certain jobs.
In cactus, leaves are modified into spines or thorns for protection and to prevent
water loss through transpiration. Some climbing plants have leaves modified into
tendrils that can curl around surfaces and allow the plant to climb higher to reach
more sunlight for photosynthesis. Label the modified leaves in Figure 5. Color the
thorns orange and the tendrils blue.
Flowers & Their life Cycles
A flower is a specialized reproductive structure in angiosperms
(flowering plants). The male and female gametophytes develop within the
flowers, which promote pollination (the spreading of pollen from the male
to the female part of a flower) and fertilization (the sperm and egg
joining to form a zygote) more efficiently. The female reproductive part
of a flower provides a pathway that enables sperm to reach and fertilize
the eggs but does not require the sperm to swim through water.
Flower parts are arranged in four concentric whorls, one inside the
other. The outermost whorl consists of sepals. Sepals may appear leaf
like or be the same color and shape as petals. Sepals are always below the
petals and enclose and protect the flower bud. Label and color the sepals
dark green. All sepals together formed a whorl called the calyx. The
second whorl consists of petals and is called the corolla. Add a bracket to
the flower diagram and Color and label the calyx and the corolla. The
petals in animal pollinated flowers are usually brightly colored with nice
scents to attract their pollinators. Insects, bats, and some mammals help
spread pollen as they feed on nectar from the flower. Color and label the
petals orange. In dicot flowers, the floral parts are in multiples of 4's or
5's, while monocot floral parts are in multiples of 3.
The third whorl consists of the male part of the plant called the
stamens. Stamens produce pollen in sacs at the top called anthers.
Anthers are supported on a stalk like structure called the filament. Color
and label the anthers yellow and the filaments light green. Place a
bracket and label the stamens. The fourth and innermost whorl consists
of the female part of the flower called the pistil. The pistil has a sticky
top called the stigma that may also serve as a landing platform for insects.
A stalk called the style is found below the stigma. The style widens into
a swollen portion at the base called the ovary. The eggs or ovules are
found inside the ovary.
When wind, water, or insects spread pollen to the stigma of a flower,
pollination occurs. If the pollen stays on the same flower or a flower on
the same plant, self-pollination occurs. Cros-pollination occurs whenever
the pollen is transferred to a flower on another plant. The pollen grain
contains sperm cells, which must reach the eggs (ovules) at the base of
the pistil to fertilize them. Label the pollen grains on the picture of the
pistil and color them yellow. To do this, a pollen tube forms from the
pollen grain that goes down the style and to the opening in the ovary called
the micropyle. Label the pollen tube and color it light green. Color and
label the micropyle a color of your choice. Once the tube forms, the
sperm travels down the tube and fertilizes the egg or ovule to form a
zygote. Label the ovule on the pistil drawing and color it dark green.
Following fertilization, seeds with a tiny plant embryo form inside the
ovary.
Some flowers are called compound flowers or composites. The
amazing thing that composites have done is to miniaturize and simplify
each flower, then pack a number of these tiny flowers on their ends next
to one another, on a platform called a receptacle, and finally to organize
the whole resulting cluster so that the many flowers look like just one
flower. Color and label the receptacle light green on the composite
flower diagram. Sunflowers are examples of composite flowers. The
composite 'flower" is actually two kinds of flowers. The two compositeflower types are usually known as disk flowers and ray flowers. The
"flower's" broad central area is composed of hundreds of disk flowers,
and the yellow "petals" are the ray flowers. Color and label the disk
flowers brown and the ray flowers yellow on the composite flower diagram.
Composite flower heads bear scale-like bracts, which are usually green and
overlapping. Bracts are just modified leaves. Label and color the bracts
dark green on the composite flower.
Comparing Monocots and Dicots
Both monocot and dicot seeds develop in similar ways and have the same parts. There
are a few minor differences: monocots start out with one seed leaf, while dicots have
two. The technical word for seed leaf is cotyledon: you can find it on the coloring sheet;
it is the first leaf to emerge from a developing seed. Color all the cotyledons (A) on the
seeds dark green. As a seed, both monocots and dicots are covered by a seed coat.
Color the seed coat (B) yellow.
The seed consists of the outside seed coat and a large area called the endosperm which
functions as a source of reserve materials and food for the developing embryo. As
germination occurs, the endosperm will be broken down and used by the plant. Color the
endosperm blue (C).
Germination occurs when the seed begins to sprout, usually in the spring and under
appropriate conditions the radicle, the part of the seed that will become the root, begins
to elongate and grow downward. Color the root brown (D). Meanwhile, the coleoptile
begins to grow upward. The coleoptile is a sheath that encloses the shoot of the embryo.
The primary function of the coleoptile is to provide protection to the developing shoot as
it is passing through the soil. Color the coleoptile orange (E). Extending out from the
coleoptile is the shoot. Color the shoot purple (F).
Eventually adult leaves grow on the plant. Color these leaves light green. (G)
Comparing Adult Monocots and Dicots
Angiosperms are divided into two classes, the monocots and the dicots. The majority of
flowering plants are dicots. Dicots include maples, oaks, and magnolias. Monocots are
grasses, wheat, corn, and rice. Most of our food supply comes from monocots. The
diagram compares the differences between the two.
First of all look at the roots. The root of a monocot is called a fibrous root and the root
of a dicot is a taproot. Notice how taproots have one main part – called the primary
root. In a taproot the primary root grows very large and small roots spread out from it.
Fibrous roots, on the other hand, do not have very large primary roots, and many small
roots develop and remain near the surface. Color the taproot dark brown and the
fibrous root light brown.
Monocots and dicots also differ in their leaf structure. Adult monocots usually have
parallel venation, whereas dicots have net-like venation. For monocots and dicots, color
the leaves green and outline the veins in a darker green. The flowers of monocots and
dicots differ in the number of petals they have. Monocots tend to have flower parts that
occur in 3’s ( 3, 6, 9, 12…). Dicot flowers usually have 4 to 5 petals.
Monocot and dicots also differ in the way their vascular systems are arranged. In
monocots, the vascular bundles are scattered throughout the stem. In dicots, the
vascular bundles are arranged in a ring. Color the vascular bundles in both types of
plants purple (V), color the stems green.
Flower Structure and Reproduction
Flowers are the plant's reproductive structures. Angiosperms are
types of plants that bear fruits and flowers. Flowers are usually both
male and female and are brightly colored to attract insects to help them
carry pollen used for sexual reproduction. Not all flowers are colorful,
though. These flowers usually use the wind for pollination.
Parts of the Flower
The receptacle is the part of the branch on which a flower forms.
Color and label the receptacle (B) brown. Sepals are leaf like structures
that surround and protect the flower before it blooms. Color and label
the sepals (C) green. Petals are the colorful part of the flower that
attracts insects and even other small animals, such as mice, birds, and
bats. Color and label the petals (D) a bright color of your choice. All
flowering plants have flowers, but some are not brightly colored. The
petals of these flowers are reduced or absent, and the plant relies on the
wind or water for pollination.
The flower has both male and female reproductive parts. The
female reproductive structures are called carpels. In most flowers, the
carpels are fused together to form a pistil. Color and label the pistil (P)
pink. The pistil has three parts, which can be seen, in the box labeled
"pistil.” The stigma at the top is often sticky and is where the pollen
attaches. Color and label the stigma (J) purple. The style is the long
tube that attaches the stigma to the ovary. Color and label the style (K)
red. Sperm from the pollen will travel down this tube to the ovules. The
ovules, or eggs, are stored in the ovary until they are fertilized. Color
and label the ovary (L) pink. Plants can only fertilize eggs of the same
species. Special chemicals prevent sperm from fertilizing the eggs of
flowers that are not the same kind. Color and label the ovules (O) black.
The male reproductive structures are called the stamens. Color and
label the stamens (H) blue. Each stamen consists of an anther (A), which
produces pollen, and a filament (F), which supports the anther. In the box
labeled "stamen" Color and label the anther dark blue, and the filament
light blue. The anther produces pollen. Insects or other animals carry
pollen to the pistil of another flower where it may fertilize the eggs.
The other flowers in the picture follow the same plan, although they
come in many different colors and styles. Color and label each of the
flowers according to the colors above (blue for stamen, pink for pistil,
bright colors for the petals. etc.). Note that in some of the flowers, not
all the structures are visible.
Plant Reproduction
Sexual reproduction in plants occurs when the pollen from an anther
is transferred to the stigma. Plants can fertilize themselves. This is
called self-fertilization. Self-fertilization occurs when the pollen from an
anther fertilizes the eggs on the same flower. Cross-fertilization
occurs when the pollen is transferred to the stigma of an entirely
different plant.
When the ovules are fertilized, they will develop into seeds. The
petals of the flower fall off leaving only the ovary behind, which will
develop into a fruit. There are many different kinds of fruits, including
apples, oranges, and peaches. A fruit is any structure that encloses and
protects a seed, so fruits are also "helicopters,” acorns, and bean pods.
When you eat a fruit, you are actually eating the ovary of the flower.