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 4. Color the thorns orange and the
1. What is the stalk that joins the leaf to the stem called? ____________
2. How does water vapor escape from a leaf? What is the process called?___________________________________
3. Where would the greatest number of chloroplasts be found in a leaf?_________________________________________
4. What protects the surface of a plant from water loss? _______________
5. Why are the air spaces between the spongy mesophyll cells are important?__________________________________
6. When water is lost from a plant, why does the plant looked wilted?___________________________________________
7. What is the edge of a leaf called? ____________________________
8. If the edge of the leaf appears toothed, what type of leaf edge is this? ___________________________________
9. The smaller veins in the leaf connect to the _____________ of the leaf.
10. Leaves attach to a stem at a site called the ____________.
11. A(n) _________________ or scar appears at the base of the petiole where the petiole attaches to the stem.
12. Give 2 examples of modified leaves.____________________________________________________________
Figure 1 - Parts of a Leaf
Figure 2 – Leaf Margins
Figure 3 – Cross Section of a Leaf
Figure 4 – Twigs
Figure 5 – Leaf Modifications
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
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 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. Label and color 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. Label and color 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 stigma is found below the style. 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. Cross 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 grows down the style and to the opening in the ovary called the micropyle. Label the pollen tube and
color it light green. Label the micropyle. 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 composite-flower 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.
1. Name the four whorls found on simple flowers.
2. What part of a flower produces pollen?
3. What is the difference between pollination and fertilization?
4. Name the 3 parts of the pistil of a flower.___________________________________________
5. What supports the anther of a flower?___________________________________________
6. Where are the eggs or ovules located in a flower?__________________________________________
7. Explain how sperm are able to reach an egg to fertilize it.
8. Explain the difference in ray and disc flowers in composites.
9. What are the leaf like parts in simple flowers called? In composite flowers?____________________________________
10. What helps attract pollinators?
Label and Color the Parts of a Simple Flower!
Label and color the parts of the pistil!
Color and Label the Parts of a Composite Flower!