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Flowering Plants – The Angiosperms
• Flowering plants dominate most terrestrial ecosystems
• Success results from
• Structural diversity
• Efficient vascular systems
• Symbiotic association with fungi
• Short generation times
• Variety of seed dispersal mechanisms
• Adaptations that encourage insect pollinators

Part 1. Vascular Tissue
• Roots, stems, and leaves have vascular
tissue
• There are two cell types
• Xylem
• Conduct water and minerals from the roots
through the plant
• Phloem
• Transports the products of photosynthesis
through the plant

Part 1. Vascular Tissue – Procedures
• Observe the transport demonstration
• What cell type transported the colored water to the petals of the flower?

Part 2. Plant Organs
• Plant organs include roots, stems, and leaves
• Each organ has a specialized function
• Roots
• Store sugars and starches produced during
photosynthesis
• Stems
• Support the leaves, flowers, and seed stalks
• Transport water and nutrients through the plant
• Leaves
• The primary organ of photosynthesis
• The main site of gas exchange

Part 2. Plant Organs
• Roots
• The actively growing regions of the root are formed by meristems where cells
undergo mitotic division
• Primary meristems lengthen roots
• Secondary meristems increase root girth

Part 2. Plant Organs
• Roots
• As the primary root grows, secondary roots develop to form the root
system
• Tap root systems have a large primary root with small secondary roots
• Name a plant with a taproot system.
• Fibrous root systems have similar appearing primary and secondary
roots
• Name a plant with a fibrous root system.

• The Shoot System – Flowers, Stems, and Leaves
• A flower is a highly specialized stem tip.
• Modified leaves (petals and sepals) are clustered in
whorls.
• The flower consists of
• sepals and petals
• The stamen is made of a filament with an anther
which forms pollen grains
• The female flower parts include the ovary, stigma,
and style

4. Filament, 5. Petal

Part 2. Plant Organs –
Procedures
• Flowers
• Pollination occurs when wind or insects
carry pollen to the stigma
• During double fertilization, one sperm
fertilizes the egg, the second sperm
nucleus fuses with the two polar nuclei to
form polyploid endosperm to feed the
developing embryo
• The entire structure develops into a seed.
• What is the difference between pollination
and fertilization?

Part 2. Plant Organs –
Procedures
• Flowers
• The developing seed are protected by
the ovary
• The result is a fruit, which protects the
seeds and enhances seed dispersal
• Seeds may be dispersed by animals,
wind, water, etc.
• Name two ways that seeds are
dispersed by animals.

Part 2. Plant Organs
• Stems
• Leaves may be arranged on stems in specific patterns
• Opposite leaves have two leaves per node.
• Alternate leaves have one leaf per node.
• Whorled leaves have three or more leaves per node.
• What is the leaf arrangement in the plants around you?

Plant Structures

Seed Plants

Seed plants, the most abundant form of terrestrial plants, are divided into two classes: gymnosperms and angiosperms.

Gymnosperms have seeds that are not protected, and they lack flowers. Angiosperms, also called the flowering plants, have seeds that are enclosed within a reproductive structure called the fruit.

Gymnosperms

The name gymnosperm means "naked seed" and implies that the seeds are developed in an exposed position on the parent plant. The largest and most important group of gymnosperms are the conifers, a group of cone-bearing gymnosperms that includes redwoods, giant sequoias, and bristlecone pine trees. Other gymnosperms include cycads (palm trees) and ginkgoes.

Most gymnosperms are woody plants, plants that form wood as a structural tissue to give them hard stems. Wood, along with seeds, allows the gymnosperms to cope with a wide range of environmental conditions, including cold, dry habitats. Most gymnosperm leaves are shaped as needles, fans, or scales - shapes that minimize water loss. Unlike deciduous trees that lose their leaves annually at the end of every growing season, most gymnosperms are evergreen trees, trees that keep their leaves for several years.

Angiosperms

The name angiosperm means "enclosed seed" and implies that the seeds of these plants are enclosed within a protective fruit.

Angiosperms tend to have broad leaves and are deciduous.

Angiosperms are further divided into two groups: monocots and eudicots. As noted in the table below, there are several structural differences between the two.

Stacked

Examples include yucca, lilies, orchids, and grasses

Examples include eucalyptus trees, oak trees, roses, and sunflowers

The General Structure of Seed Plants

The general structural components of all seed plants are leaves, stems, and roots. All seed plants have vascular tissue, which is found in all three of these structures. Vascular tissue is composed of xylem cells, which transports water and nutrients from the roots to the stems and leaves, and phloem cells, which transports sugars formed by photosynthesis in the leaves to where it is needed in the rest of the plant. Procambium is a type of tissue that gives rise to primary xylem and primary phloem cells. Additionally, procambium, may give rise to vascular cambium, a type of tissue that gives rise to secondary xylem and secondary phloem cells, and cork cambium, one of the many layers of bark in woody plants that is responsible for producing protective cork material.

Leaves

Leaves are the primary site of photosynthesis. Their structure allows for gas exchange with the environment, as well as evaporation of excess water through specialized pore structures called stomata (singular: stoma).

The leaves of most angiosperms are broad and flat to maximize the surface area facing the sun. They are composed of several layers.

The epidermis is the outer layer of cells. The upper and lower epidermis are single layers of cells that sandwich the remaining leaf layers. A waxy, waterproof layer called the cuticle covers the epidermal layers to protect against desiccation and stress from other environmental factors. Below the upper epidermis is the palisade layer, a layer densely packed with cylindrical-shaped, chlorophyll-rich cells which produce most of the food for the plant. Beneath the palisade layer is the spongy cell layer (spongy mesophyll), which stores sugars synthesized by cells in the palisade layer. Spongy layer cells are more irregular in shape and are loosely arranged. This arrangement creates air spaces (intracellular chambers) that are connected and open to the environment through the stomata and function to facilitate gas exchange. Spongy layer cells release oxygen and water into the air spaces and uptake carbon dioxide from the air spaces. Within the spongy layer, there are vascular bundles (or veins) that contain xylem and phloem cells. Finally, the lower epidermis contains the stomata. Guard cells are found on either side of each stoma. These guard cells regulate the opening and closing of the stomata.

Some gymnosperms, including pine trees, have specialized leaves that have evolved to help the tree thrive in cold, dry environments. To conserve water, pine needles have a smaller surface area than the typical leaf. They are covered with a thick cuticle over the epidermal layer and a layer of compact, thick-walled cells just beneath the epidermis called the hypodermis.

The stomata in the epidermal tissue are sunken into the leaf. Because the leaves are smaller, there is only one middle layer: the photosynthetic mesophyll cells. The endodermis is the innermost layer of cells that lie outside the vascular bundles.

Resin ducts, which are intracellular tubes lined with resin-secreting cells, are found throughout the mesophyll cells. The resin ducts transport resin, a viscous substance that protects the plants from insect or pathogen injury.

Stems

The stem is the major support structure of a plant, lifting the leaves up to the sun and supporting flowers and fruits. The stem is also responsible for transporting nutrients, minerals, and water between the roots and leaves. Green stems are actually photosynthetic and can produce some energy for the plant. Stems can be as small as the stem of a clover, or as thick and long as the trunk of a 90-meter tree.

The stems of monocots and cudicots have similar but distinct structures. Both monocot and eudicot stems have an epidermal

layer, an outer covering of cells that provides protection to the cells within the stem, and sclerenchyma, dead, fibrous cells that have thick walls and function to structurally support the stem.

Additionally, both monocot and eudicot stems contain parenchyma, cells with thin cell walls that are the most common cells within a plant. Parenchyma cells contain large vacuoles, membrane-bound organelles that store nutrients and food. These cells are loosely packed, creating air spaces for gas exchange. Monocot and eudicot features are compared in the table below.

Stems can be herbaceous, meaning soft or green like a clover stem, or woody like a tree trunk. Herbaceous stems are mostly composed of parenchyma, whereas woody stems are mostly composed of dead vascular tissue. The stems of woody plants undergo secondary growth, growth that causes stems to thicken. The old vascular rings form the woody part of the stem.

Rays are radial lines that run perpendicular to the vascular rings and function to transport water and other substances radially.

Resin ducts are also present in woody stems.

Roots

In addition to being an anchor for the plant, roots absorb water and minerals from the environment. Additionally, many plants, such as carrots, store food in their roots.

Roots, like stems, have vascular structures and tissue. Pericycle, located between the xylem and phloem and the cortex, gives rise to branch roots. Epidermis is the outer layer of root cells and endodermis lies between the cortex and the vascular tissue.

Eudicots have a taproot system, a system with a central, dominant root and other roots that branch off laterally, whereas monocots have fibrous roots. The taproot system can develop into the anchor for a large tree over the years, whereas fibrous roots are not strong enough to provide sufficient support for annual growth.