Seed Plant Structure and Growth
Section 2
Section 2: Roots, Stems, and Leaves
Preview
• Bellringer
• Key Ideas
• Roots
• Stems
• Leaves
• Summary
Seed Plant Structure and Growth
Section 2
Bellringer
Inspect a variety of leaves. Identify the external features of
the leaves. Notice the variety of external features across
the different leaves. This is because different species of
plants have adapted to different habitats.
Seed Plant Structure and Growth
Key Ideas
• What are roots, and what is their function?
• What are stems, and what is their function?
• What are leaves, and what is their function?
Section 2
Seed Plant Structure and Growth
Section 2
Roots
• Most plants are anchored to the spot where they grow by
roots, which absorb water and mineral nutrients.
• In many plants, roots also function in the storage of
organic nutrients, such as sugar and starch.
• Highly branched, fibrous root systems are found in most
monocots, such as grasses.
• Many dicots have a large central root from which smaller
roots branch. This is called a taproot system.
Seed Plant Structure and Growth
Structure of Roots
Section 2
Seed Plant Structure and Growth
Visual Concept: Types of Roots
Section 2
Seed Plant Structure and Growth
Section 2
Stems
• Stems support the leaves and house the vascular tissue,
which transports substances between the roots and the
leaves.
• Many plants have stems that are specialized for other
functions, such as water storage in cactus.
• A plant with stems that are flexible and usually green is
called a herbaceous plant.
Seed Plant Structure and Growth
Visual Concept: Stem
Section 2
Seed Plant Structure and Growth
Section 2
Stems, continued
• The stems of herbaceous plants contain bundles of
xylem and phloem called vascular bundles.
• Vascular bundles are surrounded by ground tissue. The
tissue at the center of the stem of most vascular plants is
called the pith.
• The pith is used for storage.
Seed Plant Structure and Growth
Dicot and Monocot Stem Structures
Section 2
Seed Plant Structure and Growth
Section 2
Stems, continued
• Woody stems, such as those of trees and shrubs, are
stiff and nongreen.
• The wood in the center of a mature stem or tree trunk is
called heartwood.
• Sapwood, which lies outside the heartwood, contains
vessel elements that can conduct water.
Seed Plant Structure and Growth
Structure of Stems
Section 2
Seed Plant Structure and Growth
Xylem
Section 2
Seed Plant Structure and Growth
Section 2
Leaves
• Leaves are the primary photosynthetic organs of plants.
• Most leaves have a flattened portion, the blade, which is
usually attached to a stem by a stalk, called the petiole.
• A leaf blade may be divided into two or more sections,
called leaflets.
Seed Plant Structure and Growth
Section 2
Leaves, continued
• A leaf is a mass of ground and vascular tissue covered
by epidermis.
• In leaves, the ground tissue is called mesophyll.
Mesophyll cells are packed with chloroplasts, where
photosynthesis occurs.
• One or more rows of closely packed, columnar cells
make up the palisade layer, which lies just beneath the
upper epidermis.
Seed Plant Structure and Growth
Structure of a Leaf
Section 2
Seed Plant Structure and Growth
Section 2
Leaves, continued
• Many plants have modified leaves that are specialized
for particular functions.
• For example, water lily leaves are specialized for floating
on the surface of ponds.
• Cactus spines are modified leaves.
• Venus’ flytrap leaves are modified to catch insects.
Seed Plant Structure and Growth
Modified Leaves
Section 2
Seed Plant Structure and Growth
Visual Concept: Leaf Adaptations
Section 2
Seed Plant Structure and Growth
Section 2
Summary
• Most plants are anchored to the spot where they grow by
roots, which absorb water and mineral nutrients.
• Stems support the leaves and house the vascular tissue,
which transports substances between the roots and the
leaves.
• Leaves are the primary photosynthetic organs of plants.