Assessment 2

• Minitest 1 in week 6:

• Topic: Lectures 1 to 8

•  19 questions

• Single best answer

Lecture 8

The Plant Body

Dr. Angelika Stollewerk

Chapter 34

The Plant Body

Aims: •  To be able to distinguish between monocot

and eudicot plants

•  To be able to identify the component parts of plants, including their modifications

•  To introduce the three tissue systems of plants

•  To look at how leaf anatomy supports photosynthesis

The Plant Body

Aims:

•  To be able to distinguish between monocot and eudicot plants

•  To be able to identify the component parts of plants, including their modifications

•  To introduce the three tissue systems of plants

•  To look at how leaf anatomy supports photosynthesis

These lecture aims form part of the knowledge required for learning outcome 2:

Describe basic organism structure and diversity (LOC2).

The Plant Body

Essential reading •  pages 744–750

•  pages 752-754

•  pages 760-761

• 34.1 How Is the Plant Body Organized?

• 34.3 How Do Meristems Build the Plant Body? (Part)

• 34.4 How Does Leaf Anatomy Support Photosynthesis?

Angiosperms

Eudicots

Monocots

(Flowering Plants)

34.1 How Is the Plant Body Organized?

Ninety-seven percent of angiosperms (flowering plants) are in two clades:

• Monocots: narrow-leaved; grasses, lilies, orchids, palms

• Eudicots: broad-leaved; soybeans, roses, sunflowers, maples

Remaining species have structure similar to eudicots: water lilies and magnoliids.

Figure 34.1 Monocots versus Eudicots

(embryonic leaves)

34.1 How Is the Plant Body Organized?

Angiosperms (flowering plants) are vascular plants with double fertilization (1 female gametophyte fertilized by 2 male gametes), a triploid endosperm (tissues surrounding embryo), seeds enclosed in modified leaves which are called carpels.

They have three types of vegetative organs: roots, stems, leaves.

They are organized in two systems: shoot system and root system.

Figure 34.2 Vegetative Organs and Systems

34.1 How Is the Plant Body Organized?

Shoot system: stems, leaves, flowers. Leaves are the main organs of photosynthesis.

Stems hold and display leaves in the sun; connection between roots and leaves.

Nodes: points of attachment of leaf to stem. Regions in between are internodes.

34.1 How Is the Plant Body Organized?

Root system: anchors plant and provides nutrition.

Extreme branching of roots provides large surface area for absorption of water and mineral nutrients.

Structure of vegetative organs (leaf, stalk, roots) determines the overall form or morphology.

34.1 How Is the Plant Body Organized?

Water and minerals enter through the root system in most plants.

Taproot systems: single, large, deep-growing root and small side roots. The root may also function as food storage.

Fibrous root systems: many thin roots of equal diameter. Have large surface area; cling to soil well.

Figure 34.3 Root Systems

34.1 How Is the Plant Body Organized?

Adventitious roots: arise above ground from stem or leaves.

Adventitious roots may arise from cuttings, and can start a new plant—vegetative reproduction (asexual).

Adventitious roots also help support many plants, such as corn.

34.1 How Is the Plant Body Organized? Stems elevate and support flowers and leaves; have buds or embryonic shoots. Stems bear leaves at the nodes, and buds in the angle or axil between shoot and leaf (axillary buds). Axillary buds can develop into a branch. Apical buds form at the tips, produce cells for upward growth; some may develop into flowers.

34.1 How Is the Plant Body Organized?

Stems can be modified:

Potato tuber is an underground stem.

Many desert plants have enlarged stems that store water.

Runners are horizontal stems, roots grow at intervals and independent plants can arise from them.

Figure 34.4 Modified Stems

Root

34.1 How Is the Plant Body Organized?

Most photosynthesis occurs in the

leaves.

The blade is a thin, flat organ attached

to stem by the petiole. Angle may be perpendicular to sun’s rays to provide maximum area for light gathering.

Some leaves change position during

the day to track the sun.

34.1 How Is the Plant Body Organized?

Leaves on one plant may have different shapes, resulting from a combination of genetic, developmental, and environmental influences.

Simple leaves consist of a single blade.

Compound leaves have multiple blades or leaflets.

Figure 34.5 Simple and Compound Leaves

34.1 How Is the Plant Body Organized?

Leaves can be highly modified during development.

Some function as food storage, (e.g., onion bulbs). Leaves of succulents store water.

Cacti spines are modified leaves.

Climbing plants have modified leaves called tendrils that wrap around other structures.

34.1 How Is the Plant Body Organized?

Tissue: organized group of cells with similar structure and function.

Tissues are grouped into tissue systems.

Vascular, dermal, and ground tissue systems extend throughout the plant body in a concentric arrangement.

Figure 34.6 Three Tissue Systems Extend Throughout the Plant Body

34.1 How Is the Plant Body Organized?

The vascular tissue system: the transport system.

Xylem distributes water and minerals taken up by roots to all parts of the plant. Xylem can also function in storage and support.

Phloem transports carbohydrates from site of production (sources) to sites of utilization or storage (sinks).

34.1 How Is the Plant Body Organized?

The dermal tissue system: the outer covering.

The epidermis: single layer of cells or several layers. May contain specialized cells such as guard cells around stomata.

Shoot and leaf epidermis secretes waxy cuticle that retards water loss.

• Stems and roots of woody plants have a periderm.

34.1 How Is the Plant Body Organized?

The ground tissue system makes up the rest of the plant.

Functions in storage, support, photosynthesis, and production of defensive and attractive chemicals.

34.3 How Do Meristems Build the Plant Body?

During early embryonic development, two patterns contribute to the basic body plan:

• Arrangement of cells and tissues along the main axis from root to shoot.

• Concentric arrangement of tissue systems.

34.3 How Do Meristems Build the Plant Body?

The growing stem consists of modules laid down one after another.

Each module is a node with attached leaves, the internode below, plus axillary buds at the base of that internode.

34.3 How Do Meristems Build the Plant Body?

Each branch may be thought of as a separate module.

Branches form one after another (unlike animal limbs). Branches may differ in number of leaves, and number of subsequent branches.

Branches are long-lived.

34.3 How Do Meristems Build the Plant Body?

Leaves are modules that are short-lived—weeks to a few years.

Root systems are also branching. Lateral roots may be semi-independent. As root systems grow, roots may die and be replaced by new ones.

34.3 How Do Meristems Build the Plant Body?

All plants have a primary plant body: all non-woody parts of the plant. Growth lengthens the plant body.

Monocots consist entirely of primary plant body.

Trees and shrubs have a secondary plant body consisting of wood and bark. Tissues are laid down as stems and roots thicken. The plant grows throughout its life.

34.3 How Do Meristems Build the Plant Body?

Meristems are localized regions of cell division. Can produce new cells indefinitely.

Cells that perpetuate the meristem are called initials (comparable to stem cells in animals).

When initials divide, one daughter cell becomes specialized, the other remains a meristem cell.

Figure 34.11 Apical and Lateral Meristems

34.3 How Do Meristems Build the Plant Body?

Animal growth is determinate; growth ceases when adult state is reached.

Some plant growth is also determinate— leaves, flowers, fruits.

Growth of stems and roots is indeterminate—generated from specific regions of cell division and expansion.

34.3 How Do Meristems Build the Plant Body?

Apical meristems at tips of roots and stems, and in buds, give rise to the primary plant body.

Shoot apical meristems extend stems and branches.

Root apical meristems extend roots.

Apical meristems give rise to a set of cylindrical primary meristems that produce the three tissue systems.

34.3 How Do Meristems Build the Plant Body?

The primary meristems: protoderm, ground meristem, procambium.

Figure 34.12 A Woody Tree Twig Has Both Primary and Secondary Growth

34.3 How Do Meristems Build the Plant Body?

Lateral meristems produce secondary growth:

• Vascular cambium: supplies cells of secondary xylem (towards the inside) which become wood; and secondary phloem (towards the outside) which becomes bark.

• Cork cambium: produces waxy-walled cork cells. Some of the cells become the bark.

34.3 How Do Meristems Build the Plant Body?

• Wood is secondary xylem.

• Bark: everything external to the vascular cambium (periderm plus secondary phloem).

A twig illustrates both primary and secondary growth. Apical meristems are enclosed in buds.

Only the buds are entirely primary tissues.

34.3 How Do Meristems Build the Plant Body?

As tree grows in diameter, outermost layers, including the epidermis, dry and crack off.

The cork cambium produces new protective cells, called the periderm, with walls impregnated with suberin.

• Stems and roots of woody plants have a periderm.

34.3 How Do Meristems Build the Plant Body?

Meristems may remain active for years, or centuries.

Oldest known living plant: a bristlecone pine, about 4,900 years-old.

34.4 How Does Leaf Anatomy Support Photosynthesis?

Leaf anatomy is adapted to carry out photosynthesis, and the exchange of O2 and CO2 with the environment, while limiting water losses.

34.4 How Does Leaf Anatomy Support Photosynthesis?

Two zones of parenchyma cells make up the mesophyll in the leaves:

• Palisade mesophyll

• Spongy mesophyll

Also includes air space for diffusion of gases.

Figure 34.23 The Eudicot Leaf (A)

Figure 34.23 The Eudicot Leaf

34.4 How Does Leaf Anatomy Support Photosynthesis?

Vascular tissue forms veins in leaves.

Veins extend to within a few cell diameters of all the cells, so mesophyll cells are well supplied with water and minerals, and products of photosynthesis can be conducted to the phloem.

34.4 How Does Leaf Anatomy Support Photosynthesis?

The epidermal cells are nonphotosynthetic, and have a waxy cuticle that is impermeable to water.

The cuticle prevents water loss, but also prevents diffusion of gases.

Pores called stomata allow gas exchange. They are opened and closed by guard cells.

34.4 How Does Leaf Anatomy Support Photosynthesis?

C4 plants have a modified leaf anatomy that allows them to fix CO2 at low levels (production of 4-carbon sugar compounds).

The photosynthetic cells are grouped around the veins forming an outer mesophyll and a bundle sheath.

CO2 is first fixed in mesophyll cells, then moves to bundle sheath cells for photosynthesis.

Figure 8.17 Leaf Anatomy of C3 and C4 Plants

Palisade mesophyll cells

The Plant Body

Check out

34.1 Recap, page 748

34.2 Recap, page 752, first two questions only

34.4 Recap, page 761

34.1 Chapter summary, page 762

34.2 Chapter summary, page 762

34.4 Chapter summary, page 762, see WEB/CD Activity 34.5

Self Quiz

Pages 762-763: Chapter 34 questions 1-6 and 10

For Discussion

Page 763: Chapter 34, questions 3 and 5

Key terms:

adventitious root, apical bud, axillary bud, blade, bud, chloroplast, collenchyma cell, compound leaf, cuticle, cutin, dermal tissue, determinate growth, embryonic shoot (bud), epidermis, Eudicot, flowering plant, fibrous root, ground tissue, guard cell, indeterminate growth, internode, leaf (pl: leaves), meristem, mesophyll cell, Monocot, node, parenchyma tissue, petiole, phloem, plasmodesma (pl: plasmodesmata), palisade cells, plastid, root, sclereid, sclerenchyma cell, shoot system, simple leaf, spongy mesophyll, stem, taproot, vascular plant, vascular tissue, vacuole, vegetative (non-reproductive), vein,

xylem

The Plant Body