L26 Chapter 35
The Plant Body
The Plant Body
Vegetative Organs of the Flowering Plant Body
Plant Cells
Plant Tissues and Tissue Systems
Forming the Plant Body
Leaf Anatomy Supports Photosynthesis
Vegetative Organs of the Flowering Plant Body
Plants are __________ and have double fertilization, a triploid endosperm, and seeds enclosed in modified leaves called carpels.
Flowering plants possess three kinds of vegetative (nonreproductive) organs: roots, stems, and leaves.
Vegetative Organs of the Flowering Plant Body
Most flowering plants belong to one of two major lineages.
__________ are generally narrow-leaved flowering plants such as grasses.
__________ are broad-leaved flowering plants such as roses.
Monocots and eudicots account for __________ percent of the species of flowering plants.
Most of the remaining species (including water lilies and magnolias) are structurally similar to eudicots.
Vegetative Organs of the Flowering Plant Body
The shoot system of a plant consists of the stems and the leaves, as well as flowers.
Leaves are the main sites of __________ in plants.
Stems hold and display the leaves to the sun and provide connections for the transport of materials between roots and leaves.
A __________ is the point where a leaf attaches to a stem.
Regions of stem between nodes are the internodes.
The root system provides support and nutrition.
Vegetative Organs of the Flowering Plant Body
There are two main types of root system: __________ and fibrous root.
Many eudicots have a taproot system: a single, large, deep-growing primary root with smaller lateral roots.
Monocots and some eudicots have a fibrous root system composed of numerous thin roots roughly equal in diameter.
A fibrous root system holds soil in place very effectively.
Some plants have adventitious roots, which arise from points along the stem where roots would not usually occur.
Vegetative Organs of the Flowering Plant Body
A bud is an embryonic shoot.
A stem bears leaves at its nodes, and where each leaf meets the stem, there is a lateral bud.
At the tip of each stem or branch there is an apical bud, which produces the cells for the growth and development of that stem or branch.
Some stems are highly modified.
A potato is a portion of the plants stem, and its eyes contain lateral buds.
The runners of strawberries are horizontal stems.
Vegetative Organs of the Flowering Plant Body
Leaves are well adapted for gathering light.
The blade of a leaf is a thin, flat structure, attached to the stem by the __________, which holds the leaf at an angle almost perpendicular to the sun.
Leaves at different sites on a single plant can be shaped differently.
A simple leaf has a single blade.
A compound leaf has multiple blades (or leaflets) arranged along an axis or radiating from a central point.
In some plant species the leaves are highly modified, such as the thorns of a cactus.
Plant Cells
Plant cells have all the organelles common to eukaryotes.
Some plant cells have additional distinguishing features including chloroplasts (or other plastids) and vacuoles.
Every plant cell is surrounded by a cellulose-containing cell wall.
Plant Cells
Formation of the cell wall is the final step of plant cytokinesis.
The cell __________ is the first barrier to form.
The daughter cells secrete the middle lamella, which forms a layer between them.
Next, each daughter cell secretes cellulose and other polysaccharides to form a primary wall.
Once cell expansion stops, some plant cells may deposit more layers, sometimes impregnated with material such as lignin or suberin to form a secondary wall.
Plant Cells
Plasmodesmata are pore-like structures that pass through primary cell walls, allowing substances to move freely from cell to cell without crossing the plasma membrane.
A __________ is wide enough for portions of the endoplasmic reticulum to extend between cells.
Pits allow water and nutrients to pass between cells that have a secondary wall.
Plant Cells
Parenchyma cells are the most numerous type of cell in young plants.
Parenchyma cells usually have thin walls and large central vacuoles.
The photosynthetic cells in leaves are parenchyma cells filled with chloroplasts.
Some parenchyma cells store lipids or starch.
Other parenchyma cells serve as packing material and play a vital role in supporting the stem.
Plant Cells
Collenchyma cells are supporting cells that lay down primary cell walls that are thick in the corners.
Collenchyma cells provide support to leaf petioles, nonwoody stems, and growing organs.
Plant Cells
Sclerenchyma cells are the main supporting cells of a plant.
There are two types of sclerenchyma cells: elongated fibers and variously shaped sclereids.
Fibers often organize into bundles.
Sclereids may pack together very densely.
Plant Cells
The xylem conducts water from roots to above ground plant parts. It contains conducting cells called tracheary elements.
Tracheids are evolutionarily more ancient tracheary elements found in gymnosperms.
Both tracheary elements and tracheids undergo __________ and do their jobs as empty cells (only the cell walls remain).
Vessel elements are the water pipeline system in flowering plants, also formed from dead cells.
Vessel elements are generally larger in diameter than tracheids and are laid down end-to-end to form hollow tubes.
Plant Cells
Cells of the phloem are alive when they do their job, unlike those of the xylem.
The characteristic cell of the phloem is the sieve tube member.
Cells of the phloem are arranged end-to-end and form long sieve tubes, which transport carbohydrates and other materials.
Plant Cells
The plasmodesmata in sieve tube members enlarge as they mature, resulting in end walls that look like sieves.
At functional maturity, a sieve tube is filled with sieve tube sap (water, sugars, and other solutes).
The sieve tube members have adjacent __________ cells.
Companion cells retain all their organelles and may regulate the performance of the sieve tube members.
Plant Tissues and Tissue Systems
A tissue is an organization of cells that work together as a functional unit.
Parenchyma cells make up parenchyma tissue, which is a simple tissue.
Xylem and phloem are complex tissues; they are composed of a number of different cell types.
Tissues are grouped into tissue systems that extend throughout the body of the plant from organ to organ.
There are three plant tissue systems: vascular, dermal, and ground.
Plant Tissues and Tissue Systems
The vascular tissue system includes the xylem and phloem; it is the conductive or plumbing system of the plant.
The phloem transports carbohydrates from sites of production (sources such as leaves) to sites of utilization (sinks) elsewhere in the plant.
The xylem distributes water and mineral ions taken up by the roots to the stem and leaves.
Plant Tissues and Tissue Systems
The dermal tissue system is the outer covering of the plant.
All parts of the young plant body are covered by an epidermis, which is a single layer or multiple layers of cells.
The epidermis contains epidermal cells and other specialized cells such as guard cells.
The shoot epidermis secretes a layer of wax-covered cutin, the cuticle, which helps retard water loss from stems and leaves.
Plant Tissues and Tissue Systems
The __________ tissue system makes up the rest of a plant and consists primarily of parenchyma tissue.
Ground tissue functions primarily in storage, support, photosynthesis, and the production of defensive and attractive substances.
Forming the Plant Body
The plant establishes its basic body plan in early __________ stages.
Two patterns contribute to the plant body plan:
Cells and tissues are arranged along the main axis from root to shoot.
Tissue systems have a concentric arrangement.
Forming the Plant Body
The growing stem of a plant consists of modules or units laid down one after another.
Each unit consists of a node with its attached leaf or leaves, the internode below that node, and the later bud or buds at the base of that internode.
New units are formed as long as the stem continues to grow.
Leaves are units of another sort, produced in fresh batches to take over the daily function of gathering energy for the plant.
Root systems are also branching structures and lateral roots are semi-independent units.
Forming the Plant Body
In __________, the body grows as an individual develops from embryonic stages but ceases to __________ once adulthood is reached (determinate growth).
In plants the growth of roots and stems is indeterminate and is generated from specific regions of active cell division.
Forming the Plant Body
The localized regions of cell division in plants, called meristems, are forever embryonic. They have the ability to produce new cells indefinitely.
The cells of meristematic tissues are analogous to the stems cells found in animals.
When a meristem cell divides, one daughter cell develops into another meristem cell, and the other differentiates into a more specialized cell.
Forming the Plant Body
There are two types of meristems:
Apical meristems give rise to the primary plant body, which is the entire body of many plants.
Lateral meristems give rise to the secondary plant body.
The stems and roots of some plants form wood and become thick; it is the lateral meristems that give rise to the tissues responsible for this thickening.
Forming the Plant Body
Apical meristems are located at the tips of roots and stems and in buds.
Shoot apical meristems supply the cells that extend stems and branches.
Root apical meristems supply the cells that extend roots.
Apical meristems are responsible for primary growth, which leads to elongation and organ formation.
Forming the Plant Body
Shoot and root apical meristems give rise to three types of cylindrical primary meristems that produce the primary tissues of the plant body:
Protoderm
Ground meristem
Procambium
Forming the Plant Body
Some roots and stems develop a secondary body (wood and bark).
Secondary body tissues are derived from two lateral meristems: vascular cambium and cork cambium.
Vascular cambium is a cylindrical tissue consisting of cells that divide frequently. These cells form the secondary xylem toward the inside, and the secondary phloem towards the outside of the stem.
Forming the Plant Body
The cork cambium produces protective cells that protect the outermost layers of the stem from water loss and microorganisms.
The layer of growth of the cork cambium is the periderm.
Growth in the diameter of the stems and roots, produced by vascular and cork cambia, is called secondary growth.
Wood is secondary xylem.
Bark is everything external to the vascular cambium (periderm plus secondary phloem).
Forming the Plant Body
The root apical meristem produces all the cells that contribute to growth in the length of the root.
The root cap protects the delicate growing area of the root as it pushes through the soil.
The root cap also detects the pull of gravity and controls the downward growth of roots.
Tissues of the root are divided into three zones: cell division, cell elongation, and cell differentiation.
The growing region above the apical meristem comprises the three cylindrical meristems: protoderm, ground meristem, and procambium.
Forming the Plant Body
The protoderm gives rise to the epidermis, adapted for protection and absorption of water and minerals. Root hairs are long, flattened epidermal cells that increase the roots surface area.
The ground meristem gives rise to the cortex, which functions in storage.
The endodermis contains suberin, which makes the cells waterproof and enables control of water into the vascular tissue.
Forming the Plant Body
The stele is produced by the procambium, and includes xylem, phloem, and pericycle tissues.
The pericycle consists of one or more layers of undifferentiated cells and has three important functions.
It is the tissue in which lateral roots arise.
It can contribute to secondary growth by giving rise to a lateral meristem that thickens the root.
Its cells contain membrane transport proteins that export nutrient ions into the cells of the xylem.
Forming the Plant Body
The shoot apical meristem also forms the three primary meristems: protoderm, ground meristem, and cambium.
It also lays down the beginnings of leaves and lateral buds, called leaf primordia and bud primordia.
Vascular tissue in the stem is arranged in vascular bundles.
The eudicot stem also contains pith and cortex storage tissues.
Forming the Plant Body
Secondary growth increases the __________ of stems and roots.
Secondary growth results from the activity of vascular and cork cambia.
Vascular rays connect storage parenchyma to the sieve tubes of the phloem.
Only eudicots have a vascular cambium and a cork cambium and thus undergo secondary growth.
Forming the Plant Body
Cross sections of most tree trunks in temperate zone forests have annual rings.
Annual rings form due to differential rates of growth in spring (when water is plentiful) and in summer.
Wood that is no longer conducting water is known as __________.
Sapwood is wood that is actively conducting water and minerals in the tree.
Forming the Plant Body
As secondary growth continues, expanding vascular tissue stretches and breaks the epidermis and cortex.
Cells lying near the surface of the secondary phloem begin to divide and produce cork, thick-walled cells with suberin.
The cork becomes the outermost tissue, and the dividing cells become the cork cambium.
Phelloderm is cork produced toward the inside of the stem or root.
Lenticels allow gas exchange when bark forms on a stem or root.
Leaf __________ Supports Photosynthesis
Leaf anatomy is adapted to carry out photosynthesis, limit evaporative water loss, and transport the products of photosynthesis to the rest of the plant.
The two zones in leaf parenchyma that photosynthesize are the palisade mesophyll and the spongy mesophyll.
Within the mesophyll is air space through which CO2 can diffuse to the photosynthesizing cells.
Leaf __________ Supports Photosynthesis
Veins supply mesophyll cells with water and minerals, and they transport the products of photosynthesis to the rest of the plant.
The epidermis of the leaf is the outermost cell layer, which is covered by a waxy cuticle. The epidermis functions to keep water and photosynthetic products in the leaf.
Guard cells allow controlled gas exchange through pores in the leaf (the stomata).
Animation 35.1 Secondary Growth: The Vascular Cambium
Video 35.1 Time-lapse of bud burst in plants
Video 35.2 Cell walls and stomatal complexes in Tradescantia
Video 35.3 Germination of soybean plants
Video 35.4 Stomatal complexes forming