Bio Lecture 15

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Seed germination and development

1. Eudicot (garden bean)
2. Monocot (corn)

1. Eudicot (garden bean)

Foliage leaves

2. Monocot (corn)

Coleoptile

Foliage leaves

The Plant Body Plan

vascular tissue system: The vascular tissue system carries out long-distance transport of materials between the root and shoot systems.

Flower

In an angiosperm, a specialized shoot with up to four sets of modified leaves, bearing structures that function in sexual reproduction.

Apical bud

A bud at the tip of a plant stem; also called a terminal bud.

Node

A point along the stem of a plant at which leaves are attached.

Internode

A segment of a plant stem between the points where leaves are attached.

Vegetative shoot

Vegetative growth—production of nonreproductive leaves, stems, and roots

Leaf

The main photosynthetic organ of vascular plants.
- Blade: The flattened portion of a typical leaf.
- Petiole:

Axillary bud

- The stalk of a leaf, which joins the leaf to a node of the stem.

Stem

A vascular plant organ consisting of an alternating system of nodes and internodes that support the leaves and reproductive structures.

Taproot

- A main vertical root that develops from an embryonic root and gives rise to lateral (branch) roots.

Lateral branch roots

- Root: A root is an organ that anchors a vascular plant in the soil, absorbs minerals and water, and often stores carbohydrates.
- A main vertical root that develops from an embryonic root and gives rise to lateral (branch) roots.

Basic Cell Types

1. Parenchyma
2. Collenchyma
3. Sclerenchyma

1. Parenchyma

- photosynthesis occurs in their chloroplasts
- storage
- healing damage
- progenitor cell type
- primary walls that are thin celled
- most lack secondary walls
- large central vacuole
- metabolic functions- synthesizing and storing various organic products

2. Collenchyma

- elongated, unevenly thickened cell walls provide flexible support, but do not restrain growth
- grouped in strands
- help support young parts of the plant shoot

3. Sclerenchyma

- thick and rigid, function as supporting elements but are much more rigid than collenchyma cells
- may contain large amounts of lignin
- can't elongate (occur in regions of the plant that have stopped growing in length)
- sclereids: boxier than fibers and irregular in shape, have very thick, lignified secondary walls.
- fibers: long, slender, and tapered. Some are used commercially, such as hemp fibers for making rope and flax fibers for weaving into linen.
- many are dead at functional maturity

Basic tissue systems of a plant

1. Dermal: The dermal tissue system (blue) provides a protective cover for the entire body of a plant.
2. Ground: The ground tissue system (yellow), which is responsible for most of the plant's metabolic functions, is located between the dermal tissue and the vascular tissue in each organ.
3. Vascular: The vascular tissue system (purple), which transports materials between the root and shoot systems, is also continuous throughout the plant, but is arranged differently in each organ.

1. Dermal

The dermal tissue system (blue) provides a protective cover for the entire body of a plant.

2. Ground

- Tissues that are neither dermal nor vascular are part of the ground tissue system
- pith: Ground tissue that is internal to the vascular tissue
- Cortex: ground tissue that is external to the vascular tissue
- The ground tissue system is not just filler.
- It includes various cells specialized for functions such as storage, photosynthesis, and support.

3. Vascular

- vascular tissue system: carries out long-distance transport of materials between the root and shoot systems.
- Xylem: conducts water and dissolved minerals upward from roots into the shoots.
- Phloem: transports sugars, the products of photosynthesis, from where they are made (usually the leaves) to where they are needed—usually roots and sites of growth, such as developing leaves and fruits.

Stem of a monocot

- cross section of a stem with scattered vascular bundles (typical of monocots)
- Dermal: Epidermis
- Ground: Ground tissue
- Vascular: Vascular bundles

Stem of a "dicot"

- cross section of stem with vascular bundles forming a ring (typical of "dicots")
- Dermal: Epidermis
- Ground: Cortex; Pith
- Vascular: Phleom, Xylem, Sclerenchyma (fiber cells), Vascular bundles

Yellow Bellied Sapsucker

- Like other sapsuckers, these birds drill holes in trees and eat the sap and insects drawn to it.
- phloem

Vascular tissue: Xylem

Xylem conducts water and dissolved minerals upward from roots into the shoots.
1. Vessel elements; vessels
2. Tracheids
These are tubular, elongated cells that are dead at functional maturity

Vessel elements

Vessel element: A short, wide water-conducting cell found in the xylem of most angiosperms and a few nonflowering vascular plants. Dead at maturity, vessel elements are aligned end to end to form micropipes called vessels.

Vessel: A continuous water-conducting micropipe found in most angiosperms

Tracheids

Tracheids: A long, tapered water-conducting cell found in the xylem of nearly all vascular plants; Functioning tracheids are no longer living.

Pits: The secondary walls of tracheids and vessel elements are often interrupted by pits, thinner regions where only primary walls are present. Water can migrate laterally between neighboring cells through pits.

Water conducting cells of the Xylem

Vessel elements: A short, wide water-conducting cell found in the xylem of most angiosperms and a few nonflowering vascular plants. Dead at maturity, vessel elements are aligned end to end to form micropipes called vessels.

Tracheids: A long, tapered water-conducting cell found in the xylem of nearly all vascular plants; Functioning tracheids are no longer living.

Vessel element

Perforation plate: The end walls of vessel elements have perforation plates that enable water to flow freely through the vessels.

Vessel Element: A short, wide water-conducting cell found in the xylem of most angiosperms and a few nonflowering vascular plants. Dead at maturity, vessel elements are aligned end to end to form micropipes called vessels.

Tracheids

Pits: The secondary walls of tracheids and vessel elements are often interrupted by pits, thinner regions where only primary walls are present. Water can migrate laterally between neighboring cells through pits.

Vascular Tissue: Phloem

Phloem transports sugars, the products of photosynthesis, from where they are made (usually the leaves) to where they are needed—usually roots and sites of growth, such as developing leaves and fruits.
- sieve-tube elements
- plate and pore
- nucleus of companion cell

Sieve plate with pores

- sieve plate: An end wall in a sieve-tube element, which facilitates the flow of phloem sap in angiosperm sieve tubes.
- have pores that facilitate the flow of fluid from cell to cell along the sieve tube

Sieve-tube elements and companion cells

- sieve-tube elements: A living cell that conducts sugars and other organic nutrients in the phloem of angiosperms; also called a sieve- tube member. Connected end to end, they form sieve tubes.

Sieve-tube elements and companion cells

- sieve-tube companion cell: A type of plant cell that is connected to a sieve-tube element by many plasmodesmata and whose nucleus and ribosomes may serve o

Modified stems

1. Stolons
2. Tubers
3. Blub
4. Rhizomes

1. Stolons

Shown here on a straw- berry plant, stolons are horizontal shoots that grow along the surface. These "runners" enable a plant to reproduce asexually, as plantlets form at nodes along each runner.

2. Tubers

Tubers, such as these potatoes, are enlarged ends of rhizomes or stolons specialized for storing food. The "eyes" of a potato are clusters of axillary buds that mark the nodes.

3. Blub

Bulbs are vertical underground shoots consisting mostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise.

4. Rhizomes

The base of this iris plant is an example of a rhizome, a horizontal shoot that grows just below the surface. Vertical shoots emerge from axillary buds on the rhizome

* Plant growth

- Indeterminate growth: growth occurs throughout the plant's life
- meristems: Plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth
- apical meristems: located at the tips of roots and shoots and in axillary buds of shoots, provide additional cells that enable growth in length, a process known as primary growth
- lateral meristems: Woody plants, however, also grow in circumference in the parts of stems and roots that no longer grow in length. This growth in thickness, known as secondary growth, is caused by lateral meristems called the vascular cambium and cork cambium

Shoot apical meristem

-apical meristems: located at the tips of roots and shoots and in axillary buds of shoots, provide additional cells that enable growth in length, a process known as primary growth

axillary bud meristem

A structure that has the potential to form a lateral shoot, or branch. The bud appears in the angle formed between a leaf and a stem.

vascular cambium

adds layers of vascular tissue called secondary xylem (wood) and secondary phloem.

cork cambium

replaces the epidermis with the thicker, tougher periderm.

lateral meristems

- the cork cambium and the vascular cambium

root apical meristems

- apical meristems: located at the tips of roots and shoots and in axillary buds of shoots, provide additional cells that enable growth in length, a process known as primary growth

* Plant growth: primary and secondary

- elongation occurs at shoot apical meristems
- widening occurs at lateral meristems
- elongation occurs at root apical meristems

* Primary growth at the shoot apical meristem

- Shoot apical meristem
- leaf primordia
- young leaf
- developing vascular strand
- axillary bud meristems

Shoot apical meristem

- is a dome-shaped mass of dividing cells at the shoot tip

leaf primordia

A finger-like projection along the flank of a shoot apical meristem, from which a leaf arises.

young leaf

- Within a bud, young leaves are spaced close together because the internodes are very short. Shoot elongation is due to the lengthening of internode cells below the shoot tip.

developing vascular strand

axillary bud meristems

- Within each axillary bud is a shoot apical meristem. Its dormancy depends mainly on its proximity to an active apical bud. Generally, the closer an axillary bud is to an active apical bud, the more inhibited it is.

* Primary and secondary growth in stems

Primary growth in stems

primary growth: Growth produced by apical meristems, lengthening stems and roots.
- epidermis
- cortex
- primary phloem
- primary xylem
- pith

epidermis

the dermal tissue system of non-
woody plants, usually consisting of a single layer of tightly packed cells.

cortex

- In plants, ground tissue that is between the vascular tissue and dermal tissue in a root or eudicot stem.
- outter layer of dermal tissue

primary phloem

- primary growth of phloem
- Vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant.

primary xylem

- primary growth of xylem
- Vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from the roots to the rest of the plant.

pith

Ground tissue that is internal to the vascular tissue in a stem; in many monocot roots, parenchyma cells that form the central core of the vascular cylinder.

Secondary growth in stems

Secondary growth: produced by lateral meristems, thickening the roots and shoots of woody plants.
- Periderm
- Cork cambium
- cortex
- primary phloem
- secondary phloem
- vascular cambium
- secondary xylem
- primary xylem
- pith

Periderm

The protective coat
that replaces the epidermis in woody plants during secondary growth, formed of the cork and cork cambium.

Cork cambium

A cylinder of meristematic tissue in woody plants that replaces the epidermis with thicker, tougher cork cells
- produces a tough, thick covering consisting mainly of wax- impregnated cells that protect the stem from water loss and from invasion by insects, bacteria, and fungi.

cortex

In plants, ground tissue that is between the vascular tissue and dermal tissue in a root or eudicot stem.

primary phloem

secondary phloem

vascular cambium

A cylinder of meristematic tissue in - woody plants that adds layers of secondary vascular tissue called secondary xylem (wood) and secondary phloem.

secondary xylem

primary xylem

pith

Ground tissue that is internal to the vascular tissue in a stem; in many monocot roots, parenchyma cells that form the central core of the vascular cylinder.

* Primary and Secondary growth in a two-year old stem

Cross section of a three year old stem

- track the divisions in the cells of the vascular cambium (on the left) to understand how the secondary xylem and phloem are generated
- A cambial initial (C) can divide to form two cambial initials, increasing the circumference of the vascular cambium.
- A cambial initial can also divide to form an initial and either a secondary xylem cell (X) or secondary phloem cell (P).
- Although secondary xylem and phloem are shown being added equally, cambial initials usually produce much more xylem.

Most of the thickening is from secondary xylem.

Girdling a tree

Secondary growth

Monocots vs Dicots

- secondary growth characterizes the gymnos and most of the dicots, but no the monocots

Cross section of a three-year-old stem

- late wood: Wood produced during the rest of the growing season is called late (or summer) wood. It is composed of thick-walled cells that do not transport as much water but provide more support.
- early wood: In temperate regions, wood that develops early in the spring, known as early (or spring) wood, usually consists of secondary xylem cells with relatively large diameters and thin cell walls. This structure maximizes delivery of water to new leaves
- Vascular ray: radial files of mostly parenchyma cells that connect the secondary xylem and phloem
- Bark:

Anatomy of a tree trunk

- growth ring: there is a marked contrast between the large cells of the new early wood and the smaller cells of the late wood of the previous growing season. A year's growth appears as a distinct ring in the cross sections of most tree trunks and roots.
- vascular ray: radial files of mostly parenchyma cells that connect the secondary xylem and phloem
closer to the center of a stem or root

Heartwood

- heartwood: As a tree or woody shrub ages, the older layers of secondary xylem no longer transport water and minerals (a solution called xylem sap). These layers are called heartwood because they are

Sapwood

- sapwood: The newest, outer layers of secondary xylem still transport xylem sap and are therefore known as sapwood

Annual growth rings

- note that the large cells are typical of the rapid, early season growth, and these produce the lighter buds
- growth ring: there is a marked contrast between the large cells of the new early wood and the smaller cells of the late wood of the previous growing season. A year's growth appears as a distinct ring in the cross sections of most tree trunks and roots.

Dendrochronology

- the science of tree ring analysis can provide unique insight into past growth conditions, for example in relation to climate change
- the figure above is based on cored from conifer trees in Mongolia. Relatively high ring-width indices suggest rapid growth in the late 1900's, possible in relation to global warming

Johann Wolfgang von Goethe (1749-1832)

- coined term "Morphology"
- described the Urpflanze or plant archetype
- everything is a derived leaf

Leaf morphology

- Leaf: the main photosynthetic organ, although green stems also perform photosynthesis.
- Blade: flattened
- Petiole: which joins the leaf to the stem at a node
- Base: attaches leaf to stem

Types of leaves

1. simple
2. compound
3. double compound

1. simple

A simple leaf has a single, undivided blade. Some simple leaves are deeply lobed, as shown here.

2. compound

In a compound leaf, the blade consists of multiple leaflets. A leaflet has no axillary bud at its base.

3. double compound

In a doubly compound leaf, each leaflet is divided into smaller leaflets.

Leaves of grass

- apical meristem is at the base

Cutaway diagram of a leaf

- palisade mesophyll:
- spongy mesophyll:
- stomata with guard cells:
- bundle sheath cells:
- cuticle:

palisade mesophyll

- mesophyll:
- Palisade mesophyll consists of one or more layers of elongated parenchyma cells on the upper part of the leaf.

spongy mesophyll

- mesophyll:
- Spongy mesophyll is below the palisade mesophyll. These parenchyma cells are more loosely arranged, with a labyrinth of air spaces through which CO2 and oxygen circulate around the cells and up to the palisade region. The air spaces are particularly large in the vicinity of stomata, where CO2 is taken up from the outside air and O2 is discharged.

stomata with guard cells

- stomata: A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant.
- guard cell: The two cells that flank the stomatal pore and regulate the opening and closing of the pore.

bundle sheath cells

- Each vein is enclosed by a protective bundle sheath, consisting of one or more layers of cells, usually parenchyma cells.

cuticle

A waxy covering on the surface of stems and leaves that prevents desic- cation in terrestrial plants.

Cutaway of a leaf (another view)

Phenotypic plasticity

- The underwater leaves of Cabomba are feathery, an adaptation that protects them from damage by lessening their resistance to moving water. In contrast, the surface leaves are pads that aid in flotation. Both leaf types have genetically identical cells, but their different environments result in the turning on or off of different genes during leaf development.
- Cell differentiation is the process by which cells with the same genes become differ- ent from one another.

Modified Leaves

1. Bracts
2. Spines
3. Tendrils
4. Reproduction
5. Storage

1. Bracts

Bracts. Often mistaken for petals, the red parts of the poinsettia are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators.

2. Spines

Spines. The spines of cacti, such as this prickly pear, are actually leaves; photosynthesis is carried out by the fleshy green stems.

3. Tendrils

Tendrils. The tendrils by which this pea plant clings to a support are modified leaves. After it has "lassoed" a support, a tendril forms a coil that brings the plant closer to the support. Tendrils
are typically modified leaves, but some tendrils are modified stems, as in grapevines.

4. Reproduction

Reproductive leaves. The leaves of some succulents, such as Kalanchoë daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.

5. Storage

Storage leaves. Most succulents, such as this ice plant, have leaves adapted for storing water.

Venus fly trap

The Plant Body Plan: The Root System

- support
- absorption
- storage

Root Growth and root hairs

Monocots vs. Dicots

Soil Horizons

Distribution of water in the soil

Primary root growth

- Growth occurs just behind the tip in three overlapping zones of cells at successive stages of primary growth. These are the zones of cell division, elongation, and differentiation

Root hair

- for example, a root hair is an extension of an epidermal cell near the tip of a root.
- Root hairs, which account for much of this absorption, enhance this process by greatly increasing the surface area of the epidermis.

Epidermis

The dermal tissue system of non-
woody plants, usually consisting of a single layer of tightly packed cells.

Cortex

In plants, ground tissue that is between the vascular tissue and dermal tissue in a root or eudicot stem.

Vascular cylinder

(Stele) In angiosperm roots, the stele is a vascular cylinder, consisting of a solid core of xylem and phloem. In most eudicot roots, the xylem has a starlike appearance in cross section and the phloem occupies the indentations between the arms of the xylem "star."

Zone of differentiation

Even before the root cells finish lengthening, many begin specializing in structure and function. In the zone of differentiation, or zone of maturation, cells complete their differentiation and become distinct cell types.

Zone of elongation

- Typically, a few millimeters be- hind the tip of the root is the zone of elongation, where most of the growth occurs as root cells elongate—sometimes to more than ten times their original length. Cell elongation in this zone pushes the tip farther into the soil.

Zone of cell division

The zone of cell division includes the root apical meristem and its derivatives. New root cells are produced in this region, including cells of the root cap.

Root Cap

which protects the delicate apical meristem as the root pushes through the abrasive soil during primary growth. The root cap also secretes a polysaccharide slime that lubricates the soil around the tip of the root

Root Apical Meristem

- Meanwhile, the root apical meristem keeps adding cells to the younger end of the zone of elongation.

Cross section of a eudicot root

Root with xylem and phloem in the center (typical of eudicots). In the roots of typical gymnosperms and eudicots, as well as some monocots, the stele is a vascular cylinder appearing in cross section as a lobed core
of xylem with phloem between the lobes.

Endodermis

The inner-most layer of the cortex is called the endodermis, a cylinder one cell thick that forms the boundary with the vascular cylinder.
- the endodermis is a selective barrier that regulates passage of substances from the soil into the vascular cylinder....

Pericycle

Lateral roots arise from the pericycle, the outermost cell layer in the vascular cylinder, which is adjacent to and just inside the endodermis. A lateral root pushes through the cortex and epidermis until it emerges from the established root.

Stele

Monocots: in many monocot roots, the vascular tissue consists of a central core of parenchyma cells surrounded by a ring of xylem and a ring of phloem
Eudicots: the stele is a vascular cylinder, consisting of a solid core of xylem and phloem (Figure 35.14a). In most eudicot roots, the xylem has a starlike appearance in cross section and the phloem occupies the indentations between the arms of the xylem "star."

Vascular tissue of a eudicot root

Cross section of a eudicot root

Vascular tissue of a eudicot

Lateral root emergence

- the lateral root forms in the pericyle, pushed through the cortex and eventually ruptures the epidermis

Cross section of a monocot root

- core of parenchyma
- Root with parenchyma in the center (typical of monocots). The stele of many monocot roots is a vascular cylinder with a core of parenchyma surrounded by a ring of xylem and a ring of phloem.

Root types

1. Prop roots
2. Aerial roots
3. storage roots
4. Pneumatophores
5. Buttress roots

1. Prop roots

- provide support in sandy soils that are shallow and unstable.

2. Aerial roots

The seeds of this strangler fig germinate in the branches of tall trees of other species and send numerous aerial roots to the ground. These snakelike roots gradually wrap around the host tree and objects such as this Cambodian temple ruin. Eventually, the host tree dies of shading by the fig leaves.

3. storage roots

Many plants, such as the common beet, store food and water in their roots.

4. Pneumatophores

Also known as air roots, pneumatophores are produced by trees such as mangroves that inhabit tidal swamps. By projecting above the water's surface, they enable the root system to obtain oxygen, which is lacking in the thick, waterlogged mud

5. Buttress roots

Because of moist conditions in the tropics, root systems of many of the tallest trees are surprisingly shallow. Aerial roots that look like buttresses, such as seen in this ceiba tree in Central America, give architectural support to the
trunks of such trees.

Wild Mustard selections

Apical bud

- Cabbage

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