Plant bio exam 1

What is a plant

Organisms that are autotrophic “self-feeders” (photosynthetic organisms)

Embryophytes (land plants)

Eukaryotic

Multicellular

Photosynthetic (mostly)

Alternation of generations

Gametes protected by layer of non-reproductive cells

Cellulose cell walls

Vacuoles within cells

Store starch within cells

Four groups of embryophytes

Nonvascular plants (mosses)

Seedless vascular plants

Seed plants w “naked seeds” (gymnosperms)

Seed plants w flowers (angiosperms)

What are the major components of a plant cell

Cell wall, Plasma membrane, Protoplast = all except wall, Cytoplasm = liquid in cell, Nucleus, Organelles, Vacuole

Diff plant cell types perform diff funcs

Photosynthetic cells

Water conducting cells

Fibers (support)

Storage cells

What are plastids

Organelles found only in plants and some algae

Have a double membrane (outer & inner bilayers)

Contain DNA and ribosomes

Grow and divide similarly to bacteria

There are 6 types of plastids with diverse functions
Reproduce by fission

Types of plastids: Proplastids

Small, undifferentiated plastids

Found in young cells

In light, often develop into chloroplasts

In dark, can develop into other plastids

Type of plastids: Chloroplasts

Contain a green pigment called chlorophyll

Site of photosynthesis

Have a complex internal structure

Found mostly in shoot tissues, but any tissue exposed to light can form chloroplasts

Type of plastids: Chromoplasts

Yellow, orange, red pigments (e.g. carotenes, xanthophylls)

Lipid-soluble

Often present in flowers, fruits and leaves

Also in roots (carrots, etc)

Precise functions unclear: attractants for pollination and seed

dispersal, aid in photosynthesis

Type of plastids: Leucoplasts

colorless, no pigment

synthesize oils, proteins, other materials

Type of plastids: Amyloplasts

Stores starch (a type of leucoplast)

Involved in gravity response

Type of plastids: Elaioplasts

store oils (another type of leucoplast)

What is a vacuole?

Large membrane-bound organelle

Surrounded by a single membrane

Cells can have many small, or one large, vacuole

Function in storage

water, salts, minerals, metabolites, pigments

• anthocyanins, water-soluble

• nutrients in seeds

• toxic metabolites, cellular waste

Aids in cell growth

Digestive, recycling organelle (like lysosomes in animals)

Peroxisomes

Single-membrane

Self-replicating but no DNA

Detoxification of peroxide, other toxins

Site of many metabolic reactions and storage

Metabolites, crystals

Plant metabolites: Primary metabolites

found in all plant cells

necessary for life: lipids, amino acids, carbohydrates, nucleotides

Plant metabolites: Secondary metabolites

Found only in some cells

Function in defense, signaling, pollinator attraction

• Alkaloids, terpenoids, cardiac glycosides, phenolics (flavonoids including anthocyanins)

Cell walls are the key feature that distinguish plant & animal cells

Function: Constrain expansion, Prevent cell rupture, Provide protection

Located outside the plasma membrane

Largely determine size and shape of cells

Different cell types have different cell wall features

Permanent but dynamic

Walls of adjacent cells are separated by the middle lamella

Primary cell wall

All plant cells have a primary cell wall

Deposited before and during growth of cell

Secondary cell wall

Formed only in specialized cell types (fibers, water conducting cells)

Deposited after growth of cell stops

Provides strength but prevents further growth of cell

What are cell walls made of

Nonliving materials: cellulose microfibrils, hemicelluloses, others (pectin, proteins, ligin, suberin, waxes)

cell walls are built by the cell they surround

How do plant cells grow if they are surrounded by walls

Permanent but dynamic

Only cells that only have primary cell walls can grow

Increase in cell size is due vacuole enlargement

Cellulose microfibril orientation influences direction of expansion

Growth is perpendicular to the orientation of the fibrils

How do plant cells divide if theyre surrounded by walls

Plant cells divide from the inside out

Formation of the cell plate starts in the center of the cell

The cell plate expands to the edges, eventually dividing the cell in two

How do plant cells communicate “through” their walls

Two main pathways to exchange signaling molecules:

• Symplastic pathway (“symplast”) – through cell protoplasts, Through the living parts of plant

Apoplastic pathway (“apoplast”) – through cell walls and intercellular space

• Through nonliving parts of plant

Symplastic communication occurs through plasmodesmata

Cytoplasmic connection between cells through the

wall

Channel through the wall is lined with plasma membrane

A strand of ER extends through the channel and connects the ER of both cells (desmotubule)

Where do plant embryos form?

Embryos form in ovules that are within the carpels: ovules become seeds and carpels become fruits

What happens at the end of embryogenesis?

Cell division, growth, and differentiation stop

Food reserves are created (endosperm or cotyledons)

Desiccation: loss of water from the seed, up to 90% of water is lost, metabolism almost entirely shuts down

Seed coat hardens

Desiccation causes seeds to enter either a quiescent state: Quiescent seeds

In a “resting” state

Germinate readily in favorable environmental conditions

Desiccation causes seeds to enter either a dormant state: Dormant seeds

Do not germinate even in favorable environmental conditions

Need a second “cue” or stimulus togerminate

Dormant seeds require a second cue to break dormancy and germinate

This maximizes the seedling’s chance for survival

Some seeds require scarification: breakdown of a thick or resistant seed coat

• Passing through the digestive system of a bird or mammal

• Mechanical cracking or scraping of the seed coat

Some seeds have inhibitors in the seed coat thatmust be leached away by rain

Some seeds respond to chemicals in smoke from a fire

In the California chaparral, fire is key for seed germination

Manzanitas

Seeds survive for a long time in soil

Cannot germinate except after a fire

Water and chemicals in smoke stimulate germination

Seedlings have ample space and light

What does “seed germination” mean?

Seed germination = resumption of embryo growth

Germination depends on external (environmental) cues

• Available water, oxygen, temperature, light

• The seed must take up (imbibe) water for metabolic activities to resume

epigeous- type of germination

cotyledons above ground

hypogeous- type of germination

cotyledons below ground

What do we mean when we refer to “development”?

The events and processes that form the body of an organism after fertilization

Growth

• Irreversible increase in size

• Cell division and enlargement

Differentiation

• Cells become different from each other and functionally specialized

Morphogenesis

• Establishment of form (shape) and pattern

All post-embryonic organs are formed through the action of what

The meristems

Plant growth occurs in 2 stages: Primary growth

Growth that occurs through the action of apical meristems

Increases the length/height of the plant body

Primary tissues formed

Apical meristems don’t directly form new organs/tissues

Plant growth occurs in 2 stages: Secondary growth

Growth that occurs from lateral meristems

Vascular cambium and cork cambium

Increases the diameter of stems and roots

forms wood and barks- all woody plants have this growth, monocots don’t

Apical meristems produce primary growth

The first two apical meristems are formed during embryogenesis

An apical meristem is found at tips of all stems and roots including branches

Meristems contain “initial” cells (stem cells) that divide to produce all new cells for the life of the plant

How do apical meristems function?

Meristems balance cell division with differentiation

• Cells at center remain meristematic

• Cells away from center differentiate into organs, tissues

• Meristems are displaced apically as cells below them elongate and differentiate

• Extends plant body length (growth)

Meristematic activity is responsible for the continuous and indeterminate growth and development of plants

Meristems balance cell division with cellular differentiation

These panels show a shoot meristem over time

Cells at center

• Divide

• Remain meristematic (undifferentiated and able to divide)

Meristems balance cell division with cellular differentiation

These panels show a shoot meristem over time

Cells at center

• Divide

• Remain meristematic

Cells at the periphery

• Primary meristems

• Differentiate into tissues, organs

What are the characteristics of the three tissue systems?

Ground

• Internal, fundamental tissues

Vascular

• conducting (transport) tissues

Dermal

• Outer, protective tissues

The ground tissue typically occurs between

the epidermis and vasculature

The ground tissue consists of three basic cell types

Parenchyma

Collenchyma

Sclerenchyma

Parenchyma

Most common cell type

Living at maturity

Relatively undifferentiated

Only has primary cell walls

Maintain ability to divide

Highly metabolic

Many functions: photosynthesis, storage, secretion

Transfer cells are parenchyma with wall ingrowths

Facilitate the movement of solutes

Occur adjacent to xylem and phloem

Therefore, are ground tissue, but are next to vascular tissue

Collenchyma

Living at maturity

Only primary cell walls but unevenly thickened

Flexible (stem can bend)

Support growing stems, leaves, and flowersRarely found in roots

Collenchyma supports young growing tissue

Living at maturity

Only primary cell wall but unevenly thickened

Flexible (stem can bend)

Support growing stems, leaves, and flowers

Rarely found in roots

Sclerenchyma

Dead and empty at maturity

Thick, often lignified, 2˚ cell walls

Provide strength and support in cells and organs that have reached full size

Two types of cells: fibers and sclereids

The vascular tissue system: how plants move materials around their bodies

Conducting tissues are organized into vascular bundles

Xylem

• Conducts water and dissolved minerals

Phloem

• Conducts sugars (photosynthate), hormones, lipids, amino acids, and more

Fibers

Parenchyma

Xylem

Conducts water and dissolved minerals

Unidirectional movement from roots to shoots

Also functions in support

Phloem

Conducts sugars (photosynthates), hormones, lipids, amino acids, and more Multidirectional: source to sink

• Source = site of production or storage

• Sink = site of use

Tracheids

In all vascular plants

Water moves through pit pairs

Vessel elements

In angiosperms only

Water moves through perforated end walls and pit pairs

Xylem cell types: key features both tracheids and vessel elements:

Cells are dead at maturity

Programmed cell death

No cytoplasm, nucleus, organelles

Thick secondary walls

Pits for water flow between cells

Xylem cell types: key features of vessel elements

Shorter, wider, stacked end to end

Perforation plates between ends of cells

Elaborately patterned secondary walls

Annular, helical (spiral), scalariform, reticulate, pitted

Thick secondary walls provide support

(Wood is secondary xylem)

Secondary wall is primarily composed of lignin

Two types of sieve elements

Sieve cells (gymnosperms) & Sieve tube members (angiosperms)

Cells are alive at maturity, but nuclei degenerate

Companion cells support and direct sieve elements

Movement of substances is through plasmodesmata and sieve plates (for sieve tube elements)

Sieve cells (gymnosperms)

Narrower diameter

Narrower pores

Extensive overlap at cell ends

Sieve tube elements (angiosperms)

Sieve plates on end walls facilitate movement between sieve tube elements

Larger diameter

Larger and more pores

Cells are stacked into sieve tubes

At maturity, remaining cellular components are distributed along the wall: Sieve elements are highly connected to companion cells

Companion cells deliver all signaling and regulatory molecules, proteins, and ATP

Serves as life support system for the sieve element

Dermal Tissue system

outermost layer of plant body

Epidermis: Outer protective covering during primary growth. Cuticle covers exterior (above ground)

Periderm (bark)

Outer protective covering in plants with secondary growth

Mechanical protection

Dermal tissue features

Epidermis often a single layer of cells

Regulates gas exchange between plant and environment

Outer cell walls coated with cutin + wax = cuticle: Prevents water loss, reflects light, indigestible

Guard Cells

specialized cell type in epidermis

Pair of cells surrounding a pore (stoma, pl: stomata)

Regulate gas exchange

Open and close in responseto turgor pressure: Open when turgid. Turgid = filled with water

Subsidiary Cells

specialzied cell in epidermis

occur alognside guard cells

distinct in shape from other cells

Root hairs

Specialized cell type in epidermis

Increase surface area for uptake of water, nutrients

Trichomes

specialized cell type in epidermis

Found on any organ in shoot system

Reflect light, deter insects, hold humidity, secrete substance

What are the main functions of root systems?

Anchoring, support

Absorption

Storage

Conductance

Secondary metabolite and hormone synthesis

Modification of, and interactions with, soil and soil microbes

Eudicot plants have a tap root system

The primary root is the root that forms as a continuation of the embryonic root

Primary root gives rise to lateral

roots: Iterative root formation produces a

highly branched root system

Primary root is usually more prominent: Taproots generally penetrate deeper into the soil than fibrous root systems

Monocot plants have a fibrous root system

Primary root is short lived

Root system is formed from many

adventitious roots that grow from the base of the stem

No one root is more prominent than any other root

Adventitious roots are derived from the stem and serve many functions

Monocots have only adventitious roots

Eudicots have a taproot but can also have adventitious roots

Important in asexual reproduction, structural support, and more

fibrous root systems and adventitious roots are not synonymous

All fibrous root systems are composed of adventitious roots

All monocots have fibrous root systems

BUT

Not all adventitious roots are fibrous roots

Adventitious roots are also found in many eudicot species

Plants maintain a balance between growth of the root and shoot systems

Need to balance the surface area needed to make food vs. the surface area needed to take up water and minerals

In young plants, the uptake (root) area exceeds photosynthetic (shoot) area

Ratio becomes more balanced as plants mature (age

The root cap covers the tip of the root

Root cap is a sheath of living parenchyma cells

Thimble-like structure

Functions: Protect the apical meristem, Aid in soil penetration

Secrete mucilage: Perceives gravity

Cells of the root cap must be constantly replaced

Columella cells: Function to direct root growth through soil

Perceive water and gravity (contain amyloplasts)

Cells of the root cap are rubbed off as the root extends through the soil

These cells are constantly regenerating

The elongation zone is where increase in root length occurs

Cell division ceases

Cells elongate- Can increase in length

up to 300% in 3 hours

This moves the root tip forward through the soil

Zones overlap (gradual transition

In the maturation/differentiation zone, cells acquire specialized features and function

Cell growth ceases

cells undergo differentiation

Primary tissues (primary growth) form

Root hairs form on epidermal cells

Primary cell walls become more rigid

Secondary walls are laid down in some cells

The root epidermis absorbs water and minerals

Closely packed cells with thin walls

Absorption of water and solutes facilitated by root hairs: Increase root surface area, Invade smaller pores in soil

Beneficial symbiotic interactions: Bacteria (nitrogen fixation), Fungi (mycorrhizal associations

Root ground tissue regulates transport into/out of root vasculature: Cortex

takes up the largest amount of space in the primary tissues of the root

Intercellular air spaces (cells are loosely packed)

Plastids store starch

Root ground tissue regulates transport into/out of root vasculature: endodermis

Innermost layer of cortex

Cells are tightly spaced

Specialized secondary cell wall: Casparian strip

The Casparian strip

Forms as endodermal cells mature (differentiate)

Present in anticlinal walls (perpendicular to the root surface)

Contains lignin and suberin which make it hydrophobic

Blocks apoplasticmovement across the endodermis

The vascular cylinder contains the

primary vascular tissues and pericycle

The pericycle cells surround the vascular tissues, but are nonvascular

Derived from the procambium but do not transport materials

Key functions: Lateral root formation, Regeneration

Modified roots: aerial roots

Prop roots (e.g. maize): Support and uptake once established

Pneumatophores (air roots): aeration of root system

Stilt roots – produced from stems and branches

What is the shoot made up of?

The shoot apical meristem is formed in the plant embryo

Produces all structures of the shoot system

Consists of nodes and internodes

What is the shoot system made of

Consists of the shoot + leaves and axillary buds

Axillary buds contain axillary meristems that will form branches

Indeterminate activity of shoot meristems produces all aboveground organs

No protective cap like root meristem

Shoot apex = meristem + young leaf primordia

Small immature leaves extend over shoot meristems and protect

Primordium: Small mass of cells that

grows into organ (leaf, branch, flower, root)

Phytomeres are repeated units of:

node

attached leaf

the internode below

bud at base of internode

Boundaries indicated by dashed lines

Two basic organizational patterns of primary vasculature in stems: Eudicots and gymnosperms:

Vascular tissue is in separate bundles separated by ground tissue

Bundles are in a ring that separates cortex and pith

Vascular cambium forms a continuous ring between the xylem and phloem

Continuous between bundles

Two basic organizational patterns of primary vasculature in stems: In monocots:

Vascular bundles are scattered throughout the ground tissue

No pith

No vascular cambium

Modifications of stems

Aid in plant support: Example: tendrils

Photosynthesis: Example: cladodes

Defense: Example: thorns

Storage: Bulb: small stem with overlapping modified fleshy leaves, Corm: solid fleshy stem, Tuber: underground stems

Asexual reproduction: Rhizome: underground horizontal stems with short internodes (also storage). Stolon: slender aboveground horizontal stems with long internodes

The arrangement of leaves on a stem is

called

Phyllotaxis

Arrangement of leaves: Spiral

most common

One leaf at each node

Sometimes used synonymously with alternate

Distichous: one leaf per node, but on opposite sides of the stem (grasses)

Arrangement of leaves: Opposite

Common in many plant families

Two leaves per node opposite each other

Decussate: successive pairs are at right angles to each other

Arrangement of Leaves: Whorled

3 or more leaves per node

What are the parts of a leaf?

Petiole (stem-like) attaches blade to shoot node

Lamina (blade)

Stipules (scale or leaf-like appendages at base of petiole in some species)

Some leaves lack a petiole

In most monocots the base of the leaf forms a sheath that wraps around the stem

In some eudicots the blade attaches directly to the stem (sessile)

Simple leaves

Leaf blade is undivided, there are no completely separate sections

May have a smooth margin (entire) or may have lobes or teeth or other modifications of the margin

Compound Leaves

Leaf blade is divided up into distinct separate leaflets

Each leaflet often has its own petiole (petiolule)

The rachis is an extension of the petiole that the leaflets attach to (pinnately compound)

How do you determine if a leaf is simple or compound

Leaves have axillary buds, leaflets do not

Leaflets all lie in the same plane, leaves usually extend from the stem in various planes

External leaf anatomy: Dermal tissue layer - leaf epidermis

Compactly arranged cells

Covered by waxy cuticle

May have trichomes

Stomata: Required for gas exchange, May be on either surface (commonly on the lower side)

Depends on environment and leaf orientation