PB 200 Exam 2 Study Guide

major functions of roots

• anchor plant

• absorbing water, minerals, and transporting them to stem

• may be modified for storage → carrot/sweet potato

• prevent erosion → ecosystem service

morphology

outward structure and appearance

2 types of root morphology

Fibrous and Taproot

Fibrous Root

1. smaller roots individually

2. more branching → increase surface area

3. more spread out

4. grow closer to soil surface

5. many monocots

TAP ROOT:

• larger

• less branching

• less spread out

• grow deeper

• (many dicots and gymnosperms)

Root anatomy

Roots are composed of several tissues, some of which are unique to them

stele of a root or stem

the vascular tissues derived from primary growth

What does the stele of a root include?

In roots, it includes the pericycle (developed from the procambium) and all tissues internal to it.

What do monocots typically have in the center of their roots that is not involved in long-distance transport?

pith (parenchyma)

Specialized Tissues Found in or on Roots

Pericycle

Root Hairs

Endodermis

Pericycle

vascular tissue → type of primary growth and origin of lateral/branch roots

Root hairs

unicellular extensions of the epidermis

• function: increase surface area and absorption

• thin/fragile/temporary

Endodermis

A ground tissue that has a waxy, hydrophobic Casparian strip/layer around almost all of its cells. This strip or layer prevents water and nutrients from being transported between cells. Water and nutrients must be transported through the living components of the cell.

What is the pathway of water from the soil into and through the root to the stem?

Two major transport pathways:

1. Apoplastic

2. Symplastic

Apoplastic transport

transport between plant cells along cell walls or intercellcular spaces

Symplastic transport

(within the same cell) transport from cell via plasmodesmata. This type of transport is required at the endodermis.

Nitrogen-fixing bacteria, including Rhizobia species (associated with the legume family of alfalfa, peanuts, soybean

1. Bacteria that “infect” root hair cells and migrate into the cortex (but no further)

2. Stimulate root cell division and enlargement

3. Results in the formation of nonharmful nodules

4. The plant receives fixed nitrogen

Plants can’t access ___ so they rely on bacteria to break it down into ammonia.

nitrogen

nitrogenase

enzyme produced by bacteria that makes this conversion possible

What do bacteria get in exchange for a plant?

sugar

Mycorrhizae

1. occur in or on 80% of land plants

2. evidence suggests that mycorrhizae extending from roots can connect or network the root systems of nearby plants

3. two types:

   1. Endomycorrhizae:

   2. Ectomycorrhizae:

Endomycorrhizae

fungal cells penetrate epidermis and cortex and grow inside of plant cells

Ectomycorrhizae

fungal cells grow outside/between epidermis and cortex cells

Major Functions of Stems:

• conduct H2O and minerals from roots to leaves

• provide aerial support for leaves

• some are photosynthetic

• conduct nutrients via phloem to roots , flowers, young leaves

• some modified for storage → potato/ginger

• some horizontal and run just above or below ground

Some stems are diminished (less prominent) but still serve important functions!

carnivorous plants → stems are leaf-anchoring

Herbaceous stems

generally have not undergone significant secondary growth and are often green, fleshy, and flexible

woody stems

have undergone secondary growth and developed a periderm. They are typically not green, are harder or firmer, and less flexible.

True or false: some herbaceous stems can become woody over time

true

Examples of species that are herbaceous at maturity:

• monocots: lily, orchid, some grasses, onion

• dicots: mint, parsley, beans, Coleus, clover

Examples of species that are woody at maturity:

• monocots: palm, date, coconut

• dicots: apple, oak, maple, Azalea, pecan, redbud

node

a point of attachment, typically of a leaf or a flower

internode

the area of the stem between 2 nodes

axillary bud

a structure composed of a dormant apical meristem and scales (modified leaves) covering it. Occurs specifically in the axil, which is the angle between a leaf attachment and the main stem axis.

terminal bud

a dormant apical meristem covered by scales at the apex or end of the stem or the stem branch

leaf (petiole) scar

the location where a leaf was once attached. Vascular bundle scars may be visible.

terminal bud scale scars

a ring-like array of scars indicating the location of a previous terminal bud.

lenticels

small perforations in the periderm of woody stems through which limited gas exchange may occur.

Opposite arrangement

2 leaves per node (dogwood, maple, ash)

Alternate arrangement

1 leaf per node (ex. oak, hickory, tulip tree)

whorled

3 or more leaves per node (ex: catalpa, oleander)

Monocot Stem Anatomy

• vascular tissue arrangement: scattered

• presence of pith: no

• cortex cells: yes

Dicot Stem Anatomy

• vascular tissue arrangement: in a ring

• presence of pith: yes

• cortex cells: yes

Potato

• Solanum sp.

• Nightshade family

• Solanaceae

• Stem

• Dicot

• Temperate climate

Sweet Potato

• Ipomoea sp.

• Morning glory family

• Convolvulaceae

• Root

• Dicot

• Subtropical

Yam

• Dioscorea sp.

• Yam family

• Dioscoreaceae

• Stem

• Monocot

• Tropical

Nonbotanical factoids:

• the “candied yams” you eat are most likely sweet potatoes

• NC is the #1 sweet potato producer in the USA

-phyll

leaf

phylloplane

surface of the leaf

phyllosphere

microclimate of the leaf

What processes or activities occur in the leaf?

• photosynthesis

• storage

• protection (spikes on cacti)

• transpiration → loss of water vapor via stomata

• climbing → tendrils

• prey capture (carnivorous)

LEAF MORPHOLOGY:

• Some leaves may have leaf-like appendages at their bases called stipules.

• Not all leaves have a distinct petiole.

Leaves are perhaps the most varied plant structures. Botanists have developed ways to describe them based on certain characteristics. Among the most common, in addition to their arrangement on the stem, are the following:

1. BLADE SHAPE (many types)

   1. specific appearances of the base and/or the tip of the blade may be used

2. BLADE MARGINS (again, many types)

3. Pinnate, Palmate, (Netted/reticulated forms → common in dicots)

   1. (Pinnate. Pinna: feather. Midrib/midvein with lateral veins and minor veins)

   2. (palmate: palm-like, several major veins radiate from base)

   3. and Parallel/Linear (More common in monocots)

1. COMPLEXITY

   1. Simple: One intact blade

   2. Compound: Blade separated into leaflets

Leaf Anatomy

Epidermis (lower and upper): outer coverings of leaf that produces cuticle

• numerous stomata regulated by guard cells

Cuticle: prevents water loss

• waxy, hydrophobic

• provides protection

Trichomes: hairs on leaf → reflect light, decreases air flow across leaf, may be defensive, reduce water loss

Mesophyll: bulk of blade, ground tissue, may be columnlike in shape → if so, palisade

• may be air spaces between cells → sponge

Vascular Bundle: veins: xylem and phloem surrounded by bundle sheath cells

Some anatomical differences between dicot and monocot leaves:

Mesophyll Composition:

• Monocots: may be spongy, typically not palisade

• Dictors: often have palisade and spongy mesophyll

Stomatal Density (average number of stomata per cm²):

• Monocots:

  • Corn → Upper: 5,500, Lower, 6,800

  • Oat → Upper: 2,500, Lower: 2,300

  • Wheat → Upper: 3,300, Lower: 1,400

• Dicots: (lower is usually much higher)

  • Bean → Upper: 4,000, Lower: 28,000

  • Coleus → Upper: 0, Lower: 14,100

  • Geranium → Upper: 1,900, Lower, 5,900

spinose

sharp projections of leaves

spines

modified leaves (ex: cacti, Acacia) → have vascular tissue, protection against predation, emerging of some leaves may be spinelike (holly)

thorns

modified stem branches (ex. honey locust, some citrus) → vascular tissue, subtended by leaves

prickles

epidermis and cortex of stems or leaves (ex: rose, greenbrier) → no vascular tissue “shark fin” appearance

stinging (urticating hairs)

modified trichomes (ex: stinging nettle)

What do carnivorous plants mostly absorb?

macronutrients → N, P, Ca, Mo, poor soils

What do most terrestrial carnivorous plants possess?

small thickened stems anchoring highly modified leaves for trapping prey. The trapping mechanism is usually classified as being active or passive. Prey attraction may be visual or chemosensory.

Venus Flytrap

NC and SC only. Active.

Sundew

semi-active, leaves wrap around prey

Pitcher Plants

passive, pitfall traps, insect drowns

bladderworts

active

bracts

specialized leaves, usually below flowers that are different in form or color → attract pollinators (ex: poinsettas, dogwood → leaves inside are the flowers actually)

Tendrils

there are tendrilating stems AND tendrilating leaves: (passion flower, pea, Virginia creeper, morning glory, wisteria)

• mechanical support

• direct growth

Reproductive Leaves:

• asexual propagation → plantlets

• produced on leaf margin → Kalanchoe (mother of thousands)

Xerophytes/water-conserving succulents

(ex: aloe, jade, cacti, sedurn)

• some may have extremely deep root systems

• thickened stems/leaves

hydrophytes

water lily, lotus, rushes

sun/shade leaves

2 forms of leaves on the same plant → dimorphism (ex. maple)

• strategy to maximize light capture

rhizome

horizontal underground stems

• short internodes

• thickened for storage

stolon

horizontal stem aboveground or underground

• longer internodes

• smaller in diameter

• some produce asexual plantlets

tuber

part of stolen that is modified for storage e.g. potato

Corm

• storage stem covered by thin or scaly leaves

  • meristem grows vertical stem

  • Crocus, Gladilous, Corrieflower plants

bulb

• fleshy storage leaves covering a small stem

  • onion, amerylies, daffodil, hycanith, garlic, shallot

abscission

cutting away

environmental factors of leaf abscission

• day length, water, temperature

• hormonal changes → degradation of cell walls of petiole, suberinization of cell layer nearest stem → leaf scar

What is happening when leaves change color and drop during the fall?

1. Breakdown and transport of cellular components

• cholorophyll broken down of some minerals

• nutrients transported to stems and roots

• reclamation of nutrients

2. Pigments develop or are unmasked.

• Reds: anthocyanins

• Tans or browns: tannins/ cell death

• Yellows or golds: carotenoids → plastids

• Other hues (oranges, etc.): combo of thereof

3. leaf drop→ abscission “to cut away”

   1. due to reduced water, temp, daylength, or hormonal changes

Metabolic reactions

Biochemical reactions carried out to maintain homeostasis.

ATP

a denotive triphosphate → energy currency of cells

ATP →

ADP + Pi diphosphate

The role of NADPH:

NADPH → NADP^+ + H + 2e (which can be donated to another molecule)

6 H₂O + CO₂ → 6O₂ + C₆H₁₂O₆

bulk reaction equation for photosynthesis

6 H₂O → 6O₂ is from ___

light

CO₂ → C₆H₁₂O₆ is from ___

chloroplasts

C₆H₁₂O₆

glucose

Is glucose the first product of photosynthesis?

No

sunlight is __

electromagnetic energy

electromagnetic energy

radiation that travels through space in waves

Artifical light

• portion of spectrum → visible (mostly)

• grow lamps → optimized for photosynthesis and far red light

Plant pigments

chlorophyll a, chlorophyll b, accessory pigments

Chlorophyll a

primary pigment

• Absorption spectra: blue/violet and red visible

• Functions: convert light energy into chemical energy via loss of electrons

Chlorophyll b

• Absorption spectra: blue/green and orange

• Functions: expands on spectrum of chl. a and can transfer energy to chl. a

Accessory pigments

• Absorption spectra: most absorb in UV spectrum of some green

• Functions: carotenoids

• Transfer light energy to chlorophyll → protection

• Dissipate light energy excess short wave

How did we first find out that photosynthesis is most active in the blue- and red-light spectra?

Red light is absorbed effectively by chlorophyll which ranges within this wavelength. It is utilized in the maximum amount. This red light is followed by blue light which falls next to red in the visible spectrum, thus it is also absorbed in a very effective way for photosynthesis.

Photosynthesis reactions can be divided into 2 general “sets” of reactions:

1. Light-dependent reactions

2. Light-independent reactions

light-dependent reactions

1. in and across thyaloid membranes of chloroplasts

2. H2O split

3. O2 byproduct

4. ATP and NADPH produced

light-independent reactions

1. or “carbon reactions” or “dark reactions”

2. in chloroplast stroma

3. CO2 is input → ATP and NADPH used

4. 3-carbon compounds produced

Where are chloroplast pigments anchored to?

thylakoid membranes

What do chlorophyll a and b form when they cluster together?

light-harvesting complexes and a reaction center.

photosystems (PS)

protein complexes of 200-300 pigment molecules (from chl. a and b)