You’ll leaf this knowing more!

A presentation of Chapters 35 – 39 byClarence Lewis, Megan Baxter, Josh Newton, and Vasu Patel

∙Morphology is an organism’s external form.

∙Vascular plants have three basic organs: roots, stems, and leaves.

∙A root is an organ that anchors a vascular plant in the soil, absorbs

minerals and water, and stores food.

∙A stem is an organ consisting of alternating nodes, the points at which leaves are attached, and internodes, the stem segments between nodes.

∙Leaves are the main photosynthetic organs of most plants, although green

stems are also photosynthetic.Figure 35.2 An overview of a flowering plant.

Reproductive shoot (flower)

Terminal bud

NodeInternode

Terminalbud

Vegetativeshoot

BladePetiole

Stem

Leaf

Taproot

Lateral roots Rootsystem

Shootsystem

Axillarybud

∙Plants are composed of three tissue systems: dermal, vascular,

and ground.

∙The dermal tissue is the outer covering.

∙Vascular tissue, continuous throughout the plant, is involved

in the transport of materials between roots and shoots.

∙The functions of ground tissue include photosynthesis, storage,

and support.

Dermaltissue

Groundtissue Vascular

tissue

Figure 35.8 The three tissue systems.

∙Plant tissues are composed of three basic cell types: parenchyma, collenchyma, and sclerenchyma.

∙Parenchyma cells perform most of the metabolic functions of the plant, synthesizing and storing various organic products.

∙Collenchyma cells have thicker primary walls than parenchyma cells, though the walls are unevenly thickened.

∙Sclerenchyma cells have thick secondary walls usually strengthened by lignin and function as supporting elements of the plant.

∙Xylem is 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.

∙Phloem is vascular plant tissue consisting of living cells arranged and elongated tubes that transport sugar and other organic nutrients throughout

the plant.

∙A major difference between plants and most animals is that plant growth is not limited to an embryonic

period.

∙Annual plants complete their life cycle—from germination through flowering and seed production to

death—in a single year or less.

∙The life of a biennial plant spans two years.

∙Often, there is an intervening cold period between the vegetative growth season and the flowering season.

∙Plants such as trees, shrubs, and some grasses that live many years are perennials.

∙Perennials do not usually die from old age, but from an infection or some environmental trauma.

∙A plant is capable of indeterminate growth because it has perpetually

embryonic tissues, called meristems, in its regions of growth.

∙The pattern of plant growth depends on the location of meristems.

∙Apical meristems, located at the tips of roots and in the buds of shoots, supply cells for the plant to grow in

length.

∙Each spring and summer, as the primary growth extends the shoot,

secondary growth thickens the parts of the shoot that formed in previous

years.

Keyto labels

DermalGround

Vascular

Guardcells

Stomatal pore

Epidermalcell

50 µm

Surface view of a spiderwort(Tradescantia) leaf (LM)

(b)Cuticle

Sclerenchymafibers

Stoma

Upperepidermis

Palisademesophyll

Spongymesophyll

Lowerepidermis

Cuticle

Vein

Guard cells

Xylem

Phloem

Guard cells

Bundle-sheathcell

Cutaway drawing of leaf tissues(a)

Vein Air spaces Guard cells

100 µmTransverse section of a lilac(Syringa) leaf (LM)

(c)

Figure 35.18 Leaf anatomy.

∙Molecular biology is revolutionizing the study of plants.

∙Much of this research has focused on

Arabidopsis thaliana, a small weed in the

mustard family.

∙Growth involves both cell division and cell expansion.

∙Cell division in meristems increases cell number, increasing the potential for growth.

∙The plane (direction) and symmetry of cell division are important determinants of plant form.

∙While mitosis results in symmetrical redistribution of chromosomes between daughter cells, cytokinesis may be asymmetrical.

∙The plane in which a cell will divide is determined during late interphase.

∙The greatest expansion of a plant cell is usually oriented along the plant’s main axis.

∙Morphogenesis depends on pattern formation.

∙Morphogenesis organizes dividing and expanding cells into multicellular tissues and

organs.

∙Developmental biologists are accumulating evidence that gradients specific molecules, generally proteins or mRNAs, that provide

positional information.

∙One type of positional information is polarity, the identification of the root end and shoot end

along a well-developed axis.

∙Other genes that regulate pattern formation and morphogenesis include the homeotic

genes, which mediate many developmental events, such as organ initiation.

∙Clonal analysis of the shoot apex emphasizes the importance of a cell’s location in its

developmental fate.

∙In the process of shaping a rudimentary organ, patterns of cell division and cell expansion affect the differentiation of cells by placing them

in specific locations relative to other cells.

∙One approach to studying the relationship among these processes is clonal analysis,

mapping the cell lineages (clones) derived from each cell in an apical meristem as organs

develop.

∙In plants, a cell’s developmental fate is determined not by its membership in a particular

lineage but by its final position in an emerging organ.

∙Genes controlling transcription play key roles in a meristem’s change from a vegetative to a floral phase.

∙Unlike vegetative growth, which is indeterminate, the production of a flower by an apical meristem terminates primary growth of that shoot tip

as the apical meristem develops into the flower’s organs.

∙Once a shoot meristem is induced to flower, positional information commits each primordium arising from the flanks of the shoot tip to

develop into a specific flower organ.

∙Organ identity genes code for transcription factors.

∙The ABC model of flower formation identifies how these genes direct the formation of four types of floral organs.

Petals

Stamens

CarpelsAB

Sepals

C

C geneactivityB + C

geneactivity

A + Bgene

activity

A geneactivity

(a) A schematic diagram of the ABChypothesis. Studies of plant mutationsreveal that three classes of organ identitygenes are responsible for the spatial patternof floral parts. These genes are designated A,B, and C in this schematic diagram of a floralmeristem in transverse view. These genesregulate expression of other genesresponsible for development of sepals,petals, stamens, and carpels. Sepals developfrom the meristematic region where only Agenes are active. Petals develop where bothA and B genes are expressed. Stamens arisewhere B and C genes are active. Carpels arisewhere only C genes are expressed.

Figure 35.34The ABC

hypothesis.

(b) Side view of organ identity mutant flowers. The phenotype of mutants lacking a functional A, B, or C organ identify gene can be explained by combining the model in part (a) with the rule that is A or C activity is missing, the other activity occurs through all four whorls.

StamenCarpel

Petal

Sepal

Wild type Mutant lacking A Mutant lacking B Mutant lacking C

Activegenes:

Whorls:

A A C C C C AA CCCCCCCC A A C C C C AB B B B B B B B

A A B B A A B B AA A A A

∙Transport at the cellular level depends on the selective permeability of membranes.

∙The selective permeability of a plant cell’s plasma membrane controls the movement of solutes between the cell and the

extracellular solution.

∙Transport proteins embedded in the membrane can speed movement across the membrane. Others act as selective channels, providing a selective passageway across the

membrane. For example, the membranes of most plant cells have potassium channels that allow potassium ions (K+) to

pass, but not similar ions, such as sodium (Na+).

∙Phylloxtaxy is the arrangement of leaves on the shoot of a plant.

∙Mycorrhizae is a mutalistic association of plan roots and fungus.

MineralsH2O CO2

O2

CO2 O2

H2O Sugar

Light

Sugars are produced byphotosynthesis in the leaves.5

Sugars are transported asphloem sap to roots and otherparts of the plant.

6

Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon forphotosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.

4

3

Water and minerals aretransported upward from

roots to shoots as xylem sap.

2

Roots absorb waterand dissolved minerals

from the soil.

1 Roots exchange gases with the air spaces of soil, taking in O2 and discharging CO2. In cellular respiration, O2 supports the breakdown of sugars.

7

Transpiration, the loss of waterfrom leaves (mostly through

stomata), creates a force withinleaves that pulls xylem sap upward.

Figure 36.2 An overview of resource acquisition and transport in a vascular plant.

∙Proton pumps play a central role in transport across plant membranes.

∙The most important active transport protein in the plasma membrane of plant cells is the proton pump.

∙The proton gradient also functions in co-transport, in which the downhill passage of one solute (H+) is coupled with the uphill passage of another, such as NO3- or

sucrose.

∙The role of proton pumps in transport is a specific application of the general mechanism called chemiosmosis, a unifying process in cellular energetics.

CYTOPLASM EXTRACELLULAR FLUID

ATP

H+

H+ H+

H+

H+

H+H+

H+

Proton pump generates membrane potentialand H+ gradient.

–

––

–

– +

+

+

+

+Figure 36.3Proton pumps

provide energy for solute transport.

∙Differences in water potential drive water transport in plant cells.

∙In the case of a plant cell, the direction of water movement depends on solute concentration and physical pressure.

∙Plant biologists measure psi in units called megapascals (MPa), where one MPa is equal to about 10 atmospheres of pressure.

∙The combined effects of pressure and solute concentrations on water potential are incorporated into the following equation, where psip is the pressure

potential and psis is the solute potential (or osmotic potential).

psi = psip + psis

∙A walled cell with a greater solute concentration than its surroundings will be turgid, or firm.

∙Turgor pressure is the force directed against a plant cell wall after the influx of water and swelling of the cell due to osmosis.

∙Vacuolated plant cells have three major compartments.

∙While the thick cell wall helps maintain cell shape, it is the cell

membrane, not the cell wall, which regulates the traffic of material into

and out of the protoplast.

∙The membrane that bounds the vacuole, the tonoplast, regulates

molecular traffic between the cytosol and the contents of the

vacuole, called the cell sap.

∙In most plant tissues, two of the three cellular compartments are

continuous from cell to cell.

Figure 36.11Cell compartments

and routes for short-distance

transport.

Key

Symplast

Apoplast

The symplast is thecontinuum of

cytosol connectedby plasmodesmata.

The apoplast isthe continuumof cell walls andextracellularspaces.

Apoplast

Transmembrane route

Symplastic routeApoplastic route

Symplast

Transport routes between cells. At the tissue level, there are three passages: the transmembrane, symplastic, and apoplastic routes. Substances may transfer from one route to another.

(b)

Transport proteins inthe plasma membrane

regulate traffic ofmolecules betweenthe cytosol and the

cell wall.

Transport proteins inthe vacuolarmembrane regulatetraffic of moleculesbetween the cytosoland the vacuole.

Plasmodesma

Vacuolar membrane(tonoplast)Plasma membrane

Cell wall

Cytosol

Vacuole

Cell compartments. The cell wall, cytosol, and vacuole are the three maincompartments of most mature plant cells.

(a)

∙Root hairs, mycorrhizae, and a large surface area of cortical cells enhance

water and mineral absorption.

∙Much of the absorption of water and minerals occurs near root tips, where the

epidermis is permeable to water and where root hairs are located.

∙As the soil solution moves along the apoplast into the roots, cells of the

epidermis and cortex take up water and certain solutes into the symplast.

∙Most plants form partnerships with symbiotic fungi to absorb water and

minerals from soil.

∙The endodermis functions as a selective sentry between the root cortex and vascular tissue.

∙Water and minerals in the root cortex cannot be transported to the rest of the plant until they enter the xylem of the vascular cylinder.

∙Those minerals that reach the endodermis via the apoplast are blocked by the Casparian strip in the walls of each endodermal cell.

∙To enter the vascular cylinder, minerals must cross the plasma membrane of the endodermal cell and enter the vascular cylinder via

the symplast.

∙The last segment in the soil-to-xylem pathway is the passage of water and minerals into the tracheids and vessel elements of the xylem.

∙The ascent of xylem sap depends mainly on transpiration and the

physical properties of water.

∙Root pressure causes guttation, the exudation of water droplets that can be seen in the morning on the tips of grass blades or the leaf margins of some small, herbaceous dicots.

∙The mechanism of transpiration depends on the generation of

negative pressure (tension) in the leaf due to the unique physical

properties of water

∙The water film at the surface of leaf cells has a negative pressure, a pressure less than atmospheric

pressure.

Outside air = –100.0 MPa

Xylemsap

Leaf (air spaces) = –7.0 MPa

Leaf (cell walls) = –1.0 MPa

Trunk xylem = – 0.8 MPa

Wat

er

po

ten

tia

l g

rad

ien

t

Root xylem = – 0.6 MPa

Soil = – 0.3 MPa

MesophyllcellsStoma

Watermolecule

AtmosphereTranspiration

Xylemcells Adhesion Cell

wall

Cohesion,byhydrogenbonding

Watermolecule

Roothair

Soilparticle

Water

Cohesion and adhesionin the xylem

Water uptakefrom soil

Figure 36.15 Ascent of xylem sap.

∙The tension generated by adhesion and surface tension lowers the water potential, drawing water from an area of high water

potential to an area of lower water potential.

∙These features are morphological adaptations to enhance the absorption of light

for photosynthesis.

∙To make food, a plant must spread its leaves to the sun and obtain CO2 from air.

∙Transpiration also results in evaporative cooling, which can lower the temperature of a

leaf by as much as 10–15°C relative to the surrounding air.

∙The stomatal density of a leaf is under both genetic and environmental control.

∙Phloem translocates its sap from sugar sources to sugar sinks.

∙In contrast to the unidirectional flow of xylem sap from roots to leaves, the direction that phloem sap travels can vary.

∙A storage organ, such as a tuber or a bulb, may be either a source or a sink, depending on the season.

∙A sugar sink usually receives its sugar from the sources nearest to it.

∙Sugar from mesophyll cells or other sources must be loaded into sieve-tube members before it can be exported to sugar sinks.

∙In some plants, companion cells (transfer cells) have numerous ingrowths in their walls to increase the cell’s surface area and enhance

the transfer of solutes between apoplast and symplast.

∙Downstream, at the sink end of the sieve tube, phloem unloads its sucrose.

∙Pressure flow is the mechanism of translocation in angiosperms.

∙Phloem sap flows from source to sink at rates as great as 1 m/hr, faster than can be

accounted for by either diffusion or cytoplasmic streaming.

∙Pressure flow in a sieve tube drives the bulk flow of phloem sap.

∙The closer the aphid’s stylet is to a sugar source, the faster the sap will flow and the

greater its sugar concentration.

∙Genetic engineering of higher-yielding crop plants may depend on a better

understanding of factors that limit bulk flow of sugars.

∙Texture of soil depends on the sizes of its particles. The size of the

particles affects the availability of water, oxygen, and minerals.

∙Nutrition is the process by which an organism takes in and makes

use of food substances.

∙Humus is the remains of dead organisms and other organic

matter.

∙Soil Horizons are soil layers.

∙Loams are the most fertile soil type, made up of roughly equal amounts of sand, silt, and clay.

∙A soil’s composition is made of inorganic and

organic chemical components.

∙Topsoil’s ecosystem is made up with bacteria,

fungus, protists, animals, and the roots of plants.

∙Cation exchange is a process in which positively charged minerals are made

available to a plant when hydrogen ions in the soil

displace mineral ions from the clay particles.

∙The goal of soil conservation is to reduce damage.

∙Some agricultural practices can deplete the mineral content of soil, tax water reserves, and promote erosion.

∙Sustainable agriculture is a commitment embracing a variety of farming methods that are conservation minded, environmentally safe, and

profitable.

∙No-till agriculture is a plowing technique that involves creating furrows, resulting in minimal disturbance of the soil.

∙Phytoremediation is an emerging nondestructive biotechnology that seeks to cheaply reclaim contaminated areas by taking advantage of

some plant species’ ability to extract heavy metals and other pollutants from the soil and to concentrate them in easily harvested portions of the

plant.

∙Macronutrients are elements that are required in large amounts: such as Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphorus and Sulfur.

∙Micronutrients are elements required in small amounts, usually have catalytic functions as cofactors of enzymes.

∙Essential element is a chemical element required for the plant to grow from a seed and complete its life cycle, producing another generation in the form of

seeds.

∙Hydroponic culture is a method in which plants are grown in minerals solutions rather than soil.

Table 37.1Shows all the

essential macronutrient

and micronutrient elements in

plants.

∙Deficiency of mobile nutrient usually affects older

plants and for less mobile nutrient affects younger

plants.

∙Deficiency of potassium, phosphorus, and nitrogen especially are the most

common. Micronutrients are less common.

∙Moderation is important because overdose of many

nutrients can be toxic to plants.

Healthy

Phosphate-deficient

Potassium-deficient

Nitrogen-deficient

Figure 37.7The most common mineral deficiencies, with varying

symptoms depending on species.

∙Examples: resistance to aluminum toxicity, flood tolerance, and

smart plants.

∙Rather than tailoring the soil to match the

plant, genetic engineers are tailoring the plant to match the

soil.

∙Soil bacteria are decomposers.

∙Other soil bacteria, called rhizobacteria,

derive their energy from the rhizosphere.

Some rhizoshpere bacteria produce

antibiotics.

∙Plants satisfy most of their huge needs for nitrogen from the

bacterial decomposition of humus and the

fixation of nitrogen.

Figure 37.9 The roles of soil bacteria in the nitrogen nutrition of plants.

Atmosphere

N2

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)NH4

+

(ammonium)

H+

(From soil)

NO3–

(nitrate)Nitrifyingbacteria

Denitrifyingbacteria

Root

NH4+

Soil

AtmosphereNitrate and nitrogenous

organiccompoundsexported in

xylem toshoot system

Ammonifyingbacteria

∙Convert atmospheric N-2 to nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis. The most efficient mutualism

between plants and nitrogen fixing bacterias occurs in the nodules formed by Rhizobium bacteria growing in the roots of legumes. These bacteria obtain

sugar from the plant and supply the plant with fixed nitrogen.

∙A nodule is a swelling on the root of a legume. They are composed of plant cells that contain nitrogen-fixing bacteria of the genus Rhizobium.

∙A bacteriod is a form of the bacterium Rhizobium contained within the vesicles formed by the root cells of a root nodule.

∙Crop rotation is the practice of planting non-legumes one year and legumes in alternating years to restore concentrations of fixed nitrogen in the soil.

∙Mycorrhizae are mutualistic associations of fungi and roots.

∙There are two types of mycorrhizae: ectomycrrhizae and arbuscular

mycorrhizae.

∙Ectomycorrhiaze is an association of a fungus with a plant root system in which the fungus surrounds the roots but does not cause invagination of the host cells’

plasma membrane. Arbuscular mycorrhizae is an association of a fungus

with a plant root system in which the fungus causes the invagination of the host

cells’ plasma membranes.

∙Both absorb water and minerals, which they supply to their plant hosts.

Figure 37.12 Two types of mycorrhizae.

a Ectomycorrhizae. The mantle of the fungal mycelium ensheathes the root. Fungal hyphae extend from the mantle into the soil, absorbing water and minerals, especially phosphate. Hyphae also extend into the extracellular spaces of the root cortex, providing extensive surface area for nutrient exchange between the fungus and its host plant.

Mantle(fungal sheath)

Epidermis Cortex Mantle(fungalsheath)

Endodermis

Fungalhyphaebetweencorticalcells (colorized SEM)

100 m(a)

Epidermis Cortex

Fungalhyphae

Roothair

10 m

(LM, stained specimen)

Cortical cells

Endodermis

Vesicle

Casparianstrip

Arbuscules

2 Endomycorrhizae. No mantle forms around the root, but microscopic fungal hyphae extend into the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae that form arbuscules, providing an enormous surface area for nutrient swapping. The hyphae penetrate the cell walls, but not the plasma membranes, of cells within the cortex.

(b)

Epiphytes grow on the surface of other plants but

acquire water and minerals from rain.

Parasitic plants absorb nutrients from host plants.

Carnivorous plants supplement their mineral

nutrition by digesting animals.

∙The life cycles of plants are characterized by an alternation of generations, in which multi-cellular haploid (n) and diploid

(2n) generations take turns producing each other.

∙The diploid plant, which is

called the sporophyte, produces haploid spores by

meiosis. These spores divide by mitosis creating multi-

cellular gametophytes. Once these are fertilized they

become diploid.

∙The flower is the reproductive part of a plant.

∙There are five main parts to a flower: sepal, petal, receptacle, carpel, and stamen.

∙Sepals and petals are both sterile parts of the flower. They can be used to collect water or attract pollinators.

∙The receptacle is where the flower is attached. It supports the flower and provides it with the nutrients it needs.

∙The carpel, also called the pistil, consist of the stigma, the style, and the ovary. The stigma is a sticky structure that collects the pollen. The style is the long neck

that connects the stigma to the ovary. The ovary contains the ovules. This is where fertilization occurs.

∙The stamen includes the anther and the filament. The anther is where the micro- sporangia are located. The microsporangium are the pollen sacs. This is where the

pollen is created.

Filament

AntherStamen

Petal

Receptacle

Sepal

Style

Ovary

CarpelStigma

Figure 38.2 An idealized flower.

∙Each anther contains four pollen sacs, also known as microsporangia. These

contain many diploid cells.

∙Each cell undergoes meiosis forming four haploid microspores.

∙These will eventually turn to haploid male cells. Each then goes into mitosis to produce a mal gametophyte which

consist of only two cells.

∙After the male gametophyte is formed it matures and travels up the spore wall.

∙This cell will release the pollen into the pollen tube to be delivered to the female

gametophyte.

∙There are fifteen variations on how the female gametophyte is created.

∙One way is one that takes place only in the carpel’s ovary.

∙Each ovule consist of one megasporocyte which will expand and undergo meiosis. Only one will

survive.

∙The surviving one will continue to grow while its nucleus undergoes mitosis three times without

cytokinesis.

∙This will result in one large cell with eight haploid nuclei. This cell will now be taken to the embryo sac to be fertilized. Two cells called synergids flank the egg cell and help guide pollen to the

pollen tube.

Figure 38.3 The development of male and female gametophytes in angiosperms.

Keyto labels

MITOSIS

MEIOSIS

Ovule

Ovule

Integuments

Embryosac

Mega-sporangium

Mega-sporocyte

Integuments

Micropyle

Survivingmegaspore

AntipodelCells (3)

PolarNuclei (2)

Egg (1)

Synergids (2)

Development of a female gametophyte (embryo sac)

(b)

Within the ovule’smegasporangium is a large diploid cell called the megasporocyte (megasporemother cell).

1

Three mitotic divisions of the megaspore form the embryo sac, a multicellular female gametophyte. The ovule now consists of the embryo sac along with the surrounding integuments (protective tissue).

3

Female gametophyte(embryo sac)

Diploid (2n)

Haploid (2n)

100

m

The megasporocyte divides by meiosis and gives rise to fourhaploid cells, but in most species only one of these survives as the megaspore.

2

Development of a male gametophyte (pollen grain)

(a)

2 Each microsporo-cyte divides by meiosis to produce four haploid microspores, each of which develops into a pollen grain.

Pollen sac(microsporangium)

Micro-sporocyte

Micro-spores (4)

Each of 4microspores

Generativecell (willform 2sperm)

MaleGametophyte(pollen grain)

Nucleus of tube cell

Each one of the microsporangia contains diploid microsporocytes (microspore mother cells).

1

75 m

20 m

Ragweedpollengrain

MEIOSIS

MITOSIS

KEYto labels

Haploid (2n)Diploid (2n)

3 A pollen grain becomes a mature male gametophyte when its generative nucleus divides and forms two sperm.This usually occurs after a pollen grain lands on the stigma of a carpel and the pollen tube begins to grow. (SeeFigure 38.2b.)

∙Pollination is defined by the transfer of pollen from an anther to a stigma.

∙Wind pollinated species like grasses and most trees create more pollen to compensate for the random

dispersion of the pollen to the plants. This is why the air is full of pollen during the spring.

∙Another form of pollination is through the water for plants that grow there.

∙Most angiosperms use insects to pollinate them. This method uses an insect to directly carry pollen from one

flower to another.

∙If a plant is fertilized twice, the extra pollen connects to extra nuclei to form endosperm. This works as a food storing tissue of the seed. This is called double

fertilization.

∙After double fertilization each ovule develops into a seed while each ovary develops into the fruit holding the seed or seeds. The fruit then can act as a

sugar storage.

∙Once the seed is matured it dehydrates itself and enters dormancy.

∙When a seed is in dormancy, its metabolic processes are basically non-existent.

∙The seed is then enclosed by a hard coating. The seed consist of the radicle, the seed coat, the epicotyl, the hypocotyl, and the cotyledons.

∙Seeds can stay dormant for a long time. They won’t germinate until the conditions are right or some environmental change causes it to leave dormancy.

∙Seeds will germinate differently depending on their location. Seeds in forests where fires are common will not germinate until after a fire has cleared away all

the competing vegetation.

∙A seed will germinate after it starts to take in water. The seed will expand from the water than bust the outer coat letting the plant begin growth.

∙The first organ to emerge is the radicle which is the root.

∙Next the hypocotyl will emerge out of the soil and reacting to light straighten.

∙Lastly leaves will grow on the end of the hypocotyl.

Figure 38.8 Common garden bean, a eudicot with thick cotyledons. The fleshy cotyledons store food absorbed from the endosperm before the seed germinates.

Seed coat

Radicle

Epicotyl

Hypocotyl

Cotyledons

∙Asexual reproduction is when offspring are derived from a parent without genetic recombination.

∙One form of this type of reproduction in plants is called fragmentation. This is the separation of a parent plant into parts that develop into whole

plants. It is the most common form of asexual reproduction. Fragmentation results in an exact copy of the parent.

∙The aspen trees are an example of asexually reproducing plants. In most cases there will be thousands of trees descended from one parent. Each tree grew from part of a root of the parent. This creates several clones of

the parent.

∙Advantages are: No need for a pollinator. Allows all of the genetic information to be passed on. If the parent could survive well in the

environment than the offspring will also.

∙Disadvantages would be: The seeds are exposed to threats like animals and wind.

Figure 38.11 Asexual reproduction in aspen trees.

∙Dioecious species are species that cannot self fertilize because either they

are staminate flowers or they are carpellate flowers.

∙Staminate flowers do not have a carpel.

∙Carpellate flowers do not have a stamen.

∙The most common way of non self-pollination is called self-incompatibility.

This is the ability to reject pollen from itself and closely related individuals.

∙Special genes are able to notice the pollen and release a chemical to prevent

the egg from being fertilized.

∙Biotechnology is using plants to create something useful for humans to use.

∙This can also help with world hunger by genetically engineering plants to have chemicals in them that are only harmful to insects or creating plants that are

resistant to common viruses in that species.

∙This will help produce more food to compensate for the large human population.

∙Biotechnology can also help with the mass burning of fossil fuels. Because the plants can be grown faster and engineered for specific purposes, we can use

them for fuel and to create electricity.

∙We can make clones from cuttings by using certain parts of the plant that will grow into roots.

∙We can make a new plant by grafting. Grafting is when a bud or twig from one plant can be attached to another relative species. This will give you a new

plant.

Figure 38.14 Maize: a product of artificial selection.

∙ Etiolation is plant morphological adaptations for

growing in darkness.

∙ De-etiolation is the changes a plant shoot undergoes in

response to sunlight, informally known as

greening.

∙Signals are first detected by receptors, proteins that undergo

changes in shape in response to a specific stimulus. Unlike most

receptors, which are built into the plasma membrane, the

phytochrome that functions in the de-etiolation response is

located in the cytoplasm.

∙A second messenger in a signal transduction pathway rapidly

amplifies the signal sent from the receptor.

∙Response to pathways leads to expression of genes for proteins that function in the de-etiolation

response.

CELLWALL

CYTOPLASM

  1 Reception 2 Transduction 3 Response

Receptor

Relay molecules

Activationof cellularresponses

Hormone orenvironmentalstimulus

Plasma membrane

Figure 39.3 Signal transduction pathway.

∙A hormone is a signaling molecule that is produced in tiny amounts by one part of an organism’s body and

transported to other parts, where it binds to a specific receptor and triggers responses in target cells and

tissues.

∙Auxin, produced primarily in the apical meristem of the shoot, stimulates cell elongation in different target

tissues. Cytokinins stimulate cell division. Gibberellins, produced in roots and young leaves, stimulate growth in leaves and stems. Brassinosteroids, chemically similar to the sex hormones of animals, induce cell elongation

and division. Abscisic acid maintains dormancy in seeds. Ethylene helps control fruit ripening.

Figure 39.8 Celle elongation in response to auxin: the acid growth hypothesis.

Expansin

CELL WALL

Cell wallenzymes

Cross-linkingcell wallpolysaccharides

Microfibril

H+ H+

H+

H+

H+

H+

H+

H+

H+

ATP Plasma membrane

Plasmamembrane

Cellwall

NucleusVacuole

Cytoplasm

H2O

Cytoplasm

1 Auxinincreases the

activity ofproton pumps.

4 The enzymatic cleavingof the cross-linkingpolysaccharides allowsthe microfibrils to slide.The extensibility of thecell wall is increased. Turgorcauses the cell to expand.

2 The cell wallbecomes more

acidic.

5 With the cellulose loosened,the cell can elongate.

3 Wedge-shaped expansins, activatedby low pH, separate cellulose microfibrils fromcross-linking polysaccharides. The exposed cross-linkingpolysaccharides are now more accessible to cell wall enzymes.

∙Various blue-light receptors initiate phototropism, the light-induced opening of stomata, and the light-

induced slowing of hypocotyl elongation that occurs when a seedling breaks ground.

Phototropism is growth of a plant shoot toward or away

from light.

∙Phytochromes regulate many plant responses to

light, such as seed germination and shade avoidance, in the de-

etiolation process.

Synthesis

Far-redlight

Red light

Slow conversionin darkness(some plants)

Responses:seed germination,control offlowering, etc.

Enzymaticdestruction

PfrPr

Figure 39.19 Phytochrome: a molecular switching mechanism.

Wavelength (nm)

1.0

0.8

0.6

0.2

0

450 500 550 600 650 700

Light

Time = 0 min.

Time = 90 min.

0.4

400

Pho

totr

opic

eff

ectiv

enes

s re

lativ

e to

436

nm

(a) This action spectrum illustrates that only light wavelengths below 500 nm (blue and violet light) induce curvature.

(b) These photographs of coleoptiles were taken before and after 90-minute exposures to light sources of the colors indicated.

Figure 39.16Action spectrum for blue-light-stimulated

phototropism in maize coleoptiles.

∙ Circadian rhythm is a physiological cycle of about 24

hours that is present in all eukaryotic organisms and that persists even in the absence

of external cues.

∙Phytochrome conversion marks sunrise and sunset,

providing the clock with environmental cues.

∙ Photoperiodism is a physiological response to photoperiod, the relative lengths of night and day. A

critical night length sets a minimum or maximum number of hours of darkness required for flowering.

∙A short-day plant is a plant that flowers only when the light period is shorter than a critical length. A long-day plant is a plant that flowers only when the light period is

longer than a critical length. A day-neutral plant is a plant in which flower formation is not controlled by

photoperiod or day length.

∙Vernalization is the use of cold treatment to induce a plant to flower.

∙Gravitropism is a growth response to gravity. Roots show positive gravitropism, and stems show negative gravitropism.

Plastids called statoliths may enable plant roots to detect gravity.

∙Growth in response to touch is called thigmotropism. Rapid leaf movements involve transmission of electrical impulses called

action potentials.

∙During drought, plants respond to water deficit by reducing transpiration. Enzymatic

destruction of cells creates sir tubes that help plants survive

oxygen deprivation during flooding. Plants respond to salt stress by

producing solutes tolerated at high concentrations, keeping the water

potential of cells more negative than the soil solution. Heat-shock proteins help plants survive heat

stress. Altering lipid composition of membranes is a response to cold

stress.

∙Herbivory – animals eating plants – is a stress that plants face in any ecosystem. Plants prevent excessive herbivory by using both physical defenses, such as thorns,

and chemical defenses, such as the production of distasteful or toxic compounds.

∙Plants can recognize invading pathogens and defend against them. Pathogens against which a plant has little specific defense are said to be virulent pathogens.

Strains of pathogens that only mildly harm but do not kill the host plant are said to be avirulent pathogens.

∙ Gene-for-gene recognition is a widespread form of plant disease resistance involving recognition of pathogen-derived molecules by the protein products of

specific plant disease resistance genes.

∙Pathogen invasions promote two types of response. Hypersensitive response is a plant’s localized defense response to a pathogen, involving the death of cells around

the site of infection. Systemic acquired resistance is a defensive response in infected plants that helps protect healthy tissue from pathogenic invasion. Salicylic acid is a signaling molecule in plants that may be partially responsible for activating

systemic acquired resistance to pathogens.

3 In a hypersensitiveresponse (HR), plantcells produce anti-microbial molecules,seal off infectedareas by modifyingtheir walls, andthen destroythemselves. Thislocalized responseproduces lesionsand protects otherparts of an infectedleaf.

4 Before they die,infected cellsrelease a chemicalsignal, probablysalicylic acid.

6 In cells remote fromthe infection site,the chemicalinitiates a signaltransductionpathway.

5 The signal is distributed to the rest of the plant.

2 This identification step triggers a signal transduction pathway.

1 Specific resistance is based on the binding of ligands from the pathogen to receptors in plant cells.

7 Systemic acquiredresistance isactivated: theproduction ofmolecules that helpprotect the cellagainst a diversityof pathogens forseveral days.

Signal

7

6

54

3

2

1

Avirulentpathogen

Signal transductionpathway

Hypersensitiveresponse

Signaltransduction

pathway

Acquiredresistance

R-Avr recognition andhypersensitive response

Systemic acquiredresistance

Figure 39.29Defense responses against

an avirulent pathogen.

∙How transmittance works using spectrophotometer.

∙How heating the chloroplast can increase light transmittance.

∙Paper chromatography is a way to separate and identify pigments and other molecules from cell extracts

∙This allows you to see what chlorophyll molecules are in each cell.

·Transpiration is the evaporation of water from plants surface.

·Guttation is the loss of liquids from the ends of vascular tissues at the margins of leaves.

·In this lab you will measure transpiration under various laboratory conditions using a potometer.

·The amount of daily water needed for plants tissues is small to comparison to the amount lost. Through the process of transpiration and

guttation.

·If the water is not replaced the plant will wilt and die.

·Minerals actively transported into the root accumulate in the xylem, increasing solute concentration and decreasing

water potential. Water moves in by osmosis.

·As water enters the xylem, it forces fluid up the xylem due to hydrostatic root pressure. But this pressure can only

move fluid a short distance

·The most significant force moving the water and dissolved minerals in the xylem is upward pull as a result of

transpiration, which creates tension. The pull on the water from the transpiration results from the cohesion and

adhesion of the water molecules.

1. Which plant organ is the main photo synthesizer within the plant?

A. RootsB. Stems C. LeavesD. Green Sterns

2. Which tissue system is paired correctly with its function?

A. Dermal Tissue – PhotosynthesisB. Vascular Tissue – Transportation of materials between roots and shootsC. Ground Tissue – Outer covering of the plantD. Organ Tissue – Transportation of materials between roots and shoots

3. Which type of plant cells would you find a myriad of in the Vascular Tissue?

A. Parenchyma CellsB. Collenchyma CellsC. Sclerenchyma CellsD. Water Conducting Cells

4. If a shuck of corn silks about 65 days after emergence, matures about 125 days, then Is harvested shortly after; what kind of life cycle plant is it?

A. PerennialB. AnnualC. BiennialD. Criennial

5. Meristems, which play a vital role in primary growth, supply the plant with cells to_______?

A. Grow in thicknessB. Photosynthesize C. Produce leavesD. Grow in length

6. Cell division in meristems increases what?

A. Mutations of the organsB. Potential for growthC. Meristem cellsD. Leaf production

7. Which process is in the correct order?

A. Positional formation signals pattern formation to give certain structures a function, which then causes morphogenesis to happen inside the organ or tissue.

B. Pattern formation signals morphogenesis to give certain structures a function, which then causes positional formation to happen inside the organ or tissue.C. Pattern formation signals positional formation to give certain structures a

function, which then causes morphogenesis to happen inside the organ or tissue. D. Morphogenesis signals pattern formation to give certain structures a function, which then causes positional formation to happen inside the organ or tissue.

8. True or False? Positional information underlies all the processes of development: growth, morphogenesis, and differentiation.

A. TrueB. False

9. True or False? It is possible to pin point precisely which cells of the meristem will give rise to which organs and tissue in the plant.

A. TrueB. False

10. What does the ABC model propose?

A. The model proposes that each class of organ identity genes is switched on in two specific whorls of the floral meristem. B. The model proposes that each plant species can sing the ABC’s.C. The model proposes that each organ has a specific gene.

11. What is active transport?

A. The pumping of solutes across membranes against their electrochemical gradients.

B. A protein that binds to DNA and stimulates gene transcription. C. The amount of energy that reactants must absorb before a chemical

reaction may occur. D. A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process.

12. What is the most important transport protein in the plant cell?

A. Neutron PumpB. Electron PumpC. Proton PumpD. Ditron Pump

13. What does this equation represent? (psi = psip + psis)

A. psip is the pressure potential and psis is the solute potentialB. psis is the pressure potential and psip is the solute potentialC. psip is the solute potential and psis is the pressure potentialD. psis is the solute potential and psip is the pressure potential

14. True or False? The cell wall, not the cell membrane regulates the traffic of material into the protoplast.

A. TrueB. False

15. Why does most water absorption occur near the root tips?

A. The epidermis is more permeable to waterB. More root hairs are located near the root tips. C. More leaves occur among the root tips. D. Both A and C

16. Which is the last segment in the soil-xylem process of water and minerals?

A. It enters the vascular cylinder via the symplast.B. The passage of water and minerals into the tracheids and vessel

elements of the xylem.C. It reaches the endodermis via the apoplast.D. None of the above.

17. What does root pressure cause?

A. GuttationB. GustationC. Guard CellsD. Green House Effect

18. What must Sugar from mesophyll cells or other sources must be loaded into before it can be exported into sugar sinks?

A. The ApoplastB. The SymplastC. Sieve Tube MembersD. A storage Organ

19. ________ is the mechanism of translocation in Angiosperms?

A. Pressure FlowB. Proton PumpsC. Guttation D. Apopplast

20. True or False? The closer the aphid’s stylet is to a sugar source, the faster the sap will flow and the greater its sugar concentration.

A. TrueB. False

21. What types of plants absorb nutrients from host plants?

A. Carnivorous B. EpiphytesC. ParasitcD. Bacteriods

22. Which one of these is not a macronutrient element?

A. CarbonB. Manganese C. SulfurD. Nitrogen

23. Micronutrients mainly serve as what?

A. Most are mobile in plantsB. Cofactors of enzymesC. A minor role in growthD. Large essential elements

24. Most of the mass of organic material of a plant comes from what?

A. NitrogenB. PotassiumC. Carbon DioxideD. Manganese

25. What do both fungal hypae of both ectomycorrhizae and arbuscular mycorrhizae do?

A. Absorb water and mineralsB. Produce water and mineralsC. Provide sugar to root cellsD. Convert nitrogen to ammonium

26. A mineral deficiency is likely to affect older leaves more than younger leaves if _____?

A. The older leaves are in direct sunlightB. The mineral is a macronutrient C. It is a micronutrient elementD. The mineral is very mobile within the plant

27. All N-2 fixing organisms are

A. Parasitic B. ElementsC. Eukaryotes D. Prokaryotes

28. What affects the availability of water, soil, and minerals in the soil?

A. Soil particle sizeB. SunlightC. BacteriaD. Growth

29. What is the process by which an organism takes in and, makes use of food substances?

A. Cation ExchangeB. FertilizationC. Nutrition D. Irrigation

30. Some of the problems associated with intensive irrigation include all but _______?

A. Soil Salinization B. Mineral runoffC. Overfertilization D. Land Subsidence

31. What does the life cycle of a plant involve?

A. Haploid onlyB. Diploid onlyC. Haploid and DiploidD. None of the above

32. Which of the following is not a part of the flower in a plant?

A. CarpelB. PistilC. StyleD. Node E. Anther

33. What is the function of the stigma?

A. To provide pollenB. To house fertilizationC. To collect pollenD. To make the seeds

34. Which process forms the embryo sac?

A. Male Gametophyte productionB. Female Gametophyte reproductionC. FertilizationD. Dormancy

35. How is pollination defined?

A. The transfer of pollen from the anther to the stigma.B. The transfer of pollen from the anther to the carpel.C. The fertilization of the flower.D. The transfer of pollen from one flower to another.

36. Which is not enclosed in the seed?

A. RadicleB. EpicotylC. PistilD. HypocotylE. Cotyledons

37. When a seed is derived from a parent without genetic recombination this is the definition of_________.

A. Sexual reproductionB. Asexual reproductionC. GraftingD. Bioengineering

38. Self-incompatibility is ________.

A. The ability to reject pollen from other species.B. The ability to accept pollen from other species.C. The ability to give pollen to other species.D. None of the above.

39. What is biotechnology?

A. The process to alter plants to make them useful to humans.B. The process to prevent over growthC. The process of making biological vehiclesD. None of the above

40. Each ovule in a flower consist of one ________.

A. MegasporocyteB. Pollen tubeC. MicrosporeD. Sepal

41. What is the correct order of a signal transduction pathway?

A. Transduction, reception, responseB. Reception, transduction, responseC. Response, reception, transductionD. Response, transduction, reception

42. What is the technical term for greening?

A. De-etiolationB. TropismC. PhototropismD. Etiolation

43. What hormone typically stimulates cell elongation?

A. EthyleneB. CytokininC. AuxinD. Brassinosteroid

44. What are two light receptors used by plants that absorb mostly red light?

A. Phytochromes and gibberellinsB. Gibberellins and blue-lightC. Blue-light and phytochromesD. Gibberellins and de-etiolation

45. What is a long-day plant?

A. A plant that flowers only when the light period is shorter than a critical lengthB. A plant in which flower formation is not controlled by photoperiod or day lengthC. Growth in response to touchD. A plant that flowers only when the light period is longer than a critical

length

46. Roots show _______ gravitropism, and stems show _______ gravitropism.

A. Positive, negativeB. Negative, positiveC. Positive, positiveD. Negative, negative

47. Which of the following is not an environmental stress on plants?

A. FloodingB. Biological clocksC. SaltD. Heat

48. What type of defenses can plants use to protect themselves against herbivores and pathogens?

A. Cold and hotB. Etiolation and de-etiolationC. Blue-light photoreceptors and phytochromesD. Physical and chemical

49. True or False? Pathogens against which a plant has little specific defense are said to be virulent pathogens.

A. TrueB. False

50. What is the acid partially responsible for activating systemic acquired resistance to pathogens?

A. heat-shock proteinsB. action potentialsC. salicylic acidD. abscisic acid

1. Which plant organ is the main photo synthesizer within the plant?

A. RootsB. Stems C. LeavesD. Green Sterns

2. Which tissue system is paired correctly with its function?

A. Dermal Tissue – PhotosynthesisB. Vascular Tissue – Transportation of materials between roots and shootsC. Ground Tissue – Outer covering of the plantD. Organ Tissue – Transportation of materials between roots and shoots

3. Which type of plant cells would you find a myriad of in the Vascular Tissue?

A. Parenchyma CellsB. Collenchyma CellsC. Sclerenchyma CellsD. Water Conducting Cells

4. If a shuck of corn silks about 65 days after emergence, matures about 125 days, then Is harvested shortly after; what kind of life cycle plant is it?

A. PerennialB. AnnualC. BiennialD. Criennial

5. Meristems, which play a vital role in primary growth, supply the plant with cells to_______?

A. Grow in thicknessB. Photosynthesize C. Produce leavesD. Grow in length

6. Cell division in meristems increases what?

A. Mutations of the organsB. Potential for growthC. Meristem cellsD. Leaf production

7. Which process is in the correct order?

A. Positional formation signals pattern formation to give certain structures a function, which then causes morphogenesis to happen inside the organ or tissue.

B. Pattern formation signals morphogenesis to give certain structures a function, which then causes positional formation to happen inside the organ or tissue.C. Pattern formation signals positional formation to give certain structures a

function, which then causes morphogenesis to happen inside the organ or tissue. D. Morphogenesis signals pattern formation to give certain structures a function, which then causes positional formation to happen inside the organ or tissue.

8. True or False? Positional information underlies all the processes of development: growth, morphogenesis, and differentiation.

A. TrueB. False

9. True or False? It is possible to pin point precisely which cells of the meristem will give rise to which organs and tissue in the plant.

A. TrueB. False

10. What does the ABC model propose?

A. The model proposes that each class of organ identity genes is switched on in two specific whorls of the floral meristem. B. The model proposes that each plant species can sing the ABC’s.C. The model proposes that each organ has a specific gene.

11. What is active transport?

A. The pumping of solutes across membranes against their electrochemical gradients.

B. A protein that binds to DNA and stimulates gene transcription. C. The amount of energy that reactants must absorb before a chemical

reaction may occur. D. A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process.

12. What is the most important transport protein in the plant cell?

A. Neutron PumpB. Electron PumpC. Proton PumpD. Ditron Pump

13. What does this equation represent? (psi = psip + psis)

A. psip is the pressure potential and psis is the solute potentialB. psis is the pressure potential and psip is the solute potentialC. psip is the solute potential and psis is the pressure potentialD. psis is the solute potential and psip is the pressure potential

14. True or False? The cell wall, not the cell membrane regulates the traffic of material into the protoplast.

A. TrueB. False

15. Why does most water absorption occur near the root tips?

A. The epidermis is more permeable to waterB. More root hairs are located near the root tips. C. More leaves occur among the root tips. D. Both A and C

16. Which is the last segment in the soil-xylem process of water and minerals?

A. It enters the vascular cylinder via the symplast.B. The passage of water and minerals into the tracheids and vessel

elements of the xylem.C. It reaches the endodermis via the apoplast.D. None of the above.

17. What does root pressure cause?

A. GuttationB. GustationC. Guard CellsD. Green House Effect

18. What must Sugar from mesophyll cells or other sources must be loaded into before it can be exported into sugar sinks?

A. The ApoplastB. The SymplastC. Sieve Tube MembersD. A storage Organ

19. ________ is the mechanism of translocation in Angiosperms?

A. Pressure FlowB. Proton PumpsC. Guttation D. Apopplast

20. True or False? The closer the aphid’s stylet is to a sugar source, the faster the sap will flow and the greater its sugar concentration.

A. TrueB. False

21. What types of plants absorb nutrients from host plants?

A. Carnivorous B. EpiphytesC. ParasiticD. Bacteriods

22. Which one of these is not a macronutrient element?

A. CarbonB. Manganese C. SulfurD. Nitrogen

23. Micronutrients mainly serve as what?

A. Most are mobile in plantsB. Cofactors of enzymesC. A minor role in growthD. Large essential elements

24. Most of the mass of organic material of a plant comes from what?

A. NitrogenB. PotassiumC. Carbon DioxideD. Manganese

25. What do both fungal hypae of both ectomycorrhizae and arbuscular mycorrhizae do?

A. Absorb water and mineralsB. Produce water and mineralsC. Provide sugar to root cellsD. Convert nitrogen to ammonium

26. A mineral deficiency is likely to affect older leaves more than younger leaves if _____?

A. The older leaves are in direct sunlightB. The mineral is a macronutrient C. It is a micronutrient elementD. The mineral is very mobile within the plant

27. All N-2 fixing organisms are

A. Parasitic B. ElementsC. Eukaryotes D. Prokaryotes

28. What affects the availability of water, soil, and minerals in the soil?

A. Soil particle sizeB. SunlightC. BacteriaD. Growth

29. What is the process by which an organism takes in and, makes use of food substances?

A. Cation ExchangeB. FertilizationC. Nutrition D. Irrigation

30. Some of the problems associated with intensive irrigation include all but _______?

A. Soil Salinization B. Mineral runoffC. Overfertilization D. Land Subsidence

31. What does the life cycle of a plant involve?

A. Haploid onlyB. Diploid onlyC. Haploid and DiploidD. None of the above

32. Which of the following is not a part of the flower in a plant?

A. CarpelB. PistilC. StyleD. Node E. Anther

33. What is the function of the stigma?

A. To provide pollenB. To house fertilizationC. To collect pollenD. To make the seeds

34. Which process forms the embryo sac?

A. Male Gametophyte productionB. Female Gametophyte reproductionC. FertilizationD. Dormancy

35. How is pollination defined?

A. The transfer of pollen from the anther to the stigma.B. The transfer of pollen from the anther to the carpel.C. The fertilization of the flower.D. The transfer of pollen from one flower to another.

36. Which is not enclosed in the seed?

A. RadicleB. EpicotylC. PistilD. HypocotylE. Cotyledons

37. When a seed is derived from a parent without genetic recombination this is the definition of_________.

A. Sexual reproductionB. Asexual reproductionC. GraftingD. Bioengineering

38. Self-incompatibility is ________.

A. The ability to reject pollen from other species.B. The ability to accept pollen from other species.C. The ability to give pollen to other species.D. None of the above.

39. What is biotechnology?

A. The process to alter plants to make them useful to humans.B. The process to prevent over growthC. The process of making biological vehiclesD. None of the above

40. Each ovule in a flower consist of one ________.

A. MegasporocyteB. Pollen tubeC. MicrosporeD. Sepal

41. What is the correct order of a signal transduction pathway?

A. Transduction, reception, responseB. Reception, transduction, responseC. Response, reception, transductionD. Response, transduction, reception

42. What is the technical term for greening?

A. De-etiolationB. TropismC. PhototropismD. Etiolation

43. What hormone typically stimulates cell elongation?

A. EthyleneB. CytokininC. AuxinD. Brassinosteroid

44. What are two light receptors used by plants that absorb mostly red light?

A. Phytochromes and gibberellinsB. Gibberellins and blue-lightC. Blue-light and phytochromesD. Gibberellins and de-etiolation

45. What is a long-day plant?

A. A plant that flowers only when the light period is shorter than a critical length.B. A plant in which flower formation is not controlled by photoperiod or day length.C. Growth in response to touch.D. A plant that flowers only when the light period is longer than a critical

length.

46. Roots show _______ gravitropism, and stems show _______ gravitropism.

A. Positive, negativeB. Negative, positiveC. Positive, positiveD. Negative, negative

47. Which of the following is not an environmental stress on plants?

A. FloodingB. Biological clocksC. SaltD. Heat

48. What type of defenses can plants use to protect themselves against herbivores and pathogens?

A. Cold and hotB. Etiolation and de-etiolationC. Blue-light photoreceptors and phytochromesD. Physical and chemical

49. True or False? Pathogens against which a plant has little specific defense are said to be virulent pathogens.

A. TrueB. False

50. What is the acid partially responsible for activating systemic acquired resistance to pathogens?

A. Heat-shock proteinsB. Action potentialsC. Salicylic acidD. Abscisic acid

Hormones play important roles in regulating the lives of many living organisms.

(a) For TWO of the following physiological responses, explain how hormones cause the response in plants.

∙increase in height∙adjustment to change in light∙adjustment to lack of water

(b) Describe TWO different mechanisms by which hormones cause their effects at the cellular level.

(a) Hormones cause several physiological responses in plants. Stem elongation in the meristem causes an increase in plant height. The hormone lowers pH in the plant, thus increasing osmosis. It also loosens the cell wall via cellulose x-links. Stomates closing, root branching, and dormancy cause an adjustment to lack of water in the plant. If the cells in a leaf become flaccid, there is less pressure on the guard cells, causing the stoma to close. This allows the plant to conserve its water and carbon dioxide. Root branching causes more nutrients and water to be pulled from the environment to the plant in need. Dormancy prevents seed germination. Therefore, the plant does not require as much water and nutrients at the time for production and growth.

(b) Several mechanisms require hormones to cause their effects at the cellular level. A receptor in the cell primarily influences transcription. A hormone is not a transcription factor itself but binds to a receptor to form a gene-specific factor. Once bound together, the hormone-receptor complex binds to DNA, and can induce transcription. A receptor in the cell membrane primarily activates proteins already present through signal transduction. For many hormones, including most protein hormones, the receptor is membrane-associated and embedded in the plasma membrane at the surface of the cell.

(a) Categorize the following organs into the shoot system and root system: apical bud, node, vegetative shoot, leaf, taproot, auxiliary bud, stem, and lateral roots.

(b) Draw and label at least five organs within the shoot system on a plant.

(c) Explain the difference between the taproots and lateral roots.

Shoot System Root System

Apical Bud Taproot

Node Lateral Root (branch)

Vegetative Shoot

Leaf

Axillary Bud

Stem

(a)

(b)(c) The taproot is the main vertical root that develops from an embryonic root. The taproot in turn gives rise to lateral roots or branch roots. Taproots store sugars and starches that the plant will consume during flower and fruit production. The lateral roots are generally thin and have root hairs that consume water and nutrients from the soil.