Bio 1306 Exam 2: Plants

Front 1

Developmental Plasticity

Back 1

the ability of a plant to alter itself in response to its environment

Front 2

Roots

Back 2

Functions:
Anchoring the plant
Absorbing minerals and water
Storing organic nutrients

Front 3

Taproot
Lateral roots

Back 3

A taproot system consists of one main vertical root that gives rise to lateral roots, or branch roots - eudicots

Front 4

Stem

Back 4

Consisting of :
An alternating system of nodes, the points at which leaves are attached
Internodes, the stem segments between nodes

Front 5

Axillary Bud


Apical Bud


Apical Dominance

Back 5

An axillary bud is a structure that has the potential to form a lateral shoot, or branch
An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot
Apical dominance helps to maintain dormancy in most nonapical buds

Front 6

Leaf

Back 6

The leaf is the main photosynthetic organ of most vascular plants
Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem

Front 7

Monocots vs. Eudicots: Veins

Back 7

Most monocots have parallel veins

Most eudicots have branching veins

Front 8

Modified Roots

Back 8

prop roots
storage roots
strangling aerial roots
pneumatophores
buttress roots

Front 9

Modified Stems

Back 9

rhizomes
bulbs
stolons
tubers

Front 10

Modified Leaves

Back 10

tendrils
spines
storage leaves
reproductive leaves
bracts

Front 11

Dermal Tissue System

Back 11

epidermis; cuticle - helps prevent water loss from the epidermis; periderm - replace the epidermis in older regions of stems and roots; trichomes - outgrowths of the shoot epidermis and can help with insect defense

Front 12

Vascular Tissue System

Back 12

Xylem conveys water and dissolved minerals upward from roots into the shoots
Phloem transports organic nutrients from where they are made to where they are needed

Front 13

Stele

Back 13

The vascular tissue of a stem or root is collectively called the stele
In angiosperms the stele of the root is a solid central vascular cylinder
The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem

Front 14

Ground Tissue System

Back 14

Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex

Front 15

Major Types of Plant Cells

Back 15

Parenchyma
Collenchyma
Sclerenchyma
Water-conducting cells of the xylem
Sugar-conducting cells of the phloem

Front 16

Parenchyma Cells

Back 16

Have thin and flexible primary walls
Lack secondary walls
Are the least specialized
Perform the most metabolic functions
Retain the ability to divide and differentiate

Front 17

Collenchyma Cells

Back 17

Collenchyma cells are grouped in strands and help support young parts of the plant shoot
They have thicker and uneven cell walls
They lack secondary walls
These cells provide flexible support without restraining growth

Front 18

Sclerenchyma Cells

Back 18

Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin
They are dead at functional maturity

There are two types:
Sclereids are short and irregular in shape and have thick lignified secondary walls
Fibers are long and slender and arranged in threads

Front 19

Xylem

Back 19

The two types of water-conducting cells, tracheids and vessel elements, are dead at maturity

Front 20

Phloem

Back 20

Sieve-tube elements are alive at functional maturity, though they lack organelles
Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube
Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells

Front 21

Meristems

Apical meristems

Lateral meristems

Back 21

Meristems are perpetually embryonic tissue and allow for indeterminate growth
Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots
Lateral meristems add thickness to woody plants, a process called secondary growth

Front 22

Vascular Cambium

(meristems)

Cork Cambium

Back 22

The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem
The cork cambium replaces the epidermis with periderm, which is thicker and tougher

Front 23

Root

Back 23

The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil
in three zones of cells:
Zone of cell division
Zone of elongation
Zone of maturation

Front 24

Lenticels

Back 24

Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air

Front 25

Pattern Formation

Positional Information

Polarity

Back 25

Pattern formation is the development of specific structures in specific locations
It is determined by positional information in the form of signals indicating to each cell its location
Polarity, having structural or chemical differences at opposite ends of an organism, provides one type of positional information

Front 26

Water potential

Back 26

Water potential is a measurement that combines the effects of solute concentration and pressure; abbreviated as Ψ and measured in megapascals (MPa). The addition of solutes reduces water potential.Physical pressure increases water potential.Negative pressure decreases water potential.

Front 27

Solute potential / Osmotic potential



Pressure potential

Back 27

The solute potential (ΨS) of a solution is proportional to the number of dissolved molecules

Pressure potential (ΨP) is the physical pressure on a solution

Front 28

Aquaporins

Back 28

Aquaporins are transport proteins in the cell membrane that allow the passage of water

Front 29

Symplast; Plasmodesmata



Apoplast

Back 29

The cytoplasmic continuum is called the symplast
The cytoplasm of neighboring cells is connected by channels called plasmodesmata

The apoplast is the continuum of cell walls and extracellular spaces

Front 30

Water and minerals can travel through a plant by three routes:

Back 30

Transmembrane route: out of one cell, across a cell wall, and into another cell
Symplastic route: via the continuum of cytosol
Apoplastic route: via the cell walls and extracellular spaces

Front 31

Bulk flow

Back 31

The movement of a fluid driven by pressure, important for long distance transport; possible because mature tracheids and vessel elements have no cytoplasm, and sieve-tube elements have few organelles in their cytoplasm

Front 32

Endodermis




Casparian strip

Back 32

The endodermis is the innermost layer of cells in the root cortex; surrounds the vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue

The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder

Front 33

Root pressure






Guttation

Back 33

At night, when transpiration is very low, root cells continue pumping mineral ions into the xylem of the vascular cylinder, lowering the water potential; Water flows in from the root cortex, generating root pressure; water flows in from the root cortex

The exudation of water droplets on tips or edges of leaves that can result from root pressure

Front 34

Transpirational Pull




Cohesion / Adhesion

Back 34

Transpiration produces negative pressure (tension) in the leaf, which exerts a pulling force on water in the xylem, pulling water into the leaf

Transpirational pull is facilitated by cohesion of water molecules to each other and adhesion of water molecules to cell walls

Front 35

Xerophytes

Back 35

Xerophytes are plants adapted to arid climates
They have leaf modifications that reduce the rate of transpiration
Some plants use a specialized form of photosynthesis called crassulacean acid metabolism (CAM) where stomatal gas exchange occurs at night

Front 36

Translocation

Back 36

The products of photosynthesis are transported through phloem by the process of translocation

Front 37

Xylem sap

Phloem sap

Back 37

Water and minerals, called xylem sap

Phloem sap is an aqueous solution that is high in sucrose

Front 38

Sugar source



Sugar sink

Back 38

A sugar source is an organ that is a net producer of sugar, such as mature leaves

A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb

Front 39

Transfer cells

Back 39

Transfer cells are modified companion cells that enhance solute movement between the apoplast and symplast

Front 40

Systemic communication

Back 40

Systemic communication helps integrate functions of the whole plant
The phloem allows for rapid electrical communication between widely separated organs

Front 41

Soil horizons

Back 41

Soil is stratified into layers called soil horizons
Soil particles are classified by size; from largest to smallest they are called sand, silt, and clay

Front 42

Top soil; Humus







Loams

Back 42

Topsoil consists of mineral particles, living organisms, and humus, the decaying organic material. Topsoil contains bacteria, fungi, algae, other protists, insects, earthworms, nematodes, and plant roots. Humus builds a crumbly soil that retains water but is still porous. It also increases the soil’s capacity to exchange cations and serves as a reservoir of mineral nutrients


Loams are the most fertile topsoils and contain equal amounts of sand, silt, and clay

Front 43

Cation exchange

Back 43

During cation exchange, cations are displaced from soil particles by other cations
Displaced cations enter the soil solution and can be taken up by plant roots
Soil pH affects cation exchange and the chemical form of minerals
Cations are more available in slightly acidic soil, as H+ ions displace mineral cations from clay particles

Front 44

Fertilization

Back 44

Fertilization replaces mineral nutrients that have been lost from the soil
Commercial fertilizers are enriched in nitrogen, phosphorus, and potassium

Front 45

Erosion can be reduced by

Back 45

Planting trees as windbreaks
Terracing hillside crops
Cultivating in a contour pattern
Practicing no-till agriculture

Front 46

Phytoremediation

Back 46

Phytoremediation is a biological, nondestructive technology that reclaims contaminated areas

Front 47

Essential element

Back 47

A chemical element is considered an essential element if it is required for a plant to complete its life cycle

Researchers use hydroponic culture to determine which chemical elements are essential

Front 48

Macronutrients

Micronutrients

Back 48

C, O, H, N, K, Ca, Mg, P, S

Cl, Fe, Mn, B, Zn, Cu, Ni, Mo

Front 49

Mineral deficiency

Back 49

Deficiency of a mobile nutrient usually affects older organs more than young ones
Deficiency of a less mobile nutrient usually affects younger organs more than older ones
The most common deficiencies are those of N, K, P

Front 50

Plants and soil microbes have a mutualistic relationship

Back 50

Dead plants provide energy needed by soil-dwelling microorganisms
Secretions from living roots support a wide variety of microbes in the near-root environment

Front 51

Rhizosphere

Back 51

The layer of soil bound to the plant’s roots is the rhizosphere
The rhizosphere has high microbial activity because of sugars, amino acids, and organic acids secreted by roots

Front 52

Rhizobacteria

Back 52

Free-living rhizobacteria thrive in the rhizosphere, and some can enter roots
Produce hormones that stimulate plant growth
Produce antibiotics that protect roots from disease
Absorb toxic metals or make nutrients more available to roots

Front 53

The nitrogen cycle

Back 53

The nitrogen cycle transforms nitrogen and nitrogen-containing compounds
Plants absorb nitrogen as either NO3– or NH4+
Bacteria break down organic compounds or use N2 to produce NH3, which is converted to NH4+
Nitrification is carried out by bacteria that convert NH3 into NO3–

Front 54

Nitrogen fixation

Back 54

Nitrogen fixation is the conversion of nitrogen from N2 to NH3

Front 55

Bacteroids

Back 55

Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell
The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen

Front 56

Mycorrhizae

Back 56

Mycorrhizae are mutualistic associations of fungi and roots
The fungus benefits from a steady supply of sugar from the host plant
The host plant benefits because the fungus increases for water uptake and mineral absorption the surface area

Front 57

Ectomycorrhizae

Back 57

In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root
These hyphae form a network in the apoplast, but do not penetrate the root cells

Front 58

Arbuscular mycorrhizae

Back 58

In arbuscular mycorrhizae, microscopic fungal hyphae extend into the root
These mycorrhizae penetrate the cell wall but not the plasma membrane to form branched arbuscules within root cells

Front 59

Epiphyte

Back 59

An epiphyte grows on another plant and obtains water and minerals from rain; non-parasitic because Parasitic plants absorb sugars and minerals from their living host plant
ex. of epiphyte: staghorn fern
ex. of parasite: mistletoe, dodder, Indian pipe

Front 60

Sporophyte / Gametophyte

Back 60

Diploid (2n) sporophytes produce spores by meiosis; these grow into haploid (n) gametophytes
In angiosperms, the sporophyte is the dominant generation, the large plant that we see
The gametophytes are reduced in size and depend on the sporophyte for nutrients

Front 61

Flowers consist of four floral organs:


Receptacle

Back 61

Sepals, petals, stamens, and carpels

Flowers are the reproductive shoots of the angiosperm sporophyte; they attach to a part of the stem called the receptacle

Front 62

Stamen



Carpal; Pistal

Back 62

A stamen consists of a filament topped by an anther with pollen sacs that produce pollen

A carpel has a long style with a stigma on which pollen may land
At the base of the style is an ovary containing one or more ovules; A single carpel or group of fused carpels is called a pistil

Front 63

Complete / Incomplete flowers



Inflorescences

Back 63

Complete flowers contain all four floral organs; Incomplete flowers lack one or more floral organs

Clusters of flowers are called inflorescences

Front 64

Microspores



Pollen grain; Pollen tube

Back 64

Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers
If pollination succeeds, a pollen grain produces a pollen tube that grows down into the ovary and discharges sperm near the embryo sac. The pollen grain consists of the two-celled male gametophyte and the spore wall

Front 65

Megaspores; Embryo sac

Back 65

Within an ovule, megaspores are produced by meiosis and develop into embryo sacs, the female gametophytes

Front 66

Double fertilization



Endosperm

Back 66

Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac

One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid (3n) food-storing endosperm

Front 67

Embryo development

Back 67

The first mitotic division of the zygote is transverse, splitting the fertilized egg into a basal cell and a terminal cell

Front 68

Hypocotyl

Radicle

Epicotyl

Back 68

Below the cotyledons the embryonic axis is called the hypocotyl and terminates in the radicle (embryonic root); above the cotyledons it is called the epicotyl

Front 69

Coleoptile



Coleorhiza

Back 69

Two sheathes enclose the embryo of a grass seed: a coleoptile covering the young shoot and a coleorhiza covering the young root

Front 70

Germination; Imbibition

Back 70

Germination depends on imbibition, the uptake of water due to low water potential of the dry seed
The radicle (embryonic root) emerges first.Next, the shoot tip breaks through the soil surface.

Front 71

Fruits are also classified by their development:

Back 71

Simple, a single or several fused carpels - peas
Aggregate, a single flower with multiple separate carpels - raspberry
Multiple, a group of flowers called an inflorescence - pineapple
Accessory fruit contains other floral parts in addition to ovaries - apple

Front 72

Fragmentation

Back 72

Fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction

Front 73

Vegetative reproduction


Apomixis

Back 73

Asexual reproduction

Apomixis is the asexual production of seeds from a diploid cell

Front 74

Dioecious


Self-incompatibility

Back 74

Dioecious species have staminate and carpellate flowers on separate plants

Self-incompatibility, a plant’s ability to reject its own pollen
Some plants reject pollen that has an S-gene matching an allele in the stigma cells. Recognition of self pollen triggers a signal transduction pathway leading to a block in growth of a pollen tube.

Front 75

Callus

Back 75

A callus is a mass of dividing undifferentiated cells that forms where a stem is cut and produces adventitious roots

Front 76

Grafts; Stock / Scion

Back 76

The stock provides the root system
The scion is grafted onto the stock

Front 77

Protoplast fusion

Back 77

Protoplast fusion is used to create hybrid plants by fusing protoplasts, plant cells with their cell walls removed

Front 78

Transgenic crops have been developed that:

Back 78

Produce proteins to defend them against insect pests
Tolerate herbicides
Resist specific diseases

Front 79

Biofuels

Back 79

Biofuels are made by the fermentation and distillation of plant materials such as cellulose

Front 80

Efforts are underway to prevent crop-to-weed hybridization by introducing:

Back 80

Male sterility
Apomixis
Transgenes into chloroplast DNA (not transferred by pollen)
Strict self-pollination

Front 81

Etiolation



De-etiolation

Back 81

Morphological adaptations for growing in darkness, collectively called etiolation. After exposure to light, a plant undergoes changes called de-etiolation, in which shoots and roots grow normally

Front 82

Cell-signal processing

Back 82

The stages are reception, transduction, and response
Internal and external signals are detected by receptors, proteins that change in response to specific stimuli. Second messengers transfer and amplify signals from receptors to proteins that cause responses.In most cases, these responses to stimulation involve increased activity of enzymes, which can occur by transcriptional regulation or post-translational modification.

Front 83

Transcription factors

Back 83

Specific transcription factors bind directly to specific regions of DNA and control transcription of genes
Positive transcription factors are proteins that increase the transcription of specific genes, while negative transcription factors are proteins that decrease the transcription of specific genes

Front 84

Hormones



Tropism

Back 84

Hormones are chemical signals that coordinate different parts of an organism

Any response resulting in curvature of organs toward or away from a stimulus is called a tropism

Front 85

Charles Darwin


Peter Boysen-Jensen


Frits Went

Back 85

Darwin observed that a grass seedling could bend toward light only if the tip of the coleoptile was present; postulated that a signal was transmitted from the tip to the elongating region

In 1913, Peter Boysen-Jensen demonstrated that the signal was a mobile chemical substance

In 1926, Frits Went extracted the chemical messenger for phototropism, auxin, by modifying earlier experiments

Front 86

Auxin

Back 86

Auxin refers to any chemical that promotes elongation of coleoptiles
Indoleacetic acid (IAA) is a common auxin in plants
Auxin transporter proteins move the hormone from the basal end of one cell into the apical end of the neighboring cell
Auxin is also involved in root formation and branching
Auxin affects secondary growth by inducing cell division in the vascular cambium and influencing differentiation of secondary xylem

Front 87

Acid growth hypothesis; Expansins

Back 87

According to the acid growth hypothesis, auxin stimulates proton pumps in the plasma membrane
The proton pumps lower the pH in the cell wall, activating expansins, enzymes that loosen the wall’s fabric. With the cellulose loosened, the cell can elongate

Front 88

Cytokinins

Back 88

Cytokinins are so named because they stimulate cytokinesis (cell division). Cytokinins work together with auxin to control cell division and differentiation. Cytokinins, auxin, and other factors interact in the control of apical dominance, a terminal bud’s ability to suppress development of axillary buds.
Cytokinins also retard the aging of some plant organs by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues
Cytokinins are produced in actively growing tissues such as roots, embryos, and fruits

Front 89

Gibberellins

Back 89

Gibberellins have a variety of effects, such as stem elongation, fruit growth, and seed germination
Gibberellins stimulate growth of leaves and stems. In many plants, both auxin and gibberellins must be present for fruit to set. After water is imbibed, release of gibberellins from the embryo signals seeds to germinate

Front 90

Brassinosteroids

Back 90

Brassinosteroids are chemically similar to the sex hormones of animals
They induce cell elongation and division in stem segments

Front 91

Abscisic acid

Back 91

Abscisic acid (ABA) slows growth
Two of the many effects of ABA:
Seed dormancy - Seed dormancy ensures that the seed will germinate only in optimal conditions
Drought tolerance

Front 92

Ethylene

Back 92

Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection. The effects of ethylene include response to mechanical stress, senescence, leaf abscission, and fruit ripening

The Triple Response to Mechanical Stress - consists of a slowing of stem elongation, a thickening of the stem, and horizontal growth

Front 93

Senescence




Leaf Abscission

Back 93

Senescence is the programmed death of plant cells or organs
A burst of ethylene is associated with apoptosis, the programmed destruction of cells, organs, or whole plants

A change in the balance of auxin and ethylene controls leaf abscission, the process that occurs in autumn when a leaf falls

Front 94

Photomorphogenesis

Back 94

Effects of light on plant morphology are called photomorphogenesis

Front 95

There are two major classes of light receptors:

Back 95

Blue-light photoreceptors and phytochromes
Various blue-light photoreceptors control hypocotyl elongation, stomatal opening, and phototropism
Phytochromes are pigments that regulate many of a plant’s responses to light throughout its life
including seed germination and shade avoidance
Phytochromes exist in two photoreversible states, with conversion of Pr to Pfr triggering many developmental responses. Phytochrome conversion marks sunrise and sunset, providing the biological clock with environmental cues

Front 96

Photoperiodism

Short-day / Long-day / Neutral-day plants

Back 96

Photoperiodism is a physiological response to photoperiod
Plants that flower when a light period is shorter than a critical length are called short-day plants
Plants that flower when a light period is longer than a certain number of hours are called long-day plants
Flowering in day-neutral plants is controlled by plant maturity, not photoperiod

Front 97

Vernalization


Gravitropism; Statoliths

Back 97

Vernalization is a pretreatment with cold to induce flowering

Response to gravity is known as gravitropism. Roots show positive gravitropism, while shoots show negative gravitropism.
Plants may detect gravity by the settling of statoliths, specialized plastids containing dense starch grains

Front 98

Thigmomorphogenesis


Thigmotropism


Action potentials

Back 98

The term thigmomorphogenesis refers to changes in form that result from mechanical disturbance

Thigmotropism is growth in response to touch.
Rapid leaf movements in response to mechanical stimulation are examples of transmission of electrical impulses called action potentials

Front 99

Methyljasmonic acid

Back 99

Methyljasmonic acid can activate the expression of genes involved in plant defenses

Front 100

Drought

Back 100

During drought, plants reduce transpiration by closing stomata, slowing leaf growth, and reducing exposed surface area
Growth of shallow roots is inhibited, while deeper roots continue to grow

Front 101

Flooding

Back 101

Enzymatic destruction of root cortex cells creates air tubes that help plants survive oxygen deprivation during flooding

Front 102

Salt stress

Back 102

Salt can lower the water potential of the soil solution and reduce water uptake
Plants respond to salt stress by producing solutes tolerated at high concentrations
This process keeps the water potential of cells more negative than that of the soil solution

Front 103

Heat stress




Cold stress

Back 103

Excessive heat can denature a plant’s enzymes
Heat-shock proteins help protect other proteins from heat stress

Cold temperatures decrease membrane fluidity
Altering lipid composition of membranes is a response to cold stress
Freezing causes ice to form in a plant’s cell walls and intercellular spaces

Front 104

Virulent / Avirulent pathogens

Back 104

A virulent pathogen is one that a plant has little specific defense against
An avirulent pathogen is one that may harm but does not kill the host plant

Front 105

Gene-for-gene recognition

Back 105

Gene-for-gene recognition involves recognition of pathogen-derived molecules by protein products of specific plant disease resistance (R) genes. R proteins activate plant defenses by triggering signal transduction pathways

Front 106

The hypersensitive response

Back 106

Causes cell and tissue death near the infection site
Induces production of phytoalexins and PR proteins, which attack the pathogen
Stimulates changes in the cell wall that confine the pathogen

Front 107

Systemic acquired resistance



Salicylic acid

Back 107

Systemic acquired resistance causes systemic expression of defense genes and is a long-lasting response
Salicylic acid is synthesized around the infection site and is likely the signal that triggers systemic acquired resistance