Chapter 35: The Plant Body structure reveals interaction with

environment on two scales:– long-term = accumulate morphological

adaptations due to natural selection Ex. Cactus leaves have become so reduced that the

stem is the primary photosynthetic surface

– short-term = structural responses to specific environment

Ex. Cambomba– leaves developed while underwater

• light & feathery (increase surface area)

– leaves above water are arrowhead-shaped

• aid in floatation

plant architecture is far more flexible than animal

physiological adjustments of plant are even faster than structural ones– Ex. plant produces hormone that causes

stomata to close morphology of terrestrial plants reflects

need to inhabit and draw resources from two very different environments—soil and air– soil = source of H2O, minerals– air = source of CO2, light

3 basic plant organs

ROOT SYSTEM (subterranean)– monocots (i.e. grasses) usually have

fibrous root systems– most absorption occurs at root tips; tiny

root hairs increase surface area– some plants have adventitious roots

(grow above ground) adventitious = plant part that grows in

atypical location

3 basic plant organs SHOOT SYSTEM (stems & leaves)

– may be vegetative (leaf-bearing) or reproductive (flower-bearing)

– stem = alternating system of nodes and internodes

node = points at which leaves attach internode = stem segments between nodes

– in angle between node and internode is axillary bud

potential to form vegetative branch (most are dormant)

3 basic plant organs SHOOT SYSTEM (stems & leaves)

– growth is usually concentrated at apex, site of the terminal bud

presence is partially responsible for limiting growth of axillary buds

called apical dominance – plant concentrates resources on growing taller

increased exposure to light if an animal eats the terminal bud or light is

more available at lower levels, axillary buds break dormancy

– rationale for pruning shrubs and “pinching back” plants (makes them bushy)

3 basic plant organs

SHOOT SYSTEM (stems & leaves)– Modified shoots with diverse functions

have evolved stolons = “runners” of strawberry plants rhizomes = horizontal stems that grow

underground tubers (I.e. potatos) = swollen ends of

rhizozomes specialized for storing food bulbs = vertical, underground shoots

consisting mostly of swollen bases of leaves that store food (Ex. onion)

3 basic plant organs

LEAVES – leaves = main photosynthetic organ of

most plants vary in form, but usually have:

– (a) blade = flattened surface– (b) petiole = stalk…joins leaf to stem

shape, spatial arrangement on stem, vein pattern are used to identify leaves

plant organs are composed of 3 tissue systems

DERMAL TISSUE (epidermis, “skin”)– single layer of tightly packed cells that

covers and protects all young parts of the plant

general function: protection other functions: depend on organ its covering

– Ex. root hairs absorption– Ex. leaf cuticle water retention

plant organs are composed of 3 tissue systems

VASCULAR TISSUE– involved in transport of materials between

roots and shoots– xylem = conveys water and dissolved

minerals (roots shoots) water-conducting elements

– tracheids and vessel elements = elongated cells that are dead at functional maturity

– secondary walls interrupted by pits (only primary walls present)

– secondary walls harden with lignin, which provides structural support

plant organs are composed of 3 tissue systems

VASCULAR TISSUE– involved in transport of materials between roots

and shoots– phloem = transports food from mature leaves to

roots and nonphotosynthetic parts (ex. fruits) sucrose and other organic compounds are transported

through tubes formed by chains of cells called sieve-tube members

– alive at functional maturity, but lack many organelles

– end walls (sieve plates) facilitate flow of fluid

– companion cells have organelles…may supply sieve-tube members

plant organs are composed of 3 tissue systems

GROUND TISSUE– neither dermal nor vascular– diverse functions include photosynthesis,

storage, support

root systems

TAPROOTS (dicots)– one large, vertical roots with many

smaller lateral (branch) roots– Ex. dandelion– firmly anchors plant in soil– store more food than fibrous roots– plants consumes resources during time of

flowering or fruit production

root systems

FIBROUS ROOTS (monocots)– mat of thin roots that spread out below

the surface– increase exposure to soil water and

minerals– tenacious anchor to ground– Ex. grass roots concentrate a few cm

below the ground, holding topsoil in place (prevents erosion)

the protoplasts of neighboring cells are generally connected by plasmodesmata, cytoplasmic channels that pass through pores in the walls– the endoplasmic

reticulum is continuous through the plasmodesmata in structures called desmotubules

An adhesive layer, the middle lamella, cements together the cells wall of adjacent cells.– The primary cell wall is secreted as the

cell grows.– Some cells have

secondary walls which develop after a cell stops growing.

plant tissues are composed of three basic cell types:

parenchyma, collenchyma, and sclerenchyma

parenchyma cells are often depicted as “typical” plant cells because they generally are the least specialized, but there are exceptions

parenchyma cells perform most of the metabolic functions of the plant, synthesizing and storing various organic products– Ex. photosynthesis occurs within the chloroplasts

of parenchyma cells in the leaf– Ex. the fleshy tissue of most fruit is composed

of parenchyma cells

parenchyma cells developing plant cells of all types are

parenchyma cells before specializing further in structure and function– mature, unspecialized parenchyma cells do not

generally undergo cell division– most retain the ability to divide and differentiate

into other cell types under special conditions - during the repair and replacement of organs after injury to the plant

– in the laboratory, it is possible to regenerate an entire plant from a single parenchyma cell

collenchyma cells have thicker primary walls than parenchyma

cells, though the walls are unevenly thickened– grouped into strands or cylinders, collenchyma

cells help support young parts of the plant shoot– young cells and petioles often have a cylinder of

collenchyma just below their surface, providing support without restraining growth

– functioning collenchyma cells are living and flexible and elongate with the stems and leaves they support

schlerenchyma cells sclerenchyma cells also function as

supporting elements of the plant, with thick secondary walls usually strengthened by lignin– they are much more rigid than collenchyma cells– unlike parenchyma cells, they cannot elongate

and occur in plant regions that have stopped lengthening

– many sclerenchyma cells are dead at functional maturity, but they produce rigid secondary cells walls before the protoplast dies

– vessel elements and tracheids in the xylem are sclerenchyma cells that function for both support and transport

growth

most plants demonstrate indeterminate growth, growing as long as the plant lives

most animals (and certain plant organs such as flowers and leaves) undergo determinate growth, ceasing to grow after they reach a certain size

annual plants complete their life cycle - from germination through flowering and seed production to death - in a single year or less– many wildflowers and important food crops, such

as cereals and legumes, are annuals 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 that live many years, including trees, shrubs, and some grasses, are perennials– these often die not 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– these cells divide to generate additional

cells, some of which remain in the meristematic region while others become specialized and incorporated into the tissues and organs of the growing plant.

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– this elongation, primary growth, enables roots

to ramify through the soil and shoots to extend their exposure to light and carbon dioxide

– woody plants also show secondary growth, progressive thickening of roots and shoots

secondary growth is the product of lateral meristems, cylinders of dividing cells extending along the length of roots and shoots

one lateral meristem replaces the epidermis with bark and a second adds layers of vascular tissue

in woody plants, primary growth is restricted to the youngest parts of the plant - the tips of the roots and shoots

each growing season, primary growth produces young extensions of roots and shoots, while secondary growth thickens and strengthens the older part of the plant

at the tip of a winter twig of a deciduous tree is the dormant terminal bud, enclosed by scales that protect its apical meristem– in the spring, the bud will shed its scales

and begin a new spurt of primary growth– along each growth segment, nodes are

marked by scars left when leaves fell in autumn

– above each leaf scar is either an axillary bud or a branch twig

•farther down the twig are whorls of scars left by the scales that enclosed the terminal bud during the previous winter

•each spring and summer, as the primary growth extends the shoot, secondary growth thickens the parts of the shoot that formed in previous years

the root tip is covered by a thimblelike root cap, which protects the meristem as the root pushes through the abrasive soil during primary growth– the cap also secretes a lubricating slime

growth in length is concentrated near the root’s tip, where three zones of cells at successive stages of primary growth are located– zones: zone of cell division, zone of

elongation, zone of maturation

zone of cell division the zone of cell division includes the apical

meristem and its derivatives, primary meristems– the apical meristem produces the cells of the

primary meristems and also replaces cells of the root cap that are sloughed off

near the middle is the quiescent center, cells that divide more slowly than other meristematic cells– these cells are relatively resistant to damage

from radiation and toxic chemicals– they may act as a reserve that can restore the

meristem if it becomes damaged

zone of cell division just above the apical meristem, the

products of its cell division form three concentric cylinders of cells that continue to divide for some time– primary meristems:

protoderm procambium ground meristem will produce the three

primary tissue systems of the root…dermal, vascular, and ground tissues

zone of elongation the zone of cell division blends into the

zone of elongation where cells elongate, sometimes to more than ten times their original length– it is this elongation of cells that is mainly

responsible for pushing the root tip, including the meristem, ahead

– the meristem sustains growth by continuously adding cells to the youngest end of the zone of elongation

zone of maturation in the zone of maturation, cells begin

to specialize in structure and function.– in this root region, the three tissue

systems produced by primary growth complete their differentiation, their cells becoming functionally mature

three primary meristems give rise to the three primary tissues of roots.– dermal tissue epidermis– ground tissue endodermis and cortex.– vascular tissue stele, pericycle, pith,

xylem, and phloem.

meristems the protoderm, the outermost primary

meristem, produces the single cell layer of the epidermis– water and minerals absorbed by the plant

must enter through the epidermis– root hairs enhance absorption by greatly

increasing the surface area the procambium gives rise to the

stele, which in roots is a central cylinder of vascular tissue where both xylem and phloem develop

meristems the ground tissue between the

protoderm and procambium gives rise to the ground tissue system– these are mostly parenchyma cells

between the stele and epidermis– they store food and are active in the

uptake of minerals that enter the root with the soil solution

the innermost layer of the cortex, the endodermis, is a cylinder one cell thick that forms a boundary between the cortex and stele

shoots leaves arise as leaf primordia on flanks of

apical meristem axillary buds develop from islands of

meristem cells left by apical meristems at bases of leaf primordia

most of elongation occurs by growth in length of slightly older internodes below shoot apex– due to cell division and elongation by internode

lateral branches originate from axillary buds on surface (unlike roots where lateral roots extend from deep pericycle)

shoots—primary tissues vascular tissues run the length of the

stem in vascular bundles (perimeter) when shoot becomes root, vascular

system converges in vascular cylinder in center of roots

each vascular bundle is surrounded by ground tissue

dicot…inner core referred to as pith

shoots—primary tissues leaf epidermis is composed of tightly

interlocked cells (like pieces of a puzzle)– 1st line of defense against physical

damage and pathogens– cuticle is barrier against water loss– cuticle is interrupted by stomata flanked

by guard cells (responsible for gas exchange)

http://www.royaloakschools.com/portal/sites/default/files/apbio Genetics Review.ppt

Chapter 37: Plant Nutrition

the fact that plants are autotrophic does not mean that they are autonomous– need sunlight to drive photosynthesis– need CO2, H2O minerals to synthesize

organic compounds

mineral nutrients = essential chemical elements absorbed from the soil in the form of organic ions

80-85% of herbaceous plant mass is H2O– considered a nutrient because it supplies the

majority of H and O for organic compounds (most water is lost to transpiration)

– 90% of plant’s water is lost to transpiration– bulk of plant’s organic material comes from CO2– most of organic material is carbohydrate– plants require micronutrients (small amounts)

and macronutrients (large amounts)– essential nutrient = required for plant to grow

from seed and complete life cycle

symptoms of mineral deficiency depend on function and mobility of element

young, growing tissues have more “drawing power”

Ex. deficiency of Mg (ingredient of chlorophyll) yellow leaves (chlorosis)

signs of deficiency are seen first in older leaves

can confirm deficiency by appearance of plant or by analyzing soil

hydroponic growth of plants allows precise control of nutrients

Role of soil in plant nutrition

lichens, fungi, bacteria, mosses, roots of plants secrete acids breakdown of rock soil

topsoil = mixture of particles derived from rock and living organisms– Astonishing array of organisms

humus = residue of partially decayed organic material (prevents clay from packing together)

horizon = distinct soil layer– texture of soil depends on size of particle

loam = moist, fertile soils

AB

C

soil conservation soil conservation is related to the idea

that agriculture is unnatural to grow a ton of wheat, the soil gives

up 18.2 kg of nitrogen, 3.6 kg of phosphorus, and 4.1 kg of potassium– each year, the fertility of the soil

diminishes unless fertilizers are applied to replace lost minerals

soil conservation concerns

fertilizer irrigation erosion

– no-till agriculture– contour farming– shelter belts

nitrogen as a plant nutrient

the metabolism of soil bacteria makes nitrogen available to plants– atmosphere is 80% nitrogen, but in

gaseous form– plants require ionic form (NH4+ or NO3-)– short-term source: decomposition of

humus by microbes however, denitrifying bacteria convert NO3- to

N2

– longer-term source: nitrogen-fixing bacteria

convert N2 to NH3

soil conservation crop rotation role of clover and other legumes

mycorrhizae symbiotic association of roots and

fungi that enhance plant nutrition symbiosis is mutualistic

– fungus benefits from a hospitable environment and a steady supply of sugar donated by the host plant

– in return, fungus increases surface area for water uptake and selectively absorbs minerals from the soil to supply the plant

nutritional adaptations

parasitic plants– Ex. mistletoe = photosynthetic, but supplements

nutrition with haustoria to siphon xylem sap from host tree

– epiphytes are often confused with parasitic plants

carnivorous plants– usually live in acid bogs where soil conditions

are poor– fortify nutrition by feeding on animals– modified leaves usually equipped with glands

that secrete digestive juices

Chapter 38: Plant Reproduction sexual reproduction

– characterized by alternation of generations

sporophyte = dominant generation flower gametophyte = dramatically reduced (a few

cells)

– flowers are specialized shoots bearing the reproductive organs of the angiosperm sporophyte

flowers are determinate (stop growing once flower and fruit are formed)

sexual reproduction stamens (filament + anther) = male

reproductive organs carpels (stigma + style + ovary) = female

reproductive organs after fertilizaition, ovule that contains

embryo develops into seed entire ovary develops into fruit containing

one or more seeds numerous floral variations have evolved

– complete flower = has all 4 organs– incomplete flower = lacks one or more part(s)

sexual reproduction bisexual (perfect) flower

– has stamens and carpels unisexual (imperfect) flower

– has stamens oror carpels– monoecious (“one house”) vs. diecious

(same plant) male and female gametophytes

develop within anthers and ovaries, respectively (pollination brings them together)

Development of the male gametophyte

within sporangia (pollen sac) of anther:

Development of the female gametophyte

within ovary:

Pollination is the first step in chain of events leading to fertilization plants have various mechanisms that

prevent self-fertilization self-incompatibility = ability of plant

to reject its own pollen and the pollen of closely related individuals– analogous to immune response

however, in this case, plant is rejecting “self”

– based on “self” genes; may be as many as 50 genes at locus

– genes seem to have evolved separately in various plant families

as many as 50 different alleles at S locus

Double fertilization gives rise to zygote and endosperm after landing on a receptive stigma, a pollen

grain absorbs moisture and germinates germinated pollen grain is mature male

gametophyte double fertilization

– sperm + egg zygote– sperm + 2 polar nuclei endosperm

ensures that endosperm will develop only in ovules where egg has been fertilized

like animals, block to polyspermy occurs

The ovule develops into a seed containing an embryo and a supply of nutrients. after fertilization

– ovule seed (major nutrient sinks)seed stockpiles proteins, oils, and starch

– ovary fruit endosperm development

– usually precedes embryo development

– rich in nutrients to supply growing embryo

The ovule develops into a seed containing an embryo and a supply of nutrients. embryo development

– cotyledons = “seed leaves”

– development of embryo (a) establishes root-shot axis(b) establishes radial pattern of

protoderm, ground meristem, procambium

seed structure during the last stages of its maturation,

the seed dehydrates until its water content is only 5-15% of its weight

the embryo and its food supply are enclosed by a protective seed coat formed from the integuments of the ovule

seed structure

ovary develops into fruit adapted for seed dispersal during fruit development, the wall of the ovary

becomes the pericarp, the thickened wall of the fruit – in apples, fleshy part of fruit is derived from

swollen recepticle; only the apple core develops from the ovary

fruit usually ripens about the same time its seeds are completing their development– in fleshy fruits, the ripened fruit entices animals who

help spread the seeds– with time, the inner parts of the fruit become softer as

enzymes digest components of cell walls– organic acids are converted to sugars as fruit ripens

ovary develops into fruit adapted for seed dispersal fruit = protects enclosed seeds, aids in seed

dispersal by wind or animals pollination triggers hormonal changes that

cause ovary to begin transformation to a fruit usually ripens about same time seed is

completing its development fruits in store are products of selective breeding

to produce exaggerated forms

Evolutionary adaptations of seed germination contribute to seed survival

as seed matures, it dehydrates and enters dormancy– low metabolic rate

– suspension of growth and development conditions needed to break dormancy differ

between species dormancy increases chances that germination

will occur at a time and place most advantageous to the seedling

triggers: rainfall, heat, cold, light, chemicals

from seed to seedling germination of seeds depends on the

physical process of imbibition (uptake of water due to low water potential of dry seed)

imbibing water causes the seed to expand and rupture its coat

also triggers metabolic changes to the embryo that allow it to resume its growth

first organ to emerge is radicle next, the shoot tip must break the soil

surface

Chapter 39: Plant Responses to Hormones

signal transduction pathways link internal and environmental signals to cellular responses

hormone = chemical signals that coordinate parts of the organism– only minute amounts are required to induce

substantial change– implies that signal must be amplified in some

way– hormone actions:

(a) alter expression of genes (b) affect activity of existing enzymes (c) change properties of membranes

auxin first plant hormone to be discovered;

stimulates cell elongation for primary growth– moves shoot base at 10 mm/hour– movement requires energy– synthetic forms used as herbicides

(monocots like turfgrass can inactivate, dicots cannot…die of hormonal overdose)

cytokinins stimulate root growth and

differentiation; stimulate cell division and cell growth– produced in actively growing tissues

(especially roots, embryos, fruits)– interact with auxin to control apical

dominance

gibberellins promote seed germination; stimulate

flowering and development; promote stem elongation– Ex. treatment of seedless grapes– increase size, growth of internodes

(more space, air circulation, less infection)

abscisic acid slows down growth

(but no role in bud dormancy or leaf abscission)

– effects seed dormancy– enables plants to withstand drought

ethylene promotes fruit ripening

– produced in response to stress such as drought, flooding, mechanical pressure, injury, and infection

– triple response to mechanical stress slow stem elongation thickening of stem curvature of stem horizontal

ethylene (cont.) apoptosis

– associated with burst of ethylene– dropping of leaf, shedding of flower, formation of

xylem vessel– genetically, a very busy time

leaf abscission– dropping of leaves keeps trees from desiccating

during winter when roots cannot absorb H2O– before dropping leaves, many minerals are

salvaged and stored in stem parenchyma cells– fruit ripening = example of positive feedback

CO2 inhibits synthesis of more ethylene

brassinosteroids induce cell elongation at extremely low

concentrations (10-12 M)

Plant responses to light plants detect not just the presence of light,

but also its intensity, direction, and wavelength (color)

action spectrum relates physiological response to wavelength of light– red and blue light are most important

blue-light receptors are a heterogeneous group of pigments– blue light is most effective at initiating:

phototropism opening of stomata slowing of hypocotyl elongation

Phytochromes function as photoreceptors in many plant responses to light

regulate many of plant’s response to light

germination: red vs. far red

– seems to act as switch mechanism for many events in plant life

Biological clocks control circadian rhythms in plants (and other eukaryotes) not paced by any known environmental barrier some oscillations due to changes in light levels,

temperature, relative humidity that are part of normal 24 hour cycle

even under artificially constant conditions, many physiologic processes (I.e. opening and closing of stomata) continue to follow 24 hour periods

internal (without cues, periods vary from 21-27 hours) critical night length = controls flowering, other

responses

critical night length discovered in 1940s that night length

controls flowering and other responses to photoperiod