Chapt35_lecture Bio 101

8/8/2019 Chapt35_lecture Bio 101

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Copyright (c) The McGraw-Hill

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CHAPTER 35

AN INTRODUCTIONTO FLOWERING

PLANTS

Prepared by

Brenda Leady, University of Toledo


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Overview of Plant Structure1. Two major regions of flowering plants

a) Root systemanchor plants in the ground

absorb water and minerals

store excess sugar

transport water, minerals, sugar, hormones

produce hormones

b) Shoot system - consists of stems, leaves, buds,

flowers, fruits

for photosynthesis

transport of materials between leaves, flowers,

fruits, and rootsreproduction

hormone synthesis

2. Two groups of flowering plants

a) Monocot - grasses, lilies, orchids

b) Dicot - deciduous trees and bushes


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Alternation of generations

Gametophyte (haploid)

Microscopic in flowering plants

Produce gametes by mitosis

Sporophyte (diploid)

Large plant in flowering plants

Produces spores by meiosis


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Plant embryo is a sporophyte that liesdormant within a seed with a supplyof stored food and a seed coat

May lay dormant for long periods untilconditions are favorable

Embryo grows into seedling and thenmature plant


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Growth increase in size or weight

Development increase in number or

organs, accompanied by differentiation

Meristem region of undifferentiated cells

producing new tissues by cell division

Basic plant organs roots, stems, and

leaves contain several types of tissues


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Roots provide anchorage in the soil and

foster efficient uptake of water and

minerals

Stem produce leaves and branches and

bear the reproductive structures

Leaves foliage leaves specialized forphotosynthesis


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Radicle, embryonic root, first organ toemerge from germinating seed

Provides water and minerals for growth

Hypocotyl produces cotyledons

Eudicots 2 seed leaves

Monocots 1

seed leaf Endosperm provides food for early embryo

growth


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Plant Growth and Development

1. Two categories of cellsa) meristem cells - embryonic, undifferentiated, capable

of cell division

b) differentiated cells - are specialized in structure and

function, and usually dont divide

Meristem cells: apical meristems - located at the ends

of roots and shoots

lateral meristems or cambia - form

cylinders that run parallel to the long

axis of roots and stems

2. Two forms of plant growtha) Primary growth - occurs through mitotic cell division

of apical meristem cells by differentiation of the

resulting daughter cells; increase in length

b) Secondary growth - occurs through mitotic cell

division of lateral meristem cells, and differentiation

of their daughter cells; increase in diameter


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Development Shoot apical meristem (SAM)

Rapidly dividing cells at shoot apices

Produces shoot system Stems, leaves and other organ systems

Root apical meristem (RAM) Also rapidly dividing cells

Produces root system Roots and root branches


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Vegetative growth

Production of tissues by SAM and RAMand growth of mature plant

Plant shoots produce vegetative buds miniature shoots having a dormant SAM

Under favorable conditions, buds produce

new stems and leaves Indeterminate growth SAMs

continuously produce new stem tissue andleaves as long as conditions are favorable


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Reproductive development Mature plants produce flowers, seeds and

fruits

Flowers produced by determinate growth

growth of limited duration

Flower tissues enclose and protect tiny

male and female gametophytes

Fruits enclose seeds and function in seed

dispersal


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Seed-to-seed lifetime Annuals plants that die after producing

seeds during their first year of life; e.g.

corn

Biennials plants that do not reproduce

the first year but may the following year

Perennials plants that live for more than2 years, often producing seed each year

after maturity


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1) Distinctive architecture

2 features

1. Upper, apical pole and a lower, basal pole

SAM at upper pole, RAM at basal pole

Apical-basal polarity

Originates during embryo development

2. Radial symmetry Stem and root cylindrical

Leaves and flower parts in whorls or spirals


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2) Primary meristems SAM and RAM produce additional

meristematic tissue that increases plant

length and produces new organs

Primary meristems produce primary

tissues and organs of diverse types


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SAM and RAM both produce

Protoderm generates dermal tissue

Procambium produces vascular tissues

Ground meristem produces ground tissues

defined by location

Plant cell specialization and tissue

development do not depend much on the

lineage of a cell or tissue Chemical influences are much more

important


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Plant Tissues and Cell Types

1. Three tissue systemsa) dermal tissue - covers the outer surface of the plant

body

b) ground tissue system - consists of all the non-dermal

and nonvascular tissues

c) vascular tissue - transports water, minerals, sugars,and plant hormones

a. Dermal tissue system

Two types: a) epidermis - outermost layer

cuticle - cells secreted by epidermal cells

that reduces evaporation of water from the plantb) periderm - replaces the epidermal tissue on

the roots and stems of woody plants as they

age; composed of cork cells (form the protective

outer layer of the bark of trees, and woody

shrubs, and the woody covering of their roots).


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b. Ground tissue system - makes up the bulk of a young plant

a) Parenchyma - thin-walled cells that typically carry most of the

metabolic products of plants; for photosynthesis; storageof sugars and starches, and secretion of hormones

b) Collenchyma - consists of elongated, polygonal cells;

alive at maturity but cannot divide

c) Sclerenchyma - consists of cells with thick, hardened

secondary walls, reinforced with a stiffeningsubstance called lignin; support and strengthen the

plant body

Layer of epidermal cells showing

the stomata

Parenchyma cells


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Collenchyma cells

Sclerenchyma cells


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c. Vascular tissue system

a) Xylem

b) Phloem

Xylem - conducts water and minerals from roots to shoots in

tubes that are made from one of 2 types of cells:

tracheids and vessel elements


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Stem development and structure

New primary stem tissues arise by the celldivision activities of primary meristems locatednear the bases of SAMs

Epidermis develops at the stem surface Produces a waxy cuticle (reduces water loss)

Cortex composed of parenchyma tissue Composed of only one cell type, parenchyma cells

Stores starch in plastids

Stem parenchyma also has the ability toundergo cell division (meristematic capacity) toheal damage


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Stems also contain Collenchyma tissue composed of

collenchyma cells

Sclerechyma tissue composed of fibers and

sclerids

Vascular tissue made of xylem and phloem

arranged in vascular bundles

Ring in eudicots

Scattered in monocots


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X-section of a monocot stem

X-section of a dicot stem


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Leaf development and structure

Young leaves produced at the side of SAMs in leafprimordia

Flattening expands surface area for light collection

Being thin helps shed excess heat

Bilaterally symmetrical

Upper adaxial (stem facing) side Pallisade parenchyma absorbs sunlight efficiently

Lower abaxial (away from stem) side More stomata

Spongy parenchyma has air spaces to foster gas exchange


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Root development and structure

Eudicots taproot system with a main root

that produces branch roots

Monocots fibrous root system with

multiple roots

Adventitious roots produced on the

surface of stems of monocots andeudicots


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3) Ever-young stem cells

Plant meristems include stem cells

Term stem cell used for plant meristem

cells that remain undifferentiated but canproduce new tissues

Plant stem cell divides to produce one cell

that remains unspecialized and anothercell that is capable of differentiating intovarious types of specialized cells


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Plant Shoot Apical Meristem Size Is

Genetically Controlled

NormalArabidopsis SAM consists of several

hundred stem cells organized into at least three

distinct cell regions having different functions Central zone consists of stem cells that divide but

remain undifferentiated

Normal growth depends on maintaining normal size

of central zone and SAM Central zone cells make CLAVATA3 that controls

the size of the zone

Loss of CLAVATA3 causes peripheral zone cells to

become central zone cells


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Shoot system

Includes all of a plants stems, branchesand leaves

Also produces flowers and fruits Phytomere shoot module

1. Stem node leaves emerge

2. Internode between adjacent nodes3. Leaf

4. Axillary meristem generate axillary buds forlateral shoots


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Leaf adaptations

Leaf form Simple leaves only one blade, advantageous in

shade by providing maximal light absorption

Complex or compound leaves dissected intoleaflets, common in hot environments for heatdissipation

Leaf venation

Eudicot leaves have pinnate or palmate venation Netted veins provide more support to the leaf

Monocot leaves have parallel venation


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Leaf surface features

Cuticle on epidermis helps avoid desiccation

Filter UV radiation, reduce microbe and animalattack, and self-cleaning

Guard cells regulate stomatal opening andclosing

Trichomes offer protection from excessivelight, ultraviolet radiation, extreme airtemperature, or attack by herbivores


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Modified leaves

Most leaves function primarily inphotosynthesis

Can be modified for other roles Tendrils

Tough scales that protect buds

Poinsetta petals Cactus spines


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Stem vascular tissue

Herbaceous plants produce mostly

primary vascular tissues

Woody plants produce primary and

secondary vascular tissue

Woody plants begin as herbaceous seedling

with only primary vascular systems


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Primary vascular tissue

Primary xylem Unspecialized parenchyma cells

Stiff fibers for structural support

Tracheids and vessel elements conduct water

and dissolved minerals (not living cells) Primary phloem

Transports organic compounds and certainminerals

Sieve elements (living cells) Companion cells aid seive element metabolism

Parenchyma cells

Supportive fibers


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Secondary vascular tissue

Secondary xylem wood

Secondary phloem inner bark

Bark has both outer bark (mostly dead

cork cells) and inner bark (secondaryphloem)

Secondary vascular tissues produced by

two types of secondary Vascular cambium

Cork cambium


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Vascular cambium

Produces secondary xylem and secondaryphloem

Secondary xylem conducts most of a woody

plants water and minerals may function

several years

Usually only the current years production of

secondary phloem is active in food transport

Cork cambium Produces cork

Cork cells dead when mature and layered

with lignin and suberin


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Modified stems

Rhizomes- underground stems

Potato tubers store food

Grass stems grow as rhizomes or stolons


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Modified Stems

1. Bulbs - consists of fleshy leaves attached to a smallknoblike stem; e.g. onions, lilies, tulips

2. Corms - resembles bulbs but reveals no fleshy leaves;

have a stem with a few papery, brown nonfunctional

leaves, and adventitious roots below; e.g. gladioluses

3. Rhizomes - horizontal stems that grow underground, oftenclose to the surface; e.g. perennial grasses, ferns

4. Runners and stolons - horizontal stems that grow along the

surface of the ground; e.g. strawberry plants

5. Tubers - swollen tip of stolon due to accumulation of

carbohydrates; e.g. potato

6. Tendrils - twine around supports and aid in climbing;e.g.peas, pumpkins

7. Cladophylls - flattened photosynthetic stems that

resemble leaves; e.g. cacti


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Root system adaptations

Eudicots have taproots

Monocots have fibrous roots

Other types of roots

Prop roots

Buttress roots

Pneumatophores

Fleshy storage roots carrots, sugar beets


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Modified Roots

Taproot system - consists of a single large root withsmaller branch roots

Fibrous root system - composed of many smaller roots

1. Aerial roots - exhibited by plants that have roots extended

out into the air (orchids); have epidermis that is

several cells thick to reduce water loss; some maybephotosynthetic (vanilla orchid); prop roots grow down

to the ground and brace the plants against wind (corn);

some plants (ivy) produce roots from their stems to

anchor the stems to tree trunks or brick wall

2. Pneumatophores - some plants growing in swamps produce

spongy outgrowths called pneumatophores from their

roots; these facilitate the oxygen supply to the roots

beneath


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3. Contractile roots - roots of some plants contract by spiraling

to pull the plant a little deeper into the soil each year

until they reach an area of relatively stable temperatures

e.g. lilies, dandelions

4. Parasitic roots - certain plants (Cuscuta) that lack chlorophyll

have stems that produce peglike roots called haustoria

that penetrate the host plants around which they are

twined; the haustoria establish contact with the conducting

tissues and parasitize their their host5. Food storage roots - some plants have roots that accumulate

large quantities of carbohydrates; potatoes, carrots,

beets, radishes, turnips

6. Water storage roots - some plants (Cucurbitaceae) produce

water-storage roots

7. Buttress roots - certain species offig and other tropical

trees produce huge buttress roots toward the base of

the trunk, which provide considerable stability


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Root growth

15 distinct regions of cellular

specialization

3 major zones

1. Apical meristem producing root and root cap

2. Zone of elongation

3. Zone of maturation with specialized cells


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Root meristem and root cap

RAM contains stem cells, protoderm (epidermaltissues), ground meristem (ground tissue), and

procambium (makes vascular tissue)

Also produces protective root cap

Root tips embedded in lubricating mucigel Zone of elongation

Cells extend by water uptake

Zone of maturation

Root cell differentiation and tissue specialization

Identified by presence of root hairs (water and mineral

uptake) absent from older regions


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Epidermis of mature roots encloses region

of ground parenchyma root cortex Root cortex cells often rich in starch (food

storage site)

Primary vascular system includes xylemenclosed by phloem

Pericycle encloses root vascular tissue

Produces lateral (branch) roots Woody roots produce primary vascular

tissues followed by secondary vascular

tissues


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