• Introduction• More than 280,000 species of plants

inhabit Earth today.• Most plants live in terrestrial environments,

including deserts, grasslands, and forests.– Some species, such as sea grasses, have

returned to aquatic habitats.

• Land plants (including the sea grasses) are believed to have evolved from a certain green algae, called charophyceans.

• Bryophytes, pteridiophytes, gymnosperms, ands angiosperms demonstrate four great episodes in the evolution of land plants:– the origin of bryophytes from algal ancestors– the origin and diversification of vascular plants– the origin of seeds– the evolution of flowers

Remember the Big 4 events in Plant evolution

Plant Structure & Organization

• Cells make tissues, tissues make organs, organs make systems, systems make organisms

• 5 Basic plant cell types– Parenchymal cells– Collenchymal cells– Sclerenchymal cells– Xylem cells– Phloem cells

3 Cell types that make up all plant tissue

• Parenchyma – perform most of metabolism (including photosynthesis)– Present throughout the plant

• Collenchyma – help support growing parts of plants– Grouped in cylinders

• Schlerenchyma – support in parts that are no longer growing– Have tough cell walls– 2 types just for support

• Fibers • Scleroids

Plants have tissues:

A.) Dermal tissueB.) Ground TissueC.) Vascular tissueD.) Meristem =

embryonic tissue

3 tissue types that make up all plant organs

• Dermal – single layer, closely packed, cover and protect the entire plant (epidermis and periderm)

• Vascular – continuous throughout the plant– Transport tissue– 2 types

• Xylem – moves water and minerals up (from roots)– Made of tracheids and vessel elements (dead cells)

• Phloem - moves “food” down (from leaves)– Made of sieve tube members

• Ground – anything that isn’t dermal or vascular (fills and stores)– Pith – inside the ring of the ground tissue– Cortex – Outside the ring of the ground tissue

Parts of a Plant - Shoots and Roots

• Shoots (above ground: stems & leaves)– Produce food by photosynthesis– Carry out reproductive functions

• Roots (below ground)– Anchor the plant– Penetrate the soil and absorb water and dissolved minerals– Store food

• Roots, stems & leaves are all considered plant organs– We are going to look at these organs next

Angiosperm Body Plan

VASCULAR TISSUES

GROUND TISSUES

SHOOT SYSTEM

ROOT SYSTEM

EPIDERMIS

• Ground tissue system

• Vascular tissue system

• Dermal tissue system

Figure 29.2Page 506

Internal Anatomy : Stems• Vascular bundles (xylem and phloem)• Surrounded by ground tissue (xylem faces pith and phloem

faces cortex)• Mostly parenchyma; some collenchyma and sclerenchyma for

support

• Leaf Structure:

Internal Anatomy :Leaf Structure

UPPEREPIDERMIS

PALISADEMESOPHYLL

SPONGYMESOPHYLL

LOWEREPIDERMIS

one stoma

cuticle

O2 & H20

CO2

xylem

phloem

Figure 29.16Page 513

Guard cell

Adapted for Photosynthesis

• Leaves are usually thin – High surface area-to-volume ratio – Promotes diffusion of carbon dioxide in, oxygen

out

• Leaves are arranged to capture sunlight– Are held perpendicular to rays of sun– Arranged so they don’t shade one another

Mesophyll:Photosynthetic Tissue

• A type of parenchyma tissue

• Cells have chloroplasts

• Two layers in dicots

– Palisade mesophyll - most photosynthesis takes place here

– Spongy mesophyll - gas circulation

• One layer in monocots

Leaf Veins: Vascular Bundles

• Xylem and phloem; often

strengthened with fibers

• In dicots, veins are netlike

• In monocots, they are parallel

•

Root Systems

Taproot system Fibrous root system

Figure 29.17Page 514

2 types of root systems1. fibrous – mat of thin roots just below soil surface2. taproot – 1 thick vertical root with many lateral

roots extending from it

Internal Anatomy: Roots

-Outermost layer is epidermis

-Root cortex is beneath the epidermis

-Endodermis, then pericycle surround the vascular cylinder (this is called the Casparian Strip)

-the inner part called the stele contains the vascular tissue (xylem & phloem)

•

Root Hairs and Lateral Roots

• Both increase the surface area of a root system and help in absorption

• Root hairs are tiny extensions of epidermal cells

• Lateral roots arise from the pericycle and must push through the cortex and epidermis to reach the soil

newlateralroot

Figure 29.19Page 515

•

Root Hairs

Increase surface area for absorption

Flower Structure

• Nonfertile parts– Sepals

– Receptacle

• Fertile parts– Male stamens

– Female carpel (ovary)

filament anther stigma style ovary

receptacle

sepal (all sepals combined are the flower’s calyx)

OVULE (forms within ovary)

petal (all petals combined are the flower’s corolla)

STAMEN(male reproductive part)

CARPEL or pistil(female reproductive part)

Figure 31.3Page 538

•

• Two major groups (classes) of angiosperms

Kinds of Flowers• Perfect flowers

– Have both male and female parts• Imperfect flowers

– Are either male or female– Same plant may have both male and female flowers– Sexes may be on separate plants

Kinds ofPlants– dioecious

– Have both male and female parts– monoecious

– Sexes on separate plants

Plant Growth: Meristems• Regions where cell divisions produce plant growth• Apical meristems – located at ends (roots and shoots)

– Lengthen stems and roots– Responsible for primary growth

• Lateral meristems– Increase width of stems– Responsible for secondary growth (thickening of roots and

shoots)– 2 types

• Vascular cambium • Cork cambium

Plant growth: perpetual meristems

• Primary growth– From tips of root– From tips of shoots– Growth in length– Growth in to the

environment– Pattern can reflect

environmental pressures– Pericycle and auxiallary

• Provide branching

• Secondary growth– Growth in width– Not all plants have– Monocots lack– Comes from division of:

• Cork cambium• Vascular cambium

– Produces structural strength

Secondary Growth• Two lateral meristems• vascular cambium ~

produces secondary xylem (wood) and secondary phloem (diameter increase; annual growth rings)

• cork cambium ~ produces thick covering that replaces the epidermis; produces cork cells; cork plus cork cambium make up the periderm; lenticels (split regions of periderm) allow for gas exchange; bark~ all tissues external to vascular cambium (phloem plus periderm)

•

Major Meristems

3 growth zones• Zone of:

– Cell division – includes the meristems, rapid cell division, new growth

– Elongation – cells elongate

– Maturation – cell differentiation occurs and cells become fuctionally mature

Tissue Differentiation – three primary meristematic tissues

Protoderm

Ground meristem

Procambium

Epidermis

Ground tissue

Primary vascular tissue

•Cells descended from apical meristem divide, grow and differentiate to form shoot’s primary tissue system

Vascular cambium

Cork cambium

Secondary vascular tissue

Periderm & cork

•From lateral meristems

•

Stem growth summary

•

Plant Transport 3 types

1. Uptake and loss of water and minerals from individual cells• Occurs through:

– Osmosis – diffusion of water through the membrane– Water potential – the combined effect of solute

concentration and cell wall pressure (remember, turgor pressure is the pressure against the cell wall from water)

– Aquaporins – channels in plant cell walls designed for passage of water

– Tonoplasts – surround the vacuoles to regulate molecules going in and out of the vacuoles

2. Transport of substances short distances (from cell to cell)

• Is accomplished by:• Symplasts – cytoplasm connections between cells

through plasmodesmata• Apoplasts – nonliving continuum that is formed by

extracellular pathways through the continuous matrix of cell walls

• Water flows through both symplasts and apoplasts

• 3 major compartmentsand lateral transport!

Apoplast- between cell walls between cells of the cortex

Symplast- inside cells and thru plasmodesmata

•

3. Transport of sap within xylem and phloem (throughout the entire plant)

A. Absorption of water and minerals by roots• Usually near root tips in root hairs• Mycorrhizae – symbiosis between roots and fungi

• Helps roots absorb water and minerals • Water and minerals in root cortex must pass through

endodermis to enter the stele and get to the xylem to be transported to the rest of the plant• Endodermis contains the “Casparian strip” which

prevents subtances from going around or between the cells, therefore the water and minerals must pass through the endodermal cell to get into the vascular tissue

Casparian Stripexodermis

root hair

epidermis

forming vascular cylinder

cortex

Casparianstrip

• Prevents water and solutes from passing between cells into vascular cylinder

• Water and solutes must flow through cells

• Transport proteins control the flow

• Allows plants to adjust the quantity and types of solutes absorbed from soil water

Figure 30.4 Page 526

3. Transport of sap within xylem and phloem (throughout the entire plant), continuedB. Transport within the Xylem

-Water is “pulled” through the plant in two ways• Root pressure – water flows into the roots cause

positive pressure that forces the liquid up through the xylem

• Cohesion-Tension mechanism – water lost through the leaves creates a negative pressure which draws water up through the xylem with the help of adhesion/cohesion

- Transpiration – loss of water from leaves and other parts of plants in contact with air

-especially through open stomata -plants have guard cells around stomata that

open and close them to help control water loss

Transpiration-Cohesion-Tension

Theory of how water moves UPxylem

•

Factors in water movement up the stem by bulk transport

1.Transpiration evaporation of water from the leaf.2.Cohesion water molecules stick together by hydrogen bonding because they are polar.3. Tension is the pull as water molecule go to vapor because there is less water in the air.(Note: structure of xylem and how its function is related, how important xylem is to life on land both for support and transport, don’t forget lignin.)

Xylem

• Conducts water and

dissolved minerals• Conducting cells are

dead at maturity• hollow at maturity

vessel membertracheids

Figure 29.8 Page 509

•

• Xylem! Cells Stacked!!

Vascular Tissue

Root pressure is a PUSH!

As solutes accumulate in xylemand water transpiration has stoppedwater continues to move in to dilute.

Guttation is evidence

•

Guttation pushes water out of the tips of xylem-root pressure

Control of Stomata

• When stomata are opened; the cells have a high solute content causing water to move in building up turgor pressure (the cells swell opened)

• Close in response to water loss; ABA (abscisic acid - hormone) binds to receptors on guard cell membranes– calcium ions flow in and open gates for other solutes

(chloride, potassium and malate) to flow out from cytoplasm to extracellular matrix

• This causes a change in gradients and water moves out of guard cells, they collapse and close

•

•

How are things transported in the phloem?

Mass flow theory.From source to sink.

Sucrose is the sugar transported.

3. Transport of sap within xylem and phloem (throughout the entire plant), continuedC. Translocation of Phloem sap

-Phloem transports “food” from photosynthesis (usually in leaves) to the rest of the plant

-sieve tubes carry food from the source (where it is made) to the sink (the place that needs the food or where food is stored)

-mainly a result of bulk flow

•

Phloem: cells stacked!!

Phloem: A Complex Vascular Tissue

• Transports sugars • Main conducting

cells are sieve-tube members

• Companion cells assist in the loading of sugars

sieve plate

sieve-tubemember

companioncell

Figure 29.8 Page 509

Transport through Phloem

• Driven by pressure gradients• Fluid pressure is greatest at a source

• Solute-rich fluid flows away from the high-pressure region toward regions of lower pressure

• Sink - Region where compounds are being stored or used (ex. roots)

• Solutes are unloaded into sink cells and water follows• Called pressure flow theory or mass flow theory

• Sucrose Loading in Phloem

•

Plant Nutrition

• Require carbon dioxide, water, nitrogen,

minerals– Macronutrients – needed in large amounts

• 9 of them: C, H, O, N, S, P, K, Ca & Mg

– Micronutrients – needed in small amounts• @ least 8: Cl, Fe, B, Mn, Zn, Cu, Md, Ni

– Essential nutrients – needed for completion of life-cycle

Nitrogen

• Nitrogen must be in certain forms for the plants to be able to absorb and use it.

• Nitrogen fixing bacteria convert nitrogen to its useable form. It can do this in the soil.

– nitrogen gas (N2) to forms that plants can use (ammonium

and nitrate)

• Sometimes, nodules on roots – swelling where there is a symbiosis (mutualism) between the plant cells and the nitrogen fixing bacteria

•

Mycorrhizae

• Symbiosis between a young plant root and a fungus

• Fungal filaments may cover root or penetrate it

• Fungus absorbs sugars and nitrogen from the plant

• Roots obtain minerals absorbed from soil by fungus

Nutritional Adaptations

• Parasitic plants – rely on other plants for nutrients

• Epiphytes – not parasitic, just grow on the surface of other plants

• Carnivorous plants – can “trap” and “digest” small animals for supplemental nutrition

Moss Reproduction • At the tip of a male gametophyte are antheridia, in which swimming sperm

are produced. After rain or heavy dew, the sperm swim to the tip of a female gametophyte, where eggs have been produced within the archegonia. After an egg is fertilized, the developing sporophyte is retained within the archegonium as an embryo. The sporophyte is dependent on the gametophyte and it consists of a foot, a stalk, and an upper capsule (or sporangium) where meiosis occurs and where haploid spores are produced. When a spore is released and lands on an appropriate site, it germinates into the upright shoots of a moss gametophyte. The gametophytes produce gametes, and the moss life cycle begins again.

• See diagram on next slide

http://universe-review.ca/I10-22a-lifecycle2.jpg

Conifer Reproduction • Typically, male pine cones are quite small and develop near the tips of lower

branches. Inside each scale of the male cone pollen s produced, which is a sperm-bearing male gametophyte. The female pine cones are larger and located near the top of the tree. In each scale of the female cone ovules contain the female gametophytes (archegonia) which contain the eggs. Pollen grains are transferred from the male cone to the female cone. Once enclosed within the female cone, the pollen grain develops a pollen tube that slowly grows toward the ovule. The pollen tube discharges two nonflagellated sperms. Only one of the sperms fertilizes an egg in the ovule 15 months after pollination. After fertilization, the ovule matures and becomes the seed composed of the embryo, its stored food, and a seed coat. Finally, in the third season, the female cone, by now woody and hard, opens to release its seeds. When a seed germinates, the sporophyte embryo develops into a new pine tree, and the cycle is complete.

Steps of Angiosperm Reproduction:

• Meiosis produces heterospores which produce gametophyte stages:pollen/embryo sac

• Pollination: cross/self and wind water and animal• Formation of mature Gametophytes:

– Male = pollen tube + 2sperm (no flagella)– Female = embryo sac 8 nuclei

• Fertilization: double• Production of embryo/seed and fruit together

– Embryonic development of plant (young sporophyte)• Dispersal and dormancy• Germination of seed:

• In angiosperms, the reproductive structures are located in the flower. The flower attracts insects and birds that aid in pollination, and it produces seeds enclosed by fruit. There are many different types of fruits, some of which are fleshy (e.g., apple, tomato, peach, ...) and some of which are dry (e.g., pea enclosed by pod, nut, grain, ...).

Angiosperm Reproduction :Pollination

Pollen Formationpollen sac

anther

filament

microspore mother cell

Meiosis

pollen tubesperm nucleimature male

gametophyte

stigma

style of carpel

Diploid StageHaploid Stage

microspores

pollen grain

• Sperm packed inside a nutritious package

• Each anther has four pollen sacs

• Inside pollen sacs, cells undergo meiosis and cytoplasmic division to form microspores

• Microspores undergo mitosis to form pollen grains

Figure 31.6 Page 540

Egg Formation • The mother cell divides by meiosis to produce 4

haploid megaspores.

• Three of these 4 megaspores disintegrate.

• The fourth megaspore undergoes 3 cycles of mitosis to produce the female gametophyte, consisting of 7 cells with a total of 8 haploid nuclei. The central cell contains 2 polar nuclei.

• Three cells are found at each end of the large central cell of the ovule. The middle cell located near the micropyle, a small opening in the ovule, is the egg cell.

•

• When pollen lands on a stigma it germinates producing a pollen tube which delivers 2 sperm nuclei to the ovule.

• Double fertilization takes place to produce seeds and fruits. One sperm nucleus from the pollen tube unites with the egg nucleus, forming a diploid (2n) zygote, and the other sperm nucleus unites with the 2 polar nuclei, forming a triploid (3N) endosperm nucleus.

• The endosperm nucleus divides, forming the endosperm, which is a nutrient material for the developing embryo and sometimes for the young seedling as well.

• The zygote develops into an embryo. • The outer layers (integuments) of the ovule harden and become the seed

coat. • A seed is a structure formed by the maturation of the ovule; it contains a

sporophyte embryo plus stored food (the endopserm). • The ovary and sometimes other floral parts develop into the fruit. A fruit

is a mature ovary that usually contains seeds. Therefore, angiosperms are said to have covered seeds.

• The result is a seed - composed of the seed coat, nutritive endosperm (cotyledon), and embryo.

•

Seeds and Fruits

• The seed is the mature ovule

• The fruit is the mature ovary

•

Structure of a Seed• Protective seed coat is derived from integuments

that enclosed the ovule

• Nutritious endosperm is food reserve

• Embryo has one or two cotyledons– Monocot has one

– Dicot has two

• When the seed matures it goes dormant (slows metabolism) until conditions are right and then it will resume growth (germination)

Seed Germination

• Process by which the plant embryo resumes growth after seed

dispersal

• Depends upon environmental factors

– Temperature

– Soil moisture

– Oxygen levels

Splitting the Seed Coat

• Imbibition

– Water molecules move into a seed

• As water moves in, the seed swells and the coat ruptures

• Stages of germination of dormant seed

Imbibition-hormone signaling-response enzyme to release sugar- energy for metabolism and growth of embryo

Two Types of Angiosperms:Monocots and Dicots

The term cotyledon actually means seed leaf. So… •In monocot seeds there is 1 leaf. •In dicot seeds there are 2 leaves.•See following slides.

Nourishing the Embryo

• Dicot embryo – Absorbs nutrients from endosperm– Stores them in its two cotyledons

• Monocot embryo– Digestive enzymes are stockpiled in the single

cotyledon – Enzymes do not tap into the endosperm until the

seed germinates

Key things about seeds!• Dormancy• Dispersal• It’s the young sporophyte!• What does it contain?

– Protective coat– Food– Young embryo sporophyte plant

Asexual Reproduction - apomixis

• New roots or shoots grow from extensions or fragments of existing plants

• Proceeds by way of mitosis

• All offspring are genetically identical (unless

mutation occurs)

• Sometimes called vegetative reproduction by

fragmentation

Comparison of Monocot, Dicot and Gymnosperms

Characteristic Dicots Monocots Gymnosperms

Embryo Two cotyledons (seed leaves)

One cotyledon (seed leaf) One to many

Flowers Parts in 4 / 5 Parts in 3x No true flower

Vascular Bundles Ring Scattered Ring

Habit Herbaceous or Woody Herbaceous Herbaceous or

WoodyRoots Taproot Fibrous Taproot

Leaf Venation Net Parallel Needle-like

Pollen Tricoplate (3 furrows or pores)

Monocoplate (1 furrow or pore) Tow lobular wings

Growth Primary and Secondary Primary Primary and

Secondary

Control of Development

• Inheritable, internal mechanisms govern plant development

• Environmental cues turn such mechanisms on or off at different times, in different seasons

• Hormones are chemical signals that coordinate parts of an organism

Plant Hormones:(chemical messengers)

• Not like Animal hormones:– Do not control homeostasis– Not produced in glands– Not transported by blood

• Like Animal hormones:– Do have specific receptors in target cells– Only minute amount needed

Plant Hormones

• Gibberellins• Auxins• Cytokinins• Abscisic Acid• Ethylene

Gibberellin

• Found in meristems of apical buds and roots, young leaves and embryos

• In nature, gibberellin functions to:– Helps seeds and buds break dormancy (germination)– Makes stems lengthen– Influences leaf growth, flowering and fruit development– Influence root growth and differentiation– growth

• Applied by growers to enhance stem length, control ripening

Auxins

• Found in seed embryo, meristems of apical buds and young leaves

• Promote stem lengthening, root growth/differentiation/branching, fruit development

• Play a role in responses to gravity and light (tropisms)• Indoleacetic acid (IAA) is the most common auxin in

nature• Certain synthetic auxins are used as herbicides

Cytokinins

• Found in roots (and actively growing tissue)• Promote cell division, root growth/differentiation,

germination, delay senescence (aging)• Most abundant in root and shoot meristems and in maturing

fruits • In mature plants, produced in roots and transported to shoots• Used to artificially extend the shelf life of cut flowers; delays

leaf death

Abscisic Acid (ABA)

• Found in leaves, stems, roots and green fruit

• Causes the suspension of growth; promotes dormancy of

buds and seeds

• Used to induce dormancy in plants to be shipped

• Inhibits growth, closes stomata during stress, counteracts the

breaking of dormancy

• Also plays a role in drought response

Ethylene

• Found in ripening fruit, stems nodes and aging leaves

and flowers

• Induces aging responses (ex. ripens fruit )

• Unlike other plant hormones, ethylene is a gas

• Used to ripen fruits for market

Control of Abscission

• Abscission– Dropping of flowers, fruits, or leaves

• What brings it about?– Auxin production declines– Cells in abscission zone produce ethylene– Enzymes digest cell walls that attach leaf or fruit

to plant

Biological Clocks

• Internal timing mechanisms

– Trigger shifts in daily activity

– Help induce seasonal adjustments

• Phytochrome is part of the switching mechanism

– Blue-green plant pigment, measure length of darkness in

a photoperiod (red light)

Photoperiodism•Plants biological response to change in relative lengths of daylight and darkness

•Types of plants in terms of flowering

•Long day – flower when days are long

•Short day – flower when days are short,

•Day neutral – flower when mature, independent of light amount

Circadian Rhythm•24 hour periodicity

What is vernalization?

Period of cold required before a seed will germinate.Why would this be a selective advantage?

Senescence

• Sum total of processes that lead to death of

a plant or some of its parts

• Factors that influence senescence:

– Decrease in daylight is recurring factor

– Wounds, drought, or nutritional deficiencies can

also bring it about

Dormancy

• A predictable period of metabolic inactivity

• Short days; long, cool nights trigger dormancy

– Experiments have shown that exposure to light blocks dormancy

– Demonstrates involvement of phytochrome

Plant Tropisms

• Adjustment of plant growth toward or away

from an environmental stimulus

• Phototropism - stimulus is light• Gravitropism - stimulus is gravity• Thigmotropism - stimulus is contact with an

object

Phototropism

• Change in growth in response to light• Controlled by the flow of auxin produced in

the plant tip

Figure 32.10 Page 557

Gravitropism

• Roots tend to grow toward pull of gravity; shoots

grow against it

• Gravitational field is sensed via position of statoliths

(a type of amyloplast – a type of plastid)

• Auxin is involved in response; causes asymmetric cell

elongation

Thigmotropism

• Growth in response to contact with a solid object

• Allows vines and tendrils to wrap around supports

• Cells on contact side elongate, causing stem to curl

• Auxin and ethylene may be involved

• Mimosa ClosedThigmotropism

Ways plants protect against pathogens:

• Thick epidermis and cork layer with wax, suberin and cutin.

• Seal off the infected area: make a gall• Deposit more polysaccharides in the cell wall

to seal off the plasmodesmata• Produce defensive chemicals:

– Phytoalexin– Pathogen related proteins (PR)