Reproductive Structures in Flowering Plants

Flowers • Reproductive shoots of sporophytes• Flowering plants make sexual spores in male

stamens and female carpels of floral shoots

Gametophytes develop from the spores• Pollen grains contain male gametophytes• Ovules contain female gametophytes

Flowering Plant Life Cycle and Floral Structures

Coevolution

Flowering plants coevolved with pollination vectors that transfer pollen from stamens to carpels of flowers of the same species• Pollinators receive nectar and pollen

Attracting Pollinators

From Gametophyte to Fertilization

Male gametophyte formation• Pollen sacs form in anthers of stamens• Haploid microspores form by meiosis of diploid

spore-producing cells • Microspore develops into a sperm-bearing male

gametophyte, housed in a pollen grain

From Gametophyte to Fertilization

Female gametophyte formation• A carpel’s base has one or more ovaries • Ovules form from the inner ovary wall • One cell in the ovule (haploid megaspore) gives

rise to the mature female gametophyte • One cell of the gametophyte becomes the egg

From Gametophyte to Fertilization

Pollination• Arrival of pollen grains on a receptive stigma

Germination• Pollen grain forms a pollen tube (two sperm

nuclei inside); grows through ovary to egg

Double fertilization• One sperm nucleus fertilizes the egg, forming a

zygote; one fuses with the endosperm mother cell

From Zygote to Seed and Fruit

Seed • A mature ovule: Embryo sporophyte and

endosperm inside a seed coat • Eudicot embryos have two cotyledons; monocot

embryos have one

Fruit• Seed-containing mature ovary (and accessory

tissues)

Embryo Development: Eudicot

From Flowers to Fruits

Fig. 28.7d, p.461

remnants ofsepals, petals

ovary tissue

seed

enlargedreceptacle

Fruits: Seed Dispersal

Fruits help seeds disperse by adaptations to air or water currents, or diverse animal species

The Plant Body

Aboveground shoots• Stems that support upright growth• Photosynthetic leaves• Reproductive shoots (flowers)

Roots• Typically grow downward and outward in soil

root tiproot cap

lateral (axillary) bud

shoot tip (terminal bud)

nodeinternode

node

vascular tissues

ground tissues

SHOOTSROOTS

primary root

lateral root

young leaf

flower

dermal tissue

leaf

seedsin fruit

witheredseed leaf(cotyledon)

stem

root hairs

Epidermis

Leaf Structure

Between upper and lower epidermis• Mesophyll (photosynthetic parenchyma) • Veins (vascular bundles)

Stomata• Openings in cuticle-covered epidermis that

control passage of water vapor, oxygen, and carbon dioxide

Photosyntheticproducts (pinkarrow) entervein, will bedistributedthrough plant.

Water,dissolvedmineral ionsfrom roots andstems moveinto leaf vein(blue arrow).

Carbon dioxide(pink arrow)in outside airdiffuses intoleaf throughstomata.

Oxygen andwater vapor(blue arrow)diffuse out ofleaf throughstomata.

leaf vein (one vascular bundle)

xylem phloem cuticle

upperepidermis

palisademesophyll

spongymesophyll

lowerepidermis

epidermalcell

stoma(small gap

across lowerepidermis)

Water Conservation

Cuticle • Waxy covering that protects all plant parts

exposed to surroundings• Helps the plant conserve water

Water Conservation

Stomata• Gaps across the cuticle-covered epidermis• Closed stomata limit water loss (but prevent gas

exchange for photosynthesis and aerobic respiration)

• Environmental signals cause stomata to open and close

How Stomata Work

A pair of guard cells defines each stoma

Water moving into guard cells plumps them and opens the stoma

Water diffusing out of guard cells causes cells to collapse against each other (stoma closes)

Fig. 27.10, p.448

20 µm

chloroplast(guard cellsare the onlyepidermalcells thathave theseorganelles)

stoma

guard cellguard cell

Effects of Pollution on Stomata

Complex Vascular Tissues

Xylem• Vessel members and tracheids are dead at

maturity; their interconnected walls conduct water and dissolved minerals

Phloem• Sieve-tube members are alive at maturity, form

tubes that conduct sugars • Companion cells load sugars into sieve tubes

Fig. 26.8, p.429

onecell’swall

sieve plateof sievetube cell

pit inwall

companioncell

parenchyma

vesselof xylem

phloem

fibers ofsclerenchyma

Vascular Bundles

Bundles of xylem and phloem run through stems• Monocot stems: Vascular bundles distributed

through ground tissue• Herbaceous and young woody eudicots: Ring of

bundles divides ground tissue into cortex and pith • Woody eudicot stems: Ring of bundles becomes

bands of different tissues

How to distinguish between monocots and dicots

Stem• Monocot-randomly distributed vascular bundles• Dicot--ring of vascular bundles

Leaf• Monocot--parallel veins• Dicot--branched veins

Flowers• Monocot--petals in 3’s• Dicot--petals in 4’s or 5’s

Primary Structure of Eudicot and Monocot Stem

Eudicot and Monocot Leaves and Vein Patterns

Transpiration and Cohesion-Tension Theory

Transpiration• Evaporation of water from plant parts (mainly

though stomata) into air

Cohesion–tension theory• Transpiration pulls water upward through xylem

by causing continuous negative pressure (tension) from leaves to roots

Cohesion and Hydrogen Bonds

Hydrogen bonds among water molecules resist rupturing (cohesion) so water is pulled upward as a continuous fluid column

Hydrogen bonds break and water molecules diffuse into the air during transpiration

Root Functions

Roots• Absorb water and mineral ions for distribution to

aboveground parts of plant• Store food• Support aboveground parts of plant

Roots

Roots absorb water and mineral ions• Expand through soil to regions where water and

nutrients are most concentrated

Root hairs • Greatly increase root

absorptive surface

Root Symbionts

Draw products of photosynthesis from plants• Give up some nutrients in return

Mycorrhizae (fungal symbionts) • Increase mineral absorption

Root nodules (bacterial symbionts)• Perform nitrogen fixation

Root Nodules

Dendroclimatology

Wood cores and climate history

Processes of Survival

Plants and animals adapted in similar ways to environmental challenges • Gas exchange with the outside environment• Transportation of materials to and from cells• Maintaining internal water-solute concentrations• Integrating and controlling body parts • Responding to signals from other cells, or cues

from the outside environment

Rhythmic Leaf Movements

Responses to Environment: Thigmotropism

In some plants, direction of growth changes in response to contact with an object

28.9 Biological Clocks

Internal timing mechanisms respond to daily and seasonal cycles • Circadian rhythms (24-hour cycle)• Solar tracking