Reproductive structures in flowering plants
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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

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Reproductive Structures in Flowering Plants

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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


remnants of

sepals, petals

ovary tissue

seed

enlarged

receptacle

Fig. 28.7d, p.461


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


shoot tip (terminal bud)

young leaf

flower

lateral (axillary) bud

node

internode

node

dermal tissue

vascular tissues

leaf

seeds

in fruit

withered

seed leaf

(cotyledon)

ground tissues

SHOOTS

ROOTS

stem

primary root

lateral root

root hairs

root tip

root cap


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


leaf vein (one vascular bundle)

xylem

phloem

cuticle

upper

epidermis

palisade

mesophyll

Water,

dissolved

mineral ions

from roots and

stems move

into leaf vein

(blue arrow).

spongy

mesophyll

lower

epidermis

Photosynthetic

products (pink

arrow) enter

vein, will be

distributed

through plant.

epidermal

cell

stoma

(small gap

across lower

epidermis)

Oxygen and

water vapor

(blue arrow)

diffuse out of

leaf through

stomata.

Carbon dioxide

(pink arrow)

in outside air

diffuses into

leaf through

stomata.


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)


guard cell

guard cell

chloroplast

(guard cells

are the only

epidermal

cells that

have these

organelles)

stoma

20 µm

Fig. 27.10, p.448


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


one

cell’s

wall

sieve plate

of sieve

tube cell

pit in

wall

companion

cell

parenchyma

fibers of

sclerenchyma

vessel

of xylem

phloem

Fig. 26.8, p.429


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


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