Reproductive Structures in Flowering Plants Flowers Reproductive shoots of sporophytes Flowering...
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Transcript of Reproductive Structures in Flowering Plants Flowers Reproductive shoots of sporophytes Flowering...
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