Transcript Roots

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)
lateral (axillary) bud
node
internode
node
vascular tissues
young leaf
flower
dermal tissue
leaf
seeds
in fruit
ground tissues
SHOOTS
ROOTS
withered
seed leaf
(cotyledon)
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
Photosynthetic
products (pink
arrow) enter
vein, will be
distributed
through plant.
epidermal
cell
stoma
(small gap
across lower
epidermis)
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
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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