plant structures plant structures. plant cell structure (review) differences between plant &...
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Plant Structures
Plant cell structure (Review)
Differences between plant & animal cells? Unlike animal cells, plant cells
have . . . chloroplasts.a central vacuole.a cell wall of cellulose (angular cells not rounded).
Plant taxonomy (Review)
Of ~19 plant phyla, only 4 are wide-
spread.
Know a dichot- omous key to separate the plant phyla.
Plant structure (Dicotyledonous angiosperms)
ShootAbove- ground
RootBelow-ground
Note the ring of vascular tissue.
Plant tissues
Plants consist of 4 types of tissue.Dermal tissue – epidermal cells, often covered with a waxy layer called the cuticle.Vascular tissue – xylem and phloem cells transport water and nutrients throughout the plant.Ground tissue – parenchyma cells lying between dermal and vascular tissue provide support with thickened cell walls.Meristematic tissue – undifferentiated cells that produce all others by mitosis.
Plant tissues
Plants consist of 4 types of tissue.Dermal tissueVascular tissue
= xylem & phloem
Ground tissueMeristematic tissue creates new cells
Meristem
Plant meristemsDicotyledonous
plants have apical and
lateral meri- stems that
give birth to
new cells.Apical = at tips.Lateral = at side.
Plant meristemsGrowth due to apical and lateral
meristemsApical meristems increase plant length.
Undifferentiated cells in shoot and root.
bud
Buds will also develop their own apical meristems
Plant meristems Growth due to apical
and lateral meristemsLateral meristems increase plant girth.
Vascular cambium makes xylem and phloem.
Cork cambium makes bark (constantly
replaced).
Vascularcambium
Diagram of a dicot plant stem
Stems hold leaves toward light & transport nutrients from
roots.
As the dicot plant ages, the vascular tissues form a ring.
Young
Older
Diagram of a dicot plant stem
As the dicot plant ages, meristematic cells form a ring called vascular cambium.
Be able to draw this. (functions of tissues later)
The vascular cambium gives riseto the xylem & phloem tissues.
Vascularcambium
Diagram of a dicot plant stem
A new ring of xylem and phloem forms each year in perennial plants like trees.
Xylem rings are useful for telling the age of a tree.
Monocot vs. dicot plant stem
Recall that monocot stems (like corn & palms) have their vascular tissues in scattered bundles, not in rings (as do dicots like oak trees).
Transport within stemsWater moves from root to leaf as sap
through xylem tissue that is composed of non-living tubular cells. Xylem vessels have lateral pits and perforations at top & btm.
Diameter of xylem vessel = 50 to 100 μm
Transport within stems
Water moves by transpirational pull aided by cohesion, adhesion, & evaporation.
Evaporation removes water from the leaf surface as a result of the lower humidity in the air compared to the leaf.
Transport wihin stems
Water has polarity (the effect of having dis-tinct ends, or poles, like a magnet); water has opposite charges on opposite ends of the molecule. One pulls another.
Transport within stems
Water moves by transpirational pull aided by cohesion, adhesion, & evaporation.
Cohesion is the attractive force that one water molecule has for another (due to hydrogen bonding).
Cohesion lets the insectwalk on water.
Water ispulledup thexylemvessels.
Transport within stems
Water moves by transpirational pull aided by cohesion, adhesion, & evaporation.
Adhesion is the attractive force that one water molecule has for another substance – such as hydrophilic cellulose – (also due to hydrogen bonding).
Xylem walls are cellulose and adhere water.
Water is pulled up.
Transport within stemsSo, transpirational pull is the
movement of water up a plant against gravity aided by attractive forces on water molecules and resulting from evap- oration of water va-
por from the leaves and stems.
The tallest trees, Coast Redwoods in northern Cali-fornia, (Sequoia sempervirens),
can be nearly 380’ tall).
Transport within stems
Phloem is a vascular tissue that moves sap from sugar sources to sugar sinks.
Phloem sap contains sucrose & amino acids.Sources (where
the sugar is made) include photosynthetic tissues and storage organs.
Sinks (where the sugar is need-ed) include thefruits, seeds, &roots.
Transport within stems
Phloem is made of living cells called sieve tube members and companion cells.
(Recall: xylem cells are dead.)
Sieve tube mem-bers are stack-ed to form tubes.
Companion cells lie along each sieve tube mem-
ber & help loadsugar into the sieve tube.
Transport within stems
Active translocation of sugars from source to
sink in phloem.
1) Sugars are actively transported from source cells into sieve tube elements, so cells must be alive.
2) Because of the high sugar concen- tration in the phloem, water dif- fuses into the sieve tube elements, raising the water pressure.
3) Pressure causes the sap – sugar water – to flow through the phloem.
4) Sugars are transported out of the phloem into sink cells; water dif- fuses into the xylem, reducing the water pressure in the phloem.
Transport within stems
Active translocation of nutrients from source to sink.
Transport within stems
Review: water flows in a plant due to differences in water potential (% H2O).
Positive pressure pushes, as in the phloem.Negative pressure pulls, as in the xylem.
Plant Structures
Plant structure (Dicotyledonous angiosperms)
ShootAbove- ground
RootBelow-ground
Note the ring of vascular tissue.
Plant roots
Plant roots anchor plants in the ground and absorb water
and dissolved minerals from the soil.
Uptake by roots
Roots provide a large area for uptake of water and nutrients.
• Thousands of root hairs on each root.
• Dozens of lateral roots.• Mycorrhizae
(mutualistic fungi) grow out into soil.
Root hairs
Uptake by roots
How do minerals reach the roots?Mass flow of the water in the soil.
The roots intercept ions as they pass by.
Transport within rootsMineral ions are absorbed from the
soil into roots passively & by active transport.
Apoplast – non-living route of transport through cell walls to xylem.Symplast – transport route through the living cytoplasm to the xylem.
Absorption can create so much root pressurethat water can be forced out of leaves on humidnights.
Transport within roots
Apoplastic movement (passive):Hydrophilic cellulose in the cell walls of the epidermis (root hairs are epidermal cells) absorb water & the minerals dissolved in it.Minerals & water move from one cell wall to another toward the xylem, but the Casparian strip forces a detour into the cytoplasm.
(water insoluble materialblocks flow through cell wall.)
Transport within roots
Symplastic movement:
Once within a cell’s cytoplasm, minerals move to adjacent cells by diffusion, passing from one cell to another through plasmodes-mata – tunnels in the cell walls – moving toward the xylem.
Types of edible plant roots
Roots store energy; some are food sources.
sweet potato
Variety of plant leaves
Venusfly trap
Pitcherplant
Cactus (leavesare the needles)
Specialized leaves
Diagram of a dicot plant leaf
Leaves photosynthesize, making food for the plant.
Be able to draw this.
Functions of leaf tissuesCuticle: waxy covering to prevent loss of
moistureEpidermis: layer of protective cells (no
chloro-plasts)
Functions of leaf tissuesMesophyll: 2 layers, both contain
chloroplasts for photosynthesisSpongy parenchyma: air spaces for gas exchange
Functions of leaf tissuesVascular tissue: xylem moves water from
roots; phloem moves photosynthate away from the leaf.
Functions of leaf tissuesStoma (pl. stomata): an opening in the epider-mis through which H2O, O2 and CO2 may pass.
Guard cells: regulate gas exchange by expanding and contracting using ion pumps and osmosis to open and close the stoma.
Functions of leaf tissuesStoma (pl. stomata): an opening in the epider-mis through which H2O, O2 and CO2 may pass.
Guard cells: regulate gas exchange by expanding and contracting using ion pumps and osmosis to open and close the stoma.
Dicot flower structure
Draw and label all:
Male partsStamen
Holds pollen
Female parts Carpel (= pistil)
OvulationFertilization
Pollination
Pollination – placement of pollen onto the stigma of a carpel (pistil) by
wind or animal carriers.
Pollen is a haploid (1n) spore that carries the genes
of the male plant.
Pollination
Pollination – placement of pollen onto the stigma of a carpel (pistil) by wind or animal carriers.
Fertilization
Fertilization – union of haploid gametes to produce a diploid zygote.
After the pollen germinates on the stigma, the pollen
tube must grow down the style to
deliver the sperm to the
egg.FemaleGametophyte 1n
Sporophytetissue 2n
Seed dispersal
Seed dispersal – Process of moving seeds
away from the parent plant.
Adaptations for: Wind (feathery)Water (flotation) Animal (barbs, food source (fruit, nut)
Seed dispersal
Seed dispersal – Process of moving seeds away
from the parent plant.
Seed dispersal
Why disperse seeds?Colonize new areasGet away from the parent plant:
Excess shadeFew nutrientsPlant toxins
Control of plant growthPlants are rooted in the ground, yet
they can still move. They bend one way or the other.
Geotropism – movement due to gravityPhototropism – movement due to light
PositivePhototropism
NegativeGeotropism
Control of plant growth
Phototropism results from stimulation of plant cells by the hormone auxin. Hormones are made in one place but act
elsewhere.Auxin is made in shoot meristems.
It stimulates growth (elongation) of cells.
Cells on the shaded side grow larger,causing a bending of the plant shoot.
Control of plant growth
Phototropism results from stimulation of plant cells by the hormone auxin.
Auxin, made in shoot meristems, causes cells on the dark side to elongate by loosening their cell walls; internal water pressure causes cells to expand.
Giuseppe Arcimboldo’s painting, Vertumnus