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PLANTS
• basic Evolution & Classification
• Anatomy & Physiology of Roots,
Stems & Leaves
Plants Overview
• Evolution of plants and plant classification
• Plant anatomy:
– Tissues, Roots, Stems, Leaves
• Transport in plants
• Plant growth (primary & secondary)
• The role of Hormones in coordinating
growth & response to stimuli
For another time…
• Plant Sexual Reproduction
– Alternation of Generations
What is a plant?
• Plants are multicellular, eukaryotic
photoautotrophs
• Plants have a waxy cuticle covering that helps
them retain water
• Gas exchange occurs through holes, or stomata,
in the leaf surfaces
• They have organs such as roots, stems and leaves
• A vascular system carries water and minerals up
and nutrients down (and sometimes up again!)
• Reproductive structures, called gametangia,
contain gamete-producing cells
What is a plant?
Plant Evolution from water to land:
major adaptations & plant groups
Plant Kingdom
Byrophytes
Vascular Plants
(aka non-vascular or
non-tracheophytes)
(tracheophytes)
Mosses
Seedless
Vascular Plants
Angiosperms
Ferns, etc
Flowering plants
(“vessel seed”)
Monocots (“one cotyledon”)
Grasses, orchids, bamboo, palms,
lilies, grains
Dicots
Gymnosperms
(“naked seed”)
Conifers, etc
(“two cotyledons”)
Most shrubs & trees, many food crops
Angiosperms are broken into 2 groups:
Monocots and Dicots
Monocots & Dicots
• Cotyledons are the embryonic seed leaves
• Monocots: orchids, bamboos, palms, and
lilies AND the grasses, including wheat,
corn and rice (these are WAY important, for
obvious reasons!)
• Dicots: all the rest…(oak, maple. roses, cabbage,
beans, potatoes, most fruit trees, etc). So if you’re
asked which is more common, choose this
one
Seed germination begins the life of a
new plant
The plant: root system & shoot system
Modifications of roots and stems
• Many roots are adapted for storing food
• Rhizomes are actually modified stems that store food
• Modified stems can also act as “runners”, allowing a plant to
reproduce asexually
Three tissue
systems make
up a plant:
Epidermal tissue =
outer layer of r, s, l
Vascular tissue =
conducts water & food
(xylem & phloem)
Ground tissue = the
bulk of a young plant,
fills in space between
epidermis and vascular
tissue
How do things move around inside plants?
• XYLEM tissue = Water-conducting: made of tracheids and vessel
elements – are both dead, hollow tubes when mature
• PHLOEM tissue = Food-conducting: made of sieve-tube
members (dead when mature) & companion cells (alive when mature)
• Ferns, gymnosperms and angiosperms have these vascular tissues
and are called vascular plants or tracheophytes.
• Bryophytes (mosses) do not have xylem and phloem and so they are
non-vascular (lack specialized transport system).
ROOTS anchor the plant and allow for
absorption of water & nutrients from soil
Dissolved nutrients
move into root by
active transport …
water follows by
osmosis! Beautiful.
Plasmodesmata are openings in the walls and plasma membranes between plant cells that allow
free flow of liquids and dissolved molecules.
From root hairs into xylem – then up!!
The endodermis acts as the gate-keeper
Tissues of the leaf
• Guard cells regulate opening and closing of stomata
(openings for gas exchange: O2, CO2, H2O vapor)
• Mesophyll cells (palisade & spongy mesophyll), the ground
tissue of leaves, contain chloroplasts and perform
photosynthesis
Guard Cell Action: Bringing K+ into guard cells
causes water to follow by osmosis; cells become
turgid and stoma opens. Magic! (Flaccid guard cells =
closed stoma … not a bad idea if you’re not photosynthesizing and
trying to conserve H2O ...Like at night!)
How does water get to the top of trees?
Combo of root pressure, capillary action & transpiration pull!
Plant growth is “indeterminate”
growth - never ceasing (at root & shoot tips at least)
• Plants grow in length (primary growth) and in
thickness (secondary growth)
• Meristem tissue: unspecialized cells that divide
to generate all kinds of new plant tissue
– Apical meristem: meristem at the tips of roots and
shoots, allow them to grow in length
– Vascular cambium & Cork cambium: meristem
that allows stems & roots to thicken and branch out
Roots & stems exhibit both
primary and secondary growth
Root
Crosssection
Stem
Crosssection
Vascular cambium makes xylem & phloem
while cork cambium makes… cork!
Why do trees in temperate
climates have annual rings?
Plant hormones coordinate growth,
development & responses to stimuli
• Auxin: directs stem & root growth, responsible for
phototropism (growth towards light) and geotropism
(growth up away from gravity).
• Gibberellins: stimulate seed & bud germination,
stem elongation, flowering & development of fruit;
found in meristems of apical buds, roots, young
leaves, embryo.
• Cytokinins: promote cell division, germination &
leaf expansion; determine timing of cellular
differentiation (esp. in roots)
• Ethylene: stimulates the ripening of fruit and the
abscission (dropping) of leaves, flowers, and fruits.
The effect of gibberellin treatment on seedless grapes (treated grapes on right).
Plant Tropisms
Plant responses to external stimuli
Can you guess what these are?
• Phototropism:
• Gravitropism:
• Thigmotropism:
Classic Light/Growth Experiments with Grass Seedlings
MORE Classic Growth Experiments with Grass Seedlings
In 1926, F.W. Went extracted
the chemical messenger for
phototropism, naming it
auxin.
Plant Growth vocabulary
•Annuals: complete their life cycle in one year
•Biennials: complete their life cycle in two
years, usually flowering during the 2nd year
•Perennials: plants that live many years