Plants
Definition of a Plant:
A
multicellular, eukaryotic, photosynthetic
autotroph. The cell walls contain
cellulose and they store excess glucose as
starch. They also exhibit alternation of
generations – one will be dominant over
the other. The sporophyte generation is 2n
(diploid) and the gametophyte
generation is n (haploid).
Evolution of Plants
 Plants
evolved from aquatic green algae
about 500 mya.
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Paleozoic era
Adaptations to dry land
Most plants are land plants today
Two Groups of Plants
 Non-vascular
– Bryophytes – no xylem or
phloem
 Vascular – Tracheophytes – contain xylem
and phloem – conducting tissue
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Xylem conducts – water
Phloem conducts – dissolved sugars
Primary Functions of Plants
 Absorb
carbon dioxide
 Release Oxygen
 Hold soil in place
 Provide for the transfer of energy from the
sun to other organisms – AKA – Food
 Provides habitats for animals
Division - Bryophyta
 Non-vascular
 Mosses,
horn-worts, liverworts
 They lack any lignin-fortified tissue so they
can’t grow very tall.
 The gametophyte generation is dominant
in bryophytes (it is the green part that you
see and the sporophyte is the stalk
coming out of the gametophyte.)
Bryophyte continued
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Female gametophyte has an Archegonium
that produces the egg (n)
Male gametophyte has Antheridia that
produces sperm (n)- These are motile sperm
and must have water in order to fertilize the
egg.
Fertilization occurs within the archegonium
and produces the zygote. The Sporophyte
then grows from the zygote out of the
gametophyte and produces sporangia that
produce spores.
What do Bryophytes do?
 Stabilize
and form soil from rocks – are
pioneers in primary succession and are
necessary to form the soil.
 Used as fuel (peat moss)
 Retains moisture when mixed with soil
Tracheophytes are:
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Vascular plants
Xylem and Phloem used for transport of water
and sugars
Xylem and Phloem contain lignin that gives
the plant support so that it can stand up
against gravity
Roots absorb water and prevent desiccation
(drying out), and anchor in the soil giving
extra support
Leaves increase the photosynthetic area
Sporophyte is the dominant generation
Two Groups of Tracheophytes
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Seedless Plants – Ferns – Pteridophytes
Homosporous – They produce only one type of
spore
 Stay fairly small because they must have water
to reproduce due to the fact that sperm are
flagellated and swim to get to the archegonium
to fertilize the egg.
 Ancient Ferns were tree size
 They reabsorbed so much carbon dioxide
during the Carboniferous period that the Earth
experienced Global Cooling
 Most turned into Coal that is now one of the
causes of Global Warming
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 Life
Cycle of a Fern
Seed Plants
 Heterosporous
– Produce megaspores –
female gametophyte and microspores –
male gametophyte
 Male gametophyte does not have
flagella so they don’t need water
 Gymnosperms – Cone bearing – naked
seed (conifers – pine, firs, redwoods,
junipers, and sequoia) – long-lived
organisms
Gymnosperms
 First
seed plants to appear
 Seeds are not enclosed in a fruit
 Replaced the ferns because they were
better adapted for land
 Have needle shaped leaves with a waxy
covering that helps to prevent drying
 Use the wind for pollination
Angiosperms
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Flowering plants – seeds are enclosed in a fruit
Most diverse and abundant of all plant
species
Color and scent of flowers attracts animals for
pollination and dispersal of seeds
Ovary becomes the fruit (fruit is ripened
ovary)
Ovule becomes the seed
Seed/Fruit adaptations
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Maples have wings so that the wind can carry
them
Fruit has burrs that stick to animal fur
Brightly colored and sweet so that animals eat
them and then poop the seeds with fertilizer
so it grows rapidly
Some float on water (coconut)
Fruit prevents drying out of seeds and protects
them until they are ready to be dispersed.
Two types of Angiosperms
 Monocots
leaf)
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– have one cotyledon (seed
Scattered vascular bundles
Parallel veins in the leaves
Flower parts in 3s
Fibrous roots
 Dicots
– have two cotyledons (seed
leaves)
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Vascular bundle is arranged in a ring
Veins are netlike or branched
Flower parts are in 4s or 5s
Have taproots
Plants: Part II –How plants
Grow
 Plants
can only grow from meristematic
tissue (meristem) – it is embryonic tissue
(stem cell)
 Located at the tip of the roots and in the
buds of shoots is apical meristem.
 The plant’s roots grow down into the soil
from this tissue and grow taller from the
top of the plant.
Primary Growth
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Zone of cell division – apical meristem:
actively dividing cells
Zone of elongation – Cells are not dividing but
are getting longer and push the root cap
down deeper into the soil
Zone of differentiation: Cells become
specialized into three tissue systems
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A. The protderm becomes the epidermis
B. The ground meristem becomes the cortex for
storage
C. The procambium becomes the primary
xylem and phloem.
Vascular Cambium is what makes woody
plants thicker. Responsible for secondary
growth.
Types of Plant Tissue:
 1.
Dermal Tissue
 2. Vascular Tissue
 3. Ground Tissue
Dermal Tissue
 1.
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Covers and protects the plant.
Endodermis
Epidermis
Modified cells like guard cells, root hairs,
and cells that make waxy cuticle
Vascular Tissue
 Xylem
– conducts water and dissolved
minerals (cells are dead at maturity)
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Consists of tracheids and vessel elements
Both types of cells are dead at maturity
Tracheids – long thin cells that overlap and
are tapered at the ends. Water passes
from one cell to another through pits.
Cells walls are hardened with lignin.
Xylem is what makes up wood.
Tracheid
 Vessel
Elements – wider than tracheids,
but also shorter than tracheids.
 Aligned end to end and the ends are
perforated to allow free flow through the
vessel tubes.
 Seedless vascular plants and
gymnosperms have only tracheids.
 Seed plants have both tracheids and
vessel elements.
Comparison of Tracheid and
Vessel Element
Phloem
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Carries sugars from the leaves to the rest of
the plant by active transport.
Made of sieve tube members (elements) with
sieve plates at the end to connect them.
These cells are alive at maturity but lack a
nucleus, ribosomes and vacuoles.
Companion cells are connected to each
sieve tube member and provides the sieve
tube cells with what they need.
Ground Tissue
 Most
common type of tissue in a plant
 Functions in 1)support 2) storage 3)
photosynthesis
 Three types of ground tissue
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Parenchyma
Sclerenchyma
Collenchyma
Parenchymal Cells
 They
are like a regular plant cell but they
lack secondary cell walls
 Are totipotent
 Many contain chloroplast and carry out
photosynthesis – mesophyll cells in the leaf
Collenchymal Cells
 Unevenly
thickened primary cell walls and
lack secondary cell walls and lignin to
harden them
 They are alive at maturity and function in
support of the growing stem.
 They are the strings in celery
Sclerenchymal Cells
 Have
thick primary and secondary cell
walls
 Function in support
 Two types: 1) fibers 2) sclerids
 Fibers – in bundles and are used in making
rope
 Sclerids – short and irregular and make up
the rough seed coat and pits. They give
fruit the gritty texture like in pears.
Roots and their Function
1)
absorb water and
nutrients
2) anchor the plant in the
soil
3) store food
Dicot Root
Parts of the Root and their
Fuctions
 Epidermis
covers and protects, absorbs
Root hairs – increase surface area
 Cortex
– Storage of starch and sugar
 Stele – consists of vascular tissue and is
surrounded by the pericycle (contains
meristematic tissue)
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Lateral roots arise from the stele
 Endoderm
cylinder
– Surrounds the vascular
 Casparian
strip – a band of cell wall
containing suberin and lignin, found in the
endodermis. It restricts the movement of
water across the endodermis.
 Suberin – a waxy like substance that
surrounds the casparian strip and acts as
a barrier to water and solute movement
across the casparian strip.
Types of Roots
 1)
 2)
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 5)
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Drop – Type of aerial
taproot
fibrous
Adventitious roots
Prop
Aerial – pneumatophores - snorkel
The Leaf
Parts of the leaf
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Cuticle – covered with cutin (a wax) to
prevent water loss
Guard Cells – modified epidermal cells that
surround the stomata and help to control the
opening and closing of the stomates. They
do contain chloroplast.
Stomata – Openings on the underside of the
leaf where gases, CO2 is taken in, O2 is
released and water vapor is lost by
transpiration. 90% of water escapes through
the stomates
 Pallisade
and spongy mesophyll –
pallisade is underneath the epidermis and
the spongy is in the middle of the leaf.
The primary function is photosynthesis.
 Vascular bundles – veins – located in the
mesophyll and carry water and nutrients
from the soil to the leaves and carry
sugars from the leaves to the rest of the
plant.
Control of Stomata by Guard
Cells
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In the light, guard cells actively pump protons out,
and this increases the uptake of potassium and
chloride ions. (No light, potassium and chloride
diffuse out of guard cells)
Higher concentrations of potassium and chloride
gives guard cells a negative water potential.
This causes water to flow into the cells and
increases the turgor pressure.
Increased turgor pressure stretches the cells and
opens the stoma. (Decreased turgor pressure
(flacid), the stomata closes.
Basically, the cellulose fibers are arranged radially
so that when the cells absorb water they curve
outward and open the stomata. They curve
inward when flacid and close the stomata.
What will make the guard cells
open?
 Decreased
carbon dioxide stimulates
stomata to open. Happens when
photosynthesis begins.
 Increase in potassium ions in the guard
cells which lowers the water potential
 Stimulation of the blue light receptor
 Active transport of H+ out of the guard
cells
What will make stomates
close?
 1.
Lack of water
 2. High temperatures – stimulates cellular
respiration and increases carbon dioxide
 3. Abscisic acid – produced by mesophyll
cells in response to dehydration and
guard cells close the stomata
Transport of Water in Plants
through the Xylem
Water
rises in the xylem
against gravity.
2 forces accomplish this:
1) Root Pressure
2) Transpirational Pull
Transpirational Pull
 Transpiration
is the evaporation of water
through the stomates in the leaves.
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Causes negative pressure as the water
leaves. This negative pressure is also called
tension.
Water molecules cling to each other due to
hydrogen bonding. This is called cohesion
and to the walls of the xylem which is called
adhesion.
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Transpirational pull-cohesion
theory
The negative pressure created when water evaporates pulls
other water molecules up the xylem. This is because the water
molecules are clinging to each other.
1)Water diffuses out of the stomata by evaporation. This is called
transpiration.
2)Water evaporates from mesophyll cell walls
3)Tension pulls water from the veins into the apoplast surrounding
the mesophyll cells
4) This pulls water in the veins of the leaves upward and outward
5)This pulls the water in the xylem of the shoot and root upward
6)Cohesion between water molecules forms a continuous
column of water from the roots to the leaves
7)Water enters the root and moves into the xylem by osmosis
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Apoplast and Symplast: The movement of
water across a plant is called lateral
movement and it occurs along symplast and
apoplast.
The symplast is a continuous system of
interconnected cells via plasmodesmata.
The apoplast is the network of cell walls and
intercellular spaces within a plant body that
allows extracellular movement of water within
a plant.
 When
it gets to the endodermis it can
continue to the xylem through the
symplast, but water in the apoplast must
pass across the endodermis by diffusion.
Translocation
 The
movement of carbohydrates and
other solutes through the plant in the
phloem.
 Moves from sources to sinks.
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A source is an organ that produces by
photosynthesis sugars
A sink is an organ that uses sugars such as
a flower, fruit, etc.
Active
transport
of sugars
Sources and Sinks can change roles.
If photosynthesis is not occurring then sugars
can be released from the roots or stems to
the leaves for use in cellular respiration.