Transcript Lecture 13.PLANT DIVERSITY.032410

PLANT DIVERSITY
LAND PLANTS EVOLVED
FROM GREEN ALGAE
• The Origin of Plants from Algae
– The closest modern relatives of the ancestors
of plants are the green algae, charophytes.
– Today this species is found around the edges
of ponds and lakes.
– The theory is that some ancient charophytes
might have lived in similar locations that dried
out and adapted to the new conditions as
plants.
CHAROPHYTES
LAND PLANTS EVOLVED
FROM GREEN ALGAE
– The oldest plant fossil is approximately 475
million years ago.
– Modern plants have since diversified and is
now a multicellular autotroph in which the
embryo develops within the female parent.
• Challenges of Life on Land
– The differences between plants and
charophytes are related to living on land and
amount to four challenges.
LAND PLANTS EVOLVED
FROM GREEN ALGAE
– Obtaining Resources From Two Places at
Once
• Aquatic organisms and algae get their resources
from the surrounding water.
• Land plants (photosynthetic) get their resources
from air and soil.
– Light and carbon dioxide are available above ground.
– Water and mineral nutrients are found in the soil.
• Shoots and roots allow access to these two
environments.
ALGAE vs. PLANTS
algae are simple and unspecialized possessing a holdfast that serves as
an anchor, while plants have specialized tissues that perform specific
tasks. Plants have a root system that holds it in place and extracts
mineral and nutrients from the soil. Algae take up minerals and nutrients
directly from the water via diffusion. Algae lack specific reproductive
structure while plants have stamens and carpels. Both have
photosynthetic properties.
LAND PLANTS EVOLVED
FROM GREEN ALGAE
• The plant’s roots absorb water, minerals, and
nutrients from the soil.
• Plant shoots bear leaves above ground which use
the sun as energy for photosynthesis.
– Most plants have a vascular system that
transports the minerals, nutrients, and water
between the roots and shoots and leaves.
– Staying “Afloat” in Air
• Sea weed or kelp (both algae) stay upright
because of the buoyancy of the water.
LAND PLANTS EVOLVED
FROM GREEN ALGAE
• Plants stay upright because of the strong support
system they have.
• This terrestrial adaptation includes the chemical
lignin, which hardens the plants’ cell walls.
– Maintaining Moisture
• Even though the plant is on soil and exposed to
dry air, its cellular processes take place in an
aqueous environment.
• Plants possess the ability to maintain a watery
internal environment.
– Examples are the waxy surfaces of a cactus or apple.
PLANT SUPPORT: LIGNIN
LAND PLANTS EVOLVED
FROM GREEN ALGAE
• A waxy cuticle coats the leaves and other above
ground parts, helping maintain water internally.
– One negative of this is the slowing down of the exchange
of CO₂ and O₂.
• The result, therefore, is the exchange of gasses
through the stomata, which are microscopic pores in a
leaf’s surface.
• Two surrounding cells regulate the stoma’s opening
and closing., opening only when necessary to prevent
evaporation.
STOMATA
LAND PLANTS EVOLVED
FROM GREEN ALGAE
• An Overview of Plant Diversity
– There are four major periods of plant
evolution.
• The first dealt with the origin of plants from
charophytes, their aquatic algal ancestors.
• The bryophytes were the first to diversify.
– These are the mosses.
– These plants don’t have seeds and lack lignin-hardened
material.
• Vascular plants marked the second period of plant
evolution and saw the development of vascular
MAJOR PERIODS OF PLANT
EVOLUTION
LAND PLANTS EVOLVED
FROM GREEN ALGAE
tissue with lignin-hardened vascular tissue that
transport water and nutrients.
• The third period included the origin of the seed.
– Seeds are embryos within a seed coat that also contains
a store of food.
– Seeds allow for the spread of plants to diverse areas
without allowing the embryo to dry out.
– Early seed plants included gymnosperms (Gr. for naked
seed) that have seeds that develop without being
enclosed within a chamber on specialized leaves.
» Conifers that produce cones are examples of these.
• The fourth period of plant evolution began with
flowering plants, or angiosperms.
LAND PLANTS EVOLVED
FROM GREEN ALGAE
– In angiosperms, the seed develops within a protective
organ, the ovary, contrasting with the gymnosperm’s
naked seeds.
• Alternation of Generations
– Plant generations alternate between diploid
(2n) and haploid (n) forms.
• Recall that diploids have two sets of
chromosomes, one from each parent.
• Haploids have one set as a result of meiosis.
– In the plant life cycle, the haploid and diploid
forms are distinct, multicellular generations.
A PLANT’S LIFE CYCLE
A PLANT’S LIFE CYCLE
LAND PLANTS EVOLVED
FROM GREEN ALGAE
• Animals have a unicellular haploid stage, a single
sperm or egg cell.
– The haploid generation of plants produces
gametes called gametophytes.
– The diploid generation produces spores called
sporophytes.
• In the plant’s life cycle, each generation takes
turns giving rise to the other.
– The alternation between the haploid and
diploid forms is called the alternation of
generations.
LAND PLANTS EVOLVED
FROM GREEN ALGAES
– Spores differ from gametes in two ways.
• Spores can develop into new organisms without
fusing with another cell.
– Gametes must fuse together to produce a zygote.
• Spores of some plants have tough coats that
enable them to resist harsh environments and lay
dormant.
– Gametes cannot tolerate harsh environments and lay
dormant.
– Alternation of generations occurs only in life
cycles of plants and certain algae.
REVIEW: CONCEPT CHECK
19.1, page 424
1. Name the group of algae most closely related to plants.
What is a major difference between plants and algae?
2. Make a table listing the four major challenges to plants
living on land. In the second column, list at least one
plant adaptation for each challenge.
3. List the four main groups of plants and describe two
characteristics of each.
4. List the difference between the sporophyte and
gametophyte plant generations.
POLLEN AND SEEDS
EVOLVED IN GYMNOSPERMS
• Gymnosperm Adaptations
– Gymnosperms have adapted with a smaller
gametophyte, pollen, and seeds for survival
on land.
– Gymnosperms are plants that bear seeds
that are not enclosed in an ovary (naked).
– Here the diploid sporophyte generation is
more highly developed than the haploid
generation.
PINE TREE’S
GAMETOPHYTES
POLLEN AND SEEDS
EVOLVED IN GYMNOSPERMS
– Pine trees are sporophytes in which tiny
gametophytes live in cones.
– Pollen is a second adaptation of seed plants
to dry land.
– Pollen is male gametophytes that contain
cells that develop into sperm.
– Wind carries the pollen in many plants,
including the conifer.
– Evolution has allowed plants on dry land to
POLLEN AND SEEDS
EVOLVED IN GYMNOSPERMS
– develop pollen so that sperm can reach eggs
(female cone in the case of conifers) without
swimming through water.
– Seeds are plant embryos surrounded by a
protective coat that includes a food supply
within its confines.
– In the pine tree’s cones, there are many spore
sacs, thousands of haploid spores that
develop into pollen grains (male
gametophytes).
LIFE CYCLE OF A PINE TREE
(GYMNOSPERM)
POLLEN AND SEEDS
EVOLVED IN GYMNOSPERMS
– The female gametophytes develop in the
ovules.
– Within each of the two ovules on each scale
of the female cones, a large spore cell
undergoes meiosis and produces four haploid
cells.
• One of these will survive and grow into the female
gametophyte.
– The pollen will travel from tree to tree by the
wind.
POLLEN AND SEEDS
EVOLVED IN GYMNOSPERMS
– If a pollen grain reaches the female cone,
sperm cells mature and fertilize egg cells
within the female gametophyte.
– More often than not, both eggs in the ovule
will be fertilized but only one develops into an
embryo.
• The embryo is then the new sporophyte plant.
• The Diversity of Gymnosperms
– Four gymnosperm phyla exist today.
POLLEN AND SEEDS
EVOLVED IN GYMNOSPERMS
• Ginkgos
– Date back to dinosaur era
– Tolerates city pollution well
• Gnetophytes
– Usually located in desert locale
• Cycads
– Sago palms
• Conifers
– Evergreens like spruce, pine, firs, juniper, cedar,
redwoods
– Leaves replace only when old ones die.
GYMNOSPERMS: GINKOS
AND GNETOPHYTES
GYMNOSPERMS: CYCADS
AND CONIFERS
REVIEW: CONCEPT CHECK 19.4,
page 433
1. Name three adaptations of gymnosperms
and the advantages they provide.
2. Make a table listing the four different
gymnosperm groups and a beneficial use
or fact about each one.
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
• Angiosperm Adaptations
– These were the last major group of plants to
evolve.
– Angiosperms are flowering plants where the
reproductive structures are flowers, not cones
like the gymnosperms.
– The gametophytes develop within the flowers
of the sporophyte.
– The flower is specialized to function in
reproduction and is unique to angiosperms.
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
– Flowers are structured to attract insects and
other animals to transfer pollen from one
flower to the next.
• The following contribute to the interactions
between angiosperms and the animal pollinators:
–
–
–
–
–
Variety of flower
Shape of flower
Odor
Texture
Color
POLLINATION BY BEES AND
FLIES
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
– Grasses, an angiosperm, are wind pollinated
but have flowers which are smaller and less of
an attraction than those pollinated by animals.
– The stamen is the male reproductive organ of
a flower.
• This consists of a filament on which the anther,
which produces the pollen or male gametophyte,
sits.
– The carpel is the female reproductive organ
and is composed of the stigma, style, and
ovary.
PARTS OF A FLOWER
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
– Within the ovary, ovules or female
gametophytes (embryo sacs) develop.
– Referring to the slides with the stages of the
life cycle of an angiosperm, the following is a
description.
• During reproduction, the pollen lands on the sticky
stigma.
• A tube then grows from each pollen grain down the
style toward an ovule in the ovary.
LIFE CYCLE OF AN
ANGIOSPERM
ANGIOSPERM vs.
GYMNOSPERM LIFE CYCLE
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
• Two sperm cells in the pollen are released into the
female gametophyte.
• One sperm fertilizes an egg cell, producing a
zygote, which then develops into an embryo.
• The second sperm cell fuses with nuclei in the
larger center cell of the female gametophyte, which
then develops into a nutrient-storing tissue called
endosperm.
– This endosperm nourishes the embryo as it grows.
• This is “double fertilization” and simultaneously
produces the zygote and endosperm.
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
• The seed then develops from this whole ovule,
containing the zygote and endosperm.
– Some flowers contain many ovules and can produce
many seeds.
– This development of seeds within ovaries is in contrast to
the gymnosperm's “naked” seed development.
• As the seeds develop from the ovules, the ovary
wall thickens and forms a fruit the surrounds the
seeds.
• A fruit is the ripened ovary of a flower.
– Fruits provide protection and a means of dispersal of the
seeds.
RIPENED OVARIES OR FRUIT
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
• The Diversity of Angiosperms
– Biologists, at one time, divided angiosperms
into monocots and dicots.
• These differ in the structure of the leaves, flowers,
seeds, roots, and vascular tissue
– Recent advances have added information to
expand the cladogram.
– Some flowering plants descended from
ancestors that evolved earlier than the oldest
known monocot or dicot.
MONOCOT vs. DICOT
AMBORELLA AND WATER LILLIES
PREDATE MONOCOTS
FLOWERS AND FRUITS
EVOLVED IN ANGIOSPERMS
• Human Dependence on Angiosperms
– All fruit and most vegetables are angiosperms
that provide the food that supports life.
– Corn, rice, wheat, and other grains are fruits
of grasses.
– Angiosperms provide furniture, medicines,
perfumes, decorations, and cotton fiber.
REVIEW: CONCEPT CHECK 19.5,
page 437
1. Define and give examples of a fruit and a
flower.
2. Name three examples of monocots and
three examples of dicots.
3. Make a list of benefits angiosperms offer
humans.
4. Explain what is meant by the term double
fertilization.
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• Flowers and Reproduction
– Most flowers share the same basic pattern.
– Flowers are specialized shoots found only in
angiosperms the usually consist of four
different rings of modified leaves: sepals,
petals, stamens and carpels.
• The sepals cover and protect the flower bud
before it opens.
• The next ring is the petals, which are colorful, and
in some cases, have markings to direct the insect
toward the reproductive parts.
PARTS OF A FLOWER
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• The stamens and carpels, the reproductive parts,
are closest to the center of the flower.
• Most flowers have multiple stamens and one
carpel.
• Some plants, like wild roses, have more than one
carpel.
• The male gametophytes are produce within the
stamens.
• The stamen is composed of the filament and the
anther.
• In the anther, meiosis produces spores that
become pollen, the male haploid gametophytes.
ANGIOSPERM’S LIFE CYCLE
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• In the anther, meiosis produces spores that
become pollen, the male haploid gametophytes.
– Each pollen grain consists of two cells surrounded by a
thick protective wall.
• Female gametophytes are produced in the carpels.
– At the base is the ovary where the ovules are located.
– In each ovule, the diploid cell undergoes meiosis and
produces four haploid spores.
» Unfortunately, three of the four spores die.
– The survivor enlarges and undergoes three cycles of
mitosis, with the result becoming the female
gametophyte, or embryo sac.
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• In the embryo sac are seven cells including an egg
cell and a large, central cell with two haploid
nuclei.
• Part of the carpel is the style and stigma.
• The stigma is the tip which is sticky and the style
is a long tube leading to the ovary.
• During pollination, pollen grains from another plant
of the same species land on the stigmata.
• The pollen absorbs water and then extends a
structure called the pollen tube, which grows
toward the ovary through the style.
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• One of the pollen cells divides once, forming two
haploid sperm.
• When the pollen tube reaches the ovary, it enters
the embryo sac and releases both sperm cells.
• Next two fertilizations take place.
– One sperm cells fertilizes the egg cell producing a
zygote.
– The zygote develops, then, into the sporophyte embryo.
– The other sperm cell fertilizes the large central cell with
the two haploid nuclei, with the result being a triploid cell
(3n).
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• The triploid cell develops into the nutrient rich
tissue called the endosperm which gives
nourishment to the embryo.
• Seed Development and Dispersal
– After this double fertilization, the ovule
develops into the seed.
– The outer layer, the seed coat, protects the
embryo and endosperm.
– One can then see a miniature root and shoot.
SEED DEVELOPMENT
SEED DEVELOPMENT
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
– The cotyledon develops, which functions in
the storage and transfer of nutrients to the
embryo.
• Monocots have one cotyledon and dicots, two.
– Several cycles of mitosis takes place in the
embryo and, then, growth is suspended
(dormancy).
– At this point, the seed is ready to leave the
parent.
SEED DISPERSAL
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
– Seed dispersal occurs in many ways.
•
•
•
•
Sticking to an animals fur
In fleshy fruits, attractive to animals
Like coconuts, traveling on water
Like the dandelion, by the wind
• Seed Germination
– Germination, or the growth of the seed again,
occurs when conditions are favorable.
– This occurs after the seed soaks up water,
SEED GERMINATION
SEED GERMINATION
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
expanding and splitting the seed coat, and
triggering metabolic changes in the embryo
causing growth.
– Adaptations
• Once out of the seed coat, the shoots are
susceptible to “abrasion” by the surrounding soil.
• Some dicots have a hooked shoot tip.
– Once out of the soil, this, then, straightens out.
• In monocots, a sheath surrounding the shoot
pushes straight upward through the soil, and, after
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• emerging into the light, expands the leaves and
begins the process of photosynthesis.
• This is the stage where the plant is called a
seedling.
– Environmental Conditions
• Conditions for germinations vary among different
plant species.
• Desert plants germinate only after a heavy rainfall
to allow the seedling to push through the
moistened soil and provides a temporary water
supply.
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• Some seeds will germinate only after long periods
of cold in harsh winter climates.
• Some seeds require intense heat to germinate.
• Asexual Reproduction in Plants
– Obstacles exist to successful sexual
reproduction in plants.
– Pollen may not reach the correct species of
flower.
– Seeds can get damaged during dispersal.
– Seedlings may not survive.
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
– Asexual reproduction in plants is called
vegetative reproduction.
– These plants produce genetically identical
plants to themselves.
– This can be done naturally or with help.
– Some cacti drop sections its stems that
produce new, identical plants.
– Some plants, like the strawberry or aspen
send out runners that produce new, identical
plants.
VEGETATIVE REPRODUCTION WITH
STOLENS
REPRODUCTIVE ADAPTATIONS CONTRIBUTE
TO ANGIOSPERM SUCCESS
• How Long Does a Plant Live?
– Annuals complete their life cycles in one year.
– Biennials complete their life cycle in two years
and usually flower only in the second year.
– Perennials live and reproduce for many years.
ANNUALS, BIENNIALS, AND
PERENNIALS
REVIEW: CONCEPT CHECK 20.1,
page 446
1. Diagram the reproductive structures of a flower. For
each structure, include a label stating a brief description
of its function.
2. Describe three different methods of seed dispersal.
3. Explain how two different adaptations of seed
germination in dicots and monocots protect the
developing shoot.
4. Give two examples of vegetative reproduction in plants.
5. Compare and contrast annuals, biennials, and
perennials.
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
• A Plant’s Root System and Shoot System
– Roots function as a support and anchor
system.
– Roots absorb minerals and water.
– Most monocots have a fibrous root system
which consists of mats of thin roots spread out
below the soil surface.
– This increases the surface area to absorb
those nutrients and water.
FIBROUS vs. TAPROOT
SYSTEMS
ROOT vs. SHOOT SYSTEM
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
– Most dicots have a taproot system
characterized by one large vertical root with
branches off of it.
• Examples would includes carrots, turnips, and
beets with starchy taproots.
– The shoot system consists of stems, leaves,
and flowers.
– Stems provide support to the leaves and
flowers.
– Nodes are where leaves are attached.
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
• Internodes are the parts of the stem between the
nodes.
– Vascular tissue runs vertically in the stems,
transporting water and nutrients up the stem
and food down.
– Some photosynthesis and storage occur in
the stems.
– Shoots that have yet to develop are called
buds.
– Terminal buds are found at the tip of the stem.
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
– Axillary buds are found in the angles (axils)
formed by a leaf and the main stem.
• Growth from this area forms the plant’s branches.
– Leaves are mostly flattened and thin.
– The main part is the blade.
– The petiole connects the leaf to the stem.
– Leaf veins carry water and nutrients and
consist of vascular tissue and support tissue.
– Leaves can be modified, depending on the
plant.
LEAVES
MODIFIED LEAVES
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
•
•
•
•
Grasses lack petioles.
The celery stalk is the petiole.
Spines on a cactus are leaves.
Tendrils on pea plants or grape vines attach to
things so that they can climb.
• A Plants Main Tissue Systems
– There are three main tissue systems:
• Dermal
• Vascular
• Ground tissue
TISSUE SYSTEMS OF A PLANT
LEAF TISSUE ANATOMY
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
– Dermal Tissue
• This is the outer layer of the plant (skin).
• Epidermis, the dermal tissue of nonwoody organs
such as young roots, consists of one or more
layers of cells.
– This covers all the young parts of a plant.
– This is what secretes the waxy cuticle.
– Vascular Tissue
• This is what transports water, minerals, and
organics from the roots to the shoots.
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
• It also adds to the structure of the plant.
• This comes under the term tracheid and consists
of xylem and phloem.
• Xylem transports water and minerals from the
roots to the shoots.
• Phloem transports food from the mature leaves to
the other parts of the plant, shoots and roots,
where photosynthesis doesn’t take place.
• In the roots, the vascular tissue is in the center.
• In the stems, it is arranged in vascular bundles, or
separate strands.
MONOCOT vs. DICOT
VASCULAR SYSTEMS
VASCULAR BUNDLES:
MONOCOT
VASCULAR BUNDLES: DICOT
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
– Monocots have vascular bundles scattered throughout
the ground tissue.
– Dicots’ are arranged in a ring.
– Ground Tissue
• Between the dermal and vascular tissue is the
ground tissue which makes up most of a young,
nonwoody plant and functions in photosynthesis,
storage, and support.
• The ground tissue of the root consists primarily of
a mass of cells called the cortex.
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
• Types of Plant Cells
– Parenchyma Cells are the most abundant.
• They have thin cell walls and large central
vacuoles.
• They provide storage, photosynthesis, and cellular
respiration.
• Fruits are composed mostly of parenchyma cells.
• Phloem is composed of parenchyma cells.
– Collenchyma cells have unevenly thickened
cell walls.
PARENCHYMA CELLS
COLLENCHYMA CELLS
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
• These are usually grouped in strands or cylinders
and provide support for the growing parts of the
plant.
• These include young stems and petioles where it is
located below the surface.
– Celery stalk strings
• These cells elongate with the stem and leaves as
they grow.
– Sclerenchyma cells are for support.
• They grow and die within a mature part of a plant.
• They are rich in lignin, which is left behind, to
create a skeleton to support the plant.
SCLERENCHYMA CELLS
STRUCTURE FITS FUNCTION
IN THE PLANT BODY
– The xylem is sclerenchyma cells.
– Plants are composed of more than one of
these cell types.
REVIEW: CONCEPT CHECK 20.2,
page 451
1. Compare and contrast the functions of
roots and shoots.
2. List the functions of dermal, ground, and
vascular tissues.
3. Describe the characteristics of the three
main plant cell types.
PLANTS ACQUIRE NUTRIENTS
FROM THE SOIL AND AIR
• Seeking the Source of a Plant’s
“Substance”
– Aristotle originally hypothesized that soil
provides all the mass necessary for plant
growth.
– Van Helmont, in the 1600s, tested this and
added nothing other than water to the soil.
– He noted that the plant gained more mass
than the soil lost, proving the hypothesis
wrong.
PLANTS ACQUIRE NUTRIENTS
FROM THE SOIL AND AIR
– His new hypothesis was that plants gain
substance (mass) from water added to the
soil.
– Hales, an English botanist, proposed another
hypothesis, that plants gain substance from
the air.
– Recent studies have indicated that these early
ideas about plant nutrition might have some
truth.
• Air supplies carbon dioxide to the plant.
Van HELMONT’S EXPERIMENT
PLANTS ACQUIRE NUTRIENTS
FROM THE SOIL AND AIR
• CO₂ is used in photosynthesis to produce sugar which
might lead to cellulose.
• Hydrogen comes from water which also is a transport
mechanism.
• The soil gives up minerals that the plant needs.
• The Mineral Requirements of Plants
– Most plants need 17 chemical elements to
complete their life cycles.
– CO₂ provides carbon and oxygen and comes from
air.
PLANTS ACQUIRE NUTRIENTS
FROM THE SOIL AND AIR
– Water provides hydrogen and comes from the
soil.
– The other elements are mineral nutrients
absorbed in ionic form from the soil.
– Plants can suffer from nutritional deficiencies.
•
•
•
•
Stunted plant growth
No flowers produced
No synthesis of chlorophyll
Yellowing of young leaves
SOME ESSENTIAL PLANT MINERAL NUTRIENTS
MINERAL NUTRIENT
FUNCTIONS IN PLANT
Nitrogen
Protein and nucleic acid synthesis
Sulfur
Protein synthesis
Phosphorus
Nucleic acid and ATP synthesis
Potassium
Protein synthesis; regulation of
osmosis
Calcium
Cell wall formation; enzyme activity
Magnesium
Chlorophyll synthesis; enzyme activity
PLANTS ACQUIRE NUTRIENTS
FROM THE SOIL AND AIR
• A Closer Look at Nitrogen
– Plants use nitrogen to produce proteins,
nucleic acids, and hormones.
– Plants do suffer from nitrogen deficiency,
even though 80% of the atmosphere is
nitrogen.
– The plants must absorb it from the soil and
not as a gas.
– Nitrogen is first converted to ammonium ions
(NH₄⁺) or nitrate ions (NO₃⁻).
PLANTS ACQUIRE NUTRIENTS
FROM THE SOIL AND AIR
– Nitrogen fixation, by bacteria, converts the
gas to the ionic forms.
– Other bacteria act as decomposers.
– A third group of bacteria convert the NH₄⁺ ions
to NO₃⁻.
– Legumes such as peas, peanuts, alfalfa, and beans
contain nitrogen fixing bacteria on their roots as
lumps called root nodules.
– Farmers use crop rotation to add nitrogen to the
soil.
NITROGEN CYCLE
PLANTS ACQUIRE NUTRIENTS
FROM THE SOIL AND AIR
• Fertilizers
– These are products used by farmers amateur
gardeners that contain nitrogen, phosphorus,
and potassium.
– The bags have three-numbered codes such
as 10-12-8, meaning 10% nitrogen, 12%
phosphorus, and 8% potassium.
– Except when they are applied, these fertilizers
run off when it rains, contributing to pollution.
REVIEW: CONCEPT CHECK 21.1,
page 463
1. Did van Helmont’s experiment support or
disprove Aristotle’s hypothesis? Explain.
2. List at least three mineral nutrients required by
plants, and describe their contributions to plant
function.
3. Describe the role of three different kinds of
bacteria in making nitrogen available to plants.
4. Describe the benefits and possible problems
from fertilizer use.
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
• How Roots Absorb Water and Minerals
– Root hairs increase the surface area of the
roots to improve the absorption of water and
dissolved minerals.
• They are very small projections of the roots
epidermal cells and grow into spaces between soil
particles.
– Remember that mycorrhizae work in
symbiotic relationship to allow the absorption
of the dissolved minerals, especially
phosphate.
ROOT HAIRS
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
– Two forces id in moving the water from the
roots to the rest of the plants.
– The first, root pressure, pushes the water up
the xylem and works during the night.
– The epidermal cells and ground tissue cells
use ATP to accumulate certain minerals,
which then move from cell to cell through
cytoplasmic channels. This is the way water
and minerals move through the xylem.
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
– Endodermis is a layer of cells that surrounds
the vascular tissue.
• It is composed of waxy cells which prevents the
water and minerals from backflow out of the xylem.
– The minerals accumulate in the xylem, water
enters by osmosis, and the xylem sap is
pushed upward.
• The Upward Movement of Xylem Sap
– Root pressure is only one way the sap gets to
the top of the plant.
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
– There is a force that pulls it to the top, like a
straw.
– Transpiration, evaporation of water through
the leaves, creates this pull (transpirationpull).
• This occurs because of cohesion, the quality of the
molecules of the same kind to sick together, and
adhesion, the quality of attraction between unlike
molecules.
• Both of these forces counteract the pull of gravity,
with adhesion preventing the falling back of the
TRANSPIRATION
TRANSPIRATION
TRANSPIRATION
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
•
•
•
•
•
water due to gravity, at night.
There are two types of xylem “straws” in which
water travels through the plant.
Tracheids are long cells with tapered ends
Vessel elements are wider, shorter, and less
tapered.
These cells can overlap, forming tubes which are
hollow since the cells have died.
The lignin cell walls remain which create the tubes.
XYLEM STRUCTURE
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
• Regulating Water Loss
– Heat denatures protein, thus disabling
enzymes for photosynthesis.
– Transpiration allows for evaporative cooling
preventing this but, yet, allows for a large
amount of water loss from the plant.
– When transpiration exceeds water intake,
leaves wilt.
– The leaves’ stomata help regulate
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
transpiration according to environmental
conditions.
– Guard cells surround each stoma opening
and open and close by changing shape.
• During daylight, stomata are open allowing CO₂ to
enter.
• Sunlight and low CO₂ levels trigger the guard cells to
gather K⁺ ions that facilitates water entering the guard
cells.
• The guard cells then swell.
GUARD CELLS
GUARD CELLS
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
• They, then, buckle away from their centers so that
a gap opens.
• At night, the stomata close which also happens
when the plant is losing water from transpiration
faster than it is gaining water from the soil.
• K⁺ ions are lost from the guard cells with water
following.
• The guard cells droop, losing water, closing the stoma.
• The Flow of Phloem Sap
– Phloem transports sucrose and other organic
compounds along with water.
SIEVE TUBES
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
– This occurs through cells called sieve-tube
members.
• Their end walls are like sieves, allowing fluid to
flow through pores.
• A chain of these forms a sieve tube.
– These cells are alive, in contrast to xylem
cells.
– In maturing, the sieve-tube members lose
their nuclei along with some other organelles.
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
– As a result, they lose their ability to perform
some of the necessary cell functions.
– Companion cells, alongside the sieve tubes,
provide the proteins and other resources to
the tubes.
– From Source to Sink
• Phloem moves sugars from their source to their
need.
• Where sugar is produced or stored in the leaves is
referred to as the sugar sources.
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
• The sugar sink is the site where the sugar will be
used or further stored.
– These include roots, developing shoot tips, and fruits.
• Sugar sources can change within seasons.
– Beet taproots or potato tubers are sinks in the summer.
– The following spring, they become sugar sources.
– The Pressure-Flow Mechanism
• The pressure-flow mechanism drives the
movement of phloem sap.
• Production of sugar at the source, such as a leaf,
is actively transported into a sieve-tube member of
the phloem.
PRESSURE-FLOW MECHANISM
PRESSURE-FLOW MECHANISM
VASCULAR TISSUE TRANSPORTS
SAP WITHIN A PLANT
• A high concentration of sugar is then noted at the
source.
• Water enters the phloem by osmosis, which
causes a higher water pressure at the source than
at the sink.
• The reverse happens at the sink. Sugars leave the
sieve-tube, water follows, and pressure falls.
• Water flows from higher to lower with this process
called the pressure-flow mechanism.
• Water gets back to the source via the xylem.
REVIEW: CONCEPT CHECK 21.2,
page 468
1. Why is root pressure a pushing force?
Explain
2. Explain the role of transpiration in water
movement.
3. Describe the mechanism that opens and
closes stomata.
4. Explain how phloem sap flow from a
sugar source to a sugar sink.
HORMONES COORDINATE
PLANT FUNCTIONS
• Discovery of a Plant Hormone
– Darwin, in addition to natural selection,
studied with his son how plants grow toward
light.
– In the late 1800s, they observed how grass
seedlings would bend toward light while they
were growing.
– If they cut off the tips, the shoots would grow
straight up.
PLANT HORMONES
PLANT HORMONES
PLANT HORMONES
HORMONES COORDINATE
PLANT FUNCTIONS
– Placing dark caps on the tips would do the
same thing.
– Placing clear caps over the tips or shielding
the lower parts of the seedlings, the plants
would bend toward the light.
– The Darwin's’ hypothesized that a shoot tip
can detect light and then transmits a signal to
the growing region of the shoot.
– This was later proven to be caused by a
chemical messenger in the shoot tip.
HORMONES COORDINATE
PLANT FUNCTIONS
– The Darwin’s and other scientists discovered
other types of chemical messengers called
plant hormones.
– Hormones control a plant’s germination from
a seed, growth, flowering, and fruit
production.
– Hormones are produced in small amounts but
only a small amount can have a large effect.
• Hormones can turn genes on and off, inhibiting
enzymes, or changing plasma membrane
properties.
HORMONES COORDINATE
PLANT FUNCTIONS
• Functions of the Five Major Hormones
– There are several types of plant hormones:
auxins, cytokinins, gibberlins, abscisic acid,
and ethylene.
– No one hormone acts alone, instead they
work as a balance of hormones controls the
plant’s life.
– Auxins
• Auxins are hormones that promote plant growth,
and is from Greek and means “to increase.”
HORMONES COORDINATE
PLANT FUNCTIONS
• They are produced in the apical meristems at the
tips of the shoots and promote elongation.
• Exposing a seedling to light from one direction
causes the auxin to build up on the shaded side
stimulating growth beneath the tip.
• Those cells on the shaded side elongate further
than those on the lighted side, which causes the
shoot to bend toward the light.
– This works, hypothetically, by the auxins loosening the
bonds holding the cell walls together.
– The cell takes up more water by osmosis and then
elongates.
HORMONES COORDINATE
PLANT FUNCTIONS
• Seeds can secrete auxins that promotes the ovary
development into a fruit, especially in some plants
where fruits develop without pollination and seed
development, such as seedless tomatoes and
cucumbers.
– Cytokinins
• These hormones stimulate cell division.
• They are produced on actively growing tissues
such as embryos, roots, and fruits.
• Cytokinins can slow the aging of flowers and fruits.
• There can be and is counter-effects of cytokinins
and auxins.
HORMONES COORDINATE
PLANT FUNCTIONS
• Cytokinins from the roots affect the shoots in
promoting cell division in axillary buds,
encouraging branching, but auxins from the
terminal bud inhibits branching.
• This results in fewer and shorter branches near the
tip of the plant.
• One can trim the terminal bud to induce a more
bushy plant.
– Gibberlins
• These are produced at the tips of both stems and
roots.
AUXIN vs.
HORMONES COORDINATE
PLANT FUNCTIONS
• They stimulate growth of stems by promoting both
cell division and cell elongation.
• While similar to auxins, botanists do not
understand their relationship.
• In combination with auxins, they stimulate fruit
development.
• Applying gibberlins to the Thompson variety of
grapes makes them grow larger.
• They also promote germination, especially in some
cereal grains.
BENEFICIAL USES OF GIBBERLINS
HORMONES COORDINATE
PLANT FUNCTIONS
– Abscisic Acid
• When there are droughts or severe cold in winter,
plants tend to become dormant.
• During these times, abscisic acid (ABA) inhibits
primary and secondary growth by inhibiting cell
division in buds.
• These hormones are washed out after a
downpour.
• Abscisic acid inhibits the germinating effect of
gibberlins.
• Abscisic acid also reacts to stress, especially when
HORMONES COORDINATE
PLANT FUNCTIONS
• The plant is dehydrated, causing the stomata to
close and reduce transpiration.
– Ethylene
• This is a naturally occurring plant hormone that
stimulated fruit ripening.
• Burning kerosene release ethylene, which
artificially causes fruit to ripen.
• Ethylene also promotes leaves to drop from
deciduous trees.
• Leaf drop is caused by a shift in amounts of
ethylene and auxin in leaf petioles.
ETHYLENE AND LEAF DROP
HORMONES COORDINATE
PLANT FUNCTIONS
• With the shorter days as autumn progresses, auxin
decrease and ethylene increases with leaf drop
occurring.
• Preservation of water is the goal of leaf drop.
REVIEW: CONCEPT CHECK 22.1,
page 479
1. Explain why the Darwins did not observe
any bending of the seedlings when they
covered the tips of the seedlings with
dark caps.
2. List five major plant hormones and state
one effect of each.
3. Explain how leaf drop is an adaptive
response to winter.
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMENT
• Rapid Plant Movements
– Plants respond to stimuli such as light,
temperature, gravity, and touch.
– Most plant responses are slow but in some
instances they can be rapid as in the tropical
plant Mimosa pudica, which folds up when
touched.
• Touch causes cells at the base of the leaflet to
lose ions, with water following the ions out of the
leaf causing it to look wilted.
RAPID PLANT MOVEMENTS:
Mimosa pudica
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMENT
– This rapid movement can bump off or scare
off insects looking to eat the plant.
• Tropisms
– These are growth responses that cause parts
of a plant to grow slowly toward or away from
a stimulus.
– These are usually controlled by hormones,
typically auxins.
– Tropisms are not rapidly reversible.
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMENT
– Responses to Touch
• Thigmotropism is a change in plant growth due to
touch.
• Climbing plants have tendrils that wrap around
things, like wires.
• The area touching something slows in growth,
while the opposite side grows faster, therefore
wrapping itself around something.
• The seedling’s response to stress is an example
where one sees a plant growing away from an
object, avoiding that object and preventing
damage.
THIGMOTROPISM
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMENT
• Researchers have shown that ethylene plays a
role in thigmotropism.
– Responses to Light
• Phototropism is the growth of a plant toward or
away from light.
• This was seen in the Darwins’ experiments with
the shoot tips which contains a protein that when
activated by light signals molecules that affect
auxin transport down from the shoot tip.
– Responses to Gravity
• Gravitropism is the plant’s growth response to
gravity.
GRAVITROPISM
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMENT
• This is seen in germinating seeds where the shoot
grows upward and the root downward in the soil,
no matter where the seed is planted in the soil.
• Scientists do not know how the plant knows “up”
from “down.”
• It could be uneven distribution of organelles
containing starch grains that signals auxins to
affect the cell’s direction of growth.
• Coping With Stressful Environments
– Water content, salt content, temperature can
be stressful to the plant.
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMENT
– Drought
• Prolonged inadequate rainfall produces drought.
• The plant will become stressed and weakened in
these conditions.
• More water can be lost by transpiration than taken
up by the roots.
• The growth of young leaves is inhibited.
• Leaves wilt and photosynthesis is reduced.
• Cacti and similar plants (succulents) store water in
their stems and have a thick cuticle and spines
instead of leaves to prevent transpiration.
DROUGHT AND COLD
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMENT
• Plants in cold regions are adapted by having small
leaves and growing low to the ground, which
reduces transpiration during the limited growing
season and harsh winds.
– Flooding
• Too much water in the soil will lesson the air
spaces that provide oxygen for cellular respiration
in the roots.
• Mangroves have adapted to this by having their
roots and “knuckles” above the water.
• Having too much water in the soil causes the plant
MANGROVES
“SNORKELS” or AIR TUBES
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMEN
cells to release ethylene which causes some of the
submerged roots to die.
• This creates air tubes that function as snorkels,
which carries oxygen to the submerged roots.
– Salt Stress
• Too much salt in the soil causes the root cells to
lose water to the soil through osmosis.
• Other than halophytes, most plants cannot
survive salt stress for long times.
• Halophytes are salt-tolerant plants with salt glands
as adaptations.
PICKLEWEED, SALT
TOLERANT PLANT
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMEN
• The glands pump salt out over the leaves and the
rain washes it away.
• A marsh plant called the pickleweed pumps the
salt to the stems at the tips of the plant and the
plant then sheds the stems, eliminating the salt.
• Defending Against Disease
– Plants are subject to infections by bacteria,
viruses, and fungi.
– The plant’s epidermis is the first line of
defense.
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMEN
– Sometimes the stomata or plant wound can
let these pathogens in.
– Chemicals are the second line of defense.
– Some chemicals are antimicrobials.
– Some attack the cell walls of the bacteria.
– Some signal lignin production, hardening the
cell walls around the infected area and
sealing it off.
– Certain pathogens can be recognized and
attacked by certain plants.
PLANTS RESPOND TO CHANGES IN
THE ENVIRONMEN
– Horticulturists will select these plants or
engineer them to introduce disease resistant
genes into the pool.
– Some plants have developed poisons or
thorns to keep from being eaten.
REVIEW: CONCEPT CHECK 22.2,
page 485
1. Describe the role of osmosis in controlling the
rapid plant movements of Mimosa pudica.
2. Distinguish among thigmotropism,
phototropism, and gravitropism.
3. Contrast a desert plant’s adaptations with the
adaptations of a houseplant experiencing a
temporary drought.
4. Describe the two main adaptations in a plant’s
defense against disease.
PLANTS KEEP TRACK OF
THE HOURS AND SEASONS
• Circadian Rhythms
– Experiencing jet lag can make you too tired or
too wired.
– Your pulse, body temperature, and blood
pressure change with the time of the day.
– Plants experience the same rhythm over a 24
hour period.
– Biological cycles that occur over 24 hours are
called circadian rhythms.
PRAYER PLANT & MIMOSA,
CIRCADIAN RHYTHMS
PLANTS KEEP TRACK OF
THE HOURS AND SEASONS
– The biological clocks of organisms are set by
daily signals from the environment, especially
light.
– Being kept in the dark does not change
circadian rhythms except for the cycle
lengths, being shorter or longer that 24 hours.
– Changing from night to day is required to set
the clock exactly to a 24 hour cycle.
PLANTS KEEP TRACK OF
THE HOURS AND SEASONS
• Day Length and Seasons
– Plants respond to not only a 24 hour cycle but
changes in seasons.
– Production of flowers, germinating seeds,
dormancy occur at specific times during the
year.
– The length of the day light and night time
determine the time of the year for the plant.
– This ability to use this environmental stimulus
PLANTS KEEP TRACK OF
THE HOURS AND SEASONS
to time seasonal activities is known as
photoperiodism.
• Chrysanthemums and poinsettias flower in the fall
or winter when the dark period exceeds a certain
length, called the critical night length.
– These are examples of short-day plants (long-night
plants).
• Long-day plants (short-night plants), including
spinach, lettuce, and irises flower in late spring or
early summer when dark periods shorten.
PLANTS KEEP TRACK OF
THE HOURS AND SEASONS
– Day-neutral plants flower when a certain
stage of maturity is reached, with no
dependency to day length.
• Examples are dandelions, tomatoes, and rice.
– Flower growers can use the information about
photoperiodism to produce flowers out of
season.
– Plants can monitor day length as seasons
change, including sunrise and sunset, with
pigment proteins called phytochromes.
DAY LENGTH AFFECTING PLANTS
DAY LENGTH AFFECTING PLANTS
DAY LENGTH AFFECTING PLANTS
PLANTS KEEP TRACK OF
THE HOURS AND SEASONS
• Phytochromes absorb red light at sunrise
changing their shape to an active form
triggering certain plant responses.
• At sunset, the phytochromes change back
to their inactive form.
PHYTOCHROMES
REVIEW: CONCEPT CHECK 22.3,
page 487
1. Give an example of a circadian rhythm in
a plant or animal.
2. Describe the difference between a shortand a long-day plant and give an example
of each.
3. Explain how phytochromes are activated.