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Plant Diversity
What is a Plant?

Plants are multicellular eukaryotes that
have cell walls made of cellulose


They develop from multicellular embryos and
carry out photosynthesis using the green
pigments chlorophyll a and b
Plants are so different from animals that
sometimes there is a tendency to think of
them as not being alive

However, plants are alive, everywhere, and
highly successful
The Plant Life Cycle

Plants have life cycles that are characterized
by alternation of generations



In this life cycle, the haploid gametophyte phase
alternates with the diploid sporophyte phase
A gametophyte is a haploid, or gameteproducing, phase of an organism
A sporophyte is a diploid, or spore-producing,
phase of an organism
Alternation of Generations Life Cycle in Plants
What Plants Need to Survive

The lives of plants revolve around the
need for:




Sunlight
Water & minerals
Gas exchange
Movement of water & nutrients throughout the
plant body
Evolution of Plants

The first plants evolved from an organism much like
the multicellular green algae living today

However, the evolution of plants favored species that were
more resistant to the drying rays of the sun
Cone-bearing
plants
Ferns and
their relatives
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor
Flowering
plants
Overview of the Plant Kingdom

The great majority of plants alive today are
angiosperms (the flowering plants)
Cone-bearing plants
760 species
Ferns and
their relatives
11,000 species
Flowering
plants
235,000 species
Mosses and
their relatives
15,600 species
Figure 29.1 Some highlights of plant evolution
4 Main Groups of Land Plants

Bryophytes: non-vascular plants


Pteridophytes: seedless vascular plants


Club moss, horsetails, ferns
Gymnosperms: vascular seeded conebearers


mosses, hornworts, and liverworts
Ginkgos, cycads, gnetophytes, conifers
Angiosperms: vascular seeded flowering
plants

Monocots & dicots – any plant, tree, or shrub
that flowers or fruits
The Nonvascular Plants - Bryophytes

Mosses and their relatives are generally
called Bryophytes (nonvascular plants)




THEY HAVE NO ROOTS, STEMS, OR
LEAVES
They have a life cycle that depends on water
for reproduction
They lack vascular tissue and therefore must
grow low to the ground
Groups of Bryophytes include:
1.
2.
3.
Mosses
Liverworts
Hornworts
Mosses

The most common
bryophytes are mosses



They grow abundantly in
areas with water
They can tolerate cold
climates well
They do not have true
roots, stems, or leaves –
instead, they have
rhizoids (long, thin cells)
that anchor them to the
ground
Liverworts

Liverworts are Bryophytes that produce gametes in
structures that look like little green umbrellas during sexual
reproduction

Liverworts can also reproduce asexually by means of gemmae
(small cup-like spheres that contain haploid cells)
SEXUAL
ASEXUAL
Hornworts

Hornworts are generally found only in soil
that is damp nearly year round

Their gametophytes look like those of
liverworts
Life Cycle of Moss
http://www.sumanasinc.com/webcontent/animations/content/moss.html
Evolution of Plants
Flowering
plants
BRYOPHYTES
Cone-bearing
plants
Ferns and
their relatives
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor
Three variations on gametophyte/sporophyte relationships
Evolution of Vascular Tissue

What happened to allow plants to grow taller than
mosses?

Fossil evidence shows that these plants contained vascular
tissue – tissue that is specialized to conduct water and
nutrients through the body of a plant
Vascular Tissue

The first vascular plants had a new type of
cell that was specialized to conduct water




Tracheids are the cells found in xylem, a form
of tissue that carries water upward from the
roots to every part of a plant
Phloem transports solutions of nutrients and
carbohydrates produced by photosynthesis
Lignin is a substance produced by plants that
makes cell walls rigid
Both forms of vascular tissue, xylem and
phloem, can move fluids throughout the
plant body against the force of gravity
Seedless Vascular Plants - Pteridophytes

Seedless vascular plants include:
1.
2.
3.




club mosses
horsetails
ferns
These plants HAVE true roots, leaves,
and stems
ROOTS – underground organs that
absorb water & minerals
LEAVES – photosynthetic organs
STEMS – supporting structures that
connect roots and leaves
Club Mosses

These are small plants that live in moist
woodlands and near streambeds and
marshes

Lycopodium is the most common club moss
today – it looks like a mini pine tree
Horsetails

The only living genus of horsetails is
Equisetum

Its leaves are arranged in distinctive whorls at
joints along the stem
Ferns

Ferns are members of the phylum Pterophyta
 They have creeping or underground stems called
rhizomes and large leaves called fronds
 They are most abundant in wet habitats – water is
required for reproduction!
frond
rhizome
roots
The Life Cycle of a Fern
1
Sporangia release spores. 2 The fern spore
Most fern species produce a single
develops into a small,
type of spore that gives rise to a photosynthetic gametophyte.
bisexual gametophyte.
Key
3 Although this illustration
shows an egg and sperm
from the same gametophyte,
a variety of mechanisms
promote cross-fertilization
between gametophytes.
Haploid (n)
Diploid (2n)
Spore
MEIOSIS
Antheridium
Young
gametophyte
Sporangium
Archegonium
Mature
sporophyte
New
sporophyte
Zygote
Sporangium
Sperm
Egg
FERTILIZATION
Sorus
6 On the underside
of the sporophyte‘s
reproductive leaves
are spots called sori.
Each sorus is a
cluster of sporangia.
Fiddlehead
Figure 29.12
Gametophyte
5 A zygote develops into a new
sporophyte, and the young plant
grows out from an archegonium
of its parent, the gametophyte.
4 Fern sperm use flagella
to swim from the antheridia
to eggs in the archegonia.
Fern Sori
Evolution of Plants
Seedless
Vascular
Plants
BRYOPHYTES
Flowering
plants
Cone-bearing
plants
Ferns and
their relatives
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor
Seed Plants


Over millions of years, plants with the ability to
forms seeds became the most dominant group of
photosynthetic organisms on land
Seed plants are divided into 2 groups:
1.
Gymnosperms – bear seed directly on cones




2.
Conifers
Cycads
Ginkos
Gnetophytes
Angiosperms – flowering plants that bear their seeds
within a layer of tissue that protects the seed
 Grasses
 Flowering trees and shrubs
 All flowers
Reproduction Free From Water

Adaptations that allow seed plants to
reproduce without water include

flowers or cones

the transfer of sperm by pollination

the protection of embryos in seeds
Cones & Flowers

The gametophytes of seed plants grow
and mature within sporophyte structures
called cones or flowers


Cones are the seed-bearing structures of
gymnosperms
Flowers are the seed-bearing structures of
angiosperms
Pollen

In seed plants, the entire
male gametophyte is
contained in a tiny
structure called a pollen
grain


The pollen grain is carried
to the female gametophyte
by wind, insects, birds,
small animals, or bats
The transfer of pollen from
the male gametophyte to
the female gametophyte is
called pollination
Seeds

A seed is an embryo of a plant that is
encased in a protective covering and
surrounded by a food supply



An embryo is the early developmental stage of
the sporophyte plant
The seed coat surrounds and protects the
embryo and keeps the contents of the seed from
drying out
After fertilization, the zygote contained within a
seed grows into a tiny plant – the embryo
The Structure of a Seed
Section 22-4
Seed coat
Seed
Embryo
Wing
B
Stored
food supply
A
Seed: embryo of plant that is wrapped in a
protective covering and surrounded by a food
supply.
Presence of a seed allows for reproduction free of water.
Gymnosperms – Cone Bearers

Gymnosperms include:




Gnetophytes
Cycads
Ginkoes
Conifers
Gnetophytes

Welwitschia, an
inhabitant of the
Namibian desert in
southwestern
Africa, is one of the
most remarkable
gnetophytes

it has 2 huge
leathery leaves
which can grow
continuously and
spread across the
ground
Cycads

Cycads are members of
the phylum Cycadophyta


They are palm-like plants
that reproduce with large
cones
They can be found in all
tropical and subtropical
zones around the world
Ginkgoes

Today, the phylum Ginkgophyta contains
only one living species, Ginkgo biloba (the
maiden-hair tree)
Cultivated and protected in China
by monks
The male species of this tree is
often planted in urban settings in
the US, where their resistance to
air pollution make them popular
shade trees
The female tree smells like vomit
Conifers
Conifers are by far the most common
gymnosperms
 The phylum Coniferophyta includes:








Pines
Spruces
Firs
Cedars
Sequoias
Redwoods
Yews
Conifers

Conifers thrive in a wide variety
of habitats

Mountains, sandy soil, cool, moist
areas

Conifers have leaves that are
long and thin – which reduces
the surface area from which
water can be lost by evaporation

They also have a thick, waxy
layer that covers their leaves –
again to reduce water loss

Most conifers are “evergreens”
– meaning they retain their
leaves year round
The Life Cycle of a Pine
http://bcs.whfreeman.com/thelifewire/content/chp30/30020.html
2
An ovulate cone scale has two
ovules, each containing a megasporangium. Only one ovule is shown.
Key
1 In most
conifer species,
each tree has
both ovulate
and pollen
cones.
Ovule
Megasporocyte (2n)
Ovulate
cone
Pollen
cone
Integument
Longitudinal
section of
ovulate cone
Micropyle
Microsporocytes
(2n)
Mature
sporophyte
(2n)
Megasporangium
Germinating
pollen grain
Pollen
grains (n)
MEIOSIS
(containing male
gametophytes)
MEIOSIS
Longitudinal
section of
Sporophyll
pollen coneMicrosporangium
Seedling
Haploid (n)
Diploid (2n)
Surviving
megaspore (n)
3 A pollen cone contains many microsporangia
held in sporophylls. Each microsporangium
Germinating
contains microsporocytes (microspore mother pollen grain
cells). These undergo meiosis, giving rise to
Archegonium
haploid microspores that develop into
Egg (n)
Integument
pollen grains.
Female
Seeds on surface
gametophyte
A pollen grain
4
enters through
the micropyle
and germinates,
forming a pollen
tube that slowly
digests
through the
megasporangium.
5 While the
pollen tube
develops, the
megasporocyte
(megaspore
mother cell)
undergoes meiosis,
producing four
haploid cells. One
survives as a
megaspore.
of ovulate scale
Fertilization usually occurs
more
than a year after pollination. All
8
eggs
may be fertilized, but usually only
one
zygote develops into an embryo.
The
ovule becomes a seed, consisting
of an
Embryo
embryo, food supply, and seed
(new sporophyte)
coat.
(2n)
Figure 30.6
Germinating
pollen grain (n)
Food reserves Seed coat
(gametophyte (derived from
Discharged
tissue) (n)
parent
sperm nucleus (n)
sporophyte) (2n)
Pollen
tube
FERTILIZATION
Egg nucleus (n)
6 The female gametophyte
develops within the megaspore
and contains two or three
archegonia, each with an egg.
7
By the time the eggs are mature,
two sperm cells have developed in the
pollen tube, which extends to the
female gametophyte. Fertilization occurs
when sperm and egg nuclei unite.
Evolution of Plants
Seedless
Vascular Plants
Gymnosperms
Bryophyta
Flowering
plants
Cone-bearing
plants
Ferns and
their relatives
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor
Angiosperms – Flowering Plants


Angiosperm means “enclosed seed”
Angiosperms have unique reproductive organs
known as flowers


Flowers attract pollinators, which makes spreading seeds
more efficient than the wind pollination of most
gymnosperms
Flowers contain ovaries, which surround and
protect the seeds


After pollination, the ovary develops into a fruit, which
protects the seed and aids dispersal
Fruit is a thick wall of tissue and another reason why
angiosperms are successful – the fruit attracts herbivores
– which eat the fruit and then spread the seeds
The Angiosperm Life Cycle
http://www.sumanasinc.com/webcontent/animations/content/angiosperm.html
Key
1
Anthers contain microsporangia.
Each microsporangium contains microsporocytes (microspore mother cells) that
divide by meiosis, producing microspores.
Haploid (n)
Diploid (2n)
Microsporangium
Anther
Microsporocytes (2n)
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Ovule with
megasporangium (2n)
7 When a seed
germinates, the
embryo develops
into a mature
sporophyte.
Generative cell
Tube cell
Male gametophyte
(in pollen grain)
Ovary
Germinating
Seed
Embryo (2n)
Endosperm
(food
Supply) (3n)
6 The zygote
develops into an
embryo that is
packaged along
with food into a
seed. (The fruit
tissues surrounding the seed are
not shown).
2 Microspores form
pollen grains (containing
male gametophytes). The
generative cell will divide
to form two sperm. The
tube cell will produce the
pollen tube.
Pollen
grains
MEIOSIS
3 In the megasporangium
of each ovule, the
megasporocyte divides by
meiosis and produces four
megaspores. The surviving
megaspore in each ovule
forms a female gametophyte
Seed (embryo sac).
Stigma
Megasporangium
(n)
Surviving
megaspore
(n)
Seed coat (2n)
Female gametophyte
(embryo sac)
Pollen
tube
Sperm
Pollen
tube
Style
Antipodal
cells
Polar nuclei
Synergids
Egg (n)
Pollen
tube
Zygote (2n)
Nucleus of
developing
endosperm
(3n)
Egg
Nucleus (n)
Sperm
(n)
4 After pollination, eventually
two sperm nuclei
are discharged in
each ovule.
FERTILIZATION
Figure 30.10
5 Double fertilization occurs. One sperm
fertilizes the egg, forming a zygote. The
other sperm combines with the two polar
nuclei to form the nucleus of the endosperm,
which is triploid in this example.
Discharged
sperm nuclei (n)
Diversity of Angiosperms

Angiosperms are an incredibly diverse
group that includes:



Monocots and dicots
Woody and herbaceous plants
Annuals, biennials, and perennials
Monocots and Dicots

Monocots and dicots are named for the
number of seed leaves, or cotyledons, in
the plant embryo

Monocots have one seed leaf and dicots have
two
Characteristics of Monocots & Dicots
Woody & Herbaceous Plants

Flowering plants can be subdivided into
various groups according to the
characteristics of their stems:

Woody plants are made primarily of cells with
thick walls that support the plant body




Trees
Shrubs
Vines
Herbaceous plants do not produce wood as they
grow, but rather they have stems that are
smooth



Dandelions
Zinnias
Petunias
Annuals, Biennials, Perennials

There are 3 categories of plant life spans:

Annual – flowering plants that complete a life
cycle within one growing season


Biennial – flowering plants that complete their
life cycle in 2 years


Marigolds, pansies, zinnias, cucumbers
Primrose, parsley, celery
Perennial – flowering plants that live for more
than 2 years

Peonies, asparagus, grasses
Evolution of Plants
Vascular Seedless
Non-Vascular
Pterophyta
Vascular w/ Seeds
Gymnosperms
Bryophytes
Cone-bearing
plants
Ferns and
their relatives
Angiosperms
Flowering
plants
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor
Vascular w/ Seeds
Roots, Stems, and Leaves
Structure of Seed Plants

The three principal organs of seed plants
are:
1.
Roots



2.
Stems


3.
Absorb water and dissolved nutrients
Anchor plants to the ground
Hold plants upright
Supports body of plant
Transports nutrients
Leaves

Photosynthetic organs
Tissue Systems

Plants consist of four tissue systems:




Meristematic tissue
Dermal tissue
Vascular tissue
Ground tissue
Meristematic Tissue

Is found only in the tips of shoots and
roots

called apical meristem
Is the only plant tissue that produces new
cells by mitosis
 Is responsible for the growth that takes
place throughout the life of the plant

Dermal Tissue

The outer covering of a plant consists of
dermal tissue that consists of a single
layer of epidermal cells



The exposed outer surfaces of these cells are often
covered with a thick, waxy layer called a cuticle that
protects against water loss & injury
The surfaces of some leaves also have trichomes – tiny
projections which help protect the leaf and also give it a
fuzzy appearance
On the underside of the leaves, dermal tissue contains
guard cells, which regulate water loss and gas
exchange
Vascular Tissue

Plant vascular
tissue includes
xylem and phloem


Xylem – water
conducting tissue that
consists of tracheids and
vessel elements
Phloem – foodconducting tissue that
consists of sieve tube
elements and companion
cells
Ground Tissue

The cells that lie between dermal and
vascular tissues make up the ground
tissues in plants

In most plants, ground tissue consists of
parenchyma (packed with chloroplasts) and
may contain collenchyma or sclerenchyma
(both of which function in plant support)
Types of Roots

The two main types of roots
are:
1.
Taproots – found mainly in dicots

2.
This type of root grows long and thick
Fibrous roots – found mainly in
monocots

This type of root branches to such extent
that no single roots grows larger than
the rest
Root Structure
Root Structure
Root Growth

Roots grow in length as their apical meristem produces new
cells near the root tip. These fragile new cells are protected
by a tough root cap
Roots Functions

Roots anchor a plant in the ground and
absorb water and dissolved nutrients from
the soil


Most water & minerals enter a plant through
the tiny hairs on roots
Essential plant nutrients include:





Nitrogen
Phosphorus
Potassium
Magnesium
Calcium
Stem Function

Stems have three important functions in
plants:



Production of leaves, branches, and flowers
Holding leaves up to sunlight
Transport substances between roots and
leaves
Stem Structure

In most plants, stems
contain distinct
nodes, where leaves
are attached, and
internodes, regions
between the nodes


Small buds are found
where leaves attach to
the nodes
Buds contain
undeveloped tissue that
can produce new stems
and leaves
Monocot & Dicot Stems


In monocots, vascular bundles are scattered
throughout the stem
In dicots and most gymnosperms, vascular bundles
are arranged in a cylinder
Formation of Bark

On most trees, bark includes all of the tissues
outside the vascular cambium
Leaf Structure

The structure of a leaf is optimized for absorbing
light and carrying out photosynthesis


Blades are flattened sections that collect sunlight
The petiole is a thin stalk that attaches the blade to the
stem
blade
petiole
single blade on
petiole
blade divided into
many leaflets
Leaf Functions

Plants must take in all the materials needed
for photosynthesis


Specialized cells on the underside of the leaf
regulate this process
Leaves absorb light and carry out most of the
photosynthesis in plants
6CO2
+
Carbon dioxide +
6H2O
water
→ C6H12O6
→
sugar
+
6 O2
+ oxygen
Photosynthesis

Photosynthesis is the process whereby an
organism use light energy to convert carbon
dioxide and water into oxygen and high
energy sugars
Leaf Function & Photosynthesis

The bulk of most leaves are composed of
mesophyll tissue



Mesophyll cells are packed with chloroplasts
and carry out nearly all photosynthetic activity
of the plant
The stomata are the pore-like openings that
allow CO2 and O2 to diffuse in and out of the
leaf
Each stomata consists of 2 guard cells, which
control the opening and closing of stomata by
responding to water pressure
Leaf Function & Photosynthesis
Transpiration

Water is lost from leaves in a process
called transpiration
Gas Exchange

Plants keep their stomata open just enough to allow
photosynthesis to take place, but not so much that they lose an
excess amount of water
 Guard cells control the stomata and thus regulate the
movement of gases into and out of the leaf tissues
 In general, stomata are open during the daytime when
photosynthesis is active and then close at night when open
stomata would only lead to water loss
Water Transport

The combination of root pressure, capillary action,
and transpiration provides enough force to move
water through the xylem tissue of plants
Nutrient Transport

When nutrients are pumped
into or removed from the
phloem system, the change in
concentration causes a
movement of fluid in the
same direction
 As a result, phloem is able
to move nutrients in either
direction to meet the
nutritional needs of the
plant
source cells: cells
that produce sugars
by photosynthesis
sink cells: cells that
use or store sugars
Reproduction of Seed
Plants
Alternation of Generations

All plants have a life cycle in which a diploid
sporophyte generation alternates with a
haploid gametophyte generation



Gametophyte plants produce male and female
gametes (sperm and eggs)
When the gametes join, they form a zygote that
begins the next sporophyte generation
The sporophyte is what we recognize as the
plant and the gametophyte is hidden deep within
tissues of the sporophyte plant (inside cones or
flowers)
Alternation of Generations

An important trend in plant evolution is the
reduction of the gametophyte and the
increasing size of the sporophyte
Life Cycle of Gymnosperms

Reproduction in gymnosperms takes place in
cones, which are produced by a mature
sporophyte plant



Pollen cones are the male cones which produce
the male gametophyte pollen (sperm)
Seed cones are the female cones which produce
female gametophytes (eggs)
The gymnosperm life cycle takes 2 years to
complete

It begins in the spring when the male cones
release pollen carried by wind to fertilize the
female eggs
Pollen Cones and Seed Cones
pollen cone
(male)
seed cone
(female)
Life Cycle of Gymnosperms
Angiosperm Anatomy
Structure of Flowers

Flowers are reproductive organs that are
composed of four kinds of specialized
leaves:
1.
2.
3.
4.
Sepals
Petals
Stamens
Carples
Sepals and Petals

The outermost circle of
floral parts contains the
sepals, which in many
plants are green and
closely resemble
ordinary leaves


Sepals enclose the bud
before it opens and
protect the flower while
it is developing
Petals, often brightly
colored, are used to
attract insects and other
pollinators
Stamens and Carpels

Within the ring of petals are the structures
that produce male and female gametophytes



The male parts consist of an anther and a filament
that together make up the stamen
The filament is a stalk that supports the anther,
which produces pollen grains
The innermost floral parts are carpels, each of
which forms an ovary (containing eggs)
Stamens & Carpels
Life Cycle of Angiosperms

Reproduction in
angiosperms
takes place
within the flower

Following
pollination and
fertilization, the
seeds develop
inside protective
structures
Life Cycle of Angiosperms
Pollination

Most gymnosperms and some angiosperms are wind
pollinated, whereas most angiosperms are pollinated
by animals
Seed and Fruit Development

As angiosperms seeds mature, the ovary
walls thicken to form a fruit that encloses
the developing seed

A fruit is a ripened ovary that contains
angiosperm seeds
Seed Dispersal

Seeds dispersed by
animals are typically
contained in fleshy,
nutritious fruits

Seeds dispersed by
wind or water are
typically lightweight,
allowing them to be
carried in the air or to
float on the surface of
the water
Seed Dormancy

Many seeds enter a period of dormancy
when they first mature during which the
embryo is alive but not growing


Environmental factors such as temperature and
moisture can cause a seed to end dormancy
Seed dormancy can allow seeds to germinate
under ideal growth conditions (most seeds
germinate in spring)
Seed Germination

Seed germination is the early growth stage of the
plant embryo
Plant Responses &
Adaptations
Patterns of Plant Growth

All plants follow a highly regulated pattern
of growth that continues throughout the
life of the plant



This pattern of growth leads to distinct shapes
The secrets of plant growth are found in
meristems – regions of tissue that can
produce cells that later develop into
specialized tissue
Meristems are found only at the tips of
growing stems and roots
Plant Hormones

A hormone is a substance
that is produced in one part
of an organism and affects
another part of the same
individual



Plant hormones are
chemical substances that
control a plant’s patterns of
growth and development,
and the plant’s responses
to environmental conditions
The portion of an organism
affected by a particular
hormone is known as its
target cell
Hormones are produced in
apical meristems, young
leaves, roots, and in
growing flowers or fruits
Tropisms

The responses of plants to environmental
stimuli are called tropisms



Gravitropism – response to gravity
Phototropism – response to sunlight
Thigmotropism – response to touch
Phototropism

Phototropism is the tendency of a plant to
grow toward a source of light
Auxins and Phototropism

Auxins are produced in the apical
meristem and are transported downward
into the rest of the plant


They stimulate cell elongation and regulate cell
growth – this is what causes a plant to grow in
a direction toward sunlight
They are also responsible for gravitropism –
the tendency of a plant to grow in a direction
in response to the force of gravity
Auxins & Phototropism
A higher concentration of auxins
accumulate in shaded parts of the stem,
causing the plant to bend toward the
sunlight
Auxins and Branching

Apical dominance is a phenomenon in
which the closer a bud is to the tip of a
stem, the more its growth is inhibited


As a stem grows in length, it produces lateral
buds – an area on the side of a stem that
gives rise to side branches
If you want your plants to be fuller instead of
taller, you can clip off the top of the plant –
thus removing the auxins and change the
overall shape of the plant
Auxins and Apical Dominance
Section 251
Apical meristem
Lateral buds
Auxins produced in the apical meristem
inhibit the growth of lateral buds.
Apical meristem removed
Without the inhibiting effect of auxins
from the apicial meristem, lateral buds
produce many branches.
Cytokinins

Cytokinins are plant hormones that are
produced in growing roots and in
developing fruits and seeds


In plants, cytokinins stimulate cell division
and the growth of lateral buds, and cause
dormant seeds to sprout
Thy often produce effects opposite to auxins
Gibberellins


Plants can produce more than 60 similar compounds known
as gibberellins – growth promoting substances
Gibberellins produce dramatic increases in size,
particularly in stems and fruit
 They are responsible for the rapid early growth of many
plants
Ethylene

In response to auxins, fruit tissues release
small amounts of the hormone ethylene


Ethylene then stimulates fruits to ripen
Commercial fruits are often picked before they
ripen and then given a controlled dose of
ethylene just before delivery to the store to
produce a ripe color quickly
Photoperiodism

Photoperiodism in plants is responsible
for the timing of seasonal activities such
as flowering and growth

Short-day plants – a plant that flowers when
daylight is short

Long-day plants – a plant that flowers when
days are long
Effect of Photoperiod on Flowering
Winter Dormancy

Dormancy is the period during which an
organism’s growth and activity decrease
or stop


As cold weather approaches, deciduous plants
turn off photosynthetic pathways, transport
materials from leaves to roots, and seal leaves
off from the rest of the plant
During winter, the continued presence of
leaves would only be costly in terms of water
loss
Adaptations of Aquatic Plants

To take in sufficient oxygen, many aquatic plants
have tissues with large air-filled spaces through
which oxygen can diffuse

The reproductive adaptations of aquatic plants include
seeds that can float in water and delay germination
until after periods of flooding
Adaptations of Desert Plants

Xerophytes, or
desert plants, have
evolved
adaptations
including extensive
roots, reduced
leaves, and thick
stems that can
store water

The seeds of most
desert plants can
remain dormant for
years and germinate
only when sufficient
moisture is available
Nutritional Specialists

Plants that have specialized features for
obtaining nutrients include:

Carnivorous plants – digest insects


Parasitic plants – grow into tissues of their
host plants


Venus’ flytrap
Mistletoe
Epiphytes – grow directly on the bodies of
other plants but are non-parasitic

Spanish moss
Chemical Defenses

Many plants defend
themselves against
insect attack by
manufacturing
compounds that
have powerful
effects on animals


Foxglove is
poisonous when
eaten
Nicotine is a natural
insecticide