Transcript Plant Diversity

Plant Diversity
Chapter 22
What is a Plant?
• Plants are multicellular eukaryotes with cell
walls made of cellulose, and they carry out
photosynthesis.
Diversity of Plants
• There is a wide diversity of plants, from tiny
mosses, to huge trees such as giant redwoods
that can grow to over 100m tall.
What is a Plant?
• https://www.youtube.com/watch?v=In7Y4G1
FqaY (3 min)
The Role of Plants
• Plants play a key role in any ecosystem –
providing the basis for most food webs,
providing habitat, cleaning the air, preventing
erosion, and much more.
• While plants are different from animals in
many ways (including being stationary
autotrophs), they have found unique ways to
deal with the challenges of life.
Plant Life Cycle
• Plant life cycles include what is known as the
“alternation of generations”, where there is a
haploid and a diploid phase, each in their own
generation.
Science 9 Refresher
• Haploid refers to any cell that contains only 1
set of chromosomes (n), and diploid refers to
any cell having a double set of chromosomes
(2n)
Refresher – Haploid & Diploid
Humans
• In humans and most other animals, only our
sex cells (gametes: sperm and egg cells) are
haploid. These cells contain only 1 set of our
23 chromosomes.
• The rest of the cells in our bodies are diploid,
and they contain 2 complete sets of 23
chromosomes, for a total of 46.
Refresher – Mitosis
• When cells reproduce (duplicate), they usually
do so by mitosis, a type of cell division that
produces 2 daughter cells that are identical to
each other and to the parent cell (clones).
Refresher – Meiosis
• To produce a haploid cell from the original
diploid cell however, a different form of cell
division is required – meiosis. Meiosis
includes 2 rounds of cell division, and results
in 4 daughter cells that are all different from
each other and from the parent cells.
Meiosis
Alternation of Generation
• The diploid (2n) phase of a plant’s life cycle is known as
the sporophyte (spore-producing plant).
• Spores are haploid (n) reproductive cells produced by
meiosis in the sporophyte, and they can mature into
new haploid individuals known as gametophytes
(gamete-producing plant).
• Gametes are haploid(n) reproductive cells produces in
the gametophyte by mitosis, and they fuse with other
gametes during fertilization to produce a diploid cell
which can mature into the diploid sporophyte.
Water?
• The simplest plants, mosses and ferns, require
water to reproduce (usually to bring gametes
together for fertilization), while the more
recent seed plants can carry out reproduction
without water.
• Many plants can also carry out asexual
reproduction.
Ingredients for Plant Survival
• As stationary organisms on land, plants face a
special series of challenges. Plants have
developed many adaptations to get the
sunlight, water, minerals, and gasses that they
need, and to transport water and nutrients
throughout their bodies.
Sunlight
• Plants need the energy from sunlight in order
to carry out photosynthesis.
• This has led to many adaptations to gather
more sunlight, including broad, flat leaves,
arranged on the stem to maximize light
absorption.
• Plants may also grow taller to out-compete
others for sunlight, or grow in areas with
fewer competitors.
Adaptations to Sunlight
Gas Exchange
• Plants require carbon dioxide
to carry out photosynthesis,
as well as oxygen for cellular
respiration. They must
exchange these gasses with
the atmosphere through
their leaves, without losing
too much extra water
through transpiration.
Water
• All cells require a continuous
supply of water – for plants,
this means they must
transport the water obtained
by their roots to all other
parts of the plant, including
those found far above the
ground.
Water
• Plants also need water as a key ingredient in
photosynthesis, so when the sun is shining,
plant cells use up water very quickly, and
tissues can dry out easily. Plants have
developed adaptations such as waxy coatings
and stomata that can be closed, to prevent
excess water loss.
Stomata
Stomata
Minerals
• When plants soak up water through their
roots, they also gain minerals from the soil.
These minerals include nutrients that are
required for plant growth.
Transporting Water & Nutrients
• Plants soak up water and nutrients from their
roots, but produce food in their leaves via
photosynthesis.
• Most plants (vascular plants) have specialized
tissues to carry water and nutrients upward,
and distribute the products of photosynthesis
throughout the body tissues of the plant.
Transport of Water and Nutrients
• Simpler types of plants (non-vascular plants)
don’t have these specialized tissues, so they
simply use diffusion to transport these
substances.
Evolution of Plants
• For most of Earth’s history, almost all life was
in the water, and plants did not exist.
• Photosynthetic algae and prokaryotes added
oxygen to the atmosphere, and provided food
for aquatic animals and microbes.
Evolution of Plants
• The first plants evolved from an organism
much like multicellular green algae that exist
today.
• These algae have similar reproductive cycles
to plants, and have cellulose cell walls and use
the same photosynthetic pigments as plants.
• DNA sequences confirm that plants are closely
related to certain groups of green algae that
are found in freshwater environments.
Fossil Plants
• The oldest known fossils
of plants (450 million
years old) were very
similar to mosses found
today. These early plants
grew close to the ground,
and were dependent on
water for their
reproduction, similar to
mosses today.
Changes Over Time
• Over time, natural selection favoured
adaptations that allowed plants to move away
from the water - to be more resistant to
drying out, more capable of conserving water,
and able to reproduce without water.
Evolution of Plants
• This first group of plants led to all the current
groups of plants.
Groups of Plants
• One lineage developed into non-vascular
plants including mosses and their relatives.
Another line led to all other plants, including
ferns, seed-bearing plants, cone-bearing
plants, and flowering plants.
Plants Today
• Plants are still classified into these groups by
botanists (scientists who study pants) today.
• Each of these groups has been successful on
land, but they have all developed very
different adaptations to a wide range of
environments.
Bryophytes: Non-Vascular Plants
• Plants that do not have specialized tissues for
transporting water and nutrients (vascular
tissues) are known as bryophytes, or nonvascular plants.
• This includes mosses and their relatives:
liverworts and hornworts.
Bryophytes
• Bryophytes depend on water for
reproduction. As a result, they can only live in
areas where there is significant rainfall or dew
for at least part of the year.
• Without vascular tissues, they must use
osmosis to transport water, which can only
work for a maximum of a few centimeters.
Bryophytes
• These two features together means that
bryophytes are low-growing plants found in
moist or shaded areas.
Mosses
• Mosses are the most common bryophytes
– They are found in areas with lots of water –
swamps and bogs, near streams, and in rain
forests
– Well adapted wet habitats and nutrient-poor soils
– this allows them to grow in harsh environments
where other plants can’t survive
Mosses
• Mosses are the most common plants in the
polar regions
Mosses
• The moss plants we are most familiar with are the
gametophyte stage
• The sporophyte stage of a moss is a thin, upright
shoot topped with a capsule
Mosses
• The tissues of mosses are only 1 cell thick, so
they lose water very quickly if the air becomes
too dry.
• Mosses do not have true roots – instead they
have rhizoids, long, thin cells that anchor
them to the ground and absorb water and
nutrients from the soil
Liverworts
• Look like flat leaves attached to the soil; this is
the gametophyte stage
– Named liverworts because in some species this
“leaf” is shaped like a liver
Liverworts
• This broad, thin structure absorbs moisture
and nutrients directly from the soil
– Only found in areas where the soil is damp yearround
Liverworts
• To reproduce, the gametophyte produces
structures that look like tiny umbrellas, which
is where the eggs and sperm are produced
Liverworts
• Some liverworts can also reproduce asexually
– Small multicellular reproductive structures called
gemmae are produced
– When washed away from the main plant by water,
they can divide by mitosis to produce a new
individual
Horworts
• Gametophyte looks similar to the liverwort
gametophyte
– Also only found in areas where the soil is damp
year-round
• Hornwort sporophyte looks like a tiny horn,
which is how it got its name
Life Cycle of Bryophytes
• Like all plants, bryophyte life cycles include
alternation of generations.
• The gametophyte is the dominant form of the
plant, and this is the phase where most of the
photosynthesis takes place.
• The sporophyte is dependent on the
gametophyte to supply water and nutrition.
Dependence on Water
• Bryophytes must live in areas where water is
available at least part of the year, since the
sperm must swim through water to meet the
eggs.
Life Cycle of a Moss
• A spore lands in a moist place and germinates
to form a mass of green filaments called a
protonema
– As the protonema grows, it grows rhizoids into the
ground, and shoots into the air
– These shoots grow into the moss plants we are
familiar with gametophyte stage
Life Cycle of a Moss
• Gametes are produced at the ends of these
stalks
– Sperm produced in antheridia
– Eggs produced in archegonia
Life Cycle of a Moss
• When sperm and egg meet, form diploid
zygote matures into the sporophyte
– Sporophyte grows directly out of the
gametophyte, depends on it for nutrients & water
– Sporophyte ends in a capsule, where haploid
spores are produced by meiosis
• Spores are scattered by the wind, start the cycle over
again.
Sporophytes
Human Uses of Mosses
• Sphagnum mosses are a group of mosses that thrive
in the acidic water in bogs. In some environments,
layers of dead sphagnum moss accumulate to form
peat bogs. Peat can be harvested and then burned as
fuel.
Peat Bog
Bog Mummies!
Peat Moss
• Dried sphagnum absorbs enormous amounts
of water, so it acts like a natural sponge. For
this reason, peat is also often harvested to be
used as peat moss in gardens.
• Adding peat moss to soil helps to retain
water, plus peat has a low pH, so it can be
used to raise the acidity of the soil, which is
beneficial for some kinds of plants.
Peat Moss
Crash Course: Non-Vascular Plants
• https://www.youtube.com/watch?v=iWaX97p
6y9U (9:40)
• Take notes during the video – this will go in
your Logbook
Weekend Homework
• Textbook readings
– Section 22-1 (pg 551-555): q 1, 3, 4 (pg 555)
– Section 22-2 (pg 556-559); q 1, 3, 4 (pg 559)
• Article Assignment #2
– Due Monday night before midnight
– Submit through Google classroom please!
• Don’t forget to submit your pre-reading questions and
the copy of your article
Seedless Vascular Plants
• Since early plants were dependent on osmosis
to move water from cell to cell, they were
limited to just a few centimetres. For millions
of years, this was the maximum height of all
plants.
• About 420 million years ago, however, plants
over a metre tall appeared – these were the
first plants with vascular tissue.
Vascular Tissues
• Xylem is the transport system that moves
water upward from the roots, to every part of
the plant
– Xylem is made up of cells called tracheids, which
were an evolutionary innovation. These cells are
hollow, with thick cell walls that can resist
pressure.
• These cells contain lignin that stiffens the cell
walls. This allows plants to grow upright and to
great heights
Xylem
• These cells are connected end-to-end like a series of
straws, and they allow water to move through them,
throughout the plant body much more efficiently
than by diffusion alone.
Phloem
• Phloem is the second transport system, which
transports solutions of nutrients and the
products of photosynthesis, from the leaves
to other parts of the plant
Vascular Tissues
• Both forms of vascular tissue – xylem and
phloem – can move fluids through the plant
body, even against the force of gravity. They
form an integrated transport system to move
water, nutrients, and other dissolved materials
from one part of the plant to the other.
Seedless Vascular Plants
• Seedless vascular plants include club mosses,
horsetails, and ferns. These plants all have
true roots, leaves, and stems.
Parts of Vascular Plants
• Roots – underground organs to absorb water and
minerals. The centre of the root contains waterconducting tissues.
• Leaves – photosynthetic organs that contain one
or more bundles of vascular tissues, gathered into
veins made of xylem and phloem.
• Stems – supporting structures that connect roots
and leaves, carrying water and nutrients between
them
Parts of the Vascular Plant
Club Mosses
• Ancient club mosses made up some of Earth’s
first forests, with giant trees over 35 m tall.
These ancient forests now make up much of
the coal deposits we have today.
Club Mosses
• The club mosses still around today are fairly
small plants that live in moist forests. They
look somewhat like miniature pine trees, and
are sometimes called “ground pines”.
Horsetails
• This group of plants has scalelike leaves that are arranged
in distinctive whorls at joints
along the stem.
• They are also called “scouring
rush” because in colonial
times, they were used to
scour pots and pans, since
they contain crystals of
abrasive silica.
Ferns
• Ferns evolved approximately 350 million years
ago, and they have survived in greater
numbers than any other seedless vascular
plants. Over 11,000 species of ferns still exist
today. In addition to true roots, ferns have
creeping underground stems called rhizoids,
from which their distinctive leaves called
fronds grow.
Ferns
• Ferns can survive in areas
with very low light, and are
usually found in wet, or
seasonally wet, habitats
around the world. They are
very common in many
forests, particularly
temperate and tropical
rainforests. In tropical
forests, ferns can grow as
large as small trees.
Ferns
Fern Life Cycle
• In ferns and all vascular
plants, the sporophyte is
the dominant stage in the
life cycle.
• The haploid spores form on
the underside of the fronds
(of the sporophyte) in tiny
capsules called sporangia,
grouped into clusters called
sori.
Fern Life Cycle
• When the spores germinate, they develop into a
small haploid gametophyte. The gametophyte
grows a set of rootlike rhizoids, then flattens into
a green heart-shaped structure. This
gametophyte is tiny, but it does grow
independently of the sporophyte.
• The antheridia and archegonia are found on the
underside of the gametophyte. Fertilization
requires a thin film of water so that the sperm
can swim to the egg.
• After fertilization, a new sporophyte begins to
develop, and the gametophyte withers away. The
fern sporophyte can live for several years.
Fern Life Cycle
Homework
• No class tomorrow (Career fair)
– I’ll move your Article Deadline to Tomorrow night
– 1 Bonus mark for anyone who has it in by tonight
• There’s a time stamp, I can tell!
• Textbook Pages (for Wed)
– Section 22-3 (pgs 560-563)
– Questions 1-4 on pg 563