Evolution and Diversity of Plants
Descent with Modification
• Life evolved on Earth over 3.5
billion years ago.
• The first form of life was a
single population of bacteria.
• All of the different species
today evolved from this initial
bacterial population.
Bacteria: The First Life
• Bacteria are the oldest and most simple forms of life.
• Characteristics of Bacteria Cells
– Prokaryotic: cells do not have a nucleus or other
organelles
– Single-celled
– Bacteria are usually
surrounded by a cell
wall made of
peptidoglycan.
Bacteria: The First Life
• Bacteria can be grouped by how they
obtain energy.
– Heterotrophs: get energy from other
organisms
– Photoheterotrophs: can get some
energy from the sun but they still
need energy from other organisms.
– Photoautotrophs: get all of their
energy from the sun
– Chemoautotrophs: get all of their
energy from chemicals from the
Earth.
Bacteria: The First Life
• Reproduction: Usually asexual (a single
bacteria cell simply simply divides in two)
• Importance of bacteria
– Decomposers: help break down dead
organisms and add nutrients into the
soil.
– Producers: photosynthetic bacteria
account for 50% of photosynthesis in the
ocean
– Nitrogen Fixation: convert nitrogen gas
in the amtosphere into ammonia and
nitrates which can be used by plants.
Protists: The First Eukaryotes
• Protists are the oldest group of eukaryotic organism.
• Some ancient protists evolved to become plants,
animals and fungi.
• Characteristics of Protists
– The most diverse Kingdom of
organisms
– Can be autrotrophs
(photosynthetic or heterotrophs
(nonphotosynthetic)
– Can be unicellular or
multicellular
– All are eukaryotic
Protists: The First Eukaryotes
• Characteristics of Protists
– The most diverse Kingdom of
organisms
– Can be autrotrophs (photosynthetic
or heterotrophs (nonphotosynthetic)
– Can be unicellular or multicellular
– All are eukaryotic
Protists: The First Eukaryotes
• Reproduction in protists
– Asexual:
• A single protist is capable of producing spores
• Spores spread make several identical copies of the
organism.
– Sexual:
• Alternation of generations
• Protists are able to switch between the
gametophyte stage (gamete producing) and
sporophyte (spore producing) stage in their
lifecycle
Diversity of Photosynthetic Life
What do all plants have in
common?
• Photosynthetic: use sunlight
to make carbohydrates
• Multicellular: each individual
is made of several cells
• Eukaryotic: cells have a
nucleus
• Cell walls made of cellulose
• Alternation of generations
Plant Life Cycle
• Alternation of generations – the
plant life cycles alternates
between a haploid and a diploid
stage
The two generations:
– Gametophyte: gamete (sperm
and egg) producing stage
(haploid)
– Sporophyte: spore producing
stage (diploid).
• Spores are reproductive cells
that give rise to new
individuals.
What does haploid and
diploid mean?
Evolution of Plants
• The first plants evolved from an organism much like the
red algae living today.
Challenge
Algae’s Solution
Dehydration
Make direct contact with How will the plant absorb
water as they grow.
and store water?
Support
Supported by the
surrounding water
pressure.
Reproduction Release sperm into water
so it can swim to egg.
Problem for Land Plants
How will the hold itself
upright in air?
How will the sperm cell
reach the egg cell?
• Table 1: Challenges plants evolved to overcome as life
moves on land.
Evolution of Plants
Botanist divide plants into groups base on three
characteristics:
1. Vascular tissue
2. Seeds
3. Flowers
Moss: Non-vascular Plants
•
•
•
•
The first group of plants that lived on land.
Can only live in very damp places.
Only grow a few centimeters tall.
Why are mosses so small?
– Most plants have vascular tissue – tubes that carry
water and nutrients through the plant.
– Mosses do not have vascular tissue.
– Mosses rely on osmosis to conduct H20 a few cm.
Moss: Non-vascular Plants
Moss: Non-vascular Plants
• Gametophyte – the haploid (N) stage
– The Dominant stage in mosses
– Produces gametes (eggs & sperm)
• Bryophytes need water for fertilization so the sperm can
swim to the egg.
• Sporophyte – the diploid (2N) stage
– Begins after the sperm fertilizes the egg cell
– A stalk-like structure that produces spores.
– A young gametophyte will sprout from the spore to start
the cycle over.
Moss: Non-vascular Plants
Capsule containing
spores
Sporophyte
Stem and
Leaf-like
parts
Root-like parts
Gametophyte
Ferns: Seedless Vascular Plants
• Seedless vascular plants could
grow much taller than the
mosses.
Why?
These plants have vascular tissue to
transport food and nutrients.
Two Type of Vascular Tissue
– Xylem – carries water from the
roots to the leaves
– Phloem – carries food and nutrients
throughout the plant
Ferns: Seedless Vascular Plants
• The dominant stage in ferns is the sporophyte.
• The gametophyte looks like this:
Female
Reproductive
Structures
Male
Reproductive
Sructures
(Produces Sperm)
(Produces Eggs)
roots
• The gametophyte is small, compared to the sporophyte.
• As plant evolve, the gametophyte becomes smaller and
the sporophyte becomes larger.
Ferns: Seedless Vascular Plants
Comparison of Mosses and Ferns
Mosses
Ferns
Seed Plants: Gymnosperms and Angiosperms
The next major step in plant evolution: seeds
– Seedless plants need to be near water so the sperm
can swim to the egg.
– Seed plants rely on either wind pollination or animal
pollination to transfer sperm to the egg cells.
– Pollen and seeds allow plant to reproduce without
being near water.
Seed vs. Spore
Seeds
• Diploid
• Varies in size (can be
very large)
• Difficult to transport
• Provides protection and
food for the embryo
• Take a lot of energy to
produce
Spore
• Haploid
• Always very small
• Easy to transport by
wind
• Does not provide
protection and food
• Easy and cheap to
produce
Gymnosperms: The First Seed Plants
• All gymnosperms produce
seeds but not flowers or
fruits.
– Seeds allow gymnosperms
to grow in much dryer
environments than mosses
and ferns.
– No Flowers: Almost all
gymnosperms rely on
wind pollination.
– No Fruits: Almost all
gymnosperms rely on
wind for seed dispersal
Gymnosperms: The First Seed Plants
• Cones are the reproductive
structures of most
gymnosperms
– Male cones are small and
produce pollen
– Female cones are large and
produces egg cells
– Wind carries pollen from the
male cone to the female cone.
– Seeds would be produced on the
scales of the female cone.
Conifers
• The dominant group of
gymnosperms
• All conifers have needlelike leaves.
– Adapted for survival in cool
& dry environment
– Reduce surface for
evaporation
– Thick waxy covering (Cuticle)
– Most species are
“evergreens”
Angiosperms – Flowering Plants
Angiosperms are the most successful and evolved group of
plants
– Angiosperms contain flowers.
– What is the function of flowers?
– After pollination and fertilization the ovaries of the
flower became fruits.
– What is the function of fruits.
Angiosperms – Flowering Plants
Why are flowering
plants so much more
successful than any
other group of
plants?
• Vacular Tissue allows them to grow tall to get sunlight.
• Seeds allows them to grow away from bodies of water.
• Flower and fruit all them to use animals for pollination
and seed dispersal.
(animals are much more efficient then wind.)
Angiosperms
There are two main groups of angiosperms that
differ in several ways.
1. Monocots
2. Dicots
• Cotyledons are the first leaves of a plant that emerges from the
seed.
• Vascular bundles and veins are groups of vascular tissue (xylem
and phloem cells).
• Taproot: smaller roots are all connected to one main root.
• Fibrous Roots: all roots remain small and highly branched.
Monocot or Dicot
MONOCOT
DICOT
MONOCOT
DICOT
Fungi
• Fungi are heterotophic eukaryotes with cell
walls made of cellulose.
– Cannot photosynthesize; absorbs nutrients from
the outside of the body.
– Cells contain a nucleus
– Chitin is a chemical that is found in the skeletons
of insects (evidence that fungi are more closely
related to animals than plants)
Fungi
• Fungi can be single-celled or multicellular
– Yeast is an example of a single-celled fungus
– Multi-cellular fungi grow long, branching,
filaments called hyphae
– Mushroom is just the reproductive structure of
the fungus.
– Clusters of mushrooms are actually part of the
same organism.
Fungi
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Reproduction
Capable of sexual and asexual reproduction
Fungi spread by releaseing spores
Importance of fungi
Decomposition
Mutualism (lichens, mycrorhizzae)
parasitism