Lecture 11: Algae, Bryophytes and Ferns
• Kingdom Protista: Algae
• Red algae, diatoms, kelps, dinoflagellates,
green algae
• Significance of algae to humans
• Kingdom Plantae: moving onto land
• Features and challenges for living on land
• Bryophytes
• Ferns
ALGAE
• Algae belong to the
Kingdom Protista
• Algae are eukaryotes
(cells have organelles)
• Algae are mostly photosynthetic, like plants:
– Have 4 kinds of photosynthetic pigments
– Many accessory pigments – blue, red, brown, gold
• Require moist environments because they lack
a waxy cuticle (remember: cuticle prevents
water loss in terrestrial plants)
General features of Algae
• Can be microscopic or macroscopic:
size ranges from bacteria size to 50 meters
long!
• Lack vascular (conducting) tissues –
No xylem or phloem
– No true roots, stems or leaves
• Modes of sexual reproduction:
– Both sexual and asexual
• Algae illustrate the importance of
photosynthesis to the Earth’s ecology!
Diversity of Algae
• There are millions of algal species, but we’ll
focus in these five groups:
•
•
•
•
•
Diatoms
Dinoflagellates
Red Algae
Kelps or Brown Algae
Green algae
1. Diatoms
• Diatoms: Division Bacillariophyta
• Large group of algae (many unidentified).
Relatively recently evolved group
• Habitat: Diatoms live in cool oceans
• Structure: mostly unicellular, have silica in their
cell walls
Diatoms
• Very important for aquatic food chains: they
provide phytoplankton
sun
Phytoplankton  Zooplankton  small fish  larger fish
mollusks
whales
• Can reproduce asexually for many generations,
then sexually
3. Red Algae
• Red algae: Division Rhodophyta (4000 species)
• Are some of the oldest eukaryotic organisms on
earth (2 billion year old fossils)
• Abound in tropical, warm waters
• Act as food and habitat for many marine species
• Structure: from thin films to complex
filamentous membranes
Why are Red algae red?
• Accessory pigments! Phycobilins mask the
Chlorophyll a – thus they look red.
• Due to these accessory pigments, red algae
can photosynthesize in deeper waters (at
different light wavelengths).
Red algae
• Commercial uses: Carrageenan used for
making ice cream, jellies, syrups, breads.
• Also for lotions, toothpaste, pharmaceutical
jellies.
• Agar for growing bacteria and fungi for
research purposes.
• As food.
4. Kelps or Brown Algae
• Kelps: Division Phaeophyta
• Closely related to diatoms, also a recent group… but
look very different from diatoms!
• Habitat: rocky coasts in temperate zones or open seas
(cold waters)
• Structure: multicellular only
• Holdfast, stipe, blade, air bladder
• Up to 50 meters long
5. Green Algae
• Division: Chlorophyta
• Largest and most diverse group of algae
• Habitat: found mostly in fresh waters and on
land.
• Float in rivers, lakes, reservoirs, creeks.
• Can also live on rocks, trees, soil
Green algae
• Sea lettuce (Ulva) lives in salt waters along the
coast.
• Structure of green algae: from
• Single cells (Micrasterias)
• Filaments
• Colonies (Volvox)
• Thalli (leaf-like shape)
Green algae
• Terrestrial plants arose from a green algal
ancestor
• Both have the same photosynthetic
pigments (Chlorophyll a and b).
• Some green algae have a cell wall made of
cellulose
• Cells divide similarly
Benefits of Algae
• Beneficial algae:
• They are the base of the aquatic food chain –
photosynthetic organisms
• Lichens: algae and fungi symbiosis
• Also serve as shelters: Kelps form underwater
forests; red alga form reefs
Harmful algae
• Excessive growth of algae causes:
• Clogging of water ways, streams, filters… makes
the water taste bad.
• Can be toxic to animals
• “Red tides” caused by
dinoflagellates
Commercial uses of algae
• Algin – a thickening agent for food processing (brown
algae)
• Carrageenan – foods, puddings,
ice cream, toothpaste (red algae)
• Iodine (brown algae)
• Agar – for growth media
used in research (red algae)
• As food – red and brown algae
• As plant fertilizers
• Diatomaceous earth: used for filtering water,
insulating, soundproofing
Kingdom Plantae
• When moving from water to land, both plants
and animals faced the same challenges, but
evolved different ways to deal with them
Plants evolved from algae
• Algae cannot survive on land (only in moist
environments)
• Plants had to adapt (evolve) characteristics that
would allow them to survive and live on dry land
• Cooksonia is the earliest
known land plant (fossil)
• It’s non-vascular and
similar to today’s
bryophytes
Ancestor of plants: Green Algae
• The ancestor of land plants
was probably a green alga:
something like modern Coleochaete
• 1. They both have same photosynthetic
pigments (Chlorophyll a & b, carotenes, etc.)
• 2. Both use starch to store photosynthetic products
• 3. Both have cellulose in their wall
• 4. Both have ‘alternation of generations’…
• 5. Both form a cell plate during cell division
Kingdom Plantae
• Evolutionary tree of plants
• From primitive advanced traits
Bryophytes
Ferns
Gymnosperms
Flowers
Seeds 
Green
alga
ancestor
Vascular 
Terrestrial 
Angiosperms
Living on land
• Several environmental challenges had to be met
by early plants in order to live on land…
A. OBTAINING ENOUGH WATER
• Plants evolved roots
to anchor the plant
• Roots to absorb water
and dissolved minerals
B. PREVENTING WATER LOSS
• Plants evolved a cuticle –
waxy layer
• Evolution of multicellular
gametangia (sex organs) –
helped protect gametes
from drying out.
Evolution of a resistant coat
on spores that prevents
drying out
•
C. GETTING ENOUGH ENERGY
• In land, plants obtained enough sunlight for
photosynthesis
• Different strategies for obtaining light:
• Growing taller and above other plants –
plants began to evolve support cells
• Others had to adapt to lower light
intensities
D. Photosynthesis/water dilemma
• Problems – plants need pores for gas exchange
for photosynthesis, but open pores (stomata)
allow water to leave (95% water taken is lost)
• Solution – stomata open during the day (for
photosynthesis gas exchange) and close during
the night (to allow plant to recover from water
loss)
E. MULTICELLULARITY
• Evolved in algae
• Advantages: root better, protect gametes,
grow tall to obtain sunshine
• Disadvantage: getting water to all cells
• Plants evolved vascular tissues, xylem and
phloem
F. SEXUAL REPRODUCTION
• Algae have motile gametes and single sex organs
• Land plants developed air-borne dissemination
of desiccation-resistant stage
• Land plants developed multicellular sex organs
• Sexual reproduction gives plants genetic
variability – enable them to adapt better to their
environments
G. LIFE CYCLE
• Algae, water dependent life cycle  water
independent life cycle in land plants
• Plants developed dryness-resistant
gametophytes (spores) or zygotes (seeds)
• Smaller size primitive  larger size plants
• Dominant gametophyte stage (n) 
dominant sporophyte stage (2n)
Life cycles: animals vs. plants
• Animals like humans, live in the 2n stage.
Dominant 2n stage
• Single celled gametes are 1n
2 n = 46
1 n = 23
(meiosis)
Plant life cycle: alternation of
generations
• Plants spend part of their life cycle in the
haploid (1 n) stage, and part in the diploid (2 n)
stage – both stages are multicellular
Sporophyte generation (2n)
Gametophyte generation (1n)
• Plants display an alternation of haploid and
diploid phases in their life cycle.
• (see text and image on page 139 in the
textbook “Plants and Society”)
BRYOPHYTES
• Bryophytes include
mosses, liverworts
• Non-vascular plants,
i.e. they don’t have
xylem or phloem
• Advancements over algae: cuticle,
multicellular gametangia, stomata
• Habitat: they require moist environment for
active growth and sexual reproduction
Bryophyte life cycle
• Exhibit alternation of generations: they have a
gametophyte and sporophyte generation
• (See text image on pg. 140 please)
Bryophytes
• Gametophyte generation (1n) is dominant
• Has green “leafy stems” and root-like structures
called rhizoids, for anchoring (not true roots!)
• Have stomata and cuticle
• Bryophytes lack vascular tissue – do not have
xylem or phloem.
• This absence of vascular tissue prevents
bryophytes from having true roots, stems or
leaves.
• Also, lack of conducting tissue limits their size.
Bryophyte reproduction
• Gametophyte plant produces multicellular
sex organs:
• Archegonia – produces eggs (female)
• Antheridia – produces motile sperm (male)
• Outer layers protects
and prevents drying
• Motile sperm must swim
to archegonia.
Bryophyte reproduction
• Sporophyte occurs after egg is fertilized by
sperm (2 n)
• Sporophyte grows in the archegonium of the
gametophyte plant – it’s dependent on it
• Mature sporophyte consists of:
• Foot (point of attachment)
• Seta (stalk)
• Capsule (spore case)
Bryophytes
• Sporocytes within the Sporophyte undergo
meiosis to produce a single kind of haploid spore
• If spore lands on
suitable place,
it will germinate
into a protonema,
the initial stage of
the gametophyte plant.
Bryophyte significance
• Bryophytes are small and inconspicuous,
but important part of the biosphere
• Food for mammals, birds
• Important to prevent soil erosion along
streams
• Commercially – peat moss (Sphagnum) is
used as fuel, soil conditioner, by florists
FERNS
• An important group of plants – 10,000 species
exist
• Ferns have developed vascular tissue
• Habitat: Moist tropics, woodlands, streambanks
• Also exhibit Alternation of Generations, but…
• The diploid Sporophyte generation is dominant
(larger and more visible)
• The haploid Gametophyte is small & short lived.
Fern life cycle: dominant sporophyte
• Sporophyte generation (diploid) is dominant,
larger
• Sporophyte has well developed vascular system
(xylem, phloem)
• (See image on page 141 of the textbook please)
Fern sporophyte morphology
• Fern sporophyte
has fronds (leaves)
• Young fronds are called
fiddleheads
• They also have an
underground horizontal
stem called the rhizome
• True roots arise from
the rhizome
Fronds
• Ferns have complex leaves called fronds, for
photosynthesis and reproduction
• Under the fronds, spores are
produced in sporangia in clusters
called sori (sorus = singular)
• In sporangia, meiosis occurs
producing haploid spores
Fern Gametophyte generation (1n)
•
•
•
•
Single spore grows into the gametophyte plant
Heart-shaped called prothallus, very small.
Archegonia and antheridia produced in prothallus
Female gametophytes produce a chemical that
induces spores to produce male gametophytes
around it
Fern gametophyte
• Antheridium produces motile sperm that swim
to the archegonia’s egg – fusion occurs and the
diploid sporophyte generation begins
• Zygote develops into a new embryo – that
eventually grows into mature sporophyte
Significance of ferns
• Ecologically important: Hold and form soil to
prevent erosion
• As food – fern fiddleheads
eaten in Hawaii, Japan,
Philippines – very nutritious
and delicious!
• As ornamental plants
• Coal formation
from ancient ferns