Lecture 11: Algae, Bryophytes and Ferns

1
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

2
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)

3
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 Earths ecology!

4
Diversity of Algae

• There are millions of algal species, but well
  focus in these five groups
• Diatoms
• Dinoflagellates
• Red Algae
• Kelps or Brown Algae
• Green algae

5
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

6
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

7
(No Transcript)
8
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

9
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).

10
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.

11
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

12
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

13
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)

14
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

15
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

16
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

17
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

18
Kingdom Plantae

• When moving from water to land, both plants and
  animals faced the same challenges, but evolved
  different ways to deal with them

19
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 earliestknown land plant
  (fossil)
• Its non-vascular andsimilar to todays
  bryophytes

20
Ancestor of plants Green Algae

• The ancestor of land plants was probably a green
  alga something like modern Coleochaete
• 1. They both have same photosyntheticpigments
  (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

21
Kingdom Plantae

• Evolutionary tree of plants
• From primitive? advanced traits

Angiosperms
Gymnosperms
Ferns
Bryophytes
Flowers?
Seeds ?
Greenalga ancestor
Vascular ?
Terrestrial ?
22
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

23
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 coaton spores that
  prevents drying out

24
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 lightintensities

25
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)

26
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

27
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

28
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)

29
Life cycles animals vs. plants

• Animals like humans, live in the 2n stage.
  Dominant 2n stage
• Single celled gametes are 1n

2 n 46
(meiosis)
1 n 23
30
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)
31

• 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)

32
BRYOPHYTES

• Bryophytes include mosses, liverworts
• Non-vascular plants, i.e. they dont have xylem
  or phloem
• Advancements over algae cuticle, multicellular
  gametangia, stomata
• Habitat they require moist environment for
  active growth and sexual reproduction

33
Bryophyte life cycle

• Exhibit alternation of generations they have a
  gametophyte and sporophyte generation
• (See text image on pg. 140 please)

34
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.

35
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.

36
Bryophyte reproduction

• Sporophyte occurs after egg is fertilized by
  sperm (2 n)
• Sporophyte grows in the archegonium of the
  gametophyte plant its dependent on it
• Mature sporophyte consists of
• Foot (point of attachment)
• Seta (stalk)
• Capsule (spore case)

37
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.

38
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

39
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.

40
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)

41
Fern sporophyte morphology

• Fern sporophytehas fronds (leaves)

• Young fronds are called fiddleheads

• They also have an underground horizontal stem
  called the rhizome

• True roots arise from the rhizome

42
Fronds

• Ferns have complex leaves called fronds, for
  photosynthesis and reproduction
• Under the fronds, spores areproduced in
  sporangia in clusterscalled sori (sorus
  singular)
• In sporangia, meiosis occursproducing haploid
  spores

43
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

44
Fern gametophyte

• Antheridium produces motile sperm that swim to
  the archegonias egg fusion occurs and the
  diploid sporophyte generation begins
• Zygote develops into a new embryo that
  eventually grows into mature sporophyte

45
Significance of ferns

• Ecologically important Hold and form soil to
  prevent erosion
• As food fern fiddleheadseaten in Hawaii,
  Japan, Philippines very nutritiousand
  delicious!
• As ornamental plants
• Coal formationfrom ancient ferns