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. Diatoms1. 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 phytoplanktonsun

Phytoplankton Zooplankton small fish larger fish mollusks whales

• Can reproduce asexually for many generations, then sexually

3. Red Algae3. 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 Algae4. 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 Algae5. 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 algaeGreen 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 algaeGreen 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 earliestknown land plant (fossil)

• It’s non-vascular andsimilar 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 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

Kingdom Plantae

• Evolutionary tree of plants

• From primitive advanced traits

Bryophytes

Greenalgaancestor

Ferns Gymnosperms Angiosperms

Vascular

Seeds

Terrestrial

Flowers

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 coaton 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 lightintensities

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 areproduced in sporangia in clusterscalled sori (sorus = singular)

• In sporangia, meiosis occursproducing 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 fiddleheadseaten in Hawaii, Japan, Philippines – very nutritiousand delicious!

• As ornamental plants• Coal formation

from ancient ferns