From Algae to Terrestrial PlantsBy Marie, Rebecca and Filiam

Algae

- Algae is a photosynthetic member of the kingdom Protista; it can be either unicellular or multicellular

- The multicellular algae (otherwise known as seaweed) are categorized as three phyla based on colour: red, brown and green

Brown Algae (Phylum

Phaeophyta)-largest most complex protist-found in nutrient rich cool waters of west coast-grow up to 60 meters high, underwater forests

STRUCTUREHOLD FAST: anchorSTIPE: stem like, extends from holdfast, provides supportBLADE: leaf like, undergoes photosynthesis

Kelp

Red Algae (Phylum Rhodophyta)

-first multicellular organism on Earth-6000 living speciesWhere: found in warm coastal waters of tropical oceans

STRUCTURE-contains chlorophyll and phycoerythrin: additional pigment that makes it more sensitive to light at greater depths

COOL FACT: red algae is used for wrapping SUSHI!

Green Algae (Phylum

Chlorophyta)-most green algae are aquaticWHERE: most commonly found in fresh water but also in salt water environmentsSTRUCTURE: multicellular or unicellular Example: Chlamydomonas is unicellular, moves with a flagellaUlva is multicellular (sea lettuce)Green Algae are thought to be the closest relative of plants

Chlamydomonas

ULVA

Some botanists say that green algae are plants while others consider them to be protists

What evidence might lead some scientists to place green algae

in the plant kingdom? land plants and green algae contain

chlorophyllcellulose cell walls circular (rosette) shaped arrays of proteins

that synthesize the cellulose for the cell wall (compared to linear arrays)

both store food in the form of starch peroxisome enzymes: enzymes found in

the peroxisomes that help minimize the loss of organic products 

structure of flagellated sperm: structure of flagellated sperm in some land plants resemble that of the charophyte (green algae) sperm  

formation of a phragmoplast: in cell division of land plants and some charophytes, phragomoplast (microtubules) form between daughter nuclei. They serve as the framework for the assembly of the cell plate

Green Algae are the organisms most closely

related to plants

Differences between plants and green algae

Plants grow terrestrials environmentsPlants reproduce in the process of Alternation of

Generation (with an associated trait of multicellular, dependent embryos)

Walled spores producing in sporangiaPlants produce gametes within multicellular

organs called gametongiaPlants have roots and shoots that increase their

exposure to environmental resources.

Adaptations to Land

-Transition from aquatic to terrestial habitats took place around 460 millions years ago

ISSUES: What adaptions kept the algae from drying out on land?How would it transport nutrients from the outside environment to the plant cells?What would be the system support?

First Land Plants

Natural selection favours individual alga that can survive periods without drying out.

The first land plants were small and transferred water and dissolved substances through osmosis and diffusion, but this was inefficient & slow

However they didn’t have necessary tissues to transport different materials over long distances

Eventually vascular tissues evolved into a group called VASCULAR PLANTS

Stages of Evolution: Algae to Land Plants

1. Vascular Tissue

• Xylem and Phloem

2. Development of Roots

• Ability to anchor to soil and absorb water/nutrients

3. Development of Leaves• Leaves allow better exchange of gases during photosynthesis and

larger surface area to capture light

Vascular TissueXylem

Dead, tube like cells containing tough material

Function: transports water and minerals from the roots to the rest of the plant

Importance: permitted the growth of taller plants/trees

Phloem Made up of living cells Function:

transportation of larger molecules like sugars

Note: Vascular Tissue led to the development of roots, and leaves

Plant Reproduction

- Plants and certain green algae use sporic reproduction, which is also known as alternation of generations

- Sporic reproduction is a type of sexual reproduction that switches back and forth continuously between a haploid stage and diploid stage (this means that there are actually two multicellular stages in their life cycle)

Alternation of Generations

Continuation of reproduction

gametophyteThe gametophyte,

meaning the haploid version of the organism, makes haploid gametes through mitosis

SporophyteThe sporophyte, meaning

the diploid version of the organism, are created through the fusion of haploid gametes and make spores through meiosis

•Through the gametic fusion of the gametophytes, sporophytes are then created•The spores from the sporophyte then undergo mitotic division and create multicellular gametophytes. Finally, the continuous cycle starts up again.

In Conclusion …despite the fact that plants

live primarily on land and algae in aquatic environments:

BOTH contain chlorophyll, Photosynthesis occurs in

BOTH algae and plants; it is important to keep differences in mind

This makes it tricky to draw a clear line between what is a protist and a plant; therefore where do algae belong?