CLASSIFICATION OF LOWER ORGANISMS

Remember:

There are 6 Kingdoms for all organisms

Animalia, Plantae, Fungi, Protista, Eubacteria, Archaebacteria

“Lower organisms” are generally the Eubacteria, Archaebacteria, Protista and Fungi

Definitions

Phylum: the taxon containing closely related classes

Phylogeny: The evolutionary history of a group of organisms that share a common ancestor

Protists - Introduction

Single celled eukaryotes Appeared approximately 1.5 billion years ago 115 000 species, all very diverse in cell

structures, patterns of nutrition, reproduction and habitats

Their phylogeny is very complex and difficult to classify

To simplify in this class, protists have been broken down/classified based on their nutritional pattern: animal-like, fungus-like and plant-like

Animal-Like Protists

Also called Protozoans All are heterotrophs - they eat and ingest

material from their surroundings Are 4 phyla of protozoa, classified by

their type of locomotion Numerous in types of species and

population numbers, similar to bacteria

Animal –Like Protists:Zooflagellates Phylum Mastigophora Possess 1 or more flagella to help them move Feed on other protists or are internal

parasites on animals Reproduced asexually via longitudinal fission Example: Trypanosoma gambiensis causes

sleeping sickness that destroys RBCs, other tissues and one’s nervous system until the person loses consciousness

Animal-Like Protists:Amoebas Phylum Sarcodina Most are free-living forms No set body shape Psuedopods (projections of cytoplasm) enable

them to move and feed through endocytosis (engulfing organisms with their pseudopods)

Some are parasitic

Example: Entamoeba causes amoebic dysentery, found in the water in tropical regions

Animal –Like Protists:Ciliates Phylum Ciliophora Covered with hairlike projections called

cilia Rigid outer covering called pellicle

maintains their shape (amoebas don’t have this)

All ciliates are aquatic heterotrophs Paramecium is an example

Paramecium Digestion

Beating of its cilia sweeps food into oral groove

Membrane pinches off, surrounds food and a food vacuole is formed

Food vacuole joins up with a lysosome which breaks down the food with digestive enzymes

Usable products are absorbed in cytoplasm, undigested food is removed via anal pore

Paramecium & Structure

Have 2 types of nuclei – large macronucleus and smaller micronucleus

Reproduction by binary fission (asexual) Micronucleus (ei) divide by mitosis and

macronucelus simply pinches apart to produce two daughter macronucleus

Paramecium also use sexual reproduction via conjugation

Animal-Like Protists:Sporozoans Phylum Sporozoa Produce spores during asexual

reproduction Sporozoa are non-motile and parasitic;

get nutrients from bodies of hosts Best known sporozoan is genus

Plasmodium that causes malaria

Fungus-Like Protists

Also called....SLIME MOULDS!!!!

All are heterotrophic and most are decomposers that feed on dead plants and animals by endocytosis

Live in cool, damp habitats

Fungus-Like Protists:Acellular Slime Moulds Single celled Most of life is a wall-

less mass of cytoplasm with many nuclei

Cytoplasm moves using pseudopodia (network of strands)

Reproduce using spores; spores scatter and germinate

Fungus-Like Protists:Cellular Slime Mould Live in fresh water,

damp soil or decaying matter

Move like amoebalike cells

When food scarce, they form a large multicellular mass and eventually release spores

Fungus-Like Protists:Water Moulds

Most live in water; some on land

May have seen growing on dead fish as whitish cottony substance

Most land species decompose dead matter which is good, but few are parasitic to plants

Irish Potato famine in mid 1800s caused by Phytophthora infestans

Plant-Like Protists

Are 24 000 species of protists that contain chlorophyll and carry out photosynthesis, and so they resemble plants

We look at Euglenoids and Algae

Plant –Like Protists:Euglenoids Are unicellular

flagellates and many members of this group photosynthesize to produce food

Species called Euglena gets fed in 2 ways

In sunlight it is autotrophic (photosynthesis)

In dark feed as heterotroph on dead organic material in water

Plant –Like Protists:Algae Resemble plants because they have

chloroplasts that have chlorophyll

Some are single-celled, some live in colonies, some are multicellular

Are 6 main groups of algae; we discuss 3 here

Algae: Diatoms

Have golden colour due to yellow-brown pigments in their shells

Outer covering is made of two halves

Each species has a characteristic shape

Abundant in ocean; also classified as phytoplankton

Algae: Dinoflagellates

Are single-celled algae, have 2 flagella

Most are photosynthetic

Abundant in marine environments

Each species has a specific shape

Tend to be luminescent: when surrounding water is agitated, they give off light!!

Reproduce by mitosis

Interesting to Know....

Rapid population growth called an algal bloom

When dinoflagellate Gonyaulax polyhedron blooms it’s called a red tide

Algae: Green algae

Can be single celled or colonial Each cell has 2 flagella that move the

cell around Ancient green algae are thought to have

given rise to the first plants because they have cellulose in their cell walls and their chloroplasts are similar to those of plants

Multicellular algae known as seaweeds

Algae: Green algae

Colony of Algae (Volvex)Giant Kelp (multicellular Algae) can grow to 100 m and has the fastest growth rate of any organism.