Protista

Eukaryotic vs prokaryotic

Eukaryotic cells more complex than prokaryotic cells:

• Membrane-bound nucleus and organelles

• Many chromosomes that occur in pairs.

• Protists, fungi, plants & animals are composed of eukaryotic cells.

Origin of Eukaryotes

First eukaryotic organism thought to have evolved about 1.5 billion years ago. Prokaryotes are as old as 4 billion years

Protozoans (protists) possibly evolved from the 1st eukaryotes by Endosymbiosis

This Endosymbiotic Theory was first postulated by Lynn Margulis in 1967

Endosymbiosis

theory that explains how eukaryotic cells evolved from the symbiotic relationship between two or more prokaryotic cells.

One prokarytic cell engulfs another prokarytic cell but does not digest it.

Cells live together in a mutually benefiting relationship (symbiosis) becoming dependent upon each other.

Steps of Endosymbiosis

A prokaryote ingested some aerobic bacteria. The aerobes were protected and produced energy for the prokaryote

Over a long period of time the aerobes became mitochondria, no longer able to live on their own

Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments

Cyanobacteria became chloroplasts, unable to live on their own

Scientific Evidences for Theory of Endosymbiosis

Present day mitochondria and chloroplasts each have two membranes.

Their inner membranes are similar to those of ancestral prokaryote, while their outer membranes match the cell membrane of the eukaryote.

The ribosomes found in these organelles are more similar to prokaryotic ribosomes than to ribosomes found in eukaryotes

These organelles reproduce by binary fission within the cell

Each organelle contains a circular chromosome and gene sequences that match those of living prokaryotes

Kingdom: Protista

Domain Eukarya (eukaryotic cells)

Mainly unicellular organisms

"Misfits"

3 groupings

• Animal-like protists- amoebas, ciliates, flagellates, sporozoans

• Fungus-like protists- slime moulds, water moulds

• Plant-like protists - euglenoids, diatoms, dinoflagellates, algae (green, red, brown)

Animal Like Protists (Protozoans)

Heterotrophs – consume other prokaryotes, organic wastes, other protozoans

Some species are parasites, some are free-living

Include 4 phylums:

• Phylum Cercozoa

• Phylum Ciliophora

• Phylum Zoomastigina

• Phylum Sporozoa

Phylum Cercozoa (Cerozoans)

Cell membrane surface, no cell wall = change shape

Psuedopods (cytoplasm extensions for feeding and movement)

Habitat: Salt water, fresh water, mud, intestines

Ex. Amoeba

• Single celled

• No body shape

• Contain pseudopods (to move and eat)

• Eat by endocytosis

Ex. Trypanosoma

• flagellated protozoa

• cause tropical diseases in humans and animals

• Trypanosomes are found in the bloodstream of various mammalian hosts where they proliferate as extracellular parasites

Phylum Cilio phora (Ciliates)

Short hair-like projections on cell surface (cilia) used for movement and food sweeping

Large and complex

Free living or parasitic

Ex. Paramecium

• 2 nuclei- a large macronucleus and a smaller micronucleus

• Reproduction occurs by binary fission

• Reproduce sexually through conjugation- they line up along their oral grooves

Ciliates

Many protozoans are covered with hairlike projections, or cilia, and are called ciliates.

The cilia move back and forth like oars to move the organism through the water.

Unlike amoebas, ciliates have a rigid outer covering called a pellicle that maintains their shape.

The beating of the cilia also sweeps food into its oral groove

• Food reaches the oral groove, the membrane pinches off, surrounds the food, and a food vacuole is formed

• The food vacuole finds a lysosome within the cell, breaking down the food with digestive enzymes

• Undigested food is discharged through the anal pore

Phylum Zoomastigi na (Flagellates)

Contain a flagella for movement

Hard protective outer coating

Free living, parasitic, or mutualistic

Ex. Trichonympha

Phylum Sporozoa (Sporozoans)

Parasitic protists

Capable of asexual and sexual reproduction

Ex. Plasmodium

Fungus-Like Protists

Heterotrophic- living organisms, dead organisms and wastes

Produce spores

Divided into three main groups:

• Plasmodial (acellular) slime moulds

• Cellular slime moulds

• Water moulds

Plasmodial slime moulds (phylum myxomycota)

Not microscopic, slug like appearance

Engulf food particles

Feed on bottom of forests and dead material

Acellular Slime Mould

• Single celled protists that have many nuclei.

• During most of its life, an acellular slime mould is a plasmodium, a wall-less mass of cytoplasm with many nuclei that have divided over and over by mitosis.

• This huge mass of cytoplasm streams very slowly over an object using an extended network of strands called pseudopodia.

• If food runs out, the slime mould forms reproductive structures called fruiting bodies, which produce spores by meiosis.

• The spores scatter and germinate into flagellated cells.

• These cells fuse to produce diploid amoeboid cells

Cellular slime moulds (phylum acrasiomycota)

Feed by ingesting tiny bacteria or yeast cells

Release chemical to gather food using

pseudoplasmodium

No relation to other slime mould

Cellular Slime Moulds

Cellular slime moulds live in fresh water, in damp soil, or in decaying matter such as rotting logs.

In the feeding stage of their life cycle, they move about as amoebalike cells.

When food is scarce, they come together to form a large multicellular mass

Eventually, a fruiting body forms and releases spores.

Water Moulds (Phylum Oomycota)

Live on dead organic matter

Can be parasitic to fish, insects and plants

Extend fungus like threads into host tissues for feeding

Water Moulds

Water moulds live in water, though there are a few species in this group that live on land. If you have seen a whitish, cottony mould growing on dead fish, it was probably a water mould.

Most water moulds are aquatic and feed on the remains of dead plants and animals. Although most of the land species are helpful decomposers of dead matter, a few are serious plant parasites that attack crops such as avocados, grapes, and potatoes.

Plant-like Protists (Algae)

Make their own food by photosynthesis

Some can consume other organisms when light is unavailable

6 phylums

Phytoplankton

unicellular, free floating, aquatic microorganisms

Diatoms (Phylum Chrysophyta)

Most diverse and abundant group of phytoplankton

Rigid cell walls with silicia on surface

Reproduce asexually by mitosis

Sexual reproduction when conditions are unfavorable

Dinoflagellates (Phylum Pyrrophyta)

Phytoplankton

Have two flagella that spin the organism

Reproduce quicky = blooms

Can live inside other organisms

The Red Tide

an event that occurs on the coastline when algae—a plant-like organism—grows out of control.

Caused by Gonyaulax, a dinoflagellate protist that spreads on the surface of the water

The name “red tide” comes from the fact that overgrown algae can cause the water to change color.

Euglenoids (Phylum Euglenozoa)

Phytoplankton

Shallow fresh water

Can be autotrophs and heterotrophs if in dark

Have light detecting structure = eyespot

Euglena

Propels itself through the water by means of its flagellum.

Euglena obtains its nourishment in more than one way. In sunlight it is fully autotrophic, using its chloroplasts to produce sugars through photosynthesis.

In the dark, the organism begins to lose its chlorophyll and feeds as a heterotroph on dead organic material in the water.

Brown Algae (Phylum Phaeophyta)

Largest, most complex protists

Provide species a biodiverse ecosystem to inhabit

Present in marine and tidal environments

Ex. Rockweed, Kelp

Red Algae (Phylum Rhodophyta)

First multicellular organisms on earth 1.5 to 1.2 billion years ago

Most abundant large algae in warm coastal waters

Have green and red photopigments

Common in food

ex. Sushi, dairy products

Green Algae (Phylum Chlorophyta)

Most are aquatic- mainly fresh water, some salt water

Diverse habitats

Most plant-like of the 3 types of algae

Can cause harmful algal blooms