Protistans

Chapter 22

Characteristics of Protistans

• Have a nucleus and organelles (eukaryotes)

• Protists are mainly defined by what they are not - they are not bacteria or fungi, they are not plants or animals.

• Some protists are autotrophs• Some protists are heterotrophs• Some are parasitic.• Some are decomposers.• Most protists are aerobic. • They can be unicellular, multicellular, or

colonial.• Many live in water or moist environments.• Protists reproduce asexually by binary fission,

and a few species are capable of sexual reproduction. Many have very complex life cycles.

• Protists are so small that they do not need any special organs to exchange gases or excrete wastes. They rely on simple diffusion.

• Protists eat by phagocytosis (endocytosis) - they engulf their food in their cell membrane, and pinch off a section of membrane to form a vacuole

• contractile vacuole, which drains the cell of waste products (especially excess water in freshwater species - osmoregulation) and squirts them outside the cell.

• Classification

– Old Classification based on modes of nutrition, pigments (if present), carbohydrate food reserves, flagella, cell wall components and the environments they inhabit

– New classification based on phylogeny, still being worked on

– We will look mostly to the “old” classification

• Importance– Important components of food chains. E.g.

kelp beds are among the most productive ecosystems on earth

– Unicellular aquatic Protista (plankton) form a very important component of the food chain. The photosynthetic ones are called phytoplankton and the heterotrophic ones are called zooplankton (which also includes many animal larvae or tiny crustaceans)

– Also, many are used by humans in industry

• Classification (phyla)– we will look at 14

• Generally grouped by “feeding” style into one of three categories– Protozoans – animal like, unicellular,

heterotrophs– Algae – plant like, autotrophs– Fungus -like

Protozoans – animal like, unicellular, heterotrophs. (4 phyla)

1. Sarcodina – Amoeba like, move with pseudopods . They extend part their body in a certain direction, forming a pseudopod or false foot, and then flow into that extension (cytoplasmic streaming). They change shape. No cell wall. In water. Some have shells (foraminiferans and radiolarians). Asexual reproduction . They eat other protozoans, algae, and even tiny critters like rotifers. Many sarcodines are parasites.

2. Zoomastigina – Flagellates, move with long flagella

• Flagellates: The flagellates are motile by means of whip-like structures called flagella, attached to the surface of the cell. The eukaryotic flagella is completely different in structure and action from the bacterial. Eukaryotic flagella move in a wave-like or whip-like motion that propels the cell forward.

• Some biologists include Euglena here, others include it with the algae. We will include them with algae.

3. Ciliophora- Unicellular, heterotrophic ciliates. Aquatic. These ciliates move by means of numerous small cilia. Cilia are short, hair-like structures that cover the surface of the ciliate cell. The beat back and forth in unison, propeling the cell rapidly through the water. They are complex little critters, with lots of organelles and specialized structures. Many of them, like Paramecium, even have little toxic threads or darts that they can discharge to defend themselves.

4. Sporozoans – parasite, non-motile, produce spores

– Also called Apicomplexa – parasitic – They typically have complex life cycles with both

sexual and asexual stages. Different stages often develop in different host species. Their life cycles involve intermediate hosts such as the mosquito. They form small resistant spores, infective bodies that are passed from one host to the next. In more general terms, spores are haploid reproductive cells that can develop directly into adults. (toxoplasmosis and malaria)

• (Photosynthetic protists), Major producers in aquatic ecosystem

• Unicellular, colonial & multicellular, photosynthetic, possess chloroplasts (although some are heterotrophic)

• Unicellular forms known as phytoplankton. • Classified into six or 7 phyla –Differences between

groups are due to diversity in photosynthetic pigments, carbohydrates food reserves, number and position of flagella, life cycle patterns and cell wall characteristics.

Algae – plant like protist

• 1. Euglenophyta – euglenoids, unicellular, aquatic, have traits of both plants and animals, lack cell wall, contain chlorophyll & do photosynthesis. Eyespot, flagella, can ingest food. Both autotrophic and heterotrophic. Mostly found in freshwater.

• Instead of a cell wall they have a pellicle, a flexible layer of interlocking proteinaceous strips inside plasma membrane

• Reproduction via simple cell division. Sexual reproduction is lacking.

• This organism may actually have resulted from endosymbiosis, in which an ancestral form engulfed a green algal cell. Appears they are derived from protozoa by incorporation of chloroplasts. (If grown under proper conditions cells may replicate faster than the chloroplasts, giving rise to non-photosynthetic cells which are nearly indistinguishable from protozoa. The heterotrophs ingest food. )

Figure 22.3Page 365

Euglenoid Body Plan

pelliclemitochondrionGolgi body

ER

nucleuseyespot

long flagellum

contractile vacuole chloroplast

nucleus

Figure 22.3Page 365

• 2. Diatoms – phylum bacillariophyta, unicellular, with shells made of silica, autotrophs, in both fresh and salt water. Mostly unicellular but a few colonials. Most autotrophic, a few are heterotrophic. Lack flagella.

• Cell walls, called frustules, are polymerized, opaline silica (glass like). The two halves of the frustules fit together like a Petri dish.

• Reproduction mainly asexual. The two halves of the frustules open and each side generates a new half. Sexual reproduction may take place.

• Diatoms are so abundant that the photosynthesis of diatoms accounts for a large percentage of the oxygen added to the atmosphere each year from natural sources.

• Some books still place them with the Chrysophyta, the golden-brown algae, but they are now recognized as an entirely separate group.

• 3. Chrysophyta - golden-brown algae

• Cell wall of cellulose and silica

• Food storage of lipid and laminarin

• Unicellular or colonial

• 2 flagella (unequal length)

• 4. dinoflagellates – Phylum Pyrrophyta , unicellular with cell walls, 2 flagella, they spin when flagella beat, some in fresh but most in salt water, some are bioluminescent, red or orange usually, cause “red tides” when population booms, some produce toxins.

• Dinoflagellates are named after their two flagella, which lie along grooves, one like a belt and one like a tail.

• Many species have a heavy armor of cellulose plates, often encrusted with silica.

• Some dinoflagellate species often form algal blooms in coastal waters, building up enormous populations visible from a great distance.

• The amazingly potent toxins, that about 20 species produce, poison shellfish, fish, and marine mammals, causing the deadly red tide.

• 5. red algae – phylum rhodophyta, red seaweeds, multicellular, marine (warm tropical waters), attach to rocks by structures called hold fasts, some have pigments other than chlorophyll that allow them to photosynthesize in deeper water where only green, violet and blue light penetrate. Usually grow attached to rocks or other algae, but there are a few free floating forms and a few unicellular or colonial forms.

• No flagellated cells at all in life cycle. • Floridean starch carbohydrate food reserve is more

glycogen like (found in animals and fungi) than other plant starches.

• Cell walls of cellulose or other polysaccharides, plus gelatinous pectic materials, e.g. agar and carrageenan (sulfated polymers of galactose). Some species deposit calcium carbonate in their cell walls, called coralline algae.

• 6. brown algae – phylum phaeophyta, mostly cool saltwater on rocky coasts, attached to rocks by holdfasts , free floating forms, Some also have air bladders for flotation, brown color, multicellular

• This algal division includes the largest multicellular algae (and largest protists ). They show the greatest division of labor between cells seen in any algal phyla. In fact the larger kelp species have a primitive type of phloem tissue

• Only reproductive cells have flagella, • Like all algae, their blades are thin because they lack the

complex conductive tissues of green plants, and must rely on simple diffusion.

7. green algae – phylum chlorophyta, chlorophyll is major pigment, most freshwater. The green algae are a diverse group. They share many characteristics with plants. Most  are multicellular, but there are a few unicellular forms.

• Both plants and green algae:– have cell walls made of cellulose and hemicellose and

pectin– both groups of organisms use starch as the type of

substance used to store energy– they have the same combination of pigments: chlorophyll

a, chlorophyll b, and various carotenoids (eg beta-carotene, xanthophylls).

• Due to these similarities (as well as other sources of evidence) it is believed that higher plants evolved from an ancient species of green algae.

• slime molds and water molds and downy mildew, obtain energy from decaying organic material, live in cool moist places,

• 3 phyla – 2 are slime molds and the other is a watermold/downy mildew.

Fungus-like protist

1. plasmoidial slime molds – phylum myxomycota “acellular” slime molds. Terrestrial, Heterotrophic.

• The body form of this organism during most of its life is a multinucleated mass of cytoplasm (a type of coenocytium).

• Lack cell walls – • exist as streaming masses of naked protoplasm which

"creeps", As they travel they engulf bacteria, yeast cells, fungal spores and decayed plant and animal matter. The plasmodium contains many nuclei which undergo synchronous divisions.

• Sexual reproduction involves the fusion of amoebae and/or flagellated gametes which come from spores produced within sporangia.

• 2. cellular slime molds – phylum acrasiomycota , This phylum contains the cellular slime molds. Unlike the Myxomycota, the cellular slime molds consist of ameoba-like cells each containing a single nucleus. Chemical signals from the cells can cause them to aggregate into a mass that resembles a plasmodium, although the individual nuclei remain separated by their plasma membranes.

• 3. water molds and downy mildew – phylum oomycota . These organisms grow as cottony, mold-like filaments. The filaments have cellulose-based cell walls, but no chitin as the walls of true fungi have.

• They produce flagellated gametes (sex cells) that require an aquatic environment for dispersal.

• An example is the genus Phytophthora, the cause of the potato blight that caused the Irish potato famine in the 1840s.

New Classification based on phylogeny: still being worked out.

Red Algae (Rhodophyta)

• 4,100 species

• Most abundant in tropical seas

• Can grow at great depths – they have different pigments which can use blue

wavelengths (these are the wavelengths that go deeper)

• Complex life cycles may include very different forms

Alveolates

• Have tiny, membrane-bound sacs (alveoli) underneath their outer membranes

• Ciliates

• Sporozoans

• Dinoflagellates

Stramenopiles

• Unique trait is one of their two flagella has thin filaments projecting from it

• Cells have four outer membranes

• Include – Oomycotes– Chrysophytes– Brown algae