Protozoa And Algae

Question 1

Protozoa facts

Answer 1

• means ‘first animals’
• single cell eukaryotes
• Lack a rigid cell wall, are generally motile and inhabit ‘wet’ environments (although may also form a resting stage - cysts or spores - with thick cell wall)
• are heterotrophs
• some species are parasites of animals or plants

Question 2

Algae

Answer 2

• Essentially, protozoa that have a plastid
• Those algae in which the plastid is a chloroplast are phototrophs

Question 3

Protists

Answer 3

Collectively, the Protozoa and algae

Question 4

Polyphyletic

Answer 4

Protozoa and algae are not taxonomic groups

Question 5

Examples of Protozoa that are human parasites

Answer 5

• Trypanosomes: cause African sleeping sickness
• Leishmania: cause leishmaniasis (dumdum fever)
• Entamoeba: (Causes amoebic dysentery)

Question 6

Protozoa in plants

Answer 6

• Phytophthora - plant killers, P.infestans: cause of potato blight
• Phytophthora palmivora - affects cocoa pods

Red tides are caused by dinoflagellates

Question 7

Evolution of the eukaryotes

Answer 7

• eukaryotes are believed to have evolved from the prokaryotic Archaea, through a process of internal membrane formation (to create nucleus, ER, etc), cell enlargement and serial endosymbiosis (mitochondria and plastids)

Question 8

Four major groups of Protozoa

Answer 8

• alveolates
• Euglanoids
• Oomycetes
• Sarcodina

Question 9

The Alveolates

Answer 9

• they are called this because the cells posses alveoli - sac-like membrane structures filled with fluid that lie underneath the cell membrane

Question 10

Three main phyla of alveolates

Answer 10

• Ciliates (e.g. Paramecium)
• Sporozoans (e.g. Plasmodium, Cryptosporidium)
• Dinoflagellates

Question 11

Ciliates (form the Latin for eyelash)

Answer 11

• ~7000 species and are arguably, the most complex single celled organisms
• found almost anywhere there is water
• Some or all of the cell surface is covered with cilia that beat to propel the ciliate through the water and/or to draw in food particles
• free living ciliates feed mainly on bacteria, algae or even other ciliates
• some ciliates harbour symbiotic algae or retain functional chloroplasts from prey
• Ciliates in soils form cysts in order to survive long periods of drying

An example is paramecium which feeds mostly on bacteria. It reproduces asexually or sexually by conjugation

Other examples include:
Vorticella, Stentor, Paramecium, Mesodinium

Question 13

The sporozoans (part of ciliates)

Answer 13

• haploid parasitic Protozoa
• have a complex life cycle usually involving growth stage within the host cell
• a major sub-group of the phylum Sporozoa are the apicomplexans - have distinctive structure at apical end of sporozite (involved in host cell invasion)

Examples of apicomplexa are:
- Plasmodium
- Toxoplasma
- Emeria

Question 14

The euglenoids

Answer 14

Flagellated Protozoa including:
- Euglena
- Trypanosomes
- Leishmania

Question 15

Euglena

Answer 15

Many species of the genus possess chloroplasts , but are also capable of heterotrophic growth. In some species the chloroplast is easily lost (=‘bleaching’)

Question 16

Trypanosomes

Answer 16

• Flagellated pathogens of animals and plants.
• Life cycle involves an insect host.
• Possess a kinetoplast (specialised DNA containing structure in mitochondrion)
• T.brucei - transmitted by tsetse fly
• causes sleeping sickness - fever, joint pains, etc. followed by torpor (when parasite invades CNA), coma and ultimately death

Question 17

The Oomycetes

Answer 17

• So-called “water moulds”
• filamentous Protozoa that may be free living or parasitic
• many grow as ‘fungal-like’ hyphae and appear as rusts or mildews
• originally considered to be fungi, now clear that they are related to the Chromista (golden algae)

Question 18

Oomycetes species

Answer 18

Phytophthora infestans - causes potato and tomato blight, and responsible for the Irish potato famine of the 1840s

Plasmopara viticola - causes grape mildew and almost wiped out the entire French wine industry in the 1870s

Saprolegnia species - grow on scales of fish and on other aquatic animals. Cause lesions when fish in high density (e.g. spawning salmon)

Question 19

Sarcodina (=Rhizopoda)

Answer 19

• Largest phylum of Protozoa (~12,00 extant species)
• comprises the amoeba - unicellular Protozoa that use pseudopodia for locomotion and feeding (phagocytosis)
• Most species free living although some important parasites

Question 20

Entamoeba hostolytica (‘tissue destroyer’)

Answer 20

• a major human pathogen
• 50 million symptomatic cases/year; 100, 000 deaths
• E. Histolytica has two stages in life cycle:
  - Motile amoeba (trophozoite); cyst

Ingested cysts are resistant to stomach acid and hatch to form amoebae in colon. New cysts form and pass through the bowel

Normally no symptoms, but in some individuals amoebae become invasive and attack organs, resulting in localised infection (amoebic dysentery) or systemic infection of many organs including the brain

Question 21

Dictyostelium discoideum (‘dicty’) - amoeba

Answer 21

• Haploid unicellular amoeba feeds on bacteria in soil and divide by mitosis.
• But when food source becomes scarce, then it undergoes a developmental change.
• Amoeboid movement exploited to create a multicellular organism (a ‘slug’ 2 - 4 mm in length).
• Cells secrete cAMP that attracts other cells.
• These adhere via glycoproteins expressed on cell surface.
• The slug then moves to new environment and differentiates into an elaborate structure – the
  Fruiting body.
• When mature, it releases spores to disperse cells to new locations.
• Recently shown that some
• Dicty display ‘husbandry’ - store cells of bacterial prey as symbionts during this cycle to take with them to their new niche (Dicty farming!)