Lecture 6 Flashcards
What is a protozoan ?
Distinctly animal like : no cell wall at leat 1 motile stage in life cycle
Most ingest their food
- not a monophyletic clade
- completely contained within 1 plasma membrane
axoneme
9 pairs around central pair (9+2) arrangement.
kinetosome
9 triplets (basal body)
How do we classify protozoa ?
•constantly under revision due to new molecular data
- will focus on clades rather than taxonomic levels
Important organelles .
1) nucleus
- membrane - bound structure containing genetic material (DNA) as chromosomes
- nucleoli also often present
Mitochondria ?
- used in energy acquisition using oxygen
- also contains DNA (former prokaryote?)
- form of internal membranes (cristae)
can serve to group into clades.
Hydrogenosomes ?
substitutes where oxygen is absent
Kinetoplast?
Derivatives of mitochondria
Golgi apparatus ?
•part of secretory system
Parabasal bodies ?
They are structures with similar function to golgi apparatus
- secretory function
Plastids ?
•organelles containing photosynthetic pigments
-e.g. chloroplasts
• via ancestral engulfment of cyanobacteria
Extrusomes
•membrane-bound organelles used to
extrude something from the cell
Cilia & flagella
•same ultrastructure but different actions
differ in beating patterns
Ø flagellum with undulating motion (force generated in same direction as flagellum axis)
Ø cilia like oars (power & recovery strokes perpendicular)
The structure of cilia and flagella.
•both consist of microtubules
Ø 9 pairs around central pair (9+2) arrangement (axoneme) covered with continuous membrane
• different arrangement at entrance to cell
Ø 9 triplets ( kinetosome /basal body)
How do cilia & flagella propel protozoans ?
sliding microtubule hypothesis
Pseudopodia ( 2nd mode of movement)
- temporary protrusions of cytoplasm
- locomotion & ingestion in protozoa & other ameboid cells (e.g. leukocytes)
- Exist in several forms.
filipodia
thin extensions containing only ectoplasm
reticulopodia
Ørepeatedly rejoin to form net-like mesh
Axopodia
Øsupported by axial rods of microtubules
protozoans are categorize into 2 groups for nutrition type
1) autotroph
2) heterotrophs
Autotrophs
Synthesize own organic molecules
Heterotrophs
must obtain organic molecules from others
•heterotrophs either ingest visible food particles via phagocytosis (phagotrophs/holozoic feeders) or ingest food in soluble form (osmotrophs/saprozoic feeders).
Excretion & osmoregulation of protozoans
•taken care of by contractile vacuoles.
Ø usually in ectoplasm, act as pumps
Reproduction of protozoans
They can reproduce either asexually or sexually
Asexual reproduction
•cell multiplication producing genetically identical individuals via fission
Ø binary fission most common
multiple fission are called …
schizogony
Sexual reproduction
•all protozoans reproduce asexually but there can still be genetic recombinant
Ø sexual processes may proceed asexual processes but embryos do not result
synagmy
•fertilization of 1 individual gamete by another
Ø but not all protozoans produce gametes
Autogamy
•gametic nuclei result from meiosis & fuse to form a zygote within the same individual
conjugation
•exchange of gametic nuclei occurs between paired organisms
Encystment & excystment of protozoans ?
•ability to form cysts
Ø dormant forms with resistant covering
Ø arrested metabolism
- also important to many parasitic forms for transmission
• triggered by environmental conditions in free-living species
•excystment triggered by return to favourable conditions
Ø specific host cues stimulate parasitic excystment
Heterokont
2 different flagella located at anterior end
