Lec 10: The protists

Question 1

Unifying features

Answer 1

All are eukaryotic, have well defined organelles

Membrane bound nucleus & mitochondria for cellular respiration

Most are unicellular

Lack tissue organisation in higher eukaryotes

Sexual and asexual reproduction

Question 2

Diverse features

Answer 2

Diverse structure

Vary significantly in size

Widely distributed (terrestrial & aquatic environments)

Most are free living. Some: close beneficial symbiosis with other organisms, parasites of humans and animals

Diverse in nutrition: autotrophic (photosynthetic), heterotrophic (ingest food like animals), heterotrophic by absorption (absorb food like bacteria), mixotrophic (photosynthesis and ingest)

Different means of locomotion

Question 3

Asexual reproduction

Answer 3

Mature cells (haploid, N) undergo mitosis -> divide -> identical daughter cell -> released to repeat cycle

Question 4

Sexual reproduction

Answer 4

Conditions trigger gamete formation

Gametes (N) conjugate & nuclei fuse (2N) -> zygote -> divides by meiosis (genetic recombination through crossover of chromosomes) -> haploid sexually recombined individuals

Question 5

Autotrophic (photolithoautrophic)

Answer 5

Have photosynthetic pigments

Use sunlight for energy

Fix CO2 as source of carbon

Simple inorganic nutrients (N,P,S)

Plant-like ‘primary producers’ (microalgae, phytoplankton)

Question 6

Heterotrophic (chemoorganoheterotrophic)

Answer 6

‘Eat’ other organisms or organic matter -> obtain carbon and energy

Phagocytosis, pinocytosis

Animal-like ‘protozoans’

Question 7

Mixotrophic

Answer 7

Capable of both autotrophic and heterotrophic nutrition

Balance determined by environmental conditions

Question 8

Cytosome

Answer 8

Cell mouth

Region on surface of cell where endocytosis can occur

Question 9

Lysosomes

Answer 9

Vesicles

Contain digestive enzymes to break down food taken in via endocytosis

Question 10

Cilia and flagella

Answer 10

Used to sweep food towards cytosome

Question 11

Pseudopodia

Answer 11

Extensions of amoeba

Engulf food and form vesicles

Question 12

Phagocytosis

Answer 12

Particles/organisms engulfed & incorporated into food vacuoles -> fuse with lysozymes (vacuoles containing digestive enzymes) -> nutrients dissolved & absorbed -> waste excreted by exocytosis

Question 13

Pinocytosis

Answer 13

Cell drinking

Nutrients dissolved in external environment

Infolding of cell membrane traps small packets of solution containing dissolved nutrients

Question 14

Motility amongst protists

Answer 14

Non motile

Motile: flagella, cilia, pseudopodia

Question 15

Life cycle of silkworm (simple)

Answer 15

Intracellular stage (amoeboid stage): absorb over surface of amoeboid. Sits aside of cytoplasm of cell (for nutrients)

To get to next host -> gets into environment (needs to spend time in spore stage -> pass out of host -> environment)

No absorbing in spore stage. Only when enters new cell can absorb things

Question 16

Life cycle of plasmodium vivax (complex)

Answer 16

Sporozoites in salivary glands of mosquito -> bite -> inject sporozoites into bloodstream-> enter liver -> liver cells help proliferate -> produces copies of itself -> merozoites -> leave liver cells -> liver cells rupture into bloodstream-> target rbc -> proliferate in rbc -> rbc ruptures -> releasing merozoites -> affect new rbc -> cycle repeats

As cycle goes on -> gametes form (sexual stage)

When another mosquito comes along, merozoites, rbc and gametes into gut -> only gametocytes (gametes would survive)

Gametes fuse -> zygote (fertilisation) -> burrows into cell wall -> oocyst -> sporozoates -> rupture from gut structure -> make way to salivary glands -> make way to next host