kingdom protista

Question 1

what are protists?

Answer 1

• all unicellular eukaryotes come under protista in the Whitakers system
• the term Protista was coined by Ernest Haeckel
• ancestors of all multicellular eukaryotes

Question 2

what are the 3 types of protistans based on nutrition?

Answer 2

Unicellular protists have been broadly divided into three major groups :
(1)Photosynthetic protists : e.g., dinoflagellates, diatoms, euglenoids.

(2) Consumer protists : e.g., slime moulds or myxomycetes.
(3) Protozoan protists : e.g., zooflagellata, sarcodina, sporozoa, ciliata.

Question 3

what are the general characters of protists?

Answer 3

(1) colonial without much cellular differentiation. tissue-level organisation is absent
(2) body structure is eukaryotic type, may have a cellulosic cell wall
(3) mostly aquatic.
(4) flagella and cilia have (9+2) organisation made up of tubulin protein
(5) movement by pseudopodia, flagella or cilia, where cilia are the fastest.
(6) It may be photosynthetic, holotropic, saprotrophic, parasitic and symbionts. Some have mixotrophic nutrition (holotropic + saprobic). The photosynthetic, floating protists are collectively called phytoplankton. The free-floating, holozoic protozoans are collectively termed zooplankton.
(7) Protists reproduce asexually and sexually by a process involving cell fusion and zygote formation.
(8) they have two types of life cycle,i.e zygotic meiosis and gametic meiosis
(9) the parasitic ones cause diseases like sleeping sickness, malaria, dysentery etc.

Question 4

explain CHRYSOPHYTES?

Answer 4

(1) This group includes diatoms and desmids( golden algae ).
(2) They are found in freshwater mostly and few in marine environments.
(3) They are microscopic and float passively in water currents (pytoplankton) due to the presence of lightweight lipids. lacks flagella except in the reproductive phase.
4) The reserve food material is oil and a polysaccharide called chrysolaminarin (or leucosin). and vlutin maybe
5) In diatoms, the cell walls form two thin overlapping shells(epitheca over hypotheca), which fit together as in a soapbox.
6) The walls are embedded with silica to form a transparent siliceous shell called frustule thus, the walls are indestructible.
7) responsible for 50% of organic matter produced in the biosphere
8) Diatoms are the chief ‘producers’ in the oceans.
eg: cymbella vaciulla , melosira,triceratium

Question 5

what are diatomaceous earth’.?

Answer 5

diatoms have left behind large amounts of cell wall deposits in their habitat; this accumulation over billions of years is referred to as ‘diatomaceous earth’/diatommites /kieselguhr. Being gritty, this soil is used in polishing, filtration of oils and syrups and in the brewery industry.

Question 6

what si stratosphere?

Answer 6

resting spore especially, a thick-walled resistant spore formed within the frustules of various chiefly marine centric diatoms.

Question 7

How are diatoms good indicators of water pollution?

Answer 7

Diatom species in waters considered unimpaired were largely made up of surface-attached species; Diatoms in water considered impaired were motile — having the ability to move.

Question 8

explain nutrition in diatoms?

Answer 8

– holophytic or photoautotrophic

• -photosynthetic pigments:
• chlorophyll a
• chlorophyll c
• beta carotene
• special carotene containing fucoxanthin
• diadinoxanthin
• diatoxanthin
• xanthophyll

Question 9

explain reproduction in diatoms?

Answer 9

• asexual methode in diatoms is binary fission
• sexual methods in diatoms are : 1)isogame,2)oogamy 3)anisogamy
• gametic meiosis as their generally diploid
• zygote formed during sexual reproduction of diatoms are called auxospores.

Question 10

what is oogamy?

Answer 10

Oogamy is the type of sexual reproduction in which male gamete is small and vigorously motile while female gamete is large and either non-motile or movement is less. This is found in all the higher plants as well as animals.

Question 11

what is isogamy?

Answer 11

Isogamy is a form of sexual reproduction that involves gametes of similar morphology, found in most unicellular organisms. Because both gametes look alike, they generally cannot be classified as male or female.

Question 12

what is anisogamy?

Answer 12

Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form.

Question 13

explain dinoflagellates?

Answer 13

• golden brown photosynthetic protists
• class: Dinophycea
• includes gonyaulax
• unicellular, motile and biflagellated
• some marine Dinoflagellates show bioluminescence and due to phosphorescence, the sea glows at night.eg: noctiluca,pyrodinium , Pyrocystis
• These organisms are mostly marine and photosynthetic.some are freshwater forms
• They appear yellow, green, brown, blue or red depending on the main pigments present in their cells. The cell wall has stiff cellulose plates on the outer surface.
• they release a toxin called saxitoxin which is poisonous to vertebrates. marine shell fishes consume dinoflagellates and the toxin accumulates in them, but the toxin does not hurt the shellfish. if humans consume this shellfish, it causes severe illnesses like Paralytic shellfish poisoning(PSP)
• The reserve food material is starch in freshwater forms and oil in marine forms.

Question 14

what causes red tides?

Answer 14

Very often, red dinoflagellates (Example: Gonyaulax,gymnodinium) such rapid multiplication that they make the sea appear red (red tides).

Question 15

explain reproduction in Dinoflagellates?

Answer 15

–Dinoflagellates reproduce asexually through cell division or by the formation of zoospores and cysts.

–sexual reproduction occurs, it is isogamous or anisogamous. eg:ceratium

– life cycle involves zygotic meiosis in haploids .eg:ceratium ,guanidinium, Gonyaulax

• -life cycle involves gametic meiosis in diploids
  e. g., Noctiluca,pyrodinium

Question 16

explain flagella in Dinoflagellates?

Answer 16

• -Most of them have two flagella(biflagellated):
• the flagella are heterokont
• long one lies longitudinally, smooth,narrow and is directed towards the posterior direction
• the short one is transversely arranged in a furrow between the wall plates. It’s ribbon-like.
• they are perpendicular to each other creating a spinning movement. thus these protists are called whirling whips

Question 17

why are they called armoured Dinoflagellates?

Answer 17

the body is enclosed by theca or lorica consisting of 2 to many articulated or sculptured plates of cellulose and pectin.

Question 18

explain nutrition in

Answer 18

--they are photosynthetic. they contain  the following photosynthetic pigments are:
-
-chlorophyll a
-chlorophyll c
-beta carotene
-xanthophyll

eg: peridinin

Question 19

what are euglenoids?

Answer 19

• The majority of them are freshwater organisms found in stagnant water.
• These protists are devoid of cellulose cell walls. The body is covered by a thin, flexible and elastic and they are called covering periplast or pellicle.
• reserve food material is paramylon
• An orange-red coloured eyespot or stigma is located at the base of the flagellum attached to the membrane of the reservoir at the level of the paraflagellar body. They contain a photosensitive red pigment called astaxanthin.
• Both paraflagellar bodies and eyespot act as photoreceptors and direct the organism towards the optimum light.

Question 20

explain flagella in euglenoids?

Answer 20

• both chlorophyllous and non-chlorophyllus protists
• largest genera is euglena
• single large nucleus lies near the protoplast
• They have two flagella, a short and a long one.
• the short one is present inside and does not emerge outside
• the long one is a tinsel type and emerges out of the posterior end(stichonematic type). this flagella actively beats to move the cell
• heterokont flagella
• contractile vacuole occurs at the anterior end just below the reservoir for osmoregulation and excretion
• reserve material is paramylon( chemically beta - 1 , 3- glucans)
• The two flagella join with each other at a swelling called paraflagellar body. which is a photosensitive spot(perceives light).

Question 21

explain nutrition in euglenoids?

Answer 21

–they are mixotrophic

• they are photosynthetic in the presence of sunlight,
• when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms but usually, they are saprophytic.
• Interestingly, the pigments of euglenoids are identical to those present in higher plants. Example: Euglena.
• -they contain the following photosynthetic pigments are:
• chlorophyll a
• chlorophyll c
• beta carotene
• xanthophyll

Question 22

explain reproduction in euglenoids.

Answer 22

–Sexual reproduction has not yet been definitely proved.

-Under favourable conditions, euglenoids multiply by longitudinal binary fission.

– during unfavourable conditions, organisms are covered by cysts(membrane) and palmella stage( a condition in which the cells occur in a mucilaginous mass but continue to metabolize) are formed for perennation(tide over unfavourable conditions)

Euglena is a connecting link between animals and plants

Question 23

what are myonomes?

Answer 23

-they are oblique but parallelly arranged stripes of pellicles.

• euglenoid performs creep movement of contraction and expansion with help of myonomes
• this is called euglenoid movement or metaboly

Question 24

what are slime mould?

Answer 24

• AKA consumer - decomposers
• they are free-living
• creeping of over debris
• cell wall is absent in vegetative stage
• no chlorophyll
• thy are heterotrophs

two types:

1) Acellular
2) cellular

Question 25

explain nutrition in slime moulds?

Answer 25

• -heterotrophic
• saprobic
• phagotrophic

Question 26

what does slime mould do during favourable conditions?

Answer 26

Under suitable conditions, they form an aggregation called Plasmodium which may grow and spread over several feet.

Question 27

what does slime mould do during unfavourable conditions?

Answer 27

During unfavourable conditions, the Plasmodium differentiates and forms fruiting bodies bearing spores at their tips. The spores possess true walls. They are extremely resistant and survive for many years, even under adverse conditions. The spores are dispersed by air currents.