Kingdom Protoctista (Protista) - Theory & Question Answers

 Biology XI Notes - Kingdom Protoctista (Protista) - Theory & Question Answers

KINGDOM PROTOCTISTA (PROTISTA)

This kingdom includes all the unicellular eukaryotic organisms, which are no longer classified as animals, plants, or fungi, e.g., Euglena, Paramecium, etc. Multi-cellular algae and primitive fungi have also been included.

DIVERSITY AMONG PROTISTA (PROTOCTISTA): Due to diversification, this kingdom is regarded as a polyphyletic group of organisms. The kingdom is divided into three groups:

• Plant-like prototists: Algae
• Fungi-like prototists: Primitive fungi
• Animal-like prototists: Protozoa

PLANT LIKE PROTOCTISTS: ALGAE (CHLORELLA AND ULVA):

Algae are responsible for more than half of the amount of photosynthesis carried out in the world. Algae ranges from unicellular to filamentous and to huge multicellular structure.

Chlorella:

Introduction: It is plant-like prototist and grows in fresh water and usually floats in stagnant water of ponds, pools, ditches, etc. It is easily cultured.

Structure: Chlorella is single-celled, spherical, and solitary. The cell is surrounded by a cell wall. The body comprises a single nucleus and cup-shaped chloroplast. Pyrenoid is usually absent.

Reproduction: Chlorella reproduces asexually by autospores. The protoplast divides into 8 to 16 daughter protoplasts and develops a wall to produce non-motile autospores. After maturation, the autospores are released from the parent body. Each autospore develops into a new Chlorella.

Economic Importance:

• Chlorella cells have very high food value. They contain about 50% proteins, 20% fats, and 20% carbohydrates, amino acids, and vitamins; therefore, they are considered an alternative source of food.
• An antibiotic, chlorellin, is produced from Chlorella, which is useful for controlling bacterial diseases.
• Chlorella is an experimental organism in research of photosynthesis as it can be grown easily.

Ulva:

Introduction: Ulva is commonly known as Sea-lettuce. It is marine algae and grows between the low and high tides in Pakistan. It is found in Kemari and Manora coast. Sometimes, Ulva attaches with the rocky edges of the coast.

Structure: The plant body of Ulva is called the thallus (root, stem, and leaves are not distinguishable), which consists of erect, broad, sheet-like branches or blades. At the base of the plant, long thread-like cells are present, called holdfast, which helps in attachment with rocks bordering the tide pools. The thickness of the thallus is only two cells. Only the outer surface of Ulva is exposed to the aquatic environment. The thallus of Ulva has two types:

• Sporophyte having 26 chromosomes.
• Gametophyte having 13 chromosomes.

Morphologically, both are exactly similar, so termed as isomorphic.

Life Cycle Of Ulva: Ulva completes its life cycle in two phases. Ulva shows isomorphic alternation of generation.

Asexual Phase: Asexual reproduction takes place in diploid sporophyte plants. The spores are formed in all cells of the thallus except basal cells by meiosis. In each parent cell, 8-16 haploid zoospores are produced, which are quadriflagellated. The formation of spores is continuous until all the cells are used and nothing remains of the thallus. The liberation of spores takes place due to the incoming tides. The zoospores swim in water and lose their flagella and grow into new haploid Ulva plants.

Sexual Phase: In Ulva, sexual reproduction takes place in gametophyte plants. Sexual phase is isogamous. The haploid Ulva thallus produces the haploid gametes by mitosis. Gamete is smaller than the zoospores and biflagellate. The fusion of two haploid gametes results in the formation of a quadriflagellated diploid zygote. It loses its flagella after a period of swimming and secretes a wall, which develops into a new diploid sporophyte plant.

Alternation Of Generation Of Ulva: Ulva has distinct isomorphic alternation of generation. In the life cycle, Ulva has two morphologically identical generations. One produces gametes and is called the gametophyte, the second produces zoo spores and is called the sporophyte. They alternate to each other. The gametophyte is haploid (n) with 13 chromosomes. Zygote formed by the fusion of gametes has 26 chromosomes. This is called diploid or ‘2n’ zygote. Zygote develops into diploid (2n) gametophyte.

Euglena:

Introduction: Euglena is unicellular algae that is advanced compared to blue-green algae. It is typical algae and has both plant and animal characteristics.

• Plant-Like Characters:

  • Euglena has chloroplast.
  • It performs photosynthesis.

• Animal-Like Characters:

  • Euglena has a mouth, gullet, and flagella.
  • The body is surrounded by a pellicle.

Structure: Euglena is microscopic and spindle-shaped. The cell of Euglena is surrounded by a pellicle, and the cell cytoplasm is divided into two parts. The outer part is called ectoplasm, and the inner part is called endoplasm. The cell cytoplasm contains a plate-like structure called chloroplast, which has chlorophyll. It performs photosynthesis. The center part of the cell has a nucleus. The mouth is present at an interior part of the cell, which is open into a tube called cytostome. At the base of the cytostome, a large reservoir is present, which contains a contractile vacuole. A red color eye spot is present near the reservoir.

• Movement:
  Euglena has a long flagellum that arises from the mouth. It helps in the movement of Euglena.

• Reproduction:
  Euglena has asexual reproduction. During reproduction, the cell of Euglena simply divides by fission, and two Euglena are produced.

FUNGI LIKE PROTOCTISTA (SLIME MOLD, WATER MOLD):

Slime Mold: Slime molds are fungi-like prototists. They form a special group of organisms, which are animal-like in their body structure and plant-like in their reproduction. They are creeping multinucleated masses of cytoplasm, which look like egg white.

• Habitat:
  They grow rapidly up to one foot in damp and shady places, crawl over the grass, decaying leaves, old and rotten logs of wood. They have saprophytic nutrition because they lack chlorophyll.

• Structure:
  The body of the slime mold consists of an irregularly shaped mass of protoplasm, which is naked because a proper body wall is absent. The naked protoplasm is bounded by a non-cellular, thin, and flexible slimy layer. Due to the presence of the slimy layer, it is termed as slime mold. The protoplasm in slime layer contains plasma membrane, and cytoplasm is divided into outer ectoplasm and inner endoplasm. Slime mold has no proper shape and size.

Life Cycle Of Slime Mold: The life cycle of slime mold consists of the following stages:

1. Plasmodium Stage:
   The plasmodium consists of cytoplasm with numerous nuclei, food vacuoles, and undigested food particles. It occupies several square centimeters and looks like a creeping mass resembling a large amoeba, engulfing and digesting bacteria. The life cycle of the slime mold is completed in two phases:

   • Asexual phase.
   • Sexual phase.

2. Asexual Phase:
   In dry and warm weather, the plasmodium changes into clusters of fruiting bodies, which vary in shape and color, e.g., small golf balls, feathers, or worms. Part of each fruiting body produces a large number of spores, which are microscopic, asexual reproductive cells having a single nucleus and thick protective wall. The spores may remain inactive for a long time or may germinate soon, producing one or more tiny cells having a pair of flagella. Plenty of water and suitable temperature are required for spore germination. Slime mold resembles fungi in that they show fruiting and thick-walled spores.

Sexual Reproduction: The flagellated cells function as sex cells (gametes) and fuse together. Although the gametes are identical in structure, slime mold shows true sexual reproduction. The fusion of gametes results in the formation of cells which become amoeboid and form a new plasmodium which is multinucleated.

Water Molds (Oomycotes) Phytophthora: Phytophthora infestans is an example of a water mold. It is a pathogenic organism causing late blight in potatoes.

• Structure:
  The body of Phytophthora is known as mycelium. It is branched in nature and composed of many thread-like structures called hyphae. The mycelium is unseptate or coenocytic. The mycelium is either intercellular or intracellular and absorbs food material from host cells by haustoria.

• Reproduction:
  Phytophthora has two types of reproduction.

  • Asexual Reproduction:
    In asexual reproduction, zoospores are produced in reproductive organs called sporangia. At the time of reproduction, many erect branches arise from the mycelium called sporangiophores. They come out from the stomata of lower epidermis of host leaves. They produce more branches at the tips of which oval or lemon-shaped sporangia are formed. Many sporangia are produced due to continuous growth. A small papilla is developed at the anterior end of each sporangium. After maturation, the sporangia are scattered by wind or rain splash to different places. Further development of sporangia occurs in two ways depending upon the conditions.

    • In Dry Condition:
      In dry seasons at high temperatures, the sporangia germinate directly into a germ tube, which forms new mycelium.

    • In Moist Conditions:
      In moist conditions at low temperatures, each sporangium produces eight biflagellate zoospores. After maturation, it ruptures at the point of the papilla, and the spores are liberated. The zoospores swim for some time with the help of flagella in rain or dew drops on the leaves of the host plant. Afterwards, they lose their flagella and develop a thick wall around themselves. During favorable conditions, each zoospore forms a germ tube. It enters the host leaf through stomata or cuticle and produces a new mycelium of the Phytophthora.

  • Sexual Reproduction:
    In Phytophthora, the sexual reproduction is oogamous type. In this method, two entirely different types of male and female reproductive organs are produced. The male reproductive organ is called antheridium, and the female reproductive organ is known as oogonium. Both of them may develop on the same hypha or on two adjacent hyphae. The oogonial hypha penetrates the antheridium, where the male and female nuclei fuse. After fertilization, the thick-walled oospore develops. Sometimes parthenospores are developed without fertilization. The oospore germinates with a germ tube which develops into mycelium. Reduction division occurs during the germination of the oospore.

Animal-Like Protists: Phylum Protozoa:

General Characteristics:

• This group contains about 50,000 species.
• Protozoans are small, usually microscopic unicellular organisms that were previously regarded as animals.
• The cell mostly contains one nucleus, but in some, two nuclei are also present, which may be similar (monomorphic) or dissimilar (dimorphic).
• Some of the protozoans are multinucleated.
• Some of the species occur independently (solitary), whereas some form loose colonies in which individuals are all alike.
• Asexual reproduction takes place by fission and budding.
• Sexual reproduction occurs by the conjugation of adults or by the fusion of gametes.
• They are aquatic and are found in both fresh and marine water.
• Parasitic or symbiotic protozoans are found over or inside animals and plants.
• Respiration mostly occurs through the general body surface.
• Some of them have constant body shapes, whereas some change their shape constantly.

Classification Of Protozoa:
According to their mode of locomotion, protozoans are divided into five classes.

1. Class Flagellata:
   Characteristics:

   • The class is so named because its members contain one or more whip-like structures - flagella.
   • Some of them contain plastids, containing chlorophyll; hence these flagellates are called phytoflagellates.
   • The phytoflagellates feed autotrophically.
   • The flagellates which do not contain chloroplasts and chromatophores feed heterotrophically and are called zooflagellates.
   • Body (cell) contains only one nucleus. Example: Euglena.

2. Class Sarcodina:
   Characteristics:

   • Members of this class have no specific organs for locomotion.
   • They move through cytoplasmic projections called pseudopodia.
   • They have no constant body shape.
   • Body (cell) contains only one nucleus.
   • Some parasitic species e.g., Entamoeba histolytica cause disease of dysentery in humans.
   • Certain shelled sarcodines have deposited millions of skeletons under sea which give clues about possible petroleum deposits. Example: Amoeba.

3. Class Ciliata:
   Characteristics:

   • Members of this class contain cilia all over the body for locomotion.
   • Nearly all the ciliates are free-living.
   • Ciliates contain two types of nuclei: A macronucleus and from one to as many as 80 micronuclei.
   • The large macronucleus controls everyday activities.
   • The small micro-nuclei function in sexual reproduction.
   • Many of them contain a groove called gullet through which engulfing of food takes place. Example: Paramecium.

4. Class Suctoria:
   Characteristics:

   • Suctorians also contain two types of nuclei. The meganucles and micronucles.
   • Young individuals have cilia and are motile whereas adults have no cilia and are sedentary.
   • Body bears tentacles.
   • In some have tentacles are pointed to pierce the prey. Some have adhesive knobs to catch and hold the prey.
   • Reproduction is asexual by budding. Example: Acineta.

5. Class Sporozoa:
   Characteristics:

• This class contains exclusively parasitic forms.
• They occur both as intra and inter-cellular parasites.
• Some of them cause serious diseases Coccidiasis and malaria in poultry and man respectively.
• Sporozoans do not have any locomotory organelles. Example: Plasmodium.

Life Cycle Of Malaria Parasite: Plasmodium

Discovery Of Plasmodium:
Plasmodium is a unicellular protozoan which is the causative agent of malaria. It is first discovered by Laveran in 1878 in the blood of a malarial patient. Later on, Ronald Ross discovered the presence of plasmodium inside the stomach of the female Anopheles mosquito in 1897. After that, in 1898, Grassi discovered the life cycle of plasmodium inside the female Anopheles mosquito.

The parasite of malaria, plasmodium, completes its life cycle in two hosts: man being the secondary host involving asexual cycle (Schizogony) and Anopheles mosquito being the primary host involving sexual cycle (Gametogony).

Asexual Cycle In Man - Schizogony:
While biting a healthy person, an Anopheles mosquito inoculates its saliva to check blood clotting. Along with its saliva, sporozoites of plasmodium also enter the body. Schizogony comprises the following stages:

• Pre-erythrocytic Cycle
• Erythrocytic Cycle
• Post-erythrocytic Cycle

Pre-erythrocytic Cycle:
It is completed in the following stages:

• Sporozoites:
  When the infected female Anopheles mosquito bites a healthy person, it transfers the plasmodium in man. This stage of plasmodium is known as sporozoite. Once within the human blood, the sporozoites circulate for about half an hour and then get into the liver to invade the hepatic cells.

• Schizont:
  After penetrating the hepatic cells, each sporozoite grows for a number of days by absorbing food material and becomes a large, rounded shape structure called schizont.

Cryptozoites:
After that, the nucleus of schizont divided and produces uninucleated cryptozoites which are liberated and invade other healthy hepatocytes.

Meta Cryptozoites:
The cryptozoites invade other fresh liver cells and multiply, producing an enormous number of meta-cryptozoites after repetition of the pre-erythrocytic phase.

Erythrocytic Cycle:
This phase is completed into the following stages:

• Trophozoite:
  Meta cryptozoites leave the hepatocytes and invade the R.B.C (red blood cells) after escaping into the bloodstream. Each meta cryptozoite absorbs the food material from the R.B.C and becomes a rounded-shaped structure called trophozoite.

• Signet Ring Stage:
  When the trophozoite grows in size, the nucleus is pushed to one side into the peripheral cytoplasm. It resembles a signet ring and is referred to as the signet ring stage.

• Amoeboid Trophozoite:
  After that, trophozoite becomes irregular in shape, and pseudopodia-like structures are produced. It ingests the hemoglobin of R.B.C and converts it into a poisonous substance called haemozoin. After active feeding, it becomes rounded, grows in size, and becomes a schizont.

• Merozoites:
  The nucleus of trophozoite divides and produces 10-12 nuclei which convert into merozoites. With the rupture of RBC, the merozoites are liberated into the blood plasma. The poisonous substance haemozoin is also released with the merozoites, causing the symptoms of malaria. The merozoites again invade the fresh RBC to repeat the cycle. The time taken to complete one erythrocytic cycle depends upon the species of plasmodium.

Post Erythrocytic Cycle:
Some merozoites repeated the erythrocytic phase and reached the liver cells, undergoing schizoid development. This is known as the post-erythrocytic cycle.

Sexual Phase: (Gametogony)
When successful asexual multiplication is achieved, the merozoites do not proceed further with the erythrocytic phase but after entering the RBC increase in size to become gametocytes.

Types Of Gametocytes:
Merozoites convert into two types of gametocytes:

• Male or microgametocyte.
• Female or macrogametocyte.

The gametocytes do not divide, but remain within their host blood until they are ingested by the anopheles mosquito in which they continue their development.

Sexual Cycle in Mosquito:
The sexual cycle of plasmodium is completed in the gut of the female anopheles mosquito. This cycle is completed in the following stages.

Gametogony:
The gametocytes are taken up along with the blood into the stomach of the mosquito. The female gametocytes soon become macrogametes by absorbing food and getting ready to be fertilized. Each male gametocyte forms 6 to 8 male sperm-like microgametes by a process of exflagellation.

Conjugation or Syngamy:
The two gametes of opposite sexes fuse together to form a zygote. The process is called syngamy. The zygote becomes worm-like ookinete. It penetrates into the stomach wall to settle down just under the mid-gut. Here, after absorbing nutrients, it becomes rounded and encysts to form the oocyst.

Sporogony:
After 6 to 7 days, the sporogony takes place, which is completed in the following stages.

Formation of Sporozoites:
The oocyst absorbs the food from the wall of the stomach and enlarges in size. After that, the nucleus is divided into 10,000 nuclei, which change into spindle-like sporozoites very soon.

Liberation of Sporozoites:
When the blister of the sporoblast is ruptured, all the sporozoites come into the haemolymph (blood) of the mosquito and reach the salivary gland through the blood. Due to the bite of the mosquito, sporozoites enter the blood system of a healthy person, causing malaria, and this cycle is repeated again.

Symptoms of Malaria:
The symptoms of malaria first appear when infected R.B.C.s are broken. The time taken by the parasite from its entry into the man up to the breaking down of R.B.C.s is called the incubation period. The symptoms that appear in this period of infection include fever, nausea, loss of appetite, constipation, and insomnia. Soon, headache, muscular pains, and aches in the joints develop, followed by chills.

At the onset of malarial fever, the patient suffers from shaking chills and sweating. The body temperature may rise as high as 106°F. After a few hours of fever, there is profuse sweating, and finally, the fever disappears. The recurrence of symptoms usually occurs after 48 hours or sometimes earlier.