Ciliophora (Ciliates) PDF

Ciliophora (Ciliates) They are heterotrophic unicellular protists Most members have numerous cilia and vary in sizes Most unique feature (cilia) are arranged longitudinally or in spirals on the organisms Cilia are anchored to microtubules beneath the cell membrane Cilia beat in a c...

Ciliophora (Ciliates) They are heterotrophic unicellular protists Most members have numerous cilia and vary in sizes Most unique feature (cilia) are arranged longitudinally or in spirals on the organisms Cilia are anchored to microtubules beneath the cell membrane Cilia beat in a coordinated fashion to produce motion and also used for feeding when modif ied into mouth parts Have tough but flexible outer covering - pellicle Fig. 1 Morphology of Paramecium Ciliates have micronuclei and macronuclei Micronuclei have diploid chromosomes divide by meiosis undergo genetic recombination Macronuclei are derived from micronuclei have multiple copies of genome with DNA divided into small pieces divide by elongation and constriction Also involve in routine cell functions eg mRNA production for protein synthesis, growth and regeneration Ciliates form vacuoles for ingesting food and regulating water balance Feeding During feeding, food enters the gullet lined with cilia From the gullet to the food vacuoles where enzymes, hydrochloric acid digest the food The digested material is absorbed and the food vacuole empties its waste through the cytoproct Cytoproct is an exocytotic vesicle that appears periodically for waste removal Reproduction Ciliates reproduce by transverse f is sion of parent cell to give two identical cells (Protor and Opisthe) Both micro and macronuclei also divide In Paramecium the cells divide for up to 700 gen eration s before dyin g if n o sexu al reproduction Sexual reproduction (conjugation) also occurs in Paramecium Two individuals of different genetic make ups conjugate Meiosis in the micronuclei produce many haploid nuclei that are exchanged via a cytoplasmic bridge New micron u clei fu ses w ith existin g on e to produce new diploid micronuclei in each individual After conjugation macronucleus disintegrates New mic ron u c leu s t h en u n derg oes mitosis producing identical micronuclei in each cell One of the micronuclei remains micronucleus while the other develops into macronuclei after DNA replication – unique feature Progeny from sexual division in Paramecium must undergo about 50 asexual divisions before they can conjugate. After about 600 asexual reproductions Paramecium loses the protein molecule around the gullet that help it recognise mates Hence death ensues subsequently (generations later) Fig. 2: Conjugation in Paramecium NON MOTILE SPORE FORMERS Apicomplexa (Sporozoans) They are non motile spore forming parasites of animals Spores are small infective bodies and transmitted from host to host They are distinguished by unique arrangement of fibrils, microtubules, vacuoles and other organelles at one end of the cell Key member of this group is the Plasmodium Four species of human Plasmodium namely;  P. falciparum  P. malariae  P. ovale  P. vivax Sporozoans have complex life cycles with sexual and asexual reproduction Sexual reproduction involves fertilisation of large female gamete by small f lagellated male gamete, resulting zygote becomes an oocyst Within the oocyst meiotic divisions give rise to haploid spores – sporozoites Sporozoans ( Plasmodium ) are spread by the Anopheles mosquito from person to person When the mosquito bites a person to suck blood, it injects saliva mixed with anticoagulant It also inject the sporozoites into the person’s blood stream The parasite makes its way to the liver and quickly divide asexually After the division merozoites are formed invading more liver cells and spreading in the blood stream In the blood stream red blood cells are attacked making them enlarged and even rupture Release of toxic substances from this activity leads to the cycle of fever and chills experienced by the victim The cycle repeats every 48hrs , 72 hrs or more Plasmodium enters sexual reproduction when merozoites form gametocytes –cells capable of producing gametes Game t o c yt e s o n ly p ro d u c e g ame t e s in t h e mosquitoes outside their human hosts In the gut of the mosquito the male and female gametocyte form sperm and egg cells They unite and forms zygote in the gut which eventually differentiate into oocysts Mitotic division produce many sporozoites within the oocyts Oocysts then migrate to the salivary gland of the vector and further into the victim Plasmodium causes the disease Malaria Millions of people are infected and die of the disease (mostly children) -WHO Fig 3: Life cycle of Plasmodium Control Strains resistant to insecticides (DDT) emerged reducing possibility of eliminating vector Environmental concerns due to use of DDT also arose Strains of plasmodium resistant to early drugs have also appeared leading to more people infected In terms of vaccination efforts are underway to produce an effective one against the disease Three different stages of the life cycle produce three different antigens sensitive to different antibodies  Symptoms of malaria include sweating, chills, fever, enlarged and tender spleen and sometimes restlessness Death may result from anaemia, kidney failure and brain damage Disease may be brought under control by the immune system or drugs Some persons may be genetically resistant to malaria, others may develop immunity to it Efforts to eradicate the disease include  Elimination of the vector  Production of drugs to kill the parasite in the body  Development of vaccines PARAZOANS THE SPONGES (Phylum – Porifera) Sponges are complex multicellular parazoans They lack tissues, organs and definite symmetry Body is made up of different cells that are loosely coordinated with each other Both marine and freshwater species exist with a range of sizes Most sponges are colonial Some have low encrusting form while others are erect and bilobed Adults are sessile while larvae are mainly free living They have special cells called choanocytes/collar cells Chaonocytes line the entire body cavity or as seen in special chambers The body of the sponge is bounded by f lattened epithelial cells Some parts of the epithelia may contract when touched making pores to close There is a gelatinous protein rich layer called Mesohyl between the chaonocyte layer and the epithelia The mesohyl acts as a type of endoskeleton, helping to maintain the tubular shape of sponges. Amoeboid cells are found within the mesohyl Sponges also have calcium carbonate needles or spicules  Some have f ibre made up of tough protein called spongin Spicule or spongin give rigidity to the body of the sponge FEEDING Beating of flagella draws water in via many pores Plankton/small organism are f il tered from the water which leave through the osculum Chaonocyte It resembles a protist and has a flagellum The beating of the f lagella of many chaonocytes draws in water through pores  The action brings in food, oxygen and removes waste products Each f lagellum beat independently but collectively c reat e pressu re t h at forc e w at er ou t of t h e osculum REPRODUCTION Sponges reproduce asexually by fragmentation Sexual reproduction is also exhibited by sponges by fusion of egg and sperm cells Larval sponges are mainly free swimming and settle on suitable substrate into adult life Fig 1. Anatomy of the sponge and chaonocytes