1 RESUMEN
4.2 Liderazgo Educacional: Concepto, tipos, características de cada tipo
There is no cellulose wall. The cell is bounded by a cell membrane called a pellicle or periplast. The pellicle is flexible and elastic and this enables the cell shape to change euglenoid movement'.
Gullet and Contractile Vacuole
The organism has a flask-shaped invaginatoin at the anterior region known as the gullet. The gullet consists of an enlarged reservior and a narrow cytopharynx which is concerned with ingestion of solid food particles.
A contractile vacuole is located near the reservior. The vacuole empties into the reservoir and a new contractile vacuole is formed from smaller vacuoles. The contractile vacuoles have an osmoregulatory functions.
Flagellum
It is a whip-like structure located at the posterior end of the reservoir and passes through the cytopharynx.
plasma membrane contractile vacuole pyrcnoid
striations of pellicle nucleus chloroplast flagella sac
flagellum
front end
Euglenoid movement 1-5: A succession of characteristic shapes.
cyc spot gullet
It is used for locomotion.
Stigma or eyespot
It
is a light-sensitive spot situated near the base of the flagellum, which enables the organism to sense and move towards light needed for photosynthesis. When it encounters an unfavourable stimulus, it moves quickly away from it.
Chloroplast
Euglena contains the photosynthesis pigment of coloured euglenoids. The colour of Euglena is due to the presence of chlorophyll in its stellate chloroplasts which absorb energy from sun light.
Nucleus
The nucleus is oval and found either in the centre or at one side of the endoplasm (plasmasol). It is used for reproduction (longitudinal binary fission).
Figure 5.5: Structure of Euglena
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ACtnity 10
la. Make a large, labelled diagram of the Euglena
b. State one function each of the following organelles found in an Euglena cell:
i. chloroplast Eyespot iii. Flagellum
3.2.4 Nutrition in Euglena
Nutrition in Euglena is very interesting. Let us now go through the details of how Euglena obtains its food.
* The mode of nutrition is similar to what obtains in green plants due to the presence of chloroplasts with which Euglena manufactures its food.
By means of chloroplyll contained within chloroplasts, Euglena makes use of its surrounding water, sunlight and dissolved carbon dioxide to manufacture carbohydrates
Protozoa 41
* 'Oxygen is given out as by product.
* Although Euglena is capable of photosynthesis, all species of Euglena require some organic materials from the water in which they live, i.e. they are heterotrophic. A few species can live saprophytically in darkness e.g. Euglena gracidis. Generally, however, starch is stored in the paramylum granules and in pyrenoids.
3.2.5 Movement in Euglena (Euglenoid movements)
- Euglena can creep over surfaces as well as swim with the aid of its flagellum.
- Creeping involves marked changes in shape, known as (euglenoid movements).
- Swimming is achieved by the undulations of the flagellum.
- The beating of the flagellum is intrinsic (it will continue lashing when removed from the organism, as long as ATP is available).
It is usually held in front or at the side of the swimming cells, causing the cell to rotate and describe a spiral path as it is pulled r irward through the water
3.2.6 Reproduction in Euglena
The only form of reproduction in Euglena is asexual.
This is by longitudinal divison of the whole animal.
The nucleus and the cytoplasm divide into two longitudinal unequal halves One of the halves goes with the flagellum.
The other half grows a new flagellum.
Under unfavourable conditions Euglena may form cysts.
The protoplasmic contents contrast and are enclosed in a thick cyst to resist adverse conditions.
The contents of the cysts divide to form numerous young Euglena, which are liberated and they grow to be adults.
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List 8 processes involved in the reproduction of Euglena.
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In the two organisms discussed, there are no organs or tissues to carry out the activity of life. However, there is some degree of specialisation and differentiation of the cell protoplasm into organelles to carry out different functions in the two organisms and in the members of the group that they represent. Their study therefore, help us to know the evolutionary trend of the organisms.
5,11
In this unit, you have learned that;
1. Protozoans are microscopic and unicellular in nature 2. They belong to the kingdom protista.
3. Some are free-living (e.g. Amoeba proteus) while others are parasitic (e.g. Plasmodium, Entamoeba histolytica and Trypanosoma).
4. Typical examples include Amoeba, Paramecium, Euglena, and Plasmodium.
5. Asexual reproduction is by Binary fission and sexual reproduction is by gametic fusion and conjugation.
6. Amoeba belongs to the class Rhizopoda.
7. Euglena possesses both plant and animal features. The features of plants include the presence of chloroplasts and pyrenoids while those of animals include the presence of eyespot and pellicle.
I a. Make a large, labelled diagram of the Euglena.
b. State one plant like and one animal-like characteristics ofEuglena.
2. Describe the process of movement inArnoeba.
Further Reading'and other Rcsourter:
Idodo - Umeh (1996) College Biology, Idodo - Umeh Publishers Ltd., Benin City Sarojini T. Ramalingam (1993). Modern Biology Africana-Feb Publishers, Benin City.
A video clip of Amoeba demonstrating its structure, movement and feeding. A NOUN Production
Volume 1: Basic Concepts in Biology
Page
1.0 Introduction 44
2.0 Objectives 44
3.0 Structure of Paramecium 44
3.1 Feeding in Paramecium 45
3.2 Respiration in Paramecium 45
3.3 Excretion and Osmoregulation in Paramecium 46
3.4 Movement in Paramecium 46
3.5 Reproduction in Paramecium 47
3.6 Hydra 48
4.0 Conclusion 51
5.0 Summary 51
6.0 Tutor-Marked Assignment 52
7.0 Further Readings and other Resources 52
43
Paramecium belongs to the class ciliophora (ciliata) in the Phylum Protozoa.
It is found in pond water and streams containing decaying matter
It is a unicellular organism, however, its body is more complex than that of theAmoeba.
By the end of this unit, you should be able to;
i. describe Paramecium and its structure.
ii. explain the type of feeding in Paramecium.
iii. discuss respiration in Paramecium in comparison with Amoeba.
iv. summarise excretion, movement and reproduction in Paramecium.
v. state the economic and biological importance of protozoans.
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Lets have a run down of the distinguishing features of a Paramecium using (Fig. 6.1)
• It is slipper-shaped, with pointed and blunt ends.
• The blunt end is the anterior end while the pointed end is the posterior end.
• The whole body is protected by stiff and firm covering called the pellicle, which gives it shape
• The entire body is covered with cilia, which are used for locomotion, selection of food materials and also for wafting food into the gullet.
• The inside of the pellicle is lined with thread-like structures called trichocysts.
• Trichocysts are very sensitive. They serve as a means of defense as well as for anchorage.
• The protoplasm, found underneath the pellicle is divided into two, the dense thick ectoplasm and amore fluid endoplasm.
• The endoplasm contains the two nuclei, the contractile vacuoles and many food vacuoles.
• The large meganucleus controls digestion and excretion while the small micronucleus controls reproduction.
The two contractile vacuoles have radial canals that collects fluid and discharge same into the vacuole.
From the vacuole, the fluid is discharged through the surface to the surrounding water.
There is a wide shallow opening called the oral groove (mouth) on the ventral surface of the organism.
The groove leads into a tube called the gullet, at the base of which is a cytostome. These structures help in feeding. ,
Food enters through the oral groove, passes through the gullet and forms an oval food vacuole at the end of the gullet.
• The food vacuoles serve as food reservoir.
• The cilia are delicate extension of the ectoplasm. Each contains fibrils.
Paramecium, Biological and Economic importances of Protozoa 45
FRONT END
anterior contractile vacuole
large nucleus (mega-)
small nucleus (micro-)
food vacuole
canals of posterior contractile vacuole
tricho cysts Figure 6.1
REAR END
pellicle
outer cytoplasm (Endoplasm)
inner cytoplasm (Endoplasm)
oral groove
funnel-like end of oral groove
cilia at base of oral groove bacteria in food vacuole forming at cell mouth
supporting role of cell pharynx anal pore