MORPHOLOGY AND PHYSIOLOGY OF LIVING THINGS (INVERTEBRATES SECTION)

MORPHOLOGY AND PHYSIOLOGY OF LIVING THINGS

(INVERTEBRATES SECTION)

LECTURE NOTE

BY

OKWUOSA, OBINNA BEN

INTRODUCTION

Morphology in Biology is said to be a branch of Bioscience dealing with the study of the form and structure of organisms and their specific structural features. This study of structure includes gross morphology, which examines entire structures or systems, such as muscles or bones; histology, which examines body tissues; and cytology, which focuses on cells and their components. Many great advances made in cytology in recent years are attributable to the electron microscope and the scanning electron microscope. Special staining techniques and radioactive tracers have been used to differentiate structural detail at the molecular level. Methods have been developed for mapping neural connections between parts of the brain and for stimulating and recording impulses from specific brain sites and even individual nerve cells.

Morphology can also be said to include aspects of the outward appearance (shape, structure, colour, and pattern) as well as the form and structure of the internal parts like bones and organs. This is in contrast to physiology, which deals primarily with function. Morphology can also be said to be a branch of life science that deals with the study of gross structure of an organism or Taxon and its component parts.

BRANCHES OF MORPHOLOGY

 Experimental Morphology: This is the study of the effects of external factors upon the morphology of organisms under experimental conditions, such as the effect of genetic mutation.

 Functional Morphology: This is the study of the relationship between the structure and function of morphological features.

 Comparative Morphology: This is analysis of the patterns of the locus of structure within the body plan of an organism, and forms the basis of taxonomical categorization.

Field of morphology is divided into two distinct branches namely;

 Anatomy: This study of the form and structure of internal features of an organism.

 Eidonomy: This is the study of the form and structure of the external features of an organism.

PHYSIOLOGY

This is the branch of biology that deals with the functions and activities of living organisms and their parts, including all physical and chemical processes and the organic processes or functions in an organism or in any of its parts. It can also be defined as the scientific study of function in living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system.

Physiology, the study of function, is closely associated with morphology hence this course of study tittle. An important subdivision is cellular physiology, which is closely related to molecular biology. 

Another active field, physiological ecology, studies the physical responses of animals to their environment. Much of this work has been carried out on desert, arctic, and ocean animals that must survive extremes of temperature or pressure.

Animal behavioral studies developed along two lines. The first of these, animal psychology, is primarily concerned with physiological psychology and has traditionally concentrated on laboratory techniques such as conditioning. 

The second, ethology, had its origins in observations of animals under natural conditions, concentrating on courtship, flocking, and other social contacts. 

Both subdisciplines have recently merged in large areas of investigation, the same scientists using field and laboratory observations and incorporating many experimental techniques from neurology. 

Perhaps the most important recent development in the field is the concentration on sociobiology, which is concerned with the behavior, ecology, and evolution of social animals such as bees, ants, schooling fish, flocking birds, and humans. Sociobiology is still in its infancy and is quite controversial, chiefly because it has raised anew the old dispute about whether behavior is genetically determined.

ANIMAL

What makes an animal an animal?

If animals are a monophyletic (with common/single ancestor) taxon, then animals should be able to be defined by synapomorphies, (shared, derived characteristics). Ideally, we would NOT define this or any taxon using symplesiomorphies (shared ancestral or primitive characteristics) or homoplastic characters (the independent evolution of similarity, or "convergent evolution"). As you consider the characteristics listed below, ask yourself whether or not each is a synapomorphy.

SUMMARY OF ANIMAL CHARACTERISTICS

There is no one universally accepted definition of an animal.

Animals:

 Are multicellular, heterotrophic eukaryotes . . .

 Lack the distinctive cell walls of plants & fungi

 Share unique characteristics . . .

 Share certain reproductive characteristics . . .

 Other commonly used definitions . . .

Animals are multicellular heterotrophic eukaryotes

 Unfortunately, none of these traits is exclusive to animals:

 Plants, fungi, and some algae are multicellular.

 Many bacteria, protists, and all fungi are heterotrophic.

 Everything other than bacteria and archaea are eukaryotic.

 Moreover, all three of these characteristics also apply to fungi.

 However, there is a difference here between animals and fungi. 

Animals generally take in their food through ingestion, or eating and swallowing something. Fungi are absorptive heterotrophs; they secrete their digestive enzymes onto their food, and then absorb the resulting nutrients.

Animals share unique characteristics

 Only animals have muscle tissue and nervous tissue.

 Only animals have collagen, a structural protein

 Only animals have the following types of intercellular junctions:

 Tight junctions (sealing function)

 Desmosomes (anchoring function)

 Gap junctions (communication function)

Animals share certain reproductive characteristics

 Most animals reproduce sexually, with the diploid stage dominating.

 In most animals, a small, haploid, flagellated, motile sperm fertilizes a larger, haploid, nonmotile egg to form a diploid zygote.

 Mitotic division of the zygote yields a blastula stage, followed by a gastrula stage. A synapomorphy? This feature could be another "unique characteristic" shared by animals.

 Development may be direct to adult form, or there may be a sexually immature stage (or stages) that are morphologically & ecologically distinct from the adult called a larva (plural: larvae).

Other commonly used definitions or characterizations

 It is surprisingly difficult to find two texts that agree on a precise definition of an animal.

Here are a few perspectives from some other texts.

 Animals are multicellular eukaryotes; they are chemosynthetic heterotrophs that ingest their food.

 Animals are motile, though many are secondarily sessile. Gametes usually are produced in multicellular sex organs, and the zygote passes through embryonic stages that include a blastula.

 Animals are organisms that are multicellular, with more than one type of cell. They are heterotrophic. They reproduce sexually (at least sometimes), with a zygote formed from two different haploid gametes. They go through a developmental stage called a blastula.

 Animals are not photosynthetic, have no cell wall, and no hyphae or mycelia.

• Kingdom Animalia generally is recognized to have approximately 30 phyla ...

• There is relatively little dispute over the number of phyla recognized; however, the phylogenetic relationships among the phyla are hotly debated.

• Molecular techniques for assess similarity based on nucleotide sequences in nucleic acids are providing valuable new perspectives on this question.

• Remember that two animals in different phyla generally are considered to be more different from each other than are animals within one phylum (e.g., nematodes are more different from annelids than humans are from sharks).

LIFE CYCLE

Life cycle is stages of development of living organism: the series of changes of form and activity that a living organism undergoes from its beginning through its development to sexual maturity. It could be said to be a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction (a period from one generation of organisms to the same identical). A life cycle tend to describes the series of stages that an individual organism passes through between the series of stages that an individual organism passes through between the time it is conceived until the time it produces offspring of its own. This series of stages is referred to as a LIFE CYCLE because offspring pass through the same series before they produce their own offspring. Hence, the life cycle is repeated each generation.

The basic stages of a life cycle for all organisms include a pre-reproductive (or juvenile) stage in which individuals grow and mature and a reproductive (or adult) stage in which individuals produce offspring. However, species vary tremendously in the particular aspects of their own unique life cycles.

COMPLEXITY OF LIFE CYCLE

For some organisms, including humans, individuals in pre-reproductive and reproductive stages are morphologically very similar to one another. Although they may differ in body size, the two stages have similar appearances, live in similar habitats, and consume similar types of food. These types of life cycles are organisms that change morphology, habitat, and diet as they move from one stage to the next. These organisms have a complex life cycle.

LIVING THINGS

You are familiar with many different living things. The Earth’s organisms are so diverse that it is an overwhelming task to classify them. Nonetheless, scientists attempt to assign organisms into groups called kingdoms based on their structure, development, feeding patterns, and more recently, their genes.

There are six kingdoms in all:

 Bacteria,

 Archaea,

 Protista,

 Fungi,

 Plantae, and

 Animalia.

The Kingdoms Bacteria and Archaea both contain single-celled organisms that have no membrane-bound organelles. As a result, these organisms have no special compartments where various cell functions are carried out. In particular, their genetic material floats freely in the cell. Although the Kingdoms Bacteria and Archaea have similar structural characteristics (formerly, they were grouped together into the Kingdom Monera), genetically they are distinct, and so they are now classified into separate kingdoms.

The Kingdom Protista also includes single-celled organisms, but the protist cell has compartments in it. Each compartment, consisting of a membrane-bound organelle, serves some specialized function. For instance, genetic material is located in an organelle called the nucleus.

Like organisms in the Kingdom Protista, organisms in the next three kingdoms have compartmentalized cells. These organisms, however, are composed of many cells, and are much larger and more complex. 

The Kingdom Fungi contains organisms (for example mushrooms and molds) that decompose organic matter, such as fallen leaves, animal carcasses, and feces, into simpler chemical compounds. Decomposers absorb nutrients from the material they decompose. 

The Kingdom Plantae contains organisms (for example trees and mosses) that make their own food using the energy from sunlight.

Finally, the Kingdom Animalia contains most of the multi-celled organisms (like insects, fish, and mammals) that consume other living organisms for food. (There are a few plants and fungi that will consume other living organisms, though this is not their primary source of nourishment.)

ANIMAL KINGDOM

ELABORATE CHRACTERISTICS OF ANIMAL KINGDOM

1. Animals are multicellular organism that obtains energy by eating food.

2. Animal are over 2 million known species, and many more awaiting identification, animals are the most diverse forms of life on earth.

3. They range in size from 30-m (100-ft) long whales to microscopic organisms only 0.05 mm (0.002 in) long.

4. They live in a vast range of habitats, from deserts and Arctic tundra to the deep-sea floor.

5. Animals are the only living things that have evolved nervous systems and sense organs that monitor their surroundings. They are also the only forms of life that show flexible patterns of behaviour that can be shaped by past experience. The study of animals is known as zoology.

6. Animals as multicellular organisms, share the same characteristic with plants and many fungi. But they differ from plants and fungi in several important ways. Foremost among these is the way they obtain energy. Plants obtain energy directly from sunlight through the process of photosynthesis, and they use this energy to build up organic matter from simple raw materials. Animals, on the other hand, eat other living things or their dead remains. They then digest this food to release the energy that it contains. Fungi also take in food, but instead of digesting it internally as animals do, they digest it before they absorb it.

7. Most animals start life as a single fertilized cell, which divides many times to produce the thousands or millions of cells needed to form a functioning body. During this process, groups of cells develop different characteristics and arrange themselves in tissues that carry out specialized functions. Epithelial tissue covers the body’s inner and outer surfaces, while connective tissue binds it together and provides support. Nervous tissue conducts the signals that coordinate the body, and muscle tissue–which makes up over two-thirds of the body mass of some animals–contracts to make the body move. This mobility, coupled with rapid responses to opportunities and hazards, is one feature that distinguishes animals from other forms of life.

8. Some kinds of animal movement, such as the slow progress of a limpet as it creeps across rocks, are so slow that they are almost imperceptible. Others, such as the attacking dive of a peregrine falcon or the leap of a flea, are so fast that they are difficult or even impossible to follow. Many single-celled organisms can move, but in absolute terms, animals are by far the fastest-moving living things on earth.

9. Animal life spans vary from less than 3 weeks in some insects to over a century in giant tortoises. Some animals, such as sponges, mollusks, fish, and snakes, show indeterminate growth, which means that they continue to grow throughout life. Most, however, reach a pre-defined size at maturity, at which point their physical growth stops.

AN INVERTEBRATE AND VERTEBRATES

All animals belong to either subkingdom invertebrate or vertebrate.

Invertebrates are animals without backbones while vertebrates are those with backbones.

One phylum of animals, the chordates, has been more intensively studied than has any other, because it comprises nearly all the world’s largest and most familiar animals as well as humans. This phylum includes mammals, birds, reptiles, amphibians, and fish together with a collection of lesser-known organisms, such as sea squirts and their relatives.

The feature uniting these animals is that at some stage in their lives, all have a flexible supporting rod, called a notochord, running the length of their bodies. In the great majority of chordates, the notochord is replaced by a series of interlocking bones called vertebrae during early development. These bones form the backbone, and they give these animals their name—the vertebrates.

Vertebrates total about 40,000 species. Thanks to their highly developed nervous systems and internal skeletons, they have become very successful on land, sea, and air. Yet vertebrates account for only about 2 percent of animal species. The remaining 98 percent, collectively called invertebrates, are far more numerous and diverse and include an immense variety of animals from sponges, worms, and jellyfish to mollusks and insects. The only feature these diverse creatures share in common is the lack of a backbone.

GENERAL CHARACTERISTICS OF INVERTEBRATES

 They have no backbones

 They have no internal skeleton

 They are unicellular e.g. Amoeba, Plasmodium or multicellular e.g. Hydra, Tapeworm etc.

 They move by means of:

i. Flagella e.g. trypanosome

ii. Pseudopodia e.g. Amoeba

iii. Cilia e.g. Paramecium

iv. Whole body e.g. Tapeworm

v. Jointed legs e.g. Crabs, Insects

 They exist by either

i. Parasite e.g. Trypanosoma

ii. Free living e.g. Hydra, Earthworm

 They reproduce

i. Asexually by binary fission, budding or multiple fission

ii. Sexually by conjugation or gamete production.

Sub-kingdom invertebrate is divided into 8: Phyla

 Protozoa

 Coelentrata

 Platyhelmithes

 Nematoda

 Annelida

 Arthropoda

 Mollusca

 Echinodermata

We shall now treat them one after the other

PHYLUM PROTOZOA

INTRODUCTION

As per two-kingdom classification, Protozoa was treated as a phylum under animal kingdom. Under the three-kingdom classification, proposed by Haeckel, it was separated from animal kingdom and was included under the kingdom Protista. There are about 215000 described species of protists of which about 92000 species are protozoans. The first protozoan observed was VorticeUa convellaria by Anton Van Leeuwenhoek. Anton Van Leeuwenhoek called Protozoans as animalcules.

GENERAL CHARACTERISTICS OF PROTOZOA

 They are the most primitive in the animal kingdom.

 The body is unicellular, however they are preferably be referred to as acellular because the single cell performs all the life activities and is functionally equivalent to the whole metazoan animal.

 Division of labour occurs among various organelles of the cell.

 These may be solitary (Euglena or colonial (Proterospongia) Freeliving- Amoeba

 Symmetry - Spherical - heliozoans, (Actinopodeans), radiolarians (Collozoum) Radial - (Sessile forms) Bilateral – Giardia

 Lobose protozoans and foraminifers are asymmetrical

 Body is naked or covered by pellicle or shell made of silica or calcium carbonate

 Division of body is at subcellular level

 Locomotion is brought about by the locomotory organelles like flagella and cilia, cellular extensions like pseudopodia and in some, pellicular contractile structures like myonemes.

 Nutrition is holozoic or holophytic or osmotrophic. Euglena shows mixotrophic nutrition.

 Digestion is intracellular.

Contractile vacuoles, which are common ir freshwater forms mainly, serve for osmoregulation,

 Asexual reproduction by binary ormultiple fissions or plasmotomy or budding.

 Sexual reproduction by syngamy or conjugation.

 The phenomenon to tide over unfavourable conditions is encystment.

 They are immortal - somatoplasm and germplasrr are not differentiated.

SPECIFIC CHARACTERISTICS OF PROTOZOA

1. Unicellular eukaryotes (some multinucleate, a few loosely multicellular), not all have mitochondria (microspores, many flagellates).

2. Up to about 400 micrometer in size (some larger)

3. All have at least one nucleus

4. Most are free living, but many parasitic forms including entire phyla

5. motile by a variety of mechanisms but also several non-motile taxa.

6. Many have cyst stages secreted by trophic or spore stages

Cysts/spores have four basic functions:

• protect against unfavorable conditions

• serve as sites for multiplication

• assist in attachment to surfaces such as hosts

• Transmission stage from host to host

7. All types of nutrition are exhibited by the Kingdom.

• autotrophs: photosynthesis

• heterotrophs (holozoic vs. saprozoic)

• phagocytosis: ingestion of solid particles (e.g., bacteria)

• pinocytosis: same as phagocytosis but intake of liquid

• saprozoic or saprotrophy: diffusion or active transport across membrane

CLASSIFICATION PROTOZOA

B.M. Honigberg and others classified Phylurr Protozoa into four subphyla: Sarcomastigophora, Sporozoa, Cnidospora and Ciliophora.

Subphylum-1 Sarcomastigophora

 It is characterized by the presence of pseudopodia or flagella for locomotion, It includes three superclasses – Mastigophora, Opalinata and Sarcodina.

Superclass Mastigophora:

 Body is covered by pellicle; locomotoiy organelles are flagella;

 Asexual reproduction by longitudinal binary fission.

 It includes two classes – Phytoinastigophon and Zoomastigophora

Class Phytomastigophora:

 Some are with chlorophyll bearing chloroplasts

 Nutrition is holophytic

 Reserve food is paramylum Includes euglenoids and dinoflagllates

 Examples: Ceratium (dinoflagellate witl chloroplasts) Noctiluca (dinoflagellate without chloroplasts), Euglena

Class Zoomastigophora:

 Mostly parasitic; Chloroplasts are absent; nutrition is holozoic

 Saprobic or parasitic, Reserve food is glycogen or volutin, Examples: Trichomonas, Trichonympht (Mutualistic), Leishmania.

Superclass Opalinata:

 Commensals or parasites in the gut of anurans

 Body is covered by oblique rows of cilia but without infraciliary system.

 Some are binuleate, others are multinucleate but homokaryotic i.e. the nuclei are identical,

 Asexual reproduction by longitudinal binary fission and plasmotomy.

 Sexual reproduction is syngamy with flagellated gametes Examples Opalina, Zelleriella

Superclass Sarcodina:

 Locomotion is brought about by pseudopodia.

 It includes three classes - Rhizopodea, Piroplasmea and Actinopodea.

Class Rhizopodea:

 It includes amoebas, foraminiferans and mycetozoans.

 Amoebas have lobopodia or filopodia; foraminiferans have reticulopodia.

 In amoebas, body .is naked (Amoeba, Entamoeba) or covered by a test (Arcella).

 Foraminiferans have a calcareous porous shell.

 Calcareous shells of dead individuals form foraminiferan ooze,

Examples: Elphidium (foraminiferan), * Physarum (acellular slime mould with a Plasmodium stage in the life history), Dictyostelium (cellular slime mould with pseudoplasmodium stage in the life history).

Class Piroplasmea:

 Parasitic; locomotory structures absent; spores are absent.

Example: Babesia (causes red water fever in cattle)

Class Actinopodea:

 These are the ray footed protozoans

 Locomotory structures are axopodia

 Skeleton consists of siliceous shell (Radiolaria) or strontium sulphate spines (Acantharea) or siliceous shell or radiating needles (Heliozoa).

 Silicious shells of radiolarians form ooze Examples: Collozoum (radiolarian) Actinophrys (heliozoan) Acanthometra (acantharean), Actinosphaerium

Subphylum-II Sporozoa or Apicomplexa:

 Parasitic; no special locomotory structures;

 pseudopodia, if present, useful only in ingestion, o Sporozoites and merozoites bear anterior apical complex that helps penetrate host cells, No polar filaments

 It includes three classes - Telosporea,

 Toxoplasmea and Haplosporea.

Class Telosporea:

 Sporozoites are long, Garrtonts are large, extracellular - gregarinids

 Gamonts are small, intracellular - coccidians

 Syngamy is isogamy - Gregarinids Anisogamy - Coccidians

 Examples: Monocystis (parasite in the seminal vesicles of earthworms), Eimeria, Plasmodium, Gregarina

Class Toxoplasmea:

 Body covered by two layered pellicle

 Only asexual reproduction, by endodyogeny.

 It is internal budding wherein two daughter cells are produced within a mother cell and the mother cell is destroyed in the process, Example: Toxoplasma

Class Haplosporea:

 Spores are present and are amoeboid, o Reproduction is only asexual, by multiple fission.

 Each spore contains singl e sporozoite o Example: Haplosporidium

Subphylum-III Cnidospora:

 Parasitic.

 No special locomotory structures,

 Spores with 1 or more protoplasmic masses called – sporoplasms

 Spores are provided with one or more polar filaments, which are useful for attachment to the host.

 It includes two classes - Myxosporidea and Microsporidea.

Class Myxosporidea:

 Extracellular parasites of cold blooded vertebrates

 Spores with typically two capsules each with single polar filament.

Example: Myxobolus

Class Microsporidea:

 Intracellular parasites.

 Spore with one intrasporal or 1 -2 intracapsular filaments.

 Spores with single sporoplasm

Example: Nosema bombycis (causes pebrine disease in silkworms).

Subphylum IV Ciliophora:

 Complex protozoans.

 Cilia are useful in locomotion and food capture,

 Suctorian ciliates are sessile and are with cilia only in young stages. In adult suctorians the cilia are replaced by sucking tentacles that help in food capture,

 Dimorphic nuclei - macronucleus (vegetative and polyploid) and micronucleus (reproductive and diploid). Infraciliary system is present, Sexual reproduction by conjugation, which brings about nuclear reorganization.

 Only class under this subphylum is Class Ciliata. Example: Paramecium, Balantidium, (parasitic ciliate in man) Acineta (Suctorian)

They are further represented by 5 classes based on their locomotory organelles

 Sporozoa e.g. plasmodium, monocystis

 Rhizopada (sarcodina) e.g. Amoeba

 Mastigophora (flagellata) e.g. Euglena

 Ciliophora (ciliate) e.g. paramecium

 Opalinata e.g. opalina

AMOEBA

Amoeba (sometimes amoeba or ameba, plural amoebae or amoebas) is a genus of Protozoa that consists of unicellular organisms which do not have a definite shape. 

Furthermore, Amoeba is any of a group of unicellular organisms characterized by their locomotive method of extending cytoplasm outward to form pseudopodia (false feet). 

The amoeboid group includes hundreds of different organisms, ranging in size from about .25 to 2.5 mm (about 0.0098 to 0.098 in). Amoebas are considered the most primitive animals and are classified in the kingdom Protista. 

All amoeboid organisms have thin cell membranes, a semirigid layer of ectoplasm, a granular, jellylike endoplasm, and an oval nucleus. Some species live on aquatic plants and some in moist ground; others are parasitic in animals.

STRUCTURE OF AMOEBA

The cell's organelles and cytoplasm are enclosed by a cell membrane; it obtains its food through phagocytosis. This makes amoebae heterotrophs. 

Locomotory organ is lobe-shaped pseudopodia. They are mostly free living. The protoplasm is surrounded by a thin cell membrane. The cytoplasm is divided into an outer ectoplasm and an inner endoplasm. 

Amoebae have a single large tubular pseudopod at the anterior end, and several secondary ones branching to the sides. The cytoplasm of amoeba is divided into outer ectoplasm and inner endoplasm. 

The endoplasm consist of single nucleus, a single or more contractile vacuole which helps in maintaining the water balance by expelling out excess water (i.e. osmo-regulation free living amoeba are found among decaying vegetable matter, in ponds and slow-flow stream. 

The most famous species, Amoeba proteus, averages about 220-740 μm in length while in motion, making it a giant among amoeboids. A few amoeboids belonging to different genera can grow larger, however, such as Gromia, Pelomyxa, and Chaos.

Figure1: Structure of amoeba


Amoebae's most recognizable features include one or more nuclei and a simple contractile vacuole to maintain osmotic equilibrium - low water amounts in cell protecting cell from bursting with excess water. Food enveloped by the amoeba is stored and digested in vacuoles. Amoebae also have no definite shape.

FEEDING IN AMOEBA

They feed on diatom, algae. When it senses food in its surroundings it extends its pseudopodia in that direction and moves towards it. There are captured and engulfed by means of pseudopia. Once a prey is captured, the food enters its body the amoeba forms a food vacuole around it which contains certain enzymes to digest the food. 

Chemical stimuli from smaller organisms, the amoeba's food, induce the formation of pseudopodia, pairs of which envelop the organism, at the same time forming a cavity, or vacuole. A digestive enzyme secreted into the cavity breaks down this food into soluble chemical substances that then diffuse from the cavity into the cytoplasm. 

Undigested food and wastes are excreted through the ectoplasm, which also absorbs oxygen from the surrounding water and eliminates carbon dioxide, a by-product of metabolism, in a form of respiration.

LIFE CYCLE
Reproduction is asexual and is by binary fission.
 The nucleus of the parent cell divides into 2 with each, nucleus moving to opposite ends of the cells, followed by a construction of the cell into 2 new daughter cells each into own nucleus.


 In difficult conditions, as well as when water freezes, Amoeba cell secretes a thick resistant wall around itself. Within it, can survive for a considerable length of time. This condition is referred to as ecosystem. Within it, the amoeba divides repeatedly to release a large number of daughter amoeba when it breeds.

RECENT DISCOVERY IN AMOEBAE REPRODUCTION

Asexuality (reproduction by binary fission) is often thought to be a defining characteristic of amoebae. However, analysis of 71 isolates of amoeba from the same geographical area along a river indicated that sex must be occurring in that particular lineage. Lahr and his team in 2011 proposed that the majority of amoeboid lineages are, contrary to popular belief, at least anciently sexual, and that most current asexual groups have arisen recently and independently.

 In addition, recent evidence also indicates that several other single-celled eukaryotes that was previously regarded as asexual are, or were in the past, capable of sexual reproduction. These findings have led to the idea that sex was present in the earliest common
ancestor of all eukaryotes according to the findings of Dacks and Roger in 1999 and Bernstein and his research team in 2012.


After a period of growth, the amoeba reproduces by splitting into two equal parts. Amoebae, like other unicellular eukaryotic organisms, reproduce asexually via mitosis and cytokinesis, not to be confused with binary fission (although several authors wrote that is binary fission), which is how prokaryotes (bacteria) reproduce. In cases where the amoebae are forcibly divided, the portion that retains the nucleus will survive and form a new cell and cytoplasm, while the other portion dies (visit “Amoeba”Scienceclarified.com for more clarification).

AMOEBIC CYSTS
In environments that are potentially lethal to the cell, an amoeba may become dormant by forming itself into a ball and secreting a protective membrane to become a microbial cyst. The cell remains in this state until it encounters more favourable conditions. While in cyst form the amoeba will not replicate and may die if unable to emerge for a lengthy period of time.


At least six forms of amoeba are parasitic in humans. Most important of these is Entamoeba histolytica, which causes Amebiasis and Dysentery. The diseases often occur in epidemics when raw sewage contaminates water supplies or when soil is fertilized with untreated human wastes.

PARAMACIUM

A paramecium is a small one celled (unicellular) living organism that can move, digest food, and reproduce. They belong to the kingdom of Protista, which is a group (family) of similar living micro-organisms. Micro-organism means they are a very small living cell. 

You might be able to see one as a tiny moving speck if your eyesight is extremely good but for any detail at all you need a microscope to look at and study them. They are about .02 inches long (.5mm). They are also famous for their predator-prey relationship with Didinium. Paramecium are known for their avoidance behavior. If an encounters a negative stimiulus, 

It is capable of rotating up to 360 degrees to find an escape route. Didinium are heterotrophic organisms. They only have one type of prey; the much larger cilate Paramecium. When a Didinium finds a Paramecium, it ejects poison darts (trichocysts) and attachment lines. The Didinium then proceeds to engulf its prey. 

Although Paramecium is larger than they are, Didinium are  voracious eaters and will be ready to hunt for another meal after only a few hours.

STRUCTURE OF PARAMACIUM
When compared with the shape of amoeba, paramecium possesses a fixed or definite shape. This is because of its pellicle. They have the shape of a slipper. Radiating round the body are numerous hairs like structure called cilia which are used in movement.

Within the pellicle and before the cytoplasm are found numerous rod-like trichocysta. They are used by the animal when feeding helps it to anchor itself and are also used for defense or capturing of prey in some species.

Within the cytoplasm are found 2 nuclei, a small micro nucleus and a mega nucleus.

It also possess 2 star shaped contractile vacuole situated anteriorly and posteriorly, located near the posterior and is a funnel shaped and groove. It is ciliated.

Fig 2: structure of paramecium

FEEDING IN PARAMECIUM

Paramecium feed on microorganisms like bacteria, algae, and yeasts. The paramecium uses its cilia to sweep the food along with some water into the cell mouth after it falls into the oral groove. The food goes through the cell mouth into the gullet. When there is enough food in it so that it has reached a certain size it breaks away and forms a food vacuole. The food vacuole travels through the cell, through the back end first. 

As it moves along enzymes from the cytoplasm enter the vacuole and digest it. The digested food then goes into the cytoplasm and the vacuole gets smaller and smaller. When the vacuole reaches the anal pore the remaining undigested waste is removed. Paramecium may eject trichocyts when they detect food, in order to better capture their prey. 

These trichocyts are filled with protiens. Trichocysts can also be used as a method of self-defense. Paramecium are heterotrophs. Their common form of prey is bacteria. A single organism has the ability to eat 5,000 bacteria a day. They are also known to feed on yeasts, algae, and small protozoa. Paramecium capture their prey through phagocytosis.

LIFE CYCLE
Reproduction is either asexual or sexual. Asexual reproduction is by binary fission, sexual reproduction is by conjugation and is as follows:
 2 sexually compatible, same specie come together at their oral region to become conjugant mega nucleus disappears.

 Micronucleus then undergo 2 meiotic division to give 2 nuclei in each.


 One is stationery and referred to as a female while the other is mobile and referred to as multi nucleus.

 The niche nucleus migrate into opposite and fuses with the female nucleus to form a “zygote nucleus”. Conjugant with its own zygote nucleus separates and become known as ex-conjugant.

 Zygote nucleus then divides 3x to give 8 nuclei, 4 of it forms mega nucleus and the remaining 4 forms micronucleus.


 Ex-conjugant then divides 2 x to give 4 new daughter cells.

TO BE CONTINUE

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