Nemathelminthes and Its Feautures

Nematodes

Nematodes ( Phylum- Nemathelminthes) are simple roundworms. Colorless, unsegmented, and lacking appendages, nematodes may be free-living, predaceous, or parasitic. Many of the parasitic species cause important diseases of plants, animals, and humans. Other species are beneficial in attacking insect pests, mostly sterilizing or otherwise debilitating their hosts. A very few cause insect death but these species tend to be difficult (e.g., tetradomatids) or expensive (e.g. mermithids) to mass produce, have narrow host specificity against pests of minor economic importance, possess modest virulence (e.g., sphaeruliids) or are otherwise poorly suited to exploit for pest control purposes. The only insect-parasitic nematodes possessing an optimal balance of biological control attributes are entomopathogenic or insecticidal nematodes in the genera Steinernema and Heterorhabditis. These multi-cellular metazoans occupy a biocontrol middle ground between microbial pathogens and predators/parasitoids, and are invariably lumped with pathogens, presumably because of their symbiotic relationship with bacteria. 

Classes of Nemathelminthes:

1.Chromadorea

2. Enoplea

3. Secernentea

Major Features of Nemathelminthes:

1) They are marine or freshwater animal.

2) They are pseudocoelomate which means they have a cavity called pseudocoel between the gut and body wall.

3) They are non segmented round worm.

4) Their body is covered with cuticle .

5) They have simple type of digestive system.

6) They do not have respiratory system and circulatory system.

7) They have poorly developed nervous system.

8) They are unisexual animals.

9) They are endoparasite .

10) The mouth is provided with hooks and suckers.

Platyhelminthes and Its Features

The Platyhelminthes include free-living flatworms, like the planarians, and the parasitic tapeworms and flukes. The term flatworm refers to the fact that the body is dorsoventrally flattened. Flatworms are the first organisms to have tissues organized into organs and the first to demonstrate bilateral symmetry. Bilateral symmetry means that one plane passing through the longitudinal axis of an organism divides it into right and left halves that are mirror images. It is characteristic of active, crawling, or swimming organisms and usually results in the formation of a distinct head (cephalization) where accumulation of nervous tissue and sensory structures occurs.

 

Classes of Platyhelminthes:- There are Five Classes of Platyhelminths

1. Class Turbellaria 

2. Class Cestoda

3. Monogenea

4. Trematoda

5.Aspidogastria

Major Characteristics of Platyhelminths:

1. Bilateral Symmetry
These worm like animals are bilaterally symmetrical, which means that their right and left sides are the mirror images of each other. This also indicates that these animals have distinct head and tail ends. They are triploblastic, that is they possess three main cell layers: outer ectoderm, middle mesoderm and inner endoderm just like the other bilateral animals. The middle layer in these animals is made up of spongy mesoderm cells and is also called parenchyma.

2. Acoelomate
Unlike the other bilateral animals, these animals possess no internal body cavity. Coelomate means body cavity present and since body cavity or coelom is absent, they are termed as acoelomate.

3. Absence of Circulatory and Respiratory Organs
The animals of platyhelminthes lack circulatory and respiratory organs, which is why their bodies are so flat. The flat body shape permits the flow of oxygen and nutrients to reach all parts of the body by simple diffusion process. Carbon dioxide leaves the body by the same diffusion process. The gut of these animals is branched profusely in order to facilitate adequate diffusion of nutrients to all parts of the body.

4. Restricted to Wet Environment
Respiration occurs throughout the surface of the body, thereby making the Platyhelminthes animals susceptible to loss of precious body fluids. This can result into dehydration. Thus these animals are restricted to living in a wet environment, such as in freshwater, sea or in moist terrestrial environment. The different moist terrestrial environment comprise grains between the soil, in leaf litter or living as parasites in the bodies of other insects.

5. Possesses a Type of Skeleton
Mesenchyme, a connective tissue is seen to fill the space between the skin and gut in these animals. It consists of two kinds of cells: fixed cells and stem cells. Fixed cells have fluid filled vacuoles and stem cells are the cells capable of transforming into any other type of cell, thereby useful during the tissue regeneration and asexual reproduction. This mesenchyme is reinforced by collagen fibers that provide attachment points for the muscles, thereby acting like a skeleton. Mesenchyme comprises internal organs and permits the passage of nutrients, oxygen and waste products.

6. Digestion
The digestive system is incomplete with a single opening serving as the mouth and anus. A single layer of endodermal cells line the gut, whose role is to absorb and digest the food materials. Some species also feature the secretion of enzymes in the gut or pharynx to soften and break up the food. The undigested food material is regurgitated through the mouth as an anal opening is absent. However, there are exceptions to this. Large species do possess an anal opening and some with exceptionally profusely branched guts possess more than one anal opening. This is because solely excreting from the mouth would prove difficult for them.

7. Excretory System
The excretory system of these animals is well-developed and is called protonephredia. Protonephredia comprises a network of tubules within the animal's body tissues. One end of the tubule extends into an exterior pore on the surface of the body, while the other end leads into spherical structure called flame cells. These flame cells possess long cilia which carry out a beating function. When the cilia beats, it gives the flame cells an appearance of a flickering candle and this is where the cells get their name. Excess water and body wastes enter the flame cells, are pushed into the tubules by the movement of cilia and thrown out of the body from the pore on the surface.

8. Osmoregulation
The control or regulation of water balance and ion levels in the body is termed as osmoregulation. Platyhelminthes animals live in the environment with high concentrations of dissolved materials. All animals have to maintain the concentration of dissolved substances at a constant level. These animals let their body tissues have the same concentration level as that of the environment with the help of protonephredia network.

9. Nervous System
Nervous System marked at the head region is of the primitive type. It comprises pair of anterior ganglia or a nerve ring connected to 1-3 pairs of longitudinal nerve chords with transverse commissures. These ganglia serve as the brain.

10. Reproductive System
These animals can reproduce asexually and as well as sexually. They can reproduce asexually by transversal bipartition due to their wonderful ability to regenerate their tissues. They attach themselves to a substrate and induce a constriction in the body's mid region and get divided into two parts. The two divided body parts can regenerate into two different animal individuals. These animals are mostly hermaphrodite, that is both female and male reproductive organs are situated in one animal itself. Rarely animals with separate sex are found. Reproductive organs are highly developed. Self-fertilization (fusion of male and female gametes from the same animal) as well as cross fertilization (fusion of male and female gametes from different animals of the same species) is seen. The development is mostly direct, which means that the development does not include larval stage formation.

Cnidaria and Its Features

Cnidaria

Cnidaria Phylum

The Phylum Cnidaria includes such diverse forms as jellyfish, hydra, sea anemones, and corals. Cnidarians are radially or biradially symmetric, a general type of symmetry believed primitive for eumetazoans. They have achieved the tissue level of organization, in which some similar cells are associated into groups or aggregations called tissues, but true organs do not occur. Cnidarian bodies have two or sometimes three layers. A gastrovascular cavity (coelenteron) has a single exterior opening that serves as both mouth and anus. Often tentacles surround the opening. Some cells are organized into two simple nerve nets, one epidermal and the other gastrodermal, that help coordinate muscular and sensory functions.

  
Features:

1. Cnidarians have two basic body forms, medusa and polyp. Medusae, such as adult jellyfish, are free-swimming or floating. They usually have umbrella-shaped bodies and tetramerous (four-part) symmetry. The mouth is usually on the concave side, and the tentacles originate on the rim of the umbrella. 
2. Polyps, in contrast, are usually sessile. They have tubular bodies; one end is attached to the substrate, and a mouth (usually surrounded by tentacles) is found at the other end. Polyps may occur alone or in groups of individuals; in the latter case, different individuals sometimes specialize for different functions, such as reproduction, feeding or defense.
3. Reproduction in polyps is by asexual budding (polyps) or sexual formation of gametes (medusae, some polyps). Cnidarian individuals may be monoecious or dioecious. The result of sexual reproduction is a planula larva, which is ciliated and free-swimming.
4. If collar cells and spicules are defining characteristics of the Phylum Porifera, then nematocysts define cnidarians. These tiny organelles, likened by Hickman to cocked guns, are both highly efficient devices for capturing prey and extremely effective deterrents to predators. Each contains a coiled, tubular thread, which may bear barbs and which is often poisoned.
5. A nematocyst discharges when a prey species or predator comes into contact with it, driving its threads with barb and poison into the flesh of the victim by means of a rapid increase in hydrostatic pressure. Hundreds or thousands of nematocysts may line the tentacles or surface of the cnidarian. They are capable even of penetrating human skin, sometimes producing a painful wound or in extreme cases, death.

Cnidaria Phylum can be classified into following main groups

1. Sessile Anthozoa (sea anemones, corals, sea pens) 
2. Swimming Scyphozoa (jellyfish)
3. Cubozoa (box jellies) 
4. Hydrozoa ( Hydra)

Porifera and Its Features

Porifera

Porifera Phylum

Sponges are animals of the phylum Porifera (means "pore bearer"). They are multicellular organisms which have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells. Sponges have unspecialized cells that can transform into other types and which often migrate between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. 

  

Classes  

Sponges were traditionally distributed in three classes: calcareous sponges (Calcarea), glass sponges (Hexactinellida) and demosponges (Demospongiae).However, studies have shown that the Homoscleromorpha, a group thought to belong to the Demospongiae, is actually phylogenetically well separated. Therefore, they have recently been recognized as the fourth class of sponges 

Calcarea :Its features
Cell structure :Single nucleus, single external membrane. 

Spicules: calcite may be individual or large masses, 

Spongin fibers : never
Massive exoskeleton: made of calcite if present,  

Body form:asconoid, syconoid, leuconoid or solenoid. 

Glass sponges : Its features 

Cell structure :Mostly syncytia in all species 

Spicules: SilicaMay be individual or fused 

Spongin fibers : never  

Massive exoskeleton: never
Body form: leuconoid . 

Demosponges :- Its features

Cell structure :Single nucleus, single external membrane 

Spicules: Silica 

Spongin fibers : never In many species 

Massive exoskeleton: In some species.Made of aragonite if present. 

Body form: leuconoid . 

Homoscleromorpha: Its features

Cell structure :Single nucleus, single external membrane 

Spicules: Silica 

Spongin fibers : never In many species 

Massive exoskeleton: Never
Body form: Sylleibid or leuconoid

Protozoa and Its Features

Protozoa:- Single-celled eukaryotes or organisms that possess membrane-bound organelles and nuclei are known as Protozoa. Originally, protozoa had been defined as unicellular protists with animal-like behavior, e.g., movement. Protozoa were regarded as the partner group of protists to protophyta, which have plant-like behaviour, e.g., photosynthesis. The word protozoa means "little animal." They are so named because many species behave like tiny animals-specifically, they hunt and gather other microbes as food.

 

Features:

1. Protozoa commonly range from 10 - 52 micrometers, but can grow as large as 1 mm, and are seen easily by microscope. 
2. The largest protozoa known are the deep-sea dwelling xenophyophores, which can grow up to 20 cm in diameter. They were considered formerly to be part of the protista family. 
3. Protozoa exist throughout aqueous environments and soil, occupying a range of tropic levels. 
4. Protozoa mainly feed on bacteria, but they also eat other protozoa, bits of stuff that has come off of other living things-what's generally called organic matter-and sometimes fungi.

Classification :- The classification of protozoa has been and remains a problematic area of taxonomy. Where they are available, DNA sequences are used as the basis for classification but for the majority of described protozoa such material is not available. They have been and still are mostly on the basis of their morphology and for the parasitic species their hosts. Protozoa have been divided traditionally on the basis of their means of locomotion.

Sub Groups of protoza
Flagellates (e.g Giardia lamblia)
Amoeboids (e.g. Entamoeba histolytica)
Sporozoans (e.g.Plasmodium knowlesi)
Ciliates ( ( e.g. Balantadium Coli)

Cell Division and Its Types

Cell Division

Cell Division

Cell division is the process by which a Parent Cell divides into two or more Daughter Cell. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct type of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell , and a reductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half, to produce haploid gametes . Both of these cell division cycles are required in sexually reproducing organisms at some point in their life cycle, and both are believed to be present in the last eukaryotic common ancestor Prokaryotes also undergo a vegetative cell division known as binary fission, where their genetic material is segregated equally into two daughter cells. All cell divisions, regardless of organism, are preceded by a single round of DNA replication.

Types of Cell Division

Generally there are two types of cell division

1. Mitosis cell division :- It is the process by which new cells are generated. Mitosis is the process by which a cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is a form of karyokinesis, or nuclear division. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles, and cell membrane into two cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle: the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. This accounts for approximately 10% of the cell cycle.
2. Meiosis cell division :- It is the process by which gametes are generated for reproduction. Meiosis  is a special type of cell division necessary for sexual reproduction in eukaryotes. The cells produced by meiosis are gametes or spores. In many organisms, including all animals and land plants (but not some other groups such as fungi), gametes are called sperm and egg cells.Meiosis begins with one diploid cell containing two copies of each chromosome:one from the organism's mother and one from its father.

Basic terms to be more cleared on concept of Cell division are as follows :-
 Gene :- basic unit of heredity; codes for a specific trait   

Somatic cell :- all body cells except reproductive cells 

Locus :- the specific location of a gene on a chromosome (locus - plural loci)
Genome :- the total hereditary endowment of DNA of a cell or organism
Chromosome :-elongate cellular structure composed of DNA and protein - they are the vehicles which carry DNA in cells
Gamete :- reproductive cells (i.e. sperm & eggs)
Haploid (n) :- cellular condition where each chromosome type is represented by only one chromosome 
Diploid (2n) :-cellular condition where each chromosome type is represented by two homologous chromosomes
Chromatid :-one of two duplicated chromosomes connected at the centromere
Homologous chromosome :- chromosome of the same size and shape which carry the same type of genes
Centromere :-region of chromosome where microtubules attach during mitosis and meiosis

Animal Cell, Tissue and Organ

Animal Cell

Animal cells are eukaryotic cells, or cells with a membrane-bound nucleus. Unlike prokaryotic cells, DNA in animal cells is housed within the nucleus. In addition to having a nucleus, animal cells also contain other membrane-bound organelles, or tiny cellular structures, that carry out specific functions necessary for normal cellular operation. Organelles have a wide range of responsibilities that include everything from producing hormones and enzymes to providing energy for animal cells. There are different types of cell in organism for different purposes of body function.

Functions of the Animal Cell

The functions of animal cell are as follow, carried out by the different cell organelles.

Nucleus :- The nucleus is referred to as the heart of the cell. The nucleus houses the genetic material of the organism which is the DNA. DNA replication and RNA synthesis occurs in the nucleus. It regulates the activities of the other cell organelles thus a very important cell organelle. The cell nucleus is bound by a definite membrane called the nuclear membrane that separates the nucleus from the cytoplasm.

Endoplasmic Reticulum :- The endoplasmic reticulum is a network for transportation of certain critical substances in and out of the nucleus.The endoplasic reticulum is seen like a network of interconnecting pathways to enable the transport of molecules. There are two kinds of ER namely Rough ER and Smooth ER. Rough ER has ribosome molecules attached to its surface while the smooth ER does not have ribosome molecules attached to its surface.

Mitochondria :- The mitochondria is also referred to as the power house of the cell. It is a double membraned organelle that helps in energy production for the cell.The energy is generated in the form of ATP. Mitochondria also has its own genetic material called the mitochondrial DNA which is circular. The energy is generated from the glucose we take in by a process called the cellular respiration.

Lysososmes :- Lysososmes are referred to as suicide bags of the cell. They are involved in clearing the unwanted and waste materials from the cell. The lysososmes contain hydrolytic enzymes that are destructive. they kill the toxic materials of the cell time to time.They engulf materials like damaged organelles, virus, bacteria and food particles.

Golgi Apparatus :- The Golgi apparatus is involved with processing and packaging of the molecules synthesized by the cell mainly the proteins ready for secretion. The ER transports the proteins in their crude form to the golgi appratus. The golgi apparatus packages the proteins developing them into primary, secondary and tertiary proteins respectively.

Vacuole :- The vacuole is a large empty storage organelle. They store excess water or food. It is present in many numbers withing the cell floating in the cytoplasm.

Ribosomes :- The Ribosome is involved in protein synthesis.It consists of two sub units.Protein synthesis primarily occurs in the ribosomes. The ribosomes may be found freely floating in the cytoplasm or may be found attached to the ER.

Tissue

According to Biology, Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of similar cells from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.The study of tissue is known as histology or, in connection with disease, histopathology. The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.

Types of Animal Tissue:-

Animal Tissue

• Connective tissue

• Muscle tissue

• Nervous tissue

• Epithelial tissue

Organ

In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. There are different types organ in animal constructing a complete body. Such as Liver, Heart, Lungs etc. Organs may found in only developed animal.