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.

Classified study of zoology

All members belong to the animal kingdom are multicellular, eukaryotic, heterotrophic organisms. Zoology, the study of animals, has many subdivisions based on specific areas of interest and study.And the name of study for the classified group of animal are as below:

Invertebrate zoolgy is the study of multicellular animals without backbones.

• Entomology -is the  study of insects
• Myrmecology -is the  study of ants
• Apiology - is the study of honey bees
• Arachnology - is the study of spiders and their relatives
• Malacology - is the study of mollusks
• Conchology -  is the study of mollusk shells

Vertebrate zoology is the study of animals with backbones.

• Ichthyolgy - is the study of fish
• Herpeteology - is the study of amphibians and reptiles
• Ornithology - is the study of birds
• Mammalogy -is the study of mammals
• Cetology - is the study of marine mammals
• Primatology - is the study of primates

 
Morphology is the study of the shape, form, and structure of animals and their body parts.

Comparative anatomy is the study of the similarity and differences in the anatomy of different groups of animals.

• Structures are homologous if they have arisen from the same ancestral structure, but perform either similar or different functions in modern animals. Examples are the wings of birds, the human arm, and the forelimb of whales.
   
• Analogous structures have developed from different ancestral structures, but perform similar functions. Examples are the wings of birds and the wings of insects.

Layers of cells that originate in the developing embryo and become specific structures in the animal are known as germ layers.

• Ectoderm - the outer layer which forms the body covering.
• Mesoderm - the middle layer which forms the organs inside the body.
• Endoderm - the inner layer which forms the lining inside the body cavity.

There are four body types defined by the presence or absence of a coelom, or body cavity. The body types below are arranged from least complex to most complex:

1. Acoelomate, with only two germ layers, ectoderm and endoderm. (Hydra)
2. Acoelomate, with three germ layers, ectoderm, mesoderm, and endoderm. (Flatworms)
    
3. Pseudocoelomate, with a "cavity" forming between the mesoderm and the endoderm. (Roundworms)
    
4. Coelomate, with a true body cavity forming within the mesoderm. (Segmented worms, Freshwater muscles, all Arthropods, and all Chordates)

 Taxonomy is the science of naming and classifying organisms on the basis of their evolutionary relationships. Visible traits are most often used for this classification.

Although the binomial system requires that each species be assigned a unique, two-word (Latin) name, there must be a hierarchical system for arranging organisms in a logical and retrievable fashion. Such a system now recognizes at least seven taxonomic ranks (taxa) to which each organism must be assigned.

1. kingdom
2. phylum
3. class
4. order
5. family
6. genus
7. species

In addition to the basic seven categories above, many other taxonomic ranks exist (Subphyla, Superclasses, Subspecies, etc.).

For example, the Linnaean Classification of Human Being  is:

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Mammalia
Subclass:	Theria
Infraclass:	Eutheria
Order:	Primates
Suborder:	Anthropoidea
Superfamily:	Hominoidea
Family:	Hominidae
Genus:	Homo
Species:	sapiens

Classification of animal kingdom

 Generally animal kingdom is divided into two main group. They are invertebrates and vertebrates.

 Invertebrates :- The animal without backbone or vertebral column are known as invertebrates. Such as insects, earthworm, protozoa, etc.
It is further divided into 9 phylum.They are listed below:

1. Protozoa
2. Porifera 
3. Cnidaria 
   
4. Platyhelminthes
5. Nemathelminthes
6. Annelida
7. Arthropoda
8. Mollusca
9. Echinodermata

Vertebrates :- The animal with backbone or vertebral column are known as vertebrates.Such as Human, birds, fish, snakes etc. It is further divided into five class. They are listed as below:

1. Aves
2. Amphibia
3. Mammalia
4. Pisces
5. Reptile 

 

Introduction of zoology

Zoology,  is the branch of biology that relates to the animal kingdom, including the structure, embryology,  

evolution, classification, habits, and distribution of all animals, both living and extinct. The term is derived from Ancient Greek word zoon = animal +logos= knowledge and being zoology. 

 Although the study of animal life is ancient, its scientific incarnation is relatively modern. This mirrors the transition from natural history to biology at the start of the nineteenth century. Since Hunter and Cuvier, comparative anatomical study has been associated with morphography shapins the modern areas of zoological investigation: anatomy, physiology, histology, embryology, teratology and ethology. Modern zoology first arose in German and British universities. In Britain, Thomas Henry Huxley was a prominent figure. His ideas were centered on the morphology of animals. Many consider him the greatest comparative anatomist of the latter half of the nineteenth century. Similar to Hunter, his courses were composed of lectures and laboratory practical classes in contrast to the previous format of lectures only. This system became widely spread.

According to Darwin, ancient history of Zoology

Charles Darwin

The history of zoology traces the study of the animal kingdom from ancient to modern times. Although the concept of zoology as a single coherent field arose much later, the zoological sciences emerged from natural history reaching back to the works of Aristotle and Galen in the ancient Greco-Roman world. This ancient work was further developed in the Middle Ages by Muslim physicians and scholars such as Albertus Magnus. During the Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Vesalius and William Harvey, who used experimentation and careful observation in physiology, and naturalists such as Carl Linnaeus and Buffon who began to classify the diversity of life and the fossil record, as well as the development and behavior of organisms. Microscopy revealed the previously unknown world of microorganisms, laying the groundwork for cell theory. The growing importance of natural theology, partly a response to the rise of mechanical philosophy, encouraged the growth of natural history (although it entrenched the argument from design).

Over the 18th and 19th centuries, zoology became an increasingly professional scientific discipline. Explorer-naturalists such as Alexander Von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography, laying the foundations for bio geography, ecology and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. Cell theory provided a new perspective on the fundamental basis of life.