Science websites and articles

http://www.organsofthebody.com/spleen/

Spleen Function, Location, Size and Disorders

Spleen is the largest lymphatic organ in the human body. Lymphatic or lymphoid organs are the major parts of the immune system of our body. Function of the immune system is to protect the host (i.e. human body) from the invasion of foreign organisms. Immune system helps the body to distinguish its own tissues from external substances such as bacteria, viruses and toxins. Thus dysfunction or deficiency of components of the immune system can lead to various diseases ranging from arthritis, HIV and cancer.

Location of the spleen

Spleen weighs about 150 gm in adults and lies under the diaphragm in the left upper part of the abdomen at the level between 9th and 11th ribs. Anterior to the spleen lies stomach and medially lies the superior part of the left kidney. Spleen resembles the size and shape of a clenched fist.

Functions of the spleen

• Spleen participates in the primary immune response to invading bacteria, viruses, parasites or foreign particles. Spleen is a strong defense against blood-borne pathogens. Removal of spleen increases the risk of infection.
• Spleen acts like a filter for the blood; it removes cellular residues, particulate matter, senescent RBCs and other abnormal cells from the bloodstream.
• Spleen synthesizes antibodies, macrophages and activated lymphocytes in its white pulp. About 25% of the body's T lymphocytes and 15% of B lymphocytes are present in the spleen.
• RBCs have an average life span of 120 days after which they are destroyed mainly in the spleen. When the spleen is removed surgically due to any irreversible damage, increased numbers of abnormal RBCs are seen in blood smears. Spleen also removes old defective platelets from the circulation.
• The spleen can act like a blood reservoir. Due to its spongy structure the spleen can enlarge and store up to 1000 ml of blood and when needed it can also help to stabilize the blood volume by transferring excess plasma from the bloodstream into the lymphatic system.
• In certain diseases such as leukemia or extreme anemia the spleen can resume its role of producing blood cells; this function is usually present during fetal life.

Disorders of the spleen

Splenomegaly

It is the abnormal enlargement of spleen. When the spleen is diseased it can be 10 times larger than its normal size. Causes include:

• parasitic infection such as malaria, kala azar
• chronic tuberculosis
• typhoid, septic shock, infective endocarditis
• rheumatoid arthritis, systemic lupus erythematosus
• portal hypertension, liver diseases
• lymphomas, anemia, leukemia

Splenectomy

It is the surgical removal of spleen and is usually performed due to severe trauma or rupture of the spleen. In the long run there is an increased risk of overwhelming infections after the removal of the spleen. Numbers of platelets in the blood are also increased immediately.

http://www.organsofthebody.com/spleen/

http://www.ayurvedicindia.info/health-benefits-of-kadukkaiharitakiharde-fruit-powder/

Health Benefits Of (Kadukkai/Haritaki/Harde) Fruit & Powder

Kadukkai/Haritaki/Harde Fruit

Terminalia chebula is generally known as Harade or Haritaki in India, it is an important medicinal plant used all over India. In English it is commonly known as “black myroblans”. The herb Terminalia chebula (Haritaki) consists of approx 250 species which are widely distributed in tropical areas around the world. It is used as a traditional medicine and is one of the most important herbs used in Ayurveda to cure various ailments. The fruit of Terminalia chebula (Harade) is regarded as the “king of medicines” by the Tibetans and the second-to-none by Ayurveda, it also held in high esteem by practitioners of folk medicine.
The herb Harade is generally used as a traditional medicine by the tribe of Tamil Nadu (India) to cure various ailments such as fever, skin diseases cough, gastroenteritis, urinary tract infection, diarrhea, candidiasis, wound infection etc, it is commonly known as ‘Kadukkaai‘ in this region.

Where is Haritaki (Terminalia Chebula) Plant Found?

Terminalia chebula (Harade) are found distributed in the teak forests, mixed deciduous forest, which extends in the forests of relatively dry types. It is distributed throughout tropical and subtropical Asia, including Sri Lanka, Burma, Thailand, Indochina Tibet and southern China.
It is also found in the region of Thailand and Burma along with teak. Generally Harade plant needs lots of sunlight but withstands some shade in youth. It is plant that can tolerant to drought and frost, can resist fire, regrowth with quick recovering from burns.
In India Haritaki plant is found in the forests of northern India and region around Uttar Pradesh, Bengal, it is most commonly seen in south Maharashtra, Tamil Nadu and Karnataka.
It was also introduced to Singapore but failed, later it was successfully planted in the botanical garden in “Bogor”, later on it was introduced in Peninsular Malaysia.

How To Identify Haritaki (Harade) Plant?

Plant : It is a deciduous tree with average size up to 25 m tall, with variable appearance, with a generally short cylindrical shaft of 5.10 m long, at breast height about 60-80 cm in diameter; crown rounded, with spreading branches; dark brown bark, generally longitudinally cracked with woody scales; twigs rusty-villous or glabrescent.
Leaves: alternate or opposite leaves, thin-leathery, oval or elliptical-obovate, with 7-12 cm x 4-6.5 cm, rounded at the base, obtuse to sub acute apex, entire, pubescent below; petiole up to 2 cm long, provided with two glands at the base of the leaf blade.
Flowers: Flowers in axillary 5-7 cm long, simple or branched at some point, about 4 mm size, yellowish-white and unpleasant aroma; 5-lobed calyx, corolla absent; stamens 10 exserted; lower ovary, one-celled.
Fruits: Fruit is obovoid one or oblong-ellipsoid drupe, 2.5-5 cm long, faintly 5-angular, yellow to orange-brown when ripe, labrous.

http://www.ayurvedicindia.info/health-benefits-of-kadukkaiharitakiharde-fruit-powder/

http://www.factmonster.com/ipka/A0932480.html

Plant Kingdom

(or Plantae )

Virtually all other living creatures depend on plants to survive. Through photosynthesis, plants convert energy from sunlight into food stored as carbohydrates. Because animals cannot get energy directly from the sun, they must eat plants (or other animals that have had a vegetarian meal) to survive. Plants also provide the oxygen humans and animals breathe, because plants use carbon dioxide for photosynthesis and release oxygen into the atmosphere.
Plants are found on land, in oceans, and in fresh water. They have been on Earth for millions of years. Plants were on Earth before animals and currently number about 260,000 species. Three features distinguish plants from animals:

• Plants have chlorophyll, a green pigment necessary for photosynthesis;
• Their cell walls are made sturdy by a material called cellulose; and
• They are fixed in one place (they don’t move).

Plant Classification

In order to study the billions of different organisms living on earth, biologists have sorted and classified them based on their similarities and differences. This system of classification is also called a taxonomy and usually features both English and Latin names for the different divisions.
All plants are included in one so-called kingdom (Kingdom Plantae), which is then broken down into smaller and smaller divisions based on several characteristics, including:

• Whether they can circulate fluids (like rainwater) through their bodies or need to absorb them from the moisture that surrounds them;
• How they reproduce (e.g., by spores or different kinds of seeds); and
• Their size or stature.

The majority of the 260,000 plant species are flowering herbs. To describe all plant species, the following divisions (or phyla) are most commonly used to sort them. The first grouping is made up of plants that are non-vascular; they cannot circulate rainwater through their stems and leaves but must absorb it from the environment that surrounds them. The remaining plant species are all vascular (they have a system for circulating fluids). This larger group is then split into two groups: one that reproduces from spores rather than seeds, and the other that reproduces from seeds.

Non-Vascular Plants

Mosses and “allies,” or related species (Bryophyta and allies)
Mosses or bryophyta are non-vascular. They are an important foundation plant for the forest ecosystem and they help prevent erosion by carpeting the forest floor. All bryophyte species reproduce by spores not seeds, never have flowers, and are found growing on the ground, on rocks, and on other plants.
Originally grouped as a single division or phylum, the 24,000 bryophyte species are now grouped in three divisions: Mosses (Bryophyta), Liverworts (Hepatophyta), and Hornworts (Anthocerotophyta). Also included among the non-vascular plants is Chlorophyta , a kind of fresh-water algae.

Vascular Plants with Spores

Ferns and allies (Pteridophyta and allies)
Unlike mosses, ferns and related species have a vascular system, but like mosses, they reproduce from spores rather than seeds. The ferns are the most plentiful plant division in this group, with 12,000 species. Other divisions (the fern allies) include Club mosses or Lycopods (Lycopodiophyta) with 1,000 species, Horsetails (Equisetophyta) with 40 species, and Whisk ferns (Psilophyta) with 3 species.

Vascular Plants with Seeds

Conifers and allies (Coniferophyta and allies)
Conifers and allies (Coniferophyta and allies) Conifers reproduce from seeds, but unlike plants like blueberry bushes or flowers where the fruit or flower surrounds the seed, conifer seeds (usually cones) are “naked.” In addition to having cones, conifers are trees or shrubs that never have flowers and that have needle-like leaves. Included among conifers are about 600 species including pines, firs, spruces, cedars, junipers, and yew. The conifer allies include three small divisions with fewer than 200 species all together: Ginko (Ginkophyta) made up of a single species, the maidenhair tree; the palm-like Cycads (Cycadophyta), and herb-like plants that bear cones (Gnetophyta) such as Mormon tea.
Flowering Plants (Magnoliophyta)
The vast majority of plants (around 230,000) belong to this category, including most trees, shrubs, vines, flowers, fruits, vegetables, and legumes. Plants in this category are also called angiosperms. They differ from conifers because they grow their seeds inside an ovary, which is embedded in a flower or fruit.

http://www.factmonster.com/ipka/A0932480.html

http://www.pmfias.com/classification-animalia-animal-kingdom/

Table of Contents

• 1 Basis for Animal Kingdom Classification
• 1.1 Levels of Organisation
• 1.2 Symmetry
• 1.3 Diploblastic and Triploblastic Organisation
• 1.4 Coelom
• 1.5 Segmentation
• 1.6 Notochord
• 2 Classification of Animal Kingdom
• 3 Phylum – Porifera
• 4 Phylum – Coelenterata (Cnidaria)
• 5 Phylum – Ctenophora
• 6 Phylum – Platyhelminthes
• 7 Phylum – Aschelminthes (Nemotoda)
• 8 Phylum – Annelida
• 9 Phylum – Arthropoda

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• 9.0.1 Arachnids
• 9.0.2 Crustaceans
• 9.0.3 Insects
• 10 Phylum – Mollusca
• 11 Phylum – Echinodermata
• 12 Phylum – Hemichordata
• 13 Phylum – Chordata
• 13.1 Vertebrata

Classification of Animal Kingdom – Porifera, Coelenterata, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Chordata.]
Source | Credits | Picture Credits: NCERT General Science

Basis for Animal Kingdom Classification

Classification of Animal Kingdom is based on various fundamental features like –

1. Levels of Organisation,
2. Symmetry,
3. Diploblastic and Triploblastic Organisation,
4. Coelom development,
5. Segmentation of the body and
6. Presense or absence of Notochord.

• The broad classification of Animalia based on common fundamental features:

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Levels of Organisation

• Though all members of Animalia are multicellular, all of them do not exhibit the same pattern of organisation of cells.
• For example, in sponges, the cells are arranged as loose cell aggregates, i.e., they exhibit cellular level of organisation. Some division of labour (activities) occur among the cells.
• In coelenterates, the arrangement of cells is more complex. Here the cells performing the same function are arranged into tissues, hence is called tissue level of organisation.
• A still higher level of organisation, i.e., organ level [organ level of organisation] is exhibited by members of Platyhelminthes and other higher phyla where tissues are grouped together to form organs, each specialised for a particular function.
• In animals like Annelids, Arthropods, Molluscs, Echinoderms and Chordates, organs have associated to form functional systems, each system concerned with a specific physiological function. This pattern is called organ system level of organisation.
• Organ systems in different groups of animals exhibit various patterns of complexities.
• For example, the digestive system in Platyhelminthes (incomplete digestive system) has only a single opening to the outside of the body that serves as both mouth and anus, and is hence called incomplete. A complete digestive system has two openings, mouth and anus.
• Similarly, the circulatory system may be of two types: open type in which the blood is pumped out of the heart and the cells and tissues are directly bathed in it and closed type in which the blood is circulated through a series of vessels of varying diameters (arteries, veins and capillaries).

Symmetry

• Animals can be categorised on the basis of their symmetry.
• Sponges are mostly asymmetrical, i.e., any plane that passes through the centre does not divide them into equal halves.
• When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. Coelenterates, Ctenophores and Echinoderms have this kind of body plan.
• Animals like Annelids, Arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry.

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Diploblastic and Triploblastic Organisation

• Animals in which the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm, are called diploblastic animals, e.g., Coelenterates. An undifferentiated layer, mesoglea, is present in between the ectoderm and the endoderm.
• Those animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm, are called triploblastic animals (platyhelminthes to chordates).

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Figure: Showing germinal layers : (a) Diploblastic (b) Triploblastic

Coelom

• Presence or absence of a cavity between the body wall and the gut wall is very important in classification.
• The body cavity, which is lined by mesoderm is called coelom.
• Animals possessing coelom are called coelomates, e.g., Annelids, Molluscs, Arthropods, Echinoderms, Hemichordates & Chordates.
• In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates, e.g., Aschelminthes.
• The animals in which the body cavity is absent are called acoelomates, e.g., Platyhelminthes.

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Segmentation

• In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs.
• For example, in earthworm, the body shows this pattern called metameric segmentation and the phenomenon is known as metamerism.

Notochord

• Notochord is a mesodermally [the middle layer of cells or tissues of an embryo, or the parts derived from this (e.g. cartilage, muscles, and bone)] derived rod-like structure formed on the dorsal side [posterior] during embryonic development in some animals.
• Animals with notochord are called chordates and those animals which do not form this structure are called non-chordates, e.g., Porifera to Echinoderms.

Classification of Animal Kingdom

Animal Kingdom is classified into:

1. Phylum – Porifera
2. Phylum – Coelenterata (Cnidaria)
3. Phylum – Ctenophora
4. Phylum – Platyhelminthes
5. Phylum – Aschelminthes (Nemotoda) Annelida
6. Phylum – Arthropoda
7. Phylum – Mollusca
8. Phylum – Echinodermata
9. Phylum – Hemichordata
10. Phylum – Chordata

Phylum – Porifera

• Phylum – Porifera includes organisms with holes.
• They are primitive multicellular animals and have cellular level of organisation.
• They are non-motile animals attached to some solid support.
• The body design involves very minimal differentiation and division into tissues.
• They are commonly called sponges.
• They are generally marine and mostly asymmetrical animals.
• Sponges have a water transport or canal system.
• Water enters through minute pores (ostia) in the body wall into a central cavity, spongocoel, from where it goes out through the osculum.
• This pathway of water transport is helpful in food gathering, respiratory exchange and removal of waste.
• The body is supported by a skeleton made up of spicules or spongin fibres.
• Sexes are not separate (hermaphrodite), i.e., eggs and sperms are produced by the same individual.
• Sponges reproduce asexually by fragmentation and sexually by formation of gametes.
• Fertilisation is internal and development is indirect having a larval stage which is morphologically distinct from the adult.

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Figure: Examples of Porifera : (a) Sycon (b) Euspongia (c) Spongilla

• Examples: Sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia (Bath sponge).

Phylum – Coelenterata (Cnidaria)

• The name cnidaria is derived from the cnidoblasts or cnidocytes (which contain the stinging capsules or nematocytes) present on the tentacles and the body.
• Cnidoblasts are used for anchorage, defense and for the capture of prey.
• Coelenterata (Cnidaria) are aquatic, mostly marine sessile or free-swimming radially symmetrical
• They exhibit tissue level of organization [have more body design differentiation than sponges].
• They have a central gastro-vascular cavity with a single opening.
• They are diploblastic.
• Some of these species live in colonies (corals).
• Some have a solitary [living alone] like–span (hydra).
• Some of the cnidarians, e.g., corals have a skeleton composed of calcium carbonate.
• Cnidarians exhibit two basic body forms called polyp and medusa. The former is a sessile and cylindrical form like Hydra, Adamsia (Sea anemone), etc. whereas, the latter is umbrella-shaped and free-swimming like Aurelia or jelly fish.
• Those cnidarians which exist in both forms exhibit alternation of generation (Metagenesis), i.e., polyps produce medusae asexually and medusae form the polyps sexually (e.g., Obelia).
• Jellyfish and sea anemones are common examples.
• Digestion is extracellular and intracellular.
• Examples: Aurelia (jelly fish), Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan) and Meandrina (Brain coral).

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Phylum – Ctenophora

• Ctenophora are commonly known as sea walnuts or comb jellies.
• They exclusively marine, radially symmetrical, diploblastic
• They exhinit tissue level of organisation.
• The body bears eight external rows of ciliated comb plates, which help in locomotion.
• Digestion is both extracellular and intracellular.
• Bioluminescence (the property of a living organism to emit light) is well-marked in ctenophores.
• Sexes are not separate and reproduction takes place only by sexual means.
• Fertilisation is external [fertilization occurs outside the body] with indirect development [zygote → larvae → animal].
• Examples: Pleurobrachia and Ctenoplana.

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Phylum – Platyhelminthes

• Platyhelminthes are more complexly designed than the earlier groups.
• They are bilaterally symmetrical.
• They are triploblastic. This allows outside and inside body linings as well as some organs to be made. There is thus some degree of tissue formation [organ level of organisation].
• The body is flattened dorsiventrally, meaning from top to bottom, which is why these animals are called flatworms.
• They may be freeliving or parasitic. Hooks and suckers are present in the parasitic forms.
• Some examples are freeliving animals like planarians, or parasitic animals like
• Parisites are mostly endoparasites found in animals including human beings. Some of them absorb nutrients from the host directly through their body surface.
• Acoelomate: There is no true internal body cavity or coelom, in which well developed organs can be accommodated.
• Specialised cells called flame cells help in osmoregulation and excretion.
• Sexes are not separate.
• Fertilisation is internal and development is indirect.
• Some members like Planaria possess high regeneration capacity.

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Phylum – Aschelminthes (Nemotoda)

• Body in aschelminthes (Nemotoda) is cylindrical [bilaterally symmetrical] rather than flattened.
• They exhibit organ-system level of body organization [there are tissues, but no real organs].
• They are triploblastic. A sort of body cavity or a pseudocoelom, is present.
• They are freeliving, aquatic, terrestrial or parasitic in plants and animals.
• These are very familiar as parasitic worms causing diseases, such as the worms causing elephantiasis (filarial worms) or the worms in the intestines (roundworm or pinworms).
• The body is circular in cross-section, hence, the name roundworms.
• Alimentary canal is complete.
• An excretory tube removes body wastes from the body cavity through the excretory pore.
• Sexes are separate (dioecious), i.e., males and females are distinct.
• Often females are longer than males.
• Fertilisation is internal and development may be direct (the young ones resemble the adult) or indirect.

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Phylum – Annelida

• Annelida are aquatic [marine and fresh water] or terrestrial; free-living, and sometimes parasitic.
• Their body surface is distinctly marked out into segments or metameres [metamerically segmented] and, hence, the phylum name Annelida (Latin, annulus: little ring).
• They exhibit organ-system level of body organization.
• They are coelomate [true body cavity]. This allows true organs to be packaged in the body structure.
• They are bilateral symmetric and triploblastic.
• They possess longitudinal and circular muscles which help in locomotion.
• Aquatic annelids like Nereis possess lateral appendages, parapodia, which help in swimming.
• A closed circulatory system is present.
• Nephridia (sing. nephridium) help in osmoregulation and excretion.
• Neural system consists of paired ganglia (sing. ganglion) connected by lateral nerves to a double ventral nerve cord.
• Nereis, an aquatic form, is dioecious [Sexes are separate], but earthworms and leeches are monoecious [having both the male and female reproductive organs in the same individual].
• Reproduction is sexual.

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Phylum – Arthropoda

• Insects, arachnids and crustaceans are members of the largest category of creatures on the planet: arthropods.
• Arthropods have hard, external shells called “exoskeletons,” segmented bodies and jointed legs.
• Some familiar examples are prawns, butterflies, houseflies, spiders, scorpions and crabs and some
• They exhibit organ-system level of organisation.
• They are bilaterally symmetrical, triploblastic, segmented and coelomate The coelomic cavity is blood-filled.
• The body of arthropods is covered by chitinous The body consists of head, thorax and abdomen.
• There is an open circulatory system, and so the blood does not flow in well defined blood vessels.
• Respiratory organs are gills, book gills, book lungs or tracheal system.
• Sensory organs like antennae, eyes (compound and simple), statocysts or balance organs are present.
• Excretion takes place through malpighian tubules.
• They are mostly dioecious.
• Fertilisation is usually internal.
• They are mostly oviparous.
• Development may be direct or indirect.

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Arachnids

• Spiders, harvestmen, mites, ticks and other arachnids are members of the class Arachnida.

Crustaceans

• Crustaceans make up a large group of arthropods that includes animals such as crabs, lobsters, crayfish and shrimp. They breathe with gills and have two pairs of antennae.

Insects

• In general, insects have three-part bodies, six jointed legs, compound eyes and two antennae.
• Bees, wasps, beetles, mosquitoes, flies, grasshoppers, ants, butterflies and moths, and dragonflies and damselflies are common types of insects.

Phylum – Mollusca

• Mollusca are the second largest animal phylum. They are terrestrial or aquatic.
• They exhibit organ-system level of organization.
• They are bilaterally symmetrical, triploblastic, coelomate animals. There is little segmentation.
• They have an open circulatory system and kidney-like organs for excretion. The anterior head region has sensory tentacles.
• The mouth contains a file-like rasping organ for feeding, called radula.
• They are usually dioecious and oviparous with indirect development.
• Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump. A soft and spongy layer of skin forms a mantle over the visceral hump.
• Examples are octopus, snails and mussels.

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Phylum – Echinodermata

• These animals have an endoskeleton of calcareous ossicles [calcium carbonate structures] and, hence, the name Echinodermata (spiny skinned organisms).
• They are exclusively free-living marine animals with organ-system level of organisation.
• They are triploblastic with a coelomic cavity [coelomate animals]. The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.
• Water-driven tube system [water vascular system] are used for locomotion, capture and transport of food and respiration.
• They are triploblastic and coelomate animals.
• Digestive system is complete. An excretory system is absent.
• Sexes are separate. Reproduction is sexual. Fertilisation is usually external.
• Development is indirect with free-swimming larva.
• Examples: Star fish, Sea urchin, Sea lily, Sea cucumber, Brittle star.

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Phylum – Hemichordata

• Hemichordata was earlier considered as a sub-phylum under phylum Chordata. But now it is placed as a separate phylum under non-chordata.
• This phylum consists of a small group of worm-like marine animals with organ-system level of organisation.
• They are cylindrical [bilaterally symmetrical], triploblastic, coelomate animals.
• The body is Circulatory system is of open type.
• Respiration takes place through gills.
• Excretory organ is present.
• Sexes are separate. Fertilisation is external. Development is indirect.
• Examples: Balanoglossus and Saccoglossus.

Phylum – Chordata

• Animals belonging to phylum Chordata are fundamentally characterised by the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits.
• They are bilaterally symmetrical, triploblastic, coelomate with organ-system level of organisation.
• They possess a post anal tail and a closed circulatory system.
• Phylum Chordata is divided into three subphyla: Urochordata or Tunicata, Cephalochordata and Vertebrata.
• Subphyla Urochordata and Cephalochordata are often referred to as protochordates and are exclusively marine.
• In Urochordata, notochord is present only in larval tail, while in Cephalochordata, it extends from head to tail region and is persistent throughout their life.
• Examples: Urochordata – Ascidia, Salpa, Doliolum; Cephalochordata – Amphioxus or Lancelet.

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All chordates possess the following features:

1. have a notochord
2. have a dorsal nerve cord
3. are triploblastic
4. have paired gill pouches
5. are coelomate.

Vertebrata

• These animals have a true vertebral column and internal skeleton, allowing a completely different distribution of muscle attachment points to be used for movement.
• The members of subphylum Vertebrata possess notochord during the embryonic period.
• The notochord is replaced by a cartilaginous or bony vertebral column in the adult.
• Thus all vertebrates are chordates but all chordates are not vertebrates.
• Besides the basic chordate characters, vertebrates have a ventral muscular heart with two, three or four chambers, kidneys for excretion and osmoregulation and paired appendages which may be fins or limbs.
• Vertibrates are bilaterally symmetrical, triploblastic, coelomic and segmented, with complex differentiation of body tissues and organs.

Comparison of Chordates and Non-chordates
S.No.	Chordates	Non-chordates
1.	Notochord present.	Notochord absent.
2.	Central nervous system is dorsal, hollow and single.	Central nervous system is ventral, solid and double.
3.	Pharynx perforated by gill slits.	Gill slits are absent.
4.	Heart is ventral.	Heart is dorsal (if present).
5.	A post-anal part (tail) is present.	Post-anal tail is absent.

http://www.pmfias.com/classification-animalia-animal-kingdom/

The Human Eye Facts, Functions, Structure and Problems

The Eye Definition Biology:

What do you know about the eye definition biology? Just learn about human eye facts and you will get precious information about it. You can define the eye as an organ of vision which makes you visualize the world around you. The eyes are two in number and each is placed inside specialized compartments in the skull.
The human eye is the organ which enables you to see. The human eye does not only let you view the scenes and phenomenon in your surroundings, but also enables you to differentiate between colors. Sometimes, there is a minor defect in the eye function and the individual cannot make difference between the red and green color. What is the name for such a condition? Well, you call it ‘color blindness’.

Human Eye Diagram:

No doubt, the human eye diagram will add a lot to your knowledge. But, it cannot give you all the interesting information about its working mechanism and capabilities.

When you talk of the human eye structure, they exist in pairs, each one being approximately 2.5 cm in diameter. There are following main parts of human eye:

• Sclera: The knowledge of eye parts and functions is both useful and interesting. The white part of our eyes is known as sclera. It consists of fibrous tissues. The job of this part it to protect the internal parts of the eye.
• Cornea: The transparent tissue through which light enters the eyes is called cornea. It exists in front of the eye. That is why, it looks prominent among different parts of the human eye.
• Iris: Iris is made up of muscles which contract or relax in order to adjust the amount of light which enters the eye.
• Pupil: There are many interesting facts about the pupil. It is, actually, an aperture controlled by the iris muscles. For instance, when it is dark, the iris muscles relax, causing the pupil to open up wider. Therefore, more light enters the eyes to enable us to see better. On the other hand, the pupil becomes narrow due to the contraction of the iris muscles. It occurs in the presence of excessive light in order to protect the cells of the eyes.
• Lens: The lens is present behind the pupil. Light enters the pupil, passes through the lens and is focused on the retina of the eye. The lens is capable of changing its shape in order to help us see near or far off objects. This is about how the human eye works.
• Retina: Digging further deeper into the human eye anatomy, you will come across the retina. The retina converts light into electrical signals which are transferred to the brain for processing. The retina contains two types of cells: rods and cones. These cells are sensitive to light. Rods are important for night-time vision when there is little light. On the other hand, cones play an important role in helping us see colors.
• Optic Nerve: The optic nerve takes electrical signals from the retina of the eye to the brain.

Eye Function

Eye function renders you the sense of sight. They convert light into electrical signals. Afterwards, the brain deciphers these electrical signals into images. Properly working healthy eyes are able to perform the following functions.

• It is one of the important human eye facts that they help us view our surroundings.
• Our eyes enable us to see colors. Certain organisms, such as dogs, cannot see colors and, so, their world is black and white.
• Eyes help us see near as well as distant objects.

Human Eye Facts – How It Works

There is one of the human eye facts that these small organs perform a very complex function. The working mechanism of the eyes consists of the following simple steps.

• When we see an object, light is reflected off it into our eyes.
• The light rays entering our eyes first pass through the pupil. These are the muscles of iris that control the size of the pupil.
• After passing through the pupil, light passes through the transparent lens of the eye. There occurs the refraction and focusing of the light rays on the retina.
• Light sensitive cells, rods and cones, present in the retina covert the light rays into electrical impulses. Isn’t it one of the most amazing facts about eyes of human beings.
• The optic nerve transfers these electrical impulses from the retina to the brain which then processes these signals and translates them in the form of an image.

Eye Problems

These extremely delicate organs can fall prey to different eye problems due to allergic factors, unhygienic conditions and the old age. Below are some of the most common diseases of eyes.

Conjunctivitis

Conjunctivitis has got a common name – the pink eye disease. It is an inflammation of conjunctiva, the transparent membrane which covers the sclera. Inflammation of tiny blood vessels found in conjunctiva makes our eyes appear red.

Cataracts

Cataracts affect the eye lenses. They may occur due to old age or exist as a defect by birth. Parts of lenses become opaque, blocking the passage of light to the retina, thereby obstructing our vision.

Glaucoma

Glaucoma is a disease which leads to blindness due to a damage to the optic nerve. When the optic nerve fails to transmit electric signals to the brain, an individual is unable to see at all.

http://www.organsofthebody.com/the-human-eye/

From the above information, you can realize that eye is one of the greatest blessings of nature. The human eye facts reveal that it is very complex in terms of both structure and function. In the process of visualizing an object, the light rays fall on that object. After reflecting from there, they enter the eye. Passing through different parts of the eye, the light rays reach the retina. After that, there is conversion of light rays into electrical signals. The brain reads these signals and translates them into images of the objects. Don’t such human eye facts make you ponder about this marvelous creation of nature?

Meanwhile, if you want your eyes to keep working at their best potential throughout your life, do take proper care of them. To maintain the health of eyes, you need to take all the essential nutrients for eyes in adequate quantity as well as avoid over-burdening them.