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Eyes: How They Work, Anatomy and Common Condition

 The eye is a complex sensory organ that allows us to see the world around us. The eye works by gathering light from the environment and converting it into electrical signals that can be interpreted by the brain. The basic structure of the eye includes the cornea, iris, pupil, lens, retina, and optic nerve. The cornea is the transparent outer layer of the eye that helps to focus incoming light. The iris is the colored part of the eye that regulates the amount of light that enters the eye through the pupil, which is the black circular opening in the center of the iris. The lens is a clear, flexible structure located behind the iris that helps to focus light onto the retina. The retina is a thin layer of tissue that lines the back of the eye and contains photoreceptor cells called rods and cones. These cells convert light into electrical signals that are sent to the brain via the optic nerve. The rods are responsible for the low light vision and detecting motion, while the cones are resp
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KINGDOM - MYCOTA (FUNGI)

Fungi name was given by Gaspard Bauhin and the study of fungi is called mycology. Fungi show great diversity in morphology and habitat. They are cosmopolitan they found mostly in humus reach soil. but in the presence of moisture, these can grow on leather, wood, pickle, and bread. Some fungi live parasitically in plants, animals and human body. Chloroplast is absent in fungi, so fungi are heterotrophs. The fungi constitute the unique kingdom of heterotrophic organisms.Fungi obtained their own food from dead organic matter or living organisms.

On the basis of  source of food fungi are of two types :

  • Saprophytic: These fungi obtained their own food from dead organic matter such as bread, rottening fruit, vegetable, and dung. In these fungi nutrition is absorptive type.
  • Parasitic: These obtain their own food from living organisms such as plants, animals, and humans.They obtain nutrition with the help of haustoria.


Some fungi are found symbiotically associated with algae and form lichens. Some fungi are found symbiotically in the roots of higher plants and form mycorrhiza. The body of fungi is called mycelium. Mycelium is composed of filaments called hypha  (plural - hyphae). The cell wall is made of chitin (fungal cellulose) and polysaccharides. The cell wall of the member of class oomycetes is mainly made up of cellulose. In the fungi, the stored food remains in the form of glycogen and oil. Types of reproduction in fungi are Vegetative reproduction (Fragmentation, Budding, and fission), Asexual reproduction (by Sporangiospores and conidia formation) and Sexual reproduction (Gametangial contact and Gametangial copulation).

True fungi are divided into four classes on the basis of the structure of mycelium and sexual reproduction : 

(A) Phycomycetes : 


All fungi included in this class are called as lower fungi. Members of Phycomycetes are found in aquatic habitat so they are also known as algal fungi. They are also found on decaying wood in moist and damp places or as obligate parasites on plants. The mycelium of all the fungus included in this class is coenocytic, aseptate and branched. Phycomycetes further classified into some classes like oomycetes and zygomycetes on the basis of sexual reproduction.
Examples of Phycomycetes :
  1. Phytophthora infestans - cause "late blight of potato". This disease is known as "Famine of Ireland" - 1845
  2. Pythium species - Causes "Damping off " disease in tobacco and "vegetable crops"
  3. Sclerospora graminicola - Causes "Green ear disease" of Bajra.
  4. Albugo candida - Causes "White rust or white spots disease" in the members of the Cruciferae family.
  5. Saprolegnia parasitica - It causes salman disease in fishes.
  6. Pilobolus - It is called as "Hat thrower" or "fungal shotgun". This name is given on the basis of blasting of the sporangium.
  7. Rhizopus and Mucor - These are known as bread mold. They prefer to grow on bread. The tip of the mycelium of rhizopus is black coloured. Therefore this fungus looks black coloured. 


(B) Ascomycetes :


The fungi of this class is also known as "the sac fungi". Members of this class are mostly multicellular rarely unicellular (eg. yeast). Member of Ascomycetes are saprophytic decomposers, parasitic or coprophilous (growing on dung). Their mycelium are septate and branched. Septa are found in the mycelium of ascomycetes. Pore are present in septa. These pores allow cytoplasm to pass from one cell to other cells. Pore does not allow the passing of the nucleus. They reproduce asexually by Conidia formation and reproduce sexually by Somatogamy and gamatangial contact. Ascospores are formed during sexual reproduction. On this basis they are named as Ascomycetes. There are three stages in sexual reproduction of Ascomycetes Plasmogamy, Karyogamy and Meiosis. In it two fungal hypha of mycelium come close to each other and their cells fuse to form dikaryon. After this an outgrowth originates from dikaryon which is called ascogenous hypha. Ascogenous hypha develops and form a sac like structure which is called ascus. Due to this sac like ascus, ascomycetes are called as sac fungi. Now both the nuclei reach in ascus and fuse to form diploid nucleus. Now ascus is protected by some fungal filaments to form a fruting body, called as ascocarp in which reductional division occurs leading to formation of haploid ascospores. Minimum four ascospores are formed in one ascus but generally 8 ascospores are formed in one Ascus. By the rupturing of ascocarp and acus, ascospores become free and each ascospores form a new mycelium.
Examples of ascomycetes :
  1. Penicillium : Blue or green mold. Penicillin the first discovered antibiotc was obtained from Penicillium notatum but nowdays more quantity of penicillin is obtained from P. chrysogenum.
  2. Aspergillus : Black  or brown mold or blacky-smoky mold. An antibiotic prolifein obtained from it. It also causes aspergillosis. It secrets toxic substances  known as aflatoxins which are carcinogenic, causes liver cancer.
  3. Claviceps : It causes ergot disease of bajra. Ergotin drug it obtaind from it a narcotic drug (LSD) is also obtained from it.
  4. Morchella: Species of morchella are commony called as morels it is an edible fungus.
  5. Neurospora: Red or pink mold it is used for the study of genetics in plant kingdom so it called as drosophylla of plant kingdom.
  6. Truffles: It is an edible fungus. 
  7. Yeast : It an unicellular fungi. According to five kingdom classification, it should be placed in protista but exceptionally it is placed in fungi because its life cycle is similar to class Ascomycetes. It is used as fermentation agent in bakery and brewery so Saccharomyces cerevisiae is also called baker's yeast. Riboflavin (vitamin B2) is obtained from Saccharomyces cerevisiae.

(C) Basidiomycetes : 


Basidiomycetes are also known as Club fungi. They grow in soil on logs and tree stumps and in living plant bodies as parasites. They have branched and septae mycelium. In these fungi mycelium are of special type and they are called dolipore septum. One big pore is present between every septum. The boundary of pore is spread on both sides, this boundary is called as parenthesome. Due to the spreading of the boundary on both sides, the shape of septum becomes dome shaped due to which it is called as dolipore septum. They also have clamp connections which allow the nucleus to migrate to the neighbouring cell due to which the other cell becomes dikaryotic. In these fungi, generally asexual spores are not found but vegetative reproduction by fragmentation is common. Sexual reproduction in these fungi are performed by two methods Somatogamy and Spermatization.
Examples of Basidiomycetes ;

  1. Bracket or shelf fungi : These are epixylic fungi i.e. these like to grow on wood. Their fruiting body is similar to bracket therefore they are called as bracket fungi. 
  2. Puff balls : These are saprophytic fungi.
  3. Mushroom (Basidiocarp) : These are umbrella like fungi often seen growing in grounds during rainy season. Some mushroom are edible. 
  4. Smut fungi : It causes smut disease on plant. Ustilago nuda tritici causes loose smut of wheat.
  5. Agaricus : It is called as gill fungi because gills like pores are present in its fruiting body.
  6. Puccinia : It causes rust disease in wheat.

(D) Deuteromycetes : 


It is also called fungi imperfecti, because perfect stage or sexual reproduction is absent in this class of fungi. Those fungi are included in this class in which sexual reproduction is absent or is not discovered at yet. When the sexual forms of this class of fungi were discovered they were moved into right class ascomycetes or basidiomycetes from deuteromycetes. The mycelium of these fungi are septate and branched. Asexual reproduction take place with the help of conidia formation. Some members of this class are saprophytic or parasitic. A large number of members of this class are decomposers of litter and help in mineral cycling. 
Examples of Deuteromycetes ; 
  1. Alternaria solani : Early blight of potato.
  2. Cercospora personata : Tikka disease of groundnut.
  3. Colletotrichum falcatum : Red rot of sugarcane.
  4. Helminthosporium oryzae : Leaf spot of rice. This known as famine of bengal (1945).
  5. Trichoderma
  6. Trichophyton and microspermum : produces ringworm in humans.

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