Biology - A Science of Exceptions | Civil Services Preparation Online

Biology – A Science of Exceptions

Physical Sciences have sets of principles or laws which are universal in their application, on the other hand life sciences have very few universally applicable principles and exceptions are numerous. As a result, Biology is often called science of exceptions. The reasons of this exceptions are that living being possesses variations, have adapted themselves to different environment, modes of living and feeding.

Dicotyledonous plants have two cotyledons in their seeds. The seeds of parasitic plant, Cuscuta are devoid of any distinct cotyledons.
Dicot leaves have reticulate venation while monocot leaves have parallel venation. However, a number of monocots (eg. Smilex, Colocasia) have reticulate venation while some dicots (eg. Calophyllum, Corymbium) have parallel venation.
Stems are normally aerial but in a number of plants they are underground. Eg. Banana, Ginger, Colocasia.
Roots are normally geotropic but in mangrove plants like Sonneratia some of the roots are negatively geotropic, come out of the saline marsh and take part in aeration. They are called pneumatophores.
Roots are non-green and non-photosynthetic. They are green and photosynthetic in Tinospora.
Adventitious roots commonly develop from the nodes but in Ivy they grow from internodes as well.
DNA is the hereditary material in all organisms except in some viruses called riboviruses. Here, RNA functions as the hereditary material. Eg. TMV
DNA is usually double stranded but in virus φ x 174, it is single stranded. On the other hand RNA is commonly single stranded but in Rheovirus it is double stranded.
The heart of reptiles is 3- chambered but in crocodile it is 4 – chambered.
All land animals drink water but desert or Kangaroo Rat never does so.
Normally lunges are absent in fishes but lung fishes have both lungs and gills.
Birds fly but Ostrich and Kiwi do not do so.
Mammals are mostly terrestrial. Bats are able to fly like birds while Whale and Dolphin are aquatic and able to swim like fishes.
Mammals give birth to young ones (viviparous). Duck Billed Platypus and Spiny Ant Eater are egg laying mammals (oviparous).
RBC of mammals is circular and biconcave but RBC of camel and Lama are oval and flat.
Larval stage is juvenile stage which does not take part in reproduction but axolotl larva of american Salamander can reproduce sexually. This phenomenon is called paedogenesis (Gk. Pais- child, genesis- reproduction) or reproduction by young larval stages and neoteny (Gk. Neosyoung, tenein-stretch) or retention of larval traits in adult or occurrence of adult characters like sexual maturity in larva.
Young ones are produced by fertilization of eggs with the help of sperms. However, the drones of honey bee develop from unfertilized eggs.

Level of Organization:

Organization is the arrangement of smaller components of any structure, system or situation into larger ones into still larger ones in a hierarchy, where components of each level coordinate with one another towards a common goal.

Organisation is a sort of hierarchy or pyramid of level where each level is made of components of lower level and itself becomes a component of higher level.

Atomic level: the basic unit of component of organisation in both living and non-living object is the atom.
Molecular level: Atoms are organised to form molecules and compounds. In the living world, molecules are of two type, small simple macromolecules and large complex macromolecules. Both are collectively called as biomolecules.
Subcellular Level: In living world, molecules and compounds coordinate with one another to form subcellular components like cell organelles, membrane and cytoplasmic matrix.
Cellular Level: The subcellular components coordinate their activities to produce living cells. There are both unicellular as well as multicellular organisms. The latter has higher level of organisation like cellular organisation, tissue organisation, organ organisation and organ system organisation.
Tissue Level: In multicellular organisms, the cell may be similar (colonial organisms) or organised into distinct functional units called tissues. Tissue is a group of cells having a common origin and having a common function.
Organ Level: Two or more tissue are organised into distinct structures called organs and they are specialised for performing one or more functions.
Organ System Level: Two or more organs coordinate their activities towards a common activity. E.g. Digestive system, respiratory system etc.
Organismic or Individual Level: Living beings are called organisms because they possess high level of organisation. They are called individuals because each organism has a distinct identity or individuality.
Population Level: All the individuals of a species found in an area where they can interact with one another is called population.
Community Level: The populations of different species found in an area also interact with one another. They constitute a biotic community.
Ecosystem Level: The biotic community of an area and its abiotic environment together form an ecosystem.
Biosphere Level: All the ecosystem of the world interacts further and form biosphere or liveable space of the earth. An organism is therefore, not only an individual but also a part of population, community, ecosystem and biosphere. Biosphere has the highest level of organisation.

REGULATION OF ORGANISATION:

Organisation is regulated at each step by four processes – aggregation, interaction, equilibrium and change.

Aggregation: It is the coming together or grouping of smaller units during the formation of larger unit. Eg. Atoms aggregating to form molecules and compounds, cells joining to form tissues, tissues forming organs etc.
Interaction: The partners or participants of an aggregate do not remain unaffected. Instead, they interact amongst themselves.
Equilibrium: Interaction may directly result in the development of stability or a balance. E.g. Holding of water molecules in the liquid state by hydrogen bonds. Another example is the interaction of several organs like nose, wind pipe, lungs, rib cage and diaphragm to produce breathing movements in a highly coordinated and balanced manner.
Change: In many cases interaction brings about a change and gives rise to a new product. For example, hydrogen and oxygen interact to form water; they also interact in different manner to produce another product called hydrogen peroxide. Atoms of carbon, hydrogen and oxygen interact in various manner to form a large varieties of carbohydrates like trioses, tetroses, pentoses and hexoses. The products thus formed may interact further to give rise to new structures.

LIFE AS AN EXPRESSION OF ENERGY AND EXCHANGE OF MATTER

Working of living matter requires both energy and matter as it is continuously dissipating energy as well as producing waste products. Depending upon its relation with environment for mass and energy, material system are of two types, open system and close system.

Open System: It is the material system in which mass and energy can be lost or gain from the environment. Biological systems cannot live without input of energy. They must receive materials from outside for growth or repair and give out waste products. Accordingly, an open system is the one which receives an input of energy and exchanges materials with the environment.
Closed System: Biologically a closed system is the one that does not receive input of energy or exchange material with the environment. It is bound to perish after sometime. However, nonliving closed system can persist indefinitely. E.gl. stone

BIOENERGETICS

Branch of science that deals with energy kinetics of living system is known as bioenergetics. No physical phenomenon or chemical reaction can occur without concomitant use of energy. Thus, energy is used in all systems to do work. It is also being transferred and transformed in various activities, but the total amount of energy in the universe remains constant because gain of energy by one system is compensated by similar loss of energy form its environment.

ENERGY CHANGE

Two types of energy changes occur in nature energy transfer and energy transformation. Both the type is occurring continuously in the living matter or cell.

Energy transfer: It is the passage of energy from one area, source or substance to another in the same form. For example, respiratory substrate contains chemical energy present in the bonds amongst its atoms. The energy is released in respiration. The same is transferred to ATP during its synthesis from inorganic phosphate and ADP. Chemical energy present in ATP becomes available for active absorption, transport of ions, biosynthetic reactions required for maintenance, repair growth and development.
Energy Transformation: It is the conversion of one from of energy into another

The most important energy transformation of the biosphere is the conversion of radiant or light energy into chemical energy during photosynthesis. The chemical energy is stored in the form of potential energy in the food materials. The whole living world depends upon this transformation for its existence.
Energy transformation is always going on in the living systems. The potential energy stored is

– Liberated during respiration and stored as readily usable energy in ATP.

– The Chemical energy stored in ATP is made available to produce light in glow worms or luminescent fishes.

– ATP energy is changed to electrical energy for conduction of impulses in nerves or production of electric shock in some fishes.

– A common transformation is production of heat energy from chemical energy for keeping the body warm.

– Chemical energy is changed to mechanical energy for activity of muscles, cilia and flagella. Diversity of Life: A general View

BACTERIA

Bacteria are:

Prokaryotic.
Single celled, Microscopic organisms (Exceptions have been discovered that can reach sizes just visible to the naked eye. They include Epulopiscium fishelsoni, a bacillus-shaped bacterium that is typically 80 micrometers (μm) in diameter and 200-600 μm long, and Thiomargarita namibiensis, a spherical bacterium between 100 and 750 μm in diameter)
Generally much smaller than eukaryotic cells.
Very complex despite their small size.
They are equally varied in their nutrition saprobic, parasitic, chemoautotrophic, photoautotrophic and symbiotic. The photoautotrophs include both aerobes and anaerobes.
Cell wall is generally present. It contains peptidoglycan and polysaccharides other than cellulose.
The cells have one envelope type of organisation, i.e. the whole protoplast is covered by plasma membrane but internal compartmentalization is absent.
The genetic material is not organised into a nucleus.
DNA is naked and it is associated with histone proteins. DNA lies coiled inside the cytoplasm and the coiled mass is called as nucleoid.
All membrane bound cell organelles are absent, e.g. mitochondria, lysosomes, golgi bodies etc.
Some bacteria have the ability to convert dinitrogen into ammonia state. The phenomenon is called nitrogen fixation.

(Even though bacteria are single – celled organisms, they are able to communicate with one another through a process called quorum sensing. In this way they can function as a multicellular population rather than as individual bacteria).

Bacterial cell shape is determined primarily by a protein called MreB. BreB forms a spiral band – a simple cytoskeleton – around the interior of the cell just under the cytoplasmic membrane. It is thought to define shape by recruiting additional proteins that then direct the specific pattern of bacterial cell growth. For example, bacillus – shaped bacteria that have an inactivated MreB gene become coccoid shaped and coccus – shaped bacteria naturally lack the MreB gene.

Most bacteria come in one of three basic shapes: Coccus, Rod or Bacillus and Spiral.

1. The Coccus:

The cocci are spherical or oval bacteria having one of several distinct arrangements based on their planes of division.

(a) Division in One Plane produces either Diplococcus or Streptococcus arrangement.

Diplococcus: Cocci arranged in pairs Streptococcus: cocci arranged in chains

(b) Division in two planes produces a tetrad arrangement.

Tetrad: Cocci arranged in squares of 4

Sarcina: Cocci in arranged cubes of 8

(d) Division in random planes produces a Staphylococcus arrangement.

Staphylococcus: Cocci arranged in irregular, often grape like clusters.

An average coccus is about 0.5 – 1.0 micrometer (μm) in diameter. (A micrometer equals 1/1,000,000 of a meter.)

2. The Rod or Bacillus

Bacilli are rod-shaped bacteria, Bacilli all divide in one plane producing a Bacillus, Streptobacillus, or Coccobacillus

(a) Bacillus: Single bacilli

(b) Streptobacillus: bacilli arranged in chains

An average bacillus in 0.5-1.0 μm wide by 1.0-4.0 μm long.

3. The Spiral

Spirals come in one of three forms, a Vibrio, a Spirillum, or a Spirochete.

(a) Vibrio: a curved or comma-shaped rod

(b) Spirillum: a thick, rigid spiral

Spirals range in size from 1 μm to over 100 μm in length.

4. Exceptions to the above shapes

Trichome forming, sheathed, stalked, filamentous, square, star-shaped, spindle-shaped, lobed and pleomorphic.

Structurally a typical bacterium usually consists of:

A cytoplasmic membrane surrounded by a peptidoglycan cell wall and maybe an outer membrane;
a fluid cytoplasm containing a nuclear region (nucleoid) and numerous ribosomes; and
often various external structures such as a glycocalyx, flagella and pili.

KINGDOM PROTISTA

The term Protista was proposed by Ernst Haeckel and this kingdom includes

Protistan algae (dinoflagellates, diatoms and euglena-like flagellates)
Slime moulds and
Protozoans (zooflagellates, sarcodines, sporozoans and ciliates)

General characteristic of the kingdom Protista:

They are unicellular, eukaryotic organisms. Some individuals form colonies without much cellular differentiation. Tissue level of organisation is absent.
Mostly they are aquatic organisms. Many are plankton and some forms are parasitic.
The Protistan cells contain cell membrane, cytoplasm and nucleus. The cells may possess an outer covering of cell wall, pellicle, cuticle or shell. The cell wall when present contains cellulose.
If flagella and cilia are present, these have 9+2 pattern of Microtubules.
they commonly move with the help of pseudopodia, flagella or cilia.
Nutrition may be photosynthetic, holozoic, saprobic or parasitic. Some protists are mixotrophic in nature.
Reproduction – both Sexual and Asexual.
Under unfavourable condition some protest form cyst wall around their body and become inactive.
Protists show two types of life cycles: life cycle showing zygotic meiosis and life cycle showing gametic meiosis.
Parasitic protists may cause diseases like dysentery, malaria, sleeping sickness etc.

Locomotion in Protista:

The following are some modes of locomotion in the protists.

1. Pseudopodia locomotion: it is slow creeping type of locomotion which is performed with the help of protoplasmic outgrowth called pseudopodia. This type occurs in sarcodines and slime moulds. The rate of locomotion is 0.2-3 μm per second.

Pseudopodia are of four types Lobopodia (lope like with broad and blunt end present in Amoeba), Filopodia (find thread like tapering and are composed of ectoplasm, often found in Euglypha), Axopodia (long and stiff with hard axial filament; present in Actinophrys) and Reticulopodia (long and branching; the branches of adjacent pseudopodia may form network; often found in Golbigerina)

2. Flagellar Locomotion: flagella are long, thread like vibratile structures which show undulating and help the protists to swim in aquatic habitat. Flagella show whip-like movement. The number of flagella varies from one to four. They usually beat independently and rate of locomotion is 15-300 μm per second. This type occurs in dinoflagellates, euglenoids and zooflagellates.

3. Ciliary locomotion: Cilia are fine, vibratile thread like structures which are smaller but numerous as compared to flagella. They show bending movement for propelling the organism in the water. Cilia show car like movement. Being numerous, the cilia perform rapid locomotion at the rate of 400-2000 μm per second.

All the cilia of a cell show coordinated movements; they are of two types isochornic or synchronous rhythm in which all the cilia of a cell beat simultaneously and metachornic rhythm in which cilia move in rapid succession one after another.

4. Wriggling Locomotion: It is a slow worm like movement which is performed with the help of a wave of contraction and expansion of the body, e.g. sporozoans, nonflagellates, euglenoids etc.

5. Locomotion by Mucilage Propulsion: some protists like diatoms do not have any organelles of locomotion. They can, however, move from one place to another through secretion of mucilage. This type of locomotion occurs in direction opposite to that of the mucilage secretion.

Nutrition in Protists:

They have diverse modes of nutrition.

Photosynthetic or holophytic: in this move of nutrition, the organisms prepare their food from carbon dioxide and water by utilising sunlight with the help of photosynthetic pigments like chlorophyll. This process is called photosynthesis. The photosynthetic protists are dinoflagellates, diatoms and euglenoids.
Holozoic or Zootrophic: in this type an individual captures and ingest food like animals. It could be noticed in the case of Amoeba and Paramecium.
Saprobic or Saprophytic: in this type, the organism release enzymes into the surroundings where the enzyme converts organic matters into simpler products. These products are then absorbed through the body surface of the organism. Saprozoic nutrition could be found in slime moulds.
Parasitic: some protists gat their food from the body of other organisms. The individual which obtain its food is called parasite and the organism from which the parasite gets food is called host. Trypanasome, Giardia, Entamoeba, Plasmodium are some example of parasites.
Mixotrophic: it is a mixed type in which the organism can perform two kinds of nutrition. For example, in euglena nutrition is both holophytic and saprobic.

Reproduction in Protists:

Protists have a great power of reproduction. They reproduce by both sexual and asexual methods.

1. Asexual Reproduction: it is the rapid method of multiplication in protists. It involves only one parent and all the young ones produced asexually have the same genetic constitution as that of the parents and are called clones.

(a) Binary Fission: it is the division of a parent cell into two daughter cells by mitosis. (b) Multiple Fission: it is the division of a parent organism into several daughter cells. (c) Spore formation: in some protists spore are formed for asexual reproduction. Spores have certain covering to withstand unfavourable conditions and on germination, each spore gives rise to a new individuals. (d) Budding: In budding, a small outgrowth develops from the parent body which separate and develop into a new individual.

2. Sexual Reproduction: it originated in protists. Sexual reproduction involves two fundamental processes; meiosis and fertilization (syngamy). Meiosis reduces the number of chromosomes from 2N to 1N of an organism. In the process of syngamy, two 1N gametes (special sex cells) fuse together to form a 2N zygote. Meiosis is essential in reproduction since it reduces the chromosome number to half in gametes so that after fertilization the number of chromosome is kept constant in a species. In certain forms such as paramecium, two individuals come together for exchange of nuclei. This process is called conjugation.

Cyst Formation:

Under unfavourable condition such as lack of oxygen, extreme temperature etc. some protists form a tough cyst wall around their body and become inactive. Cysts help in perennation and dispersal of species. When favourable condition return, the organism comes out of the cyst wall and leads an active life. In certain form like Amoeba, multiple fission occurs inside cyst. Thus, it also helps in reproduction.

Major groups of protists:

The kingdom Protista has been broadly divided into three main groups. 1. Photosynthetic protists or prostistan algae 2. Consumer decomposer protists (slime moulds) 3. Protozoan protsts

Photosynthetic protists or prostistan algae : Photosynthesis takes place in these protists. They constitute an important portion of the phytoplankton. They include dinoflagellates, diatoms and euglenoids (Euglena like flagellates)

1. Dinoflagellates: they are a group of about 1000 species of golden brown photosynthetic protists. The important characters of dinoflagellates are the following

They are basically unicellular motile and biflagellate, golden brown, photosynthetic protists. A few are nonmotile, nonflegellate, amoeboid, palmelloid or filamentous. Some periplast covered golden dinoflagellates called zooxanthellae occur in a number of marine protozoan protists.
Cells are generally covered by a rigid coat, the Theca or Lorica of articulated and sculptured plates of cellulose and pectin. Because of the presence of the Sculptured plate, these protists are often known as armoured dinoflagellated.
The two flagella are different, one transverse and other longitudinal flagellum. The longitudinal flagellum. The longitudinal flagellum is narrow, smooth and directed posteriorly and the transverse flagellum is ribbon like.
Most species are brown, green or yellow chromatophores with chlorophyll a, chlorophyll c, α carotene and abundant xanthophyll’s.
Food is reserved and stored in the form of starch like carbohydrates and oils.
Mucilage bodies or vesicles occur below the cell membrane.
A non-contractile vacuole called pusule is present near the flagellar base. Pusule may take part in flotation and osmoregulation. Contractile vacuoles are absent.
Trichocysts are found in number of dinoflagellates. Nematocysts or cnidoblasts (similar to coelenterates) have been reported in a few dinoflagellates.
Some dinoflagellates such as Gumnodinium and Gonyaulax grow in large number in the sea and make the water looks red and causes the so called “red tide”.
Some marine dinoflagellates show bioluminescence. Their phosphorescence causes glowing of water bodies in the dark. E.g. Noctulica, Gonyaulax, Pyrodinium etc.
Some dinoflagellates are poisonous to vertebrates (e.g. Gonyaulax catenella). When they are large in number, they produce the toxin called saxitoxin into the sea water which kills fishes and other aquatic animals. Marine shell fish (sea mussels-molluscs) eat large number of dinoflagellates. The poisonous substance of dinoflagellates reaches the shell fishes. The poison is not harmful to the fishes but the conumption of these infected mussels may cause severe illness (called Paralytic shell fish poisoning or PFP and may be fatal).
Asexual reproduction is commonly through cell division. Cyst occurs in a number of dinoflagellates.
Sexual reproduction has been reported in some dinoflagellates (e.g. Ceratium). It is isogamous or anisogamous.

2. Diatoms: They are a group of golden brown photosynthetic protists which are covered by two valved siliceous frustules. They have the following characters.

They are microscopic protists which do not possess flagella except in the reproductive stage. The shape is various spheres, rectangles, triangles, semicircle etc.
They are basically unicellular but can form pseudo filaments and colonies.
Diatoms occur in all aquatic and moist terrestrial habitats. The aquatic habitat includes sea, brackish water and fresh water. They are very good Pollution indicators.
They may be free floating or bottom dwellers. The free floating form remains suspended on the surface of water by mucilage secretion and presence of light weight lipids.
They may show gliding type of movement with the help of mucilage.
Chloroplasts are yellowish brown to greenish brown. They contain chlorophyll a, Chlorophyll c, fucoxanthin, diatoxanthin, diadinoxanthin, β carotene etc.
The body is covered by a transparent siliceous shell known as Frustule.
The food reserve is in the form of oil and leucosin. Volutin globules (proteinaceous in nature) are also present.
The common mode of multiplication is binary fission. There may be sexual mode of reproduction in some forms too.
Diatoms resemble dinoflagellates in having fucoxanthin.
Diatoms are very important photo synthesisers. About half of all the organic matter synthesised in the world is believed to produced by them. Though microscopic, diatoms are important source of food to animals. A 60 tonne blue whale may have 2 tonne of plankton in the gut which is mostly diatoms.
The siliceous frustules of diatoms do not decay easily. They pile up at the bottom of the water and form big heaps called diatomite or diatomaceous earth. They may extend for several hundred meters in certain areas from where the same can be mined.

3. Euglena: it is a large genus having about 152 species. The following are some general features.

It is found in fresh water ponds and pools. It also occurs on moist mud.
Nutrition may be holophytic, saprobic or mixotrophic.
Asexual reproduction occurs by longitudinal binary fission. Sexual reproduction has not been recorded.
The body of Euglena is spindle like and so often called spindle organism. The body is covered by plasma membrane followed by a number of helically arranged overlapping strips of periplast or pellicle.
The anterior end bears an emergent tinsel flagellum which help in active swimming.
The posterior end is pointed. The anterior end is blunt and bears and eccentric cytostome (mouth) which lead into a tubular canal called cytopharynx (gullet)
Contractile vacuoles take part in osmoregulation.

Consumer- Decomposer Protists (slime moulds) : They were formerly included amongst mycetozoa or fungus-animals. Slime moulds are included in the division of gymnomycota by mycologists. They are also sometime Protistan fungi. The slime moulds have the following general features:

They do not have chlorophyll.
They are surrounded by the plasma membrane only.
The slime moulds live usually amongst decaying vegetation. They are quite common on lawns and moist fields.
They exhibit wide range of colouration.
They have phototrophic or saprotrophic nutrition.
Both asexual and sexual modes of reproduction are found.
The slime moulds resemble both protozoa and true fungi. They are like protozoa in their amoeboid plasmodial stage and similar to true fungi in spore formation.
Some of the common acellular slime moulds are physarella, physarum etc. and some of the common cellular slime moulds are Dictyostelium, Polysphondylim etc.

Protozoan Protists:

They are microscopic acellular organisms with varied form, shape and symmetry.
The body may be covered by a delicate or firm pellicle or calcareous or siliceous shell.
Locomotion occurs by pseudopodia, flagella, cilia or contraction.
The cells may have one or more nuclei which may be monomorphic or dimorphic.
They may be free living, commensal or parasitic.
Exchange of gases and excretion occur through the general body surface.
Cysts formation occurs during unfavourable periods. It is helpful in dispersal.
They reproduce asexually by binary fission, budding, multiple fission or schizogony.
Sexual reproduction occurs by syngamy and conjugation.
They cause various diseases to human Trypanosoma gambiense is the parasite of African sleeping sickness, Leishmania donovani is the parasite of Kala-azar or dum-dum fever, Leishmania tropica produces skin ulcers (Delhi sore), Giardia intestinalis is the parasite of diarrhoea, Trichomonas vaginalis causes leucorrhoea, Entamoeba histolytica is a human parasite that causes amaoebic dysentery or amoebiasis etc.

KINGDOM FUNGI

Fungi is a large kingdom. They are achlorophyllous, heterotrophic spore-forming, non-vascular, eukaryotic organisms which often contain fungal cellulose in their walls and possess glycogen as food reserve. The branch of biology dealing with the study of fungi is known as mycology.

General features of fungi:

It contains achlorophyllous, spore-producing, multi cellular or multi nucleate eukaryotic organisms. Basically, unicellular yeasts are also included amongst fungi because their sexual reproduction is similar to that of some fungi.
The organisms are heterotrophic with absorptive type of nutrition. It is either saprobic or parasitic. Symbiotic association also occurs with some algae and higher plants. E.g. lichens and micorrhiza.
The parasitic fungi cause a number of diseases in plants like mildew, rusts, smuts, rots, spots or wilts.
The body of fungus is filamentous and is called mycelium. The filaments are called hyphae.
The wall contains chitin and non-cellulosic polysaccharides. Cellulose may occur in few cases.
The cellular organization is two envelop type.
Reproduction is both asexual and sexual. Somatogamy is found in several cases.
Tissue differentiation is absent.
Food reserve is glycogen and fat.
Vegetative body or mycelium is not clear externally in most cases.

Reproductive bodies, are however apparent in mushroom, toad stools, puff balls, braket fungi etc.

Phycomycetes: the algal fungi

The mycelium is coenocytic.
Hyphal wall contains cellulose and other glucans in many members. In some cases chitin or fungus cellulose is also present.
Asexual reproduction involves the formation of spore containing sacs or sporangia. In aquatic forms or conditions the sporangia produce Zoospore. In terrestrial form, the sporangia often behave as pores, equivalent to conidia. Because of this reason, the sporangia are often called conidiosporangia.
Zoospores are generally biflagelates with heterokont flagellation in which one flagellum is smooth while the other is tinsel.
Gametes are usually non flagellate.
Sexual reproduction is gametangial contact in which the male sex organs or antheridium passes its product into the female sex organ or oogonium through a fertilization tube.
The product of sexual reproduction is oospore. Because of the latter, the phycomycetes are called oomycetes.
Phytophthorainfestans (which causes Late blight in Potato), Albugo candida (which causes White Rust in crucifers), Sclerosporagraminicola (which spreads downy mildew in cereals), Pennisetumtyphoids (which causes green ear disease in Bajra) etc. are some example of phycomycetes.

Zygomycetes the conjugation fungi

It is a class of terrestrial fungi which are mostly saprotrophic and rarely parasitic.
The mycelium is coenocytic.
Hyphal wall contains chitin or fungus cellulose.
Motile cells (zoospores or planogametes) are absent.
Mitospores are nonmotile. They are called sporangiospores as the spores are formed inside sporangia borne at the tips of special hyphae called sporangiophores.
Sexual reproduction occurs through gametangial copulation or conjugation. Because of this reason, zygomycetes are called conjugation fungi.
The gametes are commonly multinucleate and are called coenogametes.
Sexual reproduction produces a resting diploid spore called zygospore. Because of the presence of zygospore, the group of fungi is called zygomycetes. Zygospore differs from oospore is that during its formation a distinct food laden non motile large female gamete is not produced.
Zygospore does not give rise to new mycelium directly. Instead it produces a new sporangium called germ sporangium.
Piloboluscrystallinus or dung mould, Rhizopusstolonifer or black bread mould etc. are some examples of zygomycetes.

Ascomycetes- the sac fungi

They include pigmented moulds, powdery mildews, yeast, cup fungi, morels and truffels.
The mycelium consists of septate hyphae. Yeasts are an exception in that they are basically unicellular. They may however, form short temporary filamentous structure called pseudomycelium.
The septa possess central pores called septal pores. The pores allow communication between adjacent cells.
Cell wall contains chitin or fungus cellulose.
Motile structures do not occur in the life cycle.
In yeasts, asexual reproduction is through the process of budding and fission.
In majority of ascomycetes, the common mode of reproduction is through the formation of conidia. Conidia are non-motile fungal mitospore which are produced exogenously from the tips and the sides of the hyphae. Conidia are often coloured brown, green, blue or pink. They provide colouration to the fungus.
Greenish and bluish growth on bread, citrus, fruits and old leather is due to moulds belonging to ascomycetes eg. Penicillium, Aspergillus etc.
Sexual reproduction takes place through fusion for sex cells, somatic cells, gametangial contact between an antheridium and ascogonium and autogamy.
Fertilization occurs in two steps – plasmogamy and karyogamy. Karyogamy is delayed after plasmogamy. A new transitional phase appears in the life cycle. It is called dikaryophase. The cells of dikaryophase are called dikaryotic cells. Each such cell possesses two nuclei.
Some dikaryotic cells function as ascus mother cells. The latter act as the seats of karyogamy and meiosis. This converts the cells into asci.
Ascus is a sporangial sac pecullar to ascomycetes. 4-8 haploid meiospores named ascospores are produced internally in each ascus. In most of the cases half the number of ascospores belong to one mating type while the other half belong to the second mating type.
The asci may occur freely or get aggregated into specific fructifications called ascocarps. Ascocarps are of many types: cup like (apothecium, e.g. Peziza), flask shape (perithecium, e.g. Neurospora), elongated with a slit (hysterothecium) or closed (cleistothecium e.g. penicillium). The fructifications of some ascomycetes are edible, e.g. morels, truffles.

Basidiomycates – The club fungi

They are the most advanced and most commonly seen fungi as their fructifications are often large and conspicuous, e.g., mushrooms, toadstools, puff balls, bracket fungi etc.
They are among the best decomposers of wood. They are able to decompose both cellulose and lignin. Lignin is not metabolised by most other fungi and even bacteria. For decomposing wood the fungi secrete cellulose and lignin digesting enzymes. The enzymes create space in the wood for hyphae to pass inwardly. It is because of this that we sometimes observe toadstools and mushrooms to come out of wooden structures.
Gonaderma species causes decay of wood even of standing trees. G. pseudoferrum produces root rot of coffee, rubber, tea and cocoa plants.
Motile structures are absent.
Mycelia are of two types, primary and secondary.
Sexual reproduction does not involve sex organs. Instead fusion occurs between basidiospores and other monokaryotic spores.
There is often differentiation of two mating types, (+) and (-).
Sexual reproduction actually causes plasmogamy or fusion of protoplasts without fusion of their nuclei.
Examples of this group may include Rusts, smuts, Mushroom, Toadstools, Bracket Fungi, Puffballs, Armillariela, Hellucinogens.

Deuteromycetes – The fungi imperfection

They are the class of fungi which has been created to include all those fungi in which sexual stage is not known.
some of the deuteromycetes are unicellular like yeasts.
The mycelium is usually septate. Coenocytic forms are not known.
Asexual reproduction often occurs by conidia along with some other types of spores.
Few examples of deuteromycetes are Colletotrichumfalcatum which causes Red Rot of sugarcane, Helminthosporiumoryzae which causes leaf spot disease of rice, Alternariasolani which causes early Blight of potato and tomato etc.

Lichens

Theophrastus coined this term.
Duel organisms which contain a permanent association of a fungus or mycobiont and an alga or phycobiont.
The fungal partner is often ascomycetes or basidiomycete. The algal partner is either a green algae or a cyanobacterium.
They grow in most inhospitable and uninhabited places like barren rocks, cooled volcanic lava, icy tundra or alpines, sand dunes, roofs, wall etc.
Commonly live under humid and exposed conditions but can tolerate extreme desiccation.
Cannot tolerate air pollution, Especially due to sulphur dioxide.
The fungal part is for anchoring and absorption of water and minerals and the algal part perform photosynthesis.

Mycorrhizae

Symbiotic association of a fungus with the root of a higher plant.
Mycorrhizal roots often show a wooly covering of fungal hyphae.
The shape is different from normal root like tuberous, nodulated or coralloid. Root can and root hair are absent.
This can be of two forms extomycorrhizae, in which a bulk of the fungus lies on the surface of the root while a part of it lives in the intercellular spaces of the cortex and endomycorrhizae, in which only a little of the fungus lies on the root surface. It resides mostly inside the cortex of the root with some hyphal tips passing into the cortical cells.
The fungus is dependent upon the higher plant for shelter and food. Sometimes the fungal hyphae are spread in the soil over a large area and help in dissolving essential minerals present in the organic debris and hand over the same to the plant.

KINGDOM PLANTAE:

The kingdom contains all photosynthetic eukaryotes multicellular organisms and their nonphotosynthetic derivatives. At the lower level it contains algae which are basically multicellular green, brown and red algae. Other groups included in the kingdom plantae are bryophytes, pteridophytes and spermatophytes. Important characters of the kingdom are as follows:

Organisms are multicellular except for some algae.
They are eukaryotic.
Body form is less regular.
Growth is usually indefinite.
Irritability is poor.
Mode of nutrition is oxygenic photosynthesis.
The Photosynthetic regions contain producers. Most of the plants are restricted t land, seashores and fresh water reservoirs.
The plants are usually fixed or free floating. Active locomotion is generally absent.
Structural differentiation into tissues is found except for certain algae.
The cells contain central vacuoles.
Food reserve is usually starch and fat.
Some of the plants are heterotrophic, some are parasitic and a few are saprobes. A small group of autotrophic plants catch small animals and insects for obtaining extra nitrogen. They are called insectivorous plants.
Reproduction may be both asexual and sexual.

KINGDOM ANIMALIA

Members of this kingdom are also known as metazoan or multicellular animals. The kingdom has maximum number and most diverse type of organisms. This kingdom includes sponges, coelenterates, worms, molluscs, arthropods, star fishes and vertebrates like fishes, amphibians, reptiles, birds and mammals. Insects, a group of arthropods, outnumber all other organisms in variety and number. The important characteristics of Animalia are as follows:

Organisms are eukaryotes.
They are multicellular.
Body form is regular.
Organs are internal.
Growth is definite. Well defined growing points are absent.
Cellular, tissue and organ system levels of organization occur in different groups.
Response to stimuli is quick.
A cell does not possess central vacuole.
Plastids and photosynthetic pigments do not occur.
The organisms are with mostly holozoic or ingestive type of nutrition. A few animals are however parasitic. They live on or inside the bodies of other eukaryotes. Rarely some animals form association with photosynthetic protists.
Animals are motile or mobile as they have to search for their food. Sponges are an exception.
The organisms possess muscle cells for their mobility and nerve cells for conduction of impulses. They are however absent in sponges.
Reproduction is mostly sexual. Regeneration of the whole organism and formation of spores are found in lower animals.
Embryo stage is present.
Economically organisms are consumers. There are several types of consumers and these constitute links in the food chains and food web.