GENERAL CHARACTERS AND LIFE CYCLE OF BRYOPHYTES

 Bryophytes are the first land plants. It is believed that, they originated from aquatic plant.

Bryophytes are not considered as the successful land plants because vascular tissue is absent and they need water for fertilisation.

Bryophytes are known as amphibians of the plant kingdom, because these plants can live in soil but are dependent on water for fertilisation.

They lack true roots, stem or leaves. They may possess root-like, leaf-like or stem-like structures.

Bryophytes are Sciophytes, i.e. bryophytes prefer to grow in cool, moist (wet) and shady places.

Bryophytes in general are of little economic importance, but some mosses provide food for herbaceous mammals, birds and other animals.

The water conducting tissue in Bryophyta is parenchyma. 

Bryophytes include the various mosses and liverworts that are found commonly growing in moist and shaded areas in the hills.

Life Cycle of Bryophytes : 

• The main plant body of bryophyte is haploid. It produces gametes, hence is called a gametophyte.
• Sex organs are formed on gametophyte.
•  Sex organs are multicellular and jacketed in bryophytes. Male sex organ is called antheridium and female sex organ is called archegonium. An archegonium is flask shaped and produce single egg.
• The male gametes of bryophytes are motile. These motile male gametes are called as antherozoids. Antherozoids are usually comma shaped and biflagellate. Female gamete is called egg or ovum.
• In Bryophyta, fertilization is performed by zoidogamy i.e. male gamete swims into water to reach the female gametes and fertilizes it.
• As a result of the fertilization, a diploid zygote is formed. Zygotes do not undergo reduction division (meiosis) immediately.
• Zygote forms embryo and then sporophyte by mitosis. The zygote initiates the sporophyte generation. Sporophyte generation is a diploid stage.
• The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it. The sporophyte of Bryophyta is not made of root, stem and leaves, but it is made of foot, seta and capsule, so it is known as sporogonium. Some cells present in capsule of sporophyte function as spore mother cells. Now meiosis takes place in spore mother cells. to form haploid spores.
  In Bryophyta the sporophyte is dependent on gametophyte. This is a unique character of Bryophyta.
• The germination of spores is direct or indirect. In liverworts the germination of spore is direct i.e. each spore forms a gametophyte or a thallus after germination. The germination of spores in mosses is indirect. In mosses a multicellular filament is formed after the germination of spore. This filament is known as protonema. Protonema developed from spores is called primary protonema and the protonema developed from parts other than spores are known as secondary protonema.
• Protonema is creeping, green, branched and filamentous. Now lateral buds are formed on protonema. Each bud develops and forms a gametophyte plant. Indirect germination is best for survival. Mosses are gregarious in nature because they appear in group.

LIVERWORTS :  

• Bryophytes included in this class have shape like liver (e.g., Marchantia) or flat (e.g. Riccia) so they are known as liverworts.
• Plant body of this group is thallus like. The thallus is dorsiventral and closely appressed to the substrate.. Rhizoids and scales are present on thallus. Rhizoids are unicellular and unbranched. Scales are multicellular and protective in functions.
• The leafy members (e.g. Porella) have tiny leaf like appendages in two rows on the stem like structures.
• The sporophyte of Liverworts is completely dependent on gametophyte i.e. it is dependent on gametophyte for food, water and habitat.
• The sporophyte of Liverworts is made up of foot, seta and capsule, after meiosis, spores are produced within the capsule. These spores germinate to form free- living gametophytes. True elaters are present in sporophyte of some members of liverworts. Elaters are hygroscopic and they help in dispersal of spores.
• Asexual (vegetative) reproduction in Liverworts takes place by fragmentation of thalli, or by the formation of specialised structures called gemmae (sing. Gemma). Gemmae are green, multicellular, asexual buds, which develop in small receptacles called Gemma cups located on the thalli. The gemmae become detached from the parental body and germinate to form new individuals. e.g. Marchantia.
• During sexual reproduction male and female sex organs are produced either on same (e.g. Riccia) or on different thallus (e.g. Marchantia).

MOSSES :  

• The predominant stage of the life cycle of a moss is the gametophyte which consist of two stages. The first stage is the protonema stage, which develops directly from a spore. It is creeping, green, branched and frequently filamentous stage.
• The second stage is the leafy stage, which develops from the secondary protonema as a lateral bud. They consist of upright, slender axes bearing spirally arranged leaves.
• The main plant body or gametophyte of mosses is made up of stem like, leaf like and rhizoids (roots like). They are attached to the soil through rhizoids. The rhizoids present in the class are multicellular, branched and obliquely septate.
• Vegetative reproduction in mosses is by fragmentation and budding in the secondary protonema.In sexual reproduction, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots. After fertilization, the zygote develops into a sporophyte, consisting of a foot, seta and capsule. The capsule contains spores. Spores are formed after meiosis.
• The sporophyte in mosses is more elaborated (developed) than that in liverworts.
• The sporophyte of mosses is also partially dependent (semi parasite) like that of hornworts. i.e. it is photosynthetic. The Mosses has an elaborate mechanism of spore dispersal.
• Peristomial teeth are present in moss sporophyte which help in spore dispersal.
• Common example of mosses are Funaria, Polytrichum and Sphagnum.

Difference Between Transcription and Replication

 

Replication	Transcription
Occurrence
S phase of the cell cycle	G1 and G2 phase of the cell cycle
Primer
Requires RNA primer for replication to start	Does not require a primer
Enzymes
DNA Polymerase, DNA Helicase	RNA polymerase, Transcriptase
Genome copy
Entire genome is copied	Only certain genes are copied
Position
Found along the DNA strand	Found only along 1 strand of DNA
Raw material
dATP, dTTP, dCTP and dGTP	ATP, GTP, CTP, and UTP
Intend
Conserving genome for further generations	Making copies of RNA of genes individually
Result
Two daughter strands	mRNA, rRNA, non-coding RNA and tRNA
Degradation
Products do not degrade	Products degrade

Difference Between DNA and RNA

Territorial behavior

 A territory is an area held and defended by an organism or group of organisms of the same or different species. Territorial behavior is common to all vertebrates except amphibian but is rare in non-vertebrates.

The exact function of territory formation varies from species to species, but in all cases, it ensures that each mating pair of organisms and their offsprings are adequately spaced to receive a share of the available resources, such as food and breeding space. In this way, species achieves optimum utilization of the habitat.

The size of territories occupied by any particular species varies from season to season according to the availability of environmental resources. Birds of prey and large carnivores have territories several square miles in area in order to provide all their food requirements. Herring gulls and penguins have territories of only a few square metres, since they move out of their territories to feed and use them for breeding purposes only.

Territories are found prior to breeding, usually by males. Defense of the area is greatest at the time of breeding and fiercest between males of the same species. There are a variety of behavioral activities associated with territory formation and they involve threat displays between owners of adjacent territories. These threat displays involve certain stimuli which act as releasers. E.g. An adult male robin would attack another adult male displaying a red breast and a bunch of red feathers, but not a young male robin which did not have a red breast. The level of aggression shown by an organism increases towards the centre of the territory. The aggressiveness of males is determined partly by the level of testosterone in the body and this can affect territory size. E.g. the territory size of a red

grouse can be increased by injecting the bird with testosterone. Territories are acquired through threats, gestures and postures in place of actual fighting. Having obtained a territory, many species especially carnivores proceed to mark out the boundary by leaving a scent trail. This may be done by urinating or rubbing parts of the body against objects called scent posts along the boundary of the territory.

Altruistic behavior

Altruism is a form of social behavior whereby one organism puts itself either at risk or personal disadvantage for the good of other members of the species. In the case of activities associated with and parental care, altruism is not so difficult to comprehend since the action is clearly in the interest of the parents, offsprings and species. E.g. the female baboon protects and cares for its offspring for almost six years whilst most bird species feed and protect their demanding offprings until they are capable of fending for themselves. What is not so clear is the reason why some organisms give support to organisms which are not their offspring E.g birds and monkeys call out warnings to others in danger and female monkeys carry and care for the babies of other monkeys. In insects such as honey bees, wasps and ants, sterile female workers are prevented from producing offsprings, yet they spend their lives looking after their brothers and sisters. Hence, helping their sister (queen) to reproduce, they are effectively aiding in the production of queens, workers an drones with a genetic complement closer to their own than if they had offspring of their own. The conferring of a genetic advantage on closely related organisms forms the basis of altruistic behavior.

Altruistic behavior is very common amongst primates and varies from the extremes of social protection which exist between members of the same troop (monkeys), through acts of mutual grooming and food sharing (apes) to deliberate acts of self-sacrifice for family (God for humans). The extent of altruistic behavior appears to be related to close relatives (kin) such as offspring and siblings (brothers, sisters cousins) with whom they share certain alleles. Thus the adaptive significance of altruistic behavior is to increase the frequency of those alleles common both to the donor and recipient(s) of the altruistic behavior

Pathogenic Properties of Virus

• Viruses have mechanisms to evade host defenses viruses grow inside host cells to hide from immune defense.

• Kill immune cells e.g. HIV – TH Cells.

• Cytopathic effects: - The visible effects of viral infection on host cell. Some effects will kill the cell and some will just change the cells.

• Viruses stop DNA, RNA and/or protein synthesis e.g. Herpes virus block mitosis.

• LySOSomal autolysis of host cells e.g. Influenza: bronchiolar epithelium.

• Production of inclusion bodies (visible viral parts inside the cell) can identify a particular virus e.g. Rabies virus: Negri bodies.

•  Syncytium formation (neighboring cells fuse together) e.g. Varicella Zoster virus.

• Change in cell function e.g. Measles, production of interferons by host cell (triggers host immune response), induce antigenic changes on host cell surface (triggers destruction of infected cell by host immune response).

• Induce chromosomal changes, cell transformation: may activate or deliver oncogenes resulting in loss of contact inhibition (cancer) e.g. Papilloma virus.

Theories on membrane structures

• In 1902 it was thought that the membranes had only lipids (Overton). 
• In 1926 Gorter and Grendell proposed that lipids are capable of forming a double layer.
• In 1935 Danielli and Davson proposed the lipid bilayer model that includes proteins adhering to both lipid-aqueous interfaces.
• Artificial model systems such as the liposomes supported the idea of Danielli and Devson.
• A droplet of lipid made soluble in an organic solvent can be spread over a small hole on a septum that divides two chambers containing water.
• This set up is useful to study biophysical properties of a bilayer such as permeability and electrical resistance.
• Channels for ions can be formed by adding certain proteins or polypeptides.
• Liposomes act as excellent carriers for different molecules such as chemotherapeutic compounds, insulin and antibodies.

Fluid mosaic model

• Fluid mosaic model proposed by S.J. Singer and G.L. Nicolson (1972) was finally acceptable to most biologists.
• This model recognizes that lipids and proteins are in a mosaic arrangement.
• It also recognizes that there is translational movement of lipids and proteins within the lipid bilayer.
• Non covalent interactions ensure a fluid like state for the membranes.
• Integral proteins are intercalated into the continuous lipid bilayer.
• Polar/hydrophilic regions of proteins protrude from the surface while the nonpolar/hydrophobic regions are embedded inside.

Unit membrane model 

• Robertson in 1959 postulated the unit membrane model.
• This model stated that the central layer of plasma membranes is made up of hydrocarbon chains of lipids and the proteins constitute the dense surrounding layers on both sides when viewed through an electronmicroscope.
• Unit membrane model turned out to be an over simplification model as it can’t account for the number of protein molecules present across the membranes. 

Entomophily

• The pollination which takes place with the help of insects is known as entomophily. Most of insect pollination (80%) occurs only by honey bees.
• Favourable colour of honey bees is yellow, but they are blind to red colour.
• Majority of insect pollinated flowers are large, colourful, fragrant and rich in nectar, when the flowers are small, a number of flowers are clustered into an inflorescence to make them conspicuous.
• Night blooming plants are pollinated by moths. They are highly scented. Their flowers are generally white coloured.
• The flowers pollinated by flies and beetles secrete foul odour to attract these animals.
• The pollen grains of insect pollinated flowers become sticky due to presence of pollen kit.
• Most of entomophilous plants are ornamental plants. Ornamental plants utilize their maximum energy in this pollination and develop different types of adaptation for attraction of insects. Their flowers are attractive. Animals are attracted to flowers by colour and/or fragrance. e.g. Cucumber, Mango, Peepal, Coriander, Papaya, Onion, Lobia, Cotton, Tobacco, Rose, Lemon, Eucalyptus, Banana.
• Some of the following plants have developed special adaptation, for insect pollination.
• Yucca plant develops symbiotic relationship with a species of moth, Pronuba yuccasela moth (Tegeticula moth). The pollination in "Yucca takes place only by Pronuba female moth. This insect lays eggs in the locule of the ovary of flower. The larvae of moth come out of the eggs as the seeds start developing. Life cycle of both depends on each other. Moth and the Yucca plant can not complete their life cycles without each other.
• In tallest flower of Amorphophallus (the flower itself is about 6 feet in height), process of pollination is same as Yucca means it provides space (safe place) for laying eggs.Floral rewards : To sustain animals visits, the flowers have to provide rewards to the animals. Nectar and pollen grains are usual floral rewards. In some species floral rewards are in providing safe places to lay eggs. e.g. Yucca, Amorphophallus.
• Pollen / Nectar robbers : Many insects may consume pollen or the nectar without bringing about pollination, such floral visitors are referred to as pollen / nectar robbers.
• Orchid Ophrys flower is pollinated by wasp [Colpa aurea] by means of pseudo copulation. The appearance and odour of the flower is like female wasp [Mimicry].
• Nymphaea (water lily), water hyacinth, Nelumbo or Nelumbium (lotus), Alisma are also entomophilous plants while they are hydrophytes.
• 
  
  

Anemophily

• When the pollen grains are transferred from one flower to the another flower through the wind then it is called anemophily and flower is known as anemophilous flower.
• The anemophilous plants produce enormous amount of pollen grains.
• The pollen grains are very small, lightweight and dry (non-sticky).
• Stigma is large often hairy or feathery to easily trap air borne pollen grains and mucilaginous (Sticky).
• They often possess well exposed stamens so that the pollens are easily dispersed into wind currents.
• Yellow clouds of pollens are formed by Pinus tree due to the pollen grains which is called "sulphur Shower".
• Winged pollen grains are found in Pinus.
• Anemophilous flowers are neither attractive nor with fragrance. They do not have nectar glands. Anemophilous flowers are generally unisexual.
• Maximum loss of pollen grains takes place in this type of pollination. It is completely non-directional process.
• Wind pollinated flowers often have a single ovule in each ovary and numerous flowers are packed into an inflorescence e.g. corn cob. The tassels is styles and stigmas which wave in the wind to trap pollen grains.
• Pollination by wind is more common amongst abiotic pollinations.
• Wind pollination is quite common in grasses. e.g. - Gymnosperms, maize (corn), sugarcane, bamboo, coconut, Cannabis, grasses, date palms, papaya. 
  
  
  

Incomplete dominance

 Works on problems of heredity have shown that the dominance is not of universal occurrence and there are many examples of incomplete dominance in which the genes of an allelomorphic pair express themselves partially when present together in the hybrid. As a result the heterozygotes (Aa) are phenotypically intermediate between two homozygous types (AA* aa).

For instance, when red snapdragon plants are crossed with white snapdragon plants, all the F₁ hy­brids have pink flowers. This third phenotype results from the heterozygote flowers having less red pigment than the red homozygotes. The breeding of the F₁ hybrids produces F₂ offspring with a phenotypic ratio of 1 red to 2 pink to 1 white. In incomplete dominance we can distinguish the heterozygotes from the two homo­zygous varieties, and the genotypic and phenotypic ratios for the F₂ generation are the same, 1:2:1. The segregation of the red and white alleles in the gametes produced by the pink-flowered plants confirms that the genes for flower color are heritable factors that maintain their identify in the hybrids; that is, inheritance is particulate.

It is incomplete dominance - the kind of inheritance of allelic genes where a cross between organ­isms with two different phenotypes (AA x aa) produces offspring with a third phenotype that is a blending (Aa) of the parental traits. Incomplete dominance is manifested when the interacting enzymes are slightly different in their activity.

In humans, traits with incomplete dominant inheritance are size of nose, salience of lips, size of mouth and eyes, distance between eyes, hair types (straight, wavy) and such hereditary disorders as Friedreich’s ataxia, cystinuria are inherited according to principle of incomplete dominance. For any character, the domi- nant/recessive relationship we observe depends on the level at which we examine phenotype; e.g., con­sider a fatal recessive Tay-Sachs disease, inherited disorder of lipid metabolism when crucial enzyme hexosaminidase does not work properly. Brain cells of Tay-Sachs babies lack a crucial lipid-metabolizing enzyme. Thus, lipids accumulate in the brain, causing the disease symptoms and ultimately leading to death.

At the organism level of normal versus Tay-Sachs phenotype, the Tay-Sachs allele qualifies as a re­cessive (aa).

At the biochemical level,however, we observe intermediate phenotype characteristic of incomplete dominance. The hexosaminidase enzyme deficiency can be detected in heterozygotes who have an activity level of the lipid-metabolizing enzyme that is intermediate between individuals homozygous for the normal allele and individuals with Tay-Sachs disease. Heterozygous individuals are genetically programmed to produce only 40-60% of the normal amount of an enzyme that prevents the disease.

Mendel's first law: Law of Segregation

Mendel did not formulate his conclusions as laws or principles of genetics, but later researchers have done so. Restating and using modern, standardized terminology, this is the information that developed and expanded from his early experiments.

1. Inherited traits are encoded in the DNA in segments called genes, which are located at particular sites (loci, singular locus) in the chromosomes. (Genes are Mendel's “factors.”)
2. Genes occur in pairs called alleles, which occupy the same physical positions on homologous chromosomes; both homologous chromosomes and alleles segregate during meiosis, which results in haploid gametes.
3. The chromosomes and their alleles for each trait segregate independently, so all possible combinations are present in the gametes.
4. The expression of the trait that results in the physical appearance of an organism is called the phenotype in contrast to the genotype, which is the actual genetic constitution.
5. The alleles do not necessarily express themselves equally; one trait can mask the expression of the other. The masking factor is the dominant trait, the masked the recessive.
6. If both alleles for a trait are the same in an individual, the individual ishomozygous for the trait, and can be either homozygous dominant or homozygous recessive.
7. If the alleles are different—that is, one is dominant, the other recessive—the individual is heterozygous for the trait. (Animal and plant breeders often use the term “true-breeding” for homozygous individuals.)

Geneticists use a standard shorthand to express traits using letters of the alphabet, upper case for dominant, lower case for recessive. Red color, for example, might be Ror r so a homozygous dominant individual would be RR, a homozygous recessive individual, rr and a heterozygous individual Rr.

Crosses between parents that differ in a single gene pair (such as those that Mendel made) are called monohybrid crosses (usually TT and tt). Crosses that involve two traits are called dihybrid crosses. Symbols are used to depict the crosses and their offspring. The letter P is used for the parental generation and the letter F for the filial or offspring generation. F1 is the first filial generation, F2 the second, and so forth.

What kinds of crosses did Mendel make to conclude that factors/genes segregate? First of all, he made certain that the plants that he planned to use in the experiment were pure line for the trait—that is, that they bred true for the trait for two or more years. (Peas are self-pollinated so he simply grew the plants and examined their offspring.) Other experimenters omitted this step, which confounded their results. Mendel then made a series of monohybrid crosses for each of the seven traits he had identified using parents of opposite traits—tall (TT) vs. dwarf (tt), yellow seed (YY) vs. green (yy) seed, round seed (RR) vs. wrinkled (rr), and so forth. (He, of course, did not symbolize them with letters, but he did know that seeds from his tall pure-line plants would always produce tall plants, seeds from the dwarfs would always produce dwarf plants, and so on.)

 

Mendel then let the F1 plants self-pollinate: Tt × Tt and in the F2 generation counted the numbers of individuals with each of the traits. For the tall × dwarf crosses he got 787 tall plants and 277 dwarf plants (6,022 yellow seeds and 2,001 green seeds, and so forth).

 

An easy way to determine the possible gene combinations is to construct a Punnett square, a grid in which all the possible gametes from one parent are listed on one side and those from the second parent across the top. Combine the gametes from the side and the top in the squares, and all of the possible gamete combinations are diagrammed. The previous cross in a Punnett square would look like this:

 

You can see from the Punnett square that three of the four gamete combinations will contain at least one dominant allele (T) and that there is only one chance out of four that the recessive (t) can be expressed. Mendel's experimental results fit the phenotypic probability ratio of 3:1. The genotypic ratio, which Mendel didn't know about, is not 3:1, but 1:2:1. That is, 1 homozygous dominant (TT):2 heterozygous dominants (Tt):1 homozygous recessive (tt). The Punnett square shows only thepossible combinations, not the actual. It provides an easy way to visualize theprobabilities of a certain combination occurring. In some inherited traits, whether the allele comes from the male or the female parent can make a difference, but in most traits such information does not matter.

After making monohybrid crosses for all the traits and finding that the ratios always approximated 3:1, although the actual numbers of plants and offspring for each cross varied, Mendel concluded that the traits must be carried in pairs that segregate (separate) when gametes are formed. This conclusion is now known as Mendel's first law, the Law of Segregation.

To confirm his hypothesis, he made another kind of cross, a backcross, which mates an offspring with one of its parents. Mendel backcrossed his F2 tall plants to the dwarf parent and got half tall plants, half dwarf, a 1:1 ratio. If he had backcrossed to the tall parent, what would the ratio have been? Right, all tall; that's why breeders today maketest crosses back to the homozygous recessive parent to see if their phenotypically dominant individuals are homozygous or heterozygous.

 

General Characteristics of Viruses

 General Characteristics of Viruses

Viral structure: Typical viral components are shown in Fig. 2. These components are a nucleic acid core and a surrounding protein coat called a capsid. In addition some viruses have a surrounding lipid bilayer membrane called an envelope.

Fig. 2. The components of helical virus

A.  Nucleic acid

• Viral genomes are either DNA or RNA (not both)

• Nucleic acid may be single- or double-stranded

Fig. 3. Types of virus genomes 

B.  Capsid

• Protein coat

• Protection of Nucleic Acid

• Provides Specificity for Attachment

• Capsomeres are subunits of the capsid

Fig. 4. Capsid structure

C.  Envelope

• Outer covering of some viruses

• Envelope is derived from the host cell plasma membrane when the virus buds out

• Some enveloped viruses have spikes, which are viral glycoproteins that project from the envelope

• Naked (non-enveloped) viruses are protected by their capsid alone

Fig. 5. Enveloped helical virus

 

 

2.  Size of viruses:

• Determined by electron microscopy

• Ranges from 20 to 14000 nm in length

Fig. 6. Size of different viruses

 

3.  Shape of viruses:

 

Four basic morphologies

• Icosahedral - efficient means to conserve and enclose space; form capsomers (planar faces formed by association of proteins) 

• Helical - capsid is shaped like a hollow protein tube 

• Enveloped - outer covering derived from the host cell's nuclear or plasma membrane and often possessing spikes or peplomer projections involved in attachment and entry into a host cell sometimes via their enzymatic activity 

• Complex symmetry - viruses that fit neither of the above categories or which may employ portions in combination, e.g., bacteriophage

Fig.7. Types of viral symmetry

 

4.  Host Range: The specific types of cells a virus can infect in its host species represent the host range of the virus.

 

• Animal virus

• Plant virus

• Bacterial virus (bacteriophage)

Host range is determined by attachment sites (receptors)   

 

Important points to remember: 

• VIRION – a complete single viral particle

• Obligatory intracellular parasites

• Contain DNA or RNA

• Do not undergo binary fission

• Sensitive to interferon

• Contain a protein coat

• Some are enclosed by an envelope

• Some viruses have spikes

• Most viruses infect only specific types of cells in one host

• Host range is determined by specific host attachment sites and cellular factors (receptors)

• Viruses replicate through replication of their nucleic acid and synthesis of the viral protein.

• Viruses do not multiply in chemically defined media

• All ss-RNA viruses with negative polarity have the enzyme transcriptase (RNA dependent RNA polymerase) inside virions.

• Retroviruses and hepatitis B virus contain the enzyme reverse transcriptase.  

Ecological Pyramids

Ecological Pyramids: In a food chain, producers and consumers at different trophic level are connected in terms of number, biomass and energy. These properties reduces from producers to consumers and representing these parameters for food chain gives a pyramid with a broad base and a tapering apex (Figure 39.6). Ecological pyramids can be of three types:

(a)     Pyramid of Numbers

(b)     pyramid of biomass

(c)     pyramid of energy

Example of inverted ecological pyramid is provided by parasitic food chains (Figure 39.7). A single mango tree supports large number of birds, which in turn supports a large number of parasites like lice and bugs. Hyperparasites, such as bacteria and fungus are the greatest in the number and occupy the top of the inverted pyramids.

 

Flow of energy in food chain: Sun is the ultimate source of energy on earth and plants utilizes it to produce food for rest of the member of the ecosystem. Only the 1% of the total energy fall on green part of leaves is changed into the potential energy of the organic substances, the rest of the energy dissipates as heat. To explain the flow of energy, lindermann proposed the law of ten per cent law. This law proposed that during transfer of food energy from one trophic level to the other, only 10% is stored at higher trophic and the rest 90% is lost in respiration, decomposition and waste in the form of heat (Figure 39.8). For example, 5000 jules fall on leaves, it will convert only 50 jules into the chemical form (food). It will be eaten by rabbit, he will get only 5 jules (10% of 50 jules) on next trophic level. Rabbit will be consumed by carnivorous, and they can be able store only 0.5 jules (10% of 5 jules).

Ecological Equilibrium: Ecosystem always remains in the state of equilibrium. The equilibrium is dynamic is nature and biotic components appear and disappear time to time due to their death or predator. In addition, decomposer converts the complex organic matter of dead plant and animals into the simple inorganic substances. These simple inorganic substances pass through the soil, plants and animals in a cyclic manner, and this keeps the life going on in an ecosystem. Thus, both biotic and abiotic components are in a dynamic state.

 

ECOLOGY TERMINOLOGY

•  Ecology is a branch of biology concerned with the study of the interactions of living organisms with each other and with their environment.
• An ecosystem is a community of organisms that interact with their environment.
• Biosphere is a region of the earth where life can exist.(atmosphere, hygrosphere, lithosphere)
• A habitat is a place where an organism lives.
• An abiotic factor is anything that is non-living and has an effect on living organisms in an ecosystem. The two main types are:

1. Climatic factors are weather conditions that have an effect on living organisms in an ecosystem.
2. Edaphic factors are anything relating to the soil or geology of land that have an effect on living organisms in an ecosystem.

• A biotic factor is anything that is living and has an effect on living organisms in an ecosystem. (e.g presence of predator, presence of pathogenic organisms).
• Pathogenic: capable of producing disease.
• A grazing food chain is a relationship of the sequence of predator-prey relationships in an ecosystem.
• A food web consists of two or more interconnected food chains.
• An ecological pyramid of numbers shows the numbers of organisms at each trophic level in a food chain. (May be upright, partially upright or inverted in shape.
• Niche refers to the functional role an organism plays in its habitat.
• A population is a group of organisms living in a habitat that belong to the same species.
• A community is a group of organisms living in a habitat that belong to many different species.
• Competition is the struggle between organisms for a resource that is in limited supply.

1. Contest competition is the direct fight between two organisms for a resource that is in short supply. (e.g. two stags fighting for a mate)
2. Scramble competition is the struggle amongst a number of organisms for a resource that is in short supply. Each organism gets a small share of the resource. (e.g. a pack of vultures competing for a portion of the kill made by a large predator)

• A resource is a stock or supply (such as food) that can be drawn on.
• Predation is the catching, killing and eating of another organism.
• Symbiosis is the biological relationship in which two species live in close proximity to each other and interact regularly in such a way as to benefit one or both of the organisms.
• Mutualism is when both of the organisms benefit from the presence of each other, e.g. N2-fixing bacteria that live in root nodules of legume plants (such as peas) assimilate NO3- from N2.
• Parasitism is where one organism, called the parasite, lives in or on another organism, called the host, and the host is harmed. (e.g. aphids are parasites of plants, athletes foot and mosquitoes)