The ecosystem moves towards the climax community. A seral community is an intermediate stage in an ecosystem.  Before attaining the climax community sometimes more than one seral stage can also evolve.

Depending on the substratum and climate, a seral community can be classified into water community, rock community, sand community, dry area community & saline body ommunity. This can be termed biologically as Hydrosere, Lithosere, Psammosere, Xerosere, and Halosere respectively.

Hydrosere

It is a plant succession occurs in a freshwater lake. If the water dried up it becomes the woodland. Because of this change the land types will succeed each other.

           Mute Swan  - Hydrosere Community

The Loch a' Mhuilin lake is located in the Isle of Arran, Scotland. The lake exhibits characteristic features of a hydrosere, the succession from a fresh water surface with small pioneer plant species to a sub-climax vegetation of alder and willow.  Because of clearing grazing land by human activities and by red deer and rabbits, the climax vegetation of oak and Thomas beech woodland has not been achieved.

Loch a' Mhuilin Lake

Lithosphere

It is a plant succession that begins life on a newly exposed rock surface.  Once the Laki and Katla fissures erupted, the lava fields of Eldgjá in Iceland began to form a lithosere.

Psammosere

An ecological succession began life on newly exposed coastal sand. Example: sand dune systems

Xerosere

It is limited by water availability with xerarch succession of ecological communities originated in extremely dry situation. Example:  sand deserts, sand dunes etc.

Halosere

The succession occurs in a saline environment. Example: salt marsh

Note: A xerosere may include lithoseres and psammoseres

Climax Community

It is a biological community of plants and animals through the process of ecological succession

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Reference Links:

•     http://en.wikipedia.org/wiki/Ecological_succession
•     http://en.wikipedia.org/wiki/Seral_community
•     http://en.wikipedia.org/wiki/Climax_community

Gene – The Hereditory Material

Gene is a nucleic acid segment which contains the genetic information necessary to produce a protein. Genes have a long strand of DNA with a promoter. This promoter controls the gene activity and a coding sequence.







The gene coding determines what the gene produces. The informations present in the genes pass on to next generation. The organelle mitochondria self-replicate and they are not coded for by the organism's DNA.
 
Genes and its Bases
The genes are having 4 nucleotide bases  and hence named as polynucletides. Each nucleotide made up of a base group, a sugar and one ore phosphate groups.

1. Adenine(A)
2. Thymine (T)
3. Guanine (G)
4. Cytosine (C).
   
   
   
   
   •    The bases Adenine(A) and Guanine(G) are Purines
   •    Thymine (T) and Cytosine (C) are Pyrimidines.
   

Base Pairs
The sugar group is the backbone of DNA. The phosphate group links one nucleotide to another. The nitrogenous bases holds each other with the help of complimentary bases. Adenine is complimentary to Thymine while Guanine is complimentary to Cytosine. A forms 2 hydrogen bonds with T while G forms 3 hydrogen bonds with C.

So the  G≡C bond is more stable than an A=T bond.

Definition of Gene
The gene is a "A locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions, and or other functional sequence regions"
Gene may refer to an allele:
•    A gene is the basic instruction, a sequence of nucleic acid
•    An allele is one variant of that gene.
The genetic changes can be observed in the single letter of the genetic code and this change is termed as ‘ a single nucleotide polymorphism’.

The expression of genes
The gene expressions encoded in DNA. It begins by the transcription process into RNA. RNA contains the nitrogenous base – uracil in place of thymine of DNA. RNA molecules are  single stranded and thus they are less stable than DNA.

Genetic Code
Genes that encode proteins are composed of codons. The codons are the series of three-nucleotide sequences. For example AUG,  AGG etc.This is the gene lanugauge and it is alomost same for all organisms.

 
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