Diatoms

Diatoms are a group of algae.they are found in oceans, freshwater bodies and even on moist soil.
ecologically they are very important.they produce 20% of oxygen produced on Earth.they are of different shapes, sizes and colours. they belong to division ochrophyta and class bacillariophyceae.
diatoms are solitary they can occur as solitary organisms or they may be colonial.when colonial,they may firm ribbon shaped,star shaped or zigzag colonies. the size of a diatom ranges from 2to 200 micrometers.their number increases very rapidly.if adequate sunlight and nutrients are available their number can become double in 24 hours. they mainly multiply by binary fission.
on the basis of shape diatoms have been classified into two categories. one is centric diatoms .they are radially symmetrical. other one is pennate diatom. they are bilaterally symmetrical. the life span of a diatom is about 6days. their cell wall forms a colourful case around them due to which diatoms are also called jewels of the sea. their cell wall form case or shell around individual cell. this case is called frustule. it is made up of silica, exactly hydrated silicon dioxide.in waterbodies they are passively carried away by water currents hence fall under phytoplankton.they cannot swim. however male gametes of centric diatoms can swim .most of the diatoms float passively on the surface of water.some are benthic found attached to the benthic substrates.diatoms are able to synthesize their food by photosynthesis.they are mostly restricted to the euphotic zone where sunlight can penetrate.their shell is unique having to two halves, upper larger one is called epitheca and lower one is called hypotheca.when a diatom divides each daughter cell receives one half of shell that is one valve which acts as epitheca.the daughter individuals develop new hypotheca. as hpotheca is smaller in size the daughter cell which receives hypotheca of parent cell, remember this hypotheca will act as epitheca in daughter cell and it will develop new hypotheca which will be smaller than epitheca.in this way this daughter cell will be smaller than parent cell even after full growth.after repeated binary fission the size of diatom cell will go on decreasing.it has been seen that after some binary fission's the diatoms undergo auxospore phase in which they increase in size and produce gametes by meiosis. dead diatoms sink to bottom of oceans and their shells  form diatomaceous earth.it is rich in silica and is s dynamite stabilizer.

1. By: Ashwani, Biology Teacher, Phagwara.

Sickle Cell Anaemia : An Example of Balanced Polymorphism

Sickle cell anaemia is caused by defective hemoglobin gene. the persons homozygous for sickle cell anaemia condition have two abnormal genes, one on each homologous chromosome .such persons are likely to die in their childhood because of large number of abnormal RBCs. on the other hand persons heterozygous for sickle cell anaemia have 1 normal gene at 1 homologous chromosome and one abnormal gene at other homologous chromosome .such persons have both normal and abnormal RBCs.  Abnormal RBCs  become sickle shaped under low oxygen conditions . Heterozygotes have more chances of survival up to reproductive age. It has been found that the persons heterozygous for sickle cell trait can tolerate the infection of Malaria caused by plasmodium falciparum .actually the sickle shaped RBCs do not support erythrocytic schizogony of malaria parasite plasmodium falciparum. Hetrozygotes therefore do not suffer seriously from plasmodium falciparum infection. they have normal RBCs also which can carry oxygen. In certain parts of Africa where infection due to plasmodium falciparum is common sickle cell trait is also prevalent. the natural selection selected sickle cell trait because the heterozygous for this trait were more resistant than normal persons against malarial infection. this existence of two different types of traits or say alleles of a gene in a population  is called balanced polymorphism and this is due to the selection of heterozygotes  by nature because of selective advantage in survival.

Mad Cow Disease

Mad cow disease is a neurodegenerative disease of cattle. it is caused by prions. priors are the misfolded proteins . their normal form is present in the cells. abnormal misfolded form becomes infectious and is called prion. a prion converts same kind of normal protein into abnormally folded protein.these abnormally folded proteins aggregate to form plaques which are toxic to nerve cells and cause death of nerve cells.
the cases of this disease  were reported in UK and Canada in 1990s.at present this disease is near eradication .
cause of spread of this disease was feeding the cattle on meat and bone meal. if this meat and bone bone has come from infected cattle it can cause mad cow disease in the fed cattle.the chances are high if the cattle feeds on brain or spinal cord of infected cattle   .
the appearance of symptoms may take several months or some years.the symptoms include abnormal walking of cattle due to less of muscle control.abnormal behavior of cattle, cattle goes into coma and ultimately dies. this disease is also called bovine spongiform encephalopathy.
man can also get infected by eating meat of infected cattle. man gets variant Creutzfeldt Jakob Disease by the prions that cause mad cow disease in  cows. mad cow disease does not spread by consuming milk of infected cows.

By:Ashwani,bio-teacher ,Phagwara.

Epigenetics

Epigenetics simply means something above or on top of the genetics. it involves the study of all the mechanisms that  changes the expression of genes by turning them switch on or switch off. the structure of gene is not altered but just turning the genes switch on or off changes the expression of genes.one such mechanism is methylation of DNA bases which prevents the expression of that DNA. the modification in his histone proteins of chromosome that tightly squeeze DNA in chromosome will prevent the expression of that DNA.the modifications in histones that relax the DNAwill allow the expression of DNA.it is due to epigenetics that skin cells are different from brain cells and liver cells. all of these cells have same kind of genes but in different types of cells different genes are switched on and switched off which makes these cells unique and different from others. our environmental also effects the turning on and off of genes for example when we spend more time in sunlight the amount of melanin increase in skin. what we eat also affects the turning on and off of genes. for example eating sugar rich diet cause more formation of  insulin.our mental stage also effects the turning on and off of genes .stress causes formation of cortisone hormone..for formation of cortisone specific genes are switched on. switch on and switch off of genes is a normal thing in body of all living organisms,but when this mechanism occur abnormally it results in diseases like cancer and Alzheimer.

By: Ashwani, bio-teacher ,Phagwara.

Prions

prions cause several neurodegenerative diseases in humans and other mammals.prions are proteinaceous infectious agents.they don't have any nucleic acid.this is a unique thing about prions. all the known pathogens like bacteria,viruses and others all have nucleic acid.prions retain their ability to infect even after treatment with ultraviolet radiations or other treatments that destroy nucleic acid.scientists have discovered that prions are the misfolded proteins with abnormal structure .when this abnormal protein binds to same type of normal protein it induce the latter to change its conformation . the newly distorted protein then induces the misfolding in other similar proteins. in this way it become a chain reaction. prions cause mad cow disease also known as bovine spongiform encephalopathy. scientists believe that infected cows may transmit infection to humans .it humans this infection causes CJD that is Creutzfeldt-Jakob disease.the process by which change in structure of protein occur is not clear and research is going on to understand the mechanism .in CJD disease scientists have discovered spongy structure of Brain in dead victims.this sponginess is caused due to holes in brain due to cell death . scientists believe that abnormal shaped protein becomes toxic to cell and causes cell death.prions can be transmitted by eating infected part of victim,by inoculation into brain or skin.some prion cases of CJD and GSS have shown inheritance pattern perhaps this is due to mutation in gene which changes amino acid pattern in a protein and  convert it into a prion.

By:Ashwani, bio- teacher, Phagwara.

Parathyroid

Thyroid