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

How do mosquitoes locate their victims?

1.Eyes:Mosquitoes use their eyes to locate their victims. research has shown that people wearing dark colour clothes like red, black, navy black etc are more likely to be easily located by the mosquitoes .
2. Blood type : people with blood group O  are to twice attractive to mosquitoes than those with Type A. most of people produce blood group specific secretions mosquito can detetect.
3. carbon dioxide : carbon dioxide is attractive to mosquitoes .they can sense carbon dioxide from a distance over 150 feet away.so more carbon dioxide one exhales,more attractive he/she is  to the mosquitoes .as we exhale carbon dioxide through nose therefore while sleeping or resting  there is more carbon dioxide around our head region.no surprise often  we hear  buzzing sound mosquito offer in our ears.
4. Body heat and sweat: Mosquitoes  can  also  detect  heat  of our body  and  sweat  also.  our sweat  contains  lactic acid, uric acid, ammonia  and some other compounds. the mosquitoes can sniff these compounds . So  sweaty peoples  are likely    to be more attractive  for the mosquito.  after strenous exercise  we  sweat more,  our body  emits more  heat . in such  state  we are more likely  to be attacked  by the mosquito.
5.Type of bacteria on skin .In one study,  humans were divided into those two groups. One group  that was  highly attractive to mosquitoes and other one with  those who were not.The attractive ones had more of certain microbes on their skin than the unattractive ones.
6.pregnancy:One study revealed that pregnant women are twice as attractive to Anopheles mosquitoes  as non-pregnant women.perhaps it was because women in late pregnancy exhaled 21 percent more volume of breath,hence more carbon dioxide  than non-pregnant women. Moreover, abdomens of pregnant women are about 1.25 fahrenheit  warmer than non pregnent women.
 7.beer.researchers found that significantly more mosquitoes come close to our body after drinking a 12-ounce beer.it was due to increased ethanol content in sweat and skin temperature after drinking beer)

Arthropoda

Arthropods are  cosmopolitan .They are found almost in every habitat. They are found in desert ,inside soil, in freshwater, in marine water, in snowy areas and also as parasites. Most of these are solitary or gregarious. some form colonies with social organisation.Body is divided into 3 regions head ,thorax and abdomen. In some species head is fused with thorax  to form cephalothorax .Segmentation is external. lnternal septa are absent. Symmetry is bilateral. Coelenterates are triploblastic animals with organ level of body organisation . Spaces in between organs merge and form blood filled cavity called haemocoel.Head is formed by fusion of 6 segments .it has various types of mouth parts. Eyes are compound . Exoskeleton is mostly made up of chitin. it undergoes moulting or ecdysis at intervals . Insects have wings made up of chitin. they have jointed legs and other appendages. Digestive canal is complete . Blood circulatory system is open type. Blood vessels cannot be differentiated into arteries and veins. Blood is colourless and is called hemolymph . Excretory system consists of green glands, malpighian tubules. gills, tracheae,book gills, book lungs, respiratory siphon are respiratory organs found in various arthropods. Nervous system consists of various  ganglia ,nerves and nerve plexus. Most arthropods are unisexual, few are hermaphrodites. fertilization can be external or internal. Parthenogenetic development of eggs into young ones is found in many arthropods like Honey Bee cockroach grasshopper etc. Asexual reproduction is absent. Development may be direct or indirect involving one or more larval stages. series of changes that convert larvae into adults are together called as metamorphosis.

Annelida

A characteristic feature of annelids is metameric segmentation i.e body shows external division by circular ring like annuli and corresponding internal division by septa. segments thus formed are called metamers. they are found in marine habitat, freshwater habitat and in moist soil also . symmetry is bilateral. body is triploblastic that is made up of 3 germ layers. they have organ level of body organisation. another characteristic feature is presence of setae in most of species. Setae are absent in leeches. some species have parapodia. which act as locomotor organ.annelids are coelomates . they have true coelom, which is schizocoel. in animal evolution annelids are the first to have coelom.The coelom contains coelomic fluid with certain types of cells. Coelomic fluid inside body cavity forms hydrostatic skeleton. in most of species respiration occurs by diffusion of gases throw skin. in some species respiration occurs through gills. digestive tract is complete, that is, have both mouth and anus. excretory system contains nephridia. blood circulatory system is closed type. blood is red due to plasma dissolved pigment erythrocruorin . true Blood vascular system is lacking. nervous system consists of mid ventral nerve cord with segmental ganglia and a nerve ring at interior end. sense organs are tactile receptors,photosreceptors, gustatoreceptors and also statocysts in some species. some species like earthworm, leech are hermaphrodite, whereas others like Neries are unisexual. development is direct in most of species, that is, no larval stage in life history. in some false like Neries larval stage (trochophore larva) is present.

Platyhelminthes

Platyhelminthes include flatworms. They  are bilaterally­ symmetrical. They are acoelomate i.e, lack a coelom .they ate triploblastic  ,that is, have three germ layers.most of species are parasitic.some are free living.they show cephalization of nervous system and  their nervous system consists of a head ganglion . Excretory system consists of specialized flame cells.  respiratory or circulatory systems are absent.exchange of gases occur  by diffudion through body surface.Non parasitic forms have  incomplete gut; even this is lack­ing in many parasitic forms.Movement in some  species occur  with help of body muscle. Others move along slime trails by the beating of epidermal cilia. Sense organs like ocelli (photoreceptors), chemoreceptors,statocysts ,rheoreceptors are present in some forms. Gut if present, is incomplete (without anus).tapeworms lack gut.The nervous system is ladder-like. It consists of the brain (head ganglion) and two main longitudinal nerve cords connected at intervals by transverse commissures.These animals are generally hermaphrodite but mostly cross fertilization occur. fertilization is internal. self fertilization occur in tapeworms.in some flat worms like Planaria asexual reproduction occur  by binary fission.Life cycle consists of one or more larval stages. In liver fluke (Fasciola hepatica)the larval stages are - miracidium, sporocyst, redia, cercaria and metacercaria . larval stages in tapeworm are onchosphere, hexacanth and cysticercus larvae. Flatworms show organ level  system of organisation.