Reptiles

Explain about Reptiles.

CLASS REPTILIA:

Reptiles are adapted for complete existence on land in contrast to amphibians that are still tied more or less to water or moist habitat this indicates that reptiles have certain adaptations not found in amphibians some of these advancements shown by reptiles are their:

Characteristics Features:

(i) Reptiles have developed some sort of copulatory organs (penis like) necessary for internal fertilization.

(ii) In amniotic eggs of reptiles the shell is leathery which can resists dryness and injury. They have large yolky eggs.

(iii) Reptiles have dry scaly skin which is adapted to land life.

(iv) Reptiles have protective embryonic membranes aminion, allantois, and chorion.

(v) In reptiles the ventricle of heart is in completely partitioned ensuring more oxygen supply through blood circulation to all parts of the body.

In crocodiles, ventricle is completely partitioned into two.

(vi) Most reptiles have better developed limbs well adapted for efficient locomotion.

(vii) Reptile like amphibians are cold blooded (Poikilotherm) and hibernate in winter.

The above characteristic are for terrestrial habitat in which the reptiles mostly live.

However it is determined fact that reptiles have evolved from amphibians by undergoing the above changes and have become fully terrestrial.

  • Reptiles flourished throughout Mesozoic period (225-65 million years).
  • The climate which had been suitable for reptiles in that period, became less favourable to them in tertiary period.
  • So most of them became extinct.
  • The existing reptiles belong to four, out of a dozen or more main lines that have existed.

(i) Lizards and Snakes:

The present day repltles are, the lizards and snklaes.

(ii) Tuatara:

Secondly the tuatara (sphenodon) of New Zealand, which have survived up to today with little change.

(iii) Crocodiles:

Thirdly the Crocodiles are an offshoot from the stock from which modern birds were derived.

The reptiles of today have been derived from dinosaurs of Jurassic (195-136 million years), and cretaceous period (136-65 million years).

The modern reptile for the most part live in the temperate and tropical zone, indeed they fourish only in the latter.




Reptiles Reptiles Reviewed by SaQLaiN HaShMi on 2:37 AM Rating: 5

Apicomplexans and Dinoflagellates

Write note on Apicomplexans and Dinoflagellates?

Apicomplexans :

(i) Habitat:

Apicomplexans are a large group of parasitic protozoans some of which cause serious diseases such as malaria in humans.

(ii) Locomotion:

Apicomplexans have no specific structures for locomotion but move by flexing.

(iii) Spore Formation:

At some stage in their lives, they develop a spore. It acts as a small infective agent which is transmitted to the next host.

(iv) More than One Host:

Many organisms of this group spend part of their life in one host and part in a different host species.

(v) Life Cycle of Plasmodium:

Plasmodium (that causes malaria), enters human blood through the bite of an infected female Anopheles mosquito.

Plasmodium first enters liver cells and then red blood cells, where it multiplies.

when each infected red blood cell bursts, many new parasites are released.

The released parasites infect new red blood cells. The process is repeated.

When millions of red blood cells burst simultaneously, the symptoms of malaria appear.

Chill, followed by high fever are the symptoms of malaria. These are due to toxic substances that are released and affect other organs of the body.


Dinoflagellates (Phyrrophyta):

These are the most unusual protists because of the following characters:

(i) Unicellular:

Most dinoflagellates are unicellular.

(ii) Shell:

Their cells are often covered with, the shells of interlocking cellulose plates impregnated with silicates.

(iii) Second Group Producers:

In the marine ecosystem they are second most important group of producers (first group is diatoms).

(iv) Photosynthetic Pigments:

They have chlorophyll a and c. They contain carotenes and fucoxanthin.

(v) Population Explosions or Blooms:

They have rarely population explosions or blooms. These blooms colour the water orange, red or brown and are called as red tides.

Examples:

Gonyaulax, Ceratium.

Apicomplexans and Dinoflagellates Apicomplexans and Dinoflagellates Reviewed by SaQLaiN HaShMi on 5:49 AM Rating: 5

The Bacterial Cell Envelope

THE CELL ENVELOPE: THE OUTER WRAPPING OF BACTERIA:

Definition:

In bacteria the complex of layers external to the cell protoplasm is called as cell envelope. It includes capsule, slime and cell wall.

(i) Capsule:

Some bacteria produce capsule. It is tightly bound to the cell. Capsule is made up of of repeating polysaccharide units, or of protein, or of both.

(ii) Slime:

It is a loose, soluble cover of macromolecules called as slime capsule. It is present in some bacteria.

Slime provides greater pathogenicity to bacteria and protects them against phagocytosis.

(iii) Cell Wall:

Beneath the extracellular substances and (external to cytoplasmic membrane is cell wall).

It is rigid structure and determines the shape of bacterium.

Cell wall also protect the cells from osmotic lysis.

Cell wall is only absent in mycoplasmas.


Gram Stain Technique on the Basis of Differences in Cell Wall.

Christian Gram developed the technique of gram stain on the basis of differences in the cell wall.

On the basis of this technique bacteria can be divided into two groups.

(i) Gram Positive Bacteria:

These are the group of bacteria  that stained purple. They retain the primary dye due to the formation of CV-I complex in the cell wall.

(ii) Gram Negative Bacteria:

These bacteria are stained pink because they retain secondary dye in the cell wall.


Comparison of Gram Positive and Gram-Negative Cell Wall:

Difference in staining is due to difference in structure of cell walls of two groups. It is clear from the following table:

Characteristics

Gram Positive

Gram Negative

(i) Chemical make up.







(ii) Overall thickness

(iii) Outer membrane

(iv) Periplasmic space

(v) Permeability

(a) Peptidoglycan (50% of dry weight in some bacterial cells)

(b) Techoic acid

(c) Lipotechoic acid

(d) Lipids (1-4%)



20-80nm

No

Present in some

More permeable

(a) Lipopolysaccharides


(b) Lipoproteins

(c) Peptidoglycan 10% dry weight of some bacterial cells.

(d) Lipids (11-12%)


8-11nm

Yes

Present in all

Less permeable



Chemical Composition of Cell Wall:

(a) The cell walls of most bacteria have a macromolecules called peptidoglycan.
(b) Its amount varies in different types of bacteria.
(c) Peptidoglycan is composed of long glycan chains cross-linked with peptide fragments.
(d) The cell wall also contains sugar molecules, techoic acid, lipoproteins and lipopolysaccharides. These are linked to peptidoglycan.

Cell Walls of Archaeobacteria:
Cell walls of Archaeobacteria are different from Eubacteria. They do not contain peptidoglycan. Their cell walls are composed of proteins, glycoproteins and polysaccharides.

Cell Walls of Other Bacterial Groups:
Many bacterial group have no cell wall structure which is characteristics of gram positive or gram negative bacteria.

No Cell Wall in Some Bacteria:
Some bacteria have no cell wall (like Mycoplasmas).
The Bacterial Cell Envelope The Bacterial Cell Envelope Reviewed by SaQLaiN HaShMi on 8:45 AM Rating: 5

Nuclear War OR Ban on Nuclear Weapons

Nuclear War OR

 Ban on Nuclear Weapons

NUCLEAR WAR:

The developed countries like Russia, America, Japan and France have been making nuclear weapons for many years. America attacked the two cities of Japan, Nagasaki and Hiroshima in the Second World War with atomic bombs. It caused huge destruction in both the cities. Millions of people were wounded and killed in that bombing. Since then a serious thought has been given to the preparation of nuclear weapons. Every country considers it essential to equip itself with nuclear weapons for its security.

Nuclear energy is considered the basic armament of self-defence. In the mad race of preparing nuclear weapons, the underdeveloped countries like India, South Africa and Israel have also joined hands with the developed countries. India has already tested the capability of her nuclear weapons and has successfully exploded the atomic bomb.

 It seems that the nations of the world have forgotten the savagery of atom bombing by the Americans over the Japanese cities. The atom, despite its devastating powers, is still the favourite subject of study among scientists. They go on studying it with the sole object of killing mankind. Persistent nuclear explosions and tests in Siberia or Pacific are hailed as the greatest achievement of science.

The political rulers and statesmen of every country consider the collection of nuclear weapons as a safeguard of peace. They are mistaken in it. The piling up of nuclear weapons is an inevitable prelude to the whole destruction of mankind.

A nuclear war is an exercise is wholesale destruction. A single day's atomic bombing of the U.S.A is estimated to cause the death of about 50 million people and a serious injury to about half the number. Such a great destruction is expected to paralyse the whole steam of life. The influence of radiation will continue to haunt the world for many years. It may give rise to mysterious diseases and ailments. It may render the fertile land barren and wild.

Nobody can wish for such a gloomy and dark future. World peace can only be secured if all the countries decide to put a ban on the research, the production and preparation of nuclear weapons. No country, however powerful should be allowed to make nuclear explosion. Public opinion against the negative effects of nuclear energy should be launched by the people of world.  The existing stock of such destructive armaments must be destroyed.

A powerful organization should be set up in every country which should watch and control the production of nuclear weapons. It should mobilize the public opinion against the menace of atom bomb. People should be told that radio activity is an unchecked and uncontrollable monster. A world wide awareness against the use of nuclear weapons should be produced. The powerful and advanced countries should also be forced to stop producing the deadly weapons. This may seem to be an ideal plan to do away with nuclear weapons. But unless such drastic measure is taken, the future of mankind will continue to be dark. The statesmen, the rulers and politicians of all the countries should realize their responsibility regarding the bright future of mankind. If there is a total disarmament in all the countries, the world peace can be secured in a better way.

Nuclear War OR Ban on Nuclear Weapons Nuclear War OR Ban on Nuclear Weapons Reviewed by SaQLaiN HaShMi on 8:38 PM Rating: 5
Theme images by lucato. Powered by Blogger.