Wednesday, June 29, 2011





The tailed frogs get their name from the copulatory organ of the male, which resembles a short tail, but is really an expanded portion of the cloaca.  These species are among the very few frogs with internal fertilization; the copulatory organ is used to transfer sperm to the female. They inhabit cold streams in humid forests and the areas around them. The two species of Ascaphus range from British Columbia south to Mendocino County, California, the Rocky Mountains of Idaho and Montana, and adjacent Washington and Oregon. Ascaphus is not known to have an advertisement call, and thus many aspects of their reproductive behavior are poorly known because they cannot be easily observed.  The frogs are semi-aquatic and most active in the vicinity of streams at night.
The tadpole has a large suckerlike mouth that occupies about one-half of the ventral surface of the body. It also has a large number of denticles (2-3 upper and 7-12 lower rows). Tadpoles of most species of frogs have only two upper and three lower rows of denticles. Ascaphus uses its sucker to adhere to and move among rocks in cold, swift streams. The function of the suction mechanism was studied by Gradwell (1971).

Monday, June 27, 2011




General scheme of development in the vertebrate kidney. (A) The original tubules, constituting the pronephros, are induced from the nephrogenic mesenchyme by the pronephric duct as it migrates caudally. (B) As the pronephros degenerates, the mesonephric tubules form. (C) The final mammalian kidney, the metanephros, is induced by the ureteric bud, which branches from the nephric duct. (D) The intermediate mesoderm of a 13-day mouse embryo showing the initiation of the metanephric kidney (bottom) while the mesonephros is still apparent. The duct tissue is stained with a fluorescent antibody to a cytokeratin found in the pronephric duct and its derivatives.

Saturday, June 25, 2011


1. Define biotechnology and write its applications
Ans : It is the branch of biology that deals with the use of biological agents,such as microorganisms and certain cellular components,for beneficial purposes.
Applications of biotechnology :-
a) Pollution control
b) Pharmacology
c) Production of transgenic animals
d) Public heath
2. Distinguish between Eugenics and Euphenics
Ans: EUGENICS:- It is the branch of genetics that deals with the application of knowledge of genetics to human welfare.
EUPHENICS :- It is brach of genetics that deals with the practice of phenotypic improvement of humans after birth.
3. What are retroperitoneal organs ?Ans : The organs of vertebrates  that occur outside the coelom  and are covered by peritoneum  only on the surface facing the coelom are called “retroperitoneal organs”
4. List out the four types of cells present in the epidermis of Pheretima
Ans : The four types of cells in the epidermis of Pheretima are :
1) large glad cells 2) Supporting cells 3) Basal cells 4 ) Receptor cells

Tuesday, June 14, 2011


Cilia and Flagella

Cilia and flagella are motile cellular appendages found in most microorganisms and animals, but not in higher plants. In multicellular organisms, cilia function to move a cell or group of cells or to help transport fluid or materials past them. The respiratory tract in humans is lined with cilia that keep inhaled dust, smog, and potentially harmful microorganisms from entering the lungs. Among other tasks, cilia also generate water currents to carry food and oxygen past the gills of clams and transport food through the digestive systems of snails. Flagella are found primarily on gametes, but create the water currents necessary for respiration and circulation in sponges and coelenterates as well. For single-celled eukaryotes, cilia and flagella are essential for the locomotion of individual organisms. Protozoans belonging to the phylum Ciliophora are covered with cilia, while flagella are a characteristic of the protozoan group Mastigophora.

In eukaryotic cells, cilia and flagella contain the motor protein dynein and microtubules, which are composed of linear polymers of globular proteins called tubulin. The core of each of the structures is termed the axoneme and contains two central microtubules that are surrounded by an outer ring of nine doublet microtubules. One full microtubule and one partial microtubule, the latter of which shares a tubule wall with the other microtubule, comprise each doublet microtubule (see Figure 1). Dynein molecules are located around the circumference of the axoneme at regular intervals along its length where they bridge the gaps between adjacent microtubule doublets.

A plasma membrane surrounds the entire axoneme complex, which is attached to the cell at a structure termed the basal body (also known as a kinetosome). Basal bodies maintain the basic outer ring structure of the axoneme, but each of the nine sets of circumferential filaments is composed of three microtubules, rather than a doublet of microtubules. Thus, the basal body is structurally identical to the centrioles that are found in the centrosome located near the nucleus of the cell. In some organisms, such as the unicellular Chlamydomonas, basal bodies are locationally and functionally altered into centrioles and their flagella resorbed before cell division.

Eukaryotic cilia and flagella are generally differentiated based on size and number: cilia are usually shorter and occur together in much greater numbers than flagella, which are often solitary. The structures also exhibit somewhat different types of motion, though in both cases movement is generated by the activation of dynein and the resultant bending of the axoneme. The movement of cilia is often described as whip-like, or compared to the breast stroke in swimming. Adjacent cilia move almost simultaneously (but not quite), so that in groups of cilia, wave-like patterns of motion occur. Flagella, however, exhibit a smooth, independent undulatory type of movement in eukaryotes. Prokaryotic flagella, which have a completely different structure built from the protein flagellin, move in a rotating fashion powered by the basal motor.

Defects in the cilia and flagella of human cells are associated with some notable medical problems. For example, a hereditary condition known as Kartagener's syndrome is caused by problems with the dynein arms that extend between the microtubules present in the axoneme, and is characterized by recurrent respiratory infections related to the inability of cilia in the respiratory tract to clear away bacteria or other materials. The disease also results in male sterility due to the inability of sperm cells to propel themselves via flagella. Damage to respiratory cilia may also be acquired rather than inherited and is most commonly linked to smoking cigarettes. Bronchitis, for instance, is often triggered by a build-up of mucus and tar in the lungs that cannot be properly removed due to smoking-related impairment of cilia.