Category: Biology

Some species are more prone to extinction than others. Simberloff (1986) and Caughley (1994) have reviewed this matter and drawn some conclusions. Processes that, make populations rare in the first place [the ‘ultimate causes of extinction’ (Simberloff, 1986) and ‘the declining population paradigm’ (Caughley, 1994)] should be distinguished from those that may finally cause extinction, once populations are small (Simberloff’s ‘proximate causes’, and Caughley’s ‘small population paradigm’).Small populations still die out, even when protected, because of proximate causes. These causes include demographic and environmental stochasticity, genetic deterioration, and so­cial dysfunction (Lawton, 1994). It is the ultimate causes of extinction that make species rare in the first place.Historically, formerly widespread and abundant species have become rare and vulnerable to the proximate causes of extinction because of hunting, habitat destruction and pollution.…

Genetics is a relatively new field of biology and most associate this science with Johann Gregor Mendel (1822-84), who was the first person to formulate any laws about how characteristics are passed from one generation to the next. This kind of study is often called Mendelian genetics.His work was not generally accepted until 1900, when three men working independently rediscovered some of the ideas that Mendel had formulated thirty years earlier.However, genetics was revolutionized in 1953 when, James Watson and Francis Crick proposed a chemical structure for DNA. Image Source: williambrownscienceoflife.com ADVERTISEMENTS: Their discovery made it possible to understand more clearly the chemical basis of heredity in both eukaryotic and prokaryotic organisms. Since then the proposed double helix structure for DNA has become the cornerstone for explaining gene function, gene…

The manner in which atoms are bounded together is of critical importance in all biochemical reactions. Three kinds of bonds may be briefly considered here: electrovalent, covalent and hydrogen. 1. Electrovalent bond: An electrovalent bond is formed by the transfer (not sharing) of one or more electrons from the outer shell of one element, say sodium, to another, say chlorine. Sodium has a single (“extra”) outer electron; it lacks seven of the eight electrons needed for stability of his outer shell. Chlorine has seven outermost electrons; its outermost shell is one electron short of complete stability. Image Source: 2012books.lardbucket.org ADVERTISEMENTS: Each atom would gain greater stability by combining with the other. The sodium tends to give up its single electron; the chlorine tends to saturate its outer electron shell by…

21 Questions with Answers and Explanations on “Excretion & Osmoregulation” for Biology Students.1. Reabsorption of useful substances from glomerular filtrate occurs in (a) collecting tube Image Source: images.slideplayer.com ADVERTISEMENTS: (b) loop of Henle(c) proximal convoluted tubule(d) distal convoluted tubule. ADVERTISEMENTS: Answer and Explanation: 1. (c): The cells lining the proximal convoluted tubule are well adapted for reabsorption of materials from the filtrate. They have abundant mitochondria and bear numerous microvilli on the free side. Mitochondria power the active transport of nutrient molecules back into the blood. The cells reabsorb entire glucose, amino acids, most of the inorganic ions (Na+, K+, Cl~), much of the water as well as some urea from the filtrate.2. Brush border is characteristic of (a) neck of nephron ADVERTISEMENTS: (b) collecting tube(c) proximal convoluted tubule(d) all…

The normal white cell count is 4,000 to 10,000/ cu mm of blood. These cells can be counted with the help of haemocytometer.Principle: The whole blood is used for total white cell count. With the WBC diluting fluid, it is diluted 20 times and placed in haemocytometer. The cells are counted under proper magnification over specified area. Thus, the known factors are: Source Image:biology.clc.uc.edu/ ADVERTISEMENTS: 1. The number of cells counted.2. The volume of fluid inside the chamber (i.e. the counting area ? depth).3. Dilution of blood. ADVERTISEMENTS: With the help of these known factors, the number of WBC/ cu mm of undiluted blood can be calculated. Equipments Required: For total WBC counting following equipments are required:1. WBC diluting fluid2. WBC pipette ADVERTISEMENTS: 3. Haemocytometer4. Microscope5. Blood sample. WBC Diluting…

20 Questions with Answers and Explanations on “Evolution” for Biology Students: Image Source: charleyharperprints.comQ. 1. When did the life appear on earth? Ans. Life appeared almost 4 billion years ago. ADVERTISEMENTS: Q. 2. Which theory of origin of life is accepted by scientists? Who proposed it? Ans. Chemical evolution by Oparin and Haldane.Q.3. What are fossils? ADVERTISEMENTS: Ans. The remains of hard parts/impressions of life forms found on rocks is called fossil.Q. 4. Illustrate an example to divergent evolution. Ans. The presence of forelimbs with similar anatomical structure in different organisms is divergent evolution.Q. 5. Give one example to homology in plants with names. ADVERTISEMENTS: Ans. Thorn and tendril of Bougainvillea and Cucurbita.Q. 6. What is convergent evolution? Ans. Organs that perform similar function but are anatomically different shows convergent…

11 Questions with Answers and Explanations on “Organism and Populations” for Biology Students: Image Source: classconnection.s3.amazonaws.comQ. 1. Define the terms—eurythermal, stenothermal. Ans. Organisms that can tolerate a wide range of temperature are called eurythermals. ADVERTISEMENTS: Organisms that can tolerate narrow range of temperatures are called stenothermals.Q. 2. Why are plants and animals dependent on light?Ans. Plants are dependent on light for: ADVERTISEMENTS: (1) Photosynthesis.(2) Photoperiodism—for flowering.(3) Formation of chlorophyll.Animals are dependent on light for: ADVERTISEMENTS: (1) Photoperiodism—foraging, reproductive and migratory activities.Q. 3. What is adaptation? Why do animals/plants adapt? Ans. Any change of the organism that enables the organism to survive and reproduce in its habitat is called adaptation.It is done for reproduction i.e. to increase its population (r) and survival.Q. 4. What are behavioral responses or adaptations? Give one…