explorer blog


Wednesday, April 15, 2009

Three Methods of Plant Breeding

1) Open-pollination:

Open-pollinated or “standard” varieties of seeds breed true to their type. Seeds saved from such plants will produce a crop resembling their parents. While open-pollinated varieties may have originated from a genetic mutation, or a chance cross in the field, they have been stabilized and improved through years of selection by farmers and/or breeders choosing for desirable traits such as adaptability to climate and soil conditions, storage, disease and insect resistance, beauty, taste, ripening, and sugar content.

2) Hybridization:

Hybrids are the result of the deliberate crossing of two different parent varieties, usually inbreds. Typically, a corn variety will be crossed with a different corn variety and the result will always be a corn. Commercial growers look for “hybrid vigor” (synergistic effort which occurs when two diverse varieties are crossed), uniformity for mechanical harvesting and shipping, widespread adaptability to different climates and conditions, disease resistance, high yields, etc. Interspecific hybrids occur rarely in nature and genus boundaries are never crossed. Thus, it is not possible through sexual reproduction to cross a corn plant with a squash or a pig. Seed saved from hybrid plants is unstable. Traits from parents will segregate out in various combinations in the next generation. A fresh cross of the inbred seed lines will be required to maintain the variety.

3) Genetic Engineering:

Unlike open-pollination and hybridization, which occur in nature, genetic engineering requires human intervention in a laboratory setting directly manipulating DNA. Genetic engineers insert a foreign gene into the host DNA usually using one of two different methods: 1) ballistic — in which a gun injects foreign DNA, and 2) biological — in which a biological vector, usually a virus, carries the foreign gene into the DNA. Genetic engineering has the ability to cross all natural species boundaries and its products are often called “transgenic” (literally across genus boundaries). It is possible to insert a fish gene into a tomato or a pig gene into a corn — which would never occur in nature without human intervention.

Friday, August 29, 2008

Snake giving birth

Snake Giving Birth
Most snakes hatch from eggs that have been laid outside the mother’s body. But some kinds of snakes give birth to live young, as shown here.

Wednesday, April 02, 2008


I INTRODUCTION Topology, branch of mathematics that explores certain properties of geometrical figures. In 1930, the word topology was coined by mathematician Solomon Lefschetz. Usually classified under geometry, topology has frequently been called rubber-band, rubber-sheet, or rubber-space geometry; it deals with those properties of geometric figures in a space that remain unaltered when the space is bent, twisted, stretched, or deformed in any way. The only exceptions are that tearing the space is not allowed, and distinct points in the space cannot be made to coincide. Geometry is concerned with properties like absolute position, distance, and parallel lines, but topology is only concerned with properties like relative position and general shape. For example, a circle divides a flat plane into two regions, an inside and an outside. A point outside the circle cannot be connected to a point inside by a continuous path lying in the plane without crossing the circle. If the plane is deformed, it may no longer be flat or smooth, and the circle may become a crinkly curve; it will, however, maintain the property of dividing the surface into an inside and an outside. Straightness and linear and angular measure of the plane are some of the properties that are obviously not maintained if the plane is distorted.

An example of an early topological problem is the Kِnigsberg bridge problem: is it possible to cross the seven bridges over the Pregel River, connecting two islands and the mainland, without crossing over any bridge twice? See figure 1. The Swiss mathematician Leonhard Euler showed that the question was equivalent to the following problem: is it possible to draw the graph of figure 2 without lifting pencil from paper, and without tracing any edge twice? Euler proved that it was not possible. More generally, Euler proved that any connected linear graph, figure 3, for example, may be drawn with one continuous stroke without retracing edges if and only if the graph has either no odd vertices or just two odd vertices, where a vertice is odd if it is the endpoint of an odd number of lines. Because figure 2 has four odd vertices, it cannot be drawn by one continuous stroke without retracing lines. However, figure 3 has two odd vertices, so it is possible to draw that figure continuously without retracing edges. Later, in the 19th century, the German mathematician Johann Benedict Listing proved that a connected linear graph with 2n odd vertices can be drawn with n continuous strokes, each starting and ending at an odd vertex.

Tuesday, March 25, 2008


A habitat is a place where a plant or animal normally lives. Fish live in water. Perch are fish that live in freshwater habitats. Sharks are fish that live in saltwater habitats .
Other animals live on land. Cattle, antelopes, and buffaloes are animals that live on grasslands. Camels and kangaroo rats like the blazing hot temperature of deserts. Bats, gorillas, and elephants thrive in lush, moist rain forests.
Pine trees can live in cold, snowy habitats. Cactuses can live in hot, dry desert habitats. Water lilies live in freshwater habitats.
There are many kinds of habitats. Some habitats are along seashores. Some are high up in mountains or on flat prairies. Others are in dense forests, in sandy deserts, or in the deep sea. Different kinds of plants and animals live in different kinds of habitats.

Habitats are being destroyed around the world. As humans move into new areas, they clear the land to build on. They cut down trees for building materials and fuel. They dry out swamps for farmland. They dam rivers for electricity. The animals in the habitat must adapt to the changes or move elsewhere. If they cannot, they die. Many plants die, too.

Saturday, March 15, 2008


A food chain is the way energy goes from one living thing to another through food. Plants are the first step in most food chains.
Plants use the energy in sunlight to make their own food. Plants store the energy in their leaves and stems. Plants are called primary producers in food chains.
Animals eat the plants that use the Sun’s energy to grow. Animals are called consumers. Animals that eat plants are primary consumers. Animals that eat other animals are secondary consumers. Animals store the energy in their bodies.
Energy flows from plants to bigger and bigger animals through the steps of eating and being eaten. Each part of the food chain is directly connected to the other, just like the links in a chain.

A food web is made of many food chains in a community of plants and animals. There are many tiny animals near the beginning of a food web. There are fewer but larger animals higher up in a food web. There are many more insects than fish in a food web. There are also more small fish than big fish. Human beings are at the very top of the food web. No animals are higher up to make us their steady diet.
Decomposers play important roles in some food webs. Bacteria and fungi are decomposers. Decomposers eat dead plants and animals and cause them to rot and decay. They also eat animal wastes. They break things down into chemical parts called nutrients. The nutrients go back into the soil. Plants take up water and nutrients to make food. Nutrients move through food webs over and over again.

The Sun provides the energy that starts the whole process. A plant uses sunlight to make its own food. The energy is stored in the plant. An insect eats the plant. The insect stores the energy in its body. Then the energy is transferred to a fish that eats the insect. When you eat the fish, your body gets the energy stored in that fish.
When you eat salad, fruits, and potatoes, you take in the energy stored in these plants. When you eat fish, beef, or chicken, you take in the energy stored in these animals. When you eat your dinner, your body is getting energy that first came from the Sun. You use this energy to do your schoolwork. You use this energy to run and play.

Thursday, March 06, 2008

Fluke :

Fluke (invertebrate), common name given to members of a class of parasitic flatworm . They vary in length from 0.2 to 165 mm (up to 6y in); most species have flat, elongated bodies, although some blood flukes are nearly cylindrical. The possession of a digestive tract, specialized sensory organs, and, in most species, free-living stages places them closer in their evolutionary history to the free-living flatworms than to the parasitic tapeworms. The mouth of the fluke is situated on the underside and, in most species, near the front. Muscular sucking discs at the rear of the body serve to attach the fluke to the host; in the species that are external parasites (ectoparasites), these suckers are often equipped with hooks. Most species are hermaphroditic—that is, male and female organs are present in the same individual. Flukes that are parasitic on the surface of other organisms have a simple development; species that are internal parasites (endoparasites) frequently undergo a complex development requiring two or more hosts to complete their life cycles.
One endoparasitic species, commonly called the sheep-liver fluke, produces a disease in sheep, goats, and cattle called liver rot. This disease has a high mortality rate and is frequently epidemic in Europe and Australia. The sheep-liver fluke is about 2.5 cm (1 in) in length and has a dark red pigment, much like the liver in which it lives. The eggs leave the body of the animal in its faeces and, if they are discharged in a body of water, hatch to liberate ciliated larvae, called miracidia. Each miracidium swims in the water until it finds a snail in which it can develop. The miracidium burrows its way to the liver tissue of the snail and changes into a spore form, or sporocyst. Within the sporocyst, bodies called rediae develop by budding. These rediae produce more rediae, which then produce new larval forms called cercariae. The cercaria escapes from the snail and usually attaches itself to aquatic vegetation, where it encysts. It remains encysted until a sheep or other mammal swallows it. The cyst wall then breaks down, and the larva migrates to the liver of the host, where it develops into an adult fluke. The life cycle of this fluke is typical of the developmental history of many members of the class.
Flukes occur in most parts of the world where the hosts can thrive. They are parasitic in their adult form in many species of vertebrate animals. Each species of fluke is host-specific (able to parasitize only a few related vertebrates). Flukes commonly known as blood flukes infest the blood vessels in humans, causing the widespread, serious disease schistosomiasis, also known as bilharzia or bilharziasis.
Scientific classification: Flukes make up the class Trematoda. The sheep-liver fluke is classified as Fasciola hepatica. The flukes commonly known as blood flukes are classified in the genus Schistosoma.

Tuesday, October 23, 2007

Marigold :

Marigold, common name for several related plants of the daisy family that typically have orange to yellow flowers. True marigolds are also known as calendulas and include the pot marigolds. Another genus of marigolds is native to tropical and subtropical regions of the Western hemisphere. The African marigold, native to Mexico, is one member of the genus. It is an annualherb growing up to about 1 m (3 ft) tall and producing large, globular, golden-yellow or orange flower heads. African marigolds have been bred in both single- and double-flowered varieties. French marigold is a smaller Mexican annual, growing about 45 cm (18 in) tall and producing small yellow and red flower heads. The marsh marigold belongs to the buttercup family.
Scientific classification: Marigolds belong to the family Asteraceae (or Compositae). True marigolds are classified in the genus Calendula. The African marigold is classified as Tagetes erecta and the French marigold as Tagetes patula. The marsh marigold belongs to the family Ranunculaceae and is classified as Caltha palustris.

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