My Science School

Fish have scales as a protective coating for the skin. In fact, not all fish have them. But we usually think of a fish as a cold-blooded, aquatic animal that swims by means of fins, breathes by means of gills, and is covered with scales. Scales may be of four different kinds-placoid, ganoid, cycloid and ctenoid.

Placoid scales are long, spiny and tooth like, and are made of enamel and dentine. These are found on fishes which have a back-bone made of gristle, such as sharks and rays.

   Ganoid scales are rather like placoid scales but are mainly bony and covered with a kind of enamel called ganoin. These thick scales are found especially in garfish.

    Cycloid scales are thin, large round or oval scales arranged in an overlapping pattern. They are found in carps and similar fishes.

Ctenoid scales are similar to the cycloid ones, but have spines or comb like teeth along their free edges. These are found in the higher bony fishes, such as perches and sunfishes.

Picture credit: google

A greenshank is a little bird with a long beak and olive-green legs-a member of a group of birds known as sandpipers.

       The greenshank breeds in Scotland, Norway, Sweden and Finland. It builds its nest on the ground, being content usually to settle in a small hollow, lined with heather or dry grass. The eggs are pale buff or stone colour, blotched with purplish-grey and spotted with dark brown.

       Worms, insects and tiny fish provide the bird’s food. In winter the greenshank migrates, some-times as far south as Australia or South Africa.

Picture credit: google

Numerous fossil remains have been found of coelacanth fish which died over 70 million years ago. In fact the coelacanth is said to have first appeared some 350 million years ago.

      But to the amazement of experts the first living coelacanth was found in 1938 off the coast of South Africa. In 1952 a second one was caught on a line by a fisherman from the Comoro Islands, between Mozambique and Madagascar. Since then many more coelacanths have been taken around the Comoros.

      Modern coelacanths are bigger than most of the fossil forms. They average about five feet in length and can weigh more than 100 pounds.

      Usually they live among reefs, from which they will dart out on their prey. they are strong and powerful flesh eaters. The heart of a coelacanth is an S-shaped tube and is probably the most primitive of its kind in existence today.

Picture credit: google

Bats use high-pitched sounds to find their way about. They are nocturnal animals. That is they move about by night. So they have developed their hearing to such an extent that they can find their way by a method known as echolocation.

     The blind-flying abilities of bats were first studied by LazzaroSpallanzani (1729-1799). He surgically removed the eyeballs from several bats to prove that they did not need to see to fly.

    In the 20th century, biologists, using electronic instruments, have carried out experiments with bats. They have discovered that bats find out where to go by emitting high-frequency sounds and receiving the echoes as they bounce off objects. Most of the sounds have too high a frequency to be heard by the human ear.

    Bats commonly fly together in groups, but apparently they are not confused by he sounds and echoes produced by each other. When hunting in woods and in the rain they are able to discriminate between the faint echoes bouncing off the ground, tree-trunks, branches, twigs and raindrops.

Picture credit: google

Fertilizers are used on farms to increase crop yields by ensuring that soils contain the chemical elements required by growing plants. These chemical elements include oxygen, carbon, hydrogen, nitrogen, phosphorus, potassium, sulphur, calcium, magnesium, and iron. If soils are lacking in any of these, the deficiency can be made good by the right fertilizer.

     Until the 119th century, farmers relied mainly on the application of natural fertilizers put “goodness” back into the land. They used manure from the stock-yards and, in the case of coastal areas, seaweed from the shore. Lime was also applied to prevent acidity. This method of soil rejuvenation went a long way to maintain the presence of chemical elements. But it often did little to improve soils already lacking in certain chemicals.

      Nowadays soils are analyzed to find out deficiencies which can be made up by the application of the appropriate chemical fertilizers. Of course, the chemicals alone do not guarantee a successful crop. The continued application of the natural fertilizers, such as manure and humans (decayed vegetables matter) is also essential.

Picture credit: google

The night vision of Owls is 100 times as keen as that of human beings, because their eyes are especially adapted for seeing in the dark. But most are almost colorblind and the pictures they receive are slightly blurred. This is because their eyes contain more rod-shaped receptor cells than cone-shaped ones.

        Operating in bright light, cone cells sharpen details and react to colour. Rod cells gather light and owls have 10times as many of these as do human beings. Each cell contains “visual purple”, a substance capable of transforming the slightest glimmer of light into a sight impression.

   Owls have exceptionally large eyes and can control the amount of light entering by expanding or contracting the pupil. Each pupil can act independently of the other so that owls can see objects in the shadows and in bright light at the same time. Owls’ eyes are so large that they are supported by thin, bony, and tubular structures called sclerotic rings. Because of this the eyes are almost immovable and nature has compensated for this by giving owls extremely flexible necks, which enable them to turn their heads through an arc of 270 degrees.

     These birds have excellent binocular vision as their eyes are in the front of their heads. This gives them a tremendous advantage in swooping on small lively prey, because distance judgment depends on binocular vision. To add to their advantages at night, the owls have outstanding hearing, keener than that of any other carnivorous bird.

    But owls can also see well in the daytime. Although most species hunt by night, others are active at dusk or in full daylight.

Picture credit: google