Техт з paramecium

Discovery

In 1675 a Dutchman, Anton van Leeuwenhoek made a very important discovery. While examining a drop of rainwater under a microscope he saw that the water was full of little animals, surprisingly little ones. Very soon he realized that what he saw were tiny animals no one had even heard of before. Leeuwenhoek called then "the smallest animals". Later, having studied their structure, scientists named them Protozoa. By discovering the tiny living things that could not be detected by the naked eye, Leeuwenhoek did a great service to science and mankind, and he also was the first to use the microscope to study Nature.

Habitat (Natural Home)

A Paramecium is easier to detect in a drop or fresh water viewed under a microscope than other Protozoa. It is shaped like a slipper, after which it was named (Slipper Animalcule). Paramecia are commonly found in wet or moist places and fresh or stagnant water that contains decayed vegetable matter. This is their natural home.

Structure

To observe a Paramecium place a drop of hay infusion on a glass slide under a microscope. Only a small degree of magnification is needed to reveal the Paramecium which has a soft body, about 0.25 mm long. This is made up of protoplasm and surrounded by a somewhat tough outer layer which helps the Paramecium to maintain a constant shape. Inside is a large oval macronucleus seen only upon the introduction of certain stains. Next to it is the so called micro nucleus.

The blob of protoplasm with a nucleus inside is called a cell. The Paramecium is a one-celled living organism with two nuclei. Like all other animal cells it has no chlorophyll and is incapable of absorbing carbon dioxide from the air.

Locomotion

In its search for food the Paramecium swims rapidly about, propelled by the action of hair-like cilia, which cover its body and act like tiny oars. The beating of the cilia drives the animal forward, while at the same time its body rotates upon its own longitudinal axis.

Nutrition

The Paramecium feeds on organic matter called bacteria.

By beating its cilia, the Paramecium sets up a current which draws the bacteria into a depression called the vestibule. From there it is taken into the mouth which leads into the gullet. The food is accumulated in the gullet and surrounded by digestive juices. A food vacuole is formed, which breaks away from the gullet and travels slowly through the protoplasm. The food is gradually changed by the digestive juices, dissolved and absorbed by the protoplasm. The Paramecium assimilates the digested food while the undigested remains are thrown out of the food vacuole through a hole at the broader end of the animal's body.

Respiration

Paramecia die when placed in cool, boiled airless water. This means they cannot exist without air, and are in constant need of oxygen. Like plants, they respire, through, their body surface. Water-dissolved oxygen is brought in through the surface layer; carbon dioxide is excreted into the water.

Excretion

As the Paramecium develops, part of it is constantly being destroyed and the waste matter harmful to the organism is passed out together with surplus water through two contractile vacuoles.

The contractile vacuoles look like two silvery bubbles which fill up and contract alternately. Water which accumulates in the protoplasm and the dissolved waste materials (excreta) pass into the vacuole canals. When the canals are full they collapse discharging the waste solutions into the vacuole. The vacuoles alternately fill up and collapse and the waste materials are expelled from the animal's body.