Answer the following questions. 1. What did Harvey announce as his biological dictum?
2. What philosophical and religious ideas advanced to answer the question about the origin of life were the most popular?
3. What does the idea of evolution mean?
4. How did naturalists during the 16th, 17th, and 18th centuries imagine the origin of life?
5. Why was the publication of Darwin's book in 1859 important?
6. What did Darwin state in his book?
7. Is natural selection admitted as one of the causes of evolution?
Home Reading THE CELL
All living things are composed of cells. Very simple organisms such as yeast and bacteria consist of only one cell. They are one-celled or unicellular organisms. A large organism, such as a human being, contains billions upon trillions of cells and is called a multicellular organism. A drop of blood, for instance, contains about forty billion cells. And there are thousands of drops of blood in the average man.
Despite its small size, each cell is a tiny drop of life. Some cells can exist independently, and do, as in the case of bacteria. Human cells, however, have lost that ability. They depend on one another and specialize in one function or another. Some cells specialize in photosynthesis, some in digestion, some in excretion and some in reproduction.
Groups of cells of a similar shape, size and function form a tissue. When tissues of different types are grouped together for a common function they form an organ.
Groups of cells, taken all together, are more advanced than single cells, even if the latter are more independent.
The living matter inside a cell is called protoplasm. The protoplasm is divided into parts. Near the center of the cell is a part which is denser and thicker than the rest of the cell. It is the nucleus. The rest of the cell is cytoplasm.
Like any other living things, cells grow and multiply. Most cells multiply by dividing down the middle. Then there are two cells where only one existed a moment before. The cell nucleus is in charge of seeing that cell division takes place properly. The cytoplasm takes care of the day-by-day life of the cell. Cells in different parts of the body vary in their shape according to the work they must do. Fat cells are just tiny blobs of fat surrounded by a thin layer of protoplasm. The red cells of the blood are little disks that contain a protein called hemoglobin, which carries oxygen to all other cells of the body. Red blood cells are so simple they don't even have a nucleus and so cannot grow or divide.
Nerve cells have irregular shapes with long thread-like fibers sticking out of them. Impulses and sensations travel along those fibers. Muscle cells are long and thin. They can contract into short, thick cells whenever necessary.
Some cells are so specialized that they have abandoned almost everything but6 their main function. They have even lost the ability to multiply. A baby is born with all the brain cells, for instance, that it will ever have. Still other cells are always growing. The cells of the skin grow and divide throughout life.
Answer the following questions.
1. What arc all living things composed of?
2. What are unicellular organisms?
3. Which organisms are called multicellular?
4. How many cells does a drop of blood contain?
5. Can human cells live independently? Why have they lost that ability?
6. What does a cell consist of?
7. What are the main functions of cell?
8. What shapes do different cells of the body have and why?
9. Why cannot red blood cell grow and divide?
10. Which human cells have lost the ability to multiply?
Home Reading ENZYMES
Certain proteins are catalysts. Catalysts, as you know, are substances that make chemicals react with one another very quickly, without themselves being changed. They catalyse various chemical reactions. Our body is full of thousands of different catalysts which, it makes for itself. In their absence, the chemical reactions would proceed very slowly. Such catalytic proteins are called enzymes. Enzymes control body chemistry.
That all enzymes are proteins was proved only in 1926 when the American biochemist Sumner isolated an enzyme named urease in the form of pure crystals. He collected enough of it to work on and only then he showed that this enzyme was definitely a protein. He received a Nobel Prize for his discovery.
Each different type of cell contains a special group of enzymes. Some enzymes can be found in almost all cells, some only in a few cells.
The fact is that each cell has the kind it needs and no others.
You may wonder whether there is room in the cell for all the enzymes it needs. After all, the cell is a very small object.
Well, let us consider the liver cell. The liver is the busy organ of the body. It has more different chemical jobs to do than any other part of the body. Therefore it needs more different kinds of enzymes.
Fortunately, the liver cell is big enough to hold more than two, hundred trillion (that is, 200,000,000,000,000) molecules. Ninety-eight per cent of them are just water molecules. However, there are still 50,000,000,000 (fifty billion) protein molecules in a single liver cell. That’s quite a number. Even if we suppose that only one protein molecule in a thousand is an enzyme molecule, the liver cell still has 50,000,000 enzyme molecules. And if it takes thousand molecules of each particular enzyme to do the job, there is still room for over 50,000 different enzymes.
So you see, cells have room enough for all the enzymes they need. You can think of each cell as a tiny bag of enzymes; a tiny bag of a great many enzymes.
Answer the following questions:
1. What substances are catalysts?
2. What are enzymes? Does our body contain any? What is their function?
3. Who and when proved that enzymes are proteins?
4. What enzymes does each cell contain?
5. Why does a liver need more different kinds of enzymes than any other organ of the body?
6. How many enzyme molecules are there in the liver cell?
Home Reading
ANIMALS
Animals of many shapes and sizes live in all parts of the world. They walk or crawl on land, fly in the air and swim in the water. Horses, canaries, toads, butterflies and worms are all animals. So are oysters, beetles, elephants, lobsters, sponges, seals and snakes. Many animals are so small that they can be seen only with a microscope. The largest animal is the blue whale. Nobody knows exactly how many kinds of animals there are. So far scientists have grouped more than a million kinds of animals. But every year hundreds of new kinds are discovered.
Many scientists divide living things into five man groups — animals, plants, fungi, protists and minerals. It is usually easy to distinguish animals from other types of organisms. For example, most animals move around but most plants and fungi are held to the places.
Tame animals and wild animals are grouped according to the way they act with people. Wild animals are usually afraid to come close to people. Only a few kinds of wild animals have become tame in large numbers. Most of them are the well-known pets and farm animals. The great majority of animals are wild. Individual wild animals can usually be tamed but they easily become wild again.
Land animals include a wide variety such as apes, butterflies, eagles, elephants, horses, pigeons and spiders. Water animals include such different creatures as fishes, lobsters, sponges and whales. Some kinds of animals spend part of their lives on land and part in water. These animals include dragonflies, frogs, horseshoe crabs, salamanders, sea turtles and toads.
The temperature inside the bodies of some animals stays about the same all the time. These animals are called warm-blooded. The temperature inside the bodies of other kinds of animals varies from time to time. Such animals are called cold-blooded.
Zoologists classify animals according to their body characteristics. They separate the animals with one or more of the same body characteristics into major groups. Each of these groups is called a phylum. Every phylum is divided into groups called classes. The classes are divided into orders and the orders into families. The families are divided into genera and the genera into species.
Every kind of animals fits into a marvelous system of nature. Animals help build up life by serving as food for people and for plants. But animals also destroy life. They hunt and kill other animals and they eat plants. As a result, animals help keep in balance the total number of plants and animals. The balance of nature is so important that it is often called the web of life.
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