2.1 Read the text to get the main idea
It was Anton van Leeuwenhoek (1632-1723), a Dutch scientist, and one of the pioneers of microscopy who in the late 17th century became the first man to make and use a real microscope.
Van Leeuwenhoek achieved great success by developing ways to make superior lenses, grinding and polishing five hundred and fifty lenses to make his new lens tube that had a magnifying power of 270x and could view objects one millionth of a meter (other microscopes of the time were lucky to achieve 50x magnification).
Van Leeuwenhoek made many biological discoveries using his microscopes. He was the first to see and describe bacteria, yeast plants, the teeming life in a drop of water, and the circulation of blood corpuscles in capillaries. During a long life he used his lenses to make pioneer studies on an extraordinary variety of things, both living and non-living, and reported his findings in over a hundred letters to the Royal Society of England and the French Academy.
Van Leewenhoek's work was verified and further developed by English scientist Robert Hooke, who published the first work of microscopic studies, Micrographia, in 1665. Robert Hooke's detailed studies furthered study in the field of microbiology in England and advanced biological science as a whole.
2.2 Answer the following questions
1. When was the first real microscope invented?
2. How did Van Leeuwenhoek make his microscopes?
3. What was a magnifying power of his microscopes?
4. Whatbiological discoveries did he make using his microscopes?
5. How did Robert Hooke continue the work of Van Leeuwenhoek?
Unit V Structural units of the eukaryotic cell
Look at the picture and name the main units of the eukaryotic cell
Read the text, pay attention to the highlighted words
Eukaryotic cells have 3 main parts.
They are: cell membrane, cytoplasm and the nucleus.Some other structures are also found in eukaryotic cells
Cell membrane
The cell membrane, or plasma membrane, encloses the cell. It is made up of lipid, protein and a small amount of carbohydrate. The functions of the cell membrane are:
-to protect the cytoplasm and its organelles;
-toexchange material into or out of the cell;
-toprovide the cell with the shape;
-tolinkcells to each other and provide communication between cells
Cytoplasm
The cytoplasm is the second main part of the cell. The cytoplasm is located between the cell membrane and the nucleus, it is jelly-like (like egg white) in structure. It contains organic and inorganic materials.
Cell organelles are found in the cytoplasm. Cell organelles are the micro organs of the cell. They have special functions in the cell. We can summarize their function as follows:
1. Ribosomes produce protein.
2. Mitochondria are the power houses of the cell. They produce ATP energy.
3. Golgi bodies are the packaging system of the cell. They produce special materials such as milk.
4. Vacuoles are the storage centers of the cell. They store water, minerals and waste.
5. Lysosomes are the stomach of the cell. They enable digestion in the cell.
6. Peroxisomes are the disposal centers of the cell. They destroy harmful substances.
7. Endoplasmic reticulum is the transport system of the cell. It produces proteins, lipids and other substances and transports them through the cytoplasm.
8. Chloroplasts are found in plant cells. They produce food and oxygen by photosynthesis.
9. Centrosomes are found in animal cells. They help in cell division.
Nucleus
The nucleus is the control center of the cell (you can say the brain of the cell). In the nucleus, the genetic material (chromosomes, made up of DNA and protein) is found. The nucleus also contains the nucleolus, which produces ribosomes.
Other structures of the eukaryotic cell
Cell wall: It is a hard structure which protects the cell. For example, plant cells have a rigid structure because of the cell wall.
Flagellum and cilia: They enable movement of the cell. A flagellum is long, but cilia are short.
Material transport through the cell membrane
The cell membrane has a selectively permeable structure. That means it allows some materials to pass into or out of the cytoplasm. Some materials can pass, but others cannot pass through the cell membrane. Materials can be exchanged by different methods, including diffusion, osmosis and active transport
Diffusion
Diffusion is the movement of molecules from the areas of high concentration to the areas of low concentration. For example, perfume diffuses throughout the room until its concentration becomes constant. The cell does not use energy for this process, so it can occur in living and non-living cells.
Osmosis
Osmosis is the diffusion of water. Water molecules move from the areas of high concentration to the areas of low concentration. Like in diffusion energy is not used and osmosis occurs in living and nonliving cells.
Active transport
Active transport is the movement of molecules from the areas of low concentrationto the areas of high concentration. In this process cells use energy. Unlike diffusionand osmosis, active transport occurs only in living cells
Comparison of plant and animal cells
Plant and animal cells are both eukaryotic, so they share many common features. They have some differences too, as we can summarize in the following table
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Structure
Plant cell
Animal cell
Cell membrane
Present
Present
Nucleus
Present
Present
Cell wall
Present
Absent
Centrosome
Absent
Present
Nucleolus
Present
Present
Peroxisome
Absent
Present
Chloroplast
Present
Absent
Mitochondria
Present
Present