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Building blocks of life

All living beings are made up of (1) cells. Some of them are made up of only one cell and others have many cells. The adult human body is made up of about 60-90 trillion cells (all genetically identical to each other) …. (A)…In fact, if you (2) lined up all the cells in a human body end-to-end, you could actually circle the earth 4.5 times!

Cells got their name from an Englishman named Robert Hooke in the year 1665. First he saw and named «cells» while he was experimenting with a new instrument we now call (3) a «microscope». For his experiment he cut very thin slices from (4) cork. He looked at these slices under a microscope. He saw tiny box-like shapes. These tiny boxes reminded him of the plain small rooms that monks lived in called «cells».

What are the building blocks of a cell like?

All cells are enclosed within something called (5) a plasma membrane, and it holds parts of a cell inside. These parts of the cell are what biologists call (6) «organelles». That is a Latin name for little organs…. (B) …

Sometimes people think of cells as a balloon filled with fluid. That is not really true because a balloon does not let things move in and out like the membrane of a cell. It is important for cells to be able to move materials in and out of the cell.

The plasma membrane in cells has special structures that allow water and other food materials to pass in and out of the cell. At thousands of places across its surface, the plasma membrane holds gatekeeper structures are called (7) channels and (8) pores. These channels allow things to move in and out of the cell. Not everything can freely pass in and out of the cell. The cells allow only those things which are necessary for them to function.

Cells are amazing. They are all made of similar building blocks, but they do many different things depending on how they are programmed. Some cells carry (9) oxygen to parts of our body. Other cells defend against (10) invading bacteria and (11) viruses. There are cells that transmit signals through out the body like the signals from your eyes to your brain while reading this article. Some cells can even convert the sun's energy into food. This is called (12) photosynthesis. … (C) …There are hundreds of functions that cells can perform. … (D) …

Task 7. Read the text «Building blocks of life» again and fill in the gaps with the fragments.

1. Every day, every hour, every second one of the most important events in your life is going on in your body, cells are dividing. The ability of cells to divide into two living cells is unique for living things. The process of cell division is called mitosis.

2. In our body there are many different kinds of cells. We are made up of about 200 different types of cells. Our body also has non-living materials such as hair, finger nails, and the hard part of the bone and teeth. All these materials are made up of dead cells.

3. Some cells have a lot of these organelles, while others do many of them. All organelles in a cell perform different functions. Here are some names of organelles commonly found in cells: plasma membrane, channels and pores, nucleus, endoplasmic reticulum, ribosomes, golgi complex, mitochondria, chloroplast, vesiles, vacuole, cytoplasm, cell wall and plasmadesmata, peroxisomes, centrioles, lysosomes, cytoskeleton.

4. It is a set of chain reactions that convert light energy into chemical energy. Photosynthesis also produces energy-rich carbohydrates like starch. Photosynthesis occurs in the chloroplast of a plant cell.


Date: 2016-01-05; view: 1039

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