Презентация на тему Клетка

Cells

A cell is a tiny unit which constitutes the core of all living things: human, animal, plant or microbe. It was an English mathematician and physicist called Robert Hooke who, in 1665, first recorded his observations of cells under a microscope and published them in a book entitled Micrographia. Hooke noted that there are single-celled organisms, such as the amoeba, and multi-celled organisms, such as man. In the latter type of organism, it was revealed that the cells are grouped together to form different types of tissues, and the tissues then form organs.

The structure of a cell appears very simple. It is a jelly-like mass, called protoplasm, enclosed by a wall, with a central nucleus. Although research continued into the structure and function of cells, it was not until the late 19th century that a process of staining and fixing tissues was developed. This made it possible for scientists to preserve the cells for more detailed observation under a microscope. It was then discovered that new cells are formed by the division of old ones, and that each cell has its own lifespan. In other words, a cell is born (created), feeds, produces waste, grows, splits to create new cells or disintegrates and dies. Each cell has a specific function and specific characteristics, for example, muscle cells stretch and nerve cells carry information.

Stem cells are central to this infrastructure. These cells provide a remarkable repair system for the body, as they are able to develop into any type of cell. They can continue to redivide as often as possible to replace damaged or dying cells. The cells created from the division of a stem cell can remain stem cells, or become any of the other specific cells (blood cells, brain cells or other) in the organism. The key to the division process lies in the nucleus. The nucleus splits into two identical parts in the shape of rods or threads, which break away in opposite directions and form new nuclei. At this point the cell itself divides and two new cells are born.

The rods or threads are called chromosomes. Each chromosome is made up of links of protoplasm called genes joined together in a chain. It is the genes that determine the essence of each cell and its particular characteristics. The number of chromosomes found in a particular organism always remains the same, but it will vary depending on the species; human beings have 48, for example, and sugar cane over 200.

Gregor Mendel

Gregor Mendel was born on 20^th July, 1822, and died on 6^th January, 1884. He was a biologist and botanist whose scientific research showed that inheritance proceeds according to certain scientific laws.

Mendel was a brilliant student and his family encouraged him to study, but they were very poor so Mendel entered a monastery in 1843. There he taught Mathematics, Physics and Greek to high school students. Eight years later, in 1851, the monastery sent him to the University of Vienna where he was able to continue his education. In 1853, he returned to the monastery and began teaching and researching again.

Mendel's theories of heredity based on his work with pea plants are well known to students of Biology. But his findings were so different from the accepted views on heredity at the time that his work was ignored until long after his death. His paper, Experiments in Plant Hybridisation, in which he described how traits were inherited, has become one of the most influential publications in the history of science.

Mendel was the first person to trace the characteristics of successive generations of an organism. In Mendel's day, a number of hypotheses had been suggested to explain heredity. The most popular one was the so-called blending theory. According to this theory, inherited traits blended from generation to generation. For instance, a red rose crossed with a white rose would, over time, produce a pink rose. Another theory put forward by Charles Darwin was called pangenesis. This stated that there were hereditary particles in our bodies, and that these particles were affected by our actions. The altered particles could be inherited by the next generation. These theories were disproved by Mendel.

The first thing he noticed when he began his experiments was that traits were inherited in certain numerical ratios. This observation led him to come up with the idea of the dominance of genes and he tested it in peas. For seven years he crossed thousands of plants to prove the Laws of Inheritance. From his experiments, Mendel developed the basic laws of heredity. Those laws are the following: that traits do not combine, but are passed whole from generation to generation (which disproved the blending theory and Darwin's theory); each member of the parental generation passes on only half of its hereditary information to each offspring (with certain traits dominant over others); and different offspring of the same parents receive different sets of hereditary information.

Mendel's research formed the beginnings of the modern science of genetics. Genetic theory has had a huge impact on our lives. Many diseases, for example haemophilia, are known to be inherited, and family histories can be traced to determine the probability of passing on a hereditary disease. Scientists can now design plants that are easier to grow, or which can produce more food. This practical side of the results of Mendel's research is being used to improve the way we live.

Prepare a short presentation on the topic: "Theories of inheritance". Use the information in both texts.

Talk about:

• Mendel's theory

• Mendel's experiment

• Theories that were disproved

• Cells, chromosomes and genes

You may use these notes in your presentation"

Mendel stated that….

Mendel conducted experiments on……

The theories that Mendel disproved were ……. and ……

What are cells? How is genetic information passed on?

Write a letter to a science museum applying for a part-time job. Use these notes to help you. Use these notes to help you:

Dear (sir/madam),

I am writing to apply for the position of ………………….I believe I would be suitable for the position because …………………..

It is my intention to study Science at university, and I believe this will ……………………

I have worked in a ……………………….. for …………..years/months.

I am available for an interview ………………….

Yours faithfully,

(your first name and surname)

Prepare a short presentation on the topic: "Theories of inheritance". Use the information in both texts.

Talk about:

• Mendel's theory

• Mendel's experiment

• Theories that were disproved

• Cells, chromosomes and genes

You may use these notes in your presentation"

Mendel stated that….

Mendel conducted experiments on……

The theories that Mendel disproved were ……. and ……

What are cells? How is genetic information passed on?

Write a letter to a science museum applying for a part-time job. Use these notes to help you. Use these notes to help you:

Dear (sir/madam),

I am writing to apply for the position of ………………….I believe I would be suitable for the position because …………………..

It is my intention to study Science at university, and I believe this will ……………………

I have worked in a ……………………….. for …………..years/months.

I am available for an interview ………………….

Yours faithfully,

(your first name and surname)