have an impact threatened species uranium ore chemical elements
A treated
Be Complete the sentences with these phrases.
Down
live in
threadlike structure with genetic information
give a general idea of
characteristic
develop gradually 8 yellow powder from
flowers
В В Circle the correct answer.
The life of insects starts
when they are larva.
A cycle В field С vacuum
In the 18th century living things were into biological families.
В stated
С classified
coined a term came up with Earth's crust dominant gene
10
The biological information passed on to us from the previous generation is our
A inheritance В observation С principle
Charles Darwin is famous for
the idea of natural selection.
A disproving В adapting С formulating
It was really small - a
A pollen В microorganism С crop
They'll take a of your blood
for testing.
sample В injection С vaccine
He was immunised to have
to diseases.
recovery В application С resistance
Mendel a theory.
Suess It was biosphere.
The panda is a but efforts
are being made to save it.
is found in the ground.
When cells are making flowers, the will decide what colour they are.
The outer layer is the
You can find in
the atmosphere.
Usually advances in science
on our lives.
В : Complete the sentences with words derived from the words in red.
The scientist recorded his during the experiments, observe
Vernadsky was interested in the of various elements in the atmosphere,
hydrosphere, etc. distribute
Pasteur's of germ theory to preventing disease led to pasteurisation, apply
Mendel followed the characteristics of an organism through generations.
succession
Fortunately the patient made a quick recover
B
efore
you read
Discuss these questions with your partner.
What do you know about heredity?
What characteristics do you have in common with people in your family?
¥
A Vocabulary
Complete the sentences below with words from the box.
strand bound revealed organic base pattern
striking
substance
breakthrough
compound
coils
H Reading 1
The discovery of the structure and function of DNA
Look around you and you will see people of all different shapes and sizes, hair and eye colour. However, despite the differences that seem so striking, if you compare the genes of any two human beings they will be 99.9% the same. This similarity means we belong to the same species while the 0.1% difference makes us individuals and means we are different from each other.
What exactly is a gene? To answer that we have to look at the chromosomes inside the nucleus of a cell. We get 23 of these from our mothers and 23 from our fathers. Found in almost every cell in the body, these chromosomes consist of long strands of the chemical called deoxyribonucleic acid which is known as DNA. Each cell contains about two metres and if you put all the strands together they could travel to the Moon and back many times.
Scientists have known that DNA exists since 1869 when the Swiss scientist Johann Friedrich
Miescher noticed something he had not seen before in the nuclei of cells. He called it 'nuclein1.
It was more than 70 years later that scientists examined his theory.
It was two researchers at Cambridge University, England, who, in 1953, finally revealed the secret of DNA and its role in the pattern of life. James Watson, an American zoologist, and Francis Crick, an English biologist, had already discovered that DNA was made up of sugar and phosphates in the form of a chain. The whole structure was bound together by four compounds called guanine, adenine, thymine and cytosine. Each of these four nucleotides, as they were known, had a different organic base. They knew that guanine and adenine were the larger of the four, and that thymine and cytosine were the smaller; what they did not know was how they all fitted together.
Returning from London one day, Watson hit on the idea of experimenting with different pairs.
The two men made cardboard models of the four nucleotides and then tried systematically fitting them together. Watson later described their breakthrough in this way: 'Suddenly I became aware that an adenine-thymine pair was identical in shape to a guanine-cytosine pair'. Thus the men had discovered the relationship between the organic bases, and could see how each of these pairs of nucleotides formed a single rung on the so-called DNA ladder (DNA is shaped like a long ladder that is twisted into a spiral; this structure is known as the double helix). The discovery was the key to a much better understanding of the process of heredity.
There may be millions of these DNA ladder rungs linked to form hundreds of thousands of coils which in turn make up the structure of a single DNA molecule. In order for a cell to divide, all these coils have to be unwound. Then all the new nucleotides have to be linked in the right order and joined together by enzymes (enzymes are chemicals which we can find in all living organisms; they cause changes to take place). The entire process has to take place at great speed; in fact, in the time it takes for a cell to divide. Since bacteria cells split and form new cells in less than 20 minutes, this would mean that the DNA helix has to unwind very fast (several hundred turns a second) and a new chain has to be formed at the rate of several thousand nucleotides a second. At such a speed, a car engine would blow apart.
Pronunciation guide
adenine /‘agdaniin/ cytosine /'saitousim/
deoxyribonucleic /diioksi.raibsunju'kliak/ enzymes /enzaimz/ guanine /'gwainiin/ thymine /9ai2mi:n/
H В Comprehension
Read the text and decide if the following statements are true or false.
A particular species shares almost T Q all its genes. F Q
We get equal numbers of T Q chromosomes from our parents. F Q
Friedrich Miescher immediately revealed the importance of DNA.
The four compounds of DNA T Q are not the same size. F ЦЦ
Watson and Crick did the computer T □ modelling for nucleotide bases. F □
A new helix chain is assembled at a comparatively slow speed. F □
Before you listen
Discuss the following with your partner.
How is DNA useful to different people in different occupations?
-» Talk about: archaeologists, doctors, the police
И С Listening N)))
Listen to a talk. Then complete the information about DNA.