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L2 English 2015 .pdf


Nom original: L2 English 2015.pdf

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English exam 1:

Time allowed: 120 minutes

Nitrogen fixation
Irrespective of subfamily a feature commonly shared by nearly all legumes is the ability to fix
atmospheric nitrogen in their roots in a symbiotic association with bacteria of the genus
Rhizobium.

The bacteria, which are either present in the soil or are applied by man to the

seed at sowing, invade the roots of the plant via the root hairs. Once established within the
plant there is a proliferation of both plants cells and bacteria to form organized structures
attached to the roots, called nodules. Active nodules are usually red or pink in color due to
the presence of the chemical leghaemoglobin which has a similar chemical composition to the
haemoglobin found in blood.

It has been claimed that under favorable conditions the

legume-rhizobium association can fix up to 600 kg ha-1 of nitrogen per year.

This is

equivalent to over a ton of urea. A more normal figure would probably be from 150 to 250
kg ha-1 nitrogen fixed.
To obtain good nitrogen fixation, however, a number of conditions must be fulfilled.
Firstly the legume can not fix nitrogen unless it is associated with the right rhizobium strain.
Many legumes are not particular, or promiscuous, in their rhizobial requirements, other
legumes species are extremely strain-specific and will only fix nitrogen when inoculated with
one selected strain of bacteria.

Soil conditions can have a considerable effect on bacterial

population and efficiency, some rhizobia can not survive for long in soils in the absence of the
host plant, while others can survive for many years.
while others are destroyed by basic soils.

High soil acidity kills some rhizobia

In recent years there has been a considerable

increase in knowledge of the legume rhizobium symbiosis and the factors that control it.

Questions (6 marks)
1-What is the text about? (four sentences) (6 marks)

PART 2 (5 marks): Fill each gap in the following passage with ONE word:
List of words: in, never, some, one, but, their, full, away
It rained heavily last winter and ……..little streams near our house burst.…..…banks and the
fields all round were soon ......... of water. Luckily, the water did not reach any of the
houses…………..our village,…………it carried ............our beautiful wooden bridge. We are
building a new ……….now, but it will ............. be the same.

PART 3 (8 marks): Translate into English or French
2- En Afrique, le paludisme tue deux fois plus d’adolescents que le SIDA

10- Les géologues étudient la composition chimique de la croute terrestre

15- Why did chloroquine fail to eradicate malaria?

16-The death rate from malaria in children younger than five has fallen by forty percent

17- Nets dipped in this insecticide repel mosquitoes for up to six months according to WHO.

18- My aunt neither smokes nor drinks

19- Have him call me by ten o’clock tonight

20- Mrs. Helen won’t come to work today unless John is ill.


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L2 English 2015.pdf - page 2/2

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