PRELIMINARY CONTEST 2024
Accra Girls SHS: 39 points
Notre Dame Girls SHS: 34 Points
Aburi Girls SHS: 27 points
T.I. AMASS
KUMASI VS AMENFIMAN SHS
TUOBODOM SHTS
ROUND 2
FIRST QUESTION
QUESTION
1. What name is given to the process by which bacteria turn nitrogen into a form that plants can use?
ANSWER: Nitrogen fixation
EXPLANATION
Nitrogen fixation is the biological process by which certain microorganisms convert atmospheric nitrogen gas (N₂) — which plants cannot use — into usable nitrogen compounds, mainly ammonia (NH₃).
Key Points:
The atmosphere is about 78% nitrogen, but plants cannot absorb N₂ directly.
Nitrogen-fixing bacteria such as Rhizobium, Azotobacter, and Clostridium carry out this process.
Some of these bacteria live freely in the soil, while others live in root nodules of leguminous plants (beans, cowpea, groundnut, soybeans).
The enzyme nitrogenase helps convert N₂ into ammonia.
The ammonia produced is then converted into nitrites and nitrates, which plants absorb and use to make proteins, DNA, and other vital molecules.
PRACTICE QUESTIONS
1. What percentage of the air is nitrogen gas?
ANSWER: About 78 per cent.
2. Name a symbiotic nitrogen-fixing bacterium.
ANSWER: Rhizobium.
3. Name two free-living nitrogen-fixing bacteria.
ANSWER: Azotobacter and Clostridium.
4. Which enzyme fixes nitrogen?
ANSWER: Nitrogenase.
5. Where do Rhizobium bacteria live in legumes?
ANSWER: In root nodules.
6. What protein in nodules protects nitrogenase from oxygen?
ANSWER: Leghaemoglobin.
7. What is nitrification?
ANSWER: The oxidation of ammonia to nitrites and then nitrates by bacteria.
8. Name the two groups of nitrifying bacteria.
ANSWER: Nitrosomonas and Nitrobacter.
9. What is denitrification?
ANSWER: The conversion of nitrates back to nitrogen gas by bacteria.
10. Name one natural non-biological way nitrogen is fixed.
ANSWER: Lightning.
11. In which form do plants mostly take up nitrogen?
ANSWER: As nitrate ions.
12. What is the industrial process used to make ammonia?
ANSWER: The Haber process.