Q5. What is the main difference between archaebacteria and other bacteria, according to NCERT?
A different cell wall structure, which is responsible for their survival in extreme conditions (NCERT page 13).
Q6. Describe the cyanobacteria in five points.
They have chlorophyll a similar to green plants and are photosynthetic autotrophs; they are unicellular, colonial or filamentous; they live in fresh water, the sea or on land; colonies are generally surrounded by a gelatinous sheath; some fix atmospheric nitrogen in heterocysts (Nostoc, Anabaena), and they often form blooms in polluted water (NCERT page 13).
Q7. Which group of bacteria is the most abundant in nature, and what is the role of most of its members?
Heterotrophic bacteria; the majority are important decomposers (NCERT page 13).
Q8. In which habitats do bacteria live where very few other life forms can survive?
Hot springs, deserts, snow and deep oceans (NCERT page 12).
Q9. Assertion: archaebacteria survive in extreme conditions. Reason: they have a different cell wall structure from other bacteria. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: NCERT says this cell wall feature is responsible for their survival in extreme conditions (page 13).
Q10. What do bacteria do when conditions become unfavourable?
Some form resistant spores (NCERT page 14). In the common endospore cycle this is a survival response, not multiplication; not all bacteria form endospores.
Q11. Which pigment do cyanobacteria share with green plants?
Chlorophyll a (NCERT page 13).
Q12. Why can a nitrifying bacterium not get energy by oxidising nitrate?
Nitrogen in nitrate already has its highest oxidation number, +5, so nitrate cannot be oxidised further. Nitrifying bacteria get energy by oxidising ammonia (to nitrite) and nitrite (to nitrate) (beyond the NCERT text, which lists nitrates among the substances oxidised).