1. fixes the atmospheric nitrogen for the alga
2. provides protection, anchorage and absorption for the alga
3. provides food for the alga
4. releases oxygen for the alga
provides protection, anchorage and absorption for the alga
1. Antarctica
2. mountains
3. Greenland
4. polar ice
polar ice
1. 45° to 66°
2. 0° to 20°
3. 20° to 40°
4. 60° to 80°
45° to 66°
1. soil
2. water
3. population
4. fossils
soil
1. presence of sclerenchyma
2. presence of aerenchyma
3. absence of aerenchyma
4. presence of root nodules
presence of aerenchyma
1. water day
2. world environment day
3. conservation day
4. world earth day
world environment day
1. high percentage of young individuals
2. low percentage of young individuals
3. high percentage of old individuals
4. low percentage of old individual
high percentage of young individuals
1. population
2. organism
3. community
4. species
organism
1. detritus
2. humus
3. standing state
4. standing crop
standing crop
1. Heredity variations
2. Discontinuous varitions
3. Environmental variations
4. None of the above
Environmental variations