Answer: C. Birds moving south when the weather gets colder
Seasonal change is the change in season due to change in abiotic factors like weather conditions, sunlight availability, wind direction etc. Seasons change from summer to winter, winter to summer, summer to spring etc. These seasonal changes affect the life of biological communities including plants and animals. Some organisms adapt to changing seasonal conditions but others completely avoid them by migrating to other places where weather conditions are suitable for their survival. Therefore, birds moving south when the weather gets colder is because of seasonal change as birds cannot tolerate cold weather conditions.
Answer:
The two important conditions that must be met before gram staining are-
1. The age of the culture should not exceed 24 hours.
2. Over heating, decolonization should be avoided.
Explanation:
Gram staining is a technique developed to distinguish the bacteria on the basis of the composition of the cell wall around the bacteria.
The gram stain is a sensitive technique so must be performed carefully. The precautions should be taken to avoid any error while gram staining that is-
1. Age of the culture- The culture should be freshly prepared just 18-24 hours before the experiment as above 24 hours bacteria lose their ability to retain the color so one would not be able to differentiate between the cultures.
2. While performing the experiment one should avoid overheating and decolorization with ethanol as both the factors lead to the loss of crystal violet stain from the cell and they take pinkish color after safranin staying.
D) Amphibia was considered to be the first to develop lungs
Undergo differentiation
become stem cells
turn on all of the genes found in the nucleus
some cells can undergo cell division
