21. B. recessive
22. D. DD and dd
23. D. FF and ff
Answer:
limiting factor
Explanation:
In an ecosystem, certain factors hinder the growth or abundance of the population of organisms. These factors are called LIMITING FACTORS. Limiting factors, which can be biotic, food, drought, predation, disease etc, are factors that inhibits a population of organism from becoming enlarged. There are two types of limiting factors viz: density dependent (depends on size) and density independent (not dependent on size).
This is the case of a drought that dries up the stream that inhabits a population of salamanders. The drought causes the unavailability of water, which will ultimately have an effect on the growth of the salamander population. Hence, the DROUGHT is considered a LIMITING FACTOR.
Answer:
In nature, populations are usually evolving. The grass in an open meadow, the wolves in a forest, and even the bacteria in a person's body are all natural populations. And all of these populations are likely to be evolving for at least some of their genes. Evolution is happening right here, right now!
To be clear, that doesn't mean these populations are marching towards some final state of perfection. All evolution means is that a population is changing in its genetic makeup over generations. And the changes may be subtle—for instance, in a wolf population, there might be a shift in the frequency of a gene variant for black rather than gray fur. Sometimes, this type of change is due to natural selection. Other times, it comes from migration of new organisms into the population, or from random events—the evolutionary "luck of the draw."
I hope this helps a little bit.
Two important natural processes that release carbon into our atmosphere are photosynthesis and respiration.