Answer:
examples include, "FF" or "DD", or just two uppercase letters.
Explanation:
They use a internal pouch which is named swim bladder.
Explanation; Oxygen will enter a fish’s mouth, and passes through their gills. The oxygen will be taken and gets carried by hemoglobin through their bloodstream. Hemoglobin will take out some of the oxygen into their swim bladder. The amount of oxygen will show if they will sink or rise. Your question is how do they rise. If he goes up too much, the meaning of this is when the gas diffuses into their blood and out the gills.
Got this from a writing, but rephrased it.
Answer:

Plasmodesmata play roles in both cellular communication and in molecule translocation. Plant cells must work together as part of a multicellular organism (the plant); in other words, the individual cells must work to benefit the common good. Therefore, communication between cells is crucial for plant survival.
Answer:
It has 4 trophic levels.
Explanation:
The first level would be the producers, followed by the primary consumers, then the secondary consumers, then the tertiary comsumers.
/ Tertiary consumers \
/ Secondary Consumers \
/ Primary Consumers \
/ Producers \
/________________________________\