What are the four types of rna and how do they function?

Ribosomal RNA (rRNA): It gets its name because it is the main constituent of ribosomes. It has the highest weight and is primarily responsible for protein synthesis. Messenger RNA (mRNA): Along with ribosomal RNA, it aids in protein synthesis, guiding the order of amino acids for protein formation. It is responsible for bringing the genetic information received from DNA from the cell nucleus to the cytoplasm. Its weight is smaller than ribosomal RNA. RNA Transporter (tRNA): Its name already indicates that its function is to transport the amino acid molecules that will be used in protein synthesis. It transports these molecules to ribosomes, where they join and form proteins. Compared to the others, it has the lowest weight. Small nuclear RNA (snRNA): These are small RNA molecules that can be found in the nucleus. They are important molecules in a number of mechanisms such as RNA processing. This type of RNA is associated with some specific proteins with which it reacts to form complexes called SNRNP-small nuclear ribonucleoproteins.

Most populations do not experience: a) exponential growth

Explanation:

Populations that experience exponential growth models show an increase in proportion to their size. The increase in the population size depends on the individual´s reproduction rate: a population that grows at constant exponential rate gains individuals faster as the population increases in size.

This model states that populations live in an environment with unlimited resource availability, so the density factor does not influence population growth. There is no density-dependence effect nor competition for resources. Natality and mortality rate do not depend on density. There is a constant growth rate per capita, and it is proportional to the population size.

Exponential growth is hardly seen in nature due to its characteristics.

Almost every environment shows a carrying capacity point. Carrying capacity is the capability of the environment to support a population. Commonly environments have limited resources and space, and as the population grows, competition increases too. The per capita growth rate decreases as population size increases. Finally, the population reaches the maximum point of carrying capacity, delimited by available resources, such as food or space.

The carrying capacity might be affected by limiting factors, which might be a result of the population density (for example, competition) or might be density-independent. This last case refers to dense-independent factors, and among these, we can mention human impact or natural disasters (fires, volcanic eruption, flooding).    

Only a few species can experience exponential growth, such as bacterias.