Free «Questions and Answers - Biology» Essay

1. List and briefly describe five characteristics of living organisms. Give an example of each.

All living organisms are made of cells. Some of them are either unicellular or multicellular. For example, bacteria have one cell, while human beings and other higher organisms are composed of many cells that vary structurally and functionally. In addition, all living creatures do not only obtain, but also use nutrients and energy to make their survival feasible. For instance, human beings ingest food for energy. On the other hand, plants acquire their nutrients by using raw materials, such as water and carbon dioxide gas, in the presence of solar energy. Furthermore, living organisms respond to environmental stimuli. Some of the latter may include sound, vibration, light, temperature, and so forth. A good example is when the snake responds to vibration by either deciding to run away from the place or attacking the source producing it. The next characteristic is that all living organisms are capable of reproducing the new offspring. All creatures ranging from unicellular to large multicellular ones have DNA molecules that are passed from the parent organism to the new offspring. Reproduction can occur sexually or asexually depending on the species. A good example is human beings who reproduce sexually to give birth to a baby. Finally, all living organisms grow and develop. They acquire food or energy that aids them to produce new body cells, the multiplication of which results in their overall growth. An example is a tree seedling that grows to become a huge plant.

2. Describe the action of a buffer and how it can be important in maintaining the pH of a living system.

Buffers can release or bind hydrogen ions (H+) to maintain relatively stable pH values in a living organism. Since the human being, as well as other living creatures, release acids and bases into their body tissues, buffers are of critical importance in minimizing pH changes making them within normal physiological limits. The pH value drops immediately H⁺ is added or released into body fluids, resulting in an increase in fluid’s acidity. On the other hand, the addition of hydroxyl ions (OH-) to body fluids subsequently leads to a rise in their pH values, which makes the acidity reduce or alkalinity increase. However, living creatures are very sensitive to changes in pH, having the need to maintain it within small normal ranges. For instance, changes in its value in the human blood by more than 0.05 can result in acidosis, which is a serious health problem that can lead to death if not treated. Living organisms require buffers because they depend on biochemical processes for survival. The only problem is that the latter occur in narrow ranges of pH, yet acids and bases are always added to body fluids. Thus, only buffers aid in limiting massive changes in the alkalinity or acidity of fluids, normalizing biochemical processes. Organisms cannot survive without buffers, given that some molecules such as proteins are susceptible to denaturation when pH values vary beyond the normal narrow ranges. The three primary buffering systems are protein, phosphate, and bicarbonate ones.

3. Describe how DNA and RNA are both different from and similar to each other.

Both DNA and RNA have many similarities because the two work hand in hand to perform a particular function. DNA contains genetic instructions carried in genes that dictate specific traits of a living organism. This information is expressed through DNA’s nucleotide-produced proteins. RNA does the work of producing the latter. Both DNA and RNA molecules are composed of monomers known as nucleotides that contain phosphate groups. Furthermore, they all have pentose sugars, as well as three nitrogenous bases (cytosine, adenine, and guanine). Concerning the pairing of the latter, the two molecules are similar to some extent because they have guanine-cytosine pairs. Functionally, DNA and RNA are essential for body cells to produce protein molecules necessary for various body functions.

However, the two molecules differ from each other in a number of ways. Double-stranded DNA differs from single-stranded RNA in the 5-carbon pentose sugar it contains. Instead of having a ribose sugar like RNA, it contains deoxyribose. Notwithstanding that, the binding of bases in the two molecules varies since DNA has the thymine nitrogenous base, which is different from the uracil one found in RNA. Such a phenomenon results in the formation of the uracil-adenine pair in RNA instead of DNA’s thymine-adenine combination. Moreover, despite the fact that the two molecules are located in the nucleus, RNA can travel outside unlike DNA. In addition, the latter exists only in one form, while the former occurs in three types that include messenger, ribosomal, and transfer RNA. Finally, DNA molecules are self-replicating, unlike RNA ones that are only synthesized from DNA when required.

4. Describe the several major differences between eukaryotic and prokaryotic cells.

Prokaryotes and eukaryotes have distinctive cellular differences. Prokaryotes store their genetic material in the nucleoid since they do not have a nucleus with the surrounding protective membrane. However, eukaryotes have cells with membrane-bound nuclei, where they store their genetic material. Furthermore, such eukaryotic cell organelles as lysosomes, endoplasmic reticulum, and mitochondria are surrounded by membranes. Such a characteristic is absent in prokaryotes. Furthermore, prokaryotic cells are smaller than eukaryotic ones. This feature is replicated in the size of ribosomes. Prokaryotes’ 70S ribosomes are far much smaller that eukaryotes’ 80S ones. This phenomenon makes eukaryotes have lowered metabolic and growth rates subsequently resulting in longer generation time as compared to prokaryotes.

Moreover, cell membranes of prokaryotes lack both sterols and carbohydrates that are typically found in eukaryotic cells and serve as receptors. These two types of cells also differ when it comes to various metabolic processes. In eukaryotes, the latter are the responsibility of chloroplasts and mitochondria. However, in prokaryotic organisms, these processes occur in organisms’ cell membranes. More differences are found in cell division and reproduction. In eukaryotes occurs in the form of a unique process called mitosis. However, binary fission is a mechanism, through which cell division is achieved in prokaryotes. Reproduction involves conjugation and meiosis in prokaryotes and eukaryotes respectively.

5. Explain how the plasma membrane is selectively permeable, and tell how that is related to the movement of materials across the membrane.

The movement of substance into and out of the cell is necessary for living. Some substances should move into the cell from the extracellular fluid, while others from intracellular into the extracellular one. These movements occur across the cell membrane, which can regulate what should enter or leave cell boundaries. The plasma membrane is not completely permeable because it only allows some substances passing through it. It makes it selectively permeable. This membrane is polarized and unable to let charged particles to pass through. In addition, it has small microscopic pores that can only allow small uncharged particles, such as oxygen, going through it. Enormous and polarized molecules cannot pass through it unless aided by other mechanisms. Because of these features, the cell membrane is selectively permeable.

Selective permeability is related to the transportation of materials across the membrane and the nature of the particle to pass through it determines its mode. Small uncharged particles can move across as a result of diffusion or osmosis. Large and polarized particles can only cross this membrane through channel transporters and transmembrane protein channels. The movement using channels may require energy and active transportation. However, large particles that may not pass through these channels are forced to gain entry into the cell by endocytosis or exit it through the process of exocytosis.