Biology Answer Note #14

Question 1 On average, errors occur in DNA synthesis only once in every 10 billion nucleotides incorporated. Which of the following does NOT contribute to this high fidelity of DNA synthesis? a. A strand-directed mismatch repair system that detects and resolves mismatches soon after DNA replication b. Complementary base-pairing between the nucleotides c. Exonucleolytic proofreading by the 5'-to-3' exonuclease activity of the enzyme to correct mispairing even after monomer incorporation d. "Tightening" of the DNA polymerase enzyme around its active site to ensure correct pairing before monomer incorporation Answer The correct answer is b. Complementary base-pairing between the nucleotides. This process plays a crucial role in maintaining the high fidelity of DNA synthesis. Complementary base pairing ensures that each nucleotide is paired with its exact complementary base during DNA replication, which allows for the correct copying of genetic information. This process is highly specific and reduces the chances of errors occurring in DNA synthesis. However, it should be noted that all of the other options listed also contribute to the high fidelity of DNA synthesis. The strand-directed mismatch repair system (a) detects and resolves any errors that may occur during replication, ensuring that the final DNA sequence is accurate. The exonucleolytic proofreading (c) by the 5'-to-3' exunuclease activity of the enzyme also plays a crucial role in correcting any mispairing of nucleotides after monomer incorporation. Additionally, the "tightening" of the DNA polymerase enzyme (d) around its active site ensures the correct pairing of nucleotides before monomer incorporation, further increasing the accuracy of DNA synthesis. Question 2 what was Albrecht Kossels contribution to the discovery of dna Answer Albrecht Kossel, a German biochemist, made significant contributions to the discovery of DNA. His work laid the foundation for our understanding of the chemical composition and structure of DNA. Kossel's contributions include elucidating the structure of nucleic acids, discovering the components of DNA, and proposing the idea of base pair complementarity. Kossel's work on the chemical composition of DNA began in the late 19th century when he isolated and identified the building blocks of nucleic acids. He discovered that these building blocks consisted of four nitrogenous bases (adenine, guanine, cytosine, and thymine), a sugar molecule (deoxyribose), and a phosphate group. This finding was crucial in understanding the structure of DNA and its role in genetic information. In 1885, Kossel also proposed the idea of base pair complementarity, which states that adenine will only pair with thymine and guanine will only pair with cytosine. This concept was later confirmed by other scientists and is essential for understanding the double-helix structure of DNA. Furthermore, Kossel's research on nucleic acids led him to discover the fundamental difference between DNA and RNA. He found that DNA contains a different type of sugar molecule (deoxyribose) compared to RNA (ribose). This discovery was critical in distinguishing the two types of nucleic acids and their respective roles in genetic information. Kossel's contributions to the discovery of DNA have had a lasting impact on the field of genetics and molecular biology. His work paved the way for further research and developments in understanding the genetic code and its role in inheritance. Question 3 2. Scientist observed 4 fish species; each of them preys on different organisms as algae, other small fish and other invertebrates A, B, and C. The fish feeding habit is illustrated in the below table Fish species Their prey Species 1 Fish, invertebrate A,B Species 2 Invertebrate B Species 3 Invertebrate A,B, and C Species 4 Green algae Which of the following species feeds on the lower trophic level organism? a. Species 1 b. Species 2 c. Species 3 d. Species 4 3. Which of the following is an example of asexual reproduction? a. A plant grew from a seed of another plant b. A pine tree got branched from a root of another tree c. Cherry tree grew from wastes of an animal that ate a cherry plant d. A plant grew after pollination by insects 4. Which of the following animals have 8 appendages and exoskeleton? a. Mollusks b. Cnidarians c. Star fish d. Arthropods Answer 2. The species that feeds on the lower trophic level organism would be Species 4, which feeds solely on green algae. According to the trophic levels concept in ecology, organisms that feed on primary producers, in this case green algae, are considered to be on the lower trophic level. Primary producers are the foundation of the food web and are responsible for converting sunlight energy into usable energy for other organisms. Therefore, Species 4 feeds on the lower trophic level organism. 3. The correct answer is d. A plant grew after pollination by insects. Asexual reproduction is the process by which an organism produces offspring that are genetically identical to the parent without the involvement of gamete fusion. In this case, pollination by insects leads to the formation of a new plant, which is genetically identical to its parent. This process is known as vegetative reproduction and is a form of asexual reproduction. 4. The correct answer is d. Arthropods. Arthropods are a phylum of invertebrates that are characterized by the presence of jointed appendages and an exoskeleton. These appendages include legs, antennae, mouthparts, and other structures that are used for movement, sensing, and feeding. Some examples of arthropods include insects, spiders, crustaceans, and millipedes. Question 4 Of the following characteristics, which pair is the best used to describe all animals? • multicellular, heterotrophic • invertebrate, marine • eukaryotic, radial symmetry C segmented bodies, photosynthetic Previous Answer The best pair to describe all animals would be multicellular and heterotrophic. Explanation: Multicellularity is a defining characteristic of animals, as they are composed of multiple cells that work together to carry out essential functions. This sets them apart from singlecelled organisms, such as bacteria or protists. Additionally, the term "animal" is used to classify a wide range of organisms, including insects, mammals, and birds, all of which are multicellular. Heterotrophy refers to an organism's ability to obtain its energy and nutrients from other sources. This is in contrast to autotrophs, which are able to produce their own energy through photosynthesis. The majority of animals rely on consuming other organisms for their nutrition and energy, making heterotrophy a fundamental characteristic of the animal kingdom. Question 5 Suppose an animal has a diploid number of 16 chromosomes (2n=16). If a nondisjunction event were to occur resulting in trisomy, how many chromosomes would the somatic cell contain? ) 16 8 17 \ 7 9 Answer A non-disjunction event is a genetic abnormality in which chromosomes fail to separate properly during cell division, resulting in an abnormal number of chromosomes (Klug et al., 2018). This can lead to a condition called trisomy, where there is an extra copy of a chromosome, instead of the normal two copies. In this case, the animal has a diploid number of 16 chromosomes, so we would expect to see 2 copies of each of the 16 chromosomes, for a total of 32 chromosomes in a somatic cell. However, in the event of non-disjunction, one of the homologous chromosomes (a pair of chromosomes with the same genes) fails to separate, resulting in an extra copy of one chromosome. This means that there would be 3 copies of that particular chromosome in the resulting cell. Therefore, the somatic cell would contain a total of 17 chromosomes (16 normal chromosomes + 1 extra chromosome due to non-disjunction).