Module 5
What type of chemical bond holds the complementary nitrogenous bases together in a DNA double helix?
A) Covalent bond
B) Hydrogen bond
C) Peptide bond
D) Ionic bond
B - hydrogen
This process introduces genetic variation when homologous chromosomes exchange sections of DNA during meiosis. What is it?
crossing over
This type of immunity develops when the body produces its own antibodies and memory cells following exposure to an antigen. What is it?
Active immunity.
This cardiovascular disorder occurs when fatty deposits build up inside arteries, restricting blood flow.
Atherosclerosis
This type of error causes measurements to consistently differ from the true value in the same direction.
Systematic error.
What is the primary difference between the daughter cells produced by mitosis versus meiosis?
A) Mitosis produces 4 haploid cells; meiosis produces 2 diploid cells.
B) Mitosis produces 2 identical diploid cells; meiosis produces 4 genetically unique haploid cells.
C) Mitosis produces gametes; meiosis produces somatic cells.
D) There is no difference.
B- Mitosis produces 2 identical diploid cells; meiosis produces 4 genetically unique haploid cells.
Distinguish between somatic mutations and germ-line mutations, including their potential effects on offspring.
Somatic mutations occur in body cells and generally affect only the individual in which they arise; they are not passed to offspring. Germ-line mutations occur in cells that give rise to gametes and can be inherited by offspring, potentially introducing new alleles into a population.
Explain how Koch's postulates contributed to understanding the causes of infectious disease.
Koch's postulates provided a method for investigating whether a particular microorganism causes a specific disease. The microorganism should be found in diseased individuals, isolated and grown in culture, and then shown to cause the same disease when introduced into a healthy susceptible host. The microorganism should then be re-isolated from the newly diseased host. This helped establish a causal relationship between specific pathogens and diseases, although the postulates have limitations for pathogens that cannot be cultured or diseases with multiple causes.
This diagnostic technique uses magnetic fields and radio waves to produce detailed images of soft tissues in the body. What is it
MRI (magnetic resonance imaging).
Distinguish between accuracy and precision.
Accuracy refers to how close a measurement is to the true or accepted value. Precision refers to how close repeated measurements are to each other. A set of results can therefore be precise without being accurate.
Which enzyme is responsible for unwinding the DNA double helix and breaking hydrogen bonds between bases?
A) DNA polymerase
B) RNA polymerase
C) Helicase
D) DNA ligase
C - helicase
Explain why antibiotic resistance in bacteria is an example of natural selection rather than bacteria intentionally adapting.
Random mutations may produce antibiotic-resistant bacteria within a population. When antibiotics are applied, susceptible bacteria are less likely to survive, while resistant bacteria are more likely to survive and reproduce. Over generations, the frequency of resistance alleles increases. The antibiotic selects for existing variation rather than causing bacteria to intentionally develop resistance.
Compare active immunity and passive immunity, including how each is acquired and the duration of protection.
Active immunity develops when an individual's immune system produces its own antibodies and memory cells following exposure to an antigen, such as through infection or vaccination. It generally produces longer-lasting protection because memory cells remain. Passive immunity occurs when antibodies are transferred to an individual from another source, such as through the placenta, breast milk or an antibody treatment. It provides immediate but temporary protection because the recipient does not produce their own memory cells.
An individual experiences hearing loss after prolonged exposure to loud music. Medical examination shows that the structures responsible for transmitting sound through the outer and middle ear are functioning normally, but the sensory cells within the cochlea are damaged.
Identify the type of hearing loss experienced and what type of hearing aid to use
A: Type: Sensorineural hearing loss Technology: Cochlear implant Why: It bypasses damaged cochlear sensory cells and sends electrical signals to the auditory nerve.
Explain how a researcher could improve the reliability of an investigation measuring bacterial growth.
The researcher could increase the number of repeated trials and calculate a mean for each treatment. A larger sample size could also reduce the influence of random variation. Using standardised procedures and calibrated equipment would further improve consistency between measurements.
What is the specific role of DNA ligase in DNA replication?
A) Unwinding the supercoils
B) Adding the initial RNA primer
C) Sealing and joining sugar-phosphate backbones of DNA fragments (like Okazaki fragments)
D) Proofreading the code for mutations
C - Sealing and joining sugar-phosphate backbones of DNA fragments (like Okazaki fragments)
Compare genetic drift and natural selection as mechanisms of evolutionary change.
Both genetic drift and natural selection can change allele frequencies in a population over generations. Natural selection is driven by environmental pressures that result in differential survival and reproduction based on heritable traits. Genetic drift is a random change in allele frequencies, particularly significant in small populations, and does not necessarily favour advantageous traits. Genetic drift can reduce genetic variation, whereas natural selection may increase the frequency of alleles that improve survival or reproductive success.
Analyse how the misuse of antibiotics contributes to antimicrobial resistance and explain strategies that can reduce its development.
Random mutations or the acquisition of resistance genes can produce bacteria with reduced susceptibility to an antibiotic. When antibiotics are used, susceptible bacteria are killed or inhibited, while resistant bacteria survive and reproduce. This creates a selective pressure that increases the frequency of resistance within the population. Misuse, such as unnecessary prescriptions, incorrect dosing or failure to follow medical instructions, can increase opportunities for resistant bacteria to persist and spread. Strategies to reduce resistance include using antibiotics only when appropriate, following prescribed directions, improving infection prevention, developing surveillance programs and researching new antimicrobial treatments.
Why is there contercourrent in kidney dialysis, and what type of transport does it use?
Countercurrent flow maintains a concentration gradient between the blood and dialysis fluid along the length of the dialysis membrane. This allows urea and other wastes to continuously move from a higher concentration in the blood to a lower concentration in the dialysis fluid by diffusion, which is a form of passive transport.
A study reports a strong positive correlation between daily sunlight exposure and plant growth.
Analyse why this correlation alone cannot establish that sunlight causes increased plant growth.
Correlation demonstrates an association between two variables but does not establish causation. Other variables, such as water availability, temperature, soil nutrients or plant species, may influence plant growth. These could act as confounding variables. A controlled experiment in which sunlight exposure is manipulated while other relevant variables are controlled would provide stronger evidence for a causal relationship.
A mutation occurs in the DNA template strand of a gene. The mutation changes one DNA base, resulting in a different mRNA codon. However, the final polypeptide produced is unchanged.
Explain how this can occur, and describe the processes involved from the DNA sequence to the production of the polypeptide.
A different mRNA codon may still code for the same amino acid because the genetic code is degenerate, meaning multiple codons can specify the same amino acid. Therefore, the mutation is a silent mutation.
Transcription: RNA polymerase uses the DNA template strand to synthesise a complementary mRNA strand.
Codon change: The DNA base substitution changes one mRNA codon.
Translation: The mRNA attaches to a ribosome, which reads the codons. tRNA molecules with complementary anticodons deliver amino acids.
Unchanged polypeptide: Because the altered codon still codes for the same amino acid, the amino acid sequence—and therefore the resulting polypeptide—is unchanged.
Compare the roles of natural selection, genetic drift and gene flow in changing allele frequencies within populations.
Natural selection changes allele frequencies when environmental pressures cause individuals with advantageous heritable traits to have greater reproductive success. Genetic drift changes allele frequencies randomly, particularly in small populations, and can result in the loss or fixation of alleles. Gene flow occurs when individuals or gametes move between populations, introducing or removing alleles. Therefore, all three mechanisms can alter the genetic composition of populations, but natural selection is non-random, genetic drift is random, and gene flow results from migration or movement between populations.
Explain how antigenic variation in pathogens can reduce the effectiveness of existing immune responses.
Antigenic variation involves changes to the antigens on a pathogen's surface. These changes may prevent existing antibodies and memory cells from recognising the pathogen as effectively, allowing it to evade the immune response. Consequently, an individual may be susceptible to reinfection, and vaccines may need to be updated to target new variants.
A study investigated the relationship between exposure to a particular environmental pollutant and the incidence of a non-infectious disease. The incidence was higher in the exposed population.
Explain why the results of this study alone cannot establish that the pollutant causes the disease.
The study shows an association between pollutant exposure and increased disease incidence, but this does not establish causation. Other variables, such as lifestyle, genetics, or other environmental exposures, may differ between the populations. Therefore, without controlling these variables and establishing a suitable experimental design, the pollutant cannot be identified as the direct cause.
A researcher reports that a treatment increases the mean growth rate by 15%, but the error bars for the treatment and control groups overlap substantially.
Explain what this means for the researcher's conclusion.
although the treatment group has a higher mean, the substantial overlap in error bars indicates considerable variation in the results. The difference between the groups may therefore not be statistically significant. The researcher should use an appropriate statistical test before concluding that the treatment genuinely caused an increase in growth rate.