Biology 30

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Predator–Prey Dynamics in a Protected Valley

Biologists monitored a wolf population and its primary prey, elk, in a protected mountain valley with an area of 1 200 km². Wolves in this valley feed mainly on elk, and the two populations have historically shown linked rises and falls.

1. (2 marks) Calculate the density of the wolf population in 2021 and in 2022. Show your work.
2. (1 mark) Calculate the per capita growth rate of the wolf population from 2021 to 2022. Show your work.
3. (1 mark) Identify one likely cause of the change in the wolf population between 2022 and 2023, using the data provided.
4. (2 marks) During the study, several young male wolves left the valley and joined packs roughly 400 km away. Explain how this emigration affects the gene pools of the packs those wolves joined.
5. (2 marks) Classify the wolf as an r-selected or K-selected species. Support your classification with two life-history characteristics typical of wolves.
6. (2 marks) Wolf litter size can be estimated by counting placental scars in the uterus of deceased females. Explain one reason this method may overestimate and one reason it may underestimate the number of surviving offspring.
7. (2 marks) Describe one technology that ecologists could use to track the movement of living wolves, and state one type of data it provides.

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A Case Study in Nerve Conduction

A 28-year-old patient reports tingling in her hands and delayed responses when touching hot objects. Nerve-conduction tests show that impulses along some of her myelinated neurons travel at 25 m/s instead of the expected 100 m/s. Her physician suspects a disorder in which the immune system slowly destroys the myelin sheath of neurons.

1. (3 marks) Trace the pathway of a withdrawal reflex, naming the three types of neurons involved in order and stating the location of each.
2. (2 marks) Explain how the myelin sheath and the nodes of Ranvier normally produce fast impulse conduction.
3. (1 mark) Using the data provided, explain why the patient's response to touching hot objects is delayed.
4. (2 marks) Describe the sequence of events that occurs at a chemical synapse, from the arrival of an action potential to the response of the postsynaptic membrane.
5. (2 marks) Some medications for this disorder block the reuptake of neurotransmitters. Predict the effect of such a medication on transmission across a synapse, and justify your prediction.

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Homeostasis During Endurance Exercise

A researcher measured the blood glucose concentration of a marathon runner before, during, and after a race.

1. (2 marks) Name the hormone released in response to the glucose level measured 1 h before the race, identify the gland that secretes it, and state its effect on liver cells.
2. (2 marks) Name the hormone primarily responsible for maintaining blood glucose during the race, and describe how it acts on stored glycogen.
3. (2 marks) Explain why blood glucose regulation is described as a negative feedback system. Use the data in your answer.
4. (2 marks) A person with untreated Type 1 diabetes runs the same race. Predict how their blood glucose curve would differ, and explain why.
5. (2 marks) During the race, the runner's body also releases cortisol. Identify the gland that secretes cortisol and describe one way cortisol supports prolonged exercise.

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Investigating Infertility

A couple visits a fertility clinic. Blood tests show that the woman has unusually low levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). As part of treatment, she receives injections of a drug that mimics gonadotropin-releasing hormone (GnRH), followed by timed injections of LH.

1. (2 marks) Identify the gland that normally secretes LH and FSH, and name the structure that regulates that gland using GnRH.
2. (2 marks) Describe the role of FSH and the role of LH in the ovarian cycle.
3. (2 marks) Explain why the timed LH injection is essential for ovulation to occur in this patient.
4. (2 marks) After ovulation, the follicle becomes the corpus luteum. Name the main hormone secreted by the corpus luteum and describe its role in early pregnancy.
5. (1 mark) Identify the hormone detected by over-the-counter pregnancy tests.
6. (2 marks) In males, LH and FSH are also secreted. State the target cells of LH in the testes and the hormone those cells produce.

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Two Traits, Two Patterns of Inheritance

In domestic cats, short hair (H) is dominant over long hair (h), and this gene is autosomal. A separate gene for orange versus black coat pigment is located on the X chromosome: X^O produces orange and X^B produces black; heterozygous females (X^OX^B) are tortoiseshell.

A short-haired tortoiseshell female whose father was long-haired is crossed with a long-haired black male.

1. (2 marks) Determine the complete genotype of the female parent for both genes. Explain how you used the information about her father.
2. (3 marks) Draw a Punnett square (or clearly organized equivalent) for the hair-length gene in this cross, and state the expected phenotype ratio of the offspring.
3. (3 marks) For the coat-colour gene, determine all possible offspring genotypes and phenotypes, separating male and female kittens.
4. (1 mark) Explain why male kittens cannot be tortoiseshell under normal circumstances.
5. (1 mark) A rare tortoiseshell male kitten is born in another litter. Identify the chromosomal abnormality that could account for this, and name the process during meiosis that produces it.
6. (2 marks) Calculate the probability that a kitten chosen at random from the original cross is a short-haired orange male. Show your work.

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Analyzing a Genetic Disorder at the Molecular Level

Cystic fibrosis is caused by mutations in the CFTR gene, which codes for a chloride-transport protein. A common mutation deletes three consecutive DNA nucleotides, removing one amino acid from the protein. A rarer mutation inserts a single nucleotide early in the coding sequence.

A short section of the template strand of the normal gene reads:

3′ – TAC AAA GGC TTT ACT – 5′

1. (2 marks) Write the mRNA sequence transcribed from this template strand, labelling its 5′ and 3′ ends.
2. (2 marks) Describe the roles of mRNA, tRNA, and ribosomes in translation.
3. (2 marks) Explain why the three-nucleotide deletion changes the protein less drastically than the single-nucleotide insertion, even though the insertion is smaller.
4. (2 marks) The mutated chloride-transport protein misfolds and is destroyed by the cell. Relate this outcome to the relationship between amino acid sequence and protein function.
5. (2 marks) Cystic fibrosis is autosomal recessive. Two unaffected parents have a child with cystic fibrosis. Determine the genotypes of both parents and the probability that their next child will be an unaffected carrier. Show your work.

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Allele Frequencies in an Isolated Herd

In a fenced conservation herd of 400 bison, a recessive allele (a) causes a harmless white patch of fur on the shoulder. A survey finds 16 bison with the white patch. Assume the herd is in Hardy–Weinberg equilibrium for this gene.

1. (1 mark) Calculate the frequency of the recessive phenotype in the herd.
2. (2 marks) Calculate the frequencies of the recessive allele (q) and the dominant allele (p). Show your work.
3. (2 marks) Calculate the expected number of heterozygous bison in the herd. Show your work.
4. (2 marks) State two conditions that must hold for a population to remain in Hardy–Weinberg equilibrium.
5. (2 marks) Managers plan to introduce 40 bison from a different herd in which the recessive allele is absent. Predict the effect on the frequency of the white-patch phenotype in future generations, and name this evolutionary mechanism.
6. (1 mark) Explain why a very small isolated herd might show allele-frequency changes even without selection or migration.

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Recovery of a Burned Forest

A lightning-caused fire burns a large stand of lodgepole pine forest. Lodgepole pine cones are sealed with resin and release seeds only after intense heat. Ecologists surveyed the burned area over the following decades.

1. (1 mark) Identify the type of succession occurring in the burned area, and justify your choice.
2. (2 marks) Explain how the sealed cones of lodgepole pine are an adaptation to fire, and state the advantage this gives lodgepole pine over competing tree species after a burn.
3. (2 marks) Describe the trend in bird species richness shown in the table, and explain one reason for this trend.
4. (2 marks) Distinguish between the habitat and the niche of a fireweed plant growing in the burned area.
5. (1 mark) Snowshoe hares moving into the regrowing forest are eaten by lynx. Identify the symbiotic or trophic relationship between hare and lynx.
6. (2 marks) Fire suppression policies prevented burns in this region for decades. Using your understanding of community dynamics, evaluate one ecological consequence of long-term fire suppression.