IBDP Biology HL Paper 1B- Data-Based Question- New Syllabus

In winter when temperatures drop, brown bears (Ursus arctos) enter a cave and hibernate. The graph shows the mean values for the body temperature, heart rate, and activity of 14 brown bears throughout the year. The grey shaded areas indicate the periods when the bears are in transition between hibernation and normal activity.

(a) Estimate the difference between the highest and lowest mean body temperatures.

(b) Compare and contrast the changes in mean ambient and body temperatures during 2012.

(c) Explain the change in heart rate during the period of hibernation.

It was observed that during hibernation, bears are not susceptible to osteoporosis, a condition characterized by a decrease in bone density, resulting in porous and fragile bones. This condition may develop in humans during long periods of inactivity and with increasing age. The graph shows the porosity of the tibia bones of black bears (Ursus americanus) and humans at different ages. Age is expressed as the proportion of normal lifespan.

(d) Distinguish between the changes in porosity of the bones in humans and bears as age increases.

(e) The life expectancy of a human at the time of the study was 80 years. Estimate the porosity of the bones of an individual who was approximately 32 years old.

(f) The researchers assessed age as a proportion of normal lifespan, rather than in years. Suggest one reason for this.

Healthy bone is constantly being broken down (bone resorption) and rebuilt (bone formation). To test whether these processes occurred during hibernation in black bears, blood serum was tested for the markers ICTP (indicating bone resorption) and PICP (indicating bone formation).

(g) Describe what is happening to the bone during hibernation.

(h) Suggest how the graph would differ for a human during a long period of inactivity.

Osteocalcin is a peptide hormone that causes calcium to bind in the bones, playing a role in bone formation and regeneration. Research shows changes in the mean concentration of osteocalcin in blood serum before and after hibernation in bears. The bar chart and graph below show the concentrations of osteocalcin and parathyroid hormone in bear blood serum.

(i) Calculate the percentage increase in the mean concentration of osteocalcin from pre-hibernation to hibernation.

(j) A hypothesis has been proposed that an increase in parathyroid hormone concentration causes an increase in osteocalcin in bears. Evaluate the evidence for this hypothesis provided by the data.

(k) Discuss how helpful these studies of bears can be in developing an understanding of osteoporosis in humans.