Cell Respiration: notes and practice questions

Thermoregulation is a key homeostatic process. A study investigated the response of human participants to a cold environment ($10^\circ\text{C}$). Participants were divided into two groups: one group remained at rest, while the other performed moderate exercise on a stationary bicycle. Core body temperature was measured every 15 minutes for two hours.

![Line graph showing core body temperature (°C)

over 120 minutes for two groups: Resting and Exercising. The y-axis is Core Body Temperature (°C) from 36.5 to 37.5. The x-axis is Time (minutes) from 0 to 120. Both groups start at 37.0°C. The Resting line shows a steady decline to about 36.6°C. The Exercising line shows a very slight initial dip, then rises to about 37.2°C and remains stable.](https://jujwjkjdeuwpscvsbilk.supabase.co/storage/v1/object/public/question-images/b242d1e2-5cff-4548-9da6-249648b0b274/1791279084335.png){width="3.6in"}

(a) Describe the trend in core body temperature for the exercising group.

(b) Compare the core body temperature in the resting group with the exercising group over the 120-minute period.

(c) Suggest a reason for the difference in core body temperature observed between the two groups.

(d) The resting group then underwent a 10-week cold acclimatization program, involving regular, controlled exposure to cold. Their core body temperature response to the same cold environment ($10^\circ\text{C}$) at rest was measured again.

![Line graph comparing core body temperature (°C)

over 120 minutes for the same group Pre-acclimatization and Post-acclimatization. The y-axis is Core Body Temperature (°C) from 36.5 to 37.5. The x-axis is Time (minutes) from 0 to 120. Both lines start at 37.0°C. The Pre-acclimatization line shows a steady decline to 36.6°C. The Post-acclimatization line shows a much smaller decline, stabilizing around 36.9°C.](https://jujwjkjdeuwpscvsbilk.supabase.co/storage/v1/object/public/question-images/b242d1e2-5cff-4548-9da6-249648b0b274/1791279066631.png){width="3.6in"}

Distinguish between the results pre- and post-acclimatization.

(e) Suggest why participants were required to rest in a thermoneutral room ($24^\circ\text{C}$) for 30 minutes before each experimental trial.

(f) The study also measured the resting metabolic rate of the participants before and after the acclimatization program.

![Bar chart showing Resting Metabolic Rate (mL O2 kg⁻¹ min⁻¹)

Pre-acclimatization and Post-acclimatization. The y-axis is Resting Metabolic Rate. The Pre-acclimatization bar is lower than the Post-acclimatization bar. Error bars are shown.](https://jujwjkjdeuwpscvsbilk.supabase.co/storage/v1/object/public/question-images/b242d1e2-5cff-4548-9da6-249648b0b274/1791279048041.png){width="3.6in"}

Describe the difference in resting metabolic rate before and after the program.

(g) Suggest how an increased resting metabolic rate might contribute to the improved tolerance to cold shown in part (d).

(h) The hormone thyroxin is involved in regulating metabolic rate. Outline the role of thyroxin in thermoregulation.

The graph shows data-logging of three variables in a coastal rock pool containing the brown alga Fucus vesiculosus over a 48-hour period.

Explain the causes of the rises and falls in the pH of the rock pool water.

(b.i) State the relationship shown in the graph between light intensity and dissolved $\text{CO}_2$ concentration.

(b.ii) State the relationship shown in the graph between temperature and dissolved $\text{CO}_2$ concentration.

(c) From the graph, deduce whether light intensity or temperature has a greater effect on the dissolved $\text{CO}_2$ concentration.

(a) The table shows the areas of different membranes ($\mu\text{m}^2$) in a plasma cell (an antibody-secreting B lymphocyte).

Calculate the volume of the plasma cell, assuming it is cubic.

(b) Explain the difference in area of the inner and outer mitochondrial membranes.

(c) Justify the conclusion that the plasma cell is highly specialized for protein secretion.

(d) Comment on the area of the smooth endoplasmic reticulum in the plasma cell.

(a.i) Ruminococcus albus is a bacterium found in the rumen (first stomach) of cattle. It breaks down cellulose from ingested grass and produces acetate ($\text{CH}_3\text{COO}^-$) as a waste product.

Identify, with a reason, whether R. albus is autotrophic, heterotrophic or mixotrophic.

(a.ii) Identify, with a reason, whether R. albus is holozoic or saprotrophic.

(b) R. albus is difficult to study in standard laboratory conditions because it dies rapidly when exposed to air. Explain two conclusions that can be drawn from this observation.

(c) The epithelial cells of the cow's rumen absorb the acetate produced by the bacteria. Suggest how the cow's cells might use this substance.

(a) The graph shows the results of an experiment in which the oxygen consumption rate of deer mice (Peromyscus maniculatus) was measured at various environmental temperatures from $-5~^\circ\text{C}$ to $35~^\circ\text{C}$. Between $-5~^\circ\text{C}$ and $30~^\circ\text{C}$, the mice maintained a constant core body temperature, but above $30~^\circ\text{C}$ their body temperature increased.

Describe the relationship between environmental temperature and oxygen consumption rate in the deer mice.

(b) Explain the change in oxygen consumption rate as the environmental temperature drops from $20~^\circ\text{C}$ to $-5~^\circ\text{C}$.

(c) Suggest a reason for the change in oxygen consumption rate as environmental temperatures increased from $30~^\circ\text{C}$ to $35~^\circ\text{C}$.

(d) Suggest two reasons for the variation in oxygen consumption rate between individual mice at each environmental temperature.