IB DP Biology- D3.3 Homeostasis- IB Style Questions For HL Paper 2 -FA 2025

(a)
Cohesion—the attraction between water molecules due to hydrogen bonding—benefits organisms in several ways:
• Transport in plants: It enables water to move upward as an unbroken column through the xylem during transpiration.
• Surface tension: Water’s high surface tension allows certain insects, such as water striders, to remain on the surface, providing a habitat.
• Temperature stability: Cohesion contributes to water’s high specific heat capacity, helping aquatic ecosystems maintain stable temperatures.

(b)
• Ice melt: The reduction of sea ice removes critical habitat for polar animals like walruses and polar bears, affecting feeding and breeding behaviour.
• Ocean current disruption: Warmer water can reduce nutrient upwelling, limiting access to nutrient-rich deep water. This lowers phytoplankton productivity, which affects the entire marine food web.

(c)
Osmoregulation operates through a negative feedback mechanism to maintain blood solute concentration:
1. Detection: Osmoreceptors in the hypothalamus sense when blood becomes too concentrated (hypertonic).
2. Hormonal action: The pituitary gland releases ADH (antidiuretic hormone).
3. Kidney response: ADH increases water permeability in the collecting ducts by promoting insertion of aquaporins.
4. Effect: More water is reabsorbed into the bloodstream, producing a smaller volume of concentrated urine and lowering blood solute levels.
5. Feedback: When hydration improves, ADH secretion decreases, and the collecting ducts become less permeable to water, returning the system to baseline.