state that water is the main component of blood and tissue fluid and relate the properties of water to its role in transport in mammals, limited to solvent action and high specific heat capacity

Published by Patrick Mutisya · 14 days ago

Cambridge A-Level Biology – The Circulatory System

The Circulatory System

Objective

State that water is the main component of blood and tissue fluid and relate the properties of water to its role in transport in mammals, focusing on solvent action and high specific heat capacity.

Key Facts

  • Water constitutes about 90 % of plasma and 70–80 % of the total blood volume.
  • In interstitial (tissue) fluid, water makes up roughly 99 % of the fluid.

Why Water Is Essential for Transport

  1. Solvent Action

    Water’s polarity allows it to dissolve a wide range of substances (ions, gases, nutrients, metabolic wastes). Dissolved substances are carried in the liquid phase of blood and tissue fluid, enabling efficient distribution to cells and removal of waste.

  2. High Specific Heat Capacity

    Water can absorb or release large amounts of heat with only a small change in temperature (\$c_{\text{water}} \approx 4.18\ \text{kJ kg}^{-1}\text{K}^{-1}\$). This property stabilises the internal temperature of mammals, ensuring that enzymatic reactions and transport processes occur under optimal conditions.

Linking Properties to Physiological Functions

Property of WaterPhysiological Role in Transport
Excellent solvent (polar molecule)Facilitates dissolution and carriage of ions (Na⁺, K⁺, Ca²⁺), glucose, amino acids, hormones, and gases (O₂, CO₂) in plasma and interstitial fluid.
High specific heat capacityBuffers temperature fluctuations in blood, maintaining a stable environment for metabolic reactions and preventing denaturation of transport proteins.

Summary

Water’s dominant presence in blood and tissue fluid makes it the primary medium for transport. Its ability to dissolve many substances ensures that nutrients, gases, and wastes can move freely, while its capacity to store heat protects the organism from rapid temperature changes, both of which are vital for the efficient functioning of the mammalian circulatory system.

Suggested diagram: Cross‑section of a mammalian capillary showing plasma, interstitial fluid, and the exchange of dissolved substances.