Water
Guiding Questions
- What physical and chemical properties of water make it essential for life?
- What are the challenges and opportunities of water as a habitat?
SL and HL Content
Learning Objective: A1.1.1 - Water as the medium for life
Water & the Origin of Life
Life on Earth depends on water; no known life can exist without it.
The first cells originated in water, likely in the oceans.
Water shielded early life from harmful ultraviolet radiation.
The Earth initially lacked liquid water due to extreme heat.
As the planet cooled, water formed and the water cycle began.
Oceans provided the solvent necessary for the complex biochemical reactions that support life.
The cell membrane evolved to separate intracellular water (cytoplasm) from ocean water.
Syllabus Link: B2.1 – Membranes & Membrane Transport
Water: The Essential Component of Life
Water is the primary solvent for biological processes.
Water is the main component of living things.
Most cells are approximately 70-80% water.
Water provides the environment in which the biochemical reactions of life can occur.
Water also takes part in and is produced by many reactions.
Water is present in various biological fluids, including:
Cytoplasm (site of cellular reactions)
Organelle fluids (e.g., mitochondria, nucleus)
Tissue fluid (between cells in multicellular organisms)
Blood and lymph (essential for transport and immune responses)
Water is also a habitat for aquatic life - ocean, lakes, and rivers
