14_A1.1 WaterHodder 2025 Biology for the IB Diploma Third Edition

Guiding Questions and Diversity
- Common ancestry gives living organisms shared features, while evolution leads to biodiversity of life.
- All living organisms require water to exist.
Role of Water
- Enzymes need water to function as they work in a chemically stable medium.

Physical and Chemical Properties
- What makes water essential for life?
- Challenges and opportunities of water as a habitat.

Subtopics Covered
- A1.1.1: Water as the medium for life
- A1.1.2: Hydrogen bonds from polar covalent bonds in water
- A1.1.3: Cohesion due to hydrogen bonding
- A1.1.4: Adhesion impacts and organisms
- A1.1.5: Solvent properties in metabolism and transport
- A1.1.6: Properties' consequences in aquatic habitats
- A1.1.7: Extraplanetary origin of water on Earth (HL only)
- A1.1.8: Water's presence and search for extraterrestrial life (HL only)

Water Coverage on Earth
- 71% of Earth's surface is water; 97% is oceanic, 3% is freshwater.
- Evidence suggests water has existed for 3.8 billion years.
Origin of Life In Water
- First cells originated in water, with oceans blocking harmful UV radiation.
- Water comprises 65%-95% of mass in most multicellular organisms.
Consequences of Water Properties
- Unique properties allow life at various scales, from bacteria to trees.
- Water is essential for survival; its properties often taken for granted.

Activity
- Group work: Create a poster on threats to freshwater sources and solutions for clean drinking water.

Chemical Bond Definitions
- Covalent Bond: Between atoms sharing pairs of electrons.
- Polar Molecule: Unequal charge distribution in a molecule.
- Hydrogen Bond: Weak attractions between hydrogen (in one molecule) and electronegative atoms (like oxygen) in another.

Water Molecule Description
- Consists of one oxygen and two hydrogen atoms, covalently bonded.
- Polar nature leads to hydrogen bonding, forming a V-shaped molecule.
- Causes water's unique properties due to the charge distribution (net negative on oxygen, net positive on hydrogen).

Hydrogen Bonds
- Responsible for unique water properties.
- Intermolecular forces impact biological systems heavily.
Cohesion and Adhesion
- Cohesion: Attraction between water molecules leads to surface tension.
- Adhesion: Attraction to other polar surfaces allows water to move through substances like xylem in plants.

Transpiration Process
- Water drawn through xylem by evaporative loss from leaves.
- Cohesion allows the water column to remain unbroken despite tension.

Low Viscosity
- Water flows easily due to lower viscosity compared to other liquids.
- The property is crucial for nutrient transport in organisms.
Surface Tension Exploitation
- Allows organisms like the pond skater to move on water surfaces without sinking.

Specific Heat Capacity
- Requires significant energy to change temperature due to hydrogen bonding.
- Coral water helps maintain stable aquatic environments compared to terrestrial temperature fluctuations.

Role in Enzymatic Reactions
- Most enzymes require aqueous environments for effective function.
- Hydrogen bonds aid enzyme-substrate binding relationship during reactions.

Formation Theories
- Origin linked to asteroids and their content of ice and organic material.
- Carbonaceous chondrites may have delivered water to Earth, indicating a potential life-supporting origin.

Definition and Importance
- Goldilocks zone: Regions where conditions are just right for liquid water.
- Essential in the search for life-supporting planets beyond Earth.
Current Investigations
- NASA's quest for water on Mars, using transit spectroscopy for discovery.
- Identifying 'water signatures' in exoplanets to ascertain potential for life.