A1.1 Water Flashcards
What is the most widely supported hypothesis for the origin of water on earth?
Researchers theorize that most or all of earth’s water came from asteroids (by analyzing their composition).
What evidence supports the hypothesis that most of earth’s water’s origins?
The ratio of hydrogen isotopes in the water of two 4.5-billion-year-old meteorites matches the ratio of hydrogen isotopes in the Earth’s oceans (implying they have the same origin).
How was the water retained on the Earth’s surface?
The temperatures were cool enough to allow water vapor to condense into liquid water & gravity enabled the water to be retained.
Why are water molecules considered polar molecules?
In water, the highly electronegative oxygen pulls the electrons in the covalent bond towards it, making the hydrogen atoms slightly positive, and the oxygen atom slightly negative.
Define cohesion.
Cohesion is the attraction between one water molecule and another water molecule due to their hydrogen bonds/electrostatic force.
What are the important properties of water that can arise from this?
- Cohesion
- Adhesion
- Solvation
Give an example of a benefit of the cohesive properties of water to a plant.
Ex. It allows for transpiration
- As water molecules evaporate from the leaves of plants, they are replaced by water from the xylem.
- As water molecules move from the xylem into the leaf, tension pulls water upwards to replace it.
- The continuous water column is maintained by cohesion between the water molecules as they ‘pull’ on one another.
- This is important for evaporative cooling and the transportation of minerals & nutrients
Give an example of a benefit of the cohesive properties of water to an animal.
Ex. Allows animals to use surface tension
- Because water molecules on the surface have no molecules to form hydrogen bonds with above them, they form stronger bonds with other surface molecules.
- This makes them resistant to being moved/separated, creating surface tension
- The surface tension of water allows insects such as water striders (Gerris lacustris) to live on the surface of ponds
Define adhesion.
Adhesion is the attraction between water molecules and surrounding materials or surfaces due to electrostatic attraction.
What kinds of materials can water to adhere to?
Polar or charged materials are attracted to water and are called hydrophilic (water-loving)
Define capillary action.
The ability of a liquid to flow in narrow spaces or tubes against the force of gravity. This phenomenon occurs due to a combination of cohesive forces between liquid molecules and adhesive forces between the liquid and the surface of the container or tube.
Explain how adhesion & capillary action is beneficial to organisms living in soil.
- A lot of water is stored in the form of groundwater/ underground sources
- As water adheres to charged particles in the soil, capillary action occurs drawing moisture above the water line.
- This allows the water to be taken in by plants and other organisms in the soil close to the surface.
- As water is absorbed by roots, it is replaced with more water by capillary action, providing a consistent water source.
Explain how adhesion & capillary action is beneficial for plants.
- The cell walls of plants are made from a fibrous material called cellulose which is hydrophilic.
- As water adheres to cell walls, it is drawn by capillary action from nearby xylem vessels, keeping water flowing through plant tissue.
- This allows for water to be supplied to the entire plant and also carry nutrients from the soil upwards.
What is a solvent?
A solvent is a liquid which can dissolve another and create a solution.
What kinds of particles can water dissolve?
Water is a good solvent for:
- Polar molecules eg. sugars, amino acids
- Charged particles eg. ions: Na+, Cl- etc.
Why do enzymes work best in aqueous solutions?
Both enzymes and their substrates need to be able to move around in order to collide with each other. They can do this more easily when dissolved in water.
How does water dissolve other materials?
- The slightly negative oxygen atom of water is attracted to positive (or δ+) particles and the slightly positive hydrogen atoms are attracted to negative (or δ-) particles.
- The water molecule can then separate these particles through their attraction
- Water particles then orientate themselves around dissolved particles forming a hydration shell which prevents the dissolved particles coming out of solution.
Give two examples of how water being the ‘universal solvent’ is a benefit to life.
Ex. Metabolic Reactions
Many biochemical reactions occur in aqueous solutions. Water is able to dissolve a wide variety of substances and when dissolved, the solutes are free to move around and collide with each other, allowing essential reactions to take place.
Ex. Transport Medium
Water’s solvent properties enable it to transport a wide variety of nutrients, gases, and waste products within organisms, for example in blood plasma & xylem/phloem
The functions of some molecules in cells depend on them being hydrophobic and insoluble. Explain how this helps in the formation of cell membranes.
Cell membranes are made of phospholipids which have a hydrophilic head and a hydrophobic tail.
This enables these molecules to orient themselves to form a stable phospholipid bilayer with the heads on the outside (in contact with water) and the tails on the inside (away from water).
