BM: Water Flashcards
What is a metabolic reaction?
A chemical reaction that happens in a living organism to sustain life.
What is a metabolite?
A substance involved in a metabolic reaction.
What percentage of a cell’s contents is water?
Around 80%
Describe the structure of water:
What does this mean about its polarity?
- One atom of oxygen covalently joined to two hydrogen atoms - bent molecule.
- Because shared negative electrons are pulled towards oxygen atom, the other side of each hydrogen atom is left with a slight positive charge.
- Unshared electrons on other side of oxygen atom give it a slight positive charge.
- This makes water a polar molecule.
- Has a partial negative charge on one side and a partial positive charge on the other.
Explain hydrogen bonding:
- Slighlty negatively-charged oxygen atoms attract the slightly positively-charged hydrogen atoms of other water molecules.
- This is hydrogen bonding, and it gives water useful properties.
Explain 5 useful properties of water:
- Important metabolite.
- High latent heat of vaporisation.
- High specific heat capacity, so is a temperature buffer.
- Good solvent.
- Strong cohesion between molecules.
Explain why water is a good metabolite:
- Many metabolic reactions involve condensation or hydrolysis.
- Hydrolysis requires water to break bonds, and a water molecule is released when bonds form in condensation reactions.
- Chemical reactions take place in aqueous mediums.
- Water is also needed for photosynthesis.
Why is it useful that water has a high latent heat of vaporisation?
- It takes lots of energy to break the hydrogen bonds between water molecules.
- So water has a high latent heat of vaporisation - a lot of energy is used up when it evaporates.
- Useful for living organisms as it means they can use water loss through evaporation to cool down without losing too much water (eg sweating in humans).
Why is it useful that water can buffer changes in temperature?
How does it do this?
- Hydrogen bonds between water molecules can absorb a lot of energy.
- So water has a high specific heat capacity.
- This is useful for living organisms as it means water doesn’t experience rapid temperature changes.
- So water is a good habitat as the temperature under water is likely to be more stable than on land.
- Also, water inside organisms remains at a fairly stable temperature - helping them to mainitan a constant internal body temperature.
What is specific latent heat of vaporisation?
The amount of energy required to change the state of 1kg of that material into a gas.
What is specific heat capacity?
A measure of the energy required to raise the temperature of 1 kg of material by 1°C.
Why is water a good solvent?
- Important substances in metabolic reactions are ionic.
- Water is polar, so the positive end of a water molecule will be attracted to the negative ion and the negative end of the water molecule will be attracted tot he positive ion.
- So, the ions become totally surrounded by water molecules - they’ll dissolve.
Give examples of the types of substances water dissolves:
- Gases like oxygen and carbon dioxide.
- Wastes like amonia or urea.
- Inorganic ions or small hydrophilic molecules, like amino acids, monosaccharides or ATP.
- Enzymes, whose reactions take place within solutions.
Draw a positive and negative ion dissolved in water:
Why is it useful that water molecules are very cohesive?
- Cohesion helps water to flow, so it is great for transporting substances.
- Eg, traveling in columns up the xylem in plants.
- Strong cohesion leads to high surface tension when it comes into contact with air.
- So sweat forms droplets, which evaporate from the skin to cool an organism down.
- Pond skaters and other insects can also ‘walk’ on the surface of a pond.
