Water
- Created by: Lotto65
- Created on: 08-10-16 16:25
What is the polarity of a molecule?
When one part of the molecule has a slight positive charge and the other has a slight negative charge
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What causes polarity?
When electrons are not shared equally in covalent bonds because the nucleus of one atom is more attractive to electrons than the other
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How is water polar?
The oxygen atom is more attractive to electrons than the hydrogen atoms so the hydrogen pole has a slight positive charge and the oxygen pole has a slight negative charge
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What is a hydrogen bond?
When an intermolecular bond forms between the negative pole of one water molecule and the positive pole of another
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What is the main reason why water is useful in living organisms?
Hydrogen bonds
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What does it mean by cohesive forces?
Water molecules cohere (stick) to each other due to hydrogen bonds between them
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How are cohesive forces useful in living organisms?
In xylem vessels, pulling forces between water molecules allow water to be sucked up to the top of tall trees for photosynthesis
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What are adhesive forces?
The dipolarity of water molecules makes other polar, hydrophilic substances attractive so water sticks to surfaces
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How do adhesive forces help in living organisms?
Adhesive forces between water in the xylem and the cellulose in cell walls means water is drawn out of xylem vessels into cell walls to keep them moist and as a good gas exchange surface
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What are the thermal properties of water?
High melting point, boiling point, specific heat capacity and latent heat of vaporisation
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How do water's thermal properties help inside living organisms?
Lots of energy is needed to break the strong hydrogen bonds between water molecules. Energy is taken in to make a hydrogen bond break (evaporation). Heat from the body is taken in to evaporate sweat so it acts as a good coolant
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Why does water make a stable habitat?
It has a high specific heat capacity so temperatures changes are slow
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Name one other property of water due to hydrogen bonds
Good solvent
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Why is water being a good solvent useful to living organisms?
Chemical reactions take place because mainly when substances are dissolved in water. So water is a medium for metabolic reactions
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What is a condensation reaction?
When two molecules join together to form a larger molecule and a water molecule
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What is the name given to a pair of monomers bonded together?
Dimer
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What is a chain of monomers called?
A polymer
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Give two examples of condensation reactions
Two amino acids are bonded together to form a dipeptide by a condensation reaction. Then, amino acids can be joined to either end of the dipeptide to form a chain of amino acids called a polypeptide.
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What is the name of the bonds formed that join amino acids together?
Peptide bonds
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How are carbohydrates formed by condensation reactions?
A monosaccharide bonds with another monosaccharide to form a disaccharide and a molecule of water. Disaccharides can bonded to more monosaccharides to form a polysaccharide
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How are fats made by condensation reactions?
Fatty acids can be bonded to a molecule of glycerol (triglyceride) by a condensation reaction to form glycerides. A maximum of three fatty acids can be bonded to one glycerol molecule to produce three water molecules
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What happens in a hydrolysis reaction?
A large molecule is broken down into smaller molecules using water. The water is split into H and OH groups which are used to make new bonds when a bond in the polymer has broken
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Give a general example of when hydrolysis reactions occur?
To digest food
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Polypeptides + water -->
Amino acids or dipeptides
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Polysaccharides + water -->
Monosaccharides or disaccharides
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Glycerides + water -->
Fatty acids AND glycerol
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Is it proven that hydrogen bonds exist?
No because we can't see them
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How can you use a scientific theory that is not proven?
If it has not been falsified, if it helps predict behaviour, if it explains a natural phenomena
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Why does water having a high boiling point help in living organisms?
Water is a liquid over a broad range of temperatures so creates a stable environment
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How does dissolving actually work?
Water forms shells around polar substances to stop them clumping together and keeping them in a solution. The negative oxygen pole is attracted to positive charges and the positive hydrogen pole is attracted to negative charges.
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How is methane produced?
Waste product of anaerobic respiration
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What part of the brain controls sweat secretion?
Hypothalamus
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How do dogs and birds cool down?
Panting
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How do plants cool down?
Transpiration
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As the temperature of water increases...
The solubility of oxygen decreases
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What allows a tiny amount of oxygen to dissolve in water?
Small molecules
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How do cohesive forces help as a living environment for organisms?
Surface tension for water boatmen and pond skaters; Support in the water means aquatic animals require less of a skeletal structure
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How is the transparency of water helpful in and out living organisms?
Organisms can see food through it; Light can travel through it into chloroplasts for photosynthesis
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How does the idea of water being densest as 4 degrees and freezing from the surface help outside living organisms?
Allows nutrient cycling in aquatic ecosystems; frogs can hibernate at the bottom of ponds and not freeze
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How does the size of water molecules help?
Small molecules - more in a certain volume so more collisions, increase in reaction rate so efficient medium for reactions
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How does neutral pH help?
Keeps immune system in optimum condition - otherwise antibodies would denature
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Why does low and constant viscosity help?
Efficient transport medium because does not change state - substances stay dissolved
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How does water being virtually incompressible help?
Due to strong hydrogen bonds means cells stay supported and are harder to burst so protects them
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