Water + Inorganic Ions

• Inorganic ions occur in solution in the cytoplasm of cells and in bodily fluids.
• Inorganic ions are ions derived from non-living sources.
• Examples of inorganic ions include phosphate, sodium, chloride and potassium ions.
• Properties of Water:

  • latent heat of evaporation
  • metabolite
  • cohesion and adhesion
  • specific heat capacity
  • surface tension
  • compressibility
  • colour transmission of light
• The latent heat of evaporation of water means that when water changes state it will either take in or expel energy without a temperature change. Water is polar so many hydrogen bonds form between the molecules, which can absorb a lot of energy before breaking.

  This is important because when water evaporates a large amount of heat energy is used to break the hydrogen bonds. This means that the evaporation of a small amount of water (e.g. sweat) is an efficient cooling mechanism, helping organisms to maintain a constant body temperature.
• Water is a metabolite which means it is highly reactive. For example, condensation and hydrolysis reactions are used to make/break bonds and either expel or use up a water molecule to do this.

  This is important because it allows water to act as a transport medium for many substances that dissolve in it as it is a fluid at the temperatures at which living organisms are active (e.g. substances in the blood or in the sap of plants). Water also acts as a medium for metabolic reactions.
• Water allows for cohesion and adhesion because it is polar and its hydrogen bonds stick its molecules together to form a continuous column (cohesion). Water molecules also stick to other molecules e.g. lignin in the xylem vessels (adhesion).

  This is important because adhesion means a column of water doesn't break when pulled up a narrow tube (e.g. the xylem) and the surface tension created by cohesion allows for invertebrates such as pond skaters to walk on water (providing their habitat).
• The specific heat capacity of water is the heat energy needed to raise the temperature of 1kg of it by 1°C. The hydrogen bonds that form between water molecules can absorb a lot of heat energy before the water's temperature changes.

  This is important because water is a good habitat for aquatic organisms due to its stable temperature. Organisms also consist mostly of water and so water's SHC helps to maintain a constant body temperature.
• The surface tension of water can behave like an elastic sheet. The molecules at the surface are unaffected by the molecules above them, and therefore 'pull' together more strongly, effectively resembling a stretched membrane.

  This is important because surface tension is directly responsible for the formation of liquid droplets. It also allows for small invertebrates to walk on the water surface, as well as capillary action within xylem vessels. Without this property, water would be a slimy substance and cells would not have shape.
• The compressibility of water means that water isn't easily squashed, so it provides support to organisms (e.g. turgor pressure in plant cells).

  This is important because the density of liquid water would not remain constant if it was compressible. Water at the seafloor would pressured and compressed into ice if it could not maintain a constant density.
• The colour transmission of light refers to the transparency of water, which means it allows light to pass through.

  This is important because it means sunlight can reach and pass through cells (e.g. during photosynthesis).
• Water molecules have dipoles - they have a small negative charge on some parts of the molecule and a small positive charge on others.
• Water molecules are attracted to each other because of the dipole charges. The weak attractions are called hydrogen bonds.
• Hydrogen bonding causes water to have a high specific heat capacity, buffering temperature changes.
• Water has a high latent heat of vaporisation/evaporation, which provides a cooling effect when it evaporates.
• Water is an excellent solvent, in which metabolic reactions can take place and substances can be transported.
• Cohesion between water molecules enables tall columns of water to be supported in the xylem vessels of plants.
• Water is a metabolite in many metabolic reactions.
• The way in which water molecules 'stick' together is called cohesion.
• Normally, a water molecule is attracted to other water molecules on all of its sides. But at the surface of a body of water, the top layer of water molecules does not have any water molecules above them, so the net attraction is downwards. This produces surface tension.
• Surface tension makes water behave as though there is a thin 'skin' where it meets air.
• Surface tension allows small animals to walk on the water surface, e.g. pond skaters.
• The metabolic reactions that take place in the body only take place because the reactants are dissolved in water (the ions are free to move around).
• The energy that is lost from the liquid water as it evaporates is called the latent heat of vaporisation (or evaporation).
• Water has a relatively high latent heat of vaporisation, so the evaporation of small quantities of water has a large cooling effect.
• Water has a high specific heat capacity because a lot of heat energy has to be transferred to the water to raise its temperature by 1°C.
• Water's high specific heat capacity is very useful to living organisms.

  Because our bodies are mostly made up of water, we have a relatively high heat capacity. The water in and around our cells absorbs a lot of heat energy without its temperature rising very much.

  The water 'buffers' (tones down) heat changes.
• Water's high specific heat capacity is very useful for aquatic organisms.

  Large bodies of water do not change temperature as quickly or as greatly as the air.

  So, aquatic organisms live in an environment where temperature changes are much smaller and happen much more gradually.
• Ice floats because hydrogen bonding spaces the molecules farther apart, creating a less dense structure.
• Basilisk lizards are able to run across the surface of water. Which property of water allows the lizards to do this?

  High surface tension
• Which ion is denoted by the formula in the image?

  Phosphate

  
• 𝙋𝙃𝙊𝙎𝙋𝙃𝘼𝙏𝙀 𝙄𝙊𝙉𝙎:

  • found in ATP (adenosine 𝘵𝘳𝘪𝘱𝘩𝘰𝘴𝘱𝘩𝘢𝘵𝘦 - three phosphate ions in the chain)
  • found in DNA (phosphate group in nucleotides)
  • found in RNA (phosphate group in nucleotides)
• Ice (solid water) floats because it has a lower density than liquid water. This is because its hydrogen bonds space the molecules farther apart.
• Water is a biological molecule consisting of an oxygen atom bonded via a hydrogen bond to two hydrogen atoms in an electrostatic attraction.
• The ability of water to easily form hydrogen bonds to other water molecules due to the polarity of the molecules is essential as the constant movement of liquid water breaks the hydrogen bonds between molecules. They are also involved in changing states, e.g. solid, liquid, and gas.
• When water freezes its kinetic energy drops and the water molecules move slower, breaking less bonds, until so many hydrogen bonds form that the water molecules are stabilised and become a solid structure of ice. The hydrogen bonds push the water molecules farther away from each other in ice and so the water expands, creating a less dense structure and explaining why ice floats in liquid water.
• When water is heated, the kinetic energy of the molecules increases and they move faster, breaking their bonds and reducing the chance to form more, and as a result the water molecules evaporate to become water vapour.
• A useful real-world application of water expanding when freezing is when the surface layer of water molecules in a lake or pond freeze, an insulating barrier is created which blocks the rest of the body of water from freezing too and protects the plants and animals living underwater. Freezing is dangerous for living beings as cells contain a lot of water, which would expand in cold temperatures and break cell membranes.
• The heat capacity of water is greatly increased by the amount of hydrogen bonds that form between water molecules; these bonds can absorb a large amount of heat energy before they break. This is important because water has the ability to minimise changes in heat. For example, aquatic organisms cannot regulate their body temperatures as effectively as land animals and humans do, instead relying on the stable temperature of the water around them, which hardly changes between day and night.