Biology Topic 1

Alevel Edexcel B

Name 4 important anions

Nitrate, phosphate, chloride, hydrogen carbonate

Name 4 important cations

Sodium, calcium, hydrogen, magnesium

What is the importance of nitrate ions in living cells?

DNA and amino acids formation

What is the importance of phosphate ions in living cells?

ATP, ADP, DNA, RNA formation

What is the importance of chloride ions in living cells?

Needed in nerve impulses and secretory systems. Used in loop of Henle

What is the importance of hydrogen carbonate ions for living cells?

Buffer to prevent acidic blood

What is the importance of sodium ions on living cells?

Nerve impulses (generate action potential) and secretory systems. Used in loop of Henle

What is the importance of calcium ions for living cells?

Needed for calcium pectate in middle lamellae between 2 cell walls in plants. Also needed for bone formation and muscle contraction. Also used in synapses

What is the importance of hydrogen ions for living cells?

Needed in cellular respiration and photosynthesis, and in numerous pumps and systems. Also needed for pH balance

What is the importance of magnesium ions for living cells?

Needed for chlorophyll production

Relate the structure of water molecules to their properties and functions.

Water is made up of two hydrogen atoms covalently bonded to one oxygen.

The oxygen is slightly negative, and the hydrogens slightly positive, making water a dipole

This means that water molecules experience hydrogen bonding between their negative oxygens and their positive hydrogens, allowing water molecules to stick together in cohesion

Cohesion is strong due to large number of these hydrogen bonds, making it even stronger than adhesion to other molecules

This allows capillary action in xylem and other small tubes

It also allows surface tension, as downwards force towards other molecules is stronger than outward force to air

The large number of hydrogen bonds also means the water has a high specific heat capacity and latent heat of vaporisation.

This makes water a good habitat for aquatic animals as temperature changes are minimal

High latent heat means that water is a liquid at large range of temperatures, meaning it can’t be compressed at many temperatures, making it useful for hydraulic action in animals and plants

The polar nature of water make sit a polar solvent, meaning any polar molecules like ions, and some covalently bonded compounds can dissolve.

This is useful for transport in blood plasma and dissolved oxygen in ponds allows respiration in aquatic creatures

An additional property of water is that it has its maximum density at 4degrees, meaning ice floats, providing a habitat for many animals, and insulating the water below