3.1 Chemical Elements and Water

The most commonly occurring elements in living things

• Oxygen (65%) - used in aerobic respiration and in the air all around us
• Carbon (19%) - found in all living things, essential parts of organic molecules found in the body
• Hydrogen (10%) - ions are used in active transport, photosynthesis and cell respiration
• Nitrogen (3%) - building blocks for amino acid in the production of proteins, found in chlorophyll

Other Important Elements and Their Uses:

• Calcium (1.5%) - most common element of the body, 99% of body's calcium is in bonds, 1% in blood and tissues, maintains muscle and nerve function, used in production of enzymes and digestive hormones
• Phosphorus (1%) - Major component of bones, found in phospholipids in cell membrane, energy such as ATP which has phosphate groups, nucleic acid have phosphate groups  
• Iron (0.7%) - structural parts of hemoglobin and myoglobin (muscles) used to transport oxygen, production of neurotransmitters and collagen, found in proteins
• Sulphur (0.25%) - strengthen skin, hair and nails (fur and feathers in animals), found in amino acids in protein synthesis and enzyme reactions, cellular respiration
• Sodium (0.15%) - regulation of blood volume and pressure, nerve transmission, regulate pH in body 

Water: 

• Habitat for organisms: water's high heat capacity maintains the temperature of the habitat and keeps it from fluctuating
• Fills the spaces between the cells and inside the cells
• High heat capacity (retains a lot of heat, requires lots of energy to raise the temperature of water and a lot of energy to break the hydrogen bonds between molecules) allows for homeostasis of the body's temperature. 
• Acts as a shock absorber for the eyes, spinal cord and the fetus' surrounded by amniotic fluid which is mostly made of water. 
• Two hydrogen and one oxygen covalently bonded, but this forms a polar molecule. Hydrogen bonds can form between water molecules due to the polarity of water. This allows for the cohesion between molecules and for it to adhere to surfaces. 
• Known as the universal solvent. The polarity of water also answers why water is the universal solvent as its polarity will separate molecules into ions. Molecules that dissolve easily are called hydrophilic and they need to be polar. Non-polar molecules, lacking any charge, will repel water as separate entites and are known as hydrophobic substances (water fearing). , forming 60-70% of the body, parts of cytoplasm, blood and tissue fluid
• Medium for Metabolism and transport