3.1: Chemical Elements and Water

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3.1: Chemical Elements and Water
2013-12-23 19:21:28

3.1: Chemical Elements and Water
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  1. Identify the most abundant elements by weight in living things.
    Carbon, hydrogen, oxygen and nitrogen are the most abundant  elements by weight in living things.
  2. If oxygen is approx 65% of body weight in humans, carbon is 18%, hydrogen is 10% and nitrogen is 3.3%, what is the total percentage of these four elements in human body weight?
    The four elements C, H, O and N make up 96.3% of human body weight.
  3. State the role of other elements in living organisims.
    • 1. Sulfur (S) 
    • Animals: Needed in amino acids which make up enzymes. 
    • Plants: Needed in amino acids which make up enzymes. 
    • Prokaryotes: Some chemotrophs use sulfur compounds as a source of energy. 
    • 2. Calcium (Ca) 
    • Animals: Helps build strong bones, teeth. Assists in blood clotting and needed in nerve and muscle functioning. 
    • Plants: Part of cell walls and cell membranes. 
    • Prokaryotes: Involved in cell structure and movement. 
    • 3. Phosphorus (P) 
    • Animals/Plants/Prokaryotes: Is part of ATP/ADP for storage and release of energy. Part of nucleic acids for DNA/RNA and genetic information.
    • 4. Iron (Fe)
    • Animals: Part of haemoglobin to carry oxygen in red blood cells. 
    • Plants: Part of chlorophyll for photosynthesis. 
    • Prokaryotes: Some anaerobic bacteria use iron as part of their source of energy. 
    • Sodium (Na): 
    • Animals: Involved in transmission of nervous impulse and aids glucose transport across cells
    • Plants: Used by C4 plants to bind CO2 in photosynthesis. 
    • Prokaryotes: Helps locomotions, e.g. flagellum.
  4. What is meant by a trace element for an organism?
    Trace elements are less than 0.01% body weight.
  5. When analysing diet and food intake, suggest why many elements are called essential elements, although they are not needed in large quantities and are not as necessary for all organisms.
    Essential elements must be part of the diet and food intake or disease and malfunctioning occur. For example, humans require a daily intake of 150 micro-grams of Iodine to maintain normal functioning of the thyroid gland and the production of thyroxin. Most plant species do not require iodine in such amounts and iodine is not as necessary to plants as to humans.
  6. Outline what is meant by the thermal properties of water.
    The thermal properties of water refer to the high specific heat of water, the high boiling point and heat of vaporisation. The specific heat is the amount of heat that must be absorbed/lost for 1 g of the substance to change its temperature by 1 degree. The specific heat of liquid water is 4.18 J/degree Celsius.g and is due to hydrogen bonding - heat needs to be absorbed to break the hydrogen bonds. The high specific heat of water means that water changes temperature less than other substances. Water also has a high heat of vaporisation which means a lot of energy is required to change water from a liquid to a gas. When water freezes, the ice floats on the water and this can affect the temperature of the water below by the ice acting as an insulator.
  7. Outline what is meant by the cohesive properties of water.
    Cohesion refers to the attractive force between molecules of the same kind. Water molecules are cohesive and will stick to each other, e.g. water easily forms droplets. Cohesion in water is due to the hydrogen bonds. Water also shows adhesion and will cling to other substances, e.g. water droplets on the side of a cold glass of lemonade.
  8. Outline what is meant by the solvent properties of water.
    A solvent is a dissolving agent. A solute will dissolve in a solvent to form a solution. If water is the solvent, the solution is called an aqueous solution. The polarity of the water molecule makes it a useful agent. Ionic compounds dissolve in water and compounds that are non-ionic but polar, e.g. glucose, are also water soluble.
  9. Summarise how thermal properties of water assist processes in living organisms.
    • Water has high specific heat capacity: Transport - the water in blood carries heat from the source of heat to colder areas. Coolant/termperature control - Land/sea breezes for coastal areas are caused by different heat capacities of the continent and ocean. This affects climate and living conditions, the high heat capacity of water also causes a stable ocean temperature for marine life and the ability of organisms (which contain high amounts of water) to stabilise body temperature.
    • When water freezes ice is less dense and floats on the surface: coolant/temperature control - In harsh, cold conditions, ice forms an insulating layer on the surface enabling aquatic life to survive below. 
    • Water has high heat of vaporisation: coolant - when water evaporates from the surface of an organisms it takes heat energy from the organism in a cooling affect.
  10. Summarise how cohesion properties of water assist processes in living organisms.
    Water is cohesive and molecules bond to their neighbors: Transport - water will move against gravity in plants from roots to leaves in the xylem. As water evaporates from the leaf, cohesion pull water up from the roots.
  11. Summarise how solvent properties of water assist processes in living organisms.
    • Many solutes will dissolve in water: 
    • Transport - mineral ions dissolve in water and travel in the xylem from the roots to the leaves in plants. The sugars that ravel in the phloem are dissolved in water. 
    • Transport - many substances are dissolved in the water in blood and are transported around the body of an animal, e.g. oxygen, glucose, urea. 
    • Medium for metabolic reactions - Chemical reactions inside cells and outside cells involving polar molecules occur in aqueous solutions.