Chemistry of Life Water: The Primary Molecule of Life

1. Chemistry of LifeWater: The Primary Molecule of Life Assessment Statements 3.1.1 to 3.1.6 IB Biology Yr 1

2. What must cells do to stay alive? • Maintain regulation - Get rid of wastes/ingest food and water • Grow & Develop • Respond to changes in their environment • Reproduce • Process energy • Adapt • How does each cell do this?

3. Energy • Each cell uses energy to build the structures it needs out of the materials available in its external environment – atoms and molecules. • The cell maintains a sophisticated barrier between itself and the outside world via the cell membrane • Living things rely on chemical reactions, which take place at the molecular level.

4. Cell Membrane • Ranges in thickness from 3nm to 10 nm • Atoms are much smaller than this. • Prior to knowing what the cell membrane actually looked like, scientists used chemical knowledge and procedures to make inferences about the world of the cell, the molecules that living cells use, manufacture, excrete and interact with…. • Let me introduce you to this exciting world!

5. Biochemistry • You may not think of your body in terms of chemical reactions, yet you rely on your cells to perform trillion of chemical reactions every second. • The study of these reactions and the molecules and processes involved in them is called biochemistry. Biochemistry

6. Think about it… • You are standing outside in winter waiting for your bus…when you are “seeing your breath” what is really going on? • Condensed water vapour (H2O) from your lungs • Oxygen (O2) and • Carbon dioxide (CO2). • The oxygen is left over from the previous inhalation and the carbon dioxide gas is the result of cellular respiration.

7. Assessment statement 3.1.1 State that the most frequently occurring chemical elements in living things are C, H2, O2, N2 Living organisms are collections of elements in the form of atoms, ions, and molecules. The 4 most common elements found in living things are carbon, hydrogen, oxygen and nitrogen. Together these elements are used in the molecular structures of all carbohydrates, proteins, lipids, and nucleic acids.

8. See handout – The periodic table for biologists

9. Carbon and Hydrogen • Carbon and hydrogen are the backbone of organic molecules, they make up sugars and carbohydrates, amino acids and proteins, and lipids fats and oils • Hydrogen ions are used in active transport, photosynthesis, and cell respiration

10. Oxygen • Main role is to allow aerobic respiration to occur. This is the last stage of cell respiration (much more of this to come!) • Oxygen is also used in oxidation reactions where oxygen is put into ATP to release energy into tissues.

11. Nitrogen • The main use of nitrogen is in the production of amino acids. Amino acids are transformed into proteins which are extremely important in the cell. • Nitrogen is also used in chlorphyll. • What do you remember about the nitrogen cycle from Science 10?

12. Assessment Statement 3.1.2 & 3.1.3 • State that a variety of other elements are needed by living organisms, including sulfur, calcium, phosphorous, iron, and sodium. • State one role for each of the elements mentioned in 3.1.2

13. Assessment Statement 3.1.3

14. Water: The primary molecule of Life

15. Water! • Remains a liquid over a wide temperature range • Dissolves most substances involved in living processes, such as oxygen, carbon dioxide, glucose, amino acids (components of proteins), and sodium chloride (salt) • Gradual temperature change when heated or cooled • Expands when it becomes a solid, floats when freezes • Clings together which helps water creep up thin tubes, such as those running from roots to shoots in plants.

16. The specific properties of water are determined by its chemical structure. A water molecule has an uneven distribution of electrical charge. • Animation The hydrogen and oxygen atoms in a water molecule are held together by polar covalent bonds due to an uneven sharing of electrons. The oxygen has an overall negative charge and the hydrogen atoms a positive. Assessment statement 3.1.4 (draw and label a water molecule to show it’s polarity and hydrogen bonds)

17. Assessment statement 3.1.5 – Outline the thermal, cohesive and solvent properties of water. Assessment statement 3.1.6 – Explain the relationship between the properties of water and its uses in living organisms as a coolant, medium for metabolic reactions and transport medium.

18. Thermal properties of water • High specific heat - allows water to give off or absorb heat without changing a great deal in temperature. This means that the temperature of water can remain relatively stable. • This unique property of water is important to living things as many organisms are adapted to a narrow range of conditions. The slow heating and cooling of water are ideal for these organisms and loessesns the risk of death due to extreme temperature ranges.

19. Thermal properties of water • High heat of vaporization - Water has the ability to absorb a lot of heat when it evaporates. • It takes a lot of energy to make water evaporate, it is thus a good coolant – as evaporating water removes a lot of heat energy from the organism.

20. Cohesive properties of water • A single hydrogen bond is not that strong, but a large number of hydrogen bonds is very strong! Each water molecule bonds with 4 others in a tetrahedral arrangement. • Due to this tetrahedral arrangement, water is cohesive and water molecules “cling” to each other in groups. Water is also adhesive and will cling to other surfaces. • Demonstration “The Floating Paper Clip!”

21. Cohesive properties of water • Capillary Action: water will move against gravity up xylem from roots to shoots! • Surface Tension: the surface of water is strong enough to support insects and causes drops to form. • E.g. Pondskaters walk on water • E.g. Cohesion forms droplets, surface tension keeps them spherical and adhesion sticks them to the leaf! HOW COOL IS THAT!

22. Solvent Properties • Most molecules in the body are polar too! • Water is a good solvent because it is a polar molecule. It will dissolve polar solutes easily. • Remember that like dissolves like and water makes an excellent solvent for the chemical properties to occur in your body. • Aq = aqueous solution (latin for “dissolved in water”) Animation!

23. Water as a solvent • Ionic solids dissociate in water (they break into their ions) • Polar attractions cause water molecules to surround and isolate the solute molecules. • The more soluble a solute is, the easier it is for the ions to be isolated from each other. Water is a good solvent: It dissolves nutrients, gases, and waste products. These can be carried in the circulatory systems of animals or through xylem and phloem in plants through the water in soil or aquatic habitats.

24. Solvent properties table (p. 49)

25. Water as a medium for metabolic reactions • Water is a good solvent – dissolved particles move around and diffuse. • Moving particles are likely to collide with one another leading to a reaction. • All metabolic reactions (reactions in living things) occur in solution – the reactants are dissolved. • Membranes and biological surfaces are wet allowing molecules to dissolve, including gases, so they can diffuse through more easily. (lungs are wet allowing for oxygen diffusion into the bloodstream)

26. And yet still more properties of water! • Water is dense: allows for large mammals to be supported in it. • Water can diffuse across the cell membrane, allowing it to carry small molecules from cell to cell or inside the cell itself from one location to another.

27. Blood • The most common transport medium in animals composed mostly of water – known as plasma. • Transports – red blood cells, white blood cells, platelets, dissolved molecules, glucose, amino acids, fibrinogen, CO2

28. More than water? • Water of the future? • Breathing water? Is it possible? http://www.youtube.com/watch?v=Z6G4s8-upGk So…what do you think? http://www.guardian.co.uk/education/2004/jan/22/research.badscience