Transcript Chemical Elements and Water
Chemical Elements and Water
Presentation Modified from J. Naftzinger
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Atoms and Ions
An atom is a single particle of a chemical element If an atom either gains or loses electrons it becomes an ion Atoms are uncharged particles and ions are charged – they have either positive or negative charges For example, if a sodium atom (Na) loses an electron it becomes a sodium ion (Na + ) This is important for when discussing solubility 2
Elements Found in Living Organisms
Living organisms contain many chemical elements, some in large quantities and some in very small amounts The 4 most frequently occurring chemical elements of life are carbon, hydrogen, oxygen and Nitrogen (CHON) They are part of all the main organic compounds in living organisms Organic compounds:
contain carbon found in living organisms
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carbohydrates, lipids, amino acids are all organic molecules Other elements needed by living things: 1. Calcium (bones) 2. Phosphorus (Nucleic acids) 3. Iron (blood) 4. Sodium (Na+/K+ pumps) 5. Sulfur (amino acids) 3
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Examples of Chemical Elements and Their Roles
Element Role in Plants or Animals Sulfur Calcium Phosphorus Iron Sodium Part of the amine groups of amino acids and therefore proteins Needed to make the mineral that strengthens bones and teeth Part of the phosphate groups in ATP and DNA molecules Needed to make hemoglobin and thus to carry oxygen in blood Used in neurons (nerve cells) for the transmission of nerve impulses 5
The Significance of Water to Living Organisms
It is used by them in many different ways These uses can be explained by referring to the properties of water Water is used a coolant
Refer to thermal properties Water is used as a transport medium and medium for metabolic reactions
Refer to cohesion, solvent properties, and thermal properties Water is used as a habitat
Hydrogen bonding, refer to cohesion, transparency, and thermal properties 6
Polarity and Hydrogen Bonding in Water
Water molecules consist of 2 hydrogen atoms bonded to an oxygen atom The hydrogen atoms have a slight positive (+) charge and the oxygen atom has a slight negative (-) charge So, water molecules have 2 poles (they are dipoles) oxygen pole – a positive hydrogen pole and a negative This feature of a molecule is called polarity A bond can form between the positive pole of one water molecule and the negative pole of another This is called a hydrogen bond In liquid water, many of these bonds form Hydrogen bonds provide water with much of its basic properties 7
Water molecules form Hydrogen bonds
slightly positive charge slightly negative charge hydrogen bond between (+) and (-) areas of different water molecules 8
Thermal Properties: Heat Capacity
Water has a high heat capacity This means that large amounts of energy are needed to raise its temp The energy is needed to break one of the hydrogen bonds This heat energy is given out again when the water is cooled The temperature of water tends to remain quite stable This is useful for organisms such as fish that use water as a habitat Blood, which is mainly composed of water, can carry heat from warmer parts of the body to cooler parts 9
The Importance of Ice Floating
If ice sank to the bottom of a body of water as it cooled… Ponds and lakes would freeze up from the bottom
Fish and other organisms would be trapped in the small amount of water that is left There would be no access to the nutrients at the muddy bottom Ice atop a body of water, insulates the water below
Life persists under the frozen surface
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Thermal Properties: Boiling and freezing points
The boiling point of water is relatively high because to change it from a liquid to a gas all of the hydrogen bonds between the water molecules have to be broken
In natural habitats on Earth, water rarely boils Living organisms could not survive if the water inside them boiled Water also freezes at a relatively high temperature but because it becomes less dense as it cools to freezing point, ice forms at the surface first
The ice that forms on the surface of lakes or seas insulates the water underneath, so living organisms can survive there 11
Thermal Properties: The Cooling Effect of Evaporation
Water can evaporate at temps below boiling point
Hydrogen bonds have to be broken to do this
The heat energy needed to break the bonds is taken from the liquid water, cooling it down
Evaporation of water from plant leaves ( transpiration ) and from human skin ( sweat ) has useful cooling effects 12
Cohesion
Water molecules stick to each other because of the hydrogen bonds that form between them Strong pulling forces can be exerted to tops of the systems suck columns of water up to the tallest trees in their transport
These columns of water rarely break 13
Trees have specialized structures to transport water: xylem and phloem “plumbing” Water molecules are “dragged” from the roots to the top of the tree by capillary action (adhesion) and cohesion: hydrogen bonds help water molecules hydrogen bond to each other 14
Adhesion
Adhesion refers to attraction to other substances .
Water is adhesive to any substance with which it can form hydrogen bonds .
Think water climbing up capillary tubes… 15
Cohesion
At a surface, the cohesion of water molecules can make it difficult for small objects to break through surface tension
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a measure of the force necessary to stretch or break the surface of a liquid Some animals such as mosquito larvae use the surface of water as a habitat Though they are denser than water they remain on the surface and do not sink because of the high surface tension of water caused by cohesion 16
Solvent Properties
Many different substances dissolve in water because of its polarity
Inorganic particles such as sodium ions and organic substances such as glucose can dissolve
Water’s polarity “pulls” apart the ions of a particular substance (above NaCl). The positive hydrogen ends are attracted to the anions of a substance and the negative oxygen ends are attracted to the cations of a substance 17
Like dissolves like:
water can interact with other polar molecules 18
Water transports molecules dissolved in it
Blood , a water-based solution, transports molecules of nutrients and wastes within organisms
Nutrients dissolved in water get transported through plants
Unicellular organisms that live in water absorb needed dissolved substances 19
Transparency
The fact that
water is clear allows light to pass through it
Aquatic plants can receive sunlight
Light can pass through the eyeball to receptor cells in the back 20
Some acids and bases (HCl and NaOH) are strong or bases.
acids
These molecules dissociate completely in water.
Other acids and bases (NH 3 ) are weak
acids or bases.
For these molecules, the binding and release of hydrogen ions are reversible.
Carbonic acid (H 2 CO 3 ) is a weak acid: H 2 CO 3 <=> HCO 3 + H + 21
pH scale
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the environment needs to be at a specific pH for many organisms to survive
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Ex: most cells have an internal pH of 7 (neutral)
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If the pH changes, even slightly, this can disrupt the chemical reactions inside the cell
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Blood pH =7.4, a person will die if pH reaches 7.8 or 7 for even a little while!
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The chemical processes in the cell can be disrupted by changes to the H+ and OH- concentrations away from their normal values near pH 7.
To maintain cellular pH values at a constant level, biological fluids have buffers .
Buffers resist changes to the pH of a solution when H+ or OH- is added to the solution.
Buffers accept hydrogen ions from the solution when they are in excess and donate hydrogen ions when they have been depleted. 23