water Flashcards
Water as the medium for life
- the first cells originated in water
- water remains the medium in which most processes of life occur.
- first cells enclosing a small volume of water in a membrane, where solutes dissolved and chemical reactions occurred.
Water as the medium for life
- Water is found between cells of multicellular organism as interstitial fluid. (helps transport nutrients and waste)
- Because water is a good solvent it allows the transport of substances into and out of cells, or in the blood in form of plasma.
- Water is crucial for organism because it makes up the fluid (cytoplasm) in all cells and within organelles.
- The cytoplasm is where metabolic reactions occur - enzymes rely on the collisions between molecules to catalyze reactions.
- It is a stable medium for aquatic organisms to live and without water life would not exist on Earth.
More about water w/ organisms
- Most of a cell and its organelles are made up from water, forming the cytoplasm.
- The cytoplasm and organelles are fluid filled with 85% of that fluid being water. Chemical and metabolic reactions work best in an aqueous environment.
Students should understand that polarity of covalent bonding within water molecules is due to unequal sharing of electrons and that hydrogen bonding due to this polarity occurs between water molecules.
- Water molecules have polar covalent bonds – this is due to the unequal attraction of electrons towards the nuclei of the involved atoms. The oxygen atom has a larger nucleus with 8 protons than hydrogen with only 1 proton. Because of this, the shared electrons from the covalent bond and unshared electrons are pulled closer to the nucleus of the oxygen atom.
- The unequal sharing of electrons in the covalent bond between oxygen and hydrogen causes a partial positive charge over H: δ+ and a partial negative charge over O: δ-
Hydrogen bonds definition
Hydrogen bonds are weak forces of attractions, which are formed between the opposite polarities of adjacent water molecules. The partially positive (δ+)end of one water molecule is attracted to the partially negative (δ-) end of another water molecule.
Hydrogen bonds as a consequence of the polar covalent bonds within water molecules
- Students should be able to represent two or more water molecules and hydrogen bonds between them with the notation shown below to indicate polarity.
Cohesion of water molecules due to hydrogen bonding and consequences for organisms
+ surface tension
- Cohesive forces of water molecules are caused by the hydrogen bonds between them. A single hydrogen bond is a weak intermolecular force of attraction, but the summative force of all hydrogen bonds is very strong.
- Each water molecule hydrogen bonds with four others in a tetrahedral arrangement, making water cohesively “stick together”.
- Water can form droplets due to surface tension, which is a consequence of cohesive forces due to hydrogen bonding between water molecules.
droplet formation (explain w/ surface tension/moleculesssss)
- Surface tension causes droplet formation in water. It is established because the molecules on the outside of a water body form hydrogen bonds with the water molecules below them.
- These molecules have no neighboring molecules above them to bond with, so they have stronger attractive forces upon their nearest neighbours on and below the surface of water making them contract inwards.
Include the use of water surfaces as habitats due to the effect known as surface tension.
surface tension & small animals
- Surface tension makes water a habitat for insects to live on or underneath. The surface tension is strong enough to support the mass of insects (which is not great enough to break the hydrogen bonds responsible for surface tension).
- ex) pondskaters
Include transport of water under tension in xylem as habitats due to the effect known as surface tension.
Cohesion allows the transport of water under tension in plants. Water molecules stick together via hydrogen bonds, and the pulling forces caused by the evaporation of water from the leaves (transpiration) makes water move upwards against gravity as an intact water column.
- high surface tension - water molecules don’t break apart when moving against gravity
Adhesion of water to materials that are polar or charged and impacts for organisms
- Include capillary action in soil and in plant cell walls.
- Adhesion is the attraction between the polar ends of water molecules and polar surfaces.
- Capillary action helps water be drawn into a plant from an underground source in the soil, as soil contains many thin channels acting as capillary tubes. Adhesion between the water molecules and the soil particles cause water to move above the water table and into the roots of a plant.
- Capillary action due to adhesion allows water to be drawn up in plants because the cell walls are made of polar/hydrophilic cellulose fiber acting like wicks, causing water to adhere to the cell walls.
- Due to the capillary action, plant cells that are exposed to air (cells in the leaf) are kept continuously moist drawing in water from nearby xylem vessels as long as there is a source of water available.
Solvent properties of water linked to its role as a medium for metabolism and for transport in
- Emphasize that a wide variety of hydrophilic molecules dissolve in water and that most enzymes catalyse reactions in aqueous solution. Students should also understand that the functions of some molecules in cells depend on them being hydrophobic and insoluble.
Physical properties of water and the consequences for animals in aquatic habitats
Include buoyancy, viscosity, thermal conductivity and specific heat.
Buoyancy = the ability of any fluid to provide vertical upwards force on an object placed in or on it.
- B= weight of object, object floats (buoyancy is dependent on object density)
- Ex) bony fish, cyanobacteria, midair bird
- Viscosity is the resistance of a fluid to flow. It is due to internal friction caused when one part of a fluid moves relative to another part (depends on bonds/forces of attraction)
- The specific heat capacity of water is very high. This is due to the hydrogen bonds which restrict molecular motion (and avg kinetic energy). For a change in temperature to occur, hydrogen bonds must be broken.
- Because of the high specific heat capacity, the temperature of large bodies of water remains relatively stable, which makes it an ideal habitat for a lot of organisms which only tolerate a narrow range of conditions.
- It takes a lot of energy for water to change temperature. This means that, when water evaporates, a lot of energy is required to break the hydrogen bonds between water molecules, leaving us with a cooling sensation.
- Thermal conductivity is the rate at which heat passes through materials. (closer particles, higher conductivity)
Contrast the physical properties of water with those of air and illustrate the consequences using examples of animals that live in water and in air or on land, such as the black-throated loon (Gavia arctica) and the ringed seal (Pusa hispida).
HL
