Fig. 3-2Hydrogenbond–H+HO+++–––Slightly + H of 1 moleculeattracted to slightly – O ofnearby molecule –Hydrogen bond keepsthem together.In liq water the bond is veryweak -Continually reforming &breaking
¾ of the Earth’s surface iscovered by water of theoceans.Every cell consists of 50 –90% water.Needed to transportmolecules in & out cells.Many organisms live in water.
Water can be found in 3 phases:1. Gasses2. Liquids3. Solids
Consist of water molecules that move aroundfreely: A lot of energy and space between molecules. Attraction between molecules very weak. Called water vapour. Found in atmosphere.
When temperature increases, it causes liquidwater to change to water vapour(evaporate).
Water molecules move around lessthan gasses but more than solids. More energy than solids but lessthan gas. Attraction forces betweenmolecules is stronger than gasmolecules but weaker than solids. It takes on the shape of thecontainer it is in. Found everywhere. If solid water is heated, liquid waterforms.
Solid water molecules are called ice. Molecules only vibrate at one spot.Minimal amount of energy but verystrong attraction forces betweenmolecules. Molecules arrange in a structured waycalled a crystal lattice. Found everywhere. If liquid water is cooled down itbecomes a solid.
Water has a high heat capacity Amount of heat required to raise the temperature of 1g ofwater by 1˚C. Prevents water from freezing or boiling if atmospherictemperature changes protecting aquatic organisms. Water has a high heat of evaporation Amount of heat required to vaporize a liquid. Helps animals, they sweat, water evaporates when theyoverheat, to cool them down. Water has a high heat of fusion Amount of heat required to melt a solid.
More things can dissolve in water than anyother liquid. The liquid that a substance dissolves in iscalled a solvent. Blood contains 55% water called bloodplasma. Gasses have to dissolve in the blood plasmaand then diffuse into the red blood cells totransport the oxygen to the body cells andand carbon dioxide to the lungs.
All chemical reactions to controlmetabolism take place in water. E.g.Digestion, breathing etc. Water takes part in some chemicalreactions e.g. Photosynthesis What is photosynthesis? The processwhereby plants use water, sunlight andcarbon dioxide to produce food andoxygen. Enzymes speed up chemical reactionsin the presence of water.
Water helps transport substances in thebody of a plant or animal: E.g. In humans, food and gasses aretransported via the blood circulatorysystem (consisting of mainly water). E.g. In plants, mineral salts, absorbedfrom the soil are dissolved in water andcarried to all parts of the plant.
Most organisms need water toreproduce. Mosses and ferns can onlyreproduce if they are covered witha thin film of water. All animals need water toreproduce, the sperm needs waterto swim to the ova (egg cell). Aquatic animals reproduce in thewater.
Vertebrates (like humans)have a bonyskeleton to support the shape of theirbodies. Invertebrates do not consist of bones,most of them have water that helps tosupport the body shape, called ahydrostatic skeleton. Water pushes against the sides of the body,exerting pressure to maintain the shape. E.g.Worms and snails. Xylem tubes together with water helpsplants stay upright. (Think about a plant deprived of water)
Humans use “water” to cool down. This water is known as sweat.(perspiring) Sweat is produced by sweat glands. When the sweat evaporates from thebody, it cools down. This happens during strenuous exercise,stress and illness.
Plants lose water through theirleaves. Process of transpiration. Transpiration helps to cool theplant down. What is transpiration? Loss ofwater in the form of watervapour through openings calledstomata, on the leaves ofplants. Helps plants suck water up stemto leavesSTOMATACross section through leaf to see
Cover pot plant/branch of plantwith a plastic bag Seal bag with a string. Leave bag for few hours. Observe Result: Water droplets form onthe sides of the plastic bag. What happened? Transpirationoccurred You can try this at home