EXPLANATION

Generic Structure of Explanation:
1. General statement
2. Explanation
3. Closing

General Statement to Position the Reader

Speech production is made possible by the specialised movements of our vocal organs that generate speech sounds waves.

                                                                      

Explanation Like all sound production, speech production reguires a source of energy. The source of energy for speech production is the steady stream of air that comes from the lungs as we exhale. When we breathe normally, the air stream is inaudible. To become audible, the air stream must vibrate rapidly. The vocal cords cause the air stream to vibrate.

Explanation As we talk, the vocal cords open and close rapidly, chopping up the steady air stream into a series of puffs. These puffs are heard as a buzz. But this buzz is still not speech.

Closing  To produce speech sounds, the vocal tract must change shape. During speech we continually alter the shape of the vocal track by moving the tongue and lips,etc. These movements change the acoustic properties of the vocal tract, which in turn produce the different sounds of speech.

The effects of acid soil

Soils with a pH of less than 7.0 are acid. The lower the pH, the more acid the soil. When soil pH falls below 5.5, plant growth is affected. Crop yields decrease, reducing productivity

Soils provide water and nutrients for plant growth and development. Essential plant nutrients include phosphorus, nitrogen, potassium and sulfur. Plants require other elements such as molybdenum, in smaller quantities. Some elements eg aluminium and manganese, are toxic to plants.

Nutrients become available to plants when they are dissolved in water. Plants are able to take up phosphate, nitrate, potassium and sulfate ions in solution.

The solubility of nitients changes with pH. In acid soils (low pH), molybdenum becomes less soluble and aluminium becomes more soluble. Therefore, plant growth may be affected by either a deficiency of molybdenum or too much aluminium.

Both crop and pasture plants are affected by acid soils. there may be a range of symptoms. Crops and pastures may be poorly established resulting in patchy and uneven growth. Plant leaves may go yellow and die at the tips. The root system of the plant may be stunted. Crops may yield less.

Plants vary in their sensitivity to low pH. Canola and lucerne are very sensitive to acid soils so do not grow well. Lupins and triticale are tolerant to soils of low pH so they still perform well.

Land can become unproductive if acid soil is left untreated. Incorporating lime into the soil raises the pH. Therefore, liming soil can reverse the effects of acid soil on plants and return a paddock to productivity.