Unit 2

• Abiotic factors


  Non-living things that provide the basis of an ecosystem
• Abiotic factors include water, light, temperature, air (atmospheric gases and wind)
• Living organisms depend on abiotic factors to exist
• Abiotic factors affect the distribution and behaviour of living organisms
• Soil is one of Earth's most important resources
• Main role of soil


  To provide a medium for plants to grow in
• Main types of soil

  • Sandy soils
  • Loamy soils
  • Clay soils
• Humus


  A dark, sticky substance formed when decomposers break down dead organic matter in the soil
• Humus helps hold soil particles together to form soil crumbs
• Humus helps the soil to hold water better
• Humus contains minerals and salts that plants need for growth
• To identify soil type, rub a bit of wet soil between your fingers
• If the soil feels sticky

  It is clay soil
• If the soil feels gritty

  It is sandy soil
• If the soil feels soapy


  It is loamy soil
• Differing kinds of soil hold different amounts of water
• Water-holding capacity


  The amount of water a soil can hold
• Clay soil


  Holds a lot of water
• Sandy soil


  Holds very little water
• Loamy soil


  Holds a moderate amount of water
• Water-holding capacity is important for plant growth
• Plants that grow in sandy soils need to have large, shallow root systems to absorb a lot of water quickly
• Soil air content


  Loosely packed soils, such as sand, have large air spaces between the particles
• Clay soils


  Have small air spaces and hold small amounts of air
• Loamy soils


  Hold a moderate amount of air
• Soil pH


  The acidity or alkalinity of the soil affects plant growth
• Decomposers produce weak acids when breaking down dead organic material, making the soil acidic
• Most plants grow better in slightly acidic soil
• Some plants grow better in alkaline soil
• Plants that grow well in acidic soils

  • Maize
  • Sugar cane
  • Potatoes
• Plants that grow best in alkaline soils

  • Wheat
  • Beans
  • Onions
• Water is essential for life
• The water cycle


  A natural cycle in which water is circulated through ecosystems by means of processes such as evaporation and condensation
• Most of the Earth's water is in the seas and oceans
• Heat energy from the Sun causes some water to evaporate to form water vapour
• Plants lose some water from their leaves as water vapour during transpiration
• Water vapour rises into the atmosphere where it cools and condenses to form clouds
• Droplets of water in clouds eventually fall to the Earth's surface as rain
• Most of the rain soaks into the land and is stored as groundwater
• Groundwater is water that has filtered through the soil to the bedrock