B4

• Materials cycled through ecosystems

  • Carbon
  • Water
• The Carbon Cycle

  1. CO2 is removed from the air in photosynthesis by green plants and algae - they use the carbon to make carbohydrates, proteins, and fats

  2. CO2 is returned to the air when plants, algae, and animals respire. Decomposers (a group of microorganisms that break down dead organisms and waste) respire while they return mineral ions to the soil

  3. CO2 is returned to the air when wood and fossil fuels are burnt (called combustion) as they contain carbon from photosynthesis
• Many different microorganisms play their parts in ecosystems to ensure the cycling of materials
• The carbon and water cycles are vital for life on Earth, by maintaining habitats, fresh water, and flow of nutrients
• The Water Cycle

  1. The sun’s energy causes water to evaporate from the sea and lakes, forming water vapor

  2. Water vapor is also formed as a result of transpiration in plants

  3. Water vapor rises and then condenses to form clouds

  4. Water is returned to the land by precipitation (rain, snow, or hail), and this runs into lakes to provide water for plants and animals

  5. This then runs into seas and the cycle begins again
• Factors affecting decomposition rate


  • Temperature: Chemical reactions generally work faster in warmer conditions, but if it is too hot, the enzymes can denature and stop decomposition
  • Water: Microorganisms grow faster in conditions with water as it is needed for respiration. Water also makes food easier to digest
  • Availability of oxygen: Most decomposers respire aerobically
• Decomposition

  Decomposition is the breakdown of dead matter, fallen leaves, or animal droppings by decomposers, which can be bacteria or fungi. They secrete enzymes to break it down to smaller soluble food molecules
• Compost

  1. When biological material decays it produces compost

  2. It is used by gardeners and farmers as a natural fertilizer

  3. To do this they have to provide optimum conditions for decay. If more oxygen is available they respire aerobically, producing heat. The increased temperature increases the rate of decay so the compost is made quicker
• Secondary consumer


  Consumers that eat primary consumers
• Biotic factors affecting communities


  • Food availability
  • New predators
  • New pathogens
  • Competition
• Primary consumer


  Consumers that eat producers
• When there isn't enough prey to feed all the predators

  The population of predators will decrease, allowing the prey population to increase again
• An individual is part of a species, but lives in its habitat within a population. Many different populations interact in the same habitat, creating a community
• Abiotic factors affecting communities


  • Light intensity
  • Temperature
  • Moisture levels
  • Soil pH and mineral content
• Producer


  A photosynthetic organism (usually a green plant or algae) that produces glucose
• If the population of prey increases

  The population of predators will also increase
• Tertiary consumer


  Consumers that eat secondary consumers
• Generally, food chains do not continue past tertiary consumers
• New pathogens can lead to

  Population wipeout as there is no resistance
• Competition within and between species occurs when

  Organisms compete for the same resources
• More food availability leads to

  Successful breeding and increase in population numbers
• Increased predator population leads to


  Decrease in prey population as more would be consumed
• Interdependence in a community means


  Organisms depend on each other for vital services like food, shelter, and reproduction
• The removal or addition of a species to the community can greatly affect

  The populations of other species as it changes prey or predator dynamics
• An ecosystem is the interaction of a community with non-living (abiotic) parts of the environment. Organisms are adapted to live in the conditions of their environment
• Organisms eat. Multiple food chains can be linked in order to create a food web
• Efficiency of biomass transfers formula: (Biomass transferred to the next level / Biomass available at the previous level) x 100
• The removal or addition of a species to the community

  Can affect the populations of others greatly, as it changes prey or predator numbers
• Approximately 10% of the biomass of each trophic level is transferred to the next
• Stable community characteristics

  1. Population sizes remain roughly constant

  2. When lost, it is very difficult to replace them
• Examples of stable communities

  • Tropical rainforests, oak woodlands, coral reefs
• Stable community


  One where all the biotic (living) and abiotic (non-living) factors are in balance
• Less biomass is transferred each time, leading to a limited number of trophic levels and fewer animals in the higher trophic levels
• Producers transfer about 1% of the incident energy from light for photosynthesis
• Pyramids of biomass


  1. Show the relative biomass at each trophic level

  2. There is less biomass as you move up the trophic levels
• Vital services provided by organisms in a community

  • Food, shelter, reproduction (pollination, seed dispersal)
• Ecology


  Describes how organisms in a community depend on other organisms for vital services such as food, shelter, and reproduction