life on earth

• Habitat

  The place where a community lives and the non-living things with which it interacts
• Biodiversity

  The variety of living things in an area
• Consumers in a food chain

  • Herbivores (eat producers)
  • Carnivores (eat other consumers)
  • Omnivores (eat plants and animals)
• Food web

  Made up of many interconnected food chains
• Terms describing an organism's niche

  • Competition
  • Predation
  • Tolerance of conditions (temperature, pH, moisture)
• Intraspecific competition

  Competition between organisms of the same species
• Removal of any species from a food web has consequences for the population sizes of other species
• Abiotic factors and how they are measured

  • Soil pH (soil pH meter)
  • Light intensity (light meter)
  • Temperature (thermometer)
  • Soil moisture level (moisture meter)
  • Oxygen concentration (oxygen meter)
• Errors can creep into the measurement of abiotic factors, so a large number of readings are required for reliable averages
• Sampling organisms

  Using techniques like quadrats and pitfall traps to estimate the types and numbers of organisms present in an ecosystem
• Limitations and sources of error in quadrat and pitfall trap sampling

  • Quadrats: only suitable for low-growing, rooted plants or slow-moving animals; reliability limited by number of samples; potential errors in placement, size selection, and plant identification
  • Pitfall traps: only suitable for small, surface-crawling invertebrates; reliability limited by number of traps; potential errors in placement, size selection, and invertebrate identification
• Paired statement keys


  Used to identify species found in samples, by constructing questions that can split differences between organisms
• Factors affecting biodiversity


  • Abiotic factors
  • Biotic factors
  • Human influences (abiotic and biotic)
• Indicator species


  Organisms that, by their presence, abundance or absence, show conditions in the environment
• Biological indicators of pollution

  Indicator species that can indicate the level of pollution present
• Freshwater invertebrate indicators of water pollution

  • Mayfly nymphs (clean, well-oxygenated water)
  • Stonefly nymphs (clean, well-oxygenated water)
  • Sludge worms (low oxygen, high pollution)
• Lichen indicators of air pollution


  • Different lichen species vary in sensitivity to sulphur dioxide pollution
• Measuring rate of photosynthesis

  Using aquatic plant stems and counting oxygen bubbles produced, with higher light intensity resulting in more bubbles
• Limiting factors

  Factors that are at low levels or in short supply and can limit the rate of a chemical reaction like photosynthesis, such as light intensity, carbon dioxide concentration, or temperature
• As energy flows through a food chain or web, a progressive loss of about 90% occurs at each level due to heat, movement, and excretion
• Limiting Factors

  • The rate of chemical reactions such as photosynthesis can be limited by factors that are at low levels or are in short supply
  • Low temperature or light intensity can limit the rate of photosynthesis
  • The concentration of carbon dioxide available to the plant can also be limiting
• Light intensity

  Affects the rate of photosynthesis
• Carbon dioxide concentration

  Affects the rate of photosynthesis
• Temperature

  Affects the rate of photosynthesis
• This is one of the main arguments for veganism
• Pyramid of numbers

  Numerical relationship where the producers (the algae) are the most numerous, followed by the primary consumers and so on along the food chain, with the final consumer being the least numerous
• The relationship takes the form of a pyramid because: energy loss at each link in the food chain limits the quantity of living matter that can be supported at the next level, the final consumer tends to be larger in body size than the one below it and so on
• Pyramid of energy


  Diagram that illustrates the energy content at each level and the transfer of energy from one level to another
• A pyramid of numbers may take an irregular shape because it is based on different body sizes, but when represented as a pyramid of energy, it takes the form of a true pyramid because only a proportion of energy (10%) is successfully transferred from one level to the next
• Food chain


  Simple set of feeding links showing how energy passes from a producer to consumers
• Number pyramid


  Diagram that shows the relative numbers of organisms at each level in a food chain
• Unlike other species, human beings have managed to overcome most of the environmental factors that normally prevent a population in its natural ecosystem from increasing indefinitely in number
• Humans have used their exceptional brain power to: remove the threat of predation, develop vast areas of land for food production, improve public health
• Attempts to achieve increased food yield

  • Growing vast monocultures of food crops
  • Employing methods of intensive farming
  • Developing genetically modified crops as alternative to the uses of pesticide
• All living things need nitrogen to make protein, but plants and animals can't make direct use of the nitrogen gas present in air
• Plants absorb nitrogen from the soil in the form of nitrate, while animals must eat plant or animal protein to obtain their supply of amino acids for protein synthesis
• When a crop is grown on cleared land and then harvested and removed, the ecosystem's natural balance is disturbed, the nitrogen cycle is broken since almost no dead plant material is returned to the soil for breakdown by micro-organisms, and less nitrates are generated, making the soil less fertile
• This problem is tackled by adding fertiliser to the soil to increase its nitrate content in advance of planting the next crop
• If fertiliser from fields leaches into a river or a loch, it makes the water overly rich in mineral nutrients such as nitrates, promoting the rapid growth of algae which forms an algal bloom
• The scummy layer of algae on the surface of the water reduces the quantity of light able to reach aquatic plants below the surface, which then die of starvation