HIGHER 
  ENVIRONMENTAL 
    SCIENCE
 Unit 1: Living Environment
    Revision Notes
  ECOSYSTEM DEFINITIONS                                                                                                                                                                                      2
  • Species- organismswhich canbreed successfully and produce fertile offspring
  • Population- a group of organisms of the same species
  • Habitat - a place where an organism lives
  • Community-alloftheanimasandplantsinahabitat.
  • Ecosystem - the community and the habitat. It can also be described as all of the
        living things together with the non living environment
  • Niche - is the role occupied by an organism in a habitat - what it eats, what preys
        onit and where it lives (e.g. tree bark)
  • Ecology - the study of ecosystems and the relationship between organisms and
        their environment
   FOOD CHAINS & FOOD WEBS
  • Thesourceofenergyforafoodchain/web is always the sun.
  • Afood chain shows the relationship between organisms which pass on their energy
        by feeding
  • Thearrows in a food chain indicate the direction of energy flow e.g.
                                                                                                                                                                 
                 oak tree                                 leaf-eating insect                                             shrew                                  fox 
         
  • A food web shows all the possible feeding relationships in an ecosystem or habitat.
                                                                  Theowl is the top predator in this food web
                                                                                                              The levels within a food web are
                                                                                                              knownastrophiclevels
                                                                                                            Aheterotroph or consumer means an
                                                                                                            animal which depends on other living
                                                                                                            things (plants or other animals) for its
                                                                                                            food. There are 3 types of consumer:
                                                                                                            • Carnivores prey on other animals
                                                                                                            • Omnivores eat both plants and
                                                                                                                 animals
                                                                                                            • Herbivores eat plants only:
       The term autotroph or primary producer means a green plant which is able to
       produceits own food by photosynthesis.
 ENERGY TRANSFERS                            3
 • As energy flows through a food chain a lot of energy is "lost". Usually a maximum of
  10%ofenergyavailable is passed onto the trophic level above for new biomass
 • Energy is lost as heat, movement and undigested waste (NB not death, excrement
  andfaecesasthis is still food for microbes, bacteria and other decomposers).
 • Foodchainscanonlysupport6 trophic levels before all the energy is used.
 • Short food chains (with only 2 or three arrows) are more energy efficient and waste
  less energy than longer chains.
 • Photosynthesis is a critical process in food webs, where green plants and certain
  other organisms transform light energy into chemical energy.
                     Light energy
        carbon dioxide + water                           glucose + oxygen
                     chlorophyll
 • Respiration occurs in cells or organisms, it is the chemical process by which organic
  compounds(sugars)releaseenergyfor their metabolism.
      glucose + oxygen                              carbon dioxide + water + energy
 • Productivity is the amount of solar energy that is incorporated into biomass.
 • Gross productivity is the energy "fixed" by the producers in photosynthesis and
  stored as chemical energy in glucose.
 • Net productivity = Gross productivity - Losses (due to respiration and heat )
 • Endotherms are warm blooded animals (mammals, birds) which use more energy for
  heat and respiration, so have to eat more food to survive. As a response to this some
  species migrate, hibernate or lower their metabolic rate to conserve energy during cold
  periods and to reduce their energy demand. Food webs with many endotherms are
  often short in length (3 or 4 trophic levels)
 • Ectotherms are cold blooded animals (e.g. fish, reptiles) which use less energy for
  daily activities. They often survive long periods without food. As they struggle to
  regulate their temperatures they can bask in sunlight or seek shade to warm up or cool
  down.Foodwebswithectothermsareoftenlongerin length.
 DecayProcesses
 Decay is an essential life process, which helps to digest food, and recycle materials
 which ensure the energy in dead material is still available to food webs. Decay is the
 work of two main groups:
 • Decomposers includes fungi and bacteria (single celled organisms) which break
  downorganic matter chemically by releasing enzymes to speed up chemical reactions.
  Thesolublecomponentscanbeabsorbedbythesemicro-organisms.
 • Detritivores are larger organisms which feed on detritus (dead material) e.g.
  earthworms (break down leaves); maggots (fly larvae which eat animal tissue) and
  woodlice (eat dead wood). They also help break down organic matter into smaller
  pieces, so increasing the surface area for the bacteria and fungi.
 ECOLOGICAL PYRAMIDS                                                           4
 Energy flows in ecosystems can be shown using pyramids:
 1. Pyramid of Numbers                                                                           
 This is a very simple way of showing the number of organisms at each trophic level.
 Pyramids of numbers are often triangular (or pyramid) shaped, but can be almost any
 shape, depending of the size of the organisms. In particular very large producers
 (like trees) and very small consumers (like parasites) cause inverted pyramids.
                   mice                                          parasites
                   snails                caterpillars             aphids
                   grass
 The drawbacks with a pyramid of numbers is that they do not consider the size of
 organisms or the energy transferred.
  2. Pyramid of Biomass
  This is another fairly simple way of
  showing the number of organisms at each
  trophic level. The pyramid always narrows
  towards the top showing energy loss at
  each trophic level. However it doesn't
  reveal anything  about  the  chemical
  composition of organisms and how much
  energy is passed on (fat, protein); they
  also don't consider ecosystems with a
  high turnover rate such as grass in a field
  with an apparent low biomass.
  3. Pyramid of Energy
  This is the most reliable pyramid and
  represents the amount of energy flowing
  from one trophic level to the next. It is
  usually expressed in kilojoules per metre
  squared per year (kJ/m2/year). Since
  energy is always lost at every trophic
  level, they always form upright pyramids