Characteristics of living organisms

• Characteristics of Living Organisms

  • Movement: an action by an organism or part of an organism causing a change of position or place
  • Respiration: the chemical reactions that break down nutrient molecules in living cells to release energy for metabolism
  • Sensitivity: the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses
  • Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or both
  • Reproduction: the processes that make more of the same kind of organism
  • Excretion: the removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements
  • Nutrition: the taking in of materials for energy, growth and development; plants require light, carbon dioxide, water and ions; animals need organic compounds, ions and usually need water
• Use this mnemonic to help you remember these processes: MRS. H. GREN
• Species


  A group of organisms that can reproduce to produce fertile offspring
• How Organisms are Classified

  • There are millions of species of organisms on Earth
  • Species can be classified into groups by the features that they share
• Binomial System


  • Organisms were first classified by Linnaeus in a way that allows the subdivision of living organisms into smaller and more specialised groups
  • The scientific name of an organism is made up of two parts starting with the genus (always given a capital letter) and followed by the species (starting with a lower case letter)
  • The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus, Species
• The order of classification can be remembered by using a mnemonic like: KING PHILIP CAME OVER FOR GRAN'S SPAGHETTI
• Dichotomous Keys


  • Keys are used to identify organisms based on a series of questions about their features
  • Dichotomous means 'branching into two' and it leads the user through to the name of the organism by giving two descriptions at a time and asking them to choose
  • To successfully navigate a key, you need to pick a single organism to start with, follow the statements from the beginning, and eventually there will be no more statements or questions left and you will have the name of the organism
• Example of a dichotomous key #1


  • Example of a dichotomous key #2
• Simple dichotomous keys almost always come up in the multiple choice paper, so make sure you can use one. Very occasionally they show up in the theory paper, and when they do you almost always have to use one instead of constructing one, so focus on this rather than spending hours learning to construct them yourself!
• Reflecting Evolutionary Relationships: Extended


  • Classification systems aim to reflect evolutionary relationships between species
  • Traditional biological classification systems grouped organisms based on the features that they shared
  • Using the physical features of species has many limitations and can often lead to the wrong classification of species
• Using DNA to Classify Organisms: Extended

  • Organisms share features because they originally descend from a common ancestor
  • Originally, organisms were classified using morphology and anatomy
  • As technology advanced, studies of DNA sequences of different species show that the more similar the base sequences in the DNA of two species, the more closely related those two species are

  
• The Five Kingdoms


  • Animals
  • Plants
  • Fungi
  • Protoctists
  • Prokaryotes
• Main features of all animals

  • They are multicellular
  • Their cells contain a nucleus
• DNA sequences can show how closely related different species are

  
• Brachinus armiger and Brachinus hirsutus


  More closely related than any other species in the list as their DNA sequences are identical except for the last but one base
• As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in amino acid sequences can also be used to determine how closely related organisms are

  
• The Five Kingdoms


  • Animals
  • Plants
  • Fungi
  • Protoctists
  • Prokaryotes
• Animals


  • Multicellular
  • Cells contain a nucleus but no cell walls or chloroplasts
  • Feed on organic substances made by other living things
• Plants


  • Multicellular
  • Cells contain a nucleus, chloroplasts and cellulose cell walls
  • Feed by photosynthesis
• Vertebrate classes


  • Fish
  • Amphibians
  • Reptiles
  • Birds
  • Mammals
• Invertebrates


  • Do not possess a backbone
  • Classified based on whether they have legs or not
• Arthropod classes


  • Insects
  • Arachnids
  • Crustaceans
  • Myriapods
• Defining features set groups apart from other groups, while main features are shared between groups
• Fungi


  • Usually multicellular
  • Cells have nuclei and cell walls not made from cellulose
  • Do not photosynthesize but feed by saprophytic or parasitic nutrition
• Protoctists


  • Most are unicellular but some are multicellular
  • All have a nucleus, some may have cell walls and chloroplasts
  • Some photosynthesise and some feed on organic substances
• Prokaryotes


  • Often unicellular
  • Cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria
• Plants


  • At least some parts are green due to chlorophyll
  • Include ferns and flowering plants
• Ferns


  • Have leaves called fronds
  • Reproduce by spores produced on the underside of fronds
• Flowering plants


  • Reproduce sexually by means of flowers and seeds
  • Seeds produced inside the ovary at the base of the flower
• Monocotyledons


  One seed leaf
• Dicotyledons


  Two seed leaves
• Distinguishing monocots and dicots

  • Flowers: monocots have petals in multiples of 3, dicots have petals in multiples of 4 or 5
  • Leaves: monocots have parallel veins, dicots have reticulated veins
• Viruses are not part of any classification system as they are not considered living things
• Viruses


  • Do not carry out the seven life processes for themselves
  • Take over a host cell's metabolic pathways to make copies of themselves
  • Structure is genetic material (RNA or DNA) inside a protein coat
• Protoctists


  A group of simple organisms that are primarily unicellular but some are multicellular. All have a nucleus, some may have cell walls and chloroplasts. Some photosynthesize and some feed on organic substances.
• Unicellular


  Consisting of a single cell.
• Nucleus


  A structure in a cell that contains genetic material.
• Cell wall


  A rigid structure that surrounds the cell membrane.
• Chloroplasts


  Organelles that convert light energy into chemical energy through photosynthesis.
• Multicellular


  Consisting of many cells.