Nature & Variety of living organisms

• Criteria for something to be considered 'living'

  • Movement
  • Respiration
  • Sensitivity
  • Control
  • Growth
  • Reproduction
  • Excretion
  • Nutrition
• If something does not carry out all of these life processes, it is either dead or non-living
• Viruses are a good example of non-living particles/agents
• Nutrition


  Organisms must obtain food to provide energy
• Nutrition in plants


  Plants use sunlight, carbon dioxide and water to produce oxygen and glucose in the process of photosynthesis
• Nutrition in animals


  Animals consume other living organisms in order to obtain the energy they require
• Autotrophs make their own food whereas heterotrophs obtain it from a range of food sources
• Autotroph


  Comes from 'auto' = 'self' and 'trophic' = 'feeding'
• Heterotroph


  Comes from 'hetero' = 'different' and 'trophic' = 'feeding'
• Respiration


  A chemical reaction carried out in all living organisms
• Respiration


  1. Energy is released from glucose either in the presence of oxygen (aerobic respiration) or the absence of oxygen (anaerobic respiration)

  2. The reactions ultimately result in the production of carbon dioxide and water as waste products

  3. Energy is transferred in the form of ATP

  
• Excretion


  The removal of toxic materials and substances from organisms
• Waste products excreted by animals

  • Carbon dioxide from respiration
  • Water from respiration and other chemical reactions
  • Urea which contains nitrogen resulting from the breakdown of proteins
• Waste products excreted by plants

  • Oxygen from photosynthesis
  • Carbon dioxide from respiration
  • Water from respiration and other chemical reactions
• Sensitivity


  The ability to detect and respond to stimuli in the surroundings
• Sensitivity responses in animals

  • The nervous system provides a complex system of receptors, neurones and effectors which detect and respond to different stimuli using electrical impulses
  • The endocrine system allows a response to stimuli using chemical messengers, which travel in the blood, called hormones
• Sensitivity responses in plants

  • Geotropism describes a plant's response to gravity which causes the roots to grow down into the soil
  • Phototropism describes a plant's response to light which causes shoots to grow towards sunlight
• Movement


  An action by an organism causing a change of position or place
• Plants cannot move from place to place but can change their orientation
• Control


  Living organisms must control their internal environment in order to keep conditions within required limits
• Homeostasis


  The control of an organism's internal environment to maintain stable conditions
• Homeostatic mechanisms in humans


  • Thermoregulation (control of body temperature)
  • Glucoregulation (control of blood glucose levels)
  • Osmoregulation (control of water levels)
• Homeostatic mechanisms in plants


  • Transpiration to maintain a suitable temperature
• Reproduction


  The process that leads to the production of more of the same kind of organism
• Types of reproduction

  • Sexual
  • Asexual
• Sexual reproduction


  The male and female gametes fuse together
• Asexual reproduction


  Cells or whole organisms can reproduce using asexual reproduction
• Mitosis is an example of asexual reproduction
• Asexual reproduction in plants


  • Tubers
  • Budding
  • Runners
• Single-celled organisms such as bacteria or amoeba reproduce asexually
• Growth


  A permanent increase in size
• In animals, an individual grows larger between the zygote and adult stage with changes in proportion or shape
• All living organisms can be grouped or 'classified' using a classification system that consists of five kingdoms
• The five kingdoms

  • Animals
  • Plants
  • Fungi
  • Protoctists
  • Prokaryotes
• Animals, plants, fungi and protoctists are all eukaryotic organisms (also known as eukaryotes)
• Eukaryotic organisms can be multicellular or single-celled and are made up of cells that contain a nucleus with a distinct membrane
• Prokaryotic organisms (also known as prokaryotes) are in a separate kingdom and are different from eukaryotes as they are always single-celled and do not contain a nucleus
• Bacteria are prokaryotic organisms
• Prokaryotic cells are substantially smaller than eukaryotic cells
• The nuclear material of prokaryotic cells is found in the cytoplasm