Module 2

• Compare the differences between unicellular, colonial and multicellular organisms by:

  1. Investigating structures at the level of the cell and organelle

  2. Relating structure of cells and cell specialisation to function
• Justify the hierarchical structural organisation of organelles, cells, tissues, organs, systems and organisms
• Cells


  Carry out all the functions to sustain life
• Cells are considered living because they exhibit:

  • Growth - they get bigger over time
  • Assimilation - they take in resources from the external environment and build them into their own parts, so they can grow
  • Metabolism - biochemical reactions take place for life, and heat is produced as a by-product
  • Excretion - toxic and excess substances must be removed
  • Response - reacting to environmental stimulus
  • Reproduce
• Unicellular Prokaryotic Organisms


  • Appear in the fossil record as first life on Earth 3.8 billion years ago and are still present today
  • Single celled prokaryotes (no membrane bound organelles)
  • Each single cell must be able to carry out all the functions of life in order to survive
  • Reproduce quickly (about every 30 minutes)
  • Have adapted to a very wide range of environment - cold, hot, no oxygen, acid, basic, dry, wet, no sunlight, bright sunlight
• Unicellular Eukaryotic Organisms


  • Appear in the fossil record about 2.7 billion years ago
  • Single celled eukaryotes (membrane bound organelles - the endosymbiosis theory)
  • Specialisation occurred allowing survival in different environments. Cells with chloroplasts could make their own organic molecules. Cells with mitochondria could extract energy from organic molecules
  • These special cells later gave rise to plants and animals
• Colonial Organisms


  • Are the result of many individual cells joining together to form a colony
  • Possibly appear around 2 billion years ago
  • The cooperation between like cells is observed today when bacteria can form colonies as films
  • Living in a group provides safety in numbers, better strategy for obtaining food and therefore a survival advantage
  • Volvox is a colony organism of up to 50 000 algae cells
  • Interesting fact: the bluebottle is a colonial organism
• Multicellular Organisms


  • The fossil record shows evidence of multicellular life from about 0.7 billion years ago (700 million)
  • Multicellular life is composed of differentiated cells (they are structurally different from each other) that have specialist roles
  • Each specialist cell is more efficient at it role that a non specialist cell, Making the whole organism more efficient
  • Each group of specialist cells (tissue) are essential to the survival of the multicellular organism and without a particular specialist group the entire organism will die
  • All the cells have identical DNA, but they have different genes activated to make them differentiated and specialised
• The momentous transition to multicellular life may not have been so hard after all.
• The Octopus is an alien
• Multicellular organisms can be made of trillions of cells.
• Of those trillions there are 200 of specialist types of cells.
• Each type of cell may have different organelle numbers, e.g. muscles cells have more mitochondria than other animal specialist cells, plant leaf cells have more chloroplasts than other plant cells.
• Hierarchy

  Of cellular organisation in multicellular organisms
• The more complex an organism, the greater its specialist needs.
• Each body system in a human fulfils a life essential role.
• Auto


  Self
• Hetero


  Other
• Troph


  Feeding
• Investigate the structure of autotrophs through the examination of a variety of materials, for example:


  1. Dissected plant materials

  2. Microscopic structures

  3. Using a range of imaging technologies to determine plant structure
• Investigate the function of structures in a plant, including but not limited to:

  Tracing the development and movement of the products of photosynthesis
• Investigate the gas exchange structures in animals and plants through the collection of primary and secondary data and information, for example:

  1. Microscopic structures: alveoli in mammals and leaf structure in plants

  2. Macroscopic structures: respiratory systems in a range of animals
• Interpret a range of secondary-sourced information to evaluate processes, claims and conclusions that have led scientists to develop hypotheses, theories and models about the structure and function of plants, including but not limited to:

  1. Photosynthesis

  2. Transpiration-cohesion-tension theory
• Trace the digestion of foods in a mammalian digestive system, including:

  1. Physical digestion

  2. Chemical digestion

  3. Absorption of nutrients, minerals and water

  4. Elimination of solid waste
• Root System


  • The main function is to grow the roots towards water (hydrotropism)
  • Primary root - originates from the seed
  • Lateral (side) roots - enhance the roots anchoring and allow for greater surface area for collection of water and nutrients
  • Fibrous - an adaptation to drier conditions,spreading out under the surface soil to collect surface water quickly
  • Tap - one main root burrows deep to get stored groundwater
• Root growth zone

  • The tip of the root needs to push through abrasive soil and rock as the root grows and so it is covered in a later of dead cells called the root cap. As it wears away it is continually replaced.
  • The apical meristem contains cells that are rapidly dividing by mitosis. These new cells replace root cap cells AND mature in the zone of elongation.
  • In the zone of elongation cells become longer, increasing the length of the root. Some cells differentiate to become vascular tissue (transport tubes).
  • In the zone of maturation significant cell differentiation occurs and root 'hairs' grow.
  • Root hair cells have a unique structure that increases the root surface area for more efficient collection of water and nutrients.
• Diffusion


  The movement of particles from an area of high concentration to an area of low concentration
• Osmosis


  The movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane
• Fertile soil typically contains negatively charged clay particles to which positively charged mineral ions (cations) may attach
• Minerals that need to be taken up from the soil include Mg2+ (for chlorophyll), nitrates (for amino acids), Na+, K+ and PO43–
• Mineral ions may passively diffuse into the roots, but will more commonly be actively uploaded by indirect active transport
• Root cells contain proton pumps that actively expel H+ ions (stored in the vacuole of root cells) into the surrounding soil
• The H+ ions displace the positively charged mineral ions from the clay, allowing them to diffuse into the root along a gradient
• Negatively charged mineral ions (anions) may bind to the H+ ions and be reabsorbed along with the proton
• Transpiration

  The loss of water vapour from the stems and leaves of plants
• Light energy converts water in the leaves to vapour, which evaporates from the leaf via stomata
• New water is absorbed from the soil by the roots, creating a difference in pressure between the leaves (low) and roots (high)
• Transpiration stream


  The flow of water through the xylem from the roots to the leaves
• Xylem structure

  • Vessel elements should be drawn as a continuous tube (tracheids will consist of interlinking tapered cells)
  • The remnants of the fused end wall can be represented as indents (these forms perforated end plates)
  • The xylem wall should contain gaps (pits), which enable the exchange of water molecules
  • Lignin can be represented by either a spiral (coiled) or annular (rings) arrangement
• Water is lost from the leaves of the plant when it is converted into vapour (evaporation) and diffuses from the stomata