BIOLOGY TERM 2 - ORGANISATION OF LIVING THINGS

• Cell components


  Cell membrane, cytoplasm, ribosomes, genetic material
• Types of organisms


  • Unicellular
  • Multicellular
  • Colonial
• Unicellular organisms


  • Prokaryotes lack organelles but are efficient
  • Eukaryotes have specialised organelles
• Advantage of unicellular organisms


  Small size and high surface area to volume ratio allows easy transport of nutrients, wastes, water and gases
• Colonial organisms


  • Cells are identical
  • Some cells have specialised functions coordinated with other cells
• Seven life processes

  • Movement
  • Reproduction
  • Sensitivity
  • Growth
  • Respiration
  • Excretion
  • Nutrition
• Examples of colonial organisms

  • Volvox
  • Coral
  • Jellyfish
• Volvox


  • Colony of green algal cells in a hollow sphere
  • 500-60,000 cells
  • Each cell has a flagella and connected by cytoplasmic strands
  • Allows coordinated swimming
  • One cell thick with a red spot that detects light
  • Cells at one end have more developed eye spots to detect light
  • Most cells have chloroplasts, few absorb nutrients
• Choanaflagellates


  Collared flagellates, can exist as free-living unicellular or in colonies, evolutionary link between unicellular and multicellular
• Archea, Bacteria, Eukaryotes are the three domains of life
• Unicellular organisms are found in Archea and Bacteria, multicellular in Eukaryotes
• Prokaryotes lack nucleus and cell-bound organelles, Eukaryotes have them
• Unicellular organisms are found in Archea, Bacteria and Eukaryotes
• High surface area to volume ratio helps unicellular organisms absorb nutrients and gases
• Colonial life form


  Many cells living independently or working together
• Cell differentiation


  Process where stem cells become specialised to perform particular functions
• Multicellular organisms have small surface area to volume ratio, so cells become specialised
• Specialised cells


  • Structure modified to perform specific functions
  • Red blood cells are flat and biconcave to increase surface area for oxygen diffusion
  • Small size to pass through capillaries
  • No nucleus or organelles to carry more hemoglobin
• Tissue


  Group of specialised cells performing specific functions
• Organ


  Group of tissues with a specific function
• Organ system


  Group of organs working together
• Meristematic tissue


  Found at tips of roots and shoots, where cell division occurs
• Autotroph


  Organism that makes its own food from inorganic substances
• Heterotroph


  Organism that obtains nutrients from external sources
• Epithelial tissue


  Covers body surfaces, protects organs, forms glands
• Epithelial tissue does not contain blood vessels and relies on connective tissue for nutrients
• Epithelial tissue


  • Cells are organised and very close together, acting as barriers
• Plant organs


  • Roots
  • Stems
  • Leaves
  • Reproductive parts
• Gas exchange


  Exchange of gases, particularly oxygen and carbon dioxide, in organisms
• Root functions


  • Anchor/fix the plant
  • Absorb water and minerals
• Root structure


  • Fibrous roots
  • Tap root
  • Root cap
  • Zone of elongation
  • Zone of maturation
• Single-celled organisms


  • Diffusion is the main mode of exchange of material.
  • They use diffusion to absorb and release gases.
  • Due to their small size, single-celled organisms have high surface area where gas exchange can occur.
  • They have a thin surface which makes the diffusion pathway shorter
• Apical meristem


  Where cell division (mitosis) occurs, pushing the root through soil
• Insects


  • They have a tracheal system for gas exchange
  • Trachea contains pores called spiracles through which air moves
  • Oxygen moves into the cell down a concentration gradient
  • Carbon dioxide moves out of the cell down a concentration gradient
  • Rhythmic abdominal movements facilitate air movement in and out of the spiracles
• Plant types


  • Vascular plants
  • Non-vascular plants
• Vascular plants


  • Have a transport system of xylem and phloem to move substances
• Xylem


  Transports water and dissolved minerals from roots to leaves
• Gas exchange in humans


  1. Gases enter via nasal cavity and mouth

  2. Epiglottis ensures gases pass into trachea, not oesophagus

  3. Trachea splits into bronchi which further divide into bronchioles

  4. Bronchioles end in alveoli

  5. Capillaries surround alveoli for gas exchange

  6. Diaphragm and rib muscles control inhalation and exhalation
• Phloem


  Transports sugars and other plant products from one part to another
• Non-vascular plants


  • Do not have a transport system, rely on diffusion and osmosis