levels of organisation

• • cells are the basic building blocks of all living organisms
  • as an organism develops, cells differentiate to form different types of cells. They become specialised
  • most types of animal cell can differentiate throughout their life
  • as a cell differentiates, it may change shape or different sub-cellular structurs develop to let it carry out a specific function
• nerve cell

  A) axon

  B) ribosome

  C) nucleus

  D) cytoplasm

  E) cell membrane

  F) dendrites

  G) sheath

  
• Muscle Cell

  A) ribosomes

  B) mitochondria

  C) nuclei

  D) cell membrane

  
• Muscle cell

  • Function: contraction for movement
  • Adaptations:
  • There are three different types of muscle in animals: skeletal, smooth and cardiac (heart)
  • All muscle cells have layers of protein filaments in them. These layers can slide over each other causing muscle contraction
  • Muscle cells have a high density of mitochondria to provide sufficient energy (via respiration) for muscle contraction
  • Skeletal muscle cells fuse together during development to form multinucleated cells that contract in unison
• Sperm Cell

  A) flagellum

  B) mitochondria

  C) cytoplasm

  D) nucleus

  E) cell membrane

  F) acrosome

  
• Root hair cell

  A) ribosomes

  B) mitochondria

  C) nucleus

  D) cytoplasm

  E) vacuole

  F) root hair

  G) cell wall

  H) cell membrane

  
• Root hair cell

  • Function: absorption of water and mineral ions from soil
  • Adaptations:
  • Root hair to increase surface area so the rate of water uptake by osmosis is greater (can absorb more water and ions than if SA were lower)
  • Thinner walls than other plant cells so that water can move through easily (due to shorter diffusion distance)
  • Permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water potential gradient
  • Mitochondria for active transport of mineral ions
• Xylem

  A) continuous

  B) water

  C) lignin

  
• Xylem

  • Function: transport tissue for water and dissolved ions
  • Adaptations:
  • No top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
  • Cells are essentially dead, without organelles or cytoplasm, to allow free passage of water
  • Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant
• Phloem

  A) phloem

  B) companion

  C) sugars

  
• Phloem

  • Function: transport of dissolved sugars and amino acids
  • Adaptations:
  • Made of living cells (as opposed to xylem vessels which are made of dead cells) which are supported by companion cells
  • Cells are joined end-to-end and contain holes in the end cell walls (sieve plates) forming tubes which allow sugars and amino acids to flow easily through (by translocation)
  • Cells also have very few subcellular structures to aid the flow of materials