05 May 2021

2.2. Levels of organisation

Multicellular plants and animals contain many different types of cells. Each type of cell is designed for a particular function.

Levels of organisation: cell --> tissue --> organ --> organ system --> organism

1. Ciliated cells - in the respiratory tract

          • Feature: cilia (tiny hairs) that can move mucus
      • Function: waft mucus with bacteria and dust away from lungs through the bronchi and trachea

2. Root hair cells 

      • Feature: hair gives a large surface area
      • Function: absorb water and minerals; anchor the plant firmly in the soil

3. Xylem vessels
  • Feature:
    • long, thin cells arranged end-to-end to form vessels (tubes)
    • cells lack end walls and cell contents (cytoplasm, nucleus)
    • walls become lignified
  • Function:
    • transport water and mineral ions from roots to leaves
    • lignin provides strength for stem, makes vessels waterproof

4. Palisade mesophyll cells

      • Feature: column-shaped cells, packed with chloroplasts
      • Function: trap sunlight to make food for the plant by photosynthesis

5. Nerve cells 
  • Feature:
    • very long and able to conduct electrical impulses
    • some have fatty sheath for insulation
  • Function: carry electrical impulses to/from the brain and spinal cord

6. Red blood cells
  • Feature:
    • no nucleus
    • contains haemoglobin
  • Function: transport oxygen around the body


7. Sperm and egg cells

Sperm cells:
  • Features:
    • tail to swim
    • nucleus carries genetic information
  • Function: reproduction, by penetrating an egg cell

Egg cells:
  • Features:
    • large amount of cytoplasm containing yolk droplets, made from protein and fat
    • nucleus carries genetic information
  • Function: reproduction

Levels of organisation

  • Tissue
    • a group of cells with similar structures
    • cells work together to perform a shared function
  • Organ:
    • a structure made up of a group of tissues
    • tissues work together to perform specific functions
  • Organ system:
    • a group of organs with related functions
    • organs work together to perform body functions

For the original post, click on Cell Functions and Tissues, Organs and Organ systems
For past papers, click here.

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