3.5 Cell Specialisation and Organisation

Annotations:

• AQA A Level Biology Specification from 2015 (what will be in the exam and what you NEED to know)  states: In complex multicellular organisms, eukaryotic cells become specialised for specific functions. Specialised cells are organised into tissues, tissues into organs and organs into systems. Students should be able to apply their knowledge of these features in explaining adaptations of eukaryotic cells.

1. Tissues
   1. Tissue: A group of similar cells that perform a specific functions
   2. Epithelial tissues
      1. Found in animals
      2. Sheets of cells
      3. Line surfaces of organs and often have a protective or secretory function
      4. Some are thin, flat cells that line organs where diffusion takes place, e.g/ the alveoli of the lungs
         1. Another example is the ciliated epithelium that lines a duct such as the trachea
            1. The cilia are used to move mucus over the epithelial surface
   3. Xylem
      1. Occurs in plants
      2. Made up of similar cell types
      3. Used to transport water and mineral ions throughout the plant and also gives mechanical support
2. Organs
   1. Organ: A combination of tissues that are coordinated to perform a variety of functions, although they often have one predominant major function
   2. E.g/ Animal - Stomach
      1. Stomach is an organ that is involved in the digestion of certain types of food.
         1. Muscle tissue to churn and mix the contents
         2. epithelium to protect the stomach wall and produce secretions
         3. Connective tissue to hold together the other tissues
   3. E.g/ Plant - Leaf
      1. Palisade mesophyll made up of leaf palisade cells that carry out photosynthesis
      2. Spongy mesophyll layer adapted for gaseous diffusion
      3. Epidermis to protect the leaf and allow gaseous diffusion
      4. Phloem to transport organic materials away from the leaf
      5. Xylem to transport water and ions into the leaf
3. Organ Systems
   1. Organ System: A group of organs that work together to perform one or more functions
   2. Digestive System: Digests and processes food
      1. Salivary Glands
      2. Oesophagus
      3. Stomach
      4. Duodenum
      5. Ileum
      6. Pancreas
      7. Liver
   3. Respiratory System: Used for breathing and gas exchange
      1. Trachea
      2. Bronchi
      3. Lungs
   4. Circulatory System: Pumps and circulates blood
      1. Heart
      2. Arteries
      3. Veins