Chapter 1 Cell Structure & Organisation

• Protoplasm of a cell is made up of three parts

  – cell membrane

  – cytoplasm

  – nucleus
• Cell Membrane

  • The cell membrane surrounds the cytoplasm
  • Made up of lipids and proteins
  • It is partially permeable, allowing only small and soluble substances to pass through
• Cell Wall


  • The cell wall is made of cellulose
  • It is fully permeable
  • It protects the cell from injury and gives the cell a fixed shape
• Cytoplasm


  • Found between the cell membrane and the nucleus
  • Site of cellular activities
  • Contain specialised structures called organelles.
• Nucleus


  • Controls cell activities
  • Essential for cell division
  • Cells, without a nucleus like the red blood cells, are unable to divide

  
  

  • Chromosomes:

  1. Long thread-like structure found within the nucleus
  2. Made up of deoxyribonucleic acid or DNA which carries hereditary information
  3. Condense into thick, rod-shaped structures when the cell is dividing

  • Nuclear membrane:

  1. Separates the contents of the nucleus from the rest of the cytoplasm
• Endoplasmic Reticulum: Rough ER (RER) 


  • Network of flattened spaces lined with a membrane
  • Outer surface of RER is continuous with the nuclear envelope
  • RER appears rough because its surface is studded with ribosomes
  • Function: transports proteins made by the ribosomes to the Golgi apparatus
• Ribosomes


  • Small round structures
  • Either attached to RER or lie freely in cytoplasm
  • Responsible for protein synthesis
• Endoplasmic Reticulum : Smooth ER (SER)


  
  

  • SER is more tubular than RER
  • Does not have ribosomes attached to its surface
  • Functions:

  1. synthesises substances such as fats and steroids
  2. involved in detoxification
• Golgi Body


  • Golgi apparatus consists of flattened spaces surrounded by membranes
  • Functions:

  1. chemically modifies substances by the ER
  2. stores and packages the substances in vesicles for secretion out of the cell
• Golgi Body 


  1. Vesicles containing substances made by the ER pinch off from the ER
  2. Vesicles fuse with the Golgi body releasing the substances made by the ER which may be modified.
  3. Secretory vesicles containing modified substances pinch off from the Golgi body and move towards the cell membrane.
  4. Secretory vesicles fuse with the cell membrane and their contents exit the cell

  
• Mitochondria


  • Oval or sausage-shaped organelles
  • Site of aerobic respiration
  • They oxidise food to release energy for cellular activities.
• Chloroplasts

  • Oval structures found in plant cells
  • Contains a green pigment called chlorophyll, which is required for photosynthesis to occur
• Vacuole


  • Fluid filled space enclosed by a partially permeable membrane
  • Store substances within the cell
  • In a plant cell: usually has one large central vacuole that consists of substances such as sugars, mineral salts and amino acids
  • In a animal cell: usually has numerous small vacuoles that store water and food substances, exist temporarily
• Differentiation 


  • The process by which a cell becomes specialised for a specific function
• Red Blood Cell


  • Contains haemoglobin : Binds to oxygen and transports it around the body
  • Circular biconcave shape : Increases surface area-to volume ratio for increased rate of oxygen uptake
  • Absence of nucleus : Allows packing of more haemoglobin for transport of oxygen
  • Flexible : Easily squeezes through capillaries
• Muscle Cell


  • Contain many mitochondria : Provide energy for contraction of muscle cell
  • Has contractile protein fibres : Contract and relax to bring about movement
  • Has many nuclei : Allow for cell division
• Root Hair Cell


  • Long and narrow extension : Increase surface area to volume ratio for increased rate of absorption of water and mineral salts
  • Maintains a lower water potential in vacuole : Allow water to enter the root hair cell via osmosis