cell structure and organisation

• cell organisation

  • cells with a nucleus divide through cell division to replace worn-out or damaged cells
  • they continue to carry out the functions of the cells they replaced
  • in order to perform specific functions, cells differentiate into specialised cells
• red blood cells: adaptations to function

  • contains haemoglobin which binds reversibly to oxygen, enabling transport of oxygen from the lungs to other parts of the body
  • flat, round, biconcave shape increase SA:V, increasing the rate at which oxygen diffuses into and out of the cell
  • elastic and can turn bell shaped to squeeze through blood vessels smaller than itself in diameter
  • absence of nucleus and mitochondria, enabling the cell to carry more haemoglobin and oxygen
• root hair cells: adaptations to function

  • long and narrow root hair protrudes out of the cell, increasing SA:V, which increases rate of absorption of water molecules and inorganic ions from the soil
  • high density of mitochondria to release energy for active transport
  • thin cell wall and more concentrated cytoplasm and cell sap to facilitate transport of water into the cell
• xylem cell: adaptations to function

  • walls strengthened by lignin to prevent vessel from collapsing inwardly during water flow
  • absence of protoplasm and cross walls in central lumen prevent disruption of water flow in the vessel
  • xylem cells are bundled together to provide mechanical support to the whole plant
  • long and narrow to enhance the effect of capillary action and prevent formation of air bubbles which impede water flow
• living cells consist of protoplasm, which is made up of cell surface membrane, cytoplasm, and nucleus
• what does protoplasm consist of?

  cytoplasm, nucleus, and cell surface membrane
• an organism is a collection of chemical molecules which work together to enable life functions such as: movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition 
• • cells are the building blocks of all living organisms and are capable of specific functions to ensure the survival of the living organism
  • all cells are developed from undifferentiated cells which grow into different types of cells as they mature
• • movement: ability of the organism to move to hunt for prey or reach out to other sources of nutrients
  • respiration: the process of oxidising glucose to release energy required for locomotion and growth 
  • sensitivity: responds to external influence called stimuli 
  • growth: physical growth as the organism changes and develops
  • reproduction: produce offspring to pass on genetic materials
  • excretion: removal of metabolic waste products (substances that cannot be used by the organism)
  • nutrition: consume food and process the food into forms that can be used by the organism to sustain life
• light microscope vs. electron microscope:

  • light microscope can produce a resolution of 200um; visualises organelles such as chloroplasts, cell surface membrane, cell wall, cytoplasm, vacuole, nucleus
  • electron microscopes can produce a resolution of 0.2um; in addition to organelles visible under light microscope, it shows organelles such as endoplasmic reticulum, mitochondria, golgi apparatus, ribosomes
  • longitudinal sections are slices along the length of a cell and transverse sections are taken across the length of a cell