BIOLOGY

• Prokaryotic cells

  Cells that do not have a nucleus
• Eukaryotic cells


  Cells that have a nucleus where their genetic material is stored, are larger and more complex than prokaryotic cells
• Components of eukaryotic cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Components of plant cells

  • Rigid cell wall
  • Permanent vacuole
  • Chloroplasts
• Animal cells do not have cell walls or chloroplasts, and usually have smaller vacuoles compared to plant cells
• Bacterial cells

  Prokaryotic cells that have a single circular strand of DNA and may have additional small rings of DNA called plasmids
• Differentiation

  The process where a cell transforms into a specialised cell for a specific job, involving the development of different subcellular structures
• In mature animals, the ability to differentiate is mainly used for repairing and replacing cells, such as skin or blood cells</b>
• Plants never lose their ability to differentiate
• Specialised cells and their functions

  • Sperm cells (reproduction)
  • Nerve cells (sending electrical signals)
  • Muscle cells (contraction)
  • Root hair cells (absorbing water and minerals)
  • Phloem cells (transporting food substances)
  • Xylem cells (transporting water and minerals)
• Light microscopes


  Use light and lenses to magnify specimens, allowing us to see individual cells and large subcellular structures like nuclei
• Electron microscopes

  Use electrons to form an image and can magnify much more than light microscopes, showing finer details of cell structures like mitochondria and chloroplasts
• Magnification

  How much larger the microscope makes the object appear
• To calculate magnification, use the formula: Magnification = Size of image / Size of object
• Standard form

  A way to write very large or small numbers by moving the decimal point and multiplying by a power of 10
• Preparing and observing slides

  1. Add a drop of water to a clean slide

  2. Carefully place a piece of onion epidermal tissue onto the water

  3. Add a drop of iodine solution as a stain

  4. Carefully place a cover slip over the specimen

  5. Secure the slide on the microscope stage and use the coarse and fine adjustment knobs to focus
• Chromosomes

  Structures within the nucleus of cells containing tightly coiled DNA
• Human body cells have 46 chromosomes, which exist as 23 pairs, with each pair inherited from each parent
• Gametes

  Sex cells that have half the number of chromosomes (23)
• The cell cycle


  1. Growth and DNA replication

  2. Mitosis

  3. Cell division
• Stem cells


  Undifferentiated cells capable of becoming other types of cells through differentiation
• Types of human stem cells

  • Stem cells found in early human embryos (can turn into any cell type)
  • Adult stem cells (commonly found in bone marrow, can only differentiate into different types of blood cells)
• Stem cells can be grown in labs and differentiated into specialised cells for medicine or research
• Debate surrounds stem cell research, particularly concerning the use of human embryos
• Plant stem cells

  Found in meristem tissue at the tips of plant shoots and roots, can differentiate into any type of plant cell
• Diffusion

  The process of particles spreading from an area of higher concentration to an area of lower concentration, resulting in them being evenly spaced
• Diffusion is a passive process that does not use any energy
• Ways to increase the rate of diffusion

  • Increase the concentration gradient
  • Increase the temperature
  • Increase the surface area of the membrane
• Larger organisms have a smaller surface area to volume ratio than smaller organisms
• A high surface area to volume ratio is beneficial for diffusion as it provides a larger surface area relative to the volume of the organism
• Alveoli

  Tiny air sacs in the lungs responsible for gas exchange
• Adaptations of alveoli for gas exchange

  • Huge surface area
  • Moist lining
  • Extremely thin walls
  • Surrounded by a dense capillary network
• Stomata

  Small openings on the underside of leaves that allow carbon dioxide to diffuse in and oxygen and water vapour to exit
• Crucial exchange of gases

  Oxygen is taken in, and Carbon Dioxide is expelled
• Alveoli

  Millions of tiny air sacs where gas exchange occurs
• Adaptations of Alveoli for Gas Exchange

  • Huge surface area to increase efficiency
  • Moist lining for dissolving gases
  • Extremely thin walls to minimize diffusion distance
  • Surrounded by dense capillary network for rapid gas exchange
• Gas Exchange in Plant Leaves

  Carbon Dioxide diffuses into air spaces within the leaf for photosynthesis
• Exchange surfaces in leaves

  Small openings called stomata
• Stomata

  Flanked by guard cells that regulate their opening
• Adaptations for Gas Exchange in Leaves

  • Flattened shape increases surface area
  • Internal cell walls contribute to larger exchange surface with air spaces to facilitate diffusion