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• 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
• Undifferentiated cells are known as stem cells
• Functions of specialised cells

  • 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 cut an onion and separate it into layers

  3. Use tweezers to peel off a piece of epidermal tissue and place it on the slide

  4. Add a drop of iodine solution as a stain

  5. Place a cover slip over the specimen carefully to avoid air bubbles

  6. Secure the slide on the stage of the microscope

  7. Begin with the lowest-powered objective lens

  8. Adjust the coarse adjustment knob to bring the stage close to the lens without touching

  9. Look through the eyepiece and use the coarse adjustment knob to find the focus

  10. Fine-tune the focus with the fine adjustment knob for a clear image

  11. Switch to a higher-powered objective lens and refocus for greater detail
• Chromosomes


  Structures within the nucleus of cells containing tightly coiled DNA
• Human body cells have 46 chromosomes, which exist as 23 pairs, where each pair is inherited from each parent</b>
• Sex cells (gametes) have half the number of chromosomes (23)
• Cell cycle


  A series of events that cells go through to grow and divide, resulting in the formation of two identical daughter cells
• Stages of the cell cycle

  • Interphase
  • Mitosis
  • Cytokinesis
• Stem cells

  Undifferentiated cells capable of becoming other types of cells, undergoing a process known as differentiation
• Types of human stem cells

  • Stem cells found in early human embryos, with the potential to turn into any cell type
  • Adult stem cells, commonly found in bone marrow, with the ability to 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 on 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, due to the natural, random movement of particles
• Diffusion is a passive process which means it does not use any energy
• Ways to increase the rate of diffusion

  • Increasing the concentration gradient
  • Increasing the temperature
  • Increasing 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
• Characteristics of efficient exchange surfaces

  • Thin membrane for a short diffusion path
  • Large surface area for maximum diffusion
  • Ventilated to maintain a diffusion gradient
• The lungs are responsible for the exchange of oxygen and carbon dioxide, which occurs in millions of tiny air sacs called alveoli
• Adaptations of alveoli for gas exchange

  • Huge surface area
  • Moist lining for dissolving gases
  • Extremely thin walls
  • Surrounded by a dense capillary network
• Carbon dioxide diffuses into air spaces within the leaf for photosynthesis, and oxygen and water vapour exit the leaf through small openings called stomata
• For the crucial exchange of gases: OXYGEN is taken in, and CARBON DIOXIDE is expelled. This exchange occurs in millions of tiny air sacs called ALVEOLI.
• Alveoli

  • Have a HUGE SURFACE AREA —around 75 square meters in humans—to increase the efficiency of gas exchange
  • Possess a MOIST LINING for dissolving gases, which aids in the diffusion process
  • Their WALLS are extremely THIN to minimize the distance gases must diffuse
  • Surrounded by a dense CAPILLARY NETWORK, ensuring a rich blood supply and rapid gas exchange
• Gas Exchange in Plant Leaves

  • CARBON DIOXIDE diffuses into AIR SPACES within the leaf for photosynthesis
  • Leaves have an EXCHANGE SURFACES underneath, consisting of small openings called STOMATA
  • OXYGEN and WATER VAPOUR exit the leaf through these stomata
  • The shape of the leaf and the arrangement of cells optimize the internal surface area for gas exchange
• Adaptations for Gas Exchange in Plant Leaves

  • Stomata are flanked by GUARD CELLS that regulate their opening, ensuring gas exchange occurs only when necessary
  • The FLATTENED SHAPE of the leaf increases the surface area for gas exchange
  • Internal cell walls also contribute to a larger exchange surface, with air spaces to facilitate DIFFUSION