Biology - Science :)

• 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
• 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)
• Electron microscopes


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

  How much larger the microscope makes the object appear
• Preparing and observing slides

  1. Start with a clean microscope slide

  2. Add a drop of water

  3. Carefully place a piece of onion epidermal tissue onto the slide

  4. Add a drop of iodine solution as a stain

  5. Carefully place a cover slip over the specimen
• Using a light microscope

  1. Secure the slide on the stage

  2. Begin with the lowest-powered objective lens

  3. Adjust the coarse adjustment knob to bring the stage close to the lens

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

  5. Fine-tune the focus with the fine adjustment knob

  6. Switch to a higher-powered objective lens and refocus
• 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

  • Growth and DNA replication
  • Mitosis
  • Cell division
• 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 (can turn into any cell type)
  • Adult stem cells (commonly found in bone marrow, can only differentiate into different types of blood cells)
• 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
• Diffusion is a passive process which means it does not use any energy
• The efficiency of exchange surfaces by diffusion is determined by the surface area to volume ratio (SA:V)
• A high SA:V ratio is beneficial for diffusion as it provides a larger surface area relative to the volume of the organism
• Adaptations of alveoli for gas exchange

  • Huge surface area
  • Moist lining
  • Extremely thin walls
  • Surrounded by dense capillary network
• Adaptations of leaves for gas exchange

  • Carbon dioxide diffuses into air spaces within the leaf
  • Leaves have an exchange surface underneath consisting of stomata
  • Oxygen and water vapour exit the leaf through the stomata
  • The shape of the leaf and arrangement of cells optimize the internal surface area for gas exchange
• Crucial exchange of gases


  Oxygen is taken in, and Carbon Dioxide is expelled
• 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
• Oxygen and Water Vapour


  Exit the leaf through stomata
• Adaptations for Gas Exchange in Leaves

  • Stomata flanked by guard cells to regulate opening
  • Flattened shape increases surface area
  • Internal cell walls contribute to larger exchange surface with air spaces to facilitate diffusion
• Villi


  Tiny projections in the small intestine that expand the surface area for nutrient absorption
• Structure of Villi


  • Single layer of surface cells
  • Rich supply of blood capillaries to facilitate quick absorption of digested nutrients
• Adaptations of Gills for Gas Exchange

  • Made of thin plates called gill filaments providing large surface area
  • Filaments covered in numerous lamellae which further increase surface area
  • Lamellae rich in blood capillaries for rapid gas diffusion
  • Thin surface layer of cells in lamellae minimizes diffusion distance
  • Blood flows in one direction, water in opposite, maintaining oxygen concentration gradient
  • Oxygen concentration in water is always higher than in blood, facilitating diffusion
• Osmosis


  The process where water molecules move from an area of high water concentration to an area of low water concentration across a partially permeable membrane
• Partially Permeable Membrane


  • Has tiny holes that allow only small molecules like water to pass through, preventing larger molecules like proteins and sucrose from moving across
• Water molecules move in both directions across the membrane during osmosis, but there is a net movement of water towards the region with fewer water molecules</b>