biology paper 1 OCR a level

• The cell membrane is a selectively permeable barrier that regulates the movement of substances in and out of the cell.
• Four different types of microscopes:

  • Light or Optical microscopes have poor resolution due to the wavelength of light
  • Transmission electron microscopes have higher magnification and resolution, electrons pass through the specimen
  • Scanning electron microscopes create a 3D image by bouncing electrons off the surface
  • Laser scanning confocal microscopes are high resolution, 3D, and use laser light
• Resolution is the minimum distance between two objects where they can still be viewed as separate

  • In light microscopes, resolution is determined by the wavelength of light
  • In electron microscopes, resolution is determined by the wavelength of an electron
  • Magnification refers to how many times larger the image is compared to the actual object
• Four types of slide preparation for light microscopes:

  • Dry Mount
  • Wet Mount
  • Squash Slide
  • Smear Slide
• Eyepiece graticule:

  • Scale in the eyepiece to measure the size of the object
  • Different magnifications require calibration using a stage micrometer
• Magnification calculation:

  • Size of the image divided by the size of the real object
  • Units may need to be converted (e.g., millimeters to micrometers)
• Staining:

  • Some cell components are difficult to see without staining
  • Crystal violet and methylene blue are commonly used stains
  • Differential staining uses different stains for different cell parts
• Gram staining:

  • Used to identify bacteria types
  • Gram-positive bacteria retain Crystal Violet stain, appear blue or purple
  • Gram-negative bacteria do not retain Crystal Violet, counterstained red
• Scientific drawings:

  • Accurate drawings under a microscope
  • Must include title, magnification, annotations, no coloring or shading
• Electron microscopes:

  • Use a beam of electrons for imaging
  • Higher resolution than light microscopes
  • Specimen must be in a vacuum, image is black and white
• Transmission electron microscopes:

  • Specimen must be thin, electrons pass through
  • Useful for visualizing internal structures of cells
• Scanning electron microscopes:

  • Specimen does not need to be thin, electrons bounce off the surface
  • Creates a 3D image
• Laser scanning confocal microscope:

  • Uses high light intensity and fluorescent dye
  • Combines high resolution with depth selectivity, creates 3D images
• Organelles in eukaryotic cells:

  • Nucleus, flagella, cilia, centrioles, cytoskeleton, endoplasmic reticulum, Golgi apparatus
• Endoplasmic reticulum:

  • Rough ER: site of protein synthesis
  • Smooth ER: site of lipid and carbohydrate synthesis
• Golgi apparatus:

  • Modifies, sorts, and packages proteins for transport
• Vesicles:

  • Membrane-bound sacs that transport materials within the cell
• Mitochondria:

  • Site of cellular respiration, produces ATP
• Lysosomes:

  • Contain digestive enzymes to break down waste and cellular debris
• Vacuoles:

  • Store water, nutrients, or waste products
• Chloroplasts:

  • Site of photosynthesis in plant cells
• Ribosomes:

  • Site of protein synthesis
• Cell membrane:

  • Semi-permeable membrane that controls what enters and exits the cell
• Cell wall:

  • Provides structure and support in plant cells
• Nucleolus:

  • Site of ribosome synthesis within the nucleus
• Centrioles:

  • Involved in spindle fiber formation during cell division
• Cytoskeleton:

  • Network of fibers that provide mechanical strength and shape to the cell
• Scientific drawings:

  • Accurate representations of specimens under a microscope
  • Must include title, magnification, annotations, no coloring or shading
• Organelles in prokaryotic cells:

  • Lack membrane-bound organelles
  • Have ribosomes, cell wall, and plasma membrane
• Plasma membrane:

  • Semi-permeable membrane that controls what enters and exits the cell
• Cell wall:

  • Provides structure and support in prokaryotic cells
• Flagella:

  • Whip-like tail structure for mobility
• Pili:

  • Hair-like structures for attachment and DNA transfer
• Capsule:

  • Protective layer outside the cell wall
• Nucleoid:

  • Region where DNA is located in prokaryotic cells
• Plasmids:

  • Small, circular DNA molecules in prokaryotic cells
• Endospores:

  • Dormant, tough, non-reproductive structures for survival
• Binary fission:

  • Asexual reproduction method in prokaryotic cells
• Conjugation:

  • DNA transfer between prokaryotic cells
• Transformation:

  • Uptake of foreign DNA by prokaryotic cells