cell biology

• Cells are the basic building blocks of life and the smallest unit of life that can replicate independently
• Animal and plant cells are examples of eukaryotic cells
• Bacterial cells are prokaryotic cells
• Animal and plant cells are multicellular, while bacterial cells are unicellular
• Animal and plant cells contain cell membranes, a nucleus, cytoplasm, mitochondria, and ribosomes
• Plant cells have additional structures compared to animal cells:

  • Rigid cell wall made of cellulose for support and structure
  • Permanent vacuole containing cell sap
  • Chloroplasts for photosynthesis
• Bacterial cells have a cell membrane, cell wall, ribosomes, and cytoplasm
• Bacterial cells do not have mitochondria or chloroplasts
• Bacterial cells have a single circular strand of DNA called the nucleoid
• Some bacteria may have plasmids, which carry extra genes like antibiotic resistance
• Some bacteria have flagella for movement
• Light microscopes:

  • Small, easy to use, and relatively cheap
  • Resolution limited to 0.2 micrometers due to reliance on light with the same wavelength
  • Can be used to see individual cells like onion cells, but not suitable for studying subcellular structures like mitochondria
• Electron microscopes:

  • Big, expensive, and hard to use
  • Use electrons instead of light, with a wavelength of 0.1 nanometers
  • Maximum resolution is 0.1 nanometers, 2,000 times better than light microscopes
  • Can provide images with higher magnifications without blurriness, suitable for studying subcellular structures like mitochondria
• Comparison:

  • Light microscopes have a resolution of 0.2 micrometers
  • Electron microscopes have a resolution of 0.1 nanometers, 2,000 times better than light microscopes
• Parts of a light microscope:

  • Base: supports the entire microscope
  • Arm: connects the bottom to the top
  • Light source: can be a lamp or mirror
  • Stage: where the microscope slide is placed
  • Lenses:
  • Three objective lenses with different magnifications (e.g. 10x, 20x, 50x)
  • Eyepiece lens with fixed magnification at the top
  • Body tube
  • Coarse and fine focusing knobs
• Object vs. Image in microscopy:

  • Object: the real object or sample being observed (e.g. onion cells on a microscope slide)
  • Image: what we see when looking through the microscope (e.g. image of the onion cells)
• How a light microscope works:

  • Light from the room hits the mirror and is reflected upwards through the object on the stage (e.g. onion cells)
  • Light passes through objective lenses, then the eyepiece lens, and into the eye
  • Lenses spread out light rays to make the image appear larger than the actual object
• Magnification:

  • Definition: how many times larger the image is than the object
  • Equation: magnification = image size / object size
  • Example: if the image appears 1000 times larger than the object, the magnification is 1000x
• Resolution:

  • Definition: the shortest distance between two points on an object that can still be distinguished as two separate entities
  • Higher resolution = more details visible and less blurry image
  • Example: comparing two images of onion cells with the same magnification but different resolutions
• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration
• Molecules move about randomly and spread out over time due to their random motion
• Diffusion can happen in both gases and liquids
• For example, perfume quickly diffuses across a room when sprayed
• Food coloring diffuses through water until the whole glass is the same color
• Diffusion can take place through partially permeable membranes, such as cell membranes
• Only small molecules dissolved in the fluid inside or outside the cell can diffuse through
• Examples of molecules that can diffuse through are water, glucose, and amino acids
• Larger molecules like proteins and starch cannot fit through the membrane
• Diffusion is a passive process that does not require energy from the cell
• Factors that affect the rate of diffusion:
• Concentration gradient:

  • The larger the concentration gradient between two places, the higher the rate of diffusion
• Temperature:

  • Higher temperatures give particles more energy, causing them to move faster and diffuse more quickly
• Surface area:

  • The larger the surface area, the higher the rate of diffusion
  • More particles can fit around a larger surface area, allowing for more particles to diffuse in and out at once
• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration
• Osmosis is a special case of diffusion and specifically the diffusion of water molecules
• Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
• Water concentration refers to the amount of water compared to other molecules like sugars or salts dissolved in the water
• Higher water concentration means fewer solute molecules and lower water concentration means more solute molecules
• In cells, water particles will diffuse from a region of higher water concentration to a region of lower water concentration through osmosis
• Diffusion is the process by which substances move down their concentration gradient from a region of higher concentration to a region of lower concentration