1) Cell Structure

• In unicellular organisms, substances can easily enter the cell due to a short diffusion distance, while in multicellular organisms, the diffusion distance is larger because of a lower surface area to volume ratio
• Multicellular organisms require specialised exchange systems for efficient gas exchange of carbon dioxide and oxygen due to their lower surface area to volume ratio
• The light microscope uses light as a source of radiation to create an image of the specimen being examined
• Magnification in a light microscope is calculated by multiplying the eyepiece lens by the objective lens
• Increasing magnification in a light microscope has effects on cell size, number of cells, and level of detail until the resolution limit is reached
• Resolution in a light microscope is the ability to distinguish between two separate points as separate, depending on the radiation used
• Cells can be measured with a microscope using an eyepiece graticule and a stage micrometer to calibrate the scale
• An electron microscope uses electrons for radiation and has a higher magnification and resolution compared to a light microscope
• The cell surface membrane serves as a boundary between the cell and its environment and is partially permeable
• The nucleus is the largest organelle in the cell and contains genetic material, acting as the control center for cellular activities
• The endoplasmic reticulum is a system of membrane-bound structures involved in protein synthesis and lipid metabolism
• The Golgi apparatus is responsible for chemical modification of proteins, packaging for secretion, and synthesis of lysosomes
• Ribosomes are non-membranous organelles involved in protein synthesis and can be found in various locations within the cell
• Lysosomes are membrane-bound sacs containing hydrolytic enzymes and are involved in intracellular digestion
• Single-celled organisms have a short distance for substances to enter the cell, while multicellular organisms have a larger distance due to a smaller surface area to volume ratio
• Due to their higher surface area to volume ratio, multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen
• In multicellular organisms, the exchange of gases like carbon dioxide and oxygen occurs through specialised exchange surfaces
• The Golgi body continuously forms spherical membrane-bound sacs (0.1 – 0.5 μm) containing hydrolytic enzymes like proteases, lipases, and lysozyme
• Functions of lysosomes in animal cells:

  • Digestion of material taken in by endocytosis (food or bacteria)
  • Autophagy (digestion of worn-out organelles)
  • Autolysis (digestion of the whole cell)
• Mitochondria:

  • Rod-shaped organelle surrounded by a double membrane
  • Outer membrane is smooth, inner membrane is folded forming cristae
  • Contains 70S Ribosomes & Circular DNA in the Matrix
  • Site of aerobic respiration producing ATP
• Functions of ATP in cells:

  • Provides energy for muscle contraction
  • Facilitates active transport
  • Aids in the transmission of nerve impulses
  • Helps maintain body temperature
• Chloroplast:

  • Biconvex organelle 5 – 10 μm in diameter
  • Surrounded by a double membrane with smooth membranes
  • Contains chlorophyll for photosynthesis
  • Stacks of thylakoids form grana
• Cell Wall:

  • Rigid structure made of cellulose fibers
  • Functions include maintaining cell shape, preventing bursting, controlling growth, and allowing pressure build-up
• Large Central Vacuole:

  • Space-filled sac surrounded by a single membrane (tonoplast)
  • Contains cell sap and stores various substances
• Cytoskeleton:

  • Made up of microfilaments, intermediate filaments, and microtubules
  • Functions include determining cellular shape, cell motility, and intracellular transport
• Microtubules:

  • Long, rigid, hollow tubes made of tubulin
  • Functions include making up the cytoskeleton, intracellular transport, holding organelles in place, and forming centrioles, spindle fibers, flagella, and cilia
• Centrioles:

  • Hollow cylinder containing nine triplets of microtubules
  • Functions include forming spindle fibers during nuclear division and acting as basal bodies for cilia and flagella
• Cell Fractionation:

  • Process of dividing cells into parts or fractions
  • Achieved by centrifugation using a centrifuge
  • Allows for the isolation and study of individual organelles
• Prokaryotic Cell:

  • Average diameter of 0.5 – 5 μm
  • No distinct nucleus, circular DNA, no membrane-bound organelles like chloroplasts or mitochondria
  • Contains ribosomes, cell wall, and plasma membrane
• Comparison: Prokaryote vs. Eukaryote:

  • Differences in cell membrane, cell wall, nucleus, DNA, organelles, ribosomes, lysosomes, centrioles, chloroplasts, sap vacuole, and size
• Viruses:

  • Considered non-living, acellular entities
  • Consist of self-replicating DNA or RNA and a protein coat (capsid)
  • Range in size from 20–300 nm
  • Reproduce by infecting and taking over living cells
• Functions of viruses:

  • Reproduce by infecting and taking over living cells
  • Use the host cell's machinery to make new virus particles
• Viruses are acellular entities consisting of self-replicating DNA or RNA and a protein coat (capsid)
• In multicellular organisms, specialised exchange surfaces are required for efficient gas exchange due to the larger distance for substances to cross over
• The Golgi body continuously forms spherical membrane-bound sacs containing hydrolytic enzymes like proteases, lipases, and lysozyme
• Mitochondria are the site of aerobic respiration, producing ATP for cellular energy needs
• Chloroplasts are biconvex organelles responsible for photosynthesis, containing chlorophyll and thylakoids
• The cell wall, made of cellulose fibers, maintains cell shape, prevents bursting, and allows for pressure build-up inside the cell
• The large central vacuole stores various substances and helps regulate the osmotic properties of the cell
• The cytoskeleton, composed of microfilaments, intermediate filaments, and microtubules, plays a crucial role in determining cellular shape and motility