2. Cells

• Define the terms eukaryotic and prokaryotic cell
• Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles
• Prokaryotic: DNA is ‘free’ in cytoplasm, no organelles e.g. bacteria & archaea
• State the relationship between a system and specialised cells
• Specialised cells → tissues that perform specific function → organs made of several tissue types → organ systems
• Describe the structure and function of the cell-surface membrane
• 'Fluid mosaic' phospholipid bilayer with extrinsic & intrinsic proteins embedded

  • Isolates cytoplasm from extracellular environment
  • Selectively permeable to regulate transport of substances
  • Involved in cell signalling / cell recognition
• Explain the role of cholesterol, glycoproteins & glycolipids in the cell-surface membrane
• Cholesterol: steroid molecule connects phospholipids & reduces fluidity

  • Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together
  • Glycolipids: cell signalling & cell recognition
• Describe the structure of the nucleus
• Surrounded by nuclear envelope, a semi-permeable double membrane

  • Nuclear pores allow substances to enter/exit
  • Dense nucleolus made of RNA & proteins assembles ribosomes
• Describe the function of the nucleus
• Contains DNA coiled around chromatin into chromosomes

  • Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semiconservative replication
• Describe the structure of a mitochondrion
• Surrounded by double membrane folded inner membrane forms cristae: site of electron transport chain

  • Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins
• Describe the structure of a chloroplast
• Vesicular plastid with double membrane

  • Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll
  • Intergranal lamellae: tubes attach thylakoids in adjacent grana
  • Stroma: fluid-filled matrix
• State the function of mitochondria and chloroplasts
• Mitochondria: site of aerobic respiration to produce ATP

  • Chloroplasts: site of photosynthesis to convert solar energy to chemical energy
• Describe the structure and function of the Golgi apparatus
• Planar stack of membrane-bound, flattened sacs cis face aligns with rER

  • Molecules are processed in cisternae vesicles bud off trans face via exocytosis:
  • Modifies & packages proteins for export
  • Synthesises glycoproteins
• Describe the structure and function of a lysosome
• Sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes glycoprotein coat protects cell interior:

  • Digests contents of phagosome
  • Exocytosis of digestive enzymes
• Describe the structure and function of a ribosome
• Formed of protein & rRNA free in cytoplasm or attached to ER

  • Site of protein synthesis via translation:
  • Large subunit: joins amino acids
  • Small subunit: contains mRNA binding site
• Describe the structure and function of the endoplasmic reticulum (ER)
• Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope:

  • Rough ER: many ribosomes attached for protein synthesis & transport
  • Smooth ER: lipid synthesis
• Describe the structure of the cell wall
• Bacteria: Made of the polysaccharide murein

  • Plants: Made of cellulose microfibrils plasmodesmata allow molecules to pass between cells, middle lamella acts as boundary between adjacent cell walls
• State the functions of the cell wall
• Mechanical strength and support

  • Physical barrier against pathogens
  • Part of apoplast pathway (plants) to enable easy diffusion of water
• Describe the structure and function of the cell vacuole in plants
• Surrounded by single membrane: tonoplast contains cell sap: mineral ions, water, enzymes, soluble pigments

  • Controls turgor pressure
  • Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
• Explain some common cell adaptations
• Folded membrane or microvilli increase surface area e.g. for diffusion

  • Many mitochondria = large amounts of ATP for active transport
  • Walls one cell thick to reduce distance of diffusion pathway
• State the role of plasmids in prokaryotes
• Small ring of DNA that carries non-essential genes

  • Can be exchanged between bacterial cells via conjugation
• State the role of flagella in prokaryotes
• Rotating tail propels (usually unicellular) organism
• State the role of the capsule in prokaryotes