Biology Paper 1

• Eukaryotic cells


  Cells that contain their genetic material enclosed in a nucleus
• Eukaryotic cells


  • Contain a nucleus
  • Contain a cell membrane
  • Contain cytoplasm
• Prokaryotic cells


  Cells where the genetic material is not enclosed in a nucleus
• Prokaryotic cells


  • Do not have a nucleus
  • Have a cell membrane
  • Have a cell wall
  • Contain cytoplasm
  • May have plasmids
• Eukaryotic cells


  Are larger than prokaryotic cells
• Eukaryotes


  Organisms whose genetic material is enclosed in a nucleus
• Nucleus


  Encloses the genetic material
• Cytoplasm


  Watery solution where chemical reactions take place
• Cell membrane


  Controls the molecules that can enter and leave the cell
• Mitochondria


  • Where aerobic respiration takes place
• Ribosomes


  • Sites of protein synthesis
• Ribosomes are too small to be seen using a light microscope, an electron microscope is required
• Proteins carry out many functions, such as enzymes
• Plant cells have a regular shape, unlike animal cells which can easily change their shape
• Plant cells are packed full of green structures
• Plant cells


  • Have chloroplasts which contain chlorophyll and are sites of photosynthesis
  • Have a cell wall made from cellulose which strengthens the cell
  • Have a large permanent vacuole filled with cell sap which helps give the plant cell its shape
• Algae are very simple forms of plant life and also have a cellulose cell wall
• Specialized animal cells


  Cells that have adaptations which help them carry out a particular function
• Differentiation


  When cells become specialized
• Sperm cells


  • Long tail to swim to ovum
  • Packed with mitochondria to provide energy for swimming
  • Contain enzymes to digest outer layer of ovum
• Fertilization


  The process where the genetic information of the ovum and sperm combine
• Nerve cells


  • Long axon to transmit electrical impulses
  • Axon covered in myelin to insulate and speed up transmission
  • Cell body has dendrites to increase surface area for connections
• Muscle cells


  • Contain protein fibers that can contract to shorten the cell
  • Packed with mitochondria to provide energy for contraction
• Muscle cells work together to form muscle tissue
• Plant cell


  Differs from animal cell in regular shape, packed with green structures (chloroplasts)
• Differentiation


  The process where cells become specialized
• Root hair cells


  • Increase the surface area of the root to absorb water and dissolved minerals more effectively
  • Do not contain chloroplasts
• Xylem cells


  • Have very thick walls containing lignin to provide support
  • Have no internal structures like nucleus, cytoplasm, vacuole or chloroplasts to allow easy flow of water and dissolved minerals
• Phloem cells


  • Consist of two types: phloem vessel cells with no nucleus and limited cytoplasm, and companion cells with mitochondria to provide energy to the phloem vessel cells
  • Have pores called sieve plates in the end walls to allow flow of dissolved sugars
• Xylem cells form long tubes that carry water and dissolved minerals from the roots to the leaves
• Phloem tubes carry dissolved sugars up and down the plant
• Microscope


  Device that uses light or electrons to magnify and view small objects
• Light microscope


  • Used to study cells
  • Allows us to make important discoveries about cell structures like the nucleus
• Light microscope limitations


  • Limited magnification
  • Limited resolution - blurred image even with increased magnification
• Electron microscope


  Microscope that uses a beam of electrons instead of light to view specimens
• Electron microscope advantages


  • Much greater magnification than light microscope
  • Much greater resolution than light microscope
• Calculating microscope magnification


  Magnification = Size of image / Size of real object
• Calculating magnification


  • Nucleus image size = 45 mm, Actual nucleus diameter = 0.01 mm, Magnification = 4500x
• Calculating magnification


  • Mitochondrion image size = 30 mm, Actual mitochondrion length = 0.003 mm, Magnification = 10000x
• Calculating real object size

  • Image size = 87 mm, Magnification = 2000x, Real cell size = 0.0435 mm