cell biology

• 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
• Prokaryotic cells


  Are much smaller than eukaryotic cells
• Eukaryotic cells include animal and plant cells
• Prokaryotic cells include bacterial cells
• Order of magnitude

  A way to compare the approximate size of different objects
• How to determine order of magnitude

  Count the number of zeros - each zero represents one order of magnitude (10 times greater)
• 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
• 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
• 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
  • Phloem vessel cells have porous end walls called sieve plates to allow flow of dissolved sugars
• Photosynthesis requires energy from light, so root hair cells which are underground cannot perform photosynthesis
• Xylem cells form long tubes to carry water and dissolved minerals from roots to leaves
• Phloem tubes carry dissolved sugars up and down the plant
• Mitosis


  The process by which a cell divides into two or more cells
• Cell


  • Contains a nucleus
  • Contains chromosomes made of DNA
• Body cells contain 23 pairs of chromosomes
• Gamete cells have unpaired chromosomes
• Chromosome


  Carries a large number of genes that determine many features
• Animals and plants contain a very large number of cells
• Cell cycle including mitosis

  1. DNA replication

  2. Mitosis

  3. Cell division
• Mitosis


  • One set of chromosomes is pulled to each end of the cell
  • The nucleus also divides
  • The cytoplasm and cell membrane divide to form two identical cells
• Functions of mitosis


  • Essential for growth and development of multicellular organisms
  • Repairs organisms when damaged
  • Occurs during asexual reproduction
• Stem cell

  An undifferentiated cell which can give rise to more cells of the same type and can differentiate into other types of cells
• Fertilization

  1. Sperm cell joins with ovum

  2. Fertilized ovum undergoes mitosis

  3. Forms a ball of cells called an embryo

  4. Cells continue to undergo mitosis and begin to form specialized cells

  5. Process of differentiation
• Embryonic stem cells

  • Cells in early stage embryo that have not differentiated and are capable of differentiating into any type of body cell
• Adult stem cells

  • Found in adult organisms, cannot differentiate into any other type of cell (e.g. bone marrow stem cells form blood cells)
• Bone marrow transplant

  1. Patient's existing bone marrow destroyed

  2. Patient receives transplant of donor bone marrow

  3. Stem cells divide and form new bone marrow

  4. Stem cells differentiate and form blood cells
• Problems with bone marrow transplants

  • Donor must be compatible with patient
  • Risk of viruses being passed from donor to patient
• Therapeutic cloning

  1. Embryo produced with same genes as patient

  2. Stem cells from embryo can be transplanted into patient without being rejected

  3. Stem cells can differentiate to replace malfunctioning cells
• Therapeutic cloning could be useful for a range of medical conditions like diabetes or paralysis
• Some people have ethical or religious objections to therapeutic cloning procedure
• Plant stem cells

  • Found in meristem tissue at root tips and buds
  • Can differentiate into any type of plant tissue at any point in plant's life