Paper 1

• Cells


  The basic unit of all forms of life
• Structural differences between various types of cells

  • Enable them to perform specific functions within the organism
  • Controlled by genes in the nucleus
• Cell division by mitosis


  1. Produces two new identical cells

  2. Allows organism to grow
• Stem cell technology


  A new branch of medicine that allows doctors to repair damaged organs by growing new tissue from stem cells
• Eukaryotes and prokaryotes


  • Plant and animal cells (eukaryotic cells)
  • Bacterial cells (prokaryotic cells)
• Plant and animal cells (eukaryotic cells)


  • Have a cell membrane, cytoplasm and genetic material enclosed in a nucleus
• Bacterial cells (prokaryotic cells)


  • Are much smaller in comparison
  • Have cytoplasm and a cell membrane surrounded by a cell wall
  • Genetic material is not enclosed in a nucleus, it is a single DNA loop and there may be one or more small rings of DNA called plasmids
• Sub-cellular structures

  • Nucleus
  • Cell membranes
  • Mitochondria
  • Chloroplasts in plant cells
  • Plasmids in bacterial cells
• Most animal cells

  • Have a nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
• Plant cells

  • In addition to the parts found in animal cells, often have chloroplasts, permanent vacuole filled with cell sap, cell wall made of cellulose
• Estimations can be used to judge the relative size or area of sub-cellular structures
• Cell specialisation


  Cells may be specialised to carry out a particular function
• Specialised animal cells


  • Sperm cells, nerve cells, muscle cells
• Specialised plant cells


  • Root hair cells, xylem and phloem cells
• Animal and plant cells may be specialised to function within a tissue, an organ, organ systems, or whole organisms
• Sperm cell


  • Carries half the genetic information
  • Has tails to swim towards the egg cell
• Red blood cell


  • Adapted to carry oxygen to cells and carbon dioxide away from them
• Nerve cell


  • Can be very long (up to 2m) to carry messages around the body
• Muscle cell


  • Can change their length to help us move
• Ciliated Epithelial Cell


  • Found in tubes leading to the lungs and in the oviduct
  • The hairs (called cilia) move dirt out of the lungs and help to move eggs along the oviduct
• Root hair cell


  • The root hair gives these cells a bigger surface area to take in water from the soil
• Palisade cell


  • Contains chloroplasts to help the plant make food by photosynthesis
• Electron microscope


  Has much higher magnification and resolving power than a light microscope
• Electron microscope


  • Can be used to study cells in much finer detail
  • Enables biologists to see and understand many more sub-cellular structures
• Electron microscopy


  Has increased understanding of subcellular structures
• Prefixes


  centi (10-2), milli (10-3), micro (10-6) and nano (10-9) (in standard form)
• Calculating magnification


  Magnification = size of image/size of real object
• Light microscope


  • Can see individual cells and large subcellular structures like the nucleus
• Electron microscope


  • Uses a beam of electrons instead of a beam of light
  • Gains a much higher resolution seeing much smaller objects e.g. the structures of mitochondria, chloroplasts, ribosomes and plasmids
• Parts of a Microscope

  • eyepiece
  • objective lenses
  • coarse focus
  • fine focus
  • arm
  • stage
  • light
• Chromosomes


  Coiled DNA molecules in the nucleus of a cell, containing genetic information. Found in pairs in body cells.
• Models and analogies


  Can be used to develop explanations of how cells divide
• Cell cycle


  Series of stages a cell goes through, including mitosis, where genetic material is doubled and divided into two identical cells
• Mitosis


  1. DNA replicates to form two copies of each chromosome

  2. One set of chromosomes is pulled to each end of the cell

  3. Nucleus divides

  4. Cytoplasm and cell membranes divide to form two identical cells
• Mitosis


  • Important in the growth and development of multicellular organisms
• Stem cell

  Undifferentiated cell capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation
• Roles of stem cells


  • Important in embryos
  • Important in adult animals
  • Important in meristems in plants
• Stem cells


  • Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells
  • Stem cells from adult bone marrow can form many types of cells including blood cells
  • Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant
• Treatment with stem cells


  May be able to help conditions such as diabetes and paralysis
• Therapeutic cloning


  An embryo is produced with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body and may be used for medical treatment