B1

• Eukaryotic cells


  Animal and plant cells have genetic material (DNA) that forms chromosomes and is contained within a nucleus
• Plant cell


  • Cell wall
  • Chloroplasts
  • Permanent vacuole
• Prokaryotic cells


  • Single-celled
  • Have a single loop of DNA
  • Have small rings of DNA called plasmids
  • Smaller than eukaryotic cells
• Comparison of sub-cellular structures

  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Cell wall
  • Chloroplasts
  • Permanent vacuole
• Light microscope


  • Uses light to form images
  • Living sample can be viewed
  • Relatively cheap
  • Low magnification
  • Low resolution
• Electron microscope


  • Uses a beam of electrons to form images
  • Samples cannot be living
  • Expensive
  • High magnification
  • High resolution
• To calculate the magnification of an image


  Magnification = image size / actual size
• Electron microscopes allow you to see sub-cellular structures, such as ribosomes, that are too small to be seen with a light microscope
• Specialised cells


  • Cells in animals differentiate at an early stage of development
  • Plant cells differentiate throughout its lifetime
• Examples of specialised cells

  • Sperm cell
  • Red blood cell
  • Muscle cell
  • Neurone
  • Root hair cell
  • Palisade cell
• Sperm cell


  • Fertilise an ovum (egg)
  • Have lots of mitochondria to release energy from respiration, enabling the sperm to swim to the ovum
• Red blood cell


  • Transport oxygen around the body
  • No nucleus to have more room to carry oxygen
  • Contains haemoglobin that binds to oxygen molecules
  • Flat bi-concave disc shape to increase surface area to volume ratio
• Muscle cell


  • Contract and relax to allow movement
  • Contains protein fibres that can contract
  • Contains lots of mitochondria to release energy from respiration, allowing the muscles to contract
• Neurone


  • Carry electrical impulses around the body
  • Branched endings (dendrites) to make connections with other neurones or effectors
  • Myelin sheath insulates the axon to increase the transmission speed of the electrical impulses
• Root hair cell


  • Absorb mineral ions and water from the soil
  • Long projection to increase the surface area for absorption
  • Lots of mitochondria to release energy for the active transport of mineral ions from the soil
• Palisade cell


  • Enable photosynthesis in the leaf
  • Located at the top surface of the leaf where it can absorb the most light energy
  • Lots of chloroplasts containing chlorophyll to absorb light energy
• animal cell - cells that are found inside the body, they have a nucleus and organelles
• bacteria - single-celled microorganisms that can be seen only with a microscope
• Chromosomes


  The genetic material of a cell, containing a large number of genes made of DNA molecules
• DNA


  • The genetic material that carries the instructions for the characteristics of an organism
  • Found in the nucleus of cells
• The cell cycle


  1. Cell grows in size

  2. DNA replicates (chromosomes are duplicated)

  3. Increase in number of sub-cellular structures

  4. Chromosomes are pulled to each end of the cell

  5. The nucleus divides to form two nuclei

  6. Cytoplasm and cell membrane divide to form two identical daughter cells
• Mitosis


  Cell division that produces two genetically identical daughter cells
• Mitosis


  • Important for growth and repair of cells
  • Used for asexual reproduction
• Stem cell


  An undifferentiated cell that can develop into one or more types of specialised cell
• Types of stem cells

  • Adult stem cells
  • Embryonic stem cells
• Adult stem cells


  • Can only differentiate into certain specialised cells
  • Found in specific parts of the body
• Embryonic stem cells


  • Can differentiate into any type of specialised cell
  • Found in early human embryos
• Therapeutic cloning


  Patient's cells are used to create an early embryo clone, stem cells from the embryo can then be used to treat the patient
• Advantages of adult stem cells

  • Fewer ethical issues
  • Patients' own cells can be used, reducing risk of rejection
• Disadvantages of adult stem cells

  • Can take a long time to find a suitable donor
  • Can only differentiate into some specialised cell types
• Advantages of embryonic stem cells

  • Can differentiate into any specialised cell
  • Easier to obtain from spare embryos
• Disadvantages of embryonic stem cells

  • Ethical issues surrounding their use
  • Potential risks involved with treatments
• Plant meristems


  Regions in the tips of roots and shoots where rapid cell division occurs
• Advantages of using plant meristems to clone plants

  • Rare species can be cloned to protect them
  • Plants with desirable traits can be cloned
• Disadvantage of using plant meristems to clone plants

  No genetic variation, so entire crops are at risk
• Cell division by mitosis produces two genetically identical daughter cells
• Purpose of mitosis


  Growth and repair of cells, asexual reproduction
• First stage of cell cycle

  1. Cell grows in size

  2. DNA replicates (chromosomes are duplicated)

  3. Increase in number of sub-cellular structures
• Mitosis


  1. Chromosomes are pulled to each end of the cell

  2. The nucleus divides to form two nuclei
• Third stage of cell cycle

  Cytoplasm and cell membrane divide to form two identical daughter cells