Cell biology

• • Animal Cells contain:
  • Nucleus
  • Cytoplasm
  • Cell Membrane
  • mitochondria
  • Ribosomes
• The nucleus contains the genetic material of the cell and controls the activities of the cell.
• Cytoplasm is where most chemical reactions take place
• The cell membrane is a selectively permeable barrier that controls the movement of substances in and out of the cell
• Ribosomes are responsible for protein synthesis
• Mitochondria is where aerobic respiration takes place
• Plant cells contain all the sub-cellular structures found in animal cells, they also contain:

  • A cell wall made of cellulose
  • A permanent vacuole filled with cell sap
  • Chloroplasts
• The cell wall is only found in plant cells, it is made of cellulose and strengthens the cell
• The permanent vacuole is only found in plant cells, it contains cell sap and supports the plant.
• Chloroplasts are only found in plants and absorb light to make food (glucose) by photosynthesis
• Eukaryotic cells can be:

  • Plant cells
  • Animal cells
  • Fungal cells
• Prokaryotic cells are bacterial
• Prokaryotic cells have the following qualities:

  • Smaller in size
  • The genetic material is not enclosed in a nucleus
  • The genetic material is a single DNA loop (there can be one or many) these are called plasmids
  • They do not contain mitochondria or chloroplasts
• Bacterial cells:

  • All prokaryotic
  • Roles of mitochondria and chloroplasts are taken over by cytoplasm
  • May be one or more flagella (tail-like structures that move the bacterium)
  • Plasmids (contain genetic material) allow bacterial cells to move genes from one cell to another
• What unit of measurement is this based on the prefix?

  cm - centimetre

  mm - millimetre

  μm - micrometre

  nm - nanometre
• There are:

  100cm in a metre

  10mm in a centimetre

  1000μm in a millimetre

  1000nm in a micrometre
• Resolution - The ability to see two or more objects as separate objects
• Magnification - how many times larger the image is than the real object
• Electron microscope:+ Greater resolution and magnitude than a light microscope

  -Expensive
• Light microscope:

  + Cheap

  + Uses colour

  -Less resolution and magnitude than electron microscope
• $m=$$i/a$magnification = size of image/size of object
• The nucleus of a cell contains chromosomes made of DNA
• Chromosomes carry hundreds-thousands of genes:

  • Different genes contain the code to make different proteins and control the development of different characteristics
• Chromosomes comes in pairs, one from each parent.

  Humans have 23 pairs of chromosomes, 46 in total. This means each cell should contain 23 pairs of chromosomes
• Interphase - DNA duplicates and cell grows. Prepares for mitosis.

  Prophase - Membrane around nucleus disappears.

  Metaphase - Chromosomes and copies line up in middle of the cell.

  Anaphase - Chromosomes and copies pulled to ends of cell.

  Telophase - New membrane form around chromosome at the end of each cell.

  Cytokinesis - Cell membrane pinches and divides into two daughter cells.
• Mitosis is important because it allows growth and repair. It also ensures that all cells are genetically identical (except gametes).
• Stem cells are undifferentiated cells that can divide to produce more undifferentiated cells.
• Stem cells can be :

  • Found in embryos (embryonic cells)
  • Adult stem cells (found in organs and tissues)
• Embryonic stem cells come from embryo's and can develop into any type of specialised cell. They can be used to treat diseases such as Parkinson's disease or diabetes but they are not widely available due to ethical issues.
• Adult stem cells are found in adult tissues and only develop into specific types of cells. For example bone marrow stem cells become blood cells. Adult stem cells do not cause controversy so are easier to use than embryonic stem cells.
• Cell differentiation occurs when an unspecialised cell becomes specialised by developing certain characteristics. This happens during development, growth and repair.
• Adult stem cells can only make certain types of cells and their capacity to divide is limited

  Embryonic stem cells can make all types of cells
• Stem cells are useful in treating conditions where cells are damaged or not working properly, such as:

  • Diabetes
  • Paralysis
• Therapeutic cloning - creating a cloned embryo of the patient as a source of stem cells

  This is good as the stem cells wont be rejected from the patients body.

  People may be concerned about cloned embryos due to:

  • Risks such as transfer of viral infections
  • Ethical or religious objections
• Stem cells found in plants are called meristems, meristems allow for :

  • plants to make new cells for growth
  • clones of plants to be produced quickly

  This is useful because :

  • Rare species can be cloned to protect them from extinction
  • Large numbers of identical crops can be made with special features such as disease resistance
• Diffusion - net movement of particles from a high concentration to a low concentration

  Example :

  • Oxygen and carbon dioxide diffuse during gas exchange in lungs, gills and plant leaves
• Factors affecting diffusion :

  • Concentration gradient
  • Temperature
  • Surface area of the membrane
• Osmosis - The movement of water molecules from a region of high water concentration to a region of low water concentration through a partially permeable membrane
• Active Transport - The movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient, this requires energy from respiration