Cell biology

• Animals and plant cells have:

  Nucleus - Contains DNA - Controls the cell

  Cytoplasm - Contains enzymes

  Cell membrane - Controls what goes in and out of the cell

  Mitochondria - Where anaerobic respiration occurs

  Ribosomes - Where protein synthesis occurs
• Only plant cells contain:

  Chloroplasts - Where photosynthesis takes place - Contains chlorophyll

  Permanent vacuole - Improves cell's rigidity

  Cell wall - Provides strength to the cell
• Only in bacteria cells:

  Single circular strand of DNA

  Plasmids - Small rings of DNA
• Cell specialisation:

  Cells specialise by undergoing differentiation [a process that involves the cell gaining new sub-cellular structures to be suited to its role]. Cells can either differentiate once early on or have the ability to differentiate their whole life [stem cells]. In animals most cells only differentiate once, but in plants many cells retain the ability.
• Sperm cells: Specialised to carry the male's DNA to the egg cell for successful reproduction.

  Streamlines head and long tail to aid swimming

  Many miti=ochondri which sipple the energy to allow the cell to move

  The acrosome [top of the head] has digestive enzymes which break down the outer layers of membrane of the egg cell
• Nerve cells: Specialised to transmit electrical signals quickly from one place in the body to another.

  The axon is long, enabling the impulses to be carried along long distances

  Have lots of extensions from the cell body [dendrites] means branched connections can form with other nerve cells

  The nerve endings have many mitochondria which supply the energy to make special transmitter chemicals [neurotransmitters]. These allow the impulse to be passed from one cell to another
• Muscle cells: Specialised to contract quickly to move bones or simply to squeeze therefore causing movement.

  Special proteins slide over each other, causing the muscle to contract

  Lots of mitochondria to provide energy from respiration for contraction

  They can store a chemical called glycogen that is used in respiration
• Root hair cells: Specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots.

  Large surface area so more water can move in

  Large permanent vauole

  Mitochondria tp provide energy for active transport
• Xylem cells: Specialised to transport water and mineral ions up the plant from the roots to the shoots.

  A chemical called lignin is deposited which causes the cell to die which means they're hollow and joined from end to end which creates a continuous tube

  Lignin is deposited in spirals which helps withstand pressure
• Phloem cells: Specialised to carry the products of photosynthesis to all parts of the plant.

  Cell walls form sieve plates when they break down allowing the movement of substances from cell to cell

  Energy is supplied by mitochondria in companion cells
• Light microscope:

  Lower resolution

  Lower magnification

  Smaller

  Doesn't require cells to be dead

  Can't be used to see sub-cellular structures

  
• Electron microscope:

  Higher resolution

  Higher magnification

  Larger

  Requires cells to be dead

  Can be used to see sub-cellular structures

  
• Magnification = size of image / size of real object
• Culturing microorganisms

  1. Petri dish and culture media must be sterilised before use

  2. Inoculating loops must be sterilized by passing through a flame

  3. Lid of Petri dish should be sealed with tape

  4. The petri dish should be stored upside down

  5. The culture should be incubates at 25 degrees Celcius
• Sterilisation

  Kills unwanted bacteria
• If not sterilised

  There will likely be contamination with other microorganisms which could be harmful
• Sealing the Petri dish lid with tape

  Stops airborne microorganisms from contaminating the culture but it shouldn't be sealed all around so the bacteria can respire aerobically
• Storing the Petri dish upside down


  Prevents condensation which could distribute growth
• Incubating the culture at higher temperatures


  The bacteria could become harmful to humans
• Incubating the culture at lower temperatures


  The colonies of such bacteria would not be able to grow
• Genetic information is found in the form of chromosomes
• A gene is a short section of DNA that codes for a certain protein and as a result controls a characteristic
• There are 23 pairs of chromosomes [46 total] in each cell in the body apart from gametes
• The cell cycle:

  Stage 1 [Interphase]: The cell grows - organelles grow and increase in number - protein synthesis occurs - DNA is replicated - energy stores are increased

  Stage 2 [Mitosis]: The chromosomes line up in the middle of the cell - cell fibres pull each chromosome to either side of the cell

  Stage 3 [Cytokinesis]: Two identical daughter cells are formed when cytoplasm and cell membranes divide
• Embryonic stem cells:

  Form when and an egg form a zygote

  They can differentiate into any type of cell

  Scientists can clone these cells and direct them to differentiate into any cell

  Could potentially be used to replace insulin-producing cells in those suffering from diabetes and new neural cells for diseases such as Alzheimer's or nerve cells for those paralysed with spinal cord injuries
• Adult stem cells:

  If found in bone marrow they can form many types of cell
• Meristems in plants:

  Found in roots and shoots

  They can differentiate into any type of plant and keep this ability throughout the life of the plant

  They can be used to make clones of the plant - can be necessary if the parent plant has certain desirable features or for research or to save a plan from extinction
• Therapeutic cloning: Involves the creation of an embryo that has the same genetic material as the patient
• Benefits of research with stem cells:

  Can be used to replace damaged or diseased body parts

  Unwanted embryos from fertility clinics could be used rather than being discarded

  Research into the process of differentiation
• Negatives of research with stem cells:

  We do not completely understand the process of differentiation so it is hard to control to form the cells we desire

  Removal of stem cells results in the destruction of the embryo

  People may have religious or ethical objections as it is seen as interference with the natural process of reproduction

  If the growing stem cells are contaminated, an infection can be transferred to the individual

  Money and time could be better spent into other areas of medicine
• Diffusion:

  The movement of substances from an area of high to low concentration

  It is a passive process [doesn't require energy]
• Factors that affect the rate of diffusion:

  Concentration gradient - steeper gradient -> faster rate

  Temperature - greater temperature -> faster rate

  Surface area - greater surface are -> faster rate
• Osmosis: The movement of water molecules from a region of high water concentration to a region of low water concentration
• Osmosis in animals:

  If the external solution is less concentrated it will move into cell causing it to burst

  If the external solution is more concentrated it will move out of the cell and cell will shrivel up
• Osmosis in plants:

  If the external solution is less concentrated water will move into cell and into vacuole causing it to swell resulting in pressure called turgor

  If the external solution is more concentrated water will move out the cell and it will become more soft
• Active transport:

  The movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient

  It is an active process
• Uses of glucose in plants:

  Cellulose

  Lipids

  Amino acids

  Proteins

  Starch