B1 Cell Structure & Division

• Bacteria cells are prokaryotic and contain:

  Cytoplasm, cell membrane, cell wall, plasmids (small rings of DNA)
• Most animal cells have the following subcellular structures :

  1. Nucleus - contains genetic material that controls the activities of the cell

  2) Cytoplasm - a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions.

  3) Cell membrane - holds the cell together and controls what goes in and out.

  4) Mitochondria - these are where most of the reactions for aerobic respiration take place

  5) Ribosomes - these are where proteins are made in the cell.
• Plant Cells usually have all the bits that animal cells have, plus a few extra:

  1. Rigid Cell wall - made of cellulose. It supports the cell and strengthens it.
  2. Permanent vacuole - contains cell sap, a weak solution of sugar and salts.
  3. Chloroplasts - these are where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.
• Sperm Cells - REPRODUCTION:

  Purpose - get male DNA to female DNA

  It has a long tail and streamlined head to help it swim to the egg.

  Lots of mitochondria to provide the energy.

  Carries enzymes in its head to digest through the egg cell membrane.
• Nerve Cells - RAPID SIGNALLING:

  Purpose - carry electrical signals

  Long to cover more distance.

  Branched connections at their ends connect to other nerve cells to form a network throughout the body.
• Muscle Cells - CONTRACTION:

  Purpose - to contract quickly

  Long so they have space to contract.

  Lots of mitochondria generate the energy needed for contraction.
• Root Hair Cells - ABSORPTION OF WATER & MINERALS

  They grow into long “hairs” that stick out of the soil, which gives the plant a big surface area for absorbing water and mineral ions.
• Phloem & Xylem - TRANSPORTING SUBSTANCES

  Purpose - transport substances around plants

  Long, joined from end to end.

  They are hollow in the centre and phloem have very few subcellular structures, so stuff can flow through them.
• Cell Cycle:

  • The cell grows and increases the amount of sub cellular structures.
  • It then duplicates its DNA so there’s one copy for each cell.

  Mitosis:

  • The chromosomes line up at the centre of the cell and the cell fibres pull them apart. The two arms of each chromosome goes to opposite ends on the cell.
  • Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells as the nucleus has divided.
  • The cytoplasm and cell membrane divide.
  • Two new daughter cells have now been produced.
• • Prokaryotic cells replicated by Binary Fission.
  • The cell splits into two by:
  • The circular DNA and plasmid(s) replicate
  • The cell gets bigger and the circular DNA strands move to opposite ends of the cell.
  • The cytoplasm begins to divide and new cell walls begin to form
  • The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s).
  • Bacteria can divide very quickly if given the right conditions (warm environment and lots of nutrients).
• Chromosomes are coiled up lengths of DNA molecules. Each chromosome has a large number of genes. Different genes control the development of different characteristics.
• Embryonic Stem Cells:

  • They can turn into any type of cell.
  • As they are undifferentiated, they can divide to produce more undifferentiated cells, which can differentiate into different types of cells.

  Found in the bone marrow of a person or the meristems of a plant.
• Stem Cells may be used to cure a lot of diseases.

  • Replace faulty cells in sick people
  • Help with paralysis and neurological problems such as Parkinson’s.
  • However, there are risks as the stem cells can become contaminated in a lab.