Biology - Cell Structure + Division


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  • Cell Structure and Division
    • Stem Cells
      • Stem cells are unspecialised.
        • This means they can fulfil any role in the body.
        • They divide by mitosis rapidly and will form special cells depending on the nucleus.
      • Plants
        • Plants have stem cells called meristems.
          • Found in the roots and shoots
          • They can grow into other plant tissues ie mesophyll, phloem etc.
        • Animals
          • Adult stem cells are found in bone marrow
            • Adult stem cells can only be used for the treatment of blood diseases such as sickle cell anaemia.
          • Embryonic stem cells
            • Embryonic stem cells come from human embryos under 14 days old.
              • Extracting the stem cells from the embryo destroys it.
              • These stem cells can become any type of cell. They can treat conditions such as paralysis.
              • By the 14th day the nervous tissue begins to develop. It is controversial as some believe they can feel pain.
              • The Process
                • At fertility clinics the embryos are produced in high numbers of 14-15.
                • A small number are implanted into the womb.
                • Using excess embryos to harvest stem cells could be a less controversial way to do it.
                • Embryonic stem cell extraction is very expensive.
                  • It is a worthwhile process despite the cost due to every stem cell dividing every 30 mins.
                    • There is a low rejection rate.
                    • More research is required before treatments become widely available.
                • Embryonic stem cells can become contaminated making the patient ill.
    • Culturing
      • A disinfectant is used on surfaces but not on the skin to kill bacteria.
        • Virkon
        • Dettol
      • An antiseptic kills bacteria and prevents the growth of disease causing micro organisms.
        • Savlon
        • Rubbing alcohol
      • Microbiology Required Practical
    • Meiosis
      • The DNA in the nuclei is arranged in chromosomes
      • Meiosis produces sperm and eggs (gametes). One cell turns into four.
        • Every egg has one X chromosome. Half of the sperm at conception will carry an X and the other half will carry a Y to determine biological sex.
          • Reproduction
            • Asexual
              • Produces identical offspring
              • Clones of parent
              • Any defect or disease the parent has is passed to its offspring
            • Sexual
              • Produces variation
              • Takes time to find and/or compete for a mate
      • Before cell division the DNA must replicate itself. After that, the cell can divide.
    • Binary Fission
      • When a cell divides into two for reproduction in bacteria it is binary fission.
      • A form of mitosis
    • Mitosis
      • A cell needs to divide to grow, repair and reproduce.
      • Mitosis involves one cell becoming two.
      • The nucleus tells the cell when to divide - except when in red blood cells.
      • Before cell division the DNA must replicate itself. After that, the cell can divide.
      • Cancers
        • Sometimes cell division will go wrong and mitosis doesn't stop.
        • The continuous cell divisions can form a tumour as the cells become cancerous.
          • Cancerous cells are cells that divide out of control from a mutation in cell division.
    • Microscopy
      • Light Microscopes
        • Use light and lenses to form an image and magnify it
        • Individual cells and subcellular structures such as the nuclei can be seen.
        • Diagram
        • Required Practical
      • Electron Microscopes
        • Use electrons instead of light to form an image
        • Higher magnification than light microscopes
        • Higher resolution than light microscopes
        • You can view smaller structures in greater detail, like ribosomes or the internal structures of chloroplasts.
      • Magnification = Image Size ÷ Real Size
    • Cell Structure
      • The Cell Cycle
        • Stage 1: The cell grows and gets enlarged. DNA, mitochondria and ribosomes are replicated.
        • Stage 2: The chromosomes are doubled up in number and line up in the centre of the cell to form an equator. They separate and move to either side of the cell in their pairs (mitosis)
        • Stage 3: The cell splits into two (cytokinesis)
        • The time taken to complete a cell cycle depends on the cell type and the environmental conditions it is in.
      • Cell Types
        • Animal
          • Nucleus
            • Plant
              • Cell wall
              • Permanent vacuole
              • Chloroplasts + Chlorophyll
          • Cytoplasm
            • Plant
              • Cell wall
              • Permanent vacuole
              • Chloroplasts + Chlorophyll
          • Cell membrane
            • Mitochondria
              • Ribosomes
              • Bacterial
                • Prokaryotes
                • Small circular strand of DNA in place of nucleus
                • Plasmids
                • No chloroplasts or mitochondria
              • Prokaryotes and Eukaryotes
                • Prokaryotes
                  • Single celled organisms
                • Eukaryotes
                  • Eukaryotic celled organisms ie animal cells
          • Chromosomes
            • Humans have 23 pairs of chromosomes in every body cell except red blood cells.
            • 44/46 chromosomes are body chromosomes
            • One pair of human chromosomes are the sex chromosomes - female chromosomes are **, male is XY.
            • A full set of chromosomes is diploid (two copies of each).
            • A half set of chromosomes is haploid (one copy).

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