Cell Structure and Division

• Therapeutic cloning can be used to produce stem cells that have identical genes to the patient
• Theraputic cloning cannot be rejected by the patient
• Theraputic cloning - There is a shortage of egg donors, and they are still seen as unethical due to the destruction of embryos
• Stem cells are undifferentiated cells which can differentiate into other cell types
• Embryonic stem cells from human embryos can differentiate into any cell type, so can treat more diseases such as paralysis and diabetes type 1, but are unethical because using them destroys a ‘potential life’
• Adult stem cells from bone marrow are more ethical as people can consent to donating them, but can differentiate into fewer cell types, so are less useful than embryonic stem cells
• Plant stem cells are found in the meristem tissue (in the tips of roots and shoots), they can be used to produce clones of whole plants quickly and cheaply – for example rare plants
• Mitosis

  Stage 1 • Cell grows in size • Increases amount of subcellular structures e.g mitochondria and ribosomes • Duplicates its DNA Stage 2 (mitosis) • One set of chromosomes is pulled to each end of the cell • The nucleus divides Stage three • The cytoplasm and cell membrane divide, forming 2 identical daughter cells
• New cells are needed for growth, repairing tissues & replacing damaged/worn out cells
• Chromosomes are coiled up lengths of DNA molecules, which carry genes, they are found in the nucleus in pairs in body cells
• Magnification = image size/ actual size
• actual size = image size/magnification
• image size = magnification x actual size
• Specialised cells are adapted to carry out a specific function, e.g by having different subcellular structures
• Animal cells can only differentiate at an early stage of the animal’s life, where as plant cells can differentiate throughout their lifetime
• Sperm cell - Fertilises the egg cell - Has a long tail - Many mitochondria
• Muscle cell - Allows movement - Contains many mitochondria
• Nerve cell - Transmits electrical impulses - Branched to make connections, long
• Prokaryotes are much smaller than eukaryotes
• Phloem cell - Carries dissolved sugars - Contain sieve plates with pores
• Xylem cell - Carries water and minerals - Dead cells form hollow tubes, rings of lignin
• Palisade cell - To carry out photosynthesis - Lots of chloroplasts
• Root hair cell - To absorb water and minerals - Large surface area