2.6 Cell diversity

• The role of mitosis and the cell cycle is to produce identical daughter cells for growth and asexual reproduction of cells.
• All the cells produced by mitosis are genetically identical, therefore mitosis does not give rise to genetic variation.
• During the cell cycle, a cell grows and then divides to form daughter cells.
• The cell cycle is controlled by checkpoints.
• Mitosis is a form of cell division that produces identical cells, with four stages: prophase, metaphase, anaphase and telophase.
• Cytokinesis is the process where the parent and replicated organelles move to opposite sides of the cell and the cytoplasm divides, producing two daughter cells.
• Interphase is the stage where the cell grows and prepares to divide, chromosomes and some organelles are replicated, and chromosomes begin to condense.
• During prophase, the nuclear envelope breaks down and subsequently disappears.
• During prophase, the chromosomes condense and the centrioles move to opposite poles of the cell for the purpose of spindle formation.
• During metaphase, the chromosomes move to the equator and attach to the spindle fibres via centromeres.
• In the anaphase stage, the sister chromatids are separated.
• During telophase, the nuclear envelope reforms around haploid nuclei containing half the number of chromosomes.
• Meiosis is a form of cell division that gives rise to genetic variation, with the main role being production of haploid gametes as cells produced by meiosis have half the number of chromosomes.
• Meiosis produces genetically different cells, genetic variation is achieved through crossing over of chromatids and independent assortment of chromosomes.
• Meiosis is a two phase process in which four haploid gametes are generated from a diploid cell.
• During meiosis I, homologous chromosomes separate therefore there is only one chromosome of every pair per gamete, whereas in meiosis II the sister chromatids separate.
• The stages of meiosis I are prophase I, metaphase I, anaphase I and telophase I.
• Prophase I closely resembles the prophase stage of mitosis, with the exception of synapsis and crossing over of homologous chromosomes (at chiasmata) which allow the genetic exchange to occur.
• Metaphase I is when each pair of bivalents align at the equator.
• During anaphase I, the homologous chromosomes separate whereas during telophase I the nuclear envelope reforms around haploid nuclei containing half the number of chromosomes.
• During meiosis II composed of prophase II, metaphase II, anaphase II and telophase II, another round of cell division occurs, leading to formation of four haploid daughter cells, containing single chromosomes.
• It is during Anaphase II that the centromeres split separating chromatids.
• Cells group together to form tissues with the purpose of performing a common function.
• Examples of tissues include xylem and phloem tissues in plants.
• Organs are groups of tissues which work together to perform a wider function whereas an organ system is composed of many organs which work together to perform an essential life function.
• Tissue types and their functions include: Xylem - transport water and minerals as well as provide structural support.
• Stem cells are undifferentiated cells which are genetically identical and have the ability to develop into any of the various kinds of cells.
• The process by which a cell specialised to carry out a particular function is known as differentiation.
• Epithelial tissue is a sheet of cells that serves as a lining/cover a surface.
• Other specialised cells include sperm cells, palisade cells, root hair cells, and guard cells.
• Xylem vessels consist of parenchyma, fibres and vessels and are produced by meristem cells which produce smaller cells that elongate.
• Stem cells can be found in the bone marrow where they differentiate into erythrocytes (red blood cells) and neutrophils (white blood cells).
• Palisade cells are the most basic plant cell type, contain many chloroplasts and are specialised for photosynthesis.
• Phloem tubes are made of living cells which are involved in translocation, the movement of food substances and nutrients from leaves to storage organs and growing plants of the plant.
• Guard cells are found in pairs in the epidermis of leaves and are involved in controlling the opening and closing of stomata.

  <flashcard
• Erythrocytes are relatively short lived as they are constantly destroyed and created.
• The meristem tissue produces cells that elongate and line up end-to-end to form a long tube.
• Sperm cells are male gametes, made in the testes throughout a man’s life, they are adapted to reach, penetrate and fertilise the ovum.
• Ciliated epithelium is also found in the oviducts.
• Division of plant cells occurs at a high rate in meristems.