cell division, diversity and organisation

• eukaryotic cells enter the cell cycle and divide by mitosis or meiosis
• Prokaryotic cells replicate by binary fission.
• Viruses do not undergo cell division as they are non living
• what are the three key stages of the cell cycle?

  Interphase ( G 1, S [synthesis], G 2 )

  Nuclear division (Meiosis or mitosis)

  Cytokineses
• interphase is the longest stage in the cell cycle
• What happens in the G 1 phase of the interphase?

  Protein synthesis occurs to make proteins involved in synthesizing organelles. Organelles replicate. The cell is checked that it is the correct size, has the correct nutrients, growth factors are checked and it is checked that there is no damaged DNA- if the cell doesnt pass these checks, then replication will not continue.
• What happens in the synthesis (S) phase of the cell cycle?

  DNA replication
• What happens in the G2 phase of the cell cycle?

  Cell continues to grow, energy stores increase, newly replicated DNA is checked for copying errors.
• mitosis creates two identical diploid cells and is used for growth, tissue repair and asexual reproduction in plants, animals and fungi
• What are the key phases of mitosis?

  Prophase

  Metaphase

  Anaphase

  Telophase
• what happens in the prophase phase of mitosis?

  Chromosomes condense and become visible. In animal cells, the centrioles separate and move to opposite poles of the cell. The centrioles will create spindle fibres which are released from both poles to create spindle apparatus. The spindle apparatus will attach to the centromere and chromatids on the chromosome in later stages.
• What happens in metaphase of mitosis?

  The chromosomes align along the equator of the cell. The spindle fibres are released from the centrioles and attach to the centromere and chromatids. The spindle assembly checkpoint occurs in this stage; there is a check to ensure that every chromosome has attached to a spindle fibre before mitosis can proceed into anaphase.
• What happens in anaphase of mitosis?

  The spindle fibres start to shorten and move towards the centrioles and pull the centromere and chromatids- they are bound to towards the opposite poles of the cell. This causes the centromere to divide into two and the individual chromatids and pulled to each opposite pole of the cell. This stage requires energy in the form of ATP which is provided by respiration in the mitochondria.
• what happens in telophase of mitosis?

  The chromosomes are now at each pole of the cell, and become longer and thinner again; the spindle fibres disintegrate and the nuclear membrane reforms
• In a plant cell, what happens in the cytokinesis of the cell cycle?

  A cleavage furrow forms in the middle of the cell and the cytoskeleton causes the cell membrane to draw inwards until the cell splits into two.
• In a plant, what happens in the cytokinesis of the cell cycle?

  The cell membrane splits into two new cells due to the fusing of vesicles from the golgi apparatus. The cell wall forms two new selection around the membrane to complete the division into two cells.
• two nuclear divisions occur in mitosis, this results in four genetically unique haploid daughter celsl
• How many copies of each chromosome does a haploid have?

  one
• How many copies of each chromosome does a diploid have?

  Two
• what two processes in mitosis cause genetically unique daughter cells?

  Crossing over, independent assortment
• What occurs during the crossing over process of meiosis?


  During the first prophase, homologous chromosomes pair to form bivalents. Crossing over genetic material can occur between the non sister chromatids of bivalents. Breaks can occur in the genetic material where the chromatids cross over and parts of the chromatids are exchanges between the homologous pairs. This results in new combinations of alleles in the resulting gamete
• what happens during independent assortment in meiosis?

  During the first metaphase, the homologous pairs of chromosomes line up opposide eachother on either side of the equator. It is random on which side of the equator that the paternal and maternal chromosome of each pair aligns.
• Describe the structure and function of erythrocytes?

  They have a biconcave shape to increase the surface area for diffusion and icnrease the cell flexibility for it to fit through narrow capilliaries. These cells have no nucleus so that there is more space to hold haemoglobin to increase the transport of oxygen.
• Describe the structure of neutrophils??

  It has a lobed nucleus and granular cytoplasm. The cells are flexible to allow them to surround pathogens and engulf them. They contain lysosomes filled with a hydrolytic enzyme called lysozyme. Neutrophils are made from stemcells in the bone marrow.
• Describe the structure of sperm cells?

  The flagellum of sperm contain many mitochondria to release energy for locomotion to enable the sperm cell to move towards an egg cell. The acrosome in the head of a sperm cell contains digestive enzymes to digest the wall of the egg cell so that the sperm can fertilise the egg cell.
• Describe the structure of a palisade cell?

  They are lcoated in the mesophyll tissue of leaves. They are rectangular, tightly packed cells that contain many chloroplasts to absorb and maximise light energy for photosynthesis. Theey have thin cell walls to reduce the diffusion distance of carbon dioxide.
• Describe the structure of guard cells?

  These pair of cells have flexible walls, more so on one side, so that when turgid the cells bend- when turgid they open the stomata and close when flaccid to help control water loss.
• describe the structure of squamous epithelial tissues?

  They are usually only a single layer of flat cells in contact with the basement membrane of the epithelium. This provides a short diffusion distance.
• describe the structure of cilliated epithelial cells?

  These cells have hair like projections that sway to move substances, such as mucous, out of the lungs or an egg in the oviduct. Goblet cells are also located within the epithelium and these cells release mucous to trap molecules such as dust in the trachea.
• Describe the structure of cartiliage tissues?

  A connective tissue that is firm and flexible, located in the outer ear, nose and at the ends of bones. It provides structural support and it prevents the bones from rubbing together which would damage them. It is made of elastin and collagen fibres and chondrocyte cells with an extracellular matrix.
• Describe the structure of muscle tissues?

  Muscle tissues are composed of tissues that can contract and relax to create movement. Skeletal muscles cause the skeleton to move and are made of myofibrils containing the proteins actin and myosin. Smooth muscle is located within organs and cardiac muscle is within the heart. Muscles have multiple fibres connecting with connective tissues in between.
• Describe the structure of xylem tissues?

  These are the cells that make up the part of the vascular bundle in plants that are responsible for transproting water and mineral ions; the tissue is made up of elongated, hollow and dead cells with lignin in the walls to strengthen and waterproof the walls. Xylem tissues are made from stem cells in the meristem
• describe the structure of the phloem?

  The cells that make up the part of the vascular bundle responsible for transporting organic substances made in photosynthesis. It is made up of sieve tube elements which have perforated end walls- they are lacking most organelles to make the transport of sugars easier and companion cells which contain organelles to make resources for the sieve tube elements. Phloem sieve tube cells are made by the stem cells in the meristem.
• what are the different types of stemcelsl?

  Totipotent

  Pluripotent

  Multipotent

  Unipotent#
• totipotent cells can divide and produce any type of body cells. during development, totipotent cells translate only part of their DNA resulting in a cell specialisation. Totipotent cells occur only for a limited time in early mammalian embryos.
• pluripotent cells are found in embryos and can become almost any type of cells. For this reason they are sued in research with to prospect of using them to treat human disorders. There are issues with this as sometimes the treatment doesnt work, or the stem cells continually divide into tumours. Additionally, ethically there is debate on whether it is right to make a therapeutic clone of yourself to make an embryo to get the stem cells to cure a disease and then destroy the embryo.
• Multipotent and unipotent cells are found in mature mammals and can divide to form a limited number of cell types. Multipotent cells, such as in bone marrow, can differentiate into a limited number of cells- whereas unipotent cells can only differentiate into one type of cell.
• Stem cells could be used in both research and medicien:

  Repairing damaged tissues

  Treatment of neurological conditions e.g. Alzheimer's and Parkinson's

  Research into developmental biology