D 2.1 - CELL AND NUCLEAR DIVISION, B 1.1 CARBOHYDRATES & LIPIDS

• why do all organisms need to produce new cells

  growth, maintenance and reproduction
• how do organisms produce new cells

  cell division - one cell divides into two (mother cell too two daughter cells)
• what happens to the mother cell in the process of cell division


  mother cell disappears as an entity in the process
• what are the three factors of cell theory

  1. All organisms consist of cells2. All cells come from pre-existing cells3. Cells are the smallest units of life
• what evidence can we give that cells are formed from pre-existing cells

  zygote which was formed by the fusion of a sperm and egg cell
• What is cytokinesis?

  splitting of the cytoplasm // cytoplasm of a cell is divided between two daughter cells
• when does/can the process of cytokinesis happen

  as soon as chromosomes have separated and are far enough apart to ensure that none of them ends up in the wrong cell
• is cytokinesis in plant cells the same as in animal cells

  no
• process of cytokinesis in an animal cell

  plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow - done by using a ring of contractile proteins immediately inside the plasma membrane
• What is a cleavage furrow?

  indentation of the cell's surface that begins the progression of cleavage, by which animal and some algal cells undergo cytokinesis, the final splitting of the membrane, in the process of cell division
• What are the contractile proteins?

  actin and myosin and are similar to those that cause contraction in muscles
• happens when the cleavage furrow reaches the centre

  cell is pinched apart into two daughter cells
• how many stages of cytokinesis do plants have

  2
• first process of cytokinesis in a plant cell

  microtubules are built into a scaffold straddling the equator, which is used to assemble a layer of vesicles - vesicles fuse together to form plate-shaped structures
• what happens in plant cells when more vesicles fuse together - cytokinesis


  two complete layers of membrane are formed across the whole of the equator of the cell - plasma membranes which connect to the pre-existing plasma membrane completing the division of the cytoplasm
• what is the second part for plants

  pectin's and other substances are brought in vesicles and deposited by exocytosis between the two new membranes - forms middle lamella which link the new cell walls. Both daughter cells will bring cellulose into the equator and deposit it by exocytosis adjacent tot he middle lamella
• what is equal cytokinesis


  where the cytoplasm of the mother cell has been divided into equal halves
• where does equal cytosis take place - one example

  growing root tip
• why is the root growth


  grows due to enlargement and division of cells arranged in columns
• why is root growth equal cytokinesis

  cells in a column all differentiate in the same way so cytoplasm is apportioned equally when they divide
• what is unequal cytokinesis


  where the cytoplasm does not split equally
• what must be ensured for an unequal split in cytoplasm to allow the cell to keep on living

  can survive and grow if they have a nucleus and at least one of each organelle that can't be assembled from components in the cell
• how can mitochondria be produced

  by division of pre-existing mitochondrion
• examples of unequal division

  budding in yeast and oogenesis in humans
• how do yeast cells reproduce

  reproduce asexually in a process called budding
• What is budding?

  a new individual grows on the parent then separates
• how does the nucleus in yeast cells divide

  by mitosis and is given to the small outgrowth on the parent cell
• describe the process of budding

  nuclei and small amounts of cytoplasm is given to small outgrowth; a dividing wall is constructed separating the two cells and the small cell splits away
• what is left once budding has ended

  a scar to where it was attached on the larger cell
• is budding a repeated process


  yes and it does not have to double in size between each division
• What is oogenesis?

  production of female gametes
• what happens during sperm production

  the cytoplasm is divided equally in the first and second divisions, resulting in four, equally sized small cells, each of which develops into a mature sperm
• why is there unequal distribution of cytoplasm in oogenesis


  only one egg produced at a time, with enough stored food to sustain the developing embryo
• what does the first division in oogenesis produce


  one large cell with nearly all the cytoplasm and a small polar body which does not develop further
• which out of large cell and small polar body carries out the second division

  large cell
• what happens in the second division in oogenesis

  the large cell experiences unequal division of the cytoplasm resulting in one large cell and one very small polar body
• what happens to the large cell produced

  develops into a mature oocyte that is ready for fertilisation
• what surrounds the oocyte

  zona pellucida
• what is zona pellucida

  thick outer, protective covering of human egg cell. penetrated by sperm acrosome
• What are anucleate cells?


  without a nucleus