bio topic 1 - cell biology

• prokaryotic cells 


  smaller and simpler than eukaryotic, they do not contain their genetic information in a nucleus. e.g. bacteria cells
• eukaryotes


  contain their genetic information inside the nucleus, they are complex and include plant and animal cells.
• animal cells 


  contain nucleus, cytoplasm, mitochondria, ribosomes, cell membrane
• plant cells


  contain cell wall, permanent vacuole, chloroplasts, nucleus, cell membrane, mitochondria, ribosomes, cytoplasm
• nucleus


  contains genetic material that controls the activities of the cell
• cytoplasm


  gel-like substance where most chemical reactions take place. it contains enzymes that control these chemical reactions.
• cell membrane


  holds the cell together and controls what goes in and out
• mitochondria


  where most of the reactions for aerobic respiration take place. respiration transfers energy that the cell needs to work
• ribosomes

  where proteins are made in the cell - protein synthesis
• cell wall


  made of cellulose - supports the cell and strengthens it
• permanent vacuole


  contains cell sap, a weak solution of sugar and salts. keeps the cells shape
• chloroplasts


  where photosynthesis occurs, which makes food for the plant. they contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis
• bacteria cells


  contain cytoplasm, cell membrane, cell wall. they do not have mitochondria or chloroplasts. they also don't have a nucleus but instead a single circular strand of DNA that floats freely in the cytoplasm. they may also contain one or more small rings of DNA called plasmids.
• light microscopes


  use light and lenses to form an image of a specimen and magnify it. they have a lower magnification and resolution than electron microscopes.
• electron microscopes

  they use electrons instead of light to form an image. they have a much higher resolution and magnification to light microscopes. thye let us see much smaller things in more detail, like the internal structure of mitochondria and chloroplasts.
• magnification

  image size / real size
• differentiation


  process by which a cell changes to become specialised for its job
• when does differentiation occur

  as an organism develops. in most animal cells the ability to differentiate is lost at an early stage, after they become specialised. lots of plant cells do not lose this ability
• what are cells that differentiate in mature animals used for

  repairing and replacing cells
• what are cells that are undifferentiated called?

  stem cells
• sperm cells

  specialised for reproduction. it has a long tail and a streamlined head to help it swim to the egg. lots of mitochondria in the cell to provide it with energy to swim. carries enzymes in its head to digest through the egg cell membrane
• nerve cells

  specialised for rapid signalling. the function of nerve cells is to carry electrical signals from one part of the body to another. these cells are long to cover more distance and have branched connections at their ends to connect to other nerve cells and form a network throughout the body.
• muscle cells

  specialised for contraction. they need to contract quickly. these cells are long (so they have space to contract) and contain lots of mitochondria to generate the energy needed for contraction.
• root hair cells

  specialised for absorbing water and minerals. root hair cells are on the surface of plant roots, which grow into long "hairs" that stick out into the soil. this gives the plant a big surface area for absorbing water and mineral ions from the soil.
• phloem and xylem cells

  specialised for transporting substances. they transport substances such as food and water around plants. to form the tubes, the cells are long and joined end to end. xylem cells are hollow in the centre and phloem cells have very few subcellular structures, so that things can flow through them.
• chromosomes

  they contain genetic information. they are found in the nucleus. they are coiled up lengths of DNA molecules. each chromosomes carry a large number of genes. different genes control the development of different characters. body cells have two copies of each chromosome (23)
• cell cycle

  makes new cells for growth, development and repair. body cells in multicellular organisms divide to produce cells as part of a series of stages called the cell cycle.
• mitosis


  is a stage in the cell cycle where the cell divides. multicellular organisms use mitosis to grow or replace cells that have been damaged. it results in two new cells identical to the original cell, with the same number of chromosomes.
• what are the two main stages of the cell cycle

  growth and DNA replication, mitosis
• explain the first stage of the cell cycle, growth & DNA replication


  before a cell divides it has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes. it then duplicates its DNA - so there is only one copy for each new cell. the DNA is copied and forms X-shaped chromosomes. each 'arm' of the chromosome is an exact duplicate to the other.
• explain the second stage of the cell cycle, mitosis

  the chromosomes line up in the centre of the cell and cell fibres pull them apart. the two arms of each chromosome go to the opposite ends of the cell. membranes form around each of the sets of chromosomes. these become the nuclei of the two new cells - the nucleus has divided. lastly the cytoplasm and the cell membrane divide.
• what is the result of the cell cycle

  the cell has now produced two daughter cells. the daughter cells contain exactly the same DNA - they're identical. their DNA is also identical to the parent cell.
• explain binary fission

  1. the circular DNA and plasmids replicate.
  2. the cell gets bigger and the circular DNA strands move to opposite 'poles' of the cell
  3. the cytoplasm begins to divide and new cell walls begin to form
  4. the cytoplasm divides and two daughter cells are produced. each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmids.
• where are stem cells found

  in early human embryos or adult bone marrow
• what is different about embryonic stem cells to stem cells found in bone marrow?

  stem cells found in bone marrow cant turn into any cell type at all, only certain ones such as blood cells.
• why are stem cells useful?

  medicine uses adult stem cells to cure disease. in a type of cloning (therapeutic cloning), an embryo could be made to have the same genetic information as the patient. this means that stem cells produced from it would also contain the same genes and so wouldn't be rejected by the patients body if used to replace faulty cells.
• is there any risks to stem cells?

  stem cells grown in a lab may become contaminated with a virus which could be passed on to the patient and so make them sicker.
• why are some people against stem cell research?

  ethical concerns - each embryo is a potential human life.
• where are stem cells found in plants?

  meristems - cells in the meristem tissue can differentiate into any type of plant cell.
• why is stem cells in plants beneficial?

  these stem cells can be used to grow clones of whole plants quickly and cheaply. they can be used to grow more plants of rare species. they can grow plants that have desired features for farmers e.g. disease resistance.