B1 cell biology

• Eukaryotic cells

  • animals and plants are eukaryotes
  • eukaryotes are organisms that are made up of eukaryotic cells
  • complex
• subcellular structures of animal cells

  • Nucleus ; contains genetic material that controls activities of cell
  • Cytoplasm ; gel-like substance where most chemical reactions occur. It contains enzymes that control chemical reactions
  • Cell membrane ; holds the cell together and controls what goes in and out
  • Mitochondria ; where most of the reactions for aerobic respiration occurs. Respiration transfers energy cell needs to work
  • Ribosomes ; where proteins are made in the cell
• subcellular structures of plant cells

  • Plants have all the bits that animal cells have and a few extra that animal cells don't have ;

  1. Rigid cell wall ; made of cellulose. It supports the cell and strengthens it.
  2. Permanent vacuole ; contains cell sap (a weak solution of sugar and salts)
  3. Chloroplasts ; where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.
• subcellular structure of Prokaryotic cells (bacteria)

  • cell wall
  • cell membrane
  • cytoplasm
  • may contain one or more small rings of DNA called plasmids
  • A single circular strand of DNA that floats freely in the cytoplasm
• Light microscopes

  • Use light and lenses to form an image of specimen and magnify it (make it look bigger)
  • They let us see individual cells and large subcellular structures like nuclei
  • Cheaper than electron microscopes
• Electron microscopes

  • Use electrons instead of light to form an image
  • They have a much higher magnification than light microscopes
  • Also have a higher resolution (provide sharper , clearer and detailed image)
  • Allow us to see very small things such as internal structures of mitochondria and chloroplasts in more detail. Also ribosomes and plasmids.
• How to convert from μm to mm

  • MUST ALWAYS DO THIS
  • divide by a 1000
• How to draw observation from what you see from eyepiece on the microscope

  • Use a pencil with a sharp point
  • Make sure drawing takes up at least half the space available
  • Make sure it is drawn clear with no broken lines
  • Should NOT include any colouring or shading
  • Subcellular structures should be drawn in proportion
  • Include title of what you are observing
  • Write magnification
  • Label important features using straight , uncrossed lines
• What is the formula triangle for magnification , image size and actual size 


  Here:

  
• Differentiation (cells differentiate to become specialised)

  • Process where a cell changes to become specialised for its job
  • As cells change , they develop new subcellular structures and turn into different types of cells, allowing them to carry specific functions
  • Most differentiation occurs when an organism develops. Eg in most animals the ability to differentiate is lost at an early stage, after becoming specialised. Plants never lose this ability
  • Cells that differentiate in animals are mainly used for repairing cells eg skin or blood cells.
  • Undifferentiated cells are called stem cells
• Specialised cell-sperm and its function and adaptation

  • Function : to get the male DNA to the female DNA
  • Adaptation : streamlined head, long tail, lots of mitochondria to provide energy
• Specialised cell-nerve cells and its function and adaptation

  • Function : to send electrical impulses around the body
  • Adaptation : long to cover more distance. Has branched connections to pass messages around the body.
• Specialised cell-muscle cells and its function and adaptation

  • Function : to contract quickly
  • Adaptation : long so that they have space to contract , and contain lots of mitochondria to generate energy needed for contraction
• Specialised cell-root hair and its function and adaptation

  • Function : to absorb water from the soil
  • Adaptation : Has long hairs that stick out into the soil which provides a large surface area for absorbing water and mineral ions from the soil.
• Specialised cell-phloem and its function and adaptation

  • Function : transports substances (e.g. food and water) around the plant
  • Adaptation : Pores to allow cell sap to flow. Cells are long and joined end to end to form tubes to transport substances. Have very few subcellular structures
• Specialised cell- xylem cells and its function and adaptation

  • Function : transports water through the plant
  • Adaptation : Hollow in the centre. Tubes connected from end to end
• chromosomes

  • most cells in your body have a nucleus which contains your genetic material in the form of chromosomes.
  • chromosomes are coiled up lengths of DNA molecules (double helix)
  • Each chromosome contains a large number of genes which control the development of different characteristics.
  • In a human nucleus there are 23 pairs of chromosomes
• The cell cycle

  • the stage of the cell cycle when the cell divides is called mitosis
  • Multicellular organisms use mitosis to grow or replace cells that have been damaged
  • The end of the cell cycle results in two new cells identical to the original cell with same number of chromosomes
• The stage of growth and DNA replication in the cell cycle

  
  

  1. In a cell that is not dividing, the DNA is all spread out in long strings
  2. Before it divides, the cell has to grow and increase the amount of subcellular structures e.g. mitochondria and ribosomes
  3. It then duplicates its DNA so there is one copy for each new cell. DNA is copied and forms X shaped chromosomes. Each arm is an exact duplicate of the other
• Mitosis steps (after DNA have been copied,the cell is ready for mitosis)
• Mitosis process

  After the DNA has been copied, the cell is ready for mitosis:

  4. The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go opposite ends of the cell.

  5. Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells- the nucleus has divided

  6. The cytoplasm and cell membrane divide. The cell has now produced 2 new daughter cells. These contain exactly the same DNA so they're identical (also identical to the parent cell)
• Embryonic Stem Cells

  Can turn into ANY type of cell
• Stem cells

  Undifferentiated cells that can divide to produce more undifferentiated cells and differentiate into different types of cells depending on instructions
• Stem cells are found in early human embryos
• Embryonic stem cells


  • Have the potential to turn into any kind of cell
  • All the different types of cell found in a human being have to come from those few cells in the early embryo
• Adult stem cells

  Found in certain places like bone marrow, can't turn into any cell type at all, only certain ones such as blood cells
• Stem cells from embryos and bone marrow

  1. Can be grown in a lab to produce clones (genetically identical cells)

  2. Can be made to differentiate into specialised cells to use in medicine or research
• Stem cells

  Cells that can develop into different cell types in the body
• Medicine already uses adult stem cells to cure disease
• Adult stem cell uses

  • Replacing faulty blood cells in patients with stem cells from a healthy person's bone marrow
• Embryonic stem cells

  Could be used to replace faulty cells in sick people, such as insulin-producing cells for diabetes, nerve cells for spinal injuries
• Therapeutic cloning

  1. Making an embryo with the same genetic information as the patient

  2. Stem cells produced would not be rejected by the patient's body
• There are risks involved in using stem cells in medicine
• Stem cells grown in the lab may become contaminated with a virus which could be passed on to the patient and make them sicker
• Reasons some people are against stem cell research

  • They feel that human embryos shouldn't be used for experiments since each one is a potential human life
  • They think that curing existing patients who are suffering is more important than the rights of embryos
  • The embryos used in the research are usually unwanted ones from fertility clinics which, if they weren't used for research, would probably just be destroyed
• Campaigners for the rights of embryos

  They feel that scientists should concentrate more on finding and developing other sources of stem cells, so people could be helped without having to use embryos
• In some countries stem cell research is banned
• In the UK, stem cell research is allowed as long as it follows strict guidelines
• Stem Cells Can Produce Identical Plants

  1. In plants, stem cells are found in the meristems (parts of the plant where growth occurs )
  2. Throughout the plant's entire life, cells in the meristem tissues can differentiate into any type of plant cell

  • These stem oells can be used to produce clones (identical copies) of whole plants quickly and cheaply
  • They can be used to grow more plants of rare species (to prevent them being wiped out).
  • can also be used to grow crops of identical plants that have desired features for farmers, for eg , disease resistance.
• Diffusion definition

  Diffusion is the spreading out (gradual movement) of particles from an area of a high to low concentration