bio

• parts of an animal cell

  cell membrane

  cytoplasm

  ribosomes

  nucleus

  mitochondria
• cytoplasm


  where chemical reactions take place
• ribosomes function


  protein synthesis
• nucleus function


  control cell activities
• parts of a plant cell


  nucleus

  ribosomes

  chloroplasts

  mitochondria

  permanent vacuole

  cell membrane

  cell wall
• animal specialised cells

  • sperm cells
  • nerve cell
  • muscle cells
• why do muscle cells have lots of mitochondria

  to provide the energy to contract
• cell differentiation


  -the process in which cells become specialised

  -where different genes are turned on and off in each cell to change their shape and sub cellular structures

  -because of this they become adapted to carry out a particular function
• what are stem cells

  undifferentiated cells which can produce different cell types through differentiation
• cell differentiation in plants

  plant cells have the ability to differentiate throughout their whole lives.

  this is what makes it possible to clone plants
• cell differentiation in animals

  animal cells differentiate at an early stage and once they are specialised very few can change, they just divide by mitosis to replace themselves
• what are the two types of microscopes

  light microscopes

  electron microscopes
• purpose of microscope 


  magnifies so we can see the actual structures larger than life
• calculation for magnification


  image size/actual size
• what can you see using a light microscope

  able to see the nucleus and just about the size of mitochondria at 1500x
• difference between electron microscopes and light microscopes

  electron microscopes have much higher magnification and resolution than light microscopes
• electron microscopes


  really important in terms of discoveries on earth because they have allowed us to see inside cells in more detail, and even inside of mitochondria, chloroplasts and bacteria.
• Onion cell microscopy practical

  1. Add drop of water to microscope slide

  2. Take very thin piece of tissue (e.g. onion skin) - thin so light can pass through

  3. Stain skin (this case iodine) - so we can see structures inside cell like nucleus and cell walls

  4. Lower a cover slip on top of stained tissue to cover it before you put it on microscope stage

  5. Use clips to hold slide in place on stage

  6. Rotate objective lens to lowest power first. Once focused increase to magnify the image

  7. Use course focus wheel to focus image so that it isnt blurry (now increase objective power by rotating)

  8. At high magnifications use fine focus wheel to make images focused at higher magnification
• DNA


  • long molecule that forms a twisted double helix
  • made up of many short sections called genes
  • coils to form structures called chromosomes to fit inside the nucleus
• chromosomes inside the nucleus

  -usually arranged in pairs

  -in humans, there are 23 pairs of chromosomes in the nucleus of every cell in the body
• what is the cell cycle


  the process that all cells go through to prepare for cell division and then to divide, and then it starts again as soon as they've divided
• what is interphase


  the cell is preparing for division so it replicates its DNA so the DNA doubles, the cell elongates and it increases the number of sub cellular structures
• what is mitosis


  the cell division from one cell into two identical daughter cells
• process of mitosis


  • chromosomes pulled apart to opposite poles of the cell
  • the cell membrane and cytoplasm divides
  • forming 2 genetically identical daughter cells with the same chromosome number
• purpose of mitosis


  allows organisms to grow and replace cells in damaged tissues or organs
• different types/sources of stem cells


  • embryonic stem cells
  • adult stem cells
  • plant stem cells
• embryonic stem cells


  can differentiate into nearly any type of animal cell
• adult stem cells


  e.g. from the bone marrow

  -can differentiate into some types of animal cell

  e.g. blood cells
• plant stem cells


  from the tips of roots and shoots (meristems)

  can differentiate into any type of plant cell

  can be used to make lots of cloned plants fast and save rare species from extinction.
• therapeutic cloning


  can be used to produce embryonic stem cells that are genetically identical to the patient

  these stem cells can be used to grow new cells to replace the damaged ones the parents need

  e.g:

  blood cells after cancer treatment

  neural cells to treat paralysis

  pancreatic cells to treat type one diabetes
• ethical issues around using embryonic stem cells


  -objection to the fact that the embryo cannot consent to be used unlike if adult stem cells are taken from a patient that is able to consent

  -an embryo is a potential life meaning that unused embryos being destroyed is unacceptable.

  -risk of viral infection transfer - especially if the stem cells are coming from another person

  -risk of cancers because stem cells can divide rapidly and lead to a tumor
• diffusion


  -the net movement of particles from an area of high concentration to an area of low concentration

  -it is a passive process because it does not require energy
• examples of diffusion 


  -oxygen and glucose diffuse into cells because they are needed in respiration, so they will be used up

  -carbon dioxide and urea diffuse out of cells because they are waste products for metabolic processes so they will build up inside cells and be in higher concentrations
• factors affecting rate of diffusion (and osmosis)


  -concentration gradient - if you increase the concentration gradient, you will increase the speed of diffusion

  -reducing the distance particles have travel increases the speed of diffusion

  -increasing the temperature increases the speed of diffusion

  -increasing the surface area of the membrane increases the speed of diffusion
• exchange surfaces adaptations to maximise the rate of diffusion

  -thin walls - reduce distance

  -large surface area

  -good blood or air supply - maintain a steep concentration gradient
• example of exchange surfaces - Alveoli

  gases diffusing between lungs and bloods in capillaries
• example of exchange surfaces - villi in the small intestine


  small molecules (amino acids, glucose, fatty acids, and glycerol) diffusing from small intestine into blood in capillaries
• examples of exchange surfaces - leaves in plants

  gasses diffusing in and out of stomata for gas exchange and into spongy mesophyll tissue layers where they will be exchanged with cells that are carrying out respiration and photosynthesis
• surface area to volume ratio


  divide the surface area of an organism by its volume

  (the larger an organism comes, the smaller the surface are to volume ratio)
• why dont single celled organisms need an exchange surface


  single celled organisms do not need an exchange surface because they have a very large surface area to volume ratio and a short distance for substances to diffuse in/out