Biology

• Two types of cells

  Eukaryotic and prokaryotic
• eukaryotic cells

  • found in plants, animals, fungi, protists
  • have a nucleus
  • 10-100 micrometers
• Prokaryotic cells

  • found in bacteria
  • dont have a nucleus
  • 0.1-5.0 micrometers
• Cell membrane (animal & plant)

  • selectively permeable (control what moves in and out)
  • seperates the interior of the cell from the outside environment
• Nucleus (animal & plant)

  • contains chromosomes that contain the cells genetic material
• Ribosomes (animal, plant & bacteria)

  • responsible for making proteins
• Mitochondria (animal & plant)

  • where aerobic respiration takes place

  aerobic respiration is a process which uses glucose and oxygen to release energy
• Cytoplasm (animal, plant & bacteria)

  • a jelly-like fluid that fills the cell
  • where chemical reactions take place
• Vacuole (plant only)

  • fluid-filled sac that stores water
  • enclosed in a membrane
  • can make up as much as 90% of a plant cells volume
• Chloroplast (plant only)

  • contains chlorophyll which is needed for photosynthesis
• Cell wall (plant only)

  • surround the cells and is made of cellulose
  • increase the structural strength of the cell
• Plasmids (bacteria only)

  • small rings of DNA
• Cell wall & membrane (bacteria only)

  • provides structure
• Flagella (bacteria only)

  • only some bacteria cells have this
  • they are whip like structures used for movement
• Sperm cell

  • example of a specialised cell
  • specialised to fertilise egg cells
  • they travel long distances, then break through the egg cell to fertilise it
• Parts of a sperm cell

  • acrosome= at tip of the head. it contains digestive enzyme needed to penetrate an egg cell
  • middle section= filled with mitochondria to give sperm enough energy to be able to travel the long distance
  • head= constains sperm nucleus which contains Half the genetic material- making the sperm cell a haploid cell
  • flagella= allows the sperm to move
• Egg cell

  • example of specialised cell
  • is fertilised by a sperm cell to become a zygote
• Parts of an egg cell

  • cytoplasm= packed with nutrients that the zygote will need to grow
  • haploid nucleus= nucleus contains half the genetic information whilst the sperm cell contains the other half
  • cell membrane= adapted to change structure once the egg is fertilised so no more sperm can get it
• How many chromosomes are there in a haploid cell?

  23
• Ciliated epithelia

  • example of a specialised cell
  • main function is to waft mucus to the back of the throat to be swallowed
  • found in the lining of airways
• Parts of ciliated epithelia

  • cilia= hair like structures that move in unison
  • mitochondria= releases lots of energy for the cilia to be able to move
• Specialised cells:

  • sperm cells: fertilise the egg cell
  • egg cell: fertilised by the sperm cell to become a zygote
  • ciliated epithelia: waft mucus to back of throat to be swallowed
• Magnificaction tells us how many times larger an image seen through a micrscope is compared to the real object
• Resolution is the ability to distinguish between two or more objects that are close together
• What are the two important variables when using a microscope?

  Magnification and resolution
• Magnification= Image size/ actual size
• Light microscope

  This passes light through a specimen, and creates a magnified image using the lenses. it has a resolution better than the human eye.

  light microscopes allowed us to see bacteria cells for the first time and enabled us to see plant and animals cells as separate objects. however, we could still not see lots of the sub-cellular structures apart
• Electron microscope


  Passes electrons through the specimen and is seen through the lenses. They have a better resolution than light microscopes as they resolve distances of 1nm. they also have magnifications of x500,000.

  high level of detail allowed us to see sub-cellular structures more clearly. it also allowed scientists to see how the structures functioned.
• Light microscope experiment

  1. put a thin sample of tissue onto a microscope slide
  2. add a few drops of a suitable stain (iodine)
  3. place a coverslip on top of the tissue and place the slide onto the microscope stage
  4. use the objective lens with the lowest magnification, and focus on the sample
  5. increase the magnification and refocus to see the different features of the cell
• Why is a stain used when using a light microscope?

  To give contrast to the features of the cell
• Name the process in which a cell develops new sub-cellular structures to let it perform a specific function

  Cell differentiation
• Axons are part of the cell that electrical signals travel along
• Dendrites receive messages from other neurones
• What do stem cells do?

  • create more stem cells
  • differentiate to perform another function
• Where are stem cells in plants?

  Meristem
• Where are stem cells in animals?

  bone Marrow
• Enzymes

  Enzymes increase the speed of reactions. they are often called biological catalyst.
• What is the active site?

  to catalyse (speed up) a reaction, the reacting chemical (substrate) must bind to the enzymes active site. the active site will only fit one specific substrate
• what is the lock and key?

  The active site is the lock and the substrate is the key. Only one active site can bind with one substrate
• enzyme activity

  The substrate bind to the active site of an enzyme, which has a complementary shape. Here, its reaction is sped up.