biology p1

• why is the human circulatory system a double circulatory system

  blood passes through the heart twice for every circuit around the body

  deoxygenated blood is pumped from the right side of the heart to the lungs and the oxygenated blood that returns is pumped from the left side of the heart to the body
• where does the artery carry blood and what pressure

  away from the heart

  (high pressure)
• where does the vein carry blood and what pressure

  carries blood to the heart (low pressure)
• where does the capillary carry blood and what does it connect

  carries blood to tissues and cells

  connects arteries and veins
• structure of arteries

  thick

  muscular

  elastic walls - withstrand high pressure

  small lumen
• structure of veins

  valves to stop blood flowing the wrong way

  thin walls

  large lumen
• structure of capillaries

  one cell thick - short diffusion distance for substances to move between blood and tissues

  very narrow lumen
• two types of microscopes

  electron

  light
• what does light use to form an image and magnify it

  light

  lenses
• what can a light microscope see

  individual cells and large sub cellular substances like nuclei
• what does an electron microscope use to form an image

  electrons instead of light
• which microscope has a higher magnification and resolution

  electron
• what can a electron microscope see

  smaller things like mitochondria or even plasmids and ribosomes
• magnification equation


  image size/real size
• how to prepare a slide

  1. add a drop of water in the middle of a clean slide
  2. peel with tweezers an epidermal tissue from the layer of the onion
  3. place that onto the water
  4. put a drop of iodine solution onto the water as it acts as a stain, highlighting object
  5. place a cover slip on top, making sure there are no air bubbles
• um into mm


  /1000
• what does um stand for

  micrometers
• use light microscope to look at the slide:

  1. clip the slide onto stage
  2. select lowest-powered objective lens
  3. use coarse adjustment knob to move stage just below objective lens
  4. look down eyepiece, use coarse adjustment knob to move stage down to roughly focused
  5. adjust focus with fine adjustment knob, until clear image
  6. if slide needs to be greater magnification, swap to higher-powered objective lens
• what is cell differentiation 


  a process in which a cell changes to become specialised
• an example of undifferentiated cell

  stem cell
• what are sperm cells used for

  reproduction
• what are sperm cells adaptations

  long tail to swim to egg

  lots of mitochondria to provide energy

  enzymes to digest through egg cell membrane
• what are nerve cells use

  carrying out electrical signals to one part of the body to another
• nerve cell adaptations 


  long to cover more distance

  branched connections at their ends to connect other nerve cells making a network
• muscle cell use

  contraction
• muscle cell adaptations


  long so they have space to contract

  lots of mitochondria to provide energy for contraction
• what are root hair cells used for

  absorbing water and minerals
• where do you find root hair cells

  on the surface of plant roots that stick out in the soil
• adaptation of root hair cell

  large surface area to absorb water and mineral ions
• phloem and xylem use

  transporting substances
• xylem cells are...


  hollow in the centre
• phloem cells...


  have few sub-cellular structures, so things can flow through them