gas exchange

• role of villi?

  increases the SA for absorption of molecules
• 1 feature of villi?

  contains microvilli on the surface which increases the SA even more than usual
• adaptations of villi

  • very good blood supply = bloodstream rapidly removes the producs of digestion
  • capillaries = increases conc gradient
  • thin membrane = short diffusion pathway
  • all increase the rate of diffusion if any molecules cannot be absorbed by diffusion, they are by active transport
• where are villi found?

  the small intestines for absorption
• first step of gas exchange in plants - stomata?

  stomata (contains small pores)= surrounded by two specialized guard cells. guard cells open and close the pores to regulate gas exchange and water loss. guard cells take in water= turgid = causes stomata to open lose water= flaccid= stomata closes
• step 2 how gas exchange takes place in plants - diffusion of gases?

  once stomata opens, gases like CO2, O2, water vapour diffuses in and out of leaf this diffusion occurs along a conc gradient (gases move from areas of high to low conc)
• step 3 of gas exchange in plants - photosynthesis?

  plants take in CO2 which enters leaf through stomata & diffuses into the cells where photosynthesis takes place. inside the leaf cells CO2 is used for photosynth where it is converted into glucose and O2. O2 produced during photosynthesis exits the leaf through the stomata
• step 4 how gas exchange occurs in plants - respiration?

  during respiration plants take in O2 from the atmosphere through the stomata and release CO2 as a waste product.
• what is fertlisation?

  when a sperm cell joins with an ovum (egg cell)
• 6 features of sperm cells

  - contain DNA in nucleus

  - contains half the DNA of a normal adult cells - haploid

  - long tail = allowing them to swim to the egg cell

  - streamlined= making it easier to swim

  - contains mito = provides energy for movement

  - contain enzymes= allow them to digest their way through the outer layer of the egg cell

  -acrosome in the head= contains enzymes so sperm can penetrate egg
• 4 features of nerve cells

  • job= carry electrical impulses from 1 part of body to another
  • axon covered with myelin= insulates the axon and speeds up the transmission of nerve impulses
  • end of axon contains synapses= allows impulses to pass from 1 nerve cell to another
  • dendrires = increase the SA so other nerve cells can connect more easily
• 4 features of muscle cells

  • contract (get shorter) by = contains protein fibres which changes length
  • when muscles contract, the protein fibres shorten= decreasing the length of cell
  • contains lots of mito to provide energy for muscle contraction work together to form muscle tissue
• Why should a Petri dish be stored upside down?


  To prevent condensation forming on the lid and then dripping onto the agar, contaminating the sample