2.6.4- 2.6.5- Cell diversity

• Unicellular:

  • relies on diffusion
  • large SA:V
  • single cell that carries out all functions
• Multicellular:

  • requires a transport system
  • smaller SA:V
  • needs specialised cells and systems as cells arnt in contact with the external environment
• Differentiation: eukaryotes start life as a zygote and differentiate into different types of specialised cells when certain genes are turned on/expressed
• Fertilised egg + spermatozoon = zygote
• Genes can:

  • Alter proportions of organelles
  • Change cell shape
  • Change contents of the cell
• Red blood cells/erythrocytes:

  • carries oxygen from the lungs to respiring cells
  • large SA:V- allows gases to diffuse easier
  • flexible due to a well developed cytoskeleton
  • no organelles- more space to carry haemoglobin
• White blood cells/neutrophil:

  • 2 times the size of erythrocytes
  • contains a large lobed nucleus
  • travel to site of infection by chemotaxis- moves out of the blood to the body tissue
  • They ingest bacteria by phagocytis- SED
• Spermatozoon:

  • lots of mitochondria- provides ATP for mobilisation
  • haploid amount of chromosomes
  • acrosome- enzymes in the head to digest egg outer shell
  • lots of microtubules in tail to allow for better mobilisation
  • tail is undulipodium- rotates
• Epithelial cells are found in the, skin, alveoli, villi and intestinal walls. Squamous shape to reduce diffusion distance, ciliates epithelium to increase SA.
• Palisade cells:

  • contains many chloroplasts needed for photosynthesis- packed closely together on the upper surface
  • contains many cytoskeleton threads and motor proteins to move chloroplasts nearer to the surface in low light conditions
  • large vacuole near the cell peripheray, to reduce the diffusion distance
• Guard cells open and close:

  • ATP is produced
  • ATP is used to move ions into the guard cells by active transport
  • water potential lowers inside
  • water moves in by osmosis
  • cell becomes turgid
• Root hair cells have a large surface area to absorb water and minerals from the soil. They’re squamous to reduce diffusion distance.
• Xylem is hollow and lignified

  Phloem has companion cells