Plant cell biology 1

• what keeps plants upright

  internal cellular pressure
• what is turgor pressure

  an intracellular hydrostatic force that pushes the plasma membrane against the cell wall
• what percentage of cell volume does the vacuole take up

  90%
• two types of vacuoles

  • lytic vacuoles
  • protein storage vacuoles
• what do lytic vacuoles do

  functions in degradation, stores ions and anthocyanins and generates turgor pressure
• what do PSVs do

  function as storage compartment (alkaloids, enzymes, salts, sugar, but also defence proteins to fight pathogens)
• why are vacuoles red

  Anthocyanins protect against oxidative stress (they scavenge free electrons) and attract pollinating insects
• primary cell wall

  • flexible and unorganised
  • Primary wall: cellulose, hemicellulose and pectin; cellulose fibrils laid down at all angles; flexible; gets deformed by turgor pressure
• secondary cell wall

  • is formed in fully developed cells
  • rigid and cellulose fibrils show a high degree of order
  • The secondary wall consists of cellulose, xylan, lignin (wood)
  • The microfibrils are aligned mostly in the same direction and form layers this provides strength to the secondary cell wall and makes it rigid
• what does the cellulose synthase complex consist of

  several isoforms of the CesA protein
• what does the CesA protein do

  forms a pore in the plasma membrane through which the nascent glucan chain is extruded into the wall.
• what are plasmodesmata

  connects plant cells, allow free passage of small molecules (ions, water, sugar, amino acids)
• what seals plasmodesmata

  Callose is a glucose-based sugar polymer, which is formed by callose synthase and degraded by beta-1,3-glucanases
• thylakoid

  a membrane compartment; the thylakoid membrane surrounds the thylakoid lumen
• granum

  a stack of thylakoids
• stroma

  matrix of the chloroplast
• what does the stroma contain

  1. Carbon fixation enzymes
  2. Chloroplast DNA
  3. Ribosomes
• what does the membrane contain

  Chloroplast import and export machinery
• what does the thylakoid contain

  1. Light capturing system
  2. ATP synthase
• what light do chlorophyll absorb

  blue and red
• electron transfer in photosynthesis

  1. Red light is absorbed by chlorophyll which cleaves water thereby generating 1 oxygen, 4 protons and 1 electron
  2. The electron is transferred across the membrane which pumps 1 proton across the membrane.
  3. The electron is further excited in the photosystem I
  4. The electron is transferred onto NADP+ resulting in NADPH
  5. The proton gradient is utilised to generate ATP
• how much sun is absorbed and how much energy is chemically bound

  1%, 28%
• process of leaf change

  • During senescence in autumn, cellular component get recycled
  • Before senescence, leaves are green leaf due to chloroplasts (green) + chromoplasts (yellow)
  • During senescence, Chloroplasts are degraded and yellow chromoplasts are left
  • Red anthocyanins are formed that may protect the senescing tissue from light damage (optimises gain from recycling)