9.3 Flashcards
What allows indeterminate growth
Undifferentiated cells in the meristems of plants
plants divide by mitosis (genetically identical cells produced)
indeterminate= cells continue to divide indefinitely
animals have determinate growth
most plant cells are totipotent
describe what happens to the cells in the shoot apical meristem as they divide and differentiate
some cells always remain in the meristem, continuing through the cell cycle producing new cells
these new cells produced can push existing cells to the edge of the meristem, where they stop dividing, and undergo rapid growth & differentiation into stem or leaf tissue
How does auxins affect plant growth
auxin is produced by cells in the apical meristem
auxin enters the cells by facilitated diffusion through AUX1 channels on the apical side of a cells membrane
once inside, auxin loses a proton and become negatively charged
the negatively charged auxin molecules are then actively transported out of the cell by PIN protein pumps on the basal side of the cell membrane
auxin stimulates cell elongation:
auxin activates proton pumps that actively transport H+ ions out of cells into cell walls
this increase in H+ ions activates expansion proteins that loosen the connections b/w cellulose fibres
this allows cells to slide past each other so the cell can elongate when it fills with water
Explain how auxin efflux pumps cause:
positive phototropism in shoots
light is detected by phototropins in the top of a shoot
if more light is detected on one side; PIN protein pumps move to the shadier side of the cell
therefore, auxin is transported laterally across to the shadier side of the cell & promotes cell elongation on that side
thus, the shoot bends towards the light
Explain how auxin efflux pumps cause:
positive geotropism in roots
gravity causes accumulation of statoliths on the lower side of the cell
so, PIN proteins move to the lower side of the cell and transport auxin out of the cells on the lower side of the root
auxin inhibits cell elongation in roots and thus the cells elongate more on the upper side & the root bends downwards
Explain how micropropagation produces large numbers of genetically identical plants
A plant with a desirable feature is identified and a small piece of tissue is taken, usually from the shoot apex
this tissue is placed in sterile nutrient agar gel with high auxin concentration to stimulate cell division and growth
this then forms a callus which is cut up and transferred to another nutrient rich agar gel with high auxin concentration to continue cell division and growth as necessary
a callus is then transferred to nutrient agar gel with low auxin concentration and high cytokinin concentration to stimulate plantlets
these plantlets are then transferred to soil to continue growth and development as necessary
What is micropropagation used for?
for rapid bulking of new varieties
production of virus free strains of existing varieties
propagation of orchids and other rare species
