Plant Adaptations & Homeostasis

How do plants maintain homeostasis? What are some common issues/problems plants may have?

PROBLEMS ON HOT DRY DAYS If stomata are open to receive CO2 . . . results in water loss (transpiration) On hot, dry days if plant shuts stomata to conserve water . . . photosynthesis slows http://www.ipm.iastate.edu/ipm/icm/files/images/spider-mite-field.jpg

Plant responses to water limitations When plants under water stress, they close their stomata and decrease their transpiration rates (water loss that occurs when stomata open to get carbon dioxide for photosynthesis) Would this be an example of positive or negative feedback? Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College.

PHOTORESPIRATION C3 ____ plants (Ex: rice, wheat, soybeans) (1st product of carbon fixation has 3 C’s- 3PG) On hot, dry days when plant shuts stomata plant switches to ______________________ Rubisco adds O2 to Calvin cycle instead of CO2 Product broken down by mitochondria/peroxisomes to release CO2 COUNTERPRODUCTIVE: Makes NO ATP Makes NO sugar Uses ATP Decreases photosynthesis by siphoning molecules from Calvin cycle PHOTORESPIRATION

Some plants have evolved different METHODS of CARBON FIXATION ______ plants (Ex: corn & sugarcane Spatial separation of steps for carbon fixation and calvin cycle in different types of cells ______ Crassulacean acid metabolism (Ex: succulents, cactus, pineapple,) Temporal separation of steps, carbon fixation and calvin cycle occur in same cell one at night and other during day WAYS TO AVOID DECREASE IN PHOTOSYNTHESIS DUE TO PHOTORESPIRATION CAM SEE ANIMATION

CALVIN CYCLE found in BUNDLE SHEATH CELLS in C4 plants * PEP CARBOXYLASE ________________________ adds CO2 to make a 4 carbon molecule before entering Calvin Cycle

How do plants transfer/communicate between cells? Plasmodesmata (gap junctions) between plant cells that allow material to be transported from cell to cell

Plant immune responses invading pathogen are deprived of nutrients because the plant sends signals to kill cell surrounding the region where the pathogen infected the plant. Plant also induces the production of antimicrobial proteins. When herbivores start eating plant, cell sends chemical signals to other regions of the plant Some chemicals can inhibit leaf digestion in the insect’s gut

Plants even exhibit positive feedback…

Ripening of Fruit First fruit that starts to ripen releases ethylene gas that stimulates other fruits to ripen and create more ethylene gas