1. Plant Adaptations & Homeostasis

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

3. PROBLEMS ON HOT DRY DAYS
If stomata are open to receive CO results in water loss (transpiration)
On hot, dry days if plant shuts stomata to conserve water photosynthesis slows

4. 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.

5. 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

6. 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

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

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

10. 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

11. Plants even exhibit positive feedback…

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