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14.5 Homeostasis in plants - Coggle Diagram
14.5 Homeostasis in plants
Features/adaptations of guard cells
Cell surface membrane is often folded and contains many transporter proteins
Many chloroplasts and mitochondria
Thick cell wall facing outside, thin cell wall facing inside
Many small vacuoles rather than one large one
Stomata OPEN in response to
Increase in light intensity
Low carbon dioxide concentrations in leaf air spaces
Stomata CLOSE in response to
Darkness
High carbon dioxide concentrations in leaf air spaces
Low humidity
High temperature
Limited water supply
Guard cell mechanisms
Opening
Proton pumps use ATP to actively transport H+ ions out of the guard cells
K+ ions flow into the guard cell down the electrochemical gradient
Electrochemical gradient = electrical gradient + concentration gradient
Electrical gradient = one side has a different amount of charge to the other
Increase in K+ ions in guard cell lowers the water potential
Water flows into guard cell via osmosis
Turgor pressure of guard cell increases and stoma opens
Closing
Proton pumps stop
K+ ions leave the guard cell
Water potential increases
Water flows out of guard cell via osmosis
Turgor pressure of guard cell decreases and stoma closes
ABA (abscisic acid) causes stomatal closure
ABA stimulates movement of Ca2+ ions
Ca2+ ions act as second messengers to activate and open channel proteins for negatively charged ions
Negatively charged ions leave the cell, causing positively charged K+ ions to leave too
Ca2+ ions cause closure of K+ ion channels that allow K+ to move back into the cell, meaning overall ion concentration decreases
Water potential increases, water moves out of guard cell via osmosis, guard cell becomes flaccid, stoma closes