Topics to Study for the Plants Section of the Final Exam

Bio 1B Section 120 May 11, 2005

Topics to study for the Plants section of the final exam

Water relations  How does water flow up plant? Chain of water molecules. Driven by transpiration.  Water potential: tendency of water to move from one area to another. Denoted by (psi).  Water moves from an area of higher (less negative) to lower (more negative) .

P: Pressure/tension, caused by mechanical forces: Can be 0, <0, or >0.

: Osmotic potential, caused by solutes. Always ≤ 0.

P +  (can be 0, <0, or >0)

System P   Open container of pure water 0 + 0 = 0 Open container of salty water 0 + -1 = -1 Pressurized container of pure water +1 + 0 = +1 Xylem (water sucked upward) -5 + -5 = -10 Turgid plant cells +2 + -5 = -3 Cells at incipient plasmolysis 0 + -5 = -5

 We can measure the total water potential of a plant with a Scholander bomb (pressure bomb).  Plants control transpiration (water loss) by opening and closing their stomata.  Incipient plasmolysis is when the cell is just about to “collapse” from dehydration, i.e. the

walls are no longer pushing back against the cell contents and therefore P is 0.

Hormones  Auxin (=IAA) o How was it discovered? Plants (coleoptiles) bending toward light. o Most important effects: apical dominance; root formation. o Also ripening of fruit and abscission of leaves. o Different parts of plant are sensitive to different concentrations.

 Giberellins o Discovered in spindly rice seedlings with fungus infection: “foolish seedling disease.” o Causes stem elongation by increasing cell length. o Also breaks dormancy and has several other effects.

 Ethylene

1 o Fruit ripening, flower and leaf senescence. o Only plant hormone which is a gas. o Has commercial importance to make fruit ripen on demand.

 Cytokinins o Cause cell division. o Can cause differentiation of organs (e.g. leaves), if auxin also present in right amount.. Can cause tumors if too much.

 Abscisic acid (=ABA) o Inhibits growth o Plays a role in germination and breaking winter dormancy. o Not actually involved in abscission, that was a mistake.

Controls on flowering  We don’t know what “florigen” is, but grafting experiments suggest that it is a physical substance that flows in the plant.  Plant flowering controlled by night length: o Long-night plants will only flower if there is a long enough dark period. o Short-night plants will only flower if there is a short enough dark period.  Short-day = long-night; Long-day = short night  Sometimes, cold period is necessary to make plants flower heavily (e.g. magnolias)  Cold (stratification) also sometimes crucial for seeds sprouting.

Mineral nutrition  A nutrient is an element that is essential for the survival of an organism.  The following substances are crucial for the survival of plants but are not usually considered nutrients because they are required in such large amounts: C, O, H2O (also light).  Macronutrients are required in fairly large quantities: N, P, K, S, Ca, Mg  Micronutrients are required in smaller quantities: Fe, Mn, Zn, Cu, Mb, Ni, Cl, B  Some nutrients, such as N, are mobile (meaning that the plant can move them to where they are needed. If a plant has healthy young leaves and sick old leaves, it is probably suffering from a deficiency of a mobile nutrient.  Other nutrients, such as Fe, are immobile. Once they become incorporated into the plant’s body, they cannot be moved. If a plant has healthy old leaves and sick young leaves, it is probably suffering from a deficiency of an immobile nutrient.