Plant Nutrition And Transport

Front 1

What is the difference between a macronutrient and a micronutrient?

Back 1

Macronutrients are elements required in large quantities (>1 mg/g dry matter) by a plant (e.g.
carbon, hydrogen, oxygen, nitrogen, phosphorous,...), whereas micronutrients are elements
required in trace amounts (<100 μg/g dry matter) by a plant (iron, manganese, zinc, copper, ...)

Front 2

What is responsible for most of the increase in the organic mass of a plant as it grows?

Back 2

Most of a plant’s organic mass is derived from the fixation (assimilation) of carbon dioxide into
organic molecules during photosynthesis

Front 3

What nitrogen-containing product is formed when nitrogenase reduces atmospheric nitrogen?

Back 3

NH3 (ammonia)

Front 4

Why is nitrogen fixation such an important process?

Back 4

The availability of fixed nitrogen (e.g. NO3
!, NH4
+) is most often the limiting factor in plant
growth. Nitrogen deficiency is the most common elemental deficiency of plants.

Front 5

Why do plants require such a large surface area for gas exchange?

Back 5

The concentration of carbon dioxide (CO2) in air is extremely low (air is a mixture of gases...
~79% N2, ~21% O2, ~0.03% CO2, + various trace gases)

Front 6

Which of the following factors would favour the opening of stomata? a) high internal [CO2], b)
lots of sunlight, c) plentiful water supply

Back 6

B and C

Front 7

What is the significance of having water and its dissolved minerals pass through at least one live
cell before entering the vascular tissue of a root?

Back 7

Since water and its dissolved minerals must pass through at least one live cell before entering the
vascular tissue, the plant can control the kinds and amounts of minerals that it takes up from the
soil. Without this feature, the xylem sap of a root would have the same basic composition as soil
water in which case many of the plant’s metabolic processes would be at the near total mercy of
fluctuating soil water conditions.

Front 8

In the pressure-flow mechanism, what causes the high water pressure in the phloem nearest the
source?

Back 8

The high water pressure is brought about by the active transport of sugars from the source into the
phloem, causing the osmotic flow of water into that phloem.

Front 9

How do plants control the entry of substances into their roots?

Back 9

water & minerals must pass through the membrane of at least 1 cell before entering vascular
tissue,

Front 10

Describe the intracellular pathway.

Back 10

water first crosses cell wall and plasmalemma of an epidermal cell (usually at a root hair), then
moves via plasmodesmata from cell-to-cell (from epidermal cells, to cells of the cortex, then to
endodermal cells, and finally to xylem of a vascular bundle

Front 11

Describe the extracellular (intercellular) pathway.

Back 11

water moves between epidermal cells and cells of the cortex... water moves in and between
those cell walls; this extracellular path is eventually blocked by the waxy Casparian strip of
endodermal cells; note that in this pathway the first cells that water molecules enter are
endodermal cells, followed by passage into xylem of a vascular bundle

Front 12

a continuum
of cell walls and
extracellular spaces

Back 12

apoplasm
extracellular route = apoplastic route

Front 13

a continuum
of cytosol connected by
plasmodesmata

Back 13

intracellular route =
symplastic route
• symplasm

Front 14

evaporative loss of water from a plant

Back 14

transpiration

Front 15

(negative pressure) is created by transpirational loss of water
• pulls column of water up xylem

Back 15

tension

Front 16

tightly joined to each other
at the tips, have thickened inner walls, and are reinforced by radial bands of inelastic
cellulose fibrils
increase in length more than girth
• buckle and open, allowing gas exchange between atmosphere and interior of leaf

Back 16

guard cells of the stomata

Front 17

What happens when the stomata needs to be opened?

Back 17

• an active transport system is responsible for drawing K+ into central vacuoles...
• H+ are actively pumped out of the guard cells
• results in hyperpolarization of the cells
• this very negative membrane potential draws K+ in through K+ channels
• H2O follows by osmosis...
• results in swollen , turgid guard cells...