Chapter 35 Flashcards
stems can be:
- herbaceous, with soft tissues
2. woody, with extensive hard tissues of wood and bark
three main functions of stems
- support
- internal transport
- production
stems of some species are modified for ___ reproduction
stems of some species are modified for asexual reproduction
primary growth
occurs in all plants
increase length of a plant
occurs at apical meristems at root tips, shoots, and within buds of stems
secondary growth
increase in the girth of a plant, adds wood and bark in woody plants
occurs at lateral meristems of stems and roots
Herbaceous Eudicot Stems
Vascular bundles are arranged in a circle in cross section
pith
storage of nutrients
monocot stems
vascular bundles are scattered throughout the stem, each vascular bundle is enclosed in a bundle sheath of sclerenchyma cells
monocot stems have no distinct areas of ___ and ___
monocot stems have no distinct areas of cortex and pith - ground tissue around the vascular tissues performs the functions of cortex and pith
monocot stems have no ___ and no ___ growth
monocot stems have no meristems and no secondary growth
water and minerals travel only ___ in xylem, whereas translocation of dissolved sugar may occur ___ or ___ in separate phloem cells
water and minerals travel only upward in xylem, whereas translocation of dissolved sugar may occur upward or downward in separate phloem cells
transport of xylem ___ is the most rapid of any movement of materials in plants
transport of xylem sap is the most rapid of any movement of materials in plants
water moves by
water potential
water potential
the free energy of water: a measure of a cells’s ability to absorb water by osmosis
The water potential of pure water is conventionally set at
0 megapascals
when solutes dissolve in water, free energy
decreases because ions induce hydration
water moves from a region of ___ water potential to a region of ___ water potential
water moves from a region of higher water potential to a region of lower water potential
Water moves by osmosis from soil into roots because roots contain
more dissolved materials (have lower water potential)
The Tension-Cohesion Model
water is pulled up the plant as a result of tension produced at the top of the plant
- the atmosphere has extremely negative water potential
- Tension is caused by the evaporative pull of transpiration - the evaporation of water vapor from the plant
- Tension pulls water from leaves, where most transpiration occurs (through stomata), up through stems and roots
water molecules are cohesive because of
hydrogen bonding
adhesion of water to xylem walls is due to
hydrogen bonding and helps maintain an unbroken column of water
Root pressure
pushes water up through xylem toward the top of the plant
water moves into roots by osmosis because of the difference in water potential between the soil and the root cell
mineral ions that are actively absorbed from the ___ are pumped into the ___, decreasing its water potential
mineral ions that are actively absorbed from the soil are pumped into the xylem, decreasing its water potential
sugar produced during photosynthesis is converted into
sucrose
sucrose is translocated from a source to a ___
sink
type of sinks for sucrose
- roots
- apical meristems
- fruits
- seeds
Pressure-flow model
solutes move in phloem by means of a pressure gradient that exists between the source and the sink
at the ___, sucrose is moved from leaf ___ cells into ___ cells, which load it into ___ tube elements of phloem by active transport
at the source, sucrose is moved from leaf mesophyll cells into companion cells, which load it into sieve tube elements of phloem by active transport
A proton gradient drives ___ uptake through specific channels by cotransport of H+ back into ___ tube elements
A proton gradient drives sugar uptake through specific channels by cotransport of H+ back into sieve tube elements
Water moves by osmosis from xylem cells into sieve tube, increasing
Water moves by osmosis from xylem cells into sieve tube, increasing turgor pressure there
At the sink, sugar is unloaded from sieve tube elements, increasing ___ ___ in sieve tube elements at the sink
At the sink, sugar is unloaded from sieve tube elements, increasing water potential in sieve tube elements at the sink
water moves out of sieve tubes by ___ and into surrounding cells, decreasing turgor pressure in sieve tubes at the sink
water moves out of sieve tubes by osmosis and into surrounding cells, decreasing turgor pressure in sieve tubes at the sink
