BFG Ch 2 Flashcards
Purpose of roots (3)
Anchor plant in soil
Absorb water and minerals
Store excess foods
Two ways that roots anchor plants in soil
diffuse root system (occupy large shallow area; decreases soil erosion)
tap root system: sends one/two rapidly growing sparsely branched roots straight down to get deep water
Storage capacity of roots
tap roots have better storage than diffuse roots.
tap roots can enlarge in diameter as well as length (ex. carrot)
enables plants to regenerate quickly in the spring (new foliage)
Tree roots
sometimes can be diffuse systems (unexpectedly)
Advantage for trees to have shallow diffuse roots:
collect nutrients released from rotting vegetation before they’re washed away by heavy rains.
drip zone
distribution of tree roots to catch the dripping rainwater from their branches
horticultural and agronomic root systems
usually shallow; wild counter parts can have much deeper tap roots.
Describe root growth (components, branching)
Apical meristems (1/4” at tip of roots)
covered by root cap: cells that are readily rubbed off if need be to protect the meristems
root hairs occupy a set region after the meristems to increase by several 100x the absorptive surface of the organ.
Branching begins in slightly older root sections deep within the parent root and tend to grow at right angles.
What is a shoot
the principle aerial stems, branches, and attached leaves of a plant
Apical bud
stem’s growing tip; much more complex than a root’s
Apical bud of a stem
involved in cell devision and elongation
initiates the arrangement of leaves on the stem
makes provisions for the eventually development of branches
occupies about 1/10” of stem.
Components of the apical bud
apical meristem: dome of actively dividing cells
leaf primordia (on either side of meristem): fold over and protect meristem
axillary bud primordium at base of leaf primordia
-site of future branching
Nodes and internodes
Nodes: point where leaf and axillary bud primordia develop
internode: section of stem between nodes; spread the leaves apart to ensure maximum exposure to sunlight
Basic leaf arrangements by the apical meristem placement of leaf primordia
alternate
opposite
whorled
Why do plants bother making axillary buds?
to act as points of reserve branch growth in the case apical buds are destroyed by disease, frost, wind, or animals
usually developed low on the stem to maintain a low center of gravity (until wood)
What evolved to increase the capacity of support in upright growing plants?
wood
trees
one or a small number of main trunks to support their leaf crowns
shrubs
smaller plants with many woody stems branching closer to the ground
Roots of woody plants
develop a wood core as a consequence of their age and in conjunction with the thickening of trunks and branches.
roots maintain their important role as anchors and transport ever-increasing amounts of water to supply the needs of aboveground parts.
Ground covers
plants that grow along the ground instead of upward to avoid the expensve of supporting a trunk
-ivy, some grasses
advantage to elevating leaves upright
woody plants:
get more sunlight
secondary growth
when plants increase their supportive role- usually making wood
pretty costly
Features of a woody twig
Transition: green to brown, hardens.
Outer bark = cork
Lenticils: breathing pores that appear as bumps on bark
leaf scars: reminders of foliage that fell; dots represent where food/water conducting cells were sealed off.
bud scales: form a tight apical/terminal bulb in the winter to protect the dormant bud
concentric rings of scars left after the bud scales fall off (count the rings to find out twig’s age) = called Terminal bud scars
Leaf blades
must be thin and translucent to allow light to penetrate
held in outstretched positions
often attached to a petiole (leaf stalk) to allow rotation of leaf blade to track sun and greater flexibility
petiolate leaf
a leaf with a petiole
