Download Phloem

Phloem
Two types of cells: sieve tube members with no nuclei for
transport and companion cells to support the sieve tube
members via plasmodesmata cell junctions. Large pores
or sieve plates connect individual sieve tube members.
Carry sugars (sap) source to sink. Source is where it is
made and sink is where it is used or stored.
Movement
• Where sugar is made cells have more
solute concentration
• Water enters due to increased sugar
• Pressure goes up causing material to
move to adjacent cell via bulk flow
• This continues until it gets to the sink.
• Pressure at the sink builds, but this is
where sugars are being utilized so that
pressure is offset.
Xylem
• Xylem: composed of two types of cells that are both dead at
maturity. Both are connected by pits or perforations at the
ends. Tracheids are tapered at the end whereas vessel
members form a more blunt end. Vessels are more
advanced as the perforations at the end allow for more
efficient water and mineral transfer. They move water from
roots (root hairs) to the needed cells in the plant.
Primary growth in root
• Roots have three regions: cell division (mitosis counting),
elongation, and maturation or differentiation depending
on the text. Root cap protects zone of cell division. Root
hairs grow from zone of maturation. Apical meristem is a
region of cell division at the root tips and shoot tips.
Secondary growth
• Secondary growth is
slower and makes the
plant wider. It occurs at
two lateral meristems
(regions of cell
division). The first is the
vascular cambium. It
makes new secondary
xylem on the inside that
becomes wood and
secondary phloem on
the outside that
increases the
circumference of the
tree causing the skin to
split. The second
lateral meristem is the
cork cambium that
makes cork cells on the
outside that protect and
waterproof. This outer
growth region is called
the bark.
Seedling parts
• Epicotyl (above
cotyledon) is the shoot tip
• Cotyledons: seed leaves
from seed itself.
• Hypocotyl: (below
cotyledon)
• Radicle: embryonic root
• Coleoptile: in monocots a
protective sheath around
the epicotyl