Transcript Plant Growth - mvhs

Plant Growth
AP Biology
Unit 5
Plant Growth
• Plant growth occurs at specific tissues
called meristems
– Apical Meristem
– Lateral Meristems
Plant Growth
• Plants can go through
two different types of
growth
– Primary Growth- growth
in length
– Secondary Growthgrowth in width
Primary Growth- in Roots
• In roots, primary growth
occurs in 3 different zones
– Zone of Cell Division
(contains root apical meristem)
– Zone of Elongation
– Zone of Maturation
Zone of Cell Division
• Lots of mitosis
occurring in the cells
here
• Contains the newest
cells (newly divided)
Zone of Elongation
• Cells get longer to
push the root tip into
the soil
• Cells start developing
their specialized
functions
Zone of Maturation
• Cells become fully
specialized
• Considered mature
cells
Root Cap
• Root cap protects
the root apical
meristem as root
pushes through the
soil
– Like a helmet for
the root cells
Primary Growth- Stems
• Growth occurs at the shoot
apical meristems
• Shoot apical meristems are
located at the tips of buds
• Plants grow from the top,
not the bottom of the stem
Secondary Growth
• Growth in width of stems and roots
• Degree of secondary growth varies–
some plants barely have any, others
have extensive secondary growth.
• Results in the formation of wood and
bark
• Results from activity in the lateral
meristems
– Vascular Cambium
– Cork Cambium
Vascular Cambium
• Divides into
– Secondary Xylem
• On the side closer to the center
of the stem/root
– Secondary Phloem
• On the side closer to the
outside of the stem/root
– As the vascular cambium
divides, it continues to push
older cells farther away.
Cork Cambium
• As the secondary phloem
grows, it breaks the outer layer
of the stems and root
(epidermis)
• Secondary phloem on the very
outside becomes cork cambium
• Cork cambium grows into cork
• Cork cells contain suberin to
protect from water loss,
physical damage and harmful
substances.
Question…
• Where is the oldest part of a tree?
– The very center – oldest xylem that has been
pushed all the way in
– Outer layers keep flaking off
Types of wood
• Heartwood
– Older secondary xylem
– Cells get clogged 
stop conducting water
– Darker in color
• Sapwood
– Newer secondary xylem
– Still actively conducting
water (and minerals)
– Lighter in color
Annual Rings in Wood
• The age of a tree can be
determined by looking at the
number of rings that it has.
• Wood = secondary xylem
• What forms the rings?
– Spring: water most available, water
transport cells are large and have
thin walls
– Summer: less water available,
water transport cells have thicker
walls and are darker