Download Roots

Two Types of Roots
Fibrous Root
• All roots are
the same size
– no taproots
Onion roots
Tap Root
• Primary root is
longer and thicker
• Secondary roots
are small and
branch off
Carrots
3 Types of Root Tissues
1. Epidermis – Thin layer of cells that take in
water and nutrients from soil
2. Cortex – transports water and nutrients in
through the root
•
Stores sugars or starches
3. Vascular Cylinder – Contains Xylem and Phloem
Epidermis is the outermost layer of cells
• Absorbs water and nutrients from
soil
• Grow projections called ‘root hairs’
(hundreds to millions!)
• Root hairs penetrate the spaces
between soil particles and give root plenty
of surface area to absorb water
•
Root hairs absorb nutrients
from soil via ACTIVE
transport
• Active transport (A.T.) –
cell uses energy to move a
substance across a
membrane
• A.T. requires ATP and oxygen
• Roots obtain oxygen from
spaces between soil
• If soil is flooded with water
plants suffocate
•
Water transport by root
hairs done via osmosis
•
•
Osmosis – movement of water
from an area of high
concentration of water to an
area of low concentration of
water – remember, Nature
likes everything to be equal!!
NOTE – if the soil has too
many minerals, water may
EXIT the plant = root burn.
•
Transport done by parenchyma cells
•
Active Transport moves water from cortex to
xylem in the middle; How?
•
A.T. pumps minerals to root center
•
As Mineral Concentration increases, Water
concentration decreases.
•
Water follows nutrients toward root center to equalize
concentrations.
•
Endodermis – single layer of cells at inner
boundary of the cortex
•
•
Composed of brick shaped cells
surrounded by a water proof strip
called the Casparian strip
Since water can’t move around
endodermal cells (only through them),
A.T. is used to pump nutrients into
the vascular cylinder followed by
water (trying to equalize concentration)
•
Endodermis – single layer of cells at boundary
of the cortex
•
As nutrients are pumped into the vascular
tissue more water follows
•
Due to the “one-way” passage, water and nutrients
can not move back into the cortex
•
•
‘Root Pressure’ builds up in the vascular tissue and
forces water into the xylem
As more water enters the xylem, the water that was
already in there gets pushed up the stem
•
In short plants, root pressure alone can deliver water
to all parts of the plant
Two important functions:
1. Hold leaves up to the sun
2. Transport substances between roots and
leaves
4 types of tissue in the stem
Parenchyma (pith)
2. Vascular tissue (xylem and phloem)
3. Cambium tissue (vascular cambium and cork
cambium)
4. Cork tissue (outer bark)
1.
Monocots – parenchyma distributed
throughout the stem
• Used for storage
•
Dicots – distinguished into pith in the
center and into cortex outside the ring of
vascular bundles
Monocots – parenchyma distributed
throughout the stem
• Used for storage
Monocot stem
•
Dicots – distinguished into pith in the
center and into cortex outside the ring of
vascular bundles
Vascular tissue – conducts water, nutrients
and food up and down the plant in
continuous tubes of xylem and phloem
Dicots
o Bundles of xylem, vascular cambium and
phloem are arranged in a ring
• Vascular cambium makes new xylem and
phloem,
•
Allows stem to grow
thicker
• Xylem faces interior of
stem
• Phloem faces exterior
of stem
Monocots
o Bundles of xylem, and phloem are
scattered throughout
• Xylem faces Interior of stem
• Phloem faces Exterior of stem
In woody stems, xylem tissue makes up the
rings of trees
o You can use the number of rings on a tree
to estimate age
• Thick rings show weather conditions were
favorable (lots of water!)
• Thin rings = poor conditions
As woody stems grow thicker the older xylem
(near the center of the stem) becomes
heartwood
o Heartwood does NOT conduct water
o Outer living rings called
Sapwood DO conduct water
Phloem tissue forms inner part of bark
o Carries sugar and other products of
photosynthesis from leaves to other plant
parts that don’t make food
Outside the phloem in woody dicots is cork
cambium
Produces cork tissue (outer bark of trees)
• Cork cells have thick cell walls and have fats,
oils or waxes that help prevent water loss
•
•
Stems also store food to help them
survive dormancy
•
Dormancy = plant growth stops or slows
•
Occurs during cold winters or long dry periods
•
Stems modified for food storage
Rhizomes
• Tubers
• Bulbs
• Corms
•
Rhizomes – thick fleshy stems
• Grow underground or along surface of ground
• Leaves and buds grow along rhizomes
•
When cold kills above ground parts, the
underground parts survive to grow again the
following spring
Tubers – underground stems
• Swollen with stored food (usually starch)
• Ex. potatoes
Bulbs – underground stems with bulbs
•
Stem in center of bulb
•
Food stored in leaves that wrap around and
protect the stem
• Ex. Tulips
Corms – similar to bulbs but have thinner
leaves
Food located in stem
• Thin leaves surround the stem and protect it
•
What are the general functions of the stem?
 Hold leaves up to the sun
 Transport materials to between roots and leaves
What are the different functions of the stem
tissues?
 Parenchyma - Store food
 Vascular tissue – transport water, nutrients and
food
 Cork cambium and cork –
o
o
Cambium – make new cork cells
cork cells - prevent water loss and provide protection of
vascular tissues
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HOMEWORK:

READ PAGES 494 – 502
Do Questions on pages 498, 502
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