Roots

Report
Anatomy, Morphology, & Growth
of Angiosperms – Ch. 5-8
Two plant groups: monocots & dicots
Structure Reflects Function
http://www.fugu-sg.org/~elia/cambodia/templesfacesweb/pages/A3_Embracing_Roots.htm
Structure of a plant determined by:
1. Genetics
2. Environment – two time scales:
1. Long-term:
2. Short-term: plasticity = wide range of
phenotypes for each genotype. Allows plants
to adjust to changing environment (ex.
Shorter plant in dry year so that it can still
reproduce)
Cells
Muscle cell
Tissues
Muscle tissue
Organs
Heart
Systems
Circulatory
system
Three organs: Roots, stems, leaves
1. Roots–
•
•
Store food (carbos from photosynthesis) to be
used for flowering & fruiting
Covered with root hairs – increased surface
area for absorption
Fig 35.2
Prop roots
Aerial
strangler roots
Sweet Potato –
storage root
Buttress roots
Modified
Roots – Fig
35.4
Pneumatophores
2. Stems/shoots
•
•
•
Support, transport
Some photosynthesis
Two types of shoots
1. Vegetative –
2. Reproductive –
• Two parts of stem:
1. Node –
2. Internode – stem segments between nodes
Two types of buds
1. Terminal bud – contains a shoot apical
meristem; shoot growth is concentrated here
2. Axillary buds –
Apical dominance = the presence of an apical bud
inhibits the growth of axillary buds.
-remove or depress apical bud, axillary buds
begin to grow.
Modified Shoots (stems):
• Stolons –
Asexual, vegetative
propagation
• Rhizomes –
• Bulbs – swollen underground
shoots
• Tubers – swollen rhizomes
Stores food for
later growth
Fig 35.5
3. Leaves – main photosynthesis organs
http://www.knotweed.co.uk/japknot_Info.htm
Modified
leaves
• Compound, doubly
compound – why??
Tendrils
Spines
Fig 35.7 –
Modified
leaves
Succulents
Leaf types:
Simple leaf =
Compound leaf = divided into distinct units called leaflets
Four types of leaf arrangement:
1. Acaulescent –
2. Alternate –
3. Opposite – leaves borne across from each other at
the same node
4. Whorled – 3 or more leaves arising from the same
node.
Three main
tissues:
Dermal,
Vascular,
Ground
Fig 35.8
1. Dermal tissue or epidermis
•
•
Root hairs are specialized epidermal extensions
Secretes waxy cuticle of the leaf
2. Ground Tissue
• fills the space between dermal and vascular
tissue systems.
• Diverse functions:
pith
In dicots:
cortex
3. Vascular Tissue
• function in transport between roots &
shoots, and structural support of plant
– Xylem:
– Phloem: Food transported to roots & nonphotosynthetic parts such as the flowers
The Plant Cell
Fig 7.8
5 Differentiated Plant Cell Categories
1.
2.
3.
4.
5.
Parenchyma
Collenchyma
Schlerenchyma
Water-conducting cells of the xylem
Sugar-conducting cells of the phloem
1. Parenchyma
• thin and flexible cell walls
2. Collenchyma
• Usually grouped in strands to support young parts
of plants without restraining growth
• Flexible, elongate with growing shoots
3. Schlerenchyma
• May be dead at functional maturity – ???
• cell walls left behind as skeleton
4. Water conducting cells of the xylem:
• 2 types: tracheids & vessel elements
Tracheids
• Water flows from cell to cell (laterally) through
pits in cell wall
• Support function
Vessel Elements
• End walls are perforated for free flow of water
• More efficient as water conductors than tracheids
Fig 35.9
5. Sugar-conducting cells of the phloem
Sieve-tube members:
• Lack a nucleus, ribosomes, vacuole
• Cells separated by perforated sieve plates –
allow sugar movement
Fig 35.9
Growth & Development
http://www.cneccc.edu.hk/subjects/bio/album/Chapter20/PLANT_GROWTH.html
• Development =
Three processes of development:
1. Growth =
2. Cellular differentiation = generation of different
cell types
3. Morphogenesis – creation of body form &
organization.
1. Growth
• Cell division no expansion
Growth
• = due to water uptake in the vacuole
Fig 35.24
Cell division
• Occurs in only in meristems!
Meristems
•
•
=
Two types of meristems:
1. Apical meristem –
2. Lateral meristems – extend lengthwise along the
axis of the stem & roots. Responsible for
growth in girth in older parts of the plant (called
secondary growth). Exist only in perennials
Fig 35.10
Primary Growth of Roots
•
Root cap – layer of cells that protect the RAM as
it pushes through the soil
Fig 35.12
Arrangement of Primary Tissues in Roots
1. Epidermis –
2. Stele –
3. Ground tissue – mostly parenchyma cells of the
cortex – area between the stele & epidermis;
stores food & takes up minerals.
• Endodermis – single cell layer between cortex
& stele. Selective barrier for uptake of soil
solution contents into vascular system.
Eudicot/Gymnosperm root cross section
Epidermis
Endodermis
Cortex
Stele
xylem
phloem
Fig 35.13
Primary Growth of Shoots
• Bud = cluster of leaf primordia created by
meristem. No internodes
• Lateral branches arise from axillary buds
Fig 35.15
Primary tissue arrangement of stems
– Ground tissue = pith & cortex
Eudicot/Gymnosperm stem cross section
pith
phloem
cortex
xylem
epidermis
Fig 35.16
Schlerenchyma
cells
Tissue arrangement of leaves
•
3 parts:
1. Upper & lower epidermis – tightly interlocked
cells, secrete waxy cuticle. Contains stomata
flanked by guard cells
2. Vascular tissue –
3. Mesophyll – ground tissue between upper &
lower epidermis
Fig 35.17
Secondary Growth
•
Two lateral meristems:
1. Vascular cambium – produces secondary
xylem (= wood) & phloem
2. Cork cambium – replaces the epidermis with
cork: tough, thick cover for stems, roots.
Secondary growth of stems
• Vascular cambium – layer of cells between
primary xylem & primary phloem. Puts on
successive layers of secondary phloem to outside
& secondary xylem to inside =====> stem widens
• Wood = accumulation of secondary xylem. Dead
at maturity, contains lignin
Cork cambium
• “bark” =
• Cork continually sloughs off
Fig 35.18
Fig 35.20
Three types of life cycles:
1. Annual –
2. Biennial – complete life cycle in two years (first
year = vegetative, second year = reproductive).
Some need a cold winter period to initiate
flowering from vegetative state. Ex. carrots
3. Perennial – live year after year, do not die after
reproduction. Examples: trees, shrubs, some
grasses. Causes of death = fire, disease

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