Download Plant Structure and Growth

Plant Structure and Growth
Two major groups of angiosperms
• Monocots
– Seed leaves
• One cotyledon.
– Leaf veins
• Main veins usually
parallel.
– Stems
• Vascular bundles in
complex arrangement
– Flowers
• Floral parts usually in
multiples of three
– Roots
• Fibrous root system
• Dicots
– Seed leaves
• Two cotyledons
– Leaf veins
• Main veins usually
branched
– Stems
• Vascular bundles in ring
– Flowers
• Floral parts usually in
multiples of four or five
– Roots
• Taproot usually present
Plant Structure and Growth
Two major groups of angiosperms
• Monocots
– Species
• Orchids, bamboo, palms, lilies, grains, grasses
– Roots
• Form a fibrous system-a mat of threads- that spread
out below the soil surface.
• Few centimeters below the surface.
– Make excellent ground that reduces erosion
Plant Structure and Growth
Two major groups of angiosperms
• Dicots
– Most angiosperms are dicots (170,000 species)
– Species
• Most shrubs and trees (except for the conifers)
• Majority of ornamental plants and many food crops
The Plant Body consists of
Roots and Shoots
• Roots and shoots depend on each other.
• Root system
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Anchors plant in the soil.
Absorbs and transports minerals and water
Stores food
Monocots
• Fibrous root system provides broad exposure to soil water and
minerals, as well firm anchorage.
– Dicots
• Many secondary roots growing out from one large taproot
– Root hairs
• Near the root tip, Outgrowth of an epidermal cell
• Increase surface area
• Absorb water and minerals
The Plant Body consists of
Roots and Shoots
• Shoot system
– Made up of stems, leaves, and flowers
• Stems support the leaves and flowers
– Tree: stems are the truck and all the branches.
– Stems have nodes, the points at which leaves are attached.
– Internodes, the portion of the stem between nodes.
• Leaves are the main site of photosynthesis
– Consists of a flattened blade and a stalk, or petiole, which
joins the leave to the stem.
The Plant Body consists of
Roots and Shoots
• Shoot system Cont’
– Two types of buds
• When a plant stem is growing in length, the Terminal buds, at
the apex (tip) of the stem, has developing leaves and a compact
series of nodes and internodes.
• The Axillary buds, one in each of the angles formed by a leaf
and the stem, are usually dormant.
• In many plants, the terminal bud produces hormones that
inhibit growth of the axillary buds, called Apical dominance.
– By concentrating resources on growing taller, it increases the
plant’s exposure to light.
» Especially important where vegetation is dense.
The Plant Body consists of
Roots and Shoots
• Apical dominance cont’
– Branching is also important and under certain conditions
the axillary buds begins growing
– Some develop into shoots bearing flowers, and others
become nonreproductive branches complete with their
own terminal buds, leaves, and axillary buds.
– In some cases, removing the terminal bud stimulates the
growth of axillary buds
» This is why fruit trees and houseplants become more
bushy when they are pruned.
Plant cells and tissues are diverse
in structure and function
• Plant cells uniqueness.
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Chloroplasts
Photosynthetic pigments chlorophyll a and b
Large central vacuole
Cell wall
• Mainly made of the structural carbohydrate cellulose
• Two-part cell wall
– Primary cell wall is laid down first
– Secondary cell wall is formed next between the plasma
membrane and the primary cell wall.
• Pits—where the cell wall is relatively thin.
– Allows the contents of adjacent cells to lie close together.
• Plasmodesmata—channels of communication and circulation
between adjacent plant cells.
Five major types of plant cells
1. Parenchyma cells
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Most abundant type of cell
Remain alive when mature
Have only primary walls (often thin)
Functions:
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Food storage; photosynthesis; aerobic respiration
Often multisided
Can divide and differentiate into other types of plant
cells
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Process of repairing an injury
Five major types of plant cells
2. Collenchyma cells
• Lack secondary walls, like parenchyma
• Unevenly thickened primary walls
• Function:
– Provide support in parts of the plant that are still
growing.
– Young stems have collenchyma cells just below the
surface.
• Living cells that elongate with the growing stem.
Five major types of plant cells
3. Sclerenchyma
• Have rigid secondary cell walls hardened with
lignin
– Lignin is the main chemical component of wood.
• Mature cells cannot elongate
• Occur in regions that have stopped growing in
length.
• When mature, most sclerenchyma cells are dead,
their cell walls form the rigid scaffold that
supports the plant.
Five major types of plant cells
4. Water-conducting cells (Xylem tissue)
• Have rigid, lignin containing secendary walls
• Two types of xylem cells
– Tracheids- Long cells with tapered ends.
– Vessels elements- Wider, shorter, and less tapered
– Chains of these cells with overlapping ends forms a
system of tubes that convey water from the roots to the
stems and leaves.
– Tubes are hollow> mature cells are dead and only their
cell walls remain.
– Water passes through pits in the walls of tracheids and
vessel elements.
Five major types of plant cells
5. Food-conducting cells (Phloem tissue)
• Made of Sieve-tube members
• Arranged end-to-end, forming tubes
• Thin primary walls and no secondary walls
• Remain alive at maturity
• End walls are perforated large plasmodesmata,
form sieve plates, through which sugars, other
compounds, and some mineral ions move between
adjacent food-conducting cells.
• Companion cells
Three tissue systems make
up the plant body
• Epidermis or “skin”
– Covers and protects its leaves, young stems, and young
roots.
– Epidermal cells secrete a waxy coating called the
cuticle.
• Vascular tissue system
– Made of xylem and phloem.
– Provides support and transports water and nutrients.
• Ground tissue system
– Parenchyma; Collenchyma; Sclerenchyma cells
Plant Growth
Primary Growth Lengthens Roots and Shoots
• Most plants continue to grow as long as
they live.
– Indeterminate growth
– Plants grow through their environment.
• Most animals cease growing after reaching
a certain size.
– Determinate growth
– Most animals move through their environment.
Plant Growth
Primary Growth Lengthens Roots and Shoots
• Meristem
– Consists of localized, unspecialized cells that
divided and generate new cells and tissues.
– Apical meristems
• Located at the tips of roots and in the terminal (top)
and axillary buds of shoots.
Plant Growth
Primary Growth Lengthens Roots and Shoots
• Growth of the root
– Root cap (root tip)
• protects the apical meristem
– Zone of cell division
• dividing cells of the apical meristem.
– Zone of elongation
• Newly formed cell absorb water and elongate
– Zone of maturation (differentiation)
• Cells mature into xylem, phloem, parenchyma, or epidermal
cells.
• Root hairs may form as extensions of epidermal cells.
Primary Growth
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Growth only at the apical meristems.
Most monocots and some dicots
Tissue produced are primary tissues.
Primary xylem and primary phloem refer
to vascular tissues originating from apical
meristem.
Secondary Growth
• Other plants, like conifers and the woody
dicots, undergo secondary growth in
addition to primary growth.
• Primary growth
– vertical direction
• Secondary growth
– increases the girth, or lateral dimension
– Origin of woody plant tissues
Secondary Growth
• Occurs at two lateral meristems, the
vascular cambium, and the cork cambium
• Tissues that originate from the vascular
cambium are the secondary xylem and the
secondary phloem.
Primary Structure of Roots
• Epidermis
– Lines the outside surface
– In the zone of maturation, epidermal cells produce root
hairs.
• As the zone of maturation ages, root hairs die.
– New epidermal cells from the zone of elongation,
become the new zone of maturation as they form root
hairs.
– Roots must constantly grow to provide new root hairs.
– Older epidermis functions to protect the root.
Primary Structure of Roots
• Cortex
– Makes up the bulk of the root.
– Main function is the storage of starch.
– Contains numerous intercellular spaces,
providing aeration of cells for respiration.
Primary Structure of Roots
• Endodermis
– Ring of tightly packed cells at the innermost portion of
the cortex.
– Casparian strip
• Water impenetrable barrier created by adjoining cell
walls between cells containing a fatty substance called
suberin.
– Result: All water passing through the endodermis
must pass through the endodermal cells and not
between the cells.
– Endodermal cells control the movement of water into
the center of the root and prevent water movement
back out to the cortex.
Primary Structure of Roots
• Vascular cylinder or Stele
– Makes up the tissue inside the endodermis.
– Pericycle
• Outer part of the vascular cylinder consisting of one to several
layers of cells.
• Lateral roots arise from this area.
– Inside the pericycle is the vascular tissue.
• Dicots:
– Xylem cells fill the center (central hub with lobes)
– Phloem cells occupy the regions between the lobes
• Monocots:
– Groups of xylem cells alternate with groups of phloem cells in a
ring that encircles a central tissue are called the pith.
Primary Structure of Stems
• Similar to roots with the exception of the
endodermis and casparian strip.
• Epidermis
• Cortex
• Vascular cyclinder or Stele
– Phloem
– Xylem
• Pith
Primary Structure of Stems
• Epidermis
– Epidermal cells covered with a waxy (fatty)
substance called cutin.
– Cutin forms a protective layer called the
cuticle.
– Other epidermal cells include various
specialized cells:
• Guard cells
• Stinging cells
Primary Structure of Stems
• Cortex
– consists of various ground tissue types that lie
between the epidermis and the vasxular
cylinder.
– Many of these cells contain chloroplasts.
Primary Structure of Stems
• Vascular cylinder
– Consists of xylem, phloem, and pith.
– Conifers and dicots xylem and phloem are
grouped in bundles which ring a central pith
region.
• Phloem to the outside of each bundle.
• Xylem to the inside of each bundle.
– Monocots, the xylem and phloem bundles are
scattered throughout a mass of ground tissue.
Secondary Structure of
Stems and Roots
• Vascular cambium
– Originates between the xylem and phloem and becomes
a cylinder of tissue that extends the length of the stem
and root.
– The cambium layer is meristematic, producing new
cells on both the inside and outside of the cambium
cylinder.
• Cells on the inside differentiate into secondary xylem.
• Cells on the outside differentiate into secondary phloem.
– Over the years, secondary xylem accumulates and
increases the girth of the stem and roots.
– Also, new secondary phloem is added yearly to the
outside of the cambium layer.
Secondary Structure of
Stems and Roots
• As a result, tissues beyond the secondary
phloem are pushed outward as the xylem
increases in girth.
• The outside tissues, which include the
primary tissues (epidermis and cortex),
break apart as they expand and are
eventually shed as they separate from the
stem or root.
Secondary Structure of
Stems and Roots
• Periderm
– New protective covering produced by the cork
cambium to replace the shed epidermis.
– Consists of protective cork cells impregnated
with suberin.
Secondary Structure of
Stems and Roots
• Wood
– Each year, new layers of secondary xylem are produced
by the vascular cambium.
– Xylem tissue, which is the actual wood of the plant, is
dead at maturity.
– Only xylem produced during the more recent years
remains active in the transport of water.
• This xylem is sapwood.
– Older xylem, located toward the center of the stem, is
called heartwood, and functions only as support.
Secondary Structure of
Stems and Roots
• Annual rings
– Environmental conditions vary during the year, creating
seasons during which plants alternate growth with
dormacy.
– Alternation of growth and dormancy produces annual
rings in the secondary xylem tissue.
– Can be used to determine the age of a tree.
– Since the size of the rings is related to the amount of
water available during the year, rings can be used to
provide a rainfall history for regions.
Secondary Structure of
Stems and Roots
• Annual rings
– During periods of growth, the vascular
cambium is actively dividing.
– As the season draws to an end, divisions and
growth slow and gradually come to an end.
– When the next season begins, the vascular
cambium begins dividing again.
Structure of the Leaf
• Epidermis
– Protective covering of one or more layers of
cells.
– Covered by the cuticle
• Protective layer consisting of cutin.
• Reduces transpiration.
Structure of the Leaf
• Palisade mesophyll
– Consist of parenchyma cells with numerous
chloroplasts for photosynthesis.
– Photosynthesis is the primary function.
– Parenchyma cells are usually tightly packed in
one or more layers at the upper surface.
• In some plants the parenchyma cells may be located
in the upper and lower surfaces for plants adapted to
dry habitats.
Structure of the Leaf
• Spongy mesophyll
– Consists of parenchyma cells loosely arranged
below the palisade mesophyll.
– Numerous intercellular spaces provide air
chambers that provide CO2 to photosynthesizing
cells and O2 to respiring cells.
Structure of the Leaf
• Guard cells
– Specialized epidermis cells
– Control the opening and closing of stomata.
• Vascular bundles
– Consists of xylem and phloem tissues.
– Bundle sheath cells surround the the vascular
bundles to prevent air bubbles from getting into
the vessels where they could impede the
movement of water.
Life Cycle of a
Generalized Angiosperm
Ovary,
containing
ovule
Fruit,
containing
seed
Seed with
embryo
Mature plant with
flowers, where
fertilization occurs
seedling
Germinating
seed
The Seed
• Pollination
– Anther produces spores through meiosis.
• Pollen grain is produced by mitosis of spore
• And released from the anther.
– Pollen is delivered to the stigma of the carpel.
The Seed
• Fertilization
– Pollen grain germinates on the stigma.
• Produces a pollen tube, which grows downward into the ovary.
• When the pollen tube reaches the base of the ovule, it enters
the embryo sac through a pore and discharges two sperm.
– Two sperm are produced by mitosis
– One sperm fertilizes the egg, forming the zygote
– Other sperm contributes its halpoid nucleus to the large
central cell of the embryo sac making it triploid (3N).
• This cell will give rise to tissue that nourishes the embryo that
develops from the zygote.
– Double fertilization
The Seed
• Ovule develops into a seed.
– Endosperm
• Nutrient rich , multicellular mass developed from the triploid
central cell.
– Embryonic development
• Zygote to embryo
• Cotyledon(s) develop from the embryo.
– Seed coat
• Encloses the embryo and endosperm
• Protective and drought resistant
– Seed dormancy
The Seed
• Embryo
– Epicotyl
• Top portion of the embryo, becomes the shoot tip
– Plumule
• Young leaves often attached to the epicotyl
– Hypocotyl
• Young shoot (embryonic shoot)
– Radicle
• Young roots (embryonic roots)
Germination
• Begins with the absorption of water
• Water initiates the activity of various enzymes
which activate biochemical processes including
respiration.
• Water absorption causes the seed to swell and the
seed coat to crack.
• The growing tips of the radicle produce roots that
anchor the seedling.
• Elongation of the hypocotyl follows, producing a
young shoot.
• Growth occurs at the apical meristems.