Transcript Essentials of Biology Sylvia S. Mader

Essentials of Biology
Sylvia S. Mader
Chapter 20
Lecture Outline
Prepared by: Dr. Stephen Ebbs
Southern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
20.1 Plant Organs
• Flowering plants have two major
components to their structure.
– A root system
– A shoot system composed of the stem,
leaves, and reproductive organs.
• At the end of the root and shoot system is
a terminal bud from which vertical growth,
called primary growth, occurs.
20.1 The Body’s Organization
(cont.)
Leaves
• Recall that photosynthesis, the process by which
plants make carbohydrates, occurs in the
leaves.
• To conduct photosynthesis, leaves need solar
energy, water, and carbon dioxide.
• Photosynthetic leaves share similar structural
components.
– The blade, the wide part of the leaf
– The petiole, the stalk connecting leaf to stem.
Leaves (cont.)
• There is tremendous diversity in leaf
structure between plant species.
• In some plant species, leaves may serve
additional functions, such as storage.
• Some plants are deciduous, meaning that
they drop their leaves during certain
seasons.
Leaves (cont.)
Stems
• The stem is the main axis of the plant.
• Stems can produce side (lateral) branches
from lateral (axillary) buds.
• Nodes are the points where leaves attach
to stems.
• An internode is the region between nodes.
Stems (cont.)
• The stem also contains the vascular tissue
that transports water and nutrients to
leaves to support photosynthesis.
• In some plant species, stems may also
carry out photosynthesis or serve as a
storage organ.
Roots
• Roots anchor plants to the soil.
• Roots also absorb water and nutrients
from the soil.
• The surface area of roots is greatly
increased by the production of root hairs.
Roots (cont.)
• There are different types of root systems.
– Some plants have a single taproot.
– Grasses have fibrous root systems.
– Some plants have prop roots for support.
• For perennial plants, the roots act as a
storage order that allows the shoot system
to regrow each year.
Roots (cont.)
Monocot Versus Eudicot Plants
• Flowering plants are divided into two major
groups based upon the difference in
embryonic leaves (cotyledons).
– Plants that produce a single cotyledon are
called monocots.
– Plants that produce two cotyledons are called
eudicots.
• Cotyledons provide developing plants with
nutrients and serve other roles.
Monocot Versus Eudicot Plants
(cont.)
• The arrangement of the vascular tissue
differs between monocots and eudicots.
• Plants have two types of vascular tissue.
– The xylem transports water and minerals.
– The phloem transports organic nutrients.
• The vascular tissues serve as a type of
circulatory system for plants.
Monocot Versus Eudicot Plants
(cont.)
• The pattern of venation in the leaves of
monocots and eudicots differs.
– Monocots have parallel venation.
– Eudicots have a net-like pattern.
• The number of species also differs
between monocots and eudicots.
– Eudicots include a large number of species.
– There are fewer monocots species.
Monocot Versus Eudicot Plants
(cont.)
20.2 Plant Tissues and Cells
• Plant growth occurs continually from
dividing cells called the meristem.
• The apical meristems are located at the tip
of the root and shoot.
• Cellular division of the apical meristems
increase the length of the root and shoot.
20.2 Plant Tissues and Cells
(cont.)
• The outer cell layer of
plant tissues is the
epidermis.
• The root epidermis
can also have
epidermal root hairs
to increase surface
area.
20.2 Plant Tissues and Cells
(cont.)
• The leaf epidermis is
covered with a waxy
cuticle, providing a
barrier to water loss.
• The leaf epidermis
also have stomata
which regulate gas
and water exchange.
20.2 Plant Tissues and Cells
(cont.)
• In tree trunks,
epidermis is replaced
by cork, produced by
the cork cambium.
• Cork is waterproof
because of a
chemical called
suberin.
20.2 Plant Tissues and Cells
(cont.)
• The interior of the plant leaves, stems, and roots
is composed of ground tissue.
• There is also a meristematic vascular tissue
called the vascular cambium, which produces
new vascular tissue.
• There are three cell types in ground tissue.
– Parenchyma
– Collenchyma
– Sclerenchyma
20.2 Plant Tissues and Cells
(cont.)
• Parenchyma cells are
the least specialized
cell type.
• Parenchyma cells are
photosynthetic cells
found throughout the
plant.
20.2 Plant Tissues and Cells
(cont.)
• Collenchyma cells
have thick cell walls.
• Collenchyma cells are
arranged in bundles
to provide flexible
support below the
epidermis.
20.2 Plant Tissues and Cells
(cont.)
• Sclerenchyma cells
have cell walls
reinforced with lignin.
• Sclerenchyma cells
are often dead cells.
• Sclerenchyma cells
provide support in
mature tissues.
20.2 Plant Tissues and Cells
(cont.)
• The xylem is the vascular tissue that
transport water and minerals from roots.
• Vessel elements are one type of xylem
with large, perforated cell walls.
• Tracheids are smaller xylem cells whose
walls have numerous pits.
20.2 Plant Tissues and Cells
(cont.)
20.2 Plant Tissues and Cells
(cont.)
• The phloem of the vascular system is
composed of sieve-tube members.
• The sieve-tube members have perforated
plates on each end of the cell.
• Each sieve-tube member has a
companion cell which controls the activity
of the enucleated sieve-tube member.
20.2 Plant Tissues and Cells
(cont.)
20.3 Organization of Leaves
• Leaf structure varies from plant species to
plant species.
• There may be a single blade of the leaf or
multiple blades, forming a compound leaf.
20.3 Organization of Leaves
(cont.)
20.3 Organization of Leaves
(cont.)
• The top and bottom of a typical eudicot leaf is
composed of epidermis
– The epidermis often has hairs or glands.
– Stomata are located on the lower epidermis.
• The interior of the leaf is composed of
photosynthetic mesophyll cells.
– The spongy mesophyll is arranged randomly to
increase surface area for gas exchange.
– The palisade mesophyll is comprised of elongated,
vertically-oriented cells.
20.3 Organization of Leaves
(cont.)
20.4 Organization of Stems
• Primary growth,
driven by cell division
in the apical
meristem, contributes
to the growth of
stems.
• The organization of
the terminal bud
protects the apical
meristem.
Nonwoody Stems
• Plant stems that do not contain wood are
called herbaceous stems.
• The vascular bundles of herbaceous
eudicot stems are arranged in a ring under
the epidermal layer.
• The vascular bundles of herbaceous
monocot stems are randomly distributed.
Nonwoody Stems (cont.)
Nonwoody Stems (cont.)
Woody Stems (cont.)
• Woody stems undergo both primary and
secondary growth.
• Secondary growth is an increase in girth.
• The vascular cambium of woody plants is
meristematic and produces new xylem and
phloem cells each year.
Woody Stems (cont.)
• Woody stems have three distinct regions.
– Bark
– Wood
– Pith
• The vascular cambium occurs between
the bark and the wood.
Woody Stems (cont.)
Bark
• Tree bark contains several cell types.
– Cork
– Cork cambium
– Cortex
– Phloem
• The cork cells have several functions.
– Cork cells protect the stem
– Specialized cork cells form lenticels to
facilitate gas exchange.
Wood
• Wood is composed of the secondary xylem
produced each year by the stem.
• Spring wood has wide xylem vessels with thin
walls, due to transport of large amounts of water.
• When water is scarce later in the summer, the
xylem vessels of summer wood become
narrower with thicker walls.
• Spring and summer wood together make an
annual ring.
20.5 Organization of Roots
• Within the eudicot root, there are
longitudinal zones where cells are in
different stages of differentiation.
– The apical meristem is composed of dividing
cells protected by a root cap.
– Cells in the next zone are elongating
vertically.
– In the last zone, the cells mature before
completing their development.
20.5 Organization of Roots
(cont.)
Tissues of the Eudicot Root
• The eudicot root has several tissue types.
– The epidermis is the outermost layer.
– The cortex in the center of the root is
comprised parenchyma cells.
– The endodermis is an internal cell layer that
regulates the movement of water and
nutrients into the vascular tissue.
– The pericycle is an inner ring of dividing cells
that can produce lateral roots.
– The vascular tissue in the center of the root
contains xylem and phloem for transport.
Tissues of the Eudicot Root
(cont.)
Organization of Monocot Roots
• Monocots have the same growth zones as
eudicot roots but do not undergo secondary
growth.
• The center of monocot roots is composed of
ground tissue called pith.
• The pith is surrounded by a vascular ring with
alternating bundles of xylem and phloem.
Comparison With Stems
• Roots and stems are both produced by primary
growth from apical meristems.
• However, the branching of roots and stems
occur differently.
– Stems branch from buds on the stem.
– Roots branch from the internal pericycle.
• The vascular cambium of eudicot stems and
roots produces secondary growth.
20.6 Plant Nutrition
• Plants are unique in that they require only
inorganic nutrients to survive.
• Plants convert these inorganic nutrients to
the organic compounds needed for life.
• Some inorganic elements are essential,
meaning that plants have an absolute
requirement for those elements.
20.6 Plant Nutrition (cont.)
• The essential nutrients are divided into two
categories based upon their relative
concentrations in plant tissues.
– Macronutrients are elements that are required
in large amounts.
– Micronutrients are required in small amounts
for specialized functions.
20.6 Plant Nutrition (cont.)
• There are nine macronutrients.
– Carbon
– Hydrogen
– Oxygen
– Phosphorus
– Potassium
– Nitrogen
– Sulfur
– Calcium
– Magnesium
20.6 Plant Nutrition (cont.)
• There are seven micronutrients, which
serve primarily as enzyme cofactors.
– Iron
– Boron
– Manganese
– Copper
– Zinc
– Chloride
– Molybdenum
20.6 Plant Nutrition (cont.)
• Deficiencies in one or more of these nutrients
can stunt plant growth.
Adaptations of Roots for Mineral
Uptake
• Mineral nutrients enter plants through the
root system.
• Roots have several modifications that
enhance their ability to acquire nutrients.
• Some of those modifications involve
specific symbiotic relationships.
Adaptations of Roots for Mineral
Uptake (cont.)
• In plants such as legumes, specialized
bacteria reside in root nodules.
• These bacteria are capable of converting
atmospheric nitrogen gas into a form
useable by the plants.
• The plant roots provide carbohydrates to
the bacteria to support their growth.
Adaptations of Roots for Mineral
Uptake (cont.)
• Most plants have a symbiotic relationship
with mycorrhizal fungi.
• The fungal hyphae increases the surface
area available for water and nutrient
uptake.
• The plant roots provide the fungi with
carbohydrates and amino acids.
Adaptations of Roots for Mineral
Uptake (cont.)
20.7 Transport of Nutrients
• The water and nutrients taken up by roots
and root hairs are transported to leaves
via the interconnected vessel elements of
the xylem.
• This movement is provided in part by root
pressure, a positive pressure created
when water enters the root by osmosis.
20.7 Transport of Nutrients
(cont.)
• The cohesion-tension model explains how water
travels up the xylem to leaves.
• Recall that leaves have numerous openings
called stomata.
• When these stomata are open, water evaporates
from the interior of the leaf to the outside air, a
process called transpiration.
20.7 Transport of Nutrients
(cont.)
• As plant leaves transpire water, a tension is
created that pulls water from roots to leaves.
• This tension is maintained because water
molecules display an attraction to one another
called cohesion.
• Water also adheres to the xylem elements in a
process called adhesion.
20.7 Transport of Nutrients
(cont.)
Opening and Closing of
Stomata
• The opening and closing of the leaf
stomata is controlled by turgor pressure
within the guard cells.
• As water enters the guard cells, these
cells swell, opening the stomate.
• As water exits the guard cells, the loss of
turgor causes the stomate to close.
Opening and Closing of
Stomata (cont.)
Organic Nutrients in the Phloem
• The phloem transport carbohydrates from
photosynthesizing leaves to roots, young
leaves, and other tissues that require
carbohydrates.
• The transport of carbohydrates through
the phloem occurs by a mechanism called
the pressure-flow model.
Organic Nutrients in the Phloem
(cont.)
• Phloem transport is considered source to
sink transport.
• As mature leaves photosynthesize, they
become a source of sugar.
• The carbohydrates in the phloem are
transported to tissues that require sugars,
called sink tissues.
Organic Nutrients in the Phloem
(cont.)