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Chapter 35: Plant Structure, Growth, and Development
The plant body has a hierarchy of organs, tissues, and cells
• Plants, like multicellular animals, have organs composed of different tissues, which are in turn are composed of cells
The Three Basic Plant Organs: Roots, Stems, and Leaves
• Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below-ground and
above-ground
• Three basic organs are evolved:
– Roots
– Stems
– Leaves
• They are further organized into a __________________________ system and a __________________________
system
Roots
• Functions of roots:
– __________________________ the plant
– __________________________ minerals and water
– Often storing organic nutrients
• In most plants, absorption of water and minerals occurs near the root tips,
– The vast numbers of tiny root hairs increase the __________________________
– Many plants have modified roots
• Prop roots: arises from the stem, penetrates the soil, and helps support the stem; corn
• Storage roots: modified for storage of food or water; carrots and beets
• Strangling aerial roots: entirely above the ground; ivy
• Buttress roots: large roots on all sides of a tall or shallowly rooted tree; rainforest trees
• Pneumatophores: roots rising above the ground, especially above water, contain a large number of
breathing pores for exchange of gases; mangrove genera
Stems
• A stem is an organ consisting of:
– An alternating system of nodes and internodes
• __________________________: points at which leaves are attached
• __________________________: stem segments between nodes
• __________________________ bud: structure that has the potential to form a lateral shoot, or branch
• __________________________ bud: located near the shoot tip and causes elongation of a young shoot
• Many plants have modified stems
– Stolons: specialized type of above ground shoot, a colonizing organ that arises from an axillary bud near the
base of the plant; strawberry
– Bulbs: underground vertical shoot that has modified leaves that are used as food storage organs by a
dormant plant; daffodil
– Tubers: enlarged stems to store nutrients, used to survive the winter or dry months, means of asexual
reproduction; potatoes
– Rhizomes: horizontal stem that is usually found underground, often sending out roots and shoots from its
nodes; ginger
Leaves
• The leaf is the main photosynthetic organ of most vascular plants
• Leaves generally consist of
– Flattened blade
– Stalk
– __________________________: joins the leaf to a node of the stem
• Some plant species have evolved modified leaves that serve various functions
– Tendrils: threadlike shape that is used for support and attachment, generally by twining around whatever it
touches; clematis
– Spines: sharp, pointy ends, used to protect themselves from herbivores; cactus
– Storage leaves: serve as food storage organs; aloe
– Bracts: associated with a reproductive structure such as a flower, poinsettia
– Reproductive leaves: contain new plants at tips; walking fern
The Three Tissue Systems: Dermal, Vascular, and Ground
• Each plant organ has dermal, vascular, and ground tissues
– The dermal tissue is the outside protect layer, specifically known as the __________________________
– Vascular tissue: carries out long-distance transport of materials between roots and shoots
• __________________________: conveys water and dissolved minerals upward from roots into the
shoots
• __________________________: transports organic nutrients from where they are made to where
they are needed
– Ground tissue includes cells specialized for storage, photosynthesis, and support
Common Types of Plant Cells
• Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in
structure and function
• Some major types of plant cells:
– Water-conducting cells of the xylem
– Sugar-conducting Cells of the phloem
Types of Plant Cells
1. Water-conducting cells of the xylem
– __________________________: long thin cells with tapered ends
• Water moves through pits
– Vessel elements: wider, shorter, less tapered cells
• Aligned end to end, forming long pipes
• Ends are perforated
2. Sugar-conducting cells of the phloem
– Sieve-tube members: chains of cells
• Ends are connected with __________________________, that have pores to allow nutrients through
Meristems generate cells for new organs
• Plants grow throughout their lives
– __________________________: complete life cycle in 1 year or less
– __________________________: complete life cycle in 2 years or less
– __________________________: live many years
• Plants can constantly grow because of meristems: perpetual embryonic tissue
Root Meristems
– Apical meristems are located at the tips of roots and in the buds of shoots
• Elongate shoots and roots, a process called __________________________
Shoot Meristems
• Lateral meristems add thickness to woody plants, a process called __________________________
– There are two layers of lateral meristems
• __________________________ cambium: adds layers of vascular tissue called secondary xylem
(wood) and secondary phloem
•
__________________________ cambium: replaces the epidermis with periderm, which is thicker
and tougher
Primary growth lengthens roots and shoots
• Primary growth produces:
– Primary plant body
– Parts of the root
– Parts of the shoot systems
Primary Growth of Roots
• The root tip is covered by a __________________________, which protects the apical meristem as the root pushes
through soil
• Growth occurs just behind the root tip, in three zones of cells:
– Zone of cell division
– Zone of elongation
– Zone of maturation
Primary Growth of Shoots
• A shoot apical meristem is a dome-shaped mass of dividing cells at the tip of the terminal bud
• It gives rise to a repetition of internodes and leaf-bearing nodes
Tissue Organization of Leaves
• The epidermis in leaves is interrupted by __________________________
– Allow CO2 exchange between the air and the photosynthetic cells in a leaf
• Flanked by __________________________, which regulate opening
• The ground tissue in a leaf is sandwiched between the upper and lower epidermis
– This region is the __________________________
– Cells are loosely arranged to allow CO2 and O2
• The vascular tissue of each leaf is continuous with the vascular tissue of the stem
Morphogenesis and Pattern Formation
• Morphogenesis in plants, as in other multicellular organisms, is often controlled by __________________________
genes
• Pattern formation is the development of specific structures in specific locations
– It is determined by positional information in the form of signals indicating to each cell its location
• __________________________ is one type of positional information
• In the gnom mutant of Arabidopsis, the establishment of polarity is defective
Gene Expression and Control of Cellular Differentiation
• In cellular differentiation, cells of a developing organism synthesize different proteins and diverge in structure and
function even though they have a common genome
– A cell’s position in a developing organ determines its pathway of differentiation
• Cellular differentiation to a large extent depends on positional information and is affected by homeotic genes
Genetic Control of Flowering
• Flower formation involves a phase change from __________________________ growth to
__________________________ growth
– It is triggered by a combination of environmental cues and internal signals
• Transition from vegetative growth to flowering is associated with the switching-on of floral meristem identity genes
• The __________________________ of flower formation identifies how floral organ identity genes direct the
formation of the four types of floral organs
• An understanding of mutants of the organ identity genes depicts how this model accounts for floral phenotypes