plant structure and organization 1 ch. 25 – plant structure & organization
TRANSCRIPT
1Plant Structure anPlant Structure and Organizationd Organization
Ch. 25 – Plant Structure & Organization
2Plant Structure anPlant Structure and Organizationd Organization
Plant Organs
Plants possess two types of systems:
Root System
Simply consists of roots
Shoot System
Consists of stems & leaves
Vegetative Organs
Roots, stems & leaves
Reproductive Organs
Flowers, seeds & fruits
3Plant Structure anPlant Structure and Organizationd Organization
Plant Organs
Roots
Generally, the root system is at least equivalent in size and extent to the shoot system
Anchors plant in soil; gives support
Absorbs water and minerals
Produces hormones that stimulate growth of stems
Root hairs:
Projections from epidermal root hair cells
Greatly increase absorptive capacity of root
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Plant Organs
Roots (cont’d)
Perennial plants
Vegetative structures live year to year
Herbaceous Perennial plants
Upper parts die back in winter
Store energy in roots
Examples: carrots, sweet potatoes
5OrganizationofPlantBody
6VegetativeOrgansofSeveralEudicots
7Plant Structure anPlant Structure and Organizationd Organization
Stems
Shoot system of a plant is composed of the stem, branches, and leaves
Stem is the main axis of a plant that elongates and produces leaves
Nodes occur where leaves are attached to the stem
Internode is region between nodes
Stem also has vascular tissue that transports water and minerals from roots through stem to leaves & transports products of photosynthesis
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Stems
Other functions of stems:
Primary photosynthetic organ in cactus
Water reservoir in succulents
Store nutrients
Tubers are horizontal or underground stems
i.e. Potatoes
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Leaves
Leaves are the major part of the plant that carries on photosynthesis
- Size, shape, color & texture of leaves vary.
- Used for identification of plants
Two main types of plants based on leaves:
- Evergreens – retain leaves for 2-7 years
- Deciduous – lose leaves every year
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Leaves
Foliage leaves are usually broad and thin for maximum surface area for absorption
Blade - Wide portion of foliage leaf
Petiole - Stalk attaches blade to stem
Leaf Axil is the upper acute angle where axillary bud originates. May become leaf or flower.
Tendrils - Leaves that attach to objects
Bulbs - Leaves that store food
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Monocots versus Eudicots
Flowering plants are divided into 2 groups depending on number of cotyledons, or seed leaves in the embryonic plant.
Monocots
- One cotyledon
Eudicots
- Two cotyledons
12FloweringPlants:MonocotsorEudicots
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Monocot vs. Eudicot
Monocots (grasses, palm trees, rice, wheat, corn)
Cotyledons act as transfer tissue; nutrients are derived from endosperm prior to the development of true leaves
Root vascular tissue occurs in a ring
Leaf veins are vascular bundles
Parallel leaf venation
Flower parts arranged in multiples of three
14FloweringPlants:MonocotsorEudicots
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Monocot vs. Eudicot
Eudicots (dandelions to oak trees)
Cotyledons supply nutrients to seedlings
Root phloem located between xylem arms
- Pattern looks like a star
Netted leaf venation
- Pinnate – major veins originate from central vein
- Palmate – major veins originate from point of attachment of blade to petiole
16FloweringPlants:MonocotsorEudicots
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Plant Tissues
Plants have ability to grow during entire lives because they possess meristematic tissue.
Apical meristems - located at or near tips of stems & roots
- increase the length of stems & roots
- Increase in length is called primary growth
- produce 3 types of tissues:
epidermal, ground & vascular
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Plant Tissues
Epidermal Tissues Form protective outer covering called epidermis
Contain closely packed epidermal cells
Walls of epidermal cells exposed to air are covered with a waxy cuticle to minimize water loss
Cuticle also protects against bacteria & disease
Roots contain root hairs
Leaves can have trichomes (hairs) to protect from sun & to conserve water. These can inject toxins into animals.
Lower leaf surface contain stomata surrounded by guard cells. These regulate gas exchange & water loss.
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Plant Tissues
Epidermal tissues (cont’d)
In woody plants, the epidermis of stem is replaced by periderm.
- Major component is cork
- Mature cork cells can be sloughed off
- New cork cells are made by a meristem called the cork cambium
20ModificationsofEpidermalTissue
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Ground Tissue
Ground tissue forms bulk of interior of plant
Formed of three types of cells:
parenchyma, collenchyma & sclerenchyma
Parenchyma cells:
Most abundant & alive at maturity
Least specialized and are found in all organs of plant. Can divide and give rise to more specialized cells
Functions: photosynthesis, food storage, respiration
22GroundTissue
Cells
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Ground Tissue
●Collenchyma cells:
Alive at maturity
Have thicker primary walls
Form bundles underneath epidermis
Flexible support to immature regions of the plant
Strands of celery are composed of these cells
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Cells
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Ground Tissue
Sclerenchyma cells:
Have thick secondary walls impregnated with lignin, a highly resistant substance that makes walls tough and hard
Most are nonliving; dead at maturity
Primary function is to support mature regions of the plant
Two types of cells: fibers & sclereids
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Cells
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Vascular Tissue
There are two types of vascular tissues:
Xylem
Transports water & minerals from roots to leaves
Phloem
Transports sucrose & other organic compounds, including hormones, usually from leaves to roots
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Vascular Tissue
Both xylem & phloem are considered complex tissues (those made of 2 or more kinds of cells)
Xylem is made of:
Tracheids (hollow non-living cells)
Long, with tapered ends
Pits in end walls help water move
Vessel Elements (hollow non-living cells)
Larger, with perforated plates in their end walls
29XylemStructure
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Vascular Tissue - Phloem
Phloem is composed of living cells:
Sieve-tube members are conducting cells
Form a continuous sieve tube; have pores in end walls
Contain cytoplasm but no nuclei
●Companion cells attached to each sieve-tube
Plasmodesmata extend between 2 types of cells. Companion cell’s nucleus might control sieve-tube.
31PhloemStructure
32Plant Structure anPlant Structure and Organizationd OrganizationOrganization of Roots -
Longitudinal section
Apical meristemLocated in the root tipProtected by root cap
Zones of Root:
Zone of cell division - primary meristems
Zone of elongation - cells lengthen
Zone of maturation - contains fully differentiated (specialized)cells. Cells on epidermis have root hairs.
33EudicotRoots
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Tissues of Eudicot Root - Cross Section
Epidermis - single layer of cells
Cortex
- Large thin-walled parenchyma cells
- Loosely packed
- Possible for water to move without entering cells
- Functions in food storage.
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Tissues of Eudicot Root - Cross Section
Endodermis -
- Single layer of rectangular cells
- Between cortex and inner vascular cylinder
- Bordered on four sides by Casparian Strip. • This is a layer of impermeable lignin & suberin.
• Prevents passage of water & mineral ions between adjacent cell walls.
access to vascular cylinder is through endodermal cells themselves
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Tissues of Eudicot Root - Cross Section
Vascular Tissue Pericycle - First layer of cells within vascular cylinder
- Retains capacity to divide to start development of branch, or lateral, roots.
•Xylem - Appears star-shaped in eudicots
•Phloem - found between arms of xylem
37BranchingofEudicotRoot
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Organization of Monocots Roots
Monocot roots have same growth zones as eudicot roots, but do not undergo secondary growth.Ground tissue of root’s pith is surrounded by vascular ring
- Ring composed of alternating bundles of xylem and phloem
Have pericycle, endodermis, cortex & epidermis
39MonocotRoot
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Root Diversity
Primary root (taproot) - Fleshy, long single root, that grows straight downOften stores food Examples: carrots, beets, turnips, radishes
Fibrous root system - Large # of slender roots and lateral branchesAnchors plant to soilFound in grasses
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Root Specializations
Adventitous roots - Roots that develop from organs of the shoot system instead of root system
Prop roots - emerge above soil line & function to help anchor the plant
Others are found on horizontal stems or at nodes & help vines to climb (English Ivy)
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Root Specializations
Haustoria:Parasitic rootlike projections that grow into host plant
Make contact with vascular tissue and extract water and nutrients
Mycorrhizae:Associations between roots and fungiExtract water and minerals from soil better than roots alone
• Example of mutualism (plants/fungus benefit)
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Root Specializations
Root nodules - Contain nitrogen-fixing bacteria
• Found in peas, beans, and other legumes
• Bacteria can take up atmospheric nitrogen & make it available to plants
• Thus, plants aren’t dependent on supplies of nitrogen in the soil
• Legumes often planted to bolster N supply of soil.
44RootDiversity
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Organization of Stems
Shoot apical meristemProduces new cells that elongate and increase length of stem
Protected by terminal bud
Enveloped by leaf primordia (immature leaves)
46WoodyTwig
47ShoottipandPrimaryMeristems
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Organization of Stems
● Specialized primary meristemsProtoderm – gives rise to epidermisGround Meristem – produces 2 tissues composed of parenchyma cells:
- pith (center of stem)
- cortex (between epidermis & vascular tissue)
49ShoottipandPrimaryMeristems
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Organization of Stems
●Procambium
Produces first xylem cells, primary xylem & first phloem cells, primary phloem.
Differentiation occurs which produces mature xylem, phloem and a lateral meristem called vascular cambium. This tissue will lead to secondary growth (growth in width)
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Herbaceous Stems
Mature nonwoody stems that exhibit only primary growth
Outermost tissue is epidermis covered with waxy cuticle
Stems have distinctive vascular bundles
Herbaceous eudicots - Vascular bundles arranged in distinct ring
Monocots - Vascular bundles scattered throughout stem
52HerbaceousEudicotStem
53MonocotStem
54MonocotStem
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Woody Stems
Woody plants have both primary and secondary tissuesPrimary tissues formed each year from primary meristems
Secondary tissues develop during first and subsequent years from lateral meristems
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Woody Stems
Woody stems have no distinct vascular bundles, and instead have three distinct regions:
●BarkWoodPith
Vascular cambium occurs between the bark and the wood
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Secondary Growth
Secondary growth adds cells on either side of the vascular cambium:
● Secondary xylem – inner side
● Secondary phloem – outer side
Each year new phloem is added to the outside of the trunk of a tree. This creates bark.
Each year new xylem is added to the inside of the trunk of the tree. This creates wood.
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Wood
Wood is secondary xylem that builds up year after year In trees that have a growing season, vascular cambium is dormant during winter
- In spring, when moisture is plentiful secondary xylem contains wide vessel elements with
thin walls.
- This creates the spring wood.
- Later in season, moisture is scarce, vessels are small and are many thick-walled tracheids
- This creates the summer wood.
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Wood
When the trunk of a tree has spring wood followed by summer wood, the two together make up one year’s growth, or an annual ring.
You can tell the age of a tree by counting the annual rings.
Two Types of Wood:
The outer annual rings, where transport occurs, are called sapwood.
In older trees, inner annual rings, heartwood, no longer function in water transport.
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Bark
Bark of a tree contains periderm (cork & cork cambium) and phloem.
Phloem does not build up season to season like wood. Instead it dies and is shed over time.
Bark can be removed, but it is harmful to the plant due to lack of organic nutrient transport
Cork cells are impregnated with suberin, a waxy layer that makes them waterproof but causes them to die. This makes them harder and less edible & thus protects the tree.
62Three-year-oldWoodyTwig
63TreeTrunk
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Stem Diversity
Stolons:Above-ground horizontal stemsProduce new plants where nodes touch the ground. This is called vegetative reproduction.
Example: strawberry plantsOther Modifications:
•Succulent stems on cacti store water •Stems that become tendrils to climb
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Stem Diversity
Rhizomes:Underground horizontal stemsContribute to asexual reproduction because each node bears a bud.
Variations:Tubers - Enlarged portions functioning in food storage
Example: potato eyes are budsCorms - Underground stems that produce new plants during the next season
Example:gladiolus“bulbs”
66StemDiversity
67LeafStructure
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Leaf Structure
Parts of a leaf:
•Epidermis
•Outer waxy cuticle
•Stomata & guard cells
•Body of leaf composed of mesophyll tissue in two types:
- palisade mesophyll - elongated cells
- spongy mesophyll - irregular cells bounded by air spaces
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Leaf Diversity
Blade of a leaf can be simple or compound:
• Simple leaf - single blade
• Compound leaf - divided into leaflets
- Pinnately compound leaves have leaflets occurring in pairs
- Palmately compound leaves have all of the leaflets attached to a single point
- Bipinnately compound leaves have leaflets subdivided into even smaller leaflets
70ClassificationofLeaves
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Leaf Diversity
Leaves can be arranged in stem in 3 ways:
• Alternate
• Opposite
• Whorled
Leaves are adapted to environmental conditions.Shade plants - broad, wide leavesDesert plants have reduced leaves, sunken stomata. Cactus spines are leaves.
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Leaf Diversity
Other specialized leaves:
• Onion bulbs
• Head of cabbage
• Large petiole (celery & rhubarb)
• Tendrils
• Specialized for catching insects:
- Sundews, Venus flytrap, pitcher plants
- These plants commonly live in marshy regions with low supply of soil nitrogen.
73LeafDiversity
Sundew
Pitcher
plant