seed plant structure and function chapter 23. seed plant overview: the plant body consists of two...
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Seed Plant Overview: • The plant body consists of two basic parts---
the shoot system and the root system • Shoot system is above ground and includes
organs such as leaves, buds, stems, flowers, and fruits
• The functions of the shoot system include photosynthesis, reproduction, storage, transport, and hormone production
• The root system is below ground and includes roots as well as modified stem structures such as tubers and rhizomes
• The functions of the root system include anchorage, absorption, storage, transport, and production of certain hormones
Seed Plant Overview Cont.:
• Seed plants contain 2 types of vascular tissue (xylem & phloem) to help transport water, minerals, & food throughout the root & shoot systems
• Plant cells have several specialized structures including a central vacuole for storage, plastids for storage of pigments, and a thick cell wall of cellulose
• Plant cells are all box-shaped in appearance
Plant Cell Organization• Plant cells are arranged
into tissues and tissue systems
• A simple tissue is composed of only one type of cell; a complex tissue is composed of more than one cell type.
• Plants are composed of specialized cells and tissues
• In plants, the formation of new cells, tissues and organs is restricted almost entirely to regions known as meristems
Meristems:
• There are 3 main types of meristematic tissue in vascular seed plants ---- apical, intercalary, & lateral meristems
Meristems:
• Apical Meristem occur at the tips of roots and shoots and are responsible for the length-wise extension of the plant body known as primary growth
• Cells in apical meristems are produced by mitosis & then differentiate into specialized cells & tissues
Intercalary Meristems
• Some monocots, such as grasses & bamboo, have intercalary meristems located above the bases of leaves and stems allowing them to regrow quickly after being cut down
Growth in Plants
• Woody plants have meristem between xylem & phloem to produce wood
• Lateral meristems produce outward growth in plants or secondary growth
• Lateral meristems are called cambium (cambia, plural)
• Vascular cambium makes wood & vascular tissues and cork cambium makes cork & bark
• Plants without lateral meristems have only primary, not secondary growth and are called herbaceous plants
Specialized Plant Cells:
• Plants have 3 basic types of cells --- parenchyma, collenchyma, & sclerenchyma
• Parenchyma cells are the most abundant & least specialized
• Parenchyma are loosely-packed, cube shaped or elongate cells with a large central vacuole & thin cell walls
Parenchyma
• Parenchyma cells can specialize for various functions (storage,
photosynthesis, etc.) • Parenchyma form the bulk of non-
woody plants such as the fleshy part of an apple
• Collenchyma cells are irregular in shape with thicker cell walls & support the growing parts of plants
Collenchyma
Collenchyma cell walls are also flexible to support new growth regions of the plant (example: tough strings on a celery stalk)
Sclerenchyma• Sclerenchyma cells support non-growing parts of
plants because they have thick, rigid, non-stretchable cell walls
•Sclerenchyma Cells
• Sclerenchyma cells often die at maturity leaving empty, box-like structures
• Two types of sclerenchyma cells are fibers & sclereids
• Fibers are cells up to 50cm long that usually occur in strands such as linen & flax
•Sclerenchyma Fibers
• Sclereids have thicker cell walls & come in many shapes
• Sclereids may be single cells or groups of cells and give pears their gritty texture & give hardness to peach pits & walnut shells
Other Plant Tissues & Systems:
• Tissues are groups of cells with similar structures & functions
• Plants have 3 tissue systems --- ground, dermal, and vascular tissues
• Plant tissues make up the main organs of a plant --- root, stem, leaf, & flower
• Ground tissue makes up most of the plant's body, dermal tissue covers the outside of the plant, & vascular tissue conducts water & nutrients
Dermal Tissue: • Covers the plant body
and consists of epidermis in young plants & non-woody plants that is replaced later by periderm in woody plant
• Epidermis is made of parenchyma cells in a single layer
• Epidermis on stem and leaves prevents water loss by transpiration & produces a waxy material called cuticle
Dermal Tissue:• Openings in the
epidermis on the underside of a leaf where gases are exchanged are called stomata (stoma, singular)
• Sausage-shaped guard cells are found on each side of the stoma to help open and close the pore to prevent water loss
• Dead cork cells replace epidermis in woody stems & roots
Guard Cells surrounding stoma
Ground Tissue:
• Ground tissue constitutes the majority of the plant body and contains parenchyma, collenchyma, and sclerenchyma cells
• Ground tissue of the leaf (called mesophyll) uses the energy in sunlight to synthesize sugars in a process known as photosynthesis
• Spongy Mesophyll of Leaf• Ground tissue of the stem (called pith and
cortex) develops support cells to hold the young plant upright
• Ground tissue of the root (also called cortex) often stores energy- rich carbohydrates
Vascular Tissue:• Vascular tissues transport water and
dissolved substances inside the plant and helps support the stem
• The 2 types of vascular tissue are xylem & phloem
• Xylem carries water and dissolved ions from the roots to stems and leaves
• Phloem carries dissolved sugars from the leaves to all other parts of the plant
• Xylem has 2 kinds of conducting cells --- tracheids & vessel elements
Vascular Tissue:
• Tracheids are long, narrow sclerenchyma cells with walls and pits for water to move between them
• Vessel elements are short, wide sclerenchyma cells without end walls stacked on top of each other
• Angiosperms (flowering plants) have tracheids & vessel elements, while gymnosperms (cone bearers) only have tracheids
• Phloem moves sap (dissolved sugars & minerals) from source (where they are made) to sink (where they will be used)
Vascular Tissue:
• Phloem is made of cells called sieve tube members and companion cells
• sieve tube members are stacked to form tubes called sieve tubes with porous sieve plates between the cells for movement of sugars
• Companion cells are along each sieve tube member & help in loading sugar into the sieve tube
Root System:
• Roots grow underground (subterranean part of the plant)
• Roots have 3 main functions --- (1)anchor plants (2) absorb and conduct water & minerals (3) store food
• The first root to emerge from the most seeds is called the primary root or taproot & can grow deep to reach water
• Taproots may store food (carrot & beet)
Root Systems
• Monocots have highly branched, roots called fibrous roots that grow near the surface & spread out to collect water
• Fibrous roots such as in grasses often help prevent erosion
• Adventitious roots grow from a stem or leaf above ground in some plants and serve to prop up or support the plant (corn)
• Aerial roots obtain water & minerals from the air & enable the plant to climb (orchids & ivy)
Structure of the Root:• Root cap covers the apical meristem
(growth tissue) at the tip of the root & produces a slimy substance so roots can more easily grow through the ground
• Apical meristem replaces cells of the root cap as they are damaged
• Epidermis covers the outside of the root & has extensions called root hairs that absorb water & minerals and increase the surface area of the root
Structure of the Root:• The core of the root is called the
vascular cylinder, contains xylem & phloem
• A band of ground tissue called cortex surrounds the vascular cylinder
• A single cell layer called endodermis separates the cortex & vascular tissue
• Endodermal cells are coated with a waxy layer called the Casparian strip so water is channeled into the vascular tissue
• The Pericycle is the outermost layer of central vascular tissue & forms lateral roots
Stem Structure & Function:
• Adapted to support leaves • Transport water & minerals • Transport sugars (usually sucrose) from
Source (where they're made) to Sink (where they're stored)
• Movement of sugars is called translocation • Store food and/or water • Tubers (potatoes) underground food storage
stems • Stems grow from the tip or apical meristem • Stems increase in circumference by lateral
meristems • Leaves are attached to stems at nodes & have
lateral buds that can develop into new stems or branches
• Internode is space between nodes on a stem
• The tip of each stem usually has a Terminal Bud enclosed by specialized leaves called Bud Scales
• Vascular Tissue is arranged in bundles with xylem toward the inside & phloem toward the outside
• Vascular bundles are scattered throughout monocot stems
• Vascular bundles are arranged in rings in dicot stems
Stem Structure
• Secondary grow (woody growth) occurs in dicots, but less often in monocots
• Plants with only primary growth (non-woody) are called herbaceous
• Darker wood in the center of a tree trunk is called Heartwood and is composed of old, non-functional xylem
• New, functional xylem makes up lighter wood in the tree trunk and is called Sapwood
• Sapwood gets wider, but heartwood remains the same size
• Bark is the protective covering of Woody Plants & consists of Cork, Cork Cambium, and Phloem
Translocation of Sugars:
• Phloem cells move sugars through a plant • Sugars made in photosynthetic cells are
PUMPED into Sieve Tubes by ACTIVE TRANSPORT at the Source
• Turgor Pressure Increases as Water enters the Sieve Tube by Osmosis
• TURGOR moves the SAP toward the SINKS • Known as the PRESSURE-FLOW
HYPOTHESIS
Transport of Water:• Transport of Water and mineral Nutrients
occurs in the Xylem • Water movement in plants is driven by
Transpiration (evaporation of water from leaves & stems)
• As water evaporates, more water is pulled into the roots
• Transpiration produces a NEGATIVE pressure in the xylem pulling water UPWARD
• Water molecules are cohesive (attracted to each other) which also pulls water upward
• Water is also adhesive sticking to the walls of the xylem
• Known as Cohesion Theory of water movement
Leaf Structure & Function:
• Flat surfaces helps leaves capture sunlight for photosynthesis
• Convert carbon dioxide and water into simple sugars (glucose)
• Some leaves store food (onion) and water
• Protect (cactus spines) • Used Dyes, Fibers, Fuels, Drugs,
Wax, Soap, Spices and Food
Leaf Structure & Function:
• Attached by a stem-like petiole to the plant
• Simple leaves have one blade, while compound leaves have several leaflets
• Covered with a single layer of cells called epidermis (upper & lower)
• A waxy cuticle prevents water loss • Openings called stomata on the underside
of leaves for gas exchange (CO2 & O2) • Two guard cells on either side of the
stomata open & close the openings
• Two guard cells on either side of the stomata open & close the openings
• When guard cells LOSE water, the stoma CLOSE, while the stoma OPEN when guard cells gain water & swell
• Stomata are CLOSED during the HOTTEST parts of the day to prevent water loss from leaves
• Below the epidermis are 2 types of chlorophyll containing MESOPHYLL cells ---palisade & spongy
• PALISADE mesophyll cells are closely packed columnar cells (most photosynthesis occurs here)
• SPONGY mesophyll cells are loosely packed with air spaces containing CO2 & O2
• VASCULAR BUNDLES (xylem & Phloem) in the spongy mesophyll appear as VEINS on the surface of the leaf
• VENATION is the arrangement of veins in a leaf
• Monocots leaves (such as Grasses or Corn Plants) have Parallel Venation
• Dicots leaves form a Branched network called Net Venation
• In carnivorous plants (Venus Fly Trap), the leaves trap insects for food so the plant can get enough nitrogen (grow in N2 poor soil)
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