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Plants-Form and Function (Plant organs (Roots (Taproot system- one main…
Plants-Form and Function
Plant organs
Roots
organ that anchors a vascular plant in the soil, absorbs minerals and water, and often stores carbohydrates
Taproot system- one main vertical root (taproot) that penetrates soil deeply and helps prevent plant from toppling over
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Evolutionary adaptations of roots-
- Pneumatophores- (air roots)- project above water's surface at low tide, enabling root system to obtain oxygen lacking in mud
- Storage roots- root used to store food and water
- Strangling aerial roots- seeds germinate in tall trees crevices; roots grow down and wrap around host and shoots grow up and shade out host tree
Adventitious- plant organ that grows in an unusual location EX: fibrous root system that many small roots emerging from the stem
Root hairs- thing finger-like extensions of root epidermal cells- present in large number at the tip of most roots to increase surface area for absorption--> many terrestrial plants for mycorrhizal relationships with fungi to increase the plant's ability to absorb minerals
Stems
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Apical bud- bud a the tip of a plant system, also called a terminal bud-> composed of developing leaves and compact series of nodes + internodes
Grows up or down
Axillary buds- structure that has the potential to form a lateral shoot, or branch. The bud appears in the angle formed between a leaf and a stem
Grows laterally
Evolutionary adaptations of stems-
- Rhizomes- horizontal shoot that grows just below the surface. Vertical shoots emerge from axillary buds
- Stolons- horizontal shoots that grow along the surface.These "runners" allow plant to reproduce asexually as plantlets form at nodes along each runner
- Tubers- enlarged ends of rhizomes or stolons specialized for storing food
Leaves
main photosynthetic organ that is responsible for photosynthesis, for gas exchange, for heat dissipation, and for defense against pathogen and herbivores
consists of a flattened blade and a stalk called the petiole that joins the leaf to the stem as a node
also consists of veins (vascular tissue) --> that transport the supplies for photosynthesis to the leaf and the products of photosynthesis away, to the rest of the plant
tremendous amount of variation in leaf morphology--> also some leaves with adaptations for specific functions like support, protection, storage and reproduction
Evolutionary adaptations of leaves
- Tendrils- use to cling to a support. first it lassoes a support then forms a coil that brings the plant closer to the support.
- Spines- photosynthesis carreied out by fleshy green stem, not leaves
- Storage leaves- leaves are modified to store food
- Reproductive leaves- some succulent leaves produce adventitious plantlets that fall off the lead and take root in the soil
Different tissues:
- Mesophyll- contains cells specialized for photosynthesis
- Stomata- allows gas exchange between environmental air and photosynthetic cells in leaf
- Guard cells- regulate opening and closing of stomata
- Vascualr tissue- consists of xylem and phloem that transports nurtrients and photosynthetic products
Tissue sytems:
Dermal tissue system- plants outer protective covering
- defense against pathogens and physical damage
- non woody plants have epidermis and cuticle
woody plants have periderm instead of epidermis in older regions of stems and roots
Vascular tissue system- facilitates transport of materials through plant
- provides mechanical support
- xylem- conducts water and dissolved minerals up from roots into shoots
phloem- transports sugars
- stele- vascular tissue of a root of stem
- vascular cylinder in root
vascualr bundles in stems and leaves
Ground tissue system- tissues that are neither dermal nor vascular
Pith- ground tissue that is internal to vascular tissue
Cortex: ground tissue that is external to the vascular tissue
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