AICE Bio Unit 7- Transport in Plants

Major plant organs:

• roots

• stems

• leaves

Types of tissue:

• Dermal tissue

• Ground tissue

• Vascular tissue

DERMAL tissue:

• epidermis of the plant.

• above ground (aerial) parts secrete a waxy cuticle.

• STOMATA: pores that allow for gas exchange

• Periderm: bark (specialized epidermis)

• ENDODERMIS: inner layer separating the tissue layer

GROUND tissue:

• structural support and storage

• 3 types

  • PARENCHYMA: thin & flexible walls. most common

  • Collenchyma: flexible support

  • Schlerenchyma: cell walls with lignin

* VASCULAR TISSUE:

• vessels that connect the organs

• 2 types:

  • XYLEM: carry water & minerals from the soil to the rest of the plant. (only up)

  • PHLOEM: Carry organic materials (food- sugar and proteins, “assimilates”) around the plant (up or down)

  • show up in vascular bundles

MONOCOT VS DICOTS:

ROOTS:

• epidermis, ground tissue (cortex), stele (vascular bundle), casparian strip, (waxy band along endodermis)

MONOCOT (left): ringed vasuclar in center

DICOT (right): cross-shaped vascular in center, no pith

STEMS

• epidermis, ground tissue, vascular bundles.

MONOCOT (top): only cortex, vascular bundles are scattered & look like faces

DICOT (bottom): cortex and pith, vascular bundles are in a ring, cortex outside bundles and pith in the middle

LEAVES:

• epidermis, cuticle, stomata, mesophyll (ground tissue directly below epidermis)

MONOCOT (top): n/a

DICOT (bottom): clear division between palisade mesophyll/parenchyma and the spongey parenchyma/mesophyll

XYLEM:

• water transport (and minerals in water)

• uptake starts with the root hair cells

• water moves through the root cortex into the xylem, up the xylem (high and low water potential), and to the leaf, where it is lost through stomata.

• high water potential in roots, low in leaves

• dead cells at maturity

• LIGNIN- strong, waterproof material

Apoplast pathway: water enters and moves through cell walls (intercellular spaces)

Symplast pathway: water enter the cytoplasm and moves via plasmodesmata

Casparian strip: made of suberin, found on the wall of the endodermis in roots, stops the apoplast pathway. After Casparian strip, water only travels by the symplast

PHLOEM:

• transports sugars mainly

• pores separate sieve tube elements and sieve platess

• cells are ALIVE

• lack organelles

• companion cells: perform vital functions that sieve members can’t, made of modified parenchyma cells, dense cytoplasm and small vacuoles

• translocation: movement in the phloem

• transport of manufactured substances via mass flow

• source-to-sink: source is anywhere sugar is produced (leaves) or stored, and sink is anywhere the sugar is needed

• water follows solutes, so a hydrostatic gradient forms when water leaves the phloem as well.

• sucrose: made by mesophyll cells in the leaves during photosynthesis

• sucrose leaves the phloem by diffusion, and then is broken down by invertase

most water goes through this pathway: root hairs, cortex, xylem, mesophyll, stomata.

STOMATA:

• pores at the surface of leaves, open and close to regulate water intake and loss.

• transpiration: the loss of water vapor from the leaves by evaporation

• transpiration pull: the idea the evaporation from the leave drives the concentration gradient (by pulling water up)

• water will escape via transporation inevitably.

Xerophytes:

• plants that posses physical modifcations to their structure to reduce water loss

• Not CAM or C4 plants!

adaptations:

• smaller leaves (smaller surface area)

• thicker cuticle

• waxy/powdery deposits on the leaves

• less stomata, stomata concentrated on the bottom of the leaves, and sunken stomata

• rolled leaves

• epidermal hairs to trap moisture around stomata