[bio] 06 - Plant Transport Crisologo

Transport and Circulation

We’ll be discussing 1. Cellular Transport 2. Plant Tissues and Transport in Plants 3. Trends and Various Strategies Used by Animals to Transport Materials 4. Transport in Man 5. Disorders of the Circulatory System

Membranes and cellular transport

Active vs Passive Transport

Transport of large molecules

Summary of Transport Processes Diffusion

Direction

Osmosis

Facilitated Diffusion

Pumps

High to Low High to Low High to Low Low to High

Endocytosis /exocytosis N/A

Transport Mechanism

Pores

Pores

Channels

Pumps

Membrane

Energy Required?

No

No

No

Yes

Yes

Type of particle

Small, nonpolar

Water

Smallmedium

Ions

Small-large

Examples of particles

CO2, O2

H2O

Glucose, fructose, Na+, Ca+2

Na+, K+, H+

Food, waste

Transport within the eukaryotic cell

Endomembrane system • Endoplasmic reticulum – manufacturing and transport facility – proteins produced in rough ER are packaged in vesicles

• Golgi apparatus – modification and storage facility – receiving end and shipping end

• Vacuole – large membrane bound sacs – usually stores undigested nutrients

Cyclosis/cytoplasmic streaming

TRANSPORT IN PLANTS

VASCULAR TISSUES: XYLEM AND PHLOEM
Xylem





Tracheids* Vessel elements* Parenchyma cells Fiber


Phloem





Sieve-tube members Companion cells Sclerenchyma fibers Parenchyma cells


Both

are continuous throughout the plant body

TRANSPORT OCCURS ON THREE LEVELS 1.

2.

3.

Uptake and release of water and solutes by individual cells Short-distance transport of substances by tissues and organs Long-distance transport of minerals in water and sap within xylem and phloem by the whole plant body

A VARIETY OF PHYSICAL PROCESSES ARE INVOLVED IN THE DIFFERENT TYPES OF TRANSPORT

4 Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon for photosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.

CO2

O2

5 Sugars are produced by photosynthesis in the leaves.

Light H2O

Sugar

3 Transpiration, the loss of water

from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward.

6

Sugars are transported as phloem sap to roots and other parts of the plant.

Water and minerals are transported upward from roots to shoots as xylem sap. 2

1 Roots absorb water and dissolved minerals from soil.

O2 H2O Minerals

CO2

7 Roots exchange gases with the air spaces of soil, taking in O2 and discharging CO2. In cellular respiration, O2 supports the breakdown of sugars.

TRANSPORT OF IONS AT THE CELLULAR LEVEL DEPENDS ON SELECTIVELY PERMEABLE MEMBRANES

Controls the movement of solutes into and out of the cell
With specific transport proteins
Enable plant cells to maintain an internal environment different from their surroundings


SHORT-DISTANCE H2O TRANSPORT IN THE ROOT

WATER AND MINERALS ASCEND FROM ROOTS TO SHOOTS THROUGH THE XYLEM ROOT PRESSURE TRANSPIRATION–COHESION– TENSION THEORY

Tension – negative pressure

STOMATA HELP

Cuticle Upper epidermal tissue

REGULATE THE RATE OF TRANSPIRATION

Leaves – broad surface areas Increase photosynthesis
Increase water loss through stomata (transpiration)


Turgid

Lower epidermal Trichomes Stomata tissue (“hairs”)

Flaccid

100 µm

Flaccid

Turgid

ORGANIC NUTRIENTS

ARE

Vessel (xylem)

Sieve tube (phloem)

Source cell (leaf)

1

TRANSLOCATED THROUGH THE PHLOEM (PRESSURE – FLOW MODEL)

H2O

Sucrose

1

H2O

Translocation – transport of organic molecules in the plant
Phloem sap


2

Pressure flow

Transpiration stream

Mostly sucrose
Sugar source  sugar sink
Source is a producer of sugar
Sink is a consumer/storage facility for sugar


2

4

3 H2O

3

4 Sink cell (storage root)

Sucrose

Loading of sugar (green dots) into the sieve tube at the source reduces water potential inside the sieve-tube members. This causes the tube to take up water by osmosis.

This uptake of water generates a positive pressure that forces the sap to flow along the tube. The pressure is relieved by the unloading of sugar and the consequent loss of water from the tube at the sink. In the case of leaf-to-root translocation, xylem recycles water from sink to source.

PRESSURE – FLOW MODEL 1.

2.

3.

high solute concentration at source increase in hydrostatic pressure sugars in sink draw water out of phloem