IB Biology - Plants: gas exchange and transport

Transpiration

the passive movement of water through the plant and evaporation from leaves

Epidermal tissue:

forms outer boundaries

Mesophyll tisue:

internal structure

Vascular tissue:

transports the subtances between the leaf and plant

spongy mesophyll

Loose tissue beneath the palisade layer of a leaf; has many air spaces between its cells

palisades mesophyll

tightly packed cells in the leaf containing chloroplasts

Draw a cross-section of a leaf:

Functions of trasnpiration stream:

• supplies water for photosynthesis

• carries Mineral ions dissolves

• water for tugor

• evaporation which cools the plants

Xylem

vascular tissue that carries water upward from the roots to every part of a plant through capillary action (cohesion and adhesion)

Xylem adaptations

• Lignin walls: can withstand very low internal pressures

• Broken down cell wall + now cell contents: continous flow of water

• Pits: pores that allow water to neter and move sideways between vessels

Phloem

the vascular tissue in plants that conducts sugars and other metabolic products downward from the leaves.

Phloem adaptations:

• sieve plates: allows for the continous movement of the organic compounds between cells + ↑ resistance so pressure gradient maintained

• Cellulose cell wall: strengthens the wall to wwithstand the hydrostatic pressures that move assimilates

• ↓ organelles in mature cells: maximises the space for the translocation of assimilates

• Thin cytoplasm: reducesfriction to facilitate the movement of assimilates

Companion cell structure:

• Nucleus and other organelles: Provides metabollic support to sieve tube elements

• Transport proteins in plasma membrane: moves assimilates into and out of the sieve tube elements

• Mant Mitochondria: provide ATP for the active transport of assimilates into or out of the companion cells

• Plasmodesmata: link with sieve tube elements to allow assimilates to move from the companion cells into the sieve tubes

Describe how trasnlocation takes place:

1. The source loads sucrose into the companion cell by active transport

2. The high conc. of solute lowers the water potential →water from xyelm flows into plhoem by osmosis

3. ↑ water so ↑ hydrostatic pressure ↑ pressure gradient

4. water + contents flow down the ploem to the sink where contents unload from companion cell to sink by difussion

dicotyledons (dicots)

two cotyledon, broad leaf, network of veins, vascular bundles in a ring, floral parts in multiples of 4 or 5

root hairs

tiny hair-like extensions that increase the surface area of the root allowing it to absorbs more water and nurtients

dicot root cross section

An X of xylem, and phloem is between the lines in the X.

dicot stem cross section

has a circular arrangement of vascular bundles with primary xylem pointing towards the center and primary phloem pointing out, has a central pith and an outer cortex

epidermis (root)

the outermost part of the root that protects the root

cortex (root)

Very extensive in the root

Serves as the main physical barrier for water

Forces water to travel around the cells, blocking out certain things, like a sieve

root hairs

tiny hair-like extensions that increase the surface area of the root allowing it to absorbs more water and nurtients

indirect active transport

Occurs when hydrogen ions are pumped out of the root hair, bind to negatively charged clay in the soil and then release K+ and Mg2+ as free chemicals to go into the root hair

root pressure

The upward push of water within the stele of vascular plants, caused by active pumping of minerals into the xylem by root cells

pith

ground tissue internal to the vascular tissue

cortex (dicot stem)

corklike parenchyma cells after hypodermis that store carbohydrates & other nutrients (oils, resin, etc.)

plant capillary action

Occurs in a plant through cohesion and adhesion in the xylem.

transpirational-pull cohesion tension

water moves from roots to leaves without energy

Cellulose in xylem tubes

Hydrophilic - water adheres to it during transpiration in xylem

Lignin

complex polymer that hardens cell walls of some vascular tissues in plants

pits

openings in the lateral walls of xylem cells allowing water and nutrients to leak into surrounding tissues.

sieve tube cells

Living cells without nuclei that conduct phloem in plants

Sieve tube plate

Pore in the end wall of a sieve-tube member through which phloem sap flows

companion cells

the active cells found next to sieve tube elements that supply the phloem vessels with all of their metabolic needs

hydrostatic pressure

Pressure exerted by a volume of fluid against a wall, membrane, or some other structure that encloses the fluid.

parenchyma cells

play a role in storage, secrection, and photosynthesis in cells

Sink (in a plant)

where oranic compounds are needed and stored for growth

• roots, young leaves

source (plant)

where organic solutes originate

• mature green leaves, green stems

• tap roots

• food stores in seeds

translocation in phloem

1. active and passive loading of carbon by sources

2. water follows by osmosis, increasing hydrostatic pressure

3. at sink, sugar is unloaded

Stomata

Small openings on the underside of a leaf through which oxygen and carbon dioxide can move

when low hydrostatic pressure: flaccid: close

when high hydrostatic pressure: turgid:open

guard cells

control the opening and closing of stomata

Cuticle

A waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial plants.

CAM pathway

a water-conserving, carbon-fixing process; CAM plants take in carbon at night and fix it into various organic compounds and release it during the day

Xerophytes

plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment.

Halophytes

plants that live in highly saline (salty) soil

Plasmodesmata

channels through cell walls that connect the cytoplasms of adjacent cells

Factors affecting rate of transpiration;

• air movement: ↑ wind, ↑ transpiration ↓ H2O in air so ↑ conc. gradient for diffusion

• Light: ↑ light ↑ transpiration ↑ photosynthesis → ↑ stomata opening

• temperature: ↑ temp↑ kinetic enrgy ↑ evaporation

• Humidity: ↑ humid ↑ water in surroundings↓ conc. gradient ↓ transpiration

How does transpiration occur(stream):

• water uptake from soil to roots hairs by osmosis

• water moves from root hairs to the xylem vessel

• adhesion with the xylem wall + coheison between water molecules create a continous column of water that moves up by capillary action

• the pulling force is caused by the evaporation of water → root pressure ≠ leaves pressure → causes tension pressure (Pv=Pv)