Plants do not have special respiratory or circulatory systems, and therefore must rely on the direct exchange of gases with their environment

The and of plants depend on gas exchange

with the air and the soil

The surface of the root is covered with

Root hairs increase the and also provide a moist surface area for

roots

root hairs

rhizomes

surface area gas exchange

As long as the soil is and contains , the oxygen will diffuse from the air into the air spaces of the soil and then into the moisture film surrounding the soil particles and root hairs The dissolved enters the by diffusion and is then passed on to other cells of the root

At the same time diffuses out of the root hairs and into the soil

aeratedwater

oxygen

root hairs

CO2

Gas Exchange in Leaves

The main job of leaves in plants is

During photosynthesis, plants absorb and give off

During respiration plants absorb and give off

During the day both process occur in the

CO2

CO2

O2

O2

leaves

photosynthesis

Because gas exchange is constantly occurring, the leaf has to protect itself against too much water loss, therefore it is covered with a waxy waterproof coating called the

The leaf also has tiny pores in it called that allow for the passage of gases in and out of the leaf

These stomata (singular ) are bordered by a pair of

The guard cells allow the pore to be opened to permit for or close to prevent

cuticle

stomata

stoma guard cells

gas exchange

water loss

Cross section of a leaf:

Gases are held in the and can be used for

either respiration ( ) or photosynthesis ( )

Every cell is close to air spaces so that the gases can readily into the cells and be used for either process

intercellular air spaces O2

CO2

diffuse

STOMATES & GUARD CELLSScattered about the lower epidermis are small openings called stomata.  It is through these holes that carbon dioxide enters the leaf, & oxygen & water vapor exit.

Each stoma is surrounded by a pair of guard cells.  When guard cells swell, the stomates open when the guard cells shrink, the stomates are closed.  Plants respond to changes in temperature & humidity by opening or closing their stomata (an example of maintaining ... homeostasis).

Gas Exchange in Stems

Every stem contains

The green flexible stems of grasses and other nonwoody stems photosynthesize and thus contain

Woody stems contain small white markings called

pores

stomata

lenticels

Lenticels are normally found where stoma were once situated when the stem was young and capable of photosynthesis

Diffuses into the stoma or lenticels and enter the here every cell in the stem is able to obtain gases they need for photosynthesis or respiration

intercellular air spaces

O2

Quest Review on Monday

Review Questions

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