As2 Principles And Transport Flashcards Preview

Biology > As2 Principles And Transport > Flashcards

Flashcards in As2 Principles And Transport Deck (13):

What is gas exchange

The process by which oxygen reaches cells and carbon dioxide is removed from them


What is respiration

Release of energy from food to synthesis ATP within all living cells


Where does the exchange of substances takes place

At moist permeable surfaces

Prevent water loss by evaporation - mammals possess an impermeable surface (skin with a cornified layer onto which an oily substance is secreted.

Flowering plants covered by waxy cuticle secreted by upper epidermis


What is surface area

The total number of cells that are in direct contact with the environment


Small organisms- large surface area to volume ratio

Large organisms - small surface area to volume ratio

External surface of a small organisms can be used for gas exchange surface because large surface area is able to supply sufficient oxygen to the small volume

Large organisms have small surface area to volume ratio, large volume creates a demand for oxygen which the small surface area is unable to supply

Large organisms need specialised permeable surfaces whereby the absorption or exchange area is increased to satisfy the needs of the organism


Absorption surfaces in plants - leaf mesophyll

Flattened structure - thinness ensures short diffusion distance
Tightly packed upper palisade mesophyll layer and a loosely packed lower spongy mesophyll layer

Function - wide expanse of palisade tissue is efficient at trapping light

Loose arrangement of spongy layer provides air space system through leaf and creates huge surface area for gas exchange


Absorption surface - root hairs

Tubular extensions of the epidermal cells of the young root

Increases the surface area greatly for he uptake of oxygen water and ions


What does xylem and phloem tissue transport

Xylem - water and inorganic ions
Phloem - sucrose/amino acids and organic ions


Why are xylem vessels lignified

Prevent xylem vessels collapsing under negative pressures (tension) created as a result of transpiration

Offers support to plant


What does phloem tissue consist of

Sieve tube elements - living, tubular cells that are connected end to end
End cell walls have perforations In them to make them sieve plates
Cytoplasm present but in small amounts in layer next to cell wall
Lacks nucleus and most organelles - more space for solutes to move
Cell walls made of cellulose so solutes can move laterally and vertically

Companion cell- companion cell has organelles.
Controls the movements of solutes and provides ATP for active transport I'm sieve tube element
Strands of cytoplasm called plasmodesmata connect sieve tube element and companion cells


Apoplast pathway

Water moves along the cellulose fibrils of the cell walls

Interconnected cellulose cell walls of adjacent cells which are in contact with one another therefore forming a continuous system

Water flows through spaces between cellulose myofibrils

Most water follows Apoplast as it is fastest.

Once water reaches endodermis, it's flow is barred by impermeable thickening of casparian strip. Strip contains waterproof material Suberin.
Diverts water from Apoplast to the symplast until it reaches the xylem

Why is this necessary? Barrier means ions that have been taken up by water have to go through the endodermal cells, they are pumped through by active transport. High ion concentration built up in cell endodermis provides water potential gradient, for root hairs to centre of root which allows water to reach the centre of the root by osmosis


The symplast pathway

Consists of cytoplasm, which is continuous from cell to cell via plasmodesmata

Water has to cross partially permeable membrane by osmosis


Movement of water through a plant tissues

Water moves into root hair cells by osmosis - higher water potential in soil and lower water potential in root hair cell
- water moves across root cortex along a gradient of water potential
- most water moves by Apoplast pathway as it is faster
- water may also move through cytoplasm by plasmodesmata
- water via Apoplast pathway may not pass through endodermis cells as it is prevented by doing so by casparian strip