Plant transport

Question 1

Why can simple, unicellular organisms rely on diffusion for movement of substances in and out of the cell

Answer 1

Very large SA:V ratio - distance between surface to the center of organism is very small
Diffusion, osmosis and active transport occur at a sufficient rate

Question 2

Why do multicellular organisms need transport systems

Answer 2

Relatively small SA:V ratio - distance between surface to the center of organism is relatively long
Diffusion, osmosis and active transport cannot occur at a sufficient rate
Larger organisms usually have exchange surfaces and transport systems (e.g. blood and circulatory system)

Question 3

Function and Structure of phloem

Answer 3

Transports products of photosynthesis (mainly sucrose and amino acids) to other parts of the plant
Living cells arranged end2end
Have cytoplasm and cellulose walls
End of each cell has wall of cellulose with holes (sieve plates)
Two way flow

Question 4

Function and Structure of xylem

Answer 4

Transports water and minerals across the plant
Dead cells arranged end2end
No cytoplasm, cellulose and lignin walls
Lignin very strong, impermeable to water

Question 5

How root hair cells absorb water

Answer 5

Root hair cells have a long protrusion
This increases the SA:V ratio, increases rate of osmosis and active transport
Water enters the root hair cell by osmosis
Water moves out of the root hair cell to the root cortex
Water continues this way, setting up a water potential gradient across the root cortex and finally into the xylem

Question 6

Transpiration

Answer 6

The loss of water through evaporation through the stomata

Question 7

Factors affecting transpiration

Answer 7

Wind speed(increase): Faster air movements remove water vapour, keeps concentration gradient high
Humidity(decrease): Humid air has more water vapour, less able to accept more water molecules, concentration gradient reduced
Light intensity(increase): Light causes stoma to open - Wider stoma and more stomata open, greater diffusion
Temperature(increase): Increases rate of evaporation from mesophyll cells due to increased kinetic energy, concentration gradient increased

Question 8

Potometer practical:

Answer 8

Set up potometer
Cut shoot underwater to prevent air entering xylem and place in tube
Ensure airtight seal and dry leaves
Introduce air bubble using the syringe
Leave for set duration
Measure distance bubble moves w ruler
Repeat at least 5 times
Greater distance = greater transpiration