PLANT TRANSPORT

Question 1

Areas in stem

Answer 1

Epidermis, Phloem + Xylem (Vascular bundle) , Cambium, Cortex.

Question 2

Dissecting a stem to demonstrate structure of xylem.

Answer 2

Cut stem into very thin sections (longitudinally= length ways + transverse= across the stem). Place on slide + add a drop of water and 2 drops of stain (toluidine blue O) and view under microscope.

Question 3

Structure of xylem.

Answer 3

Non-living tissue, Long, tube like structures, No end walls, No cytoplasm/ organelles, Cell walls thickened with lignin, Boarded pits (Non-lignified areas), Parenchyma (store food + tannin).

Question 4

Function of xylem.

Answer 4

To transport water and mineral ions.

Question 5

Structure of phloem.

Answer 5

Living tissues, Companion cells, Sieve tube elements.

Question 6

Structure of sieve tube elements.

Answer 6

Many cells joined end to end, Have sieve plates ( perforated walls between cells), Thin cytoplasm, Few organelles.

Question 7

Function of sieve tube elements.

Answer 7

To transport assimilates, e.g. sucrose.

Question 8

Structure of companion cells.

Answer 8

Linked to sieve tube elements by plasmodesmata, Contain nucleus and organelles, Lots of mitochondria.

Question 9

Function of companion cells.

Answer 9

To aid loading of sucrose into phloem.

Question 10

Movement of water across the root.

Answer 10

-Root absorbs mineral ions via active transport. Lowers water potential inside cell. Water diffuses in via osmosis and moves through cortex via apoplast, symplast and vacuolar pathways. Reaches endodermis which contains casparian strip (band of suberin-waterproof) which blocks the apoplast pathway and all water moves to cytoplasm of cells which gives the root more control over amount of water that enters xylem. Mineral ions pumped from cortex into xylem by at which lowers water potential of xylem water then moves in and up to rest of plant.

Question 11

Define transpiration.

Answer 11

Loss of water vapour from surface of plants via stomata into atmosphere down water potential gradient.

Question 12

Factors affecting rate of transpiration.

Answer 12

Temperature, Humidity, SA:V, Wind.

Question 13

Transpiration practical.

Answer 13

Potometer, Cut shoot under water at a slant,

Question 14

Xerophytes.

Answer 14

Adapted for dry habitats, Thick waxy cuticle, Less leaves, Sunken stomata (Less transpiration), Less stomata, Hairy/ curly leaves (traps moist air) , Succulents store water in parenchyma tissue.

Question 15

Hydrophytes.

Answer 15

Adapted to live in water, Lots of stomata, Large SA of roots and stems underwater (maximise photosynthesis), Open stomata, Air sacs to float, Wide flat leaves (light), Thin/ no waxy cuticle.

Question 16

Define translocation.

Answer 16

The movement of assimilates from source to sink.

Question 17

Translocation at source e.g. leaf.

Answer 17

Glucose is converted into sucrose and move into phloem via symplast/ apoplast pathway. Conc of hydrogen ions is low in companion cells, so atp is used to actively transport hydrogen ions into surrounding tissue (already in high conc). Hydrogen ions can then diffuse back into c cell through co-transporter protein along with sucrose. Sucrose then diffuses through plasmodesmata into sieve tube elements.

Question 18

Translocation at the sink.

Answer 18

Sucrose diffuses from c cell into surrounding tissue to be used. This is a passive process as the solutes are in a higher conc in the phloem than the surrounding tissue at the sink. Sucrose is then used up or converted by glucose, maintaining conc gradient and ensuring sucrose is moving out of phloem.

Question 19

Translocation- Mass flow.

Answer 19

When sucrose moves into phloem at the source, water potential of the sieve tube is decreased, so water enters phloem by osmosis from xylem. This increases hydrostatic pressure in the phloem. When sucrose moves out of the phloem at the sink, water also leaves via osmosis, decreasing hydrostatic pressure in phloem.