Transport in Plants

Question 1

What is the vascular bundle in roots?

Answer 1

• vascular bundle in centre
• xylem in an ‘X’ shape in the center
• phloem surrounding xylem

Question 2

What is the vascular bundle in stems?

Answer 2

• vascular bundles around the outside of stem
• xylem towards the inner part
• phloem on the outer part

Question 3

What is the vascular bundle in leaves?

Answer 3

• vascular bundles form midrib and veins
• xylem is found on the upper side of bundles
• phloem is found on the lower side of bundles

Question 4

What are the structural features of xylem vessels?

Answer 4

made of elongated dead cells that are thickened with lignin, joined end-to-end to form tubes

Question 5

What are the functional features of xylem vessels?

Answer 5

the transportation of water and soluble minerals up the plant, to give structural support

Question 6

What are the structural features of phloem sieve tubes?

Answer 6

made of elongated living cells called sieve tube elements, join to form tubes, companion cells

Question 7

What are the functional features of phloem vessels?

Answer 7

the transportation of organic compounds made by photosynthesis in the leaves to other parts of the plant

Question 8

What is transpiration?

Answer 8

the loss of water vapour from a plant to its environment by diffusion down a water potential gradient, takes place mostly through stomata in the leaves

Question 9

What are the factors that affect the rate of transpiration?

Answer 9

humidity, wind and temperature change, light intensity, dry conditions

Question 10

How does transpiration relate to gas exchange?

Answer 10

CO2 for photosynthesis also diffuses through stomata

Question 11

How can rate of transpiration be measured?

Answer 11

with a potometer

Question 12

What are the adaptations of xerophytes?

Answer 12

• hinge cells shrink allowing leaves to roll
• thick, waterproof cuticle made of cutin
• no stomata on lower epidermis
• hairs on leaf
• spines or thorns
• sunken stomata
• trichomes
• swollen, succulent stems

Question 13

How does water move from soil into the roots?

Answer 13

behind root cap, some epidermis cells are drawn out into long hairs which reach between soil particles to absorb water, which moves by osmosis down a water potential gradient into cells

Question 14

What is the symplast pathway?

Answer 14

the movement of water across the cortex of the root by moving into the cytoplasm or vacuole of a cell by osmosis and into adjacent cells through plasmodesmata

Question 15

What is the apoplast pathway?

Answer 15

the movement of water across the cortex of the root by soaking from cell to cell through the cellulose fibres of the cell wall

Question 16

What is the casparian strip?

Answer 16

a thick, waxy band of suberin in the cell walls of endodermal cells, which are impenetrable to water and so close the apoplastic pathway

Question 17

How does water move through the xylem?

Answer 17

the hydrostatic pressure at the top of the xylem becomes lower than at the bottom of the xylem, so water moves upwards by mass flow

Question 18

What is translocation?

Answer 18

the transport of assimilates (soluble organic substances) within a plant

Question 19

What is active loading?

Answer 19

the loading of a high concentration of sucrose into sieve elements from a source, creating a pressure difference for mass flow

Question 20

What is a hydrostatic pressure gradient?

Answer 20

hydrostatic pressure is the pressure exerted by a liquid, it is the same a water pressure, creating a gradient

Question 21

What are sinks and sources?

Answer 21

a source is a place where sucrose is loaded into sieve elements, like leaves, and a sink is a place where sucrose is unloaded, like roots

Question 22

What is parenchyma?

Answer 22

• thin-walled, packing tissue, air spaces
• cortex in roots, pith and cortex in stems, mesophyll with chloroplast in leaves
• metabolically active, gas exchange, water transported through cells

Question 23

What is collenchyma?

Answer 23

• modified parenchyma, extra cellulose at corners of cells for strength
• midrib in leaves

Question 24

What is the endodermis?

Answer 24

• one cell thick

- surrounds vascular tissue in stems and roots

Question 25

What is the mesophyll?

Answer 25

• specialised parenchyma in leaves, contain chlorophyll
• palisade is column shaped, near upper surface of leaf for more sunlight, contain more chlorophyll
• spongy is spongy, air spaces between cells

Question 26

What is the pericycle?

Answer 26

• a layer of cells inside the endodermis and next to the vascular tissue
• one cell thick in roots, new roots grow from it, sclerenchyma in stems

Question 27

What is vascular tissue?

Answer 27

• xylem and phloem

- centre of roots, vascular bundles in stems with sclerenchyma fibre caps

Question 28

What are the features of xylem vessel elements?

Answer 28

lignin in walls, empty lumen inside, non-lignified cell wall areas where there was once plasmodesmata called pits, end walls break down

Question 29

What are the features of phloem sieve tube elements?

Answer 29

little cytoplasm, no nucleus, no ribosomes, sieve plates

Question 30

What are the features of companion cells?

Answer 30

at least one next to each sieve tube element, large number of mitochondria and ribosomes, numerous plasmodesmata between companion cell and sieve tube element

Question 31

How does water move from xylem to leaves?

Answer 31

water is drawn into the leaf through pits in xylem vessel walls, it moves through the leaf through the apoplastic or symplastic pathway

Question 32

What is the epidermis?

Answer 32

• continuous layer of cells, one cell thick, outside of plant
• covered with waxy cuticle in stems and leaves, has stomata in leaves, root hair extensions in roots
• protection from drying out, gas exchange, more surface area

Question 33

What is cohesion?

Answer 33

the attraction of water molecules due to hydrogen bonding

Question 34

What is adhesion?

Answer 34

the attraction of water molecules to the cellulose and lignin in the walls of the xylem vessel

Question 35

What is root pressure?

Answer 35

the increase of pressure at the bottom of the xylem vessel by active pumping of solutes into the xylem, lowering water potential and causing water to be drawn into the xylem, increasing water pressure

Question 36

What is callose?

Answer 36

a carbohydrate which seals a sieve plate if a sieve tube is cut, to prevent contents from escaping

Question 37

How does water move from root hair to xylem?

Answer 37

by crossing the cortex of the root through the symplastic or apoplastic pathway down a water potential gradient into the xylem in the centre of the root

Question 38

What are passage cells?

Answer 38

endodermal cells which keep their symplastic pathways open as other cells become completely suberised