B4e: Transport in plants

Question 1

Describe xylem(4)

Answer 1

plant tissue made up of dead cells

have a hollow cavity called the lumen

stacked on top of one another to form long, hollow tube-like vessels

particularly thickened, strengthened cellulose cell walls

Question 2

What are the functions of xylems(2)

Answer 2

transports water and dissolved minerals from roots to shoots and leaves in the transpiration stream

gives plant support

Question 3

Describe phloem(2)

Answer 3

plant tissue made of columns of living cells with perforated end-plates to allow substances to flow through

cells stacked on top of one another to form long, hollow, tube-like vessels

Question 4

What are the functions of phloems(2)

Answer 4

transports food substances made in leaf to all other parts of the plant through translocation

Question 5

Vascular bundles in root (3)

Answer 5

roots have to resist crushing as they push through the soil

vascular bundles and xylem located in the centre

gives root strength; helps it act like an anchor

Question 6

Vascular bundles in stem (3)

Answer 6

located around outer edge of stem

xylem forms ‘scaffolding’; phloem always around outside of stem

provides strength to resist bending of stem in breeze

Question 7

Vascular bundles in leaf (2)

Answer 7

vascular bundles (xylem + phloem) form a network of veins

supports softer leaf tissues

Question 8

What does xylem and phloem form in leaves, stems and roots

Answer 8

continuous systems

Question 9

What is transpiration

Answer 9

the evaporation and diffusion of water from inside leaves through stomata

Question 10

What does transpiration cause? (3)

Answer 10

creates shortage of water in leaf

more water is drawn up from the rest of the plant through the xylem vessels to replace it

means more water is drawn up from the roots, so there’s a constant transpiration stream of water through plant

Question 11

What is the transpiration stream

Answer 11

continuous flow of water up through the xylem of a plant, from the roots up to the leaves where it evaporates

Question 12

What is transpiration a consequence of(3)

Answer 12

the way in which leaves are adapted for efficient photosynthesis

• leaves have stomata in them so that gases can be exchanged easily
• because there’s more water inside plant than in air outside, water diffuses from leaves through stomata

Question 13

Factors increasing transpiration rate (4)

Answer 13

+light intensity = +stomata open (because of photosynthesis) = +diffusion; (until all stomata are open)

+temperature = +KE of water molecules = +rate of evaporation/diffusion

+air movement = +water molecules outside of the plant moved away= +concentration gradient = +rate of diffusion

-humidity = -water in air = +concentration gradient = +rate of diffusion

Question 14

Roots description and purpose in the transpiration stream (2)

Answer 14

tiny root hairs extend between soil particles

increases surface area of roots for absorption of water from soil (higher conc) into root hair cell (lower conc) via osmosis

Question 15

Benefits of transpiration (4)

Answer 15

provides plants with water for:

• photosynthesis
• cooling effect during evaporation
• entering cells via osmosis, making them turgid = helps support plant
• transporting dissolved minerals in water as it moves through the plant

Question 16

How is the structure of a leaf adapted to reduce excessive water loss(6)

Answer 16

thick waxy cuticle on upper and lower surfaces = -evaporation

-stomata = -diffusion

+stomata on underside where it is darker/cooler = -rate of diffusion

stomata close at night when no ps = -diffusion

-SA:V ratio = -rate of evaporation/diffusion

changes in guard cell turgidity (due to light intensity and availability of water) to regulate the holes of the stomata

Question 17

How do stomata open and close automatically? (3)

Answer 17

thick inner walls and thin outer walls

more light and water = guard cells take up water via osmosis, photosynthesis produce sugars = guard cells turgid = guard cells curve = stoma open

less light and water = guard cells lose water via osmosis, less photosynthesis produce less sugars = guard cells = flaccid = guard cells straighten = stoma close