transport in plants exam qs

Question 1

Explain why large multicellular plants need a transport system. (3)

Answer 1

• long distance from external surface
  to cells (1)
• small surface area to volume ratio (1)
• diffusion not fast enough (1)
• named example of substance that is
  transported e.g. sucrose (1)

Question 2

Calculate the surface area to volume ratio of a bubble alga that has a diameter of 2.5 cm.
Assume the bubble alga is spherical. Show your working. (3)

Answer 2

2.4 (SA) : 1.0 (volume)

Question 3

Explain the benefit to plants of internal transport systems (2)

Answer 3

• surface area: volume ratio too small
• idea of diffusion from outer surface not sufficient
• (transport system) ensures molecules /nutrients / sugars / water, reach all tissues
• (allows) high metabolic rate ✓

Question 4

Sodium chloride in solution dissociates into Na+ and Cl−.
Explain how the Casparian strip prevents these ions from reaching the xylem of the plant by the apoplast pathway. (2)

Answer 4

two from
- strip is impervious to, water / solutions (1)
- forces water / solutions, to pass through, plasma / cell surface, membrane (1)
- phospholipid (bilayer), repels / AW, ions / charged particles (1)

Question 5

Xylem and phloem are two vascular tissues found in plants.
State one similarity and two differences between the structure of xylem and phloem. (3)

Answer 5

similarity:
- both made up of cells joined end to end
- xylem (vessels) and phloem sieve tube elements both lack, nuclei / contents
- both are, complex tissues / made up of more than one cell type
differences:
- xylem lignified /contains lignin
phloem not lignified /only contain cellulose
- xylem wide lumen
phloem lumen not wide / lumen small
- xylem no end walls / no sieve plates / continuous tube
phloem sieve plates
- xylem no companion cells
phloem companion cells
- xylem vessels
phloem no vessels
- xylem no sieve tube elements
phloem sieve tube elements
- xylem (bordered) pits
phloem no pits
- xylem no cytoplasm /no organelles
phloem has cytoplasm /has (named)
organelles

Question 6

Some plants, such as mosses, do not have xylem. Mosses are small plants that rarely grow more than a few cm in height.
Suggest why mosses do not need structures such as roots or xylem to survive. (1)

Answer 6

• large surface area to volume ratio
• the distance, water / mineral (ions),
  need(s) to travel is short

Question 7

State the function of the pits in xylem tissue (1)

Answer 7

lateral movement of water