3.1.3 - Transport In Plants (set A - The Need For Transport Systems In Multicellular Plants)

Question 1

Explain why plants require transport systems?

Answer 1

• ensures that all the cells of a plant receive a sufficient amount of nutrients (eg water,minerals and sugars)
• important as plants are multicellular and have relatively small SA:V ratios with high metabolic rates

Question 2

Explain what vascular plants are - why is a system needed?

Answer 2

Plants with a specialised transport systems

• needed due to relatively small SA:V ratio and high metabolic rates - need to provide sufficient amount of nutrients

Question 3

Explain why large organisms require specialised mass transport systems - give three reasons?

Answer 3

– Increasing transport distances (due to size) - decreases diffusion rates
– Surface area: volume ratio - less diffusion across surface
– Increasing levels of activity (metabolic rate) - more substances needed and waste produced

Question 4

Explain why plants need a specialised mass transport system - mention transport distance?

Answer 4

• all cell requires substances,nutrients and mineral ions to function
• molecules need to be transported all the way from the exchange site to other parts of the plant (root and leaves)
• simple diffusion is non-viable (big distance)

Question 5

Explain why plants need a specialised mass transport system - mention SA:V?

Answer 5

• As the size of a plant increases, its surface area to volume ratio decreases - this is because volume increases much more rapidly than surface area
• has relatively less SA available for substances to diffuse through - rate of diffusion will not be fast enough to meet cells demands (supply of substances and removal of waste)

Question 6

Explain why plants need a specialised mass transport system - mention SA:V?

Answer 6

• As the size of a plant increases, its surface area to volume ratio decreases - this is because volume increases much more rapidly than surface area
• has relatively less SA available for substances to diffuse through - rate of diffusion will not be fast enough to meet cells demands (supply of substances and removal of waste)

Question 7

Explain why plants need a specialised mass transport system - mention metabolic rate?

Answer 7

Larger organisms are more physically active and contain more cells - have a higher level of metabolic activity have a greater demand for oxygen and nutrients as well as production of waste products

• metabolic demand is less than animals

Question 8

Explain how glucose is transported and why?

Answer 8

glucose is combined with fructose forming sucrose (more efficient transport medium)

• if it was transported as glucose it would be taken in by surrounding cells

Question 9

What are cotyledons - what is their function?

Answer 9

organs that act as food stores for the developing embryo plants and for the first leaves when the seed germinates

• dicotyledonous plants (dicots) make seeds that contain 2

Question 10

Explain how plants are adapted to increase SA:V - give 3 ways?

Answer 10

• plants have a branching body shape
• leaves are flat and thin
• roots have root hairs

Question 11

Explain what dicotyledonous (dicot) plants are, give the name of the 2 main groups?

Answer 11

• plants that make seeds that contain 2 cotyledons (organs that act as food stores)
• herbaceous dicots (non-woody stem) - soft tissues and relatively short life cycle
• woody dicots (eg oak) - hard lignified tissues with long life cycle

Question 12

Explain the vascular system of a dicot plant?

Answer 12

A plant has a series of transport vessels running through the roots,stems and leaves - the system is known as the vascular system

• made up of xylem and phloem

Question 13

Explain how the vascular bundle is positioned in the roots of herbaceous plants - include xylem and phloem?

Answer 13

• in the roots the vascular bundle is found in the centre, the centre core is the xylem tissue which helps roots withstand the pulling strain during transpiration
• on the edge of the centre core is the phloem tissue

Question 14

Explain how the vascular bundle is positioned in the stems of herbaceous plants - include xylem and phloem?

Answer 14

• vascular bundles are located around the outside - xylem tissue is found on the inside (helps support the plant)
• phloem found on outside closest to the epidermis
• provides strength and support for the stem

Question 15

Explain how the vascular bundle is positioned in the leaves of herbaceous plants - include xylem and phloem?

Answer 15

• vascular bundles form midrib, with veins spreading from centre in parallel lines - xylem tissue is found on upper side (closest to upper epidermis)
• phloem tissue found on the lower side (closest to lower epidermis)

Question 16

Outline 3 functions of xylem tissue in plants?

Answer 16

• vascular tissue that transports dissolved minerals and water around plants
• structural support
• food storage

Question 17

Outline 4 cell types which make up the xylem?

Answer 17

• tracheids (long,narrow tapered cells with pits)
• vessel elements (thicken cell walls - no end plates
• xylem parenchyma (thicker walled and stores food)
• xylem fibres (provide mechanical strength)

Question 18

Outline and explain the function of lignified cell walls in xylem?

Answer 18

• adds strength to withstand hydrostatic pressure so vessels do not collapse
• impermeable to water, prevents water leaking

Question 19

Outline and explain the function of lack of end plates and non-lignified regions/pits in xylem?

Answer 19

• allows the mass flow of water and dissolved solutes as cohesive and adhesive forces are not impeded
• lateral movement of water, allows continual flow in case of air bubbles forming in the vessels

Question 20

Outline and explain the function of dead cells and small diameter of vessels in xylem?

Answer 20

• doesn’t impede the mass flow of water and dissolved solutes
• small diameter helps prevent water column from breaking and assist with capillary action

Question 21

Outline the structure of xylem?

Answer 21

• largely non-living tissue
• made up of several types of cells which are mostly dead - involved in providing mechanic strength and forming lignin spirals
• xylem vessels are main structures which are long, hollow structures made by columns of cells fusing together end to end
• spirals of lining running around lumen - helps reinforce xylem vessels preventing them from collapsing

Question 22

Outline the main function of phloem?

Answer 22

• transport organic compounds, particular sucrose from the source (leaf) to the sink (roots) - transport can occur up and down the plant

Question 23

Outline the components of the phloem?

Answer 23

• involves various cell types - including parenchyma (for storage) and strengthening fibres
• made mainly of sieve tube elements and companion cells
• contain living cells

Question 24

Outline the structure of phloem?

Answer 24

• sieve tubes made from many cells joined end to end - forming a long, hollow structure
• cells are not lignified - areas between the cells, the walls become perforated forming sieve plates with pores (allowing continuous movement)
• companion cells linked to sieve tube elements by plasmodesmata (channels through cell wall linking cytoplasm to adjacent cells)control metabolism of sieve tube elements

Question 25

Explain the function of mature cells in phloem having no nucleus,vacuoles or ribosomes - outline the importance of thin cytoplasm?

Answer 25

• maximises the space for the translocation of organic compounds
• reduces friction to facilitate movement of substances

Question 26

Outline the function of sieve plates with sieve pores - and the function of cellulose cell walls?

Answer 26

• allows the continous movement of substances
• strengthens the wall to withstand the hydrostatic pressure that moves the substances

Question 27

Explain why the nucleus and other organelles are present in phloem companion cells, why are their large numbers of mitochondria present?

Answer 27

• nucleus provides metabolic support to several tube elements - helps with loading and unloading of assimilates
• mitochondria - provide ATP for active transport of assimilates into or out of companion cells

Question 28

Explain the function of transport proteins in the plasma membrane of companion cells - and the presence of channels in the cell wall?

Answer 28

• move assimilates into and out of the sieve tube elements
• channels link to sieve tube elements which allows organic compounds to move from the companion cells into sieve tube elements

Question 29

Compare the difference in features between xylem and phloem - give 4 and explain the differences?

Answer 29

• cell wall material of xylem is lignin and cellulose - in phloem its only cellulose
• end walls are only present in phloem as sieve plates with sieve pores
• direction of flow for xylem is only one way (upwards) whereas for phloem its two ways
• xylem the cells are dead and hollow in phloem they are living (companion cells)