transport in plants

Question 1

why do plants require specialised transport systems

Answer 1

~multicellular plants are large and have a low sa:vol so cant rely on diffusion
~many parts cannot carry out photosynthesis
~mineral ions need to be transported from roots to the rest of the plant

Question 2

relate structure of xylem to its function

Answer 2

~long, continous colums made of dead tissue, allowing transportation of water
~contain pits, allowing water to move sideways between vessels
~thickened with a tought substance - providing structural support
~lignin makes walls impermeable

Question 3

relate the structure of phloem to its function

Answer 3

~sieve tube elements transport sugars around the plant
~companion cells designed for active transport of sugars into tubes
~plasmodesmata allow flow of substances between cytoplasm of different cells

Question 4

describe the structure and function of the vascular system in the roots

Answer 4

~consists of xylem and phloem, xylem arranged in an X shape to provide resistance against force. surrounded by endodermis, a water supply

Question 5

describe the structure and function of the vascular bundle in the stem

Answer 5

~consists of xylem and phloem. xylem on the inside of the bundle to provide support and flexibility, phloem on the outside. layer of meristem cells that produce new xylem and phloem tissue when required

Question 6

describe the function and structure of the vascular system in the leaves

Answer 6

~consists of xylem and phloem, forms the midrib and veins. involved in transport and support

Question 7

transpiration

Answer 7

~water vapour diffuses out of the leaf stomata into the external air
~constant removal of water vapour causes water potential inside cell to be low
~causes water to move between adjacent cells
~so when transpiration is occurring water is constantly being pulled out of the xylem vessels - effect known as tension

Question 8

name the factors that affect the rate of transpiration

Answer 8

~increased light increases transpiration
~increased temperature increases transpiration
~increased humidity decreases transpiration
~increased air movement increases transpiration
~waxy cuticle prevents transpiration

Question 9

how can we measure transpiration rate

Answer 9

~potometer, plant cutting is placed in a water filled tube that contains an air bubble. rate of transpiration is calculated by measuring the movement of the air bubble over time

Question 10

define water potential as a mechanism of movement in plants

Answer 10

~water potential= the tendency of water to move by osmosis, from high water potential to low. pure distilled water has the highest water potential of 0
~this is the basis by which water moves to the areas it is needed within plants

Question 11

define what is meant by the apoplastic pathway

Answer 11

~water moves within the cell walls and intracellular spaces by mass flow
~pathway can be used till it reaches casparian strip
~water moves due to cohesion
~is faster as less friction

Question 12

define what is meant by symplastic pathway

Answer 12

~water moves through the cytoplasm via the plasmodesmata
~to begin water must be actively transported into cells
~method of osmosis through the root hair cells
~less efficient as obstructed by cells/ organelles

Question 13

explain the cohesion tension theory

Answer 13

~water molecules form hydrogen bonds with each other, causing them to stick together(cohesion)
~the surface tension of the water also creates this sticking effect, therefore as water is lost through transpiration, more can be drawn up the stem from the roots

Question 14

explain adhesion

Answer 14

water molecules form h bonds with molecules in the xylem

Question 15

evidence of transpiration and cohesion tension theory

Answer 15

~if plant stem is cut air is sucked into xylem- xylem vessels are under tension
~if measure diameter of tree trunk it reduces when transpiration is at max

Question 16

adaptations of xerophytes that allow them to live in dry conditions

Answer 16

~small/rolled leaves
~spines instead of leaves
~thick waxy cuticle
~densely packed mesophyll
~stomata often closed / only open at night
~hairs to trap moist air

Question 17

adaptations of hydrophytes that allow them to live in wet conditions

Answer 17

~ thin or absent waxy cuticle
~stomata often open
~wide, flat leaves
~air spaces for buoyancy

Question 18

summarise the mechanism of translocation

Answer 18

~sucrose produced in leaves loaded into sieve tubes via active transport
~lowers water potential, causing water to move in from xylem
~assimilates move along the sieve tube towards areas of lower hydrostatic pressure ( sink ). sucrose diffuses into surrounding cells where it is needed