Transport In Plants

Question 1

Why do plants need a transport systems

Answer 1

High metabolic rate
Have a small SA:V ratio
Large diffusion distance
Rate of diffusion too small
Multicellular

Question 2

Function of guard cells

Answer 2

They bend to open & close stomata + control gas exchange

Question 3

How are guard cells adapted

Answer 3

Many chloroplasts & mitochondria to provide ATP
Cells able to change shape
Transport proteins in CSM
Wall thicker on one side

Question 4

Action of guard cells

Answer 4

Mineral ions actively transported into the cell
Decreased water potential & increased w.p. gradient
Water enters the cell via osmosis -> cell = turgid & stomata opens

Question 5

Vascular system in leafs, stem & root

Answer 5

Question 6

Features of the xylem

Answer 6

• dead cells
• lignified walls
• empty lumen
• bordered pits

Question 7

Function of the xylem

Answer 7

Transport water & dissolved minerals
- up the plant
- from roots to leaves & other upper parts of plant

Question 8

What’s good about each of the xylem components

Answer 8

Question 9

Features of the phloem

Answer 9

• sieve tube elements
• peforations
• companion cells
• parenchyma cells

Question 10

Function of phloem

Answer 10

Transport assimilates
Such as amino acids & sucrose from source to sink (up & down)

Question 11

How is the sieve tube element adapted for its function

Answer 11

No nucleus & little cytoplasm
Allows for mass sap flow
As it is arranged end to end to form continuous sieve tubes

Question 12

What are sieve plates

Answer 12

Separate sieve tube elements and these also filter out organelles between sieve tube elements

Question 13

What do perforations in sieve plates do

Answer 13

These allow the mass flow of sap between sieve elements

Question 14

What do parenchyma cells do

Answer 14

They’re packing cells which fill spaces between sieve tubes

Question 15

What do plasmosdesmata do

Answer 15

These are gaps in the cell wall between companion cells, & sieve tube elements

Question 16

Differences between Xylem & phloem

Answer 16

Question 17

Similarities between xylem & phloem

Answer 17

Question 18

How are stems dissected for observation

Answer 18

Question 19

What is transpiration

Answer 19

The loss of water vapour from the aerial parts of a plant (especially from the stomata) as a consequence of gas exchange

Question 20

Why is transpiration important

Answer 20

• maintains cell turgidity
• coding of plant by water evaporating out of stomata
• supplies water for growth, cell elongation & photosynthesis
• the stream transports mineral ions up the plant

Question 21

Why is transpiration unavoidable

Answer 21

Stomata has to be open
To allow for gas exchange
Gas exchange required for photosynthesis & so water vapour leaves the lead

Question 22

Why is transpiration diffusion not osmosis

Answer 22

As it doesn’t occur over a partially permeable membrane

Question 23

Environmental factors to increase transpiration

Answer 23

Question 24

Measuring transpiration using a Potometer

Answer 24

Question 25

Safety measures using a Potometer

Answer 25

- use healthy shoot - cut stem at a slant underwater - dry leaves - use petroleum jelly to ensure seal between shoot & potometer is airtight (so no leaks in apparatus)

Question 26

Why do we use these safety measures in a Potometer

Answer 26

Question 27

Movement of water into plants -> how does H2O enters via roots

Answer 27

1. Root hair cells actively take up mineral ions 2. Reduces the water potential of the root hair cells 3. Water moves by osmosis, down w.p. gradient into root hair cells 4. Through aquaporins

Question 28

How is root pressure generated

Answer 28

-> active transport by endodermis of mineral ions into xylem & medulla -> lowers w.p. -> water enters medulla & xylem of roots by osmosis -> this increases hydrostatic pressure of roots

Question 29

How does water move up the stem

Answer 29

Root pressure = high pressure @ bottom of plant Evaporation / water loss @ top = low pressure @ top of plant -> pressure gradient created therefore tension in the xylem Cohesion between H2O molecules = they stick together, forming continuous therefore, water is then pulled up by mass flow down the pressure gradient

Question 30

What’s another way water can move up the stem

Answer 30

Capillary action - water molecules attracted to side of narrow xylem vessel by adhesion therefore, H2O is pulled up the side of a xylem vessel

Question 31

What are the 3 pathways from the root hair to the xylem

Answer 31

Vacuolar Symplastic Apoplast

Question 32

Vacuolar pathway

Answer 32

Passes through vacuoles & cytoplasm of cells by osmosis

Question 33

What is the symplastic pathway

Answer 33

Passes through the cytoplasm of cells using plasmosdesmata by osmosis

Question 34

What is the apoplastic pathway

Answer 34

Passes through gaps in the cell wall via mass flow: At endodermis, blocked by Casparian strip & water + dissolved minerals forced to enter symplastic pathway -> casparian strip is impermeable to wax / waterproof

Question 35

How is H2O loss from the top of the plant replaced

Answer 35

1, apoplastic/symplastic/vacuolar pathway 2, down water potential gradient, 3, by water from xylem

Question 36

Endodermal cells -> xylem (h2o movement)

Answer 36

Endodermal cells actively transport mineral ions from cortex into medulla & xylem therefore reducing their w.p. Water moves into medulla & xylem by osmosis down w.p. gradient

Question 37

H2O -> out of leaf

Answer 37

Xylem water - > via osmosis / apoplastic pathway - > spongy mesophyll Evaporates out of the cell walls into spaces in leaves Diffuses out of open stomata down water potential gradient H2O can be lost via stomata / the epidermis

Question 38

What is translocation

Answer 38

The movement of assimilates up & down the plant

Question 39

How are assimilates actively loaded into the phloem at the source

Answer 39

Question 40

Where does sap move

Answer 40

From source to sink

Question 41

Movement of sap at source versus at sink

Answer 41

Question 42

How can the roots act as a source & a sink

Answer 42

Converts starch into sugars, which are loaded into phloem Stores sugars into starch, which requires sugars to be unloaded from the phloem

Question 43

Why are sugars transported as sucrose

Answer 43

Because it’s metabolically inactive Soluble Doesn’t get used up by respiration during transport

Question 44

Mass flow attempts to explain how solutes more from source to sink. What’s some evidence for and against it

Answer 44

Question 45

Answer 45

Question 46

Answer 46

Question 47

Answer 47

Question 48

What is meant by the term transpiration stream

Answer 48

The movement of water from roots to leaves