plant transport SLOP

Question 1

which property of water molecules causes cohesion

Answer 1

H bonds between water molecules -> many together can cause water molecules to stick together

Question 2

what must remain constant in the xylem to enable tension

Answer 2

Xylem must maintain uninterrupted column of water

Question 3

water is slightly attracted to the walls of the xylem vessels, making transpiration stream easier to maintain - what is the name of this effect and what happens?

Answer 3

adhesion- occurs when water forms H bonds with carbohydrates in cell wall of xylem

Question 4

function of companion cell

Answer 4

has many organelles that allow sieve tube to function as a normal living tissue

Question 5

function of sieve plate

Answer 5

allow phloem sap to pass through while filtering organelles

Question 6

the movement of water through the xylem is driven by hydrostatic pressure differences - explain what this means

Answer 6

water leaves the xylem and enters a leaf by osmosis = this lowers pressure in that section of xylem as vol of water decreases so water is drawn up from stem below

Question 7

how and why does decrease in light intensity affect transpiration

Answer 7

decreases transpiration -> stomata close in low light decreasing water loss

Question 8

what is the thin band of tissue on a root cell and what is its function?

Answer 8

casparian strip - waxy layer of suberin prevents water getting past

Question 9

list 2 reasons why stomata cannot remain permanently closed

Answer 9

• gas exchange for resp + PS
• evaporation of water from stomata drive the transpiration stream, allowing new water to be drawn up into the roots -> replacing water that used to be in metabolic pathways

Question 10

why are cacti adapted to have spines instead of leaves?

Answer 10

it decreases SA over which water can be lost by evaporation + decrease in stomata

Question 11

why are cacti adapted to have shallow, broad network of ground roots

Answer 11

allows quick water absorption after rain, since sand doesn’t retain water efficiently

Question 12

how might leaves folding and rolling inward in droughts reduce water loss

Answer 12

creates pocket of lost water vapour increasing WP around stomata = decreasing diffusion gradient so less water moves out by diffusion

Question 13

why do aquatic plants (hydrophytes) have spongy arenchyma tissue?

Answer 13

large air pockets -> allowing gases to diffuse quickly + makes plants buoyant

Question 14

why do aquatic plants (hydrophytes) have reduced root systems?

Answer 14

extensive roots aren’t needed cause water absorbs quickly, water + mineral ions absorbed directly from the water into the leaves

Question 15

sucrose is described as being ‘co-transported’, what does this mean?

Answer 15

energy not used to move sucrose itself but H ions out of cell. Ions then flow back into cell through transport proteins, bringing sucrose with them

Question 16

what are sources and sinks

Answer 16

sources - where there is net positive production
sinks - where substances are transported to be used/stored

Question 17

how might a scientists supply radioactive carbon dioxide to just one leaf?

Answer 17

• surround leaf in airtight container
• cover the stems that enter the container around with gel
• poke a hole in container and use to insert tube
• use to pump radioactive co2

Question 18

Explain why water in reservoir of potometer is released gradually into capillary using tap

Answer 18

bubble can be used to take measurements over distances longer than lengths of capillary tubing. by using the reservoir to release water and push bubble back to start of ruler, can reset and continue measuring transpiration

Question 19

why does fan increase the bubble’s rate of movement

Answer 19

usually air made humid by water evaporating from leaves BUT increase in windspeed increases water potential gradient between leaves and air = water evaporates

Question 20

why does removing the leaves not immediately stop the bubble from moving

Answer 20

-water continues to evaporate slowly from the upper surface where it was cut
-water molecules slightly attracted to one another by H bonds and to walls and xylem and so water can still be drawn up.

Question 21

what is the tissue found in between xylem and phloem? what is its function?

Answer 21

meristematic tissue - produce stem cells

Question 22

what is the purpose of parenchyma cells in xylem tissue?

Answer 22

to separate and support vessels

Question 23

how do bordered pits form and what is their purpose?

Answer 23

where lignin is not present = gaps left in cell wall; bordered pits in 2 adjacent vessels are aligned to allow water to leave one vessel and pass onto the next, as well as leave the xylem.

Question 24

describe adaptations of xylem vessels that relate to their structure to function?

Answer 24

• lignified walls: support + stretch
• no end walls: columns of water
• pits boarded allows sideways movement of water between vessels
  -tubes narrow: column doesn’t break easily

Question 25

why do sieve tube elements contain no nucleus and very little cytoplasm?

Answer 25

allows space for mass flow to occur

Question 26

movement of water in xylem and phloem

Answer 26

xylem - upwards
phloem - up and down

Question 27

how are companion cells adapted for active loading

Answer 27

many mitochondria to produce ATP

Question 28

why does the presence of starch in the endodermis suggest that an active process is involved?

Answer 28

starch acts as a store of sugars, which can be released and respired to release energy for active processes

Question 29

describe how water moves up the stem via transpiration pull

Answer 29

tension - loss of water by evaporation from surface of leaf must be replaces by water from xylem. Acts as a suction which pulls water up xylem.

Question 30

cacti are succulents. What does this mean?

Answer 30

they store water and flesh becomes swollen.

Question 31

why is it advantageous for some xerophytes to have low water potential inside their leaf cells?

Answer 31

decrease evaporation fo water from cell surface as water potential gradient between leaf surface and cells inside decrease.

Question 32

what is the difference between active loading and active transport.

Answer 32

active transport is movement of molecules from low to high conc. against conc. grad, pumped using ATP.

Active loading uses active transport to pump H+ ions out of companion cells = movement of sucroses by facilitated diffusion.