Chapter 7; Plants

Question 1

Difference between dicotyledons and monocotyledons

Answer 1

Dicots, have 2 cotyleodns, (2 seed leaves)
Monocytes, have 1 seed leaf

-dicots have,
Broad leaves,
Broad stalks
Branched veins

-monocytes have
-narrow leaves
-narrow stalks
-parralel veins

Question 2

Where is the xylem in a leaf and where is the phloem

Answer 2

At the top is the xylem
In the middle is the cambium
And below this is the phloem

Question 3

What is the midrib of a leaf

Answer 3

Where the vascular bundles are found

Question 4

4 differences in the structure of xyloem and of phloem

Answer 4

-xyloem has pits, phloem does not
-xylem has end walls removed so forms continuous tube, phloem has end walls called sieve plates
-xylem is impermeable, phloem is permeable
-xylem cell wall made of cellulose and lignin, phloem cell walls only made of cellulose

Question 5

3 differences in how the xylem and phloem work

Answer 5

-xylem transported water and mineral ions, phloem transports organic molecules
-xylem is one way only, phloem is both ways
-xylem is dead and phloem is living

Question 6

What does the xylem transport and for what functions does it support this for

Answer 6

Dissolved minerals and water,
For structural support
And for food storage

Question 7

Explain how xylems strutcure relates to its function

Answer 7

-has hard lignifed walls, to prevent inwards collpase under tension
Lining also allows adhesion with water molecules

-has a hollow lumen so no cell contents,
To provide less resistance to flow
To allow more space for a greater volume of water

-has end walls removed,so forms a continuous tube for water to flow

-has pits, for lateral movement of water and minerals

Question 8

What is the function of the phloem

Answer 8

Transports assimilates(, sucrose, amino acids )
From source (site of photosynthesis)
To sink (where assimilates are stored)
Via the process of translocation

Question 9

Explain how the strutcure of companion cells relates to its function

Answer 9

-Have many plasmodesma in cell wall,
So allow the loading and unloading of assimilates into companion cells
For rap;id entry of water

-have transport protiens in plasma membrane
Help to move assimilates into and out of sieve tube elements

Contain some organelles,
Eg nuclei, to provide metabolic support to help with loading and unloading of assimilates
Many mitochondria, atp for active transport and translocation
Contain ER
Contain ribosomes

Question 10

Explain how the function of sieve element relates to its function

Answer 10

Has membrane around side tube
-so osmosis can occur between cells

-has a cellulose cell wall,
Strengthens cell to withstand hydrostatic pressure that moves assimilates

-has little peripheral cytoplasm
So less resistance to facilite movement of assimilates

-sieve plates w pores
Contions movement of organic molecules

Few organelles
Provide maximum volume of assimilates to be transported
-less resistance to flow

Question 11

State the organelles that the companion cell has and the ones that the sieve plate has

Answer 11

Companion cell;

-nuclei
-mitochondria
-ribosomes
-er

Sieve tube

-mitochondria
-er
Cytoplasm

(So sieve tube has no nucleus, ribosomes, vacuoles, no tonoplast)

Question 12

What is a source and what is a sink and give examples of each

Answer 12

Source, site of photosynthesis
(Mesophyll cells, storage organs)

Sink, site where assimilates are stored and used for growth
(Meristems that are actively dividing, roots that are growing)

Question 13

Explain the first few steps of translocation until assimilates enter the sieve tube element

Answer 13

1)sugars are produced at the source via photosynthesis
2)mitochondria produce atp which releases energy and so acts as a power source to pump H plus ions through a proton pump (in the cell membrane) into companion cell wall
3)conc of H ions in the cell wall increases, so moves down conc gradient back into cytoplasm of companion cell via facilitated diffusion
Simultaneously, sucrose is transported together into the companion cell via active transport via the cotransporter pump
4)sucrose’s diffuses down a concentration gradient out of companion cells via the plasmodesmata, into sieve tube element

Question 14

Explain the steps of translocation once sucrose has entered the sieve tube

Answer 14

4)Sucrose enter sieve tube element, which lowers water potential, so water enters via osmosis down water potential gradient so increases hydrostatic pressure at sieve tube near the source
5)low hydrostic pressure towards the sink bc
(Sucrose is being actively loaded into the sink so this therfore increases water potential at the sink so water moves out of the sieve tube into the sink)
6)mass flow of phloem sap occurs from high hdyorstic pressure at the source to lower hydrtstic pressure at the sink.
7)sucrose is either actively or then through diffusion unloaded from sieve tubes into the sink,
8)due to the mass flow push, water at the sieve tubes near the sink has higher hydrostatic pressure so this causes water to move back down the xylem down a hydrtastic pressure gradient

Question 15

Through which process does h plus ion move into companion cell anc by which process does sucrose move into companion cells

Answer 15

Facilitated diffusion
Active transport

Question 16

What is the role of the proton pump

Answer 16

Uses atp produced by mitochondria to move h plus ions in the companion cell through the proton pump (in the cell membrane) into companion cell cell wall

Question 17

By which process is sucrose loaded into the sink

Answer 17

Actively or through diffusion

Question 18

What causes the mass flow of sucrose

Answer 18

High hdyrttsic pressure near siev tube near the source
(bc when sucrose enters here, water potential is decreases so water therefore moves in via osmosis down a water potetnatil gradient)

And low hydrostatic pressure h near sieve tube near the sink
(Bc when assimilates are loaded into the sink, water potential at the sieve tube here increases but this causes the water to move into surrounding cells, therfore creating low hdyrtic pressure here)

Question 19

At the sieve tube near the sink, what causes water to move back into the xylem

Answer 19

High hdyortsic pressure here,
Which is as a result of the mass flow push

Question 20

Explain the mevemtn of water form the soil into the cortex

Answer 20

-moves into root hair cells via osmosis, bc soil has higher water potential than root hairs cytoplasm,via a partially permeable membrane
-then can either move via appolast pathway, so through cellulose cell walls, or between cellulose fibres
-or can move via symplast pathway, so from cell membrane to cytoplasm, or through tomoplast into vacuole, or through plasmodesmata

Question 21

What is the appolapst pathway

Answer 21

Movement of water from cell wall to cell wall directly,
-or between intercellular spaces to get from cell wall to cell wall

(In the cortex this involves going from cellulose cell walls, or via celuluse fibres)

Question 22

What is the symplast pathway

Answer 22

Movement of water either,
Via cell membrane into cytoplasm
Via Tonoplast into vacuole
Via plasmodesmata to get form cell wall to cell wall

Question 23

By which process does water move in the asppoplast pathway and which process does it move in the symplast pathway
And which pathway is faster

Answer 23

-appoplast, it’s diffusion bc no partially permeable membrane,
-symplast, its via osmosis through partially permeable membrane

-movement in appolplast is faster than in symplast

Question 24

Explain the movement of water into the endodermis to the xylem

Answer 24

When reaches the endodermis, appoplast pathway is blocked by the casparian strip(suberized cell wall which is impermeable to water)
So water is forced to go through the symplast pathway (this means that the movement of assimilates is also controlled)
down a water potential gradient
And passes the peri cycle and enters pits to enter the xylem vessel

Question 25

Explain movement of water form the xylem to the air

Answer 25

-Once in xylem, pass into mesophyll cell wall either through appoplast or symplast pathway.
-water evaporates from meoshpyll cell wall into the air spaces
-water then diffuses out of thr leaf through the stoanat down a concentration gradient,
This creates a tarbnspriation pull, bc since water is lost form the leaf, it will continue to move up xylem vessels through transpiration stream to replace this water lost from the leaf

Question 26

Give the definition of
Transpiration
Transpiration pull
Transpiration stream

Answer 26

-loss of water from the leaves via the stomata by diffusion
-caused by the cohesive forces of water molecules, which generate a transpiration pull
-movement of water form the roots to the leaves

Question 27

Explain the two factors involved in why water moves up the xylem vessel

Answer 27

1)root hydrostatic pressure
2)transpiration pull

-solutes are pumped across membranes through active transport into the xylem
-this increases the solute concentration in the xylem so decreases the water potential
-so this results in more water uptake from the soil from high water potential to low water potential via osmosis
Therfore increase in hdyrtsic pressure at the roots

-water vapor evaporates form mesophyll cell walls into air spaces,
-so the lowered water potential at the air spaces, causes more water to evaporate from the spongy mesophyll cell walls
-so now low water potential in spongy mesophyll cell
-so water in the xylem is pulled upwards to replace water just loss and it is the cohesive forces that generates this transpiration pull

Question 28

What is tension in the xylem vessels and what is this caused by

Answer 28

-when walls pull inwards due to the transpiration stream
]caused by the polar nature of water, bc this causes it to form h bonds which causes cohesion and adhesion
-cohesion is when water meocluels can stick together so results ina conitnous flow of water
-adhesion is between cellulose in cell wall of xylem and between water molecules,

Cohesion and adhesion both result in capillary flow, ability of a fluid to move up against gravity

Question 29

Give 3 functions of transpiration

Answer 29

-turgid pressure provides support to leaves
-helps in the uptake of mienlr anions up the plant
-provides a means of cooling for the plant

Question 30

Explain what happens to stomata in high light intensity and in low

Answer 30

High, stomata are turgid, so open
Low, stomata are fl;acid, so closed

Question 31

In terms of transpiration,
State which one each factor is dependant upon from either (diffusion or evaporation)

Answer 31

Humidity and wind speed, diffusion (water vapor out of the leaf)
Temperature, evaporation (from surface of spongy mepshyl)

Question 32

Explain the rate of different light intensities on the rate of transpiration

Answer 32

Increased light intensity,
Stomata more open
So increased rate of transpiration

But very high light intensity,
Stomata close to prevent water loss
So transpiration slows

Question 33

Explain how having thick waxy cuticles is an adaptation for xerophytes

Answer 33

Being thick,
Increases diffusion distance
So reduces water loss through the cuticle through transpiration

Having a waxy cuticle
Reflect light
So reduces internal temperature of the leaf
So reduces kinetic energy
So reduces evaporation from leaf surface so less transpiration

Question 34

Explain how having spines or needles reduces leaf surface area

Answer 34

Reduces surface area for transpiration

Question 35

Which otehr factor apart from having spines or needles can reduce surface area in a xerophyte and explain how

Answer 35

Having densely packed spongy mesophyll,
Bc this reduces area that is exposed to air in a leaf
So les evaporation form spongy mesophyll into air space so ess water loss

Question 36

Explain how concentration gradient steepeness is reduced inside and outside a leaf

Answer 36

-sunken stomata,
Increases diffusion distance so decreases diffusion of water vapor out of the leaf

-trichomes/leaf hairs
Trap moist air near leaf surface,
so reduce water potential gradient between air space and atmosphere
So reduce rate of transpiration

-rolled up leaves
Trap moist air
So reduce water potential gradient between air spaces and atmosphere
So reduced rate of transpiration

Question 37

Explain how rolled up leaves can reduce trnaprtion. And give an example of the name of one of thes specific leaves in xerophyte

Answer 37

Trap moist air
So traps water potential within the leaf
So reduces water potential between leaf and atmosphere
So reduced rate of transpiration

Also has a thick waterproof cuticle exposed to the air

Question 38

Give three ways sunken stomata reduces transpiration

Answer 38

-increased diffusion distance

-traps water vapour

-minimizes effect for wind which can remove water vapour fork surface and create even steeper conc gradient

Question 39

What adaptions in terms of stomata do xerophytes have

Answer 39

Reduced number of stomata, so less water loss from pores

Only presents on inner surface,
Surface is shaded so reduced evaporation