Theme 4 Homeostasis In Land Plants Part 4

Question 1

What do endodermal cells acts as

Answer 1

A selective barrier

The ions are actively transported into the xylem (using energy)

Active because already lots of nitrate on inside but want more from outside

Less to more so active (against gradient)

Question 2

Movement of water is controlled by

Answer 2

Osmosis

Question 3

In the symplastic pathway what does the water go through

Answer 3

The vacuools or the cell cytoplasm

Question 4

What is the casparian strip

Answer 4

It’s in the roots endodermis

It forces the apoplastic water and dissolved minerals into the symplast and into the endodermis

Makes sure all solutes and water enter the xylem (vasculature) which then lets the plant regulate the ions passing into the vascular tissue

Question 5

What does the casparian strip do once solutes have passed through the xylem

Answer 5

Restricts them from flowing back out because of gravity

Leaves whatever plant doesn’t need in the roots

Question 6

How does the water go to the top of the trees (travel up the xylem) once inside

Answer 6

Transpiration
Cohesion-tension mechanism

Question 7

How does transpiration due to the leaf anatomy help water move up the xylem

Answer 7

The leaves have many stomatal Pores and large air space

The air space gives area for evaporation to happen

The small xylem veins a very close to the stomatal openings and they dump water into the stomatal pores (the water potential in leaves is lower)

A negative tension is made by evaporation and water gets pulled up from xylem and out of the pores and then the next water molecule comes up

90% of the water is lost through this

Question 8

What is the cohesion tension mechanism of transport

Answer 8

It’s driven by transpiration

There’s cohesion between water molecules (h bonds)

There’s adhesion between the xylem and the water because of the interaction with cellulose in the xylem this adds tension

So when water is evaporated the next and next and next water molecules get pulled upward while attached to the xylem

Question 9

How does the column resist the negative pressure due to transpiration and negative tension

Answer 9

To stop from collapsing due to tension, the secondary cell wall of lignin,
the adhesive forces in the xylem (with h20)
and the weight of the column help

Question 10

What is root pressure

Answer 10

Positive (upward) pressure in roots that pulls forces xylem sap upward

Happens in high humidity or low light

Cal only Move water up very short distances since transpiration is slower in high humidity

Question 11

What is guttation

Answer 11

Occurs due to root pressure

In high humidity or low light

Water is pushed out of xylem and left on the edges of plants

Only in small plants

Question 12

What conditions increase transpiration

Answer 12

Hot, dry, and windy conditions

Question 13

How do plants prevent drying out (excessive water loss) due to transpiration

Answer 13

If hot conditions the plant wants to conserve water

the stomata is closed by the guard cells

But closing it off slows down photosynthesis and causes overheating

This is the trade off to conserve water

Question 14

If it’s humid conditions what happens to the stomata

Answer 14

Stomatal open

But since so much water outside already cause of humidity the transpiration will be low

Question 15

Xylem moves what

Answer 15

Just water

Question 16

If something is talking about bulk flow, pressure flow, movement of organics, sieve tube what it it related to

Answer 16

The phloem

Question 17

What is translocation

How is it diff from the xylem

Answer 17

Long distance transport of substances through the phloem

It’s multi directional transport depending on where the pressure is (xylem xylem is unidirectional)

Question 18

Is xylem hydrophobic or hydrophilic

Answer 18

Hydrophobic

Question 19

What is phloem sap

Answer 19

Water and organic compounds

Not just sugar, has amino acids, organic acids, organic nitrogen compounds, hormone, and other signal molecules

They flow through the sieve tube

Question 20

What drives the flow of phloem sap

Answer 20

The difference in pressure between the source and the sink regions

Question 21

What is the source

Answer 21

Any area of the plant where organic stuff is loaded into the phloem

Place where food is made

Question 22

What is the sink

Answer 22

Any area of the plant where organic stuff is unloaded from phloem

Place where food is stored

Question 23

What is the sink in winter
What is the sink in spring

Answer 23

The roots
The mature leaves

Question 24

What is the source in winter
What is the source in spring

Answer 24

The leaves
The roots

Question 25

What is the phloem composed of

Answer 25

Sieve tubes and companion cells

Each dive tube has its own companion cell with a plasmodesmata in between

They’re alive at maturity

Question 26

What do sieve tubes do as they mature

Answer 26

To get more area for flow of phloem sap, they lose their nucleus, vacuoles and organelles

This is done by partial programmed cell death

Question 27

What happens in partial programmed cell death

Answer 27

The phloem mother cell undergoes asymmetric cell division to give the sieve element and companion cell

The sieve element has no space to transport nutrients so it’s does ppcd and loses its vacuole/tonoplast, ribosomes, nucleus, Golgi body, and cytoskeleton

All it’s left with after are the plasma membrane, plastids, mitochondria, the endoplasmic reticulum

It’s still alive because the companian cell has all of the things the sieve element is missing

Sieve plates are formed that connect the sieve element and companian cell

The remaining organelles line to the walls of the sieve tube

P-proteins are also there to fix breakage of the tube

Then the tube is ready to transport

Question 28

What are sieve plates

Answer 28

Modified cell walls with plasma membrane lined pores

Question 29

What are the two mechanism of sugar loading

Answer 29

Apoplastic and symplastic

Same as xylem

Question 30

Sealing up break in the phloem IDK

Answer 30

Idk

Question 31

What is similar in the xylem and phloem about sugar and water loading

Answer 31

They both have to cross the plasma membrane

They have to get into symplastic route to be transported

Question 32

Unloading of sugars is

Answer 32

Symplastic

Question 33

What is the process of sucrose being loading into the phloem at a source (leaves)

What happens to the water potential

Answer 33

It is actively loaded into the phloem (eventually gets to sieve tubes)

The photosynthetic cell accumulates simple sugars : glucose fructose and galactose

These get transported through the smaller plasmodesmata into the companion cell

The sugars are made larger in the companian cell and turn into sucrose raffinose and stachyose

These larger sugars go though the larger plasmodesmata connection and into the sieve tube

The more sucrose loaded into the sieve tubes, the lower the water potential

Question 34

Why do are the plasmodesmata connecting the photosynthetic cell and the companian cell smaller than the other ones

Answer 34

Since the sugars get converted to larger sugars, they can only go through to the sieve tube with the bigger opening

To prevent from sugars going back into the photosynthetic cell

Question 35

What do pressure flow mechanisms do in relation to the phloem

Answer 35

Moves substances by bulls flow under pressure from sources to sinks based on water potential gradients

Loading from the source then Transported to sieve tube then unloaded into sinks

Question 36

What is the water potential in the sieve tubes

What about in the xylem

So which way does water move

Then what happens

Answer 36

Lower

Higher

From the xylem to the phloem, creates more turgor pressure in sieve tubes at the top

The sap in the phloem travels IN BULK to the sink (roots) cause lower pressure there

Sucrose is unloaded to sink cells

Then water flows back to the xylem though osmosis the lower it gets in the sieve tube since water potential gets higher there