Chap 7 (Part 1b) - Transport of Water from Soil to Leaves | Cambridge A-Level 9700 Biology

Summary

This educational video script delves into the intricate process of water and mineral ion transport in plants, from soil to leaves. It explains the roles of root hairs, cortex, endodermis, and xylem in facilitating this journey. The script highlights the significance of water potential in driving transport against gravity and introduces the concepts of apoplastic and symplastic pathways. It also touches on transpiration, the loss of water vapor through stomata, and its role in plant cooling and gas exchange.

Takeaways

• 🌱 Plants transport gases, water, ions, and photosynthesis products, with gases moving by diffusion and others requiring specialized transport systems.
• 🚰 Water and mineral ions are transported from roots to the atmosphere, primarily through the xylem, while photosynthesis products are moved by the phloem.
• 🌿 The pathway for water and ions is similar, starting from the roots, moving up the trunk, and into the leaves, then released into the atmosphere through stomata.
• 🔍 Detailed structure of roots includes root hairs, cortex, endodermis, and xylem, each playing a role in the absorption and transport of water and ions.
• 💧 Root hairs are permeable to water and have a large surface area for efficient absorption, while the root cap is impermeable and protects the growing tip.
• 🌡 Water moves from areas of high water potential, like the soil, to areas of low water potential, such as the root hair cells, via osmosis.
• 🚧 The endodermis has a Casparian strip, which blocks the apoplastic pathway and forces water and ions to move through the symplastic pathway, allowing for selective transport.
• 🌳 Water enters the xylem vessels in the roots and is transported upwards to the leaves, moving down the water potential gradient.
• 🍃 In leaves, water moves through mesophyll cells via the symplastic or apoplastic pathway, eventually evaporating into the air spaces and diffusing out through stomata.
• 🌤️ Transpiration, the loss of water vapor from leaves, occurs mainly through stomata and also through the cuticle, contributing to plant cooling and water transport against gravity.

Q & A

What are the primary substances transported by plants and how do they differ in transport mechanisms?

Plants primarily transport gases, water, ions, and products of photosynthesis. Gases can be transported by simple diffusion, while water, ions, and photosynthesis products require specialized transport systems. Ions are transported by xylem, and photosynthesis products, or assimilates, are transported from source to sink by phloem.

How does water move from the soil into the root hairs?

Water moves from the soil into the root hairs through osmosis, following the water potential gradient from a region of high water potential in the soil to a region of lower water potential in the root hair cells.

What is the function of root hairs in water absorption?

Root hairs are extensions of epidermal cells that increase the surface area for absorption, allowing water to efficiently move into the root. They are permeable to water and can reach between soil particles to absorb water.

What are the two main pathways for water transport from root hairs to the cortex?

The two main pathways for water transport from root hairs to the cortex are the apoplastic pathway, where water travels through cell walls and intercellular spaces, and the symplastic pathway, where water travels through the cytoplasm and cell-to-cell via plasmodesmata.

Why is the Casparian strip in the endodermis significant for water and ion transport?

The Casparian strip in the endodermis is significant because it is impermeable to water, forcing water to take the symplastic pathway through the cytoplasm of endodermal cells. This allows for selective transport of ions and control of what enters the xylem.

How does water enter the xylem vessels?

Water enters the xylem vessels through pits in the cell walls. These pits are not lined with lignin, which is impermeable to water, allowing water to pass through.

What is the role of the xylem in the transport of water and minerals from the roots to the leaves?

The xylem plays a crucial role in transporting water and minerals from the roots to the leaves by providing a continuous pathway down the water potential gradient, allowing water and minerals to move upwards against gravity.

How does water move within the leaves from the xylem to the atmosphere?

In the leaves, water moves from the xylem vessels into the mesophyll cells, either by the apoplastic or symplastic pathway. It then evaporates into the airspaces and diffuses out into the atmosphere through the stomata.

What is transpiration and how does it relate to water movement in plants?

Transpiration is the loss of water vapor from the leaves to the atmosphere, primarily through the stomata. It is a result of water movement in plants and helps in the transport of water and nutrients from the roots to the leaves.

Why do plants need to control the transport of mineral ions at the endodermis?

Plants need to control the transport of mineral ions at the endodermis to regulate the uptake of essential nutrients and prevent the accumulation of potentially toxic ions. This selective transport is crucial for the plant's overall health and nutrient balance.

Outlines

00:00

🌱 Introduction to Water and Ion Transport in Plants

This paragraph introduces Chapter 7, focusing on the transport of water and ions in plants. It explains that plants need to transport gases, products of synthesis, mineral ions, and water. While gases can be transported via simple diffusion, water, ions, and products of photosynthesis require specialized transport systems. The paragraph outlines the general transport pathways for water and ions, which are primarily from the roots upwards through the xylem and phloem. It also mentions a diagram for revision purposes and sets the stage for a detailed exploration of the transport mechanisms, starting from the roots to the atmosphere.

05:03

🍃 Detailed Flow of Water and Ion Transport from Soil to Roots

Paragraph 2 delves into the detailed flow of water and ions from the soil, through root hairs, and into the cortex. It describes the anatomy of the root hair and its permeability to water, which allows it to absorb water and mineral ions efficiently due to its large surface area. The paragraph explains the concept of water potential and how water moves from an area of high water potential (soil) to an area of low water potential (root hair cells) through osmosis. It also introduces the apoplastic and symplastic pathways for water transport, detailing how water travels through cell walls and cytoplasm, respectively.

10:03

🌿 The Role of the Endodermis in Water and Ion Transport

Paragraph 3 discusses the transition of water and ions from the cortex to the endodermis, a layer in the root. It highlights the presence of the Casparian strip in the endodermis, which blocks the apoplastic pathway, forcing water and ions to take the symplastic pathway through the cytoplasm. This is significant because it allows for the control of mineral ion transport via carrier proteins in the endodermis. The paragraph also explains how water enters the xylem vessels through pits in the cell walls, which are not lined with lignin, allowing for water permeability.

15:04

🌳 Transport of Water from Roots to Leaves and Transpiration

This paragraph describes the journey of water from the xylem in the roots, through the stem, and into the leaves. It emphasizes that water continues to move down the water potential gradient, from higher potential in the roots to lower potential in the leaves. The paragraph also details the ultrastructure of leaves and how water moves through mesophyll cells, eventually evaporating into the air spaces and diffusing out through the stomata into the atmosphere. This process is known as transpiration, which is a key mechanism for water loss in plants and plays a role in cooling the plant. The paragraph also touches on the side effects of transpiration and sets the stage for the next video, which will cover how water moves against gravity and the factors affecting transpiration rates.

20:05

🌤 Recap and Anticipation of Upcoming Topics

Paragraph 5 provides a recap of the water transport process from the soil to the leaves, emphasizing the role of water potential gradient in guiding water movement. It also previews the topics for the next video, which will include how water moves against gravity, factors affecting transpiration rates, the use of a protometer to measure transpiration, and strategies some plants use to survive in dry environments. The recap serves to solidify the understanding of the transport mechanisms discussed in the previous paragraphs.

Keywords

💡Transport of water

The process by which water is moved from the soil, through the roots, and up to the leaves of a plant. In the video, this is a central theme as it discusses the mechanisms by which plants transport water against gravity, highlighting the importance of specialized transport systems like the xylem.

💡Root hairs

Root hairs are fine, elongated extensions of epidermal cells at the root tip that increase the surface area for water absorption. The script describes them as permeable to water, unlike the root cap, and their role in facilitating water uptake from the soil.

💡Water potential

Water potential is the measure of the potential energy of water in a system, which determines the direction of water movement. The video script explains that water moves from regions of high water potential to regions of low water potential, which is fundamental to understanding how plants transport water.

💡Osmosis

Osmosis is the movement of water across a partially permeable membrane from an area of lower solute concentration to an area of higher solute concentration. The script uses osmosis to explain how water moves into and through the root hair cells and other plant tissues.

💡Casparian strip

The Casparian strip is a waterproof layer made of suberin in the endodermis cell walls that blocks the apoplastic pathway for water and minerals. The video script discusses how this feature forces water to take the symplastic pathway, thereby allowing selective uptake of ions.

💡Xylem

Xylem is the vascular tissue responsible for the transport of water and dissolved minerals from the roots to the rest of the plant. The script details how water enters the xylem in the roots and is transported upwards to the leaves.

💡Transpiration

Transpiration is the process by which water is lost from the plant to the atmosphere as water vapor. The video script touches on transpiration as the final step in the water transport process, where water is released through stomata.

💡Stomata

Stomata are tiny pores on the surface of leaves that facilitate gas exchange and water vapor release. The script explains that stomata are crucial for transpiration, as they open to allow water vapor to escape to the atmosphere.

💡Mesophyll cells

Mesophyll cells are the photosynthetic cells found in the interior of leaves. The video script describes how water reaches these cells and how some of it is used in respiration, while the rest is released to the atmosphere.

💡Apoplastic pathway

The apoplastic pathway refers to the movement of water and solutes through the cell walls and intercellular spaces, rather than through the cytoplasm. The script discusses how this pathway is blocked at the endodermis by the Casparian strip.

💡Symplastic pathway

The symplastic pathway is the movement of substances through the cytoplasm of cells and between cells via plasmodesmata. The video script explains how water travels through this pathway in the cortex and endodermis, and how it is the only pathway available at the endodermis due to the presence of the Casparian strip.

Highlights

Plants transport gases, water, ions, and photosynthesis products, with gases moving by diffusion and others requiring specialized systems.

Mineral ions and water are transported via xylem, while photosynthesis products move from source to sink through phloem.

The transport pathway for water and ions is primarily from roots to the atmosphere, involving complex structures like the root hair zone and cortex.

Root hairs are permeable to water and play a crucial role in water uptake due to their large surface area.

Water and mineral ions move from the soil into root hairs, driven by differences in water potential.

Water travels from root hairs to the cortex through apoplastic and symplastic pathways, with the latter involving cell-to-cell movement.

The endodermis layer, with its Casparian strip, blocks the apoplastic pathway, forcing water and ions to move through cells via the symplastic pathway.

Water enters the xylem vessels by crossing the endodermis and pericycle, facilitated by the presence of pits in cell walls.

Transport of water within the xylem is driven by water potential gradients, moving from roots to leaves against gravity.

In leaves, water moves from xylem vessels into mesophyll cells, using both apoplastic and symplastic pathways.

Transpiration is the process of water loss from leaves, primarily through stomata, and also via the cuticle when stomata are closed.

Stomata play a critical role in transpiration, being the main route for water vapor to exit the leaf and enter the atmosphere.

Transpiration not only loses water but also helps in cooling the plant and facilitating gas exchange for photosynthesis.

The lecture concludes with a recap of the water transport journey from soil to leaf and the mechanisms of transpiration.

Transcripts

hi everyone and welcome to chapter 7

transport of water

from soil to leaves now last week we

sort of mentioned

um

that plants have to transport a couple

of things they transport gases they

transport products of synthesis mineral

ions and water gases can be transported

by a simple diffusion

whereas

water

ions and protozoa photosynthesis for

example sucrose will need specialized

transport systems and you already know

what they are in very simplified terms

more than ions are transported by xylem

whereas products photosynthesis or

assimilates are transported from source

to sink

by phloem

so today we're going to dive in deeper

especially into transport of water and

ions

specifically from root to the atmosphere

you might see this complicated looking

diagram in your notes

this is just

for

revision purposes and we'll come back at

the end of the chapter to just recap

okay so

transport of mineral sorry i was gonna

say mineral water but no transport of

water and mineral ions now this is a

similar pathway from both and this is

always from the root upwards

they differ a little bit but we'll get

to the details later but mostly you can

assume it's the same

similar pathway for both so

it's going to be in the roots and you

can imagine the water going up the trunk

and then up the leaves and then up into

the atmosphere

now but of course there are finer

details to that you learn

detailed structure of the roots and

therefore

let's do a more detailed flow chart

right it goes from the soil which is

like outside there front hair which is

part of the root obviously and then the

cortex which you can see here

the endodermis

and then only it goes into xylem

and from the xylem this is you in the

root okay so in the root

water enters the xylem

and this transports to

xylem

uh in the stem and cinema leaves all the

way upwards through

the xylem in the trunk

and then at the leaves

mesophyll cells would be having this

water now

some of it is used in respiration

and the rest is really released

to the atmosphere through the stomata

so that's just the overview but keep

this um vision in mind imagine you are

water you are water

and you are traveling from the soil to

heavy cortex and what pathways will you

take and how is it are you going to move

upwards against gravity

that is incredible incredibly insane

so let's start from the beginning let's

start with

step one let's just talk about soil to

root hairs

now before we get there let's talk a

little bit about the anatomy of this

root hair

and

root this is a longitudinal section

longitudinal cross section of the root

you can see here is the root cap the

root cap by the way is impermeable to

water is grow the root is actively

growing

uh in this region

and it needs like quite a hard

tough

tip in order to be protected

and penetrate the ground

the root hairs however in this diagram

are permeable to water unlike the root

cap and they are very very fine in fact

they're not even cells they are actually

um

long-term extensions of abdominal cells

so you can see the abdominal cell here

epidermis of the root epidermal cell

you can see it just has like a little

thing that extends outwards here

okay water can pass through the cell

wall and get into the cell

the root hair like this

um

mineral ions are also taken up

through here but they can't pass through

the cells because ions are charged so

they are taken up via via

diffusion or sometimes even active

transport into

the hair cell

or abdominal cell

okay why do you need this extensions

well it's able to reach between the

small spaces between soil particles you

can imagine soil particles as they go

like circles there are tiny spaces

between them those can reach in

uh they're very delicate though and it

has to be replaced after a few days but

advantage is because it can reach

between the spaces and absorb the water

it has a very large surface area so this

means that water can be efficiently

um

moving in to the root

there's an increased area of absorption

okay so this chapter we're going to talk

a lot about water potential after all it

is the transport of water and water

travels down the water potential

gradient so always think of the

direction so here we have the root hair

cell here and this circular things are

the soil and soil actually has a higher

water potential

than the root hair cytoplasm so the

water will move again from high to low

right

down the concentration gradient now why

is it that saw has a higher water

potential

it's because the root hair cell or the

epidermal cell has a high concentration

of ions and organic substances remember

it can absorb

ions by active transport right

they do have that high concentration of

high anti-organic substances like

proteins or sugars and therefore it's

lower than the outside the water could

diffuse down the water potential

gradient from a region of high water

potential to region of low for the

potential via osmosis osmosis is a very

important word nor write your mark like

your test

right so

this is also through the partially

permeable cell surface membrane and

again partially permeable is another key

word

okay

so that is from the salt root hair

now we are going to travel from the root

hair cells

into the cortex of the roots

okay so

again

the potential comes into play root hairs

has a higher water potential than the

cortex

water moves down all the picture again

water potential gradient by osmosis

again

okay so but you know

it's not going to be that simple because

there are a few possible routes

routes

for

um

hairs

to cortex okay imagine again you are

water a few ways number one is called

the apoplastic phosphate sounds

complicated but actually very simple

concept

water can pass through the cell wall

or intercellular spaces

so you can see here

that a water is going into

not into the cytoplasm of the bacterial

but

traveling

at

the cell wall

okay

between those cellular fibers

why does water tend to do this um

because water actually has adhesion

forms hydrogen bonds with cellulose

and therefore can travel in this pathway

this does not mean this this means that

water does not cross membranes and enter

into cells they are just between cells

that's why it's called

intercellular

spaces

if you are water you can also travel

using another way called sim plastic

pathway

okay simplistic pathway means

that the water travels through the

cytoplasm

and the water can travel

cell to cell by plasmodesmata so into

the

cytoplasm and then you can see here

between cells it goes through

the plasmodesmata for this martha

is where cytoplasms of the cell are

connected there is no cell wall

and third one which is very rare and

also overlapping with simplest so this

is

uh if you see this don't be scared

because vacuolar pathway just simply

means that water can pass through into

the vacuole and then back outside now

this is also a part of symplastic

pathway

a little bit different but a part of it

overlaps

because well you need to enter the cell

in order

to

travel through the vacuolar pathway

for regular pathway always comes with

simplest pathway

okay so how do you remember that you

might think oh it's quite hard isn't it

like apple plus in plus it doesn't make

sense to me now apple plus pathway or

apple plastic pathway

um

it has an a right

that's how i remember it and cell wall

wall has a so wall

like a and a

whereas thin plus and cytoplasm both

have like y's in the front c and side so

i sort of think it makes sense

so this might be a way you can remember

it

so that's from the root hair you can see

here root hair saw out there

goes the root hair

upper

and then now it ends up at the

endodermis so from the root hairs

for the cortex now we are at this layer

here the second so-called second circle

in the

roots

called the endodermis

now this is when the apple plus and sim

plus pathway becomes different or

changes a little bit

um

why because the endodermis has a

casparian strip what does that mean the

experience strip is because it's a

summarized cell wall or you know

it's a cell wall made out of subarray

suburine is a material sort of like

lignin cellulose okay so submarine is

impermeable to water

yeah so and it's in the cell walls only

and it only has like a strip that looks

like this

so it's like blocked

in this region

so you can expect uh if you are water

and you are traveling through the apple

plus pathway

you won't be able to add the endodermis

because that casparian strip is

impermeable to water so apple plus

puffer is blocked and the only way for

water to get in

to

that through the endoderm is across the

endothermic is through the cytoplasm and

this is called the simplest pathway

so all the water is forced

into the endothelial cells as well as

ions

now why is this important

okay

this is important because

if rotten ions are forced to pass

through means it will pass through the

cell membrane the cell membrane has

these transport proteins to try to

control

what mineral ions can come in

and how much exactly so transport of

mineral ions can be controlled at the

endodermis

the specifically

carrier proteins of the plasma membrane

of the endothermal cells

now

because these amino ions again they

cannot pass through the cell surface

membrane

they are absorbed

by the transport and can contribute to

something called root pressure er

pressure is something we will cover next

video

stay tuned

okay so so far we have the soil with the

root hair hyperplastin plus in the

cortex in the end is no apple plus just

simple

now we can finally go through the xylem

yay

so

throughout this process water continues

to move down the water potential

gradient okay

there is a

lower

water potential in the xylem and in the

soil okay so from the anonymous to the

xylem

they have to cross something called the

pericycle which is a layer of cells just

below the endodermis or just on the

inner side of the endodermis

or this can be true apoplast or simplest

because it doesn't matter it doesn't

have the subarring cell work here

then how does water get into design

vessels through the pits in the cell

walls the same vessels remember zion

vessels are made up of the cell walls

are made up of cellulose and lignin and

lignin again is impermeable to water

and these pits are not lined with lignin

and therefore water can pass through

so

now we are in design vessels and the

water has finally gotten into the roots

into the zone vessels in the roots

in general the roots have a higher water

potential as well

and

leaves have a very low water potential

so the water can travel upwards again

down the water potential gradient from

xylem still inside xylem from the roots

into the stem

into the leaves still in the xylem

so we went from xylem vessels

to roots from roots to leaves and now

we are at the leaves

what is happening here

so xylem has a higher water potential

than its atmosphere

obviously

and water continues to move down towards

potential gradient

as you know there's a lot of

ultrastructure there's a lot of tissues

in

the leaves as well so how many

processes how many sections locations

does it not go through in order to get

the environment so here we go

okay you are water

and now that you are in xylem vessels in

the leaves

you have to come out to the pits again

because the lignin is impermeable right

come out to the pets design vessels

and what you will have there in the leaf

in abundance is polystyrene or spongy

mesophyll cell

okay it could come out and

travel through those muscle real cells

by apple plus or simplest pathway

but

the final goal is

for

um

well of course some water is using

synthesis but after they travel travel

travel

those water will end up

onto the surface of spongy mesophyll

cell walls

okay

they are

they gather

the surface or spongy muscle fuel cell

walls

then

water in the on the surface outer

surface of the spongy mesophyll cell

walls this is in the air space

right

this

evaporates into the airspaces so at

first it's at the cell wall

then it evaporates into air space

and then

the water vapor which is in the air

space

diffuses

from

the airspace

via the stomata to the atmosphere

you might have trouble like visualizing

that so wait for next slide hang on

i just wanted to highlight that here

after evaporations in the

cellular airspaces are also saturated

with water vapor

okay evaporation here

causes it to be saturated water vapor

and therefore the air space also has a

higher water potential than the

atmosphere again water is always moving

down the water potential gradient

okay let's look at it here again and

let's talk about the same

parts again okay so

processes this is the xylem and this is

water moving out into the policy or

sponginess of cells now how does it

travel

through these cells

well by apple plus or string plus

pathway

okay so how does one mesophyll cyclone

is how does water move from one

mesophyll to another double plus or same

plus pathway

the same as you know then it gathers at

the sponge muscle fuel cell wall

style surface of the cell wall

the intercellular spaces like here the

air space

and then only the water

is evaporated into the airspace it's not

even out this hair space like

evaporation occurs

from the surface of the cell wall

to the airspace

then water vapor okay now is in fact

water has evaporated into water vapor so

water vapor doesn't

uh travel by osmosis it diffuses it's

not evaporation anymore because it's

already evaporated

the water vapor diffuses

in the form of gas

into the atmosphere

via the stomata which is

composed of two gut cells

so don't confuse this process names

as

um

marks will be deducted if they are

confused

okay

so

this loss of water

is called transpiration

why

so this is going to next video a little

bit already but i just wanted to tell

you that here

is

loss of what a wave of leaves and yes we

can see here that what is lost through

the stomata but there's also another way

of losing water

okay so let's do this again

transformation is a loss of water vapor

from leaves the side effect is that the

plant cools down it's just a side effect

just the additional bonus feature

the two ways and mainly is virus mata

which

involves the diffusion of water vapor

from the air space to the atmosphere and

this only occurs when a somata is open

why is it open well

stomata is open when photosynthesis is

needed

entry of carbon dioxide and exit of

oxygen

[Music]

yeah so when someone is open diffusion

of water vapor can occur through the

somata

but what if when the stomata is closed

is there then no transpiration no

transpiration is still occurring but at

a very small

amount and very

low rate of transpiration here when the

stomata is closed

because water is lost by the cubicle

okay and cuticle is a mostly waterproof

material it's very hard for water to

pass through but sometimes a little bit

small amount of water paper that's true

and of this also is transpiration but

mainly is the stomata now more on

transpiration next video

now

just a recap of what we just did

whoops

hang on set

let's

um i'm going to go back to this slide

here now let's don't worry about this

slide is usually used for vibration but

let me just use this to recap now water

travels from salt to hair

down the water potential gradient

from the root hair into the cortex

a symplastic pathway and hypoplastic

path is used but at the endodermis

the casparian strip is present and

therefore plus pathway is blocked and

simpler pathway is not blocked it is

open

and then it can go down the water

potential again into the xylem and from

in the xylem water is transported from

the root to the stem to the leaves these

mechanisms we for water to travel

against

um

uh against

uh gravity we will actually discuss data

okay so this one

next part but we know that in the leaves

again from leaves to metal from cells

simplest and apropas pathway are used

um

for water to be transported between

mesophyll cells

and then they use this pathway to get to

the mesophyll cell surface

and after that water evaporates into the

air space and then water vapor diffuses

out into the atmosphere through the

stomata

and that's it for now so we have part

one c on the way and we'll do why

how does water move again gravity again

and what are the factors that affect

transformation rate

how to use

protometer to measure the rate of

transpiration and how do some plants

manage to survive

in very very dry environment so that is

for next video till then

see you and