Cohesion, Adhesion, & Surface Tension

Summary

This educational script delves into the emergent properties of water, focusing on cohesion and adhesion. It explains how water molecules bond through hydrogen bonding, creating a cohesive force that allows water to stick to itself and adhere to other substances. The script further explores the significance of these properties in the biological process of transpiration in plants, illustrating how water travels from roots to leaves. Additionally, it touches on surface tension, a phenomenon where water molecules at the surface form a 'skin' due to unbalanced cohesive forces, which is crucial for various biological functions and the behavior of water in nature.

Takeaways

• 💧 Cohesion is the process where water molecules stick to each other through hydrogen bonding.
• 🔗 Adhesion is the process where water molecules stick to non-water molecules, also through hydrogen bonding.
• 🌳 Transpiration is the process by which water is pulled up from the roots and distributed throughout a plant via the xylem.
• 🌿 Xylem acts like a vascular tissue in plants, transporting water from roots to leaves and branches.
• 💧🔗 The combination of cohesion and adhesion allows water to move up the plant as a continuous column.
• 🌱 Capillary action is a key mechanism in water transport within plants, similar to how a paper towel absorbs water.
• 🔬 Surface tension is the result of water molecules at the surface being pulled inward by hydrogen bonds, forming a 'skin' on the water's surface.
• 🚀 Surface tension is biologically significant, allowing insects like water striders to walk on water and maintaining the integrity of water droplets.
• 🌧️ Raindrops and water droplets are examples of how surface tension plays a role in the natural world and the food web.
• 🤔 The script emphasizes the importance of understanding cohesion, adhesion, and surface tension for various biological processes and phenomena.

Q & A

What are the two main properties of water discussed in the script?

The two main properties of water discussed are cohesion and adhesion.

What is cohesion and how does it relate to water molecules?

Cohesion is the property where water sticks to other water molecules through hydrogen bonding, creating an attraction between the water molecules themselves.

What is adhesion and how does it differ from cohesion?

Adhesion is when water sticks to non-water molecules, also through hydrogen bonding, but the difference is that it involves the water molecule's oxygen forming a bond with a hydrogen of another substance, not another water molecule.

Why are cohesion and adhesion important in the context of plant biology?

Cohesion and adhesion are important in plant biology as they play a crucial role in the process of transpiration, allowing water to be pulled up from the roots and distributed throughout the plant.

Can you explain the process of transpiration in plants as described in the script?

Transpiration is the process where water is pulled up from the roots of a plant, moves through the xylem (vascular tissue), and is eventually released through small holes called stomata on the underside of the leaves.

How does the script describe the movement of water in the xylem?

The script describes the movement of water in the xylem as a column where water molecules cohesively bind to one another and adhere to the sides of the xylem, moving upwards due to transpiration.

What is surface tension and how does it relate to the hydrogen bonding of water molecules?

Surface tension is the phenomenon where water molecules at the surface are held together by hydrogen bonding, creating a 'skin' effect because there are no molecules above them to counteract the downward pull of the bonds.

Why is surface tension biologically significant according to the script?

Surface tension is biologically significant because it keeps water in droplets, which is important for various biological processes and interactions, such as insects walking on water or the formation of raindrops.

How does the script illustrate the concept of surface tension with an example?

The script uses the example of a beaker filled with water molecules to show how the surface molecules are pulled inwards by cohesion, forming a skin on the top due to surface tension.

What role do the concepts of cohesion, adhesion, and surface tension play in the movement and behavior of water in various biological contexts?

These concepts are fundamental to understanding how water moves within and interacts with biological systems, such as the upward movement in plants through transpiration and the formation of water droplets that insects can interact with.

What is capillary action as mentioned in the script and how does it relate to water movement in plants?

Capillary action is the process where a liquid, like water, travels up through a narrow space against gravity, similar to how water moves up a paper towel. In plants, it's how water moves up through the roots and into the xylem due to cohesion and adhesion.

Outlines

00:00

💧 Cohesion and Adhesion in Water

The script introduces the concept of emergent properties of water, focusing on its cohesive and adhesive properties. Cohesion is the attraction between water molecules through hydrogen bonding, while adhesion is the attraction of water molecules to other substances. The video explains how these properties are crucial in the process of transpiration in plants, where water moves from roots to leaves through xylem, the plant's vascular tissue. The script discusses how water molecules stick together and to the plant tissue, facilitating the upward movement of water without a mechanical pump. It also hints at the importance of these properties in biology, setting the stage for further exploration in upcoming classes and labs.

05:00

🌊 Exploring Surface Tension and Its Biological Significance

This paragraph delves into surface tension, another emergent property of water, which is a result of the cohesive forces between water molecules. The script describes how water molecules at the surface are pulled towards the center due to the lack of molecules above them, creating a 'skin' effect. This phenomenon is observable in everyday life, such as when water forms a bubble on a flat surface. The biological importance of surface tension is highlighted, explaining its role in maintaining water droplets, which are vital for various ecological processes and organisms, including insects that can walk on water. The script aims to clarify the concept of surface tension and its relevance in the biological context.

Keywords

💡Cohesion

Cohesion refers to the property of water molecules sticking together due to hydrogen bonding. In the video, cohesion is essential for the movement of water within a plant, as it allows water molecules to form a continuous column that can be pulled upwards through the xylem, the plant's vascular tissue. The script illustrates this with the example of transpiration, where water moves from the roots to the leaves and exits through the stomata.

💡Adhesion

Adhesion is the process where water molecules stick to non-water molecules, also through hydrogen bonding. The video script explains that adhesion is important for water's interaction with the walls of the xylem, allowing the water column to be pulled upwards. It is also mentioned in the context of water adhering to plant molecules, which is crucial for the water's movement and distribution within the plant.

💡Transpiration

Transpiration is the process by which water is pulled up from the roots of a plant and released through the stomata on the underside of the leaves. The video emphasizes transpiration as a key example of how cohesion and adhesion work together to move water within a plant. It is a critical process for the plant's water cycle and is a major focus of the video's discussion.

💡Xylem

Xylem is one of the vascular tissues in plants, often referred to as the plant's 'blood vessels' because it carries water and nutrients. In the video, xylem is described as the pathway through which water moves from the roots to the leaves, facilitated by the cohesive and adhesive properties of water.

💡Capillary Action

Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces, such as gravity. The video script uses the analogy of a paper towel absorbing water to explain how capillary action helps in the movement of water in plants, particularly in the context of the water column moving upwards through the xylem.

💡Surface Tension

Surface tension is the elastic-like property of water due to the cohesive forces among water molecules at the surface. The video script describes how surface tension forms a 'skin' on the water's surface, which is a result of the water molecules being pulled towards the center of the water body. This concept is important in biology, as it helps in maintaining the integrity of water droplets and is relevant to the behavior of certain insects like water striders.

💡Hydrogen Bonding

Hydrogen bonding is a type of chemical bond that occurs between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom. In the video, hydrogen bonding is the fundamental force behind both cohesion and adhesion, as well as surface tension, and is crucial for the movement and behavior of water in various biological contexts.

💡Stomata

Stomata are small openings or pores found on the underside of plant leaves, which are involved in gas exchange and transpiration. The video script mentions stomata as the exit points for water vapor as it is released from the plant during transpiration.

💡Vascular Tissue

Vascular tissue is a type of plant tissue that conducts water, minerals, and nutrients throughout the plant. The video script specifically mentions xylem as a type of vascular tissue that carries water from the roots to the rest of the plant.

💡Water Column

A water column in the context of the video refers to the continuous column of water that moves through the xylem due to the cohesive and adhesive properties of water. The script explains that this column is formed as water molecules are pulled up by transpiration and adhere to the sides of the xylem.

💡Water Strider

A water strider is an insect that is known for its ability to walk on the surface of water. The video script uses the water strider as an example to illustrate the importance of surface tension in biology, as it demonstrates how insects can exploit the cohesive properties of water for their survival.

Highlights

Emergent properties of water, specifically its cohesive and adhesive properties, are discussed.

Cohesion is the attraction between water molecules through hydrogen bonding.

Adhesion is the process where water sticks to non-water molecules, also via hydrogen bonding.

Transpiration in plants is a key process where water moves from roots to leaves.

Xylem, a vascular tissue in plants, functions like blood vessels to transport water.

Water exits leaves through small holes called stomata as part of transpiration.

The absence of a pump mechanism in plants is highlighted, questioning how water moves upwards.

Capillary action is described as a key process in water movement within plants.

Cohesion and adhesion are essential for the column of water to move upwards in plants.

Surface tension is explained as a result of water molecules being held together by hydrogen bonds.

The top layer of water molecules forms a 'skin' due to the lack of molecules above pulling them apart.

Biological importance of surface tension is highlighted, such as in the case of water striders.

Surface tension plays a role in keeping water in droplets, which is vital for various biological processes.

The role of hydrogen bonding in creating surface tension is emphasized.

The practical applications of cohesion, adhesion, and surface tension in biology are discussed.

The transcript concludes with an invitation for questions, indicating an interactive educational approach.

Transcripts

[Music]

so the first of the emergent properties

of water I want to talk about is um its

ability to um adhere to other molecules

or to cohesively stick to itself so

there's two words that we need to talk

about first and the words are cohesion

and adhesion um and these are almost

always going to be talked about together

but you need to know the difference

between them so the first thing you need

to know is that cohesion is when water

sticks to other water

molecules um and that that's going to be

through hydrogen bonding so I'm going to

have a water hydrogen bound to another

water um hydrogen bonded to another

water molecule so it's just the

attraction between the water molecules

uh adhesion is when water sticks to non

water molecules and it's going to happen

the same way it's also going to be

through hydrogen bonding it's just

instead of the oxygen from a water

molecule forming a hydrogen bond with a

hydrogen of another water molecule it's

between the negative side of a water

molecule with a positive side of

something else and that's really it so

in this example I'm going to have the

water um adhering to some type of plant

molecule that's not water so this is

important uh cohesion and adhesion are

are super important actually in biology

and the um

there dozens literally dozens of times

that we're going to talk about this this

year but the one that I want to talk

about is the one that we're going to be

focusing on the most in the next couple

weeks which is actually going to be

transpiration of plants so transpiration

of plants is the process where water is

pulled up from the roots um of the plant

so the water's going to move up uh

through the roots of this tree

and then it's going to be pulled up

through the xylem which is one of the

vascular tissues so just think of it as

like a blood vessel but it just carries

water in the tree and it's going to

distribute that water to all the leaves

and all the branches and throughout the

entire tree so I'm going to have my

water um coming up through the tree

through the roots and it's going to move

up and it's eventually going to exit the

leaves on the undersides of the leaves

there's these small holes called um

States and the water is actually going

to move up all the way through the tree

through trans through through

transpiration and then it's eventually

going to um to exit through the bottoms

of the leaves through those holes and

we're going to talk about that at length

um in class and we're going to do a

couple different Labs on it but

basically we need to talk about how does

the water move like because there's no

little pump in there right so let's look

at a blown up view of some of this

vascular tissue some of this xylem um so

the transpiration

of water that's what we're looking at so

I'm going to this is my zoomed in view

so let me draw my xyum with my brown

lines and then I'm going to have my

water so moving up

through the xylem I'm going to have the

water actually sticking to themselves so

the water molecules are going to

cohesively be bound to one another so as

one water molecule moves the next is

going to get pulled up right or as water

molecules get pulled up they're going to

keep shoving so the water's going to

move as a column right um the next thing

you need to know is that the water is

going to adhere to the sides of the xylm

so it's going to through hydrogen

bonding it's also going to stick to the

sides of the actual plant vascular

tissue and that's that's adhesion and so

the combination of cohesion and adhesion

what's going to happen is as that water

flows into the roots you're going to get

a column of water basically moving up

through capillary action um which is

just when you like you take a a piece of

paper towel and the water travels up

through it it's basically the same thing

but this is happening on on a grand

scale inside of all plants that's how

water gets from the roots of any plant

to the leaves of any plant so that's

cohesion and adhesion now the next thing

we want to talk about with cohesion is

going to be surface tension so surface

tension you've all seen before um it's

when water molecules are being held

together by um by the the hydrogen

bonding between them so let's look at an

example of of surface tension and let's

talk about um why it why we're talking

about the surface not just the whole

cohesive water so the molecules at the

surface at that top layer don't have any

water molecules on top of them so

instead what's happening is all of those

those those hydrogen bonds

are pulling them kind of down so the the

surface molecules are going to be pulled

in towards the center of the Water by

cohesion so let's look at a picture of

that so I've got my Beaker and I'm going

to fill it with water

molecules and uh in the center what

would happen is all of those white lines

are those are going to indicate the

hydrogen bonding everything's pulling

together right but if we look at one of

the water molecules at the surface

they're only being pulled kind of next

to each other and then down there's

nothing that's pulling it up so it kind

of forms a skin on the top and you've

seen that in real life if you take and

you put some water on your desk it'll

form a little bubble so let's fill that

in with my water molecules and we'll put

in all my cohesive forces right there

all those hydrogen bonds then what you

get is you get those are a normal

cohesion um you get these bonds that I'm

I'm looking at the top that's going to

kind of be that that surface tension and

it's still cohesion but what you're what

you're seeing is you're seeing the

actual hydrogen bonding that's leading

to the surface tension now why do we

care in biology I mean it's cool like

because you've all seen pictures of the

water Strider right well this is why we

care in biology surface tension is

biologically important because it keeps

water in droplets and water droplets are

important how water moves is important

and having water droplets do raindrops

those are all important because you know

insects other aspects of the the um the

food web they're going to depend on that

um that cohesive nature of water and on

um and on being able to walk across that

water so that's surface tension um and

uh hopefully that's pretty clear I think

everybody's seen examples of surface

tension

before so that's really all I want to

talk about on cohesion adhesion and

surface tension if you have questions

come on in