Lesson video

Hello, my name's Mr. Jarvis, and I'm gonna be taking you through today's lesson in the unit, Living Organisms and their Environments.

Today we're gonna be looking at material cycles, and in particular, the water cycle.

By the end of today's lesson, you should be able to describe the processes that take place in the water cycle.

There are four key words to today's lesson.

They are evaporation, condensation, transpiration, and precipitation.

Here are the definitions of those words up on the screen.

If you need some time to read through them, please pause the video, but we will go through the definitions as we go through the lesson.

Today's lesson is broken down into two parts.

First of all, we're going to look at what processes take place within the water cycle.

And then in the second part of the lesson, we're going to look at how the water availability impacts living organisms. So if you're ready, let's get started with our first section, which is all about understanding the water cycle.

Water is vital for life.

And without water, all living organisms will eventually die.

And that's because many life processes rely on water for things like chemical reactions that take place inside cells.

Water is a solvent.

Other substances can dissolve within it.

It also provides moist surfaces for diffusion of gases to take place, for example, the surfaces of your lungs.

It provides transport in terms of things like blood around the body, and water also provides structural support to plants.

Water also provides many organisms with a habitat.

70% of the planet is covered by seas and oceans.

Rivers, streams, lakes, and ponds all provide fresh water habitats for organisms to live in.

Temporary pools of water provide habitats for some species, and even our water-based bodies provide habitats for some organisms such as this roundworm in the picture.

The water cycle is the process by which water is continually transferred between the Earth's surface and the atmosphere, and it provides water for organisms over, and over, and over again.

So here's a check.

Why is water important to living organisms? Is it A, water's needed for chemical reactions in cells, B, water provides support for plants, or C, water is a habitat in which some organisms live? I'll give you a few seconds to think about your answer, and then we'll check to see whether you've got it right.

So the correct answer is all three answers.

Water's important to living organisms because it's needed for chemical reactions in cells, it provides support for plants, and it's a habitat in which some organisms live.

So let's now look at the water cycle.

The sun heats the Earth's surface, and the heating of the sun causes evaporation of water from the surface of oceans, rivers, lakes, ponds, and the land.

Evaporation is a physical change.

It happens when a liquid turns into a gas.

So when water's heated, it changes from a liquid to a gas.

And steam is a mixture of water and water vapour, with water vapour being water in its gaseous state.

As the water vapour rises, it cools.

And as it cools, it starts to condense.

And condensation is the process where a gas becomes a liquid.

So as it cools, the water changes from water vapour back to tiny droplets of water, and this is what forms clouds.

Condensation is also a physical change.

It happens when a gas turns into a liquid.

And when warm, moist air comes into contact with cold glass as an example, the water vapour cools down, and it changes from a gas to a liquid.

You may have even done that experiment for yourself.

Breathing on a cold window and seeing the the water vapour that's in your breath cool down quickly and form condensation on windows.

So here's a check.

The process of a liquid changing into a gas is called, A, condensation, B, precipitation, or C, evaporation.

I'll pause for a few seconds and then we'll check your answer.

The correct answer is C, evaporation.

Evaporation is the process of changing a liquid into a gas.

So animals and plants also release some water into the atmosphere via the process of cellular respiration.

Water also passes through plants by a process called transpiration, and we can see in the diagram that that transpiration is releasing water vapour into the air.

This water vapour also cools down and condenses.

Transpiration is the loss of water vapour through the stomata tomato of leaves.

And the stomata are tiny holes that are usually found on the underside of leaves.

You can see two examples labelled in the diagram here.

Time for another check.

What is transpiration? Is it A, how animals lose water when they breathe out, B, the loss of water in plants through the stomata in leaves, or C, the evaporation of water in the environment? I'll pause for a few seconds and then we'll check your answer.

The correct answer is B, transpiration is the loss of water in plants through the stomata in leaves.

Well done if you got that right.

More and more water vapour collects in clouds as more and more evaporation and transpiration take place.

And eventually, the water droplets get too heavy and they fall back down to the ground, and we know that as precipitation.

Precipitation is water droplets that fall from the clouds as either rain, sleet, snow, or hail.

Let's have a look at those water droplets that are within the clouds.

They are really small, but over time, those water droplets moving around in the clouds collide with each other.

And as they collide, they merge, they get bigger.

And eventually, as more and more of those droplets combine, they get so heavy, they fall from the clouds as precipitation.

The water that falls as precipitation runs back through the rivers and returns to the ocean.

Some of the water also percolates into the ground, and that also returns to the oceans.

Some of the groundwater is taken up by the roots of plants, and that eventually is returned back into the atmosphere through that process of transpiration.

So the water cycle provides all organisms with the water that they need before it continues back into the cycle, and that process continues over and over and over again.

So here's a check.

What does the term percolation mean? Does it mean A, water flowing through rivers to the sea, B, water being taken up by plants through their roots, or C, water trickling through gaps in the soil? Again, I'll pause and give you some time to think, and then we'll check your answer.

The correct answer is C.

Percolation is water trickling through gaps in the soil.

Well done if you got that.

That brings us to the first task of this lesson.

The water cycle provides organisms with the water that they need to survive.

I'd like you to look at the diagram of the water cycle.

And first of all, name the processes that take place at each stage that I've labelled on the diagram by A, B, C, and D.

And I'd also like you to describe what happens at each of those stages of the water cycle.

You'll need to pause the video at this point, write down your answers.

And then when you're ready, press play, and we'll check to see how well you've done.

Good luck.

So I asked you to name the processes A to D of the water cycle, and describe what happens at each of those stages.

So let's go through the answers.

Stage A is evaporation.

Heat from the sun changes water, a liquid, into water vapour, a gas, and the water vapour rises.

Now that water vapour can evaporate from the surface of water such as seas, oceans, rivers, lakes, or evaporate from the surface of the ground.

B is condensation.

As the water vapour rises, it cools and it turns back to a liquid, forming clouds.

Stage C is precipitation.

This is where water droplets become too heavy, and they then fall back to Earth as rain, sleet, snow, or hail.

And stage D is transpiration, and that's where plants release water vapour into the air through their stomata.

Well done if you've got all of those answers correct.

That brings us to the second part of today's lesson, which is all about how water availability impacts organisms. So if you're ready, let's move on.

The availability of water in an ecosystem is an abiotic or non-living factor.

And we've already seen today that all organisms need water to survive.

And indeed, some organisms rely on water as their habitat.

Other organisms live in places where water is scarce.

And one example of this is Death Valley in North America.

it's a really harsh environment.

It can reach 49 degrees Celsius in the day, and it only has 40 millimetres or four centimetres of rainfall each year.

And in these places, animals and plants need to have adaptations that help them to survive when water is scarce.

Some animals don't need to drink water.

They get the water that they need just from the food that they eat, and two examples of this are the kangaroo rat and the koala.

Other organisms don't need to drink as often as they might, and this is because fat is stored in some organisms such as the camel in their hump, and that can be used to produce water via metabolic processes, processes from within the cell.

Other organisms are really unique in that they act like sponges, particularly amphibians.

And some toads are able to absorb water when it rains and hold it inside their body like a sponge.

When water's scarce plants show adaptations that help to maximise the uptake in use of water too.

This is particularly seen in the cacti and succulents.

They have adapted stems that helped them to store water.

Cacti have spines that minimise surface area and reduce water loss.

Those spines are modified leaves.

And in the succulents, we see leaves coated with a thick waxy cuticle, and that helps to prevent water loss by evaporation.

The root system of succulents and cacti also help them to take up and take advantage of any water that's around.

Early morning dew can be taken up by these plants through the fine roots that occur just below the surface.

Long deep roots that cacti and succulents have help them to grab moisture from deeper underground.

So let's move to a check.

Which of the following are adaptations that might be seen in plants that live in habitats where water is scarce? Is it, A, roots are long and grow deep underground, B, spines that minimise surface area and reduce water loss, C, leaves are big and trap more sunlight, or D, flowers attract organisms to pollinate them? I'll pause for a few seconds and then we'll check your answers.

The correct answers are A and B.

When plants live in habitats where water is scarce, they might have roots that are long and grow deep underground, and they might also have spines that minimise surface area to reduce water loss.

Well done if you've got both of those answers.

Too much water can also be harmful to organisms. If plants are not adapted to living in waterlogged soil, having too much water can cause them to die, and this is because the water reduces the oxygen available to the roots.

Their leaves turn yellow as they don't get the minerals that they need, and the plants can rot and die.

Climate change impacts the amount of precipitation that there is.

In areas where temperatures have increased, the soil becomes very dry, and winds can then erode the soil.

So here we've got a picture of a dust storm.

Plant roots help to stabilise soil.

And without roots in the soil, rain water can then wash the soil away.

And if the soil is eroded, plants are not able to grow.

Plants, remember, provide food for the rest of the food chain.

And so taking plants away from a habitat will impact many more species of organism.

Climate change also impacts the amount of precipitation there is.

Warmer oceans evaporate water into the atmosphere more quickly, and this very moist air cools quickly over land, and it can produce really intense precipitation which can cause floods, and flood water can destroy habitats.

Here's our final check for today.

True or false.

A plant can have too much water.

Is that true or false? And when you've decided you answer, why? Is it A, because if plants are not adapted to living in waterlogged soil, having too much water can cause them to die, or B, increased volumes of water will increase the rate of photosynthesis and cause plants to become healthier? What's the right answer? I'll pause for a few seconds and then we'll check.

So I asked you, can a plant ever have too much water? The answer to that is false, and the reason for that is if a plant is not adapted to living in waterlogged soil, having too much water can cause them to die.

Well done if you got that.

We move on to our final task of the lesson.

I'd like you to write a paragraph to explain the importance of water to living organisms. Include some adaptations that might be found in organisms that help them to survive when water's scarce.

You'll need to pause the video, then write your answer.

And then when you're ready, press play, and we'll check to see how well you've done.

Good luck.

I asked you to write a paragraph to explain the importance of water to living organisms, and I also asked you to include some adaptations that you might find in named organisms that help plants and animals to survive when water's scarce.

So you might have included that water's important for chemical reactions in cells because water acts as a solvent, for keeping cells hydrated, that it provides moist surfaces for diffusion of gases to take place.

It's important in transporting materials around organisms, and it provides structural support for plants.

Well done if you got all or some of those answers.

I then asked you to give me some adaptations that you might find.

Some of the things that you might have considered are that some amphibians absorb water and store it in their bodies.

Some animals such as koalas get the water they need from their food.

Plants such as succulents and cacti are able to store water in their leaves and stems, and that plants like these have fine roots at the surface to collect the dew and deep roots that collect water from well below the surface.

Well done if you've got those or any other answers correct.

That brings us to the summary of today's lesson, and we've seen in the water cycle how water is cycled from the surface of the Earth to the atmosphere in a continual process.

It starts with the sun's heat causing evaporation of water from the oceans and the surface of the Earth, and is also contributed to by water vapour passing through the leaves of plants and into the atmosphere through a process called transpiration.

As the water vapour, the gas, rises, it cools and turns back into a liquid.

This is called condensation, and it's the process that enables clouds to form.

Water droplets in the clouds combine.

And eventually, when they get too heavy, they fallback to Earth as precipitation.

We've also seen that water is vital for life, and water availability is an important abiotic factor which determines which species can survive in a habitat.

I hope you've enjoyed today's lesson.

It's been great, as always, learning with you, and I look forward to seeing you again soon.

Take care.

Bye-bye for now.