Welcome to lesson number seven in the unit ecosystems. This lesson is all about using chemicals in farming.

My name's Mr. Jarvis, and I'm going to be teaching you today.

By the end of today's lesson, you should be able to describe and explain the benefits and drawbacks of using chemicals such as fertilisers and pesticides in farming.

There are five key words to today's lesson.

They are fertiliser, organic, pesticide, herbicide, and insecticide.

On the screen now, the meanings of those words.

Have a quick look at them, but don't worry too much.

We're gonna cover the the words during the lesson today, but if you want to read through them in more detail, just pause the video and then move on when you're ready.

So today's lesson is built into three parts.

First of all, we're going to look at the use of fertilisers.

Then we're going to look at how farmers grow more food.

And finally, we're going to look at the impact of using chemicals in farming on other organisms. So if you're ready, let's get started with our first section to today's lesson, and that's all about using fertilisers.

So food chains and food webs always start with a producer and producers make their own food, and they do this using the light and chemicals for my surroundings.

Producers provide all of the food for the rest of the food web.

Consumers, including humans, rely on producers for the food that we eat.

And you can see in the food web diagram on the screen that the human, the chicken, the fox, the mouse, and the cat all rely on the wheat plant for food.

Humans grow crops to provide food for the population, and plants use chemicals from their surroundings to grow bigger by making new biomass, biological mass.

Many of the chemicals that plants use come from the soil.

And one of the most important chemicals that plants need are called nitrates.

Plants take the nitrates from the soil using their roots.

And you can see in the diagram on the slide.

The roots of the producer going down into the soil in search of water and in search of nutrients such as nitrates.

They use those nitrates to make proteins and that helps the plants to be healthy and grow lots of fruit and flowers.

Farmers want to make sure that their crops are healthy and that they produce lots of fruits and flowers.

And that's because farmers want to sell their crops.

They want to feed their animals, and they want to feed the human population.

And so to make sure that the plants are healthy, they give them the chemicals that they need, which includes nitrates to grow well.

And to do this, they add fertilisers to the soil and you can see a farmer adding fertiliser to the soil in the picture on the screen.

Fertilisers contain all of the minerals that plants need to grow well.

Farmers use two types of fertiliser.

They use man-made fertilisers such as the the balls of white chemical that are seen in the top picture on the screen, and they use natural fertiliser, such as manure, and that's in the bottom part of the screen.

Organic farmers only use natural fertilisers and organic products are things that come from living things.

So let's check to see how well you've understood that first section.

Why do farmers use fertilisers on their crops? Is it A, to make sure that plants get the light that they need to produce the food? Is it B, to make sure that the plants are healthy and produce lots of food? Or is it C, to make sure that the producers make their own food? I'll give you five seconds.

The answer to the question is B, farmers use fertilisers on their crops to make sure that plants are healthy and produce lots of food.

Well done if you got that one right.

Let's move to a practise task.

A gardener adds organic fertiliser to soil in their rose garden.

I'd like you to write a paragraph to explain what organic fertiliser is and why the gardener is putting it on their roses.

You'll need to pause the video at this point so that you can write down your answer.

When you've got that done, press play and we'll check to see how well you've done.

Good luck.

Let's check to see how well you've done.

So the gardener was adding organic fertiliser to the soil in their rose garden, and you were asked to write a paragraph to explain what organic fertiliser is and why the gardener is putting it on their roses.

Well, the fertiliser is something that adds minerals to help plants work grow well, and an organic fertiliser comes from living material.

For example, manure.

The gardener adds the fertiliser to provide the plants.

That's the roses with the minerals that they need to grow healthily and to produce lots of flowers.

So the gardener's hoping that by adding this organic fertiliser to their soil, that their rose garden will be in great colour and great bloom in the summer months.

Well done if you've got those answers correct.

We're now going to move into the second part of today's lesson, which is all about growing more food.

So if you're ready, let's move on.

Farmers grow crops and crops are grown for food and to make things like biofuels, paper and textiles.

So here's a picture of a farmer growing a crop of wheat, which helps to feed the human population and animals that are farmed.

Here is a picture of a bamboo forest and it's a crop that can be used to help make paper.

When farmers are growing crops, they want to grow as much of the crop as possible and do it as cheaply as possible.

When there's lots of food for an organism to eat, we know that the population normally increases in size.

So farmers don't want organisms to eat or damage their crops.

An organism that eats or attacks a crop is called a pest.

And here's a picture of a pest.

It's a caterpillar eating a cabbage leaf.

Farmers kill pests using chemicals, which are called pesticides.

There are different types of organisms that are pests.

Some pests are producers or plants.

We sometimes call those weeds and weeds compete with the crop plant for water for minerals such as nitrates from the soil and for light.

Farmers therefore want to kill the weeds, and they do this using pesticides.

Pesticides that kill producers or plants are called herbicides.

And you may have heard of a different word for herbicide, and that's weeded killer.

So pesticides that kill plants are called herbicides.

And herbicides are what we know as weed killers.

Many herbicides are selective.

And by selective, we mean that it only kills some types of plant.

So for example, some herbicides kill plants with broad leaves like the poppies in this field of wheat, but they don't affect narrow leaved crop plants such as the wheat.

So a farmer can spray the crop with a herbicide and the herbicide will kill the poppies, but not the wheat.

Some pests are consumers, they eat the crops and reduce the amount that farmers can grow.

And insects are really common pests that eat crops.

Farmers kill insects using pesticides.

And pesticides that kill insects are known as insecticides.

Some insecticides are selective too, and they kill some types of insects, but not others.

But some insecticides kill all insects, including those that pollinate the crops.

So let's check to see how well you've understood that section.

True or false.

Farmers use herbicides to kill pests that kill crops.

Is that true or false? And then what I'd like you to do is to justify your answer.

Is it because herbicides used to kill plants can be selective, or insects eat plants and they're killed by insecticides? I'll give you a few seconds to think about that.

You can pause the video if you want to, and then when you're ready, we'll check your answer.

How was that? Let's see how well you did.

Farmers use herbicides to kill pests that eat crops.

That's false.

And the reason for that is that insects eat plants and they're killed by insecticides.

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

So now it's time for a practise task.

I'd like you to write a paragraph to explain why a farmer might need to use a selective herbicide on a young crop of wheat in a field.

You'll need to pause the video, write down your answer, and when you've finished, press play on the video and we'll check to see how well you've done.

Good luck.

How did you find that? I hope it wasn't too difficult.

You are asked to write a paragraph to explain why a farmer might need to use a selective herbicide on a young crop of wheat in a field.

Here are some of the things that you might have written.

First of all, the weeds compete with the crop plants for light water and minerals such as nitrates.

If those weeds are allowed to grow, the weeds will reduce the amount of crop that's produced.

And so a selective herbicide will kill plants, for example, those with broad leaves and leave the crop plant, for example, the crop has a narrow leaf unharmed, and that means that the farmers maximising the crop that he's growing.

Well done if you got that right.

So now we're going to move into the final part of the lesson today, and that's all about the impact on other organisms. So if you're ready, let's go.

Farming can impact environments in many ways.

And over the next few slides we're going to look at some examples.

Here's the first one.

If farmers use too much fertiliser, it can get washed into rivers and lakes.

Rivers and lakes contain producers.

They're able to grow because light passes through water as you can see in the picture of the the right hand side of the screen.

However, fertiliser causes microorganisms called algae to grow really quickly.

The algae benefit from the nutrients that are in the fertiliser.

As the algae grow, they form a blanket which blocks out the light, and the producers that use the light to make their own food won't have any light to to make food with, and so they will die.

If the algae block out light that causes the producers to die, then the producers won't release oxygen into the water because they won't be photosynthesizing.

And that means that the oxygen levels of water decrease and all living organisms need oxygen to survive.

So if we reduce the oxygen levels in the water, then other organisms such as fish can die to.

Another way that farming can impact the environment is the use of insecticide.

Some insecticides can kill the helpful insects that usually eat pests or that pollinate crops.

Some insecticides are also really long lasting.

They stay in the environment for a long time, and this can poison other organisms. If insecticides are used carelessly, they can reduce the crops that farmers grow.

And this is because the fruits and seeds won't develop if plants have been not been pollinated.

So for example, the picture of lots of bees that have been killed, those bees are not around in the environment to pollinate the crops, and so plants won't be able to form their fruits and seeds.

Another way that farming can impact environments is through the use of herbicides.

Many herbicides kill specific types of plant.

For example, those with broad leaves.

Wheat in a field isn't affected by the herbicide as the wheat has a narrow leaf.

But plants that grow in hedges or borders around a field may also be killed if the herbicide drifts in the wind.

So you can see in the picture we've got a field of wheat.

And yes, there are some poppies and corn flowers that are growing in the border of the wheat, but if a farmer sprays a herbicide on the edge of that field, it's likely that those corn flowers, the blue plants, and the poppies, the red plants will also die.

So it's time for a check.

I'd like you to match how the different chemicals can impact other organisms and the environment.

The different chemicals that we have are too much use of fertilisers, use of herbicides and use of insecticides.

The impacts on other organisms and the environment are that they cause some helpful insects, which pollinate plants, to be killed.

They cause some wild flower plants that provide a habitat for insects to die, and they cause them to get washed into the ponds and rivers.

Algae grow quickly and block out light causing reduced oxygen levels and fish To die.

You're going to need to pause the video while you match the different chemical with the impact on the organisms and their environment.

When you're ready, then press play and we'll check your answers.

Good luck.

Let's check to see how well you did.

So too much use of fertilisers cause them to get washed into ponds and rivers.

Algae grow quickly and block out light causing reduced oxygen levels and fish to die.

The use of herbicides cause some wild flower plants that provide a habitat for insects to die.

And finally, the use of insecticides cause some helpful insects which pollinate plants to be killed.

Well done if you got those three right.

Here's our final practise for today.

The class know that bees and other insects are important in farming as they pollinate crops.

They give their views about how using herbicides to kill weeds in crops may impact the insect population in the habitat.

I'd like you to write a paragraph to explain who you agree with from the class and why you agree with them.

Here's what they say.

Alex says, "Herbicides can kill the insects and stop them from pollinating the crops." Sofia says, "Herbicides can kill plants that provide bees with food and shelter.

This means that the bees may die." And Lucas says, "Herbicides don't have an impact on insects as herbicides kill weeds or plants are not bees." So you need to write your paragraph to explain who you agree with and why you agree with them.

Pause the video at this point and then when you've written your paragraph and your explanation, press play and we'll check to see who was right in the class and why.

Good luck with that.

How did you get on? I hope you didn't find it too tricky.

Sofia gave the right answer.

Sofia said that herbicides can kill plants that provide bees with food and shelter, and this means that the bees may die.

Well done if you chose Sofia.

But here's the reason why Sofia is right.

First of all, herbicides are pesticides that kill plants or weeds.

The herbicides don't harm crop plants but will kill other types of plants.

When a farmer sprays a crop, plants in and around the field die.

Many of these plants provide the habitat for insects like bees to live.

And remember, a habitat provides food, a place to live, the shelter and a place to reproduce.

And without food, shelter and a place to reproduce, the insects may not be able to survive and the population may decrease.

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

So that brings us to the final part of today's lesson, which is the summary of what we've learned today.

We've seen that farmers use fertilisers to provide plants with chemicals that help them to grow and produce good crops.

We've seen that those fertilisers can be man-made chemicals or organic.

And remember, organic fertilisers come from living things.

So things like manure.

We've seen that pests are organisms which eat crops and prevent them from growing well.

Farmers use pesticides to kill pests, and there are different types of pesticide that we've looked at.

Pesticides that kill plants are called herbicides and pesticides that kill insects are called insecticides.

And finally, we've seen that fertilisers and pesticides can be harmful to the environment and wildlife, particularly if they're not used well.

So I hope that you've enjoyed today's lesson.

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

Bye for now.