Lesson video

Welcome to today's lesson.

I'm Mr. Jarvis, and I'm gonna be taking you through the lesson today, which is in the unit, living organisms and their environments.

Today's lesson is all about the role of microorganisms in decomposition.

By the end of today's lesson, you should be able to explain the role of microorganisms and detritus feeders in decomposition.

There are five key words to today's lesson.

They are decomposer, detritus, microorganism, decay, and enzyme.

The definitions of those words are up on the screen now, but you can pause the video if you want to have a read through them.

I will be talking you through the definitions as we get to them in the lesson.

Today's lesson is broken down into two parts.

First of all, we're going to look at the decay cycle, and then we're gonna move on to look at useful products from decomposition and decay.

So if you're ready, let's get started with our first section, which is all about the decay cycle.

All living things need food to survive, and producers provide the food for all organisms within a food chain diagram.

Photosynthesis is the process that plants use.

They are producers to make carbohydrates or sugars.

Plants also, however, need nitrates and other minerals to help them stay healthy, and they get these from the soil, they absorb them through their roots.

Living things are made up of mainly carbon, hydrogen, or oxygen and nitrogen atoms, and these elements are limited in the environment, so they have to be recycled, otherwise they'd run out.

They're recycled by organisms, which we call decomposers.

And these feed on detritus, which is the remains of other living organisms. There are three main types of decomposer.

We have bacteria and fungi.

They're both examples of microorganisms. And a microorganism is an organism that can only be seen by using a microscope.

We also have detritivores or detritus feeders, and these include larger organisms such as maggots, worms, woodlice, and beetles, and they feed on dead and decaying organisms and their waste.

The decomposition of biological materials such as waste products and dead organisms ensures that all of the elements that living things need are recycled.

And the recycling process is what's known as the decay cycle.

Decay is the breakdown, or sometimes we call it rotting of organic matter by bacteria, fungi, and other organisms. And here you can see some apples that are on the ground that are decaying or decomposing.

So here's a check.

A decomposer is A, an organism that feeds on other living organisms. B, an organism that feeds onto the remains of living organisms, or C, an organism that is able to make its own food.

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

The correct answer here is B.

A decomposer is an organism that feeds on the remains of living organisms. Well done if you got that right.

Let's look at the decay cycle.

Plants make food for all other organisms within a food chain, and that includes the decomposers.

They do this by using the carbon as carbon dioxide in the air via the process of photosynthesis.

And here you can see the carbon dioxide in the air going into plants that produces via that process of photosynthesis.

The photosynthesis produces carbohydrates or sugars, and they're the plant's food, and the food is used for plants to grow and reproduce.

Plants are eaten by consumers.

Here we've got an arrow that shows that the producers are being consumed or eaten by consumers, and the animals are eaten by other animals.

Consumers use the food that they eat to grow and reproduce too.

Here's a check.

How is carbon dioxide taken out of the atmosphere? Is it A, by respiration, B, by photosynthesis, or C by animals consuming food? I'll pause for a few seconds and then we'll check your answer.

The correct answer is B.

Carbon dioxide is removed from the atmosphere via the process of photosynthesis.

Well done if you got that.

Not all molecules that are eaten are used.

Some are excreted as faeces and urine, and they go into the ground.

All organisms die.

And when this happens, the molecules such as carbohydrates remain in the organism.

They're broken down by decomposers and detritus feeders.

There's also useful molecules in the faeces and urine, and they're broken down by the detritivores and decomposers too.

Detritivores eat the detritus.

They produce waste of their own, and that's broken down as well.

And decomposers, such as bacteria and fungi decompose the organic molecules using enzymes.

Enzymes are biological catalysts.

They help to speed up reactions and in decay microorganisms secrete these enzymes onto the organic material to help break it down and digest it quickly.

They then absorb the products that they need as food.

So for example, the carbohydrates are broken down by the enzymes into sugars, and the sugars are absorbed by the microorganisms. That helps them to grow and to reproduce.

Here's an example of a microorganism that's involved in decay, but also in supporting another organism.

Leaf cutter ants go out actively cutting pieces of leaf and taking it back to their nest.

Within the nest, they use a fungus and they plant the pieces of leaf into their fungus garden.

The fungus breaks down the leaf into smaller molecules, and they're used by the fungus to grow, but they're also used by the ant as food.

So here's a check.

What are enzymes? Are they A, biological catalysts that help to speed up a reaction? B, biological catalysts that help to slow down a reaction? C, they're molecules such as carbohydrates that living things use as food, or D, there are waste product of reactions.

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

The correct answer here is A, enzymes are biological catalysts that help to speed up a reaction.

Well done if you got that one right.

Not all organic matter is used by decomposers.

Some mineral ions, such as nitrates, are released back into the soil, and those minerals are used by plants for healthy growth.

The plants take those up through their roots and use them to help them to make things like proteins.

All organisms respire, and that releases carbon molecules back into the air as carbon dioxide.

And the plants then use this to photosynthesize and the cycle begins again.

Here's a check, true or false.

Decomposers, such as bacteria and fungi release carbon dioxide into the air as they respire.

Is that true or false? And then justify your answer.

Is it A, all living organisms respire, and carbon dioxide is released as a product of respiration? Decomposers are living organisms, or is it B, that decomposers do not need to respire as they feed on dead organisms and waste materials? I'll pause for a few seconds and then we'll check to see whether you got the answer right.

The correct answer here is that it's true, decomposers, such as bacteria and fungi do release carbon dioxide into the air as they respire.

And the reason for this is A, all living organisms respire, carbon dioxide is released as a product of respiration and decomposers are living organisms. Well done if you've got those right.

Let's move on to a task.

The diagram shows a summary of the decay cycle.

I'd like you to describe and name the processes A, B, and C in the diagram, and then I'd like you to explain what's happening at D in the diagram.

You'll need to pause the video at this point, write down your answer, and then when you're ready, press play and we'll see how well you've done.

Good luck.

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

First of all, you are asked to describe and name the processes A, B, and C.

So A is photosynthesis and a description of what's happening there is carbon from the carbon dioxide in the air is made into carbohydrates or food by plants or producers.

B is the process that we know as respiration.

That's when carbon dioxide or carbon is returned to the air as organisms use the process to provide energy for life processes.

And C is death and decay.

Decomposers break down detritus for food, and in doing this, they clean the environment and the elements are recycled.

Well done if you got those.

I also asked you to explain what was happening at D.

So at D, the decomposers are returning or recycling minerals such as nitrates to the soil, and they're then taken up by the plant roots and used for healthy growth.

Well done if you got that too.

That brings us to the second part of today's lesson, which is all about useful products from decomposition and decay.

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

Decomposition, the breakdown of dead organisms and their waste is essential in the cycling of elements, and decomposers can be used to help human activities.

Here are a couple of examples.

First of all, gardeners and farmers use the process of decomposition to improve the soil by using compost and manure and biogas, which is a fuel can be made by using crops or animal waste.

As we've seen, gardeners and farmers improve the quality of soil by adding compost or manure.

Compost is made from dead plant material.

For example, grass cuttings, kitchen waste, and garden waste can all make compost.

Manure is made from the waste of animals, and farmers are often seen spreading manure on their fields.

Decomposers break down organic material.

Detritivores, such as maggots and worms start the decomposition process.

Then bacteria and fungi takeover, they break down everything including the waste of the detritivores.

Some mineral ions that are within the organic material are released back into the soil and the mineral ions that are released by decay act as organic fertiliser.

Nitrates in particular are important for healthy plant growth, and that's because they're used to make proteins which are important for growth and repair.

And when plants have a good supply of nitrates, they produce higher crop yields for gardeners and farmers and organic fertilisers are really helpful because they don't harm the environment.

And so here we've got a developing cucumber crop.

The higher the nitrates in the soil, the more likely there's a going to be a good crop of cucumbers.

Here's a check.

Which of the following statements about compost are correct? A, compost is made of dead plant material.

B, compost is a mix of animal waste and dead plants or C, compost is used to improve the quality of the soil.

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

The correct answers here are A and C.

Compost is made of dead plant material and it's used to improve the quality of the soil.

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

Sometimes decomposition can take place in the absence of oxygen and when microorganisms, such as bacteria and fungi, break down organic matter in the absence of oxygen, we call it anaerobic digestion.

Anaerobic means in the absence of oxygen.

The products of anaerobic digestion are methane and carbon dioxide.

Methane and carbon dioxide are both greenhouse gases, which can impact climate change.

Manure, sewage, household waste, and crops can be decomposed by anaerobic digestion by microorganisms, and that process produces something called biogas, and biogas is made up of mainly methane.

Biogas is a flammable gas.

It can be used for heating, cooking, generating electricity, or as a fuel for vehicles.

Methane is a flammable gas, and so it needs to be present in high concentrations in biogas because carbon dioxide is not flammable.

Biogas is what we call a renewable fuel.

It means that it's produced by using natural sources that won't run out.

Biogas generators are large containers in which animal waste or plant crops such as maize are digested and aerobically.

Remember, aerobic means in the absence of oxygen.

Let's look at how biogas generators work.

Carbon from the atmosphere is used by plants producers to make their own food, and they do this via the process of photosynthesis.

The carbon is trapped inside the plant via this process.

Some of the crop are eaten by consumers such as the cow and the cow and other consumers produce waste.

That waste or the crop, maize, is harvested and put into the biogas generator.

This is shown on the screen.

Anaerobic decomposition then takes place and this forms methane gas.

That methane is burned and combustion and the carbon dioxide that's produced within the biogas is released back into the atmosphere, and this can then be used by plants to photosynthesize.

Here's a picture of a biogas generator in the UK.

You can see the big containers that are used to store the material, which is decomposed anaerobically, and on the right hand side of the picture we have a chimney, which is where the methane is burned and carbon dioxide is released back into the atmosphere.

Let's move on to a check.

Which two gases are made during biogas production.

Is it A, nitrogen, B, carbon dioxide, C methane, or D oxygen? I'll pause for a few seconds and we'll check your answer.

The answer to this question is B and C.

The two gases that are produced during biogas production are carbon dioxide and methane.

Well done if you've got those.

Here's another check.

What flammable gas is produced during the production of biogas? Is it A, nitrogen, B, carbon dioxide, C, methane, or D oxygen? Again, I'll pause for a few seconds.

The correct answer here is methane, C.

Methane is the flammable gas that's produced during biogas production.

Here's our final check.

What type of digestion is needed for the production of biogas? Is it A, aerobic B, anaerobic or C, either aerobic or anaerobic? Again, I'll pause for a few seconds and then we'll check your answer.

The correct answer here is B, anaerobic.

Well done if you've got that one right too.

Let's move to our final practise task of the lesson.

Lucas is organising a gardening club for other pupils at the school.

The areas that have been identified in the school grounds don't look like they'll be very good for growing crops, as even the grass is not growing well, and you can see the area of ground that Lucas is working in in the picture on the screen.

I'd like you to write a paragraph to state what Lucas could do to improve the soil and explain why this will help his crops to grow well.

You'll need to pause the video, write down the paragraph that explains what Lucas could do to improve the soil and how it will help the crops to grow well, and then when you're ready to check your answer, press play and we'll see how well you've done.

Good luck.

So you are asked to write a paragraph to explain what Lucas could do to improve the soil and explain why it will help his crops to grow well.

Your answer might have included some of the following.

When digging the ground, add some compost or manure to the soil.

Decomposers will break down that organic matter and release mineral ions such as nitrates into the soil.

The plant roots can then take up the minerals and the plant can make molecules like proteins, which are important for growth and repair, and when the soils have had the nutrients that plants need, the plants will produce more fruits or flowers.

Well done if you've got all or some of those answers within your own paragraph.

That brings us to the summary of today's lesson.

We've seen that microorganisms, that's organisms that can only be seen by using a microscope and detritivores play an important role as decomposers within an ecosystem.

Decomposers feed and break down detritus, that's dead organisms and waste.

For example, faeces.

We've seen that those microorganisms, the bacteria and fungi secrete enzymes that digest the detritus into smaller molecules, which they can then absorb as food and as decomposers break down detritus, we call the process decay.

Decomposers keep ecosystems clean and recycle important elements, and humans use the process of decomposition to improve soils by adding compost and manure that improve yields of crops.

They also create biogas by decomposing organic matter in anaerobic.

That's without oxygen conditions.

Thanks for your time and for your learning with me today.

I hope you've enjoyed this lesson and I look forward to seeing you all again sometime soon.

Bye-Bye for now.