Lesson video

Hello and welcome to today's lesson.

I'm Mr. Jarvis, and I'm gonna be taking you through the lesson today.

This lesson is all about factors affecting the rate of decomposition, and it forms part of the unit on living organisms and their environments.

By the end of today's lesson, you should be able to explain why some factors affect the rate of decomposition by microorganisms. There are five key words to today's lesson.

They are decomposer, microorganism, enzyme, rate, and aerobic.

The definitions of those words are all on the screen now.

You can pause the video if you want some time to read through those definitions, but don't worry because we will go through the definitions As we progress through the lesson.

Today's lesson is broken down into two parts.

First of all, we're going to look at microorganisms and the process of decomposition, and then we'll move on to factors that affect the rate of decomposition.

So if you're ready, let's get started with our first section, which is all about microorganisms and decomposition.

Living organisms use materials from the environment to help them carry out life processes such as growth.

And an example of this is plants taking up mineral ions, for example, nitrates from the soil to help them to make proteins.

The materials within organisms are passed to animals along the food chain as they consume other organisms. The materials need to be recycled for life to continue to exist because there's a finite resource on the planet.

This recycling is carried out by a group of organisms called decomposers.

And decomposers are organisms that break down waste and dead organisms. They return the elements, for example, carbon and nitrogen back into their surroundings, and these can then be reused by other organisms. Most decomposers, but not all, are microorganisms. And a microorganism is an organism that can only be seen by using a microscope.

And examples of microorganisms are typically bacteria and fungi.

These microorganisms are the things that are responsible for recycling important elements by the process of decomposition.

Decomposers such as bacteria and fungi break down organic matter, that's living matter, to use for their food.

And these microorganisms secrete or release enzymes onto the organic matter to help break down that food.

Remember, enzymes are biological catalysts that speed up reactions, which include the reactions of decomposition.

So here's a graph to show you the rate of a reaction.

With an enzyme, it's much faster.

It takes much less time for the reaction to take place than it does without the enzyme.

So here's a check.

What are enzymes? Are they A, molecules that speed up a reaction? B, molecules that slow down a reaction? Or C, examples of chemical reactions? I'll pause for a few seconds and then we'll check to see what the right answer is.

The correct answer to this question is A, an enzyme is a molecule that speeds up a reaction.

Well done if you got that.

Enzymes only get involved in specific reactions.

The substrate, which is the substance that's acted upon by the enzyme, must collide at the enzyme's active site for a reaction to occur.

Here's a diagram to show this.

We can see the substrate, the substance that's being acted upon by the enzyme, has to collide with the active site, and that's a special site on the surface of the enzyme that allows the reaction to take place.

So if the collision of the substrate is with the active site, the enzyme then breaks down that substrate into what we call products of the reaction.

And you can see that the bigger substrate in this reaction has been broken down into two smaller parts.

If the substrate doesn't collide with the active site, then no reaction occurs.

So the reaction can only take place when the substrate collides with the active site as shown in these two diagrams on the screen.

Enzymes are essential for many life processes.

In digestion, large molecules such as carbohydrates are broken down by enzymes into smaller molecules.

For example, sugars.

They can then be used to provide energy for life processes.

In humans, digestion takes place using enzymes and it breaks down large carbohydrates into small sugars.

This is really important because the large carbohydrates are too big to be absorbed and used by our bodies.

They have to be broken down into smaller molecules that can pass into our bodies and be used to provide that energy for the life processes that we undertake.

So again, here's another example using the diagram.

We've got a carbohydrate, a large molecule.

It's going to collide with the active site.

And when it collides with the active site, the enzyme breaks down the carbohydrate and breaks it into smaller molecules of sugar.

Enzymes are specific, they only catalyse, that's speed up, one type of reaction.

Common enzymes that are used by microorganisms to decompose or decay or digest organic matter are as follows.

Carbohydrates are broken down into sugars by carbohydrases.

Proteins are broken down into amino acids by proteases, and lipids or fats are broken down into fatty acids and glycerol by enzymes called lipases.

You'll notice that many enzymes names end in, "ASE".

If you hear a sound and a molecule that ends in ase, the likelihood is is that it's an enzyme.

Microorganisms secrete enzymes from their cells onto the organic matter, and the enzymes then break down the larger molecules into smaller ones, and the small molecules can then be absorbed by the microorganisms and used for their food.

So here's an example.

We've got a picture of some bread and some fungi and bacteria secreting enzymes onto that bread to decompose it and allow them to grow by absorbing the sugars from the bread.

And as that process continues, the organic matter starts to decay or decompose.

Here's a check.

Bread contains lots of carbohydrates.

Which type of enzyme might a microorganism secrete to decompose the carbohydrate in the bread? Would it be A, carbohydrase? B, protease? C, lipase? Or D, all of the enzymes will break down the carbohydrate? I'll pause for five seconds and then we'll check to see which one is the right answer.

So the right answer to this question is carbohydrase.

Carbohydrases break down carbohydrates.

Well done if got that.

Gonna move now to our first task of the lesson, and it's broken down into three sections.

First of all, I'd like you to write down two types of organism that can cause decay or decomposition.

Then I'd like you to explain how decomposers use enzymes to break down the organic matter on which they feed.

And finally, I'd like you to draw me an enzyme.

I'd like you to label the active site, and I'd like you to draw a substrate molecule that fits into that active site.

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 how did you get on with that? First of all, I asked you to name two types of organism that cause decay or decomposition.

The answers you should have written down are bacteria and fungi.

Secondly, I asked you to explain how decomposers use enzymes to break down the organic material on which they feed.

At this time, you should have said that the decomposers secrete enzymes onto the organic material, and the enzymes break down, or decompose, the organic material into smaller molecules.

And examples include carbohydrates to sugars, proteins to fatty acids and lipids or fats to fatty acids and glycerol.

Microorganisms can then absorb these small molecules as food.

Well done if you got that.

And the third part of the task was to draw an enzyme.

I asked you to label the active site and draw a substrate molecule that fits into that active site.

So you should have drawn something like this.

First of all, the enzyme.

The enzyme should have had an area that you labelled as an active site that was a specific shape.

And that shape, whatever it might have been, should have been mirrored by the substrate.

So you can see my substrate is a shape that will fit snugly into that active site just like that.

Well done if you drew something that matched that.

It doesn't matter what shape you used as long as the shape of the substrate matches the shape of the active site.

That brings us to the second part of today's lesson, which is all about factors that affect the rate of decomposition.

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

The rate of decomposition is how quickly the process takes place.

There are three main factors that affect the rate of decomposition, i.

e.

how quickly it takes place.

They are temperature, moisture, and the availability of oxygen.

Temperature affects the rate of a reaction.

At lower temperatures, particles move really slowly and with less energy, and as a result, there's a lower frequency of successful collisions that would take place between the substrate and the active site.

At higher temperatures, particles move much faster and with more energy, and that means that there's a higher frequency, so more chance of a successful collision taking place.

In an enzyme catalysed reaction such as decomposition, there is what we call an optimum temperature.

And this is the temperature when the most successful enzyme substrate collisions happen at the highest frequency.

And at that temperature, all of the active sites are full with substrate molecules.

This causes the rate of the reaction, in this case decomposition, to increase.

So as temperature increases, up until the point that the temperature is at the optimum, the rate of the decomposition gets faster and faster.

However, at temperatures above the optimum, the rate starts to decrease.

And this is because higher temperatures cause the shapes of the enzymes' active sites to change, and that means that the substrate no longer fits in.

So if we look at this diagram here, you can see that the substrate, which is a hexagon type shape, now no longer fits into the active site of the enzyme because the enzyme has been denatured.

It's changed its shape, it's changed the shape of the active site, so even if the substrate collides with the enzyme, it doesn't fit and so no reaction occurs and the rate decreases.

So here's a check.

What happens to the speed of an enzyme catalysed reaction at temperatures above the optimum temperature? And why? Is it A, the reaction slows down because the enzyme dies? Is it B, the reaction speeds up because higher temperatures cause more collisions between enzymes and the substrate? Or is it C, that the reaction slows down because the enzyme is denatured and no longer catalyses the reaction? I'll pause for a few seconds and then we'll see what the right answer is.

Good luck.

The answer to the question is C.

When an enzyme catalyse reaction goes above the optimum temperature, the reaction slows down, and that's because the enzyme's denatured and it's no longer able to catalyse the reaction because the substrate no longer fits into the enzyme's active site.

Well done if you've got that.

Let's look at temperature and decomposition.

At hot temperatures above the optimum, enzymes denature.

And so that means that the rate of decomposition will decrease.

So at very high temperatures, decomposition takes a long time to happen.

At warm temperatures, the rate of decomposition is really high because the enzymes and the substrates move faster and with more energy so more successful enzyme substrate collisions take place.

And at low temperatures, successful enzyme substrate collisions happen at a really low frequency.

They don't happen very often.

So reaction rates are very low and the rate of decomposition will also be very low or will decrease.

So here's a check.

Why does putting food such as meat or vegetables in a fridge help to stop them decomposing? Is it A, the fridge stops all microorganisms from getting to the food to decompose it? Is it B, the fridge is cold and slows down the rate of decomposition? Or is it C, the fridge is dark when the door is closed and this stops decomposition from taking place? I'll pause for a few seconds and then we'll check to see which the right answer is.

The correct answer is B, the fridge is cold, and because the fridge is cold, the rate of decomposition slows down, and that's because there's a lower frequency of enzyme substrate interactions.

So the reaction is really slow to take place.

Well done if you got that.

Let's look at moisture and decomposition.

Water is needed for many life processes to take place, and many microorganisms secrete enzymes onto decaying organic matter.

They then absorb the products of the chemical digestion.

The secretion of enzymes and absorption of products both require water, and I can show this through the pictures on the screen.

At the top of the screen, we've got a lemon, and the lemon you can see is decomposing.

You can see the growth of the microorganisms. Below this, there's a picture of what we call desiccated or dried out lemon.

All of the water has been taken out of the lemon, and that means that decomposition doesn't take place because the secretion of enzymes and absorption of products requires water.

Decomposition of organic matter, so dead plants and animals and waste such as dung, take place more rapidly in damp conditions, and that's shown by the graph on the screen.

You can see as moisture increases, the rate of decomposition increases too.

Here's a check.

Hard tack, or ship's biscuit, was taken to sea by sailors in the 1800s.

It's a hard dry bread that's made from flour, salt, and water.

Why do you think this was taken on long voyages as food for the sailors? Is it A, that the biscuit was a fantastic source of nutrients for sailors? Is it B, that the biscuit did not decompose very quickly because it was so dry? Or C, the biscuit was a tasty treat for sailors? I'll pause for a few seconds and then we'll see what the right answer is.

The correct answer is B, hard tack, or ship's biscuit, was taken to sea because the biscuit didn't decompose.

And so as a result of it being so dry, decomposition didn't happen, and because the sailors were at sea sometimes for months on end, it meant that they had a source of food.

However, it was only made from flour, salt, and water so it wasn't very nutritious for the sailors, and often the sailors had lots of diseases that were caused by deficiency in their diet.

Let's move on to oxygen and decomposition.

Aerobic respiration is the process where oxygen is used to produce the energy needed for life processes.

For example, growth and reproduction.

Many organisms need oxygen to aspire, and in aerobic conditions, i.

e.

when oxygen is present, the rate of decomposition increases as oxygen availability increases.

And again, this is shown by the graph on the screen.

You can see as the oxygen concentration gets larger then the rate of decomposition increases.

Some microorganisms can respire anaerobically, and anaerobic respiration is where respiration takes place in the absence of oxygen.

This results in what we call anaerobic decomposition, or anaerobic decay.

And anaerobic decomposition forms two gases, carbon dioxide and methane.

And humans use this as a process to form something called, "Biogas." And biogas can be used as a source of fuel.

Here's a check.

Humans often store food in sealed cans.

Examples include fish, such as tuna, and legumes, such as baked beans.

How do cans reduce the rate of decomposition? Is it A, because they prevent the temperature of the food from increasing? Is it because there's a limited amount of oxygen available in the cans? Or C, that the cans do not contain any water? I'll pause for a few seconds and then we'll see what the right answer is.

The answer here is B.

By using the cans, there's a limited amount of oxygen that's available in the cans, and that prevents decomposition taking place.

There are often other processes that were involved to make sure that the food is sterile, i.

e.

it doesn't contain any microorganisms, which again helps to preserve it for a longer period of time.

Well done if you've got that answer.

That brings us to our final task of the lesson.

In a sewage works, human waste is broken down by microorganisms. Warm air is blown through the sewage.

Sewage is human waste.

I'd like you to write a short paragraph to explain why warm air is blown through the sewage.

And what I've done is ha given you a diagram to show the setup of what happens in a sewage works and how warm air is blown through the sewage with the microorganisms in place.

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

Good luck.

How did you find that? You were asked to write down a short paragraph to explain why warm air is blown through the sewage.

Here's what you might have written.

The air is blown through the sewage to ensure that conditions, first of all are aerobic, i.

e.

that there's plenty of oxygen available, and this means that decomposition will be faster as the microorganisms will have lots of oxygen supply available to them.

The enzymes that microorganisms use to break down organic matter will also have more energy, so they'll move faster and with more energy.

And this means that there's more successful enzyme substrate collisions and the reaction will occur at a greater rate.

And finally, warm air will help the enzymes to work at their optimum temperature.

Well done if you got that right.

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

We've seen that decomposers play an important role in the recycling of important elements.

For example, nitrates.

Decomposers, such as bacteria and fungi are microorganisms. They can only be seen under a microscope.

Microorganisms decompose organic matter, that's dead animals, dead plants and waste, and they do this using enzymes.

Enzymes are biological catalysts.

The rate or speed of decomposition is affected by three factors, temperature, moisture, and oxygen availability.

Most decomposition occurs by microorganisms that carry out aerobic respiration.

There are some microorganisms that are able to decompose organic material in anaerobic conditions, and we saw that biogas is one product that can be made by humans to help provide a source of fuel.

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

I look forward to seeing you again soon.

Bye bye for now.