GCSE Science podcasts - Ecology

Hello. I’m Dr Alex Lathbridge and this is Bitesize Biology.

This is the first in a series on Ecology. We’re going to be looking at ecosystems, biodiversity and climate change.

You might already be really familiar with some of the topics that we’re covering in this series, which is great, but don’t skip over these episodes.

I’m going to be explaining the science behind all of it and the main key terms you’ll need to pass your exams.

In this episode we’re going to be starting off talking about what an ecosystem is, how organisms interact within them, and we’re going to take a look at quadrats and transects.

Let’s go through some key ecology terms that I’m going to keep mentioning throughout this series, so it’s a good idea to write them down now. Grab a pen:

An Ecosystem is the interaction between a community of living organisms and their environment.

A community is the many populations of different species living in a habitat.

A population is all the members of a single species that live in a habitat.

And finally, a habitat is a place where plants, animals and microorganisms live.

Let’s take a look at how some of the different types of organisms all interact inside an ecosystem.

You might have heard of the term food chain.

Food chains show the feeding relationships between different species in an ecosystem, basically, what an organism eats and what eats them.

A simple food chain would be: grass, which is eaten by rabbits, which are eaten by foxes.

The first thing in a food chain is at the bottom level, and it’s always called a producer.

These are usually plants or algae that produce their own food, using photosynthesis to store energy in the form of glucose using carbon dioxide and water.

Easy to remember: Producers are often plants.

Producers produce biomass, which is the dry mass (meaning weight, but you need to write mass in your exam) of all the living material inside an organism.

The biomass is passed along the food chain from one organism to the next, when organisms eat one another.

All organisms above the producers in the food chain are called consumers.

Generally speaking, plants aren’t eating other plants. Consumers are animals.

The organism that eats the producer is called the primary consumer, then the one that eats that is the secondary consumer, and then you have the tertiary consumer.

The final level of a food chain is called an apex predator, which isn’t eaten by anything else.

So, the order of the food chains is: producer (usually a plant), primary consumer, secondary consumer, tertiary consumer, and so on, with an apex predator at the top.

There are also things known as decomposers, things like bacteria and fungi, which break down dead matter in a process called decomposition or rotting.

They do this by releasing enzymes, that break down the dead matter into simpler molecules for consumption. Plants can then absorb the broken-down nutrients through their roots.

As you can see from food chains, animals that hunt, kill and eat other organisms are called predators and animals that are eaten are called prey.

But in a healthy, balanced ecosystem the population of predators and prey remain constant.

But if the predators or prey increase or decrease in population size they affect one another, so they are linked together in a predator-prey cycle.

If the population size of a prey animal increases, the population size of the predators will increase too, because they can eat more.

But, when the population of the predators increase by a large amount, the prey will start to decrease, because they will have so many more predators eating them.

But then, the prey population decreases, and the predators will start to decrease, as they have less food to eat.

But remember, this isn’t instantaneous. The predator and prey cycle is out of sync, because it takes a while for one to respond to changes in the other and reproduce or decline.

But it’s not just predators and prey that are linked together, lots of different species all depend on one another within an ecosystem, so we call them interdependent.

If one species increases or decreases in a big way, it can affect the whole community.

Often very small changes to ecosystems have far-reaching effects, that you might not think about.

Think back to our original simple food chain: grass eaten by rabbits eaten by foxes.

If all the foxes were killed, the number of rabbits would greatly increase because there are no more foxes to eat them.

But this would also mean that the grass in the ecosystem would decrease rapidly, because of the increased population of rabbits eating it.

In reality, organisms are not in just in one simple food chain, but are instead part of a complex food web with lots of different organisms involved.

Interdependence doesn’t just refer to food. All organisms that live in an ecosystem depend on each other for food, but also protection and shelter in order to survive.

A community where the population size of many different species remains relatively constant over time is called a stable community.

In these communities, the species and environment are in a healthy balance.

Stable communities have existed for a very long time and are not affected by changes.

Examples of stable communities include ancient oak woodlands and rainforests.

So, if population sizes are so important, how do you measure them?

It's impossible to count every single animal within a population.

Instead, scientists look at a small section of a population to draw conclusions about the rest.

There are two tools to do this: quadrats and transects.

This process is called sampling and the small area or part of a population investigated is called a sample. You might have heard the term sample size.

When sampling a population, the numbers of organisms are counted within a sample site, and then the results are multiplied to get an estimate of the total number of organisms within the whole habitat.

Quadrats are square frames of wire placed on the ground used for a few things:

To record the total number of just one species within the quadrat.

To record the number of different plant or animal species, this is known as species richness.

To record the percentage cover, the percentage of the quadrat that is covered by one species.

There are two types of sampling you need to know: random sampling and systematic sampling.

Random sampling involves placing the quadrat at random coordinates within an area. Taking random samples makes a study more valid. Quadrats are placed in random areas and so they use random sampling.

Systematic sampling involves investigating a trend or pattern across a habitat, to find out how organisms are distributed along a distance, like a beach.

Transects are used to do systemic sampling. Transects are lines, created with a tape measure, which sampling can occur on along a distance.

It’s likely you might get a question in your exam about quadrats, transects and sampling, likely it's going to use maths, perhaps working out averages or percentages. If you need some help, check out our episode on Maths skills in Biology.

I’m Dr Alex Lathbridge and this is Bitesize Biology. Subscribe to the series now on BBC Sounds.

Hello. I’m Dr Alex Lathbridge and this is Bitesize Biology.

This is the second episode in a series on Ecology. Today, we’re going to talk about the resources that plants and animals compete for and the adaptations that they’ve developed. I’ll also be looking at abiotic and biotic factors, the non-living and living parts of an ecosystem that can change.

If you haven’t listened to the last episode on the organization of ecosystems, I think you should otherwise there are lots of terms that you might not understand.

But let’s quickly remind ourselves of a few key ecology terms:

A population is all the members of a single species.

A community is two or more populations of different species.

An ecosystem is the interaction between a community of living things and the environment.

Ecosystems are all about competition. Organisms need specific resources from their environment, and there is not an infinite amount for everyone. Grab a pen and write this down:

Plants need light and a regular water supply for photosynthesis to happen, as well as space for healthy growth.

All animals need food.

But animals within the same species also compete for mates. Some deer engage in physical fights locking antlers in order to win mates, also, if you haven’t seen giraffes fighting one another just using their necks it is terrifyingly fascinating. Look it up.

Animals also compete for territory. Territories contain all the resources and conditions they need to survive

So how are animals able to compete like this?

Yes, you’ve guessed it. They’ve developed adaptations that make them better suited to their environment, so they have a higher chance of survival and successfully breeding.

The adaptations that arise from competition are due to the process of evolution that we discussed on previous series.

Adaptations can be structural, behavioural or physiological – let’s start with plants:

In plants, structural adaptations are physical features like spines found on cacti that stop them being eaten or bright flowers which attract insects to pollinate them.

Behavioural adaptations of plants are behaviours which give them an advantage like growing up quickly towards light, to maximise photosynthesis, or plant roots growing downwards to take up more water.

Physiological adaptations of plants are processes like the formation of poisons for defence, found in nettle stings and deadly nightshade.

But what about in animals?

Structural adaptations of animals are physical features such as sharp claws that can catch prey or dig burrows. Predators and prey often have similar adaptations – for instance, both might have good vision and good hearing.

Behavioural adaptations of animals are behaviours such as mating rituals, like a male peacock showing his tail to attract a female. Many bird species migrate to warmer areas in winter times to avoid the cold.

Physiological adaptations of animals are processes like the production of venom in snakes and spiders, which can help them to defend themselves and kill their prey. Or dogs – like my baby boy Ollie – can have amazing sensitivity for detecting movement with their eyes, a trait that is useful for hunting and guarding.

But not all environments are the same.

An organism that lives in an extreme environment is known as an extremophile.

These organisms live in extreme environments such as frozen polar regions, the driest deserts, high pressure in the deep ocean and super-hot thermal vents or volcanoes.

Usually these are microorganisms like bacteria.

Extremophiles have a few highly specialised adaptations that help them to survive in the extreme environments. Very few other organisms would be able to survive in there.

So now we’ve understood what organisms compete over, and the adaptations they’ve developed, the final section of this episode is about abiotic and biotic factors. These are factors within an ecosystem that can affect he abundance and distribution of living organisms

The names sound complicated but honestly, it’s really not. They literally meaning “non-living” and “living.”

Let’s start with abiotic factors, the non-living elements in an ecosystem that change.

You need to be aware of these in case they pop up in your exam, grab a pen so you can write this down:

Light intensity – some plants might need shade, some might prefer bright light.

Temperature - plants and animals might prefer hot or cold areas. Polar bears have evolved to live in the cold North Pole and would not survive elsewhere, like a desert.

Moisture Levels – plants cannot survive in soils that are too waterlogged, as their roots cannot respire.

Soil pH level - different plants prefer acidic or alkaline soils.

Soil minerals – many plants need high levels of minerals in their soil for growth.

Wind intensity and direction affects the distribution of organisms (where they live in a habitat). Many prefer locations that are sheltered away from strong wind.

Carbon dioxide levels affect plants, as they need carbon dioxide for photosynthesis.

Oxygen levels affect aquatic animals (animals that live in water). Oxygen is essential for aquatic animals to survive; they would suffocate otherwise. Polluted waters often have low levels of oxygen.

An increase or decrease in an abiotic factor can have a huge impact on a species population size within a community. Remember, many organisms are interdependent, and so multiple organisms can be affected by a change in abiotic factors.

Just because a rabbit might not care about moisture levels, doesn’t mean the grass they eat is the same way. Remember animals depend on plants for food, so a lower number of a plant species could affect an animal species in a community.

Let’s look at some biotic factors now, these also affect the abundance and distribution of organisms in an ecosystem, but they are living things.

You going to need to know four biotic factors: availability of food, new predators, new pathogens and competition.

Availability of food is a major factor in how many animals live in an ecosystem. Rainforests have lots of varied food sources and so have a wider variety of species living there. Areas like deserts where there is less food have fewer species.

New predators can have a devastating impact on ecosystems. They can upset the balance of predator-prey cycles and cause a big decrease in the numbers of prey, which in turn reduces the food for existing predators, so they’re affected too.

New Pathogens. We talked about pathogens in our series on Infection. When organisms move to new habitats, they often bring with them new pathogens, like viruses that the existing organisms in the habitat aren’t immune to.

Finally let’s not forget competition. We’ve already talked about how many resources plants and animals compete over. The introduction of a new species into an ecosystem can result in it over- competing with an existing species, where the population levels of the existing species become too low to successfully breed and don’t survive.

For example, the Red Squirrel is native to Britain. It has been here for about ten thousand years. But in the 19th century, Grey Squirrels were brought over from America. They’re considered an invasive species. Why?

Red and Grey squirrels eat the same food and live in the same habitats.

Grey Squirrels are larger, can store more fat and survive harsher winters than Red ones.

Grey Squirrels carry a virus called Squirrel pox, that they are immune to, but it can be deadly to Red Squirrels.

So the numbers of Red Squirrels and where they live, reduced dramatically, as they are outcompeted for food by grey ones.

This is why certain countries like Australia are really strict about the things that people can bring into the country from overseas, as changes to the ecosystem could have huge effects.

So organisms can be affected by biotic factors too. Species can decline in numbers if they are outcompeted, or if there’s a new pathogen, or a new predator arriving.

And the same interdependent species are also affected when these things happen. Don’t forget about the knock-on effects.

I’m Dr Alex Lathbridge and this is Bitesize Biology – listen again on BBC Sounds

Hello. I’m Dr Alex Lathbridge and this is Bitesize Biology.

This is the third episode in a series on Ecology and in this episode, we’re going to talk about The Carbon Cycle.

Let’s start this chat with a little bit of philosophy.

There’s a quote I like. It is relevant to this subject I promise.

"You cannot step into the same river twice, for other waters are continually flowing on."

You take that quote lots of ways. To me, it says that things are both the same and not the same over time, even if they appear to be.

Because even if the river looks the same, the water, the dirt, and the life within are constantly in motion under your feet as the seconds pass.

I like this quote because it’s because this quote is about life, philosophically and biologically.

Why? Well, inside of you right now, there are about 7 billion billion billion atoms.

And about 99% of you is made of just six elements: oxygen, hydrogen, calcium, nitrogen, phosphorus, and carbon.

Those atoms were around long before you were born and will be around long after you go.

You do not own them. You, well, your cells, are merely a temporary vessel for atoms that have been in deep oceans, mighty volcanoes, part of other organisms, and yes, even part of other humans.

They are constantly recycled again and again and again, moving in and out of you as you breathe, eat, touch, sleep, cry, go to the bathroom, and generally live your day-to-day life.

Just like that, materials in our environment are constantly being recycled, changing to produce the key building blocks that make new organisms.

There's always enough material to make new organisms when old organisms die.

Living things are made up of materials they take from their environment, and then these materials are recycled back to the environment when they die.

Plants use oxygen, carbon, hydrogen from the soil and air and convert them into biomass, that is passed along the food chain.

These same materials are then recycled back to the environment as waste and when organisms die.

Decomposers, like bacteria and fungi, break down dead matter. Minerals and nutrients released from this dead matter are recycled back into the environment within the soil, which can then be used by other plants to help them grow and start that cycle again.

So, with all of that in mind, let’s focus on what we’re going to chat about today: how carbon moves between different parts of the environment, the carbon cycle, so grab a pen and write this down.

Carbon is an essential element for life and is used by plants and animals for important processes.

Carbon is constantly cycled between the environment and organisms.

Atoms of carbon can exist as part of different compounds at different points of the carbon cycle.

So, you need to know four stages of the carbon cycle and the processes that happen at each stage:

It might help you to draw this out so you have a little diagram, or you could look at the bitesize website while you listen. And remember you can always pause this podcast if that helps while you make any notes.

It’s a cycle, so you can start anywhere, but to make it easier, I’m going to start with carbon dioxide.

Stage One. Carbon enters the atmosphere as carbon dioxide.

This happens through respiration of animals, algae, plants, and microorganisms.

Combustion is the process of burning wood and fossil fuels and it also releases carbon dioxide into the atmosphere. (It’s important to remember what fossil fuels are made of: decayed animals and plants.)

Stage Two. Carbon in the form of carbon dioxide, is taken out of the atmosphere.

This happens via photosynthesis, where green plants and algae absorb it from the air, and that carbon gets converted into glucose.

Stage Three. Carbon moves through the food chain.

Animals feed on these plants, passing the carbon compounds along the food chain. The carbon becomes part of the fats and proteins of animals when plants are eaten.

Most of the carbon they consume is exhaled as carbon dioxide during respiration. The animals and plants in these food chains eventually die.

Stage Four. Carbon returns to the atmosphere through decomposition.

Dead organisms are broken down by decomposers, and the carbon in their bodies is returned to the atmosphere as carbon dioxide when they respire.

Ok that’s important so a quick recap:

1. Carbon enters the atmosphere by respiration and combustion.

2. It is taken out of the atmosphere by photosynthesis.

3. It moves along food chains and then decomposition of dead animals and plants, means carbon is

taken in by decomposers.

4. Carbon will then be respired out into the atmosphere again as carbon dioxide.

If you want to look at it from a different angle, let’s break the cycle down into the processes involved and what happens to the carbon at each stage:

In respiration, carbon starts in the form of glucose, and during the process it is turned into carbon dioxide.

In combustion, carbon starts as a fuel such as methane or wood, and during the burning process it turns into carbon dioxide.

In photosynthesis in plants and algae, carbon starts as carbon dioxide, and during the process it turns into glucose.

So before we go, let’s do one final turn around the carbon cycle wheel

It starts with carbon dioxide entering the atmosphere through respiration and combustion.

Then carbon dioxide leaves the atmosphere through photosynthesis in plants.

This carbon is passed along the food chain from plants to animals, which later die. Remember, when carbon is passed along the food chain from plants to animals, there’s also respiration taking place.

Decomposition of these dead plants and animals releases carbon back into the atmosphere.

I’m Dr Alex Lathbridge and this is Bitesize Biology. Listen to all the other episodes in this series, and the other topics that we cover on BBC Sounds.

Hello. I’m Dr Alex Lathbridge and this is Bitesize Biology.

This is the fourth episode in a series all about ecology and in this episode, we’re going to talk about the water cycle.

What kind of things do you think about when you’re on the toilet?

I’m usually scrolling aimlessly on my phone but every so often, a thought comes into my head.

When I’m finished up here and I flush, where does all that water go?

Obviously, down the drain and into the sewers, but where then? Does it end back in the sea? Will it ever be in a cloud again?

In the last episode, we looked at how carbon is cycled through organisms and the atmosphere, and water is the same, in fact it's even simpler as last time.

Water gets constantly recycled in a process known as the water cycle, providing water for organisms, plants and animals, including humans, over and over and over again.

Water is essential for everything. Some organisms can survive without water for a short period, but they will eventually die without it.

There are lots of different processes going on simultaneously in the water cycle.

You need to know the names of the key processes and what happens to water during each stage, and like our episode on the carbon cycle, it might help to draw a diagram.

We’re going to start with energy from the sun. It comes down and causes some of the water to evaporate.

Evaporation is the movement of water to the atmosphere from ponds, lakes, oceans and even puddles.

Evaporation turns water from a liquid into a gas: water vapour. Water vapour is carried upwards, as warm air rises. You might have seen this in action if you’ve ever hung out washing outside for it to dry.

But evaporation also happens in plants. This is known as transpiration (we talked about transpiration in plants in our series on The Cell so I’m going to take this opportunity to say ‘make sure you download that series and have a listen, as understanding the cell is key to understanding biology, so even if you’ve already heard it, listen again).

Plants maintain a constant column of water from their roots to their leaves, for transport and support. They allow some water to evaporate into the air from their leaves, so that more water is continually pulled up from their roots.

Alright, so we’ve taken lots of liquid water and turned it into water vapour, a gas.

As it moves up into the colder atmosphere, this gas cools and accumulates in the air to form clouds. This conversion from gas to liquid is called condensation. Like how if you’re taking a hot shower and the steam hits the cold window and drips down as water droplets? Exactly.

So, we have taken water vapour and made it into a liquid: clouds.

Cloud transport is the next step. This is where the water held within the clouds gets blown many miles by strong winds and so the water within travels to other areas.

And of course, all that water locked in the clouds has to go somewhere.

This is where we get precipitation: rain, snow, hail and sleet falls from the clouds onto land, providing water for plants and animals.

Much of the water from precipitation will be absorbed into the ground, this is known as infiltration.

This is where water is absorbed by the ground beyond soil and stored within underground rocks called aquifers.

But if there is a large amount of rain or if the ground is already full of water, some water runs along the surface of the ground. This is known as surface runoff. Too much can be bad as it can lead to flooding, if unmanaged.

Water then drains into the sea and rivers, where the sun evaporates it from, and the whole water cycle starts over again.

So, to do a quick recap of the water cycle:

Water evaporates (in plants, it transpirates) into the atmosphere which turns it into a gas, called water vapour

Condensation turns water vapour back into a liquid which is stored in clouds.

Cloud transportation moves water to different areas.

Precipitation takes water from the clouds and pushes it back to land.

Water goes into the soil, which is underground, and is stored in rocks called aquifers, this is known as infiltration.

But, if it doesn’t go down, this is known as surface runoff, and excess water is taken along the surface of the ground.

This is then drained into seas and rivers, that are once again, evaporated.

I’m Dr Alex Lathbridge and this is Bitesize Biology. All episodes available now on BBC Sounds.

Hello. I’m Dr Alex Lathbridge and this is Bitesize Biology.

This is the fifth episode in our series on ecology and in this episode, we’re going to talk about decomposition: dead things being broken down.

I've got some good news for you; you’re going to die one day.

And when that happens, that bacteria that you have inside of us, like in your gut, will start breaking down your moist and warm corpses, essentially, digesting us from the inside out.

And the bacteria on our skin starts breaking us down from the outside in.

And with so many different processes going on, it can take anything from five to ten years to be left

It’s the same way that rotting leaves shrivel up and die in the winter months. Or why oranges go bad when you leave them out for too long.

It’s just decomposition. And it’s a fact of life or death.

Decomposition is the breakdown of dead animals and plants, also known as dead matter and detritus.

If nobody ever died, we wouldn’t have the resources to support us all.

In the same way, if no decomposition ever happened when things die, it would cause havoc to the world.

How come?

Well, decomposition is vital to allow energy to flow through an ecosystem.

When dead organisms decompose, they are broken down into simpler materials, making nutrients available for primary producers, like plants.

Without it, vital nutrients would be locked up inside dead matter, which is no good for an ecosystem.

Decomposition is just a chemical process that happens at the end of life. Like any chemical process, there are ways to accelerate it, and other ways to slow it down.

This process is normally done by decomposers, things like bacteria and fungi, as well as things that live in soil like worms and woodlice.

They use enzymes to break down dead animals and plants, fallen leaves and animal droppings. (We did a whole podcast episode on enzymes in our series on the cell, go back and listen on BBC Sounds.)

There are several factors that determine the speed of decomposition, which is just the rate at which something decays:

Temperature. In colder environments, decomposers are less active and so the rate of decomposition is low. This is why food is kept in a fridge where temperatures are cold, to stop decay and keep food fresh. As temperatures get higher, decomposers become more active and the rate of decomposition increases. But, at really high temperatures decomposers will not survive and decomposition stops.

Water. In environments where there is little or no water, the rate of decomposition is low because decomposers can’t survive without water. As the volume of water increases, the rate of decomposition does too. Water is important for decomposers as they use enzymes to break down decaying matter into simpler molecules which they absorb. These enzyme reactions cannot happen without water.

Oxygen also affects the rate of decomposition. Decomposers will not survive in environments where there is little or no oxygen. It is important for respiration, growth and allows them to multiply. As the amount of oxygen increases in an environment, the rate of decomposition does too. This is why we often seal food away in things like bags or containers before putting it into the fridge. The containers trap the oxygen, so no more is added, and the rate of decomposition is kept low.

Understanding these factors means that you can prevent decomposition.

This is why Ancient Egyptians wrapped dead humans (and sometimes their pets) in paper to preserve them, this is known as mummification.

The process removed all moisture and water from the dead bodies and so stopped decomposers from breaking down the dead body. Basically, they felt it was important to keep the body looking as close to life-like as possible.

On the subject of death and decay, let’s have a chat about compost and manure.

Compost is a mixture of decayed organic matter, basically, dead plants and food.

Manure is the waste product from animals. If you’ve gone past a farm, you know what this smells like.

How do these two things relate to decomposition? Well, gardeners and farmers use compost or manure to improve the quality of their soil, which helps new plants to grow.

Once added to soil, compost and manure are broken down by decomposers in the soil like bacteria and worms, which release useful minerals. These minerals released from the decomposition process are then absorbed by any new plants, helping them to grow.

Now, there are some instances where decomposition occurs without oxygen.

Anaerobic decay happens when decomposers, such as bacteria and fungi, break down dead matter without oxygen (Remember anaerobic respiration? Anaerobic means without oxygen.)

This occurs naturally in places like water-logged soils, lakes and marshes. This also happens in peat bogs.

When people give their houseplants too much water (like me because I’m incompetent), it can flood the roots, and anaerobic decay can occur which unfortunately kills the plant.

The products of anaerobic decay are methane and carbon dioxide. Both are greenhouse gases which contribute towards global warming (but more on that later in this series.)

These two products are important because we can use them as biogas.

Biogas is a type of fuel that is made from the action of bacteria decomposing animal manure or other organic waste.

This process is a source of a renewable energy using natural resources (like manure) that doesn’t run out.

Biogas generators are large, industrial vessels where animal waste, or crops grown specifically for biogas production (such as maize), are allowed to anaerobically decompose.

This release of methane gas is used by humans for cooking or heating.

Advances in renewable energy are always good, but biofuels do have some negatives, which I’ll mention in the next episode.

I’m Dr Alex Lathbridge and this is Bitesize Biology. To listen to the other bitesize podcasts available search for Bitesize on the BBC Sounds app.

Hello. I’m Dr Alex Lathbridge and this is Bitesize Biology.

This is the sixth episode in our series on Ecology, and today we’re going to talk about biodiversity, how many different species of animals and plants exist. We’re also going to take a look at how humans have impacted the environment. It’s not good news. But by knowing about it and caring about it, you can pass your exams and build a better future.

Tropical rainforests have millions of different species living in them, so we say they have high biodiversity.

Biodiversity is defined as the range of different species within an ecosystem, or across Earth. So, areas like the north pole have far fewer species so we say they have low biodiversity or are less biodiverse.

But remember, it’s all about variety. An area with very large populations of a small number of species is not a diverse habitat.

Remember, organisms are interdependent. They exist in complex food webs where different organisms depend on each other.

Ecosystems that have higher biodiversity will have fewer species that solely depend on just one other species for food, shelter or maintaining their environment.

This means that the more biodiverse an ecosystem is, the more stable it generally is, and so it can easily adjust to any changes. So high diversity is important to maintain stable ecosystems.

Humans are also dependent on animals and plants too. So, the future of humanity on Earth depends on maintaining high biodiversity.

We’re not somehow separate from our ecosystem, just because we have towns and cities. We rely on high biodiversity too.

Unfortunately, biodiversity is being reduced by human activities causing pollution, which destroys the habitats of organisms and can cause them to go extinct, reducing biodiversity.

We’ve talked about how population sizes of different species need to be in balance for stable communities, but one species has increased in size beyond all others: humans.

We currently have a record level of number of people alive on Earth. In 2022 the human population exceeded eight billion. According to estimates from the United Nations, we’ll hit 10.4 billion in around 2086.

So why are there so many of us? It’s down to a few things:

Better health care enables people to live longer.

New medicines mean that people aren’t dying of diseases that would have otherwise killed them.

Farmers can produce large amounts of food using new crop breeds and specialised equipment.

Some communities and religions do not allow the use of contraception, and in some parts of the world, it’s really difficult to access.

Modern medicine and increased levels of food are good things for humans, but as the human population grows, the amount of pollution that humans produce, and the volume of waste also increases. This has a negative effect on ecosystems, habitats and organisms, which subsequently reduces biodiversity

Let’s look at some specific ways that human activities cause pollution and waste:

Water Pollution. Sewage and chemicals can pollute streams, rivers and oceans.

If fertilisers from farms get into streams and rivers, they can cause algae to grow out of control, which stops other plants from getting the sunlight that they need for photosynthesis.

Air Pollution is caused by combustion (or burning) of fossil fuels, which releases carbon dioxide into the atmosphere. This contributes to the greenhouse effect and leads to global warming and climate change.

Land Pollution. Lots of humans means lots of rubbish. Rubbish gets put into landfills, which are holes in the ground. Some of this rubbish contains harmful chemicals, or doesn’t break down, like plastics.

Land Use. The larger the human population gets, the more land that we use for building, farming, creating quarries, and dumping waste.This means that less land is available to other plants and animals, which decreases biodiversity.

Deforestation is the cutting down of trees and forests for a different use of the land. Lots of humans with industrial machines can clear huge areas of forests to build on or for farming, for things like crops or cattle.

Deforestation destroys the habitats for organisms, and this subsequently kills many species, reducing biodiversity. Scientists estimate that several hundred species of plants, animals and insects are lost each day, partly due to deforestation. Deforestation is causing extinction and reducing biodiversity.

Deforestation also increases the amount of carbon dioxide being released into the atmosphere, as carbon dioxide is released when trees are burnt to clear the land.

Cutting down a large amount of trees also means that less carbon dioxide is taken in, or removed, from the atmosphere by photosynthesis.

Finally, we’re going to look at peat bog destruction. Peat bogs are fascinating habitats and examiners love them. So even if this seems a bit random, it's important for you to learn about them.

Peat bogs are water-logged areas of land which are acidic and often have low levels of nutrients and oxygen. Because of this, the rate of decomposition is very low, and peat is formed from plants that are only partially decayed. This means that all the carbon in these plants is stored in the peat, rather than it being released into the atmosphere.

Peat bogs are very important stores of carbon, they’re known as carbon sinks. So why do you need to know this?

Peat has been removed from these peat bogs at rates that aren’t sustainable, for things like fuel or for gardeners to use in their soil, because of the nutrients inside it.

When peat is removed from the bogs, it comes into contact with microorganisms that can decompose it, which releases carbon dioxide into the atmosphere as part of respiration.

I’m afraid there’s no other way around this episode than facing the facts: human activity is increasing pollution levels and reducing biodiversity.

I’m Dr Alex Lathbridge and this is Bitesize Biology. Subscribe and listen now on BBC Sounds.

Hello. I’m Dr Alex Lathbridge and this is Bitesize Biology.

This is the seventh and final episode in our series on ecology.

In this episode we’re going to talk about something very important: climate change and global warming.

Before listening to this episode, you should have some idea about human impacts on the environment, things like deforestation. If you need a refresher, go back and listen to the last episode.

All right everyone, today a little bit different, you can tell I'm being serious today, because we need to get one thing very clear: no matter what some people might claim, climate change is not a myth, a hoax, nor is it a conspiracy. It is a real issue.

For you to understand why this topic is such a big deal, we need to start with something known as the greenhouse effect, so grab a pen and make a note.

The temperature on earth is maintained by energy being absorbed from the sun.

Some of this energy, about 30 percent, is radiated back out to space.

In our atmosphere, there are gases such as methane and carbon dioxide.

They absorb a lot of this energy that would otherwise radiate back all the way out into space, and they re-radiate it in a lot of directions, including back down to Earth.

We call this the greenhouse effect.

Because, in the same way that glass keeps a greenhouse insulated so it's warm, these gases help retain some of the energy that would radiate back to space, keeping our planet warm.

Alright, so, to define it: the greenhouse effect is the retention of heat in the atmosphere, caused by a build-up of greenhouse gases such as carbon dioxide, water vapour and methane. Now they're the most common ones, so you should remember that for your exam.

Alright, so, what does this tell us?

It says that the greenhouse effect (without recent human activities) is a good and necessary thing.

Because without it, the average temperature on Earth would be minus 18 degrees Celsius, so it basically keeps Earth at a suitable temperature for most organisms to live.

I know what's going through your head, you're like, “alright Alex, why does it sound like you’re gearing up to tell me something bad? Also, why did you whisper a bit then?”

Because, like glass on a greenhouse has to be a certain thickness to keep the perfect temperature inside, more greenhouse gases mean a much stronger greenhouse effect.

A stronger greenhouse effect means more energy is retained and the average temperature of the earth’s surface increases.

This is known as global warming, one of the types of climate change (no, global warming and climate change aren’t the same thing).

Human activity from burning fossil fuels in power stations and in vehicles, and from farming livestock, is increasing the greenhouse effect and causing global warming by increasing the amount of carbon dioxide and methane in the atmosphere.

Listen to the last episode if you need a reminder.

This is something that the scientific community have agreed on and is based on peer-reviewed evidence. Peer review is the process of scientists evaluating each other’s work to check that it’s valid

The two main worries are carbon dioxide and methane, because their levels are sharply rising.

Even though carbon dioxide is a small part of the atmosphere, an increase in its level has big effects on the climate.

I mean think about how much energy the sun releases. It's the Sun, come on, have sense!

In the UK we have temperature measurements going back to the 1850s.

Experts from our National Weather Service report that each decade from the 1980s has been successively warmer than the decade before.

The average increase in temperature over the last 100 years - that's a century - is less than one degree Celsius. Now before you start going "oh that's not a lot!", this might not seem like a huge change, but think about just how big this planet is.

It’s significantly difficult to heat up a planet on average by one degree Celsius. And this has effects on other types of climate change, like heavier rainfall and stronger storms.

Alright so you might think, “global warming, it gets a bit warmer, so what?”

Well, let’s go through a few of the consequences in detail, make sure that you have a pen.

Firstly, biodiversity. If the Earth’s temperature continues to increase, some species may not be able to adapt to temperature changes and so they won’t survive. These organisms will become extinct, leading to a decrease in biodiversity. As an example, a small rodent that lived only on a single island off of Australia was the first mammal to go extinct due to climate change.

In particular, because of the second effect: sea levels rising. When seas get warmer, they expand, which leads to a rise in sea levels. Ice also melts as temperatures increase, which runs into the sea, releasing more water and causing sea levels to rise.

If sea levels continue to rise in this way, humans and animals living in coastal and low-lying places could experience flooding, which will damage habitats.

That brings us to the third effect: changing migration patterns. It's common for birds to migrate to different areas of the world in different seasons. An increase in the Earth’s temperature could change migration patterns, where they travel to different areas at differing times to before.

And finally, the distribution of organisms. Plants and animals live in areas where they can access the resources that they require to best survive. This distribution of organisms in different habitats may change if the temperature of the Earth continues to increase. Species which need cooler temperatures to survive, will have smaller areas in which they can live optimally, so they will be distributed differently.

Alright, so by now you should know that bad things are happening.

So what can be done? Well, to start with, we need to cut our global emissions of greenhouse gases, for example, by burning less fossil fuels.

And there are positive things being done to help. For example, conservation.

Conservation is the preservation of ecosystems and the organisms that live within them.

It helps to slow down the decrease in biodiversity caused by global warming.

Remember, it's important that a high level of biodiversity is maintained so that ecosystems are stable.

Conservation scientists do lots of things to help maintain biodiversity.

You need to know the names of these:

1. Breeding programmes. These help to preserve endangered species and stop them becoming extinct. Animals, such as pandas are bred in captivity (so not in the wild).
2. Protection of habitats. As well as animals, habitats can be endangered and rare. Examples of these are coral reefs, mangrove areas and heathland. Protected areas can be made into National Parks to protect the species that live in them.
3. Replanting hedgerows. There are higher levels of biodiversity in hedgerows than the fields that surround hedges. The fields might only be growing a single crop due to farming, but hedgerows provide a habitat for more organisms. So replanting hedges helps to increase the levels of biodiversity.
4. Reducing deforestation and the release of greenhouse gases. Some governments have made rules and laws to reduce the rate of deforestation and the release of carbon dioxide into the atmosphere.
5. Recycling. If more people and companies recycle, fewer raw materials will be needed to make products and less waste will be dumped in landfill sites.

It is important to consider though, that us humans do need things like food and houses to survive, so we're stuck with these conflicting pressures when it comes to conservation.

The regeneration of habitats can be very expensive, and humans use land for important things necessary for our survival. So with that in mind, let's go over the key facts on climate change.

1. The greenhouse effect is the retention of heat caused by build up of greenhouse gases, mainly carbon dioxide and methane.
2. The increased release of greenhouse gases due to human activity is causing the greenhouse effect to be much stronger and leading to the earth's surface temperature to increase on average. This is called global warming.
3. Scientists are in agreement that climate change is real and peer-reviewed evidence has demonstrated that since the 1980s each decade is hotter than the one before. So yes, the earth is heating up.
4. Global warming has a lot of real and negative consequences: rising sea levels, reduced habitats and reduced biodiversity, meaning organisms will be distributed differently in ecosystems and migration patterns will change.
5. Conservation helps preserve habitats and species, with the aim of slowing down the reduction in biodiversity. Conservation projects include breeding programmes, protection or regeneration of habitats, replanting hedgerows, reducing deforestation and recycling.

Alright, let me try to end this on a positive note.

Now, it’s vital for the planet that we understand the science.

Because, if you understand this stuff, then you can help to find solutions and, not just that, you can help to find solutions and pass your exams. I want you to do both.

I’m Dr Alex Lathbridge and this is Bitesize Biology. To hear more, search Bitesize Biology on BBC Sounds.