ecological relationships & energy flow

Ecological relationships& energy flow

Ecologyis the study

of living thingsin their environment

Ecosystem =

community + environment

(all the living things) (all the surroundings)

What is an

Ecosystem?

An ecosystem is the name given to all the living things, community, and their non-living environment in a particular area. The living organisms are all dependent on each other through feeding relationships.

How does life on Earth rely on energy from the Sun?

Energy flow• Life can exist on Earth

because of sunlight energy.

• Plants capture light energy through the process of photosynthesis.

• And make organic compounds such as carbohydrates

• Energy is transferred through the ecosystem by feeding relationships.

Finding out about populations in a habitatFieldwork provides information about what plants and animals live in a particular habitat and their numbers. It is therefore necessary

• to be able to identify organisms, using keys• and understand the different sampling techniques used to count them.

We cannot actually count every plant or animal in a

particular place, so we count a sample of the

population to calculate an estimated population size.

Sampling populationsYou should understand the importance of random sampling. This is essential to avoid observer bias.

WHAT DOES THIS MEAN?This means that the person collecting the data does not affect the result deliberately, e.g. by only counting in one part.

QUADRATSQuadrats are usually used

to count plants, but can also be used to count slow moving

animalssuch as snails.

1. Lay out two tapes at right-angles in the area you want to sample.

2. Use random number tables to pick co-ordinates: • quadrats should be placed randomly so that a

representative sample is taken.3. Place a quadrat (of suitable size) at that point and

count the organisms within it. 4. Repeat using using at least 20 quadrats, at other

random coordinates across the grid:• repeating increases the reliability.• collecting across the whole grid area reduces the

effect of an unusual distribution5. Calculate the average number of organisms in each

quadrat 6. Use the average to calculate an estimated total

number of organisms in the grid area.

Quadrats can be used to estimate a population in an area which is fairly uniform. Examples include lawns, woods and open ground. There are three ways to count organisms to estimate population size:

• 1. Density (calculating the number of organisms per m2);

• 2. Frequency (number of number of quadrats that contain the organism)

• 3. Percentage cover (estimating the percentage of the grid area that contains the organism)

Percentage cover – do you agree with the estimates?

• Percentage cover is an easy way to estimate population size.

• However, a disadvantage is that it is difficult to estimate exactly what percentage of the quadrat is actually covered by a particular type of plant, so it is normal to round up to the nearest 10%. An exception is if there are any plants with a percentage cover of 1 -5% - this is recorded as 1 and not 0.

• This makes the results less reliable than estimating the density.

BELT TRANSECTSBelt transects can be used to

investigate changes in the distribution

of organisms along a particular habitat,

e.g. due to changing abiotic factors such as light intensity

Sampling animal populations

How do we know that the invasive harlequin ladybird is affecting the populations of native ladybirds?

used to collect small

invertebrates.

POOTERS

SWEEP NETS• Sweep nets allow you

to collect large numbers of invertebrates that live in low vegetation (stems, tall grasses, flowers etc) or in rivers and ponds

• Sweep netting involves making a large rapid sweep with a net in between large paces.

• The invertebrates can be collected in a tray and counted

Stones to prevent rain flooding the trap or birds or other

predators from removing the trapped animals

PITFALL TRAPS

jar sunk in a hole in the ground

Pitfall traps must be properly set up:

• the top of the jar should be level with the soil surface

• cover the trap with a stone or piece of wood to keep out the rain, to make it dark and to stop birds eating your catch

• the traps must be checked often to avoid the animals escaping or being eaten before they are counted

• as with most methods a large number of traps makes results more reliable and minimises the effects of unusual results

• http://www.bbc.co.uk/scotland/learning/bitesize/standard/biology/biosphere/investigating_an_ecosystem_rev5.shtml

These are the non-living, physical parts of the environment, including:

• Wind• Water• pH• Light• Temperature

These are the living parts of the environment, including:

• Predators• Disease• Waste produced by living organisms

See worksheet (pages 54 -55 textbook)

Each organism is adapted (suited) to the environment in which it lives.

This case study tries to explain why specific plants live at different distances from the seashore.

1. Describe the area that was being studied.

2. What sampling method was used to study the distribution of plants along the sand dunes?

3. How many samples were taken?

• 1km sand dune, divided into 3 sections. • Section 1 from the start of the first sand

dune inshore.• Section 2 half way between 1 and 3.• Section 3 from the end of the last dune to

to the start of the woodland.

• 3 interrupted belt transects

• 20 at each site

4. Name the biotic data collected.

5. Name the abiotic data collected

• the average percentage cover • of marram grass, common heather and gorse• along each transect

• average light intensity reaching the ground • Average soil moisture• Average pH

6. Describe the conditions in which each of the plants prefers to grow.• Marram grass: can grow in very unstable

conditions such as those found near the shore, where the sand is constantly moving in the wind. It helps to stabilise the dunes, by holding the sand together for other plants to grow in.

• Heather: small shrub, prefers stable moist soil• Gorse: large shrub, prefers very stable soil with

lots of moisture and nutrients

7. Describe the trends shown by the graphs.

• Marram grass is only common in transect 1• Heather is not found in transect 1 but is found

in transect 2• Gorse is most common in transect 3, but

uncommon or absent at transects 1 and 2.

8. Use the biological knowledge about the 3 plants and the abiotic data to explain the trends.

• Marram grass can grow at the beginning of the dunes where there is not much water available in the sand, 20%.

• It needs high light intensity to grow, 95%. • Further inland, where the conditions are more

stable, there is less light and there is more moisture, so the other plants out-compete the marram grass.

• Heather cannot grow in transect 1 because there is not enough moisture.

• Gorse grows best in transect 3 where there is most water, 60%.

• Gorse is a large shrub and creates shade, preventing the marram grass and heather from growing.

9. What features of this investigation make the results reliable?

10. How could the reliability be increased further?

• The plants were counted in 20 quadrats at each transect and an average was calculated.

• ******

11. Explain why you think this a fair test?

12. State the following: the independent variable

the dependent variable

the controlled variables

• Only one thing was being changed.

• The position of the transect along the dune.

• Percentage plant cover in each quadrat

• Size of the quadrat• Time of the year the measurements were

taken.

It was not possible to keep the wind, light intensity, soil moisture or pH controlled. However these factors were measured and helped to explain the presence or absence of the plants at the different transects.

• Keys are used to identify unknown organisms. Dichotomous keys, used in biology, consist of a series of two part statements that describe observable features of organisms.

• At each step of a dichotomous key you are presented with two choices. As you make a choice about a particular feature or characteristic of an organism you are led to a new branch of the key. Eventually you will be led to the name of the organism that you are trying to identify.

Constructing a key for objects in a pencil case

1. Look at the group of objects and separate them into two groups based on a single observable feature.

2. Look at each group separately and again separate each into two groups based on a single observable feature.

3. Continue until each group has only one object.A dichotomous key may be shown as a branching

diagram or as a numbered key.

A branching key:

A numbered key:

• Carefully examine and think about the observable features of the 8 aliens and create a dichotomous key using some of these characteristics.

Broad leaved treesThis trees leaves are green all over and have a hairy upper surface. They are rounded with a pointed tip and they are larger on one side of the midrib than the other. The edges of the leaves are toothed, but they have no lobes or prickles. The stalk is short and rounded and bears a single leaf.

LEAF LITTERThis wingless invertebrate has a waistless segmented body with 3 pairs of legs. It uses a spring under its abdomen to move by jumping.

GrasslandThis 6 legged invertebrate has a broad body with a triangle shape on its back. It has 2 pairs of wings; one pair forms a protective case. It moves by flying or walking and has no obvious snout.

Garden weedsThis spineless weed has smooth edged, arrow shaped leaves. The stem trails along the ground and produces pink and white trumpet shaped flowers.

All living organisms are divided into five large groups called Kingdoms.

The 5 kingdoms are:

All the organisms in each kingdom have specific features in common.

These include:(1) their mode of nutrition (how they feed)(2) whether they have a cell wall (3) cellular organisation;

Group Nutrition Cell wall Cellular organisation

Protoctista Saprophytic or photosynthetic

Cellulose cell wall or none

Single celled with nucleus or algae that are not truly multicellular

Bacteria Saprophytic Non-cellulose Single celled with no nucleus

Fungi Saprophytic or parasitic

Non-cellulose Single or multicellular – can be ‘acellular’ with it being difficult to distinguish individual cells and nuclei scattered throughout the organism

Plants Photosynthesis Cellulose Single or multicellular – ‘typical’ cell arrangement with a nucleus

Animals Eating organic food None Single or multicellular – ‘typical’ cell arrangement with a nucleus

fungal cell

dead food

1. Enzymes released onto food

2. Enzymes digest food

3. Soluble products absorbed

1. Some organisms are difficult to classify e.g. Euglena, which has both plant and animal characteristics. This is why single-celled plants and animals are classified in a separate group called the Protoctista.

2. Sometimes it is difficult to identify which species an organism belongs to or where one species merges into another. Definition – a species is a group of organisms, with shared features, which can breed together to form fertile offspring.

3. Viruses are a complex group and are very difficult to classify. All viruses, e.g. the HIV virus that causes AIDS, lack proper cellular organisation. They have a DNA/RNA core (DNA and RNA are nucleic acids – the building blocks of chromosomes) and an outer protein coat without the typical cytoplasm of other cells. They can only live if they gain access to other cells and many biologists therefore regard them as non-living.

Read through your notes on classification before answering

question 3 (p71) in the GCSE Biology textbook.

Classification using observable features

• Construct a table to classify the sample of organisms into vertebrates and invertebrates.

Mr D’s table….

Ecological terms

biodiversity, population, habitat, environment, community and ecosystem

Match the terms with the definitions and write them into your notes.

[Answers on next slide ]

TERM DEFINITION

Biodiversity A measure of the number of different types of plant and animal species in an area

Population The number of one type of organism (species) in an area

Habitat The place where an organism lives

Environment The factors, both physical (abiotic) and living (biotic), that affect organisms in a habitat

Community The total number of organisms from all the populations in an area

Ecosystem The community of organisms that are interdependent on each other and the environment in which they live

Population changes

• Population numbers change over time.• Many factors can contribute to population

change but they can be summarised by:

Consider how each of these factors contributes to population growth:

• Birth rate• Death rate• Immigration• EmigrationThey can be summarised by the equation:Population growth = (birth rate + immigration) –

(death rate + emigration)

The Sun as Energy Source

The Sun is the energy source for most ecosystems on Earth and green plants play a vital role as ‘producers’ in capturing this energy through the process of photosynthesis.

The plants make sugars and other organic compounds that are then eaten by other organisms, so:

plants make the sunlight energy available to other organisms.

The sequence of producers trapping the Sun’s energy and this energy then passing on to other organisms as they feed is known as energy flow.

The different stages in the feeding sequence are called trophic levels (or ‘feeding levels’). The sequence can be drawn as arrows from producer to consumers, the arrows representing energy flow.

The sequence of energy flow from producer to consumers is known as a food chain.

FOOD CHAINS

Food chains show the feeding relationships and energy transfer between a number of organisms.

Draw a food chain from the food web shown opposite and identify: (a) The trophic levels(b) Producers and

consumers.

In all food chains the first organism (at trophic level 1) is the producer (a plant) and it provides food and energy for primary consumers.

Note that in reality very few animals have only one food source, so energy flow in an ecosystem is more accurately represented by a food web, not a simple chain.

Food webs show how a number of food chains are interlinked and they give a more realistic picture of feeding relationships.

Pyramids of number and biomass

• The number of organisms at each stage of a food chain (i.e. at each trophic level) can be represented by a pyramid of numbers.

The problem with a pyramid of numbers is that it is not always pyramid-shaped, as it does not take into account the size of the organisms involved, e.g. one oak tree will support many more organisms than one grass plant

And also …. Pyramids may appear top heavy if we include parasites, as many parasites will feed on one consumer.

Advantages/disadvantagesAdvantages of pyramid of numbers Disadvantages of pyramid of numbers

Easy to count Ignores sizes of organisms

No organisms get killed Difficult to convert e.g. grass plant leaves to numbers which can be worth comparing with others

When representing energy flow through a food chain it is sometimes more accurate to use a pyramid of biomass.

These diagrams representthe mass of living tissuein the organisms.

Advantages/disadvantagesAdvantages of pyramid of biomass

Disadvantage of pyramid of biomass

Amount of energy in trophic level more accurately represented

Organisms must be collected and killed in order to measure biomass (usually dry weight of organisms).

Difficult to catch/weigh all organisms

The biomass of an individual can vary through the year, e.g. an oak tree will have a much greater biomass in June than in December

Another difficulty in producing both pyramids of number and biomass arises if organisms feed at two different trophic levels e.g. an organism that eats both plants and animals.

Review

Complete questions 1, 2 and 4 from GCSE textbook p70 – 71

[Note that this may take up to 30 minutes]

Decomposition

What happens to the energy available in dead organisms? Decomposers break down dead organisms-plants and animals. Decomposers are important to an ecosystem because they return nutrients to the environment.

Bacteria and fungi are examplesof decomposers – they are saprophytes.

Decomposing action of saprophytic fungi and bacteria

• A saprophyte is an organism that feeds on dead or decaying organic matter. Saprophytic bacteria and fungi secrete enzymes into the soil or dead organism. The enzymes break down (digest) the organic material and then it is absorbed by the bacteria or fungi. This is known as extracellular digestion.

Extracellular digestion – a reminder

Formation of humus

Humus is the organic content of the soil formed from decomposing plant and animal material. Decomposition takes place more quickly when conditions are optimum. These include:

A warm temperatureAdequate moistureA large surface area in the decomposing

organism.

Give two reasons why large, flat tropical plant leaves will decompose much more quickly than Norwegian pine needles.

Energy loss and trophic levels

Most food chains are relatively short, with just four organisms. This is because at each stage of energy transfer (including trophic level 1), some energy is lost.

5 minute task:In pairs, list as many reasons as you can for energy loss

within organisms and between organisms on different trophic levels.

Review the different reasons identified by the class.

Even at the first trophic level, the absorption of light energy by plants is not efficient e.g. energy is lost:

• as light is reflected from leaves• as light passes through leaves and misses

chloroplasts• light energy is used to evaporate water from leaves.However this loss of energy is not significant as so

much light energy comes from the Sun.

The transfer of energy between plants and animals and between animals of different trophic levels is usually 10 – 20%.

This means that for every 100g of plant material available, only between 10 and 20g is built up as a tissue (as ‘biomass’) in the herbivore’s body. The same applies when carnivores eat herbivores.

The loss of energy is due to three main reasons:

1. Not all the available food is eaten. Most carnivores do not eat the skeleton or fur of their prey, for example.

2. Not all the food is digested; some is lost as faeces in egestion.

3. A lot of energy is lost as heat in respiration. Respiration provides the energy for movement, growth, reproduction etc. Heat is produced as a by-product of respiration. Heat is lost and cannot be passed on to the next trophic level.

See sheet ‘Energy loss and trophic levels’

Nutrient cyclesThe flow of nutrients in ecosystems differs from the

flow of energy in important ways. In a stable ecosystem the overall gain or loss of nutrients from the system will be small and, unlike energy, the nutrients can be recycled as part of a nutrient cycle.

Remember that decomposers can break down organic compounds, and nutrient cycling involves the processes of decay and decomposition.

For recycling to take place, dead organisms must first be broken down during the decay process.

Organisms involved in this process include earthworms, woodlice and various types of insect – these organisms are known as ‘detrivores’.

Fungi and bacteria are the decomposers that break down the organic compounds into their simplest components.

• The decomposing action of saprophytic fungi and bacteria also helps in the formation of humus, the organic substance in soil that makes it more fertile and produces good ‘crumb structure’.

• Recall the previous notes made on the formation of humus that included the key features of the decay process - a warm temperature, adequate moisture and a large surface area in the decomposing organism.

• Read information sheet ‘Soil microorganisms’

The Carbon CycleFrom our study of diet and nutrition we know already

that carbon is an essential element in many important biological molecules e.g. ………………………………………

Using the cards supplied, identify the definition to explain each of the main processes in the carbon cycle – photosynthesis, feeding, respiration, decomposition and combustion.

Write the definitions into your notes.

Design a Carbon Cycle poster

Using diagrams from GCSE textbooks and the key terms from matching activity, create a poster on the carbon cycle that includes an annotated diagram.

The Carbon Cycle and Global Warming

Carbon dioxide gas is one of the gases present in the Earth’s atmosphere. It has been present for millions of years, but recent evidence has shown that the level of carbon dioxide in the atmosphere is rising. There is also evidence that humans are responsible for the increase in carbon dioxide levels.

Two main changes have contributed to the rise in carbon dioxide levels and therefore carbon cycling on Earth:

1. Increased combustion of fossil fuels has added more carbon dioxide to the atmosphere;

2. Increased deforestation has removed many forests, meaning that less carbon dioxide is taken out of the atmosphere by the process of photosynthesis.

The changes mean that the carbon cycle has become unbalanced.

The link between carbon dioxide levels and global warming

The atmosphere that surrounds the Earth acts as an insulator – trapping heat from the Sun’s radiation to produce a temperature suitable for life on our planet. Without carbon dioxide and water vapour, the surface of the Earth would be at -40oC. The ‘greenhouse effect’ is necessary for life as we know it, but the problem in recent years has been an increase in the concentration of gases that contribute to the greenhouse effect.

Increasing carbon dioxide levels

However, some gases add to this ‘greenhouse effect’ more than others, for example carbon dioxide, methane and water vapour. It is thought that the increase in carbon dioxide due to human activity is in turn increasing the greenhouse effect, that is, an enhanced greenhouse effect. The enhanced effect is leading to ‘global warming’.

Evidence for global warming

Scientists have been highlighting the increase in carbon dioxide levels for many years and have been attempting to persuade Governments to take global warming seriously. It is only recently that many politicians and people have accepted that it is the increase in carbon dioxide levels that are causing global warming.

It is difficult for some nations to accept the link because that also means accepting that human beings are responsible and that we must change our lifestyle to try to reduce our dependence on fossil fuels.

Effects of global warming

The warming of the atmosphere causes:• Climate change – more weather extremes

such as droughts and severe storms;• Polar ice-caps to melt;• Increased flooding;• More land to become desert.

Reducing global warming

Explain in your own words how the following actions could reduce global warming:

Planting more treesReducing deforestationBurning less fossil fuels by using alternative fuels

and/or becoming more energy efficient.

Reducing carbon emissions

• Agenda 21 is an action plan of the United Nations (UN) related to promoting sustainable development and was an outcome of a conference on the environment held in Rio de Janeiro, Brazil, in 1992. It is a recommendation for action to be taken globally, nationally, and locally by organizations of the UN, governments, and major groups in every area in which humans directly affect the environment.

North Down Borough Council Scientific evidence of human effects on the environment

informs our local government about the need to implement policies such as:

- Reductions in carbon emissions;- Increases in renewable energy; and- Changes in agricultural practices (see later notes following

eutrophication).

[Read information sheet ‘Local Agenda 21 in North Down’. From the information provided identify two questions you could ask environmental staff from NDBC regarding Council policies ]

Changes brought about by local councils in recent years include providing ‘brown bins’ to households to increase composting and ‘blue bins’ for recycling paper, some plastics and metal cans.

The recycling Centre at Balloo has a wind turbine.

Acid Rain

Using the textbook p66 – 67, create an annotated diagram/poster about:

1. the causes and 2. effects of acid rain and3. strategies to reduce acid rain.

Make sure you include detail.

The Nitrogen cycle[Use the accompanying worksheet to ‘fill in the blanks’

about the nitrogen cycle]• Most of the nitrogen in plants and animals is in the

form of amino acids and protein . The nitrogen cycle can be split into three phases:

1. The build-up of nitrogen into amino acids and protein in plants and animals and the eventual breakdown of these compounds into nitrates. Plants absorb nitrogen as nitrates and use them to make proteins . As plants (and animals) are eaten the proteins are eaten, digested and then built up into other proteins in sequence.

Eventually the nitrogen is returned to the ground as urine or through the process of death and decay.

Decay or putrefying () bacteria and fungi break down proteins to release ammonia. A second very important group of bacteria, nitrifying bacteria, convert the ammonia or ammonium compounds into nitrates (nitrification).

2. Nitrogen-fixing bacteria are a special group of bacteria that can convert nitrogen gas into nitrates. These bacteria can be found in the soil or frequently in small swellings (root nodules) in the roots of a group of plants called legumes.

• Legumes include peas, beans and clover. The relationship between the legumes and bacteria is beneficial for both organisms; the bacteria gain carbohydrates from the legumes and they in turn provide a source of nitrates for the plants. The process of converting nitrogen from the atmosphere into nitrates is called nitrogen fixation.

3. Denitrifying bacteria convert nitrates into atmospheric nitrogen. This is a wasteful and undesirable process.

Denitrifying bacteria are anaerobic and are most commonly found in waterlogged soils. Their effect in well-drained soils is much reduced. The process of converting nitrates into nitrogen is called denitrification ().

Consider: Why might ploughing a field be advantageous to a farmer growing crops?

Happy farmer with no denitrifying bacteria in his fields

Root hair cells and active uptake

Plants need nitrates to form proteins and they obtain these from the soil through root hair cells by active uptake.

The diagram of a root hair cell shows the adaptations of the cell:

• An extended shape (a ‘cytoplasmic extension’)• Providing an increase in cell surface area for

increased uptake of water and minerals.

Active uptake is a process thatrequires energy to transportminerals against a concentrationgradient.

This is because there are more nitrate ions inside the cell compared with outside in the soil. This process requires oxygen for aerobic respiration to produce the energy needed to transport the nitrates against the concentration gradient.

Review: what is meant by ‘concentration gradient’?

Replacing lost nitrogen – the use of fertilisers

When farmers harvest crops, or animals are taken to the abattoir, the nutrients they took from the soil are not replaced. The crops do not decay and decompose back into the soil to recycle the nutrients. For this reason, soil needs to be fertilised on a regular basis.

Important minerals

Calcium – needed for plant cell walls. Magnesium – needed for chlorophyll.Nitrogen – needed to make amino acids and

protein for growth.

All these minerals must be replaced in the soil to maintain plant growth.

Natural and Artificial Fertilisers

Both natural fertilisers (farmyard manure and compost) and artificial fertilisers may be used to replace nitrates and other minerals in soil.

Comparing natural and artificial fertilisers

Eutrophication

The problem with using fertilisers is that not all the nutrients sprayed onto fields gets used by plants. Both sewage and fertiliser ‘run-off’ can cause eutrophication.

Key points:Nitrates from sewage and fertiliser cause an increase in

the growth of aquatic plants and algae;The plants die due to shading (as they cannot

photosynthesise) and both plants and algae die to due the eventual decrease in concentration of nitrates available (nitrate depletion);

The dead organisms are broken down by decomposers, which further depletes oxygen levels in the water;

Other aquatic vertebrates and invertebrates die due to oxygen depletion.

Using the information in the previous slide, plus Figure 7.21, p66 in GCSE textbook,

design a summary poster to explain how eutrophication is a consequence of water pollution.Include in your poster the ways that this type of

pollution can be reduced (read section on ‘Water pollution’ p66).

Summer extended writing task

Choose one of the following topics to research over the holiday, giving details/examples of how the local environment has been impacted.

1. Methods of monitoring change in the environment2. The role of the Government in conserving the

environment3. Changes in agriculture (including EU Nitrates

Directive)4. International co-operation and legislation.