Decomposition

The diagram shows the carbon cycle.

Complete the two labels in the diagram to identify the processes involved in the carbon cycle.

Explain the role of decomposers in the carbon cycle.

Decomposition can take place aerobically or anaerobically.

What is meant by the term anaerobically ?

Human activity has led to rising carbon dioxide levels in the atmosphere.

This contributes to global warming and reduces global biodiversity.

Describe two ways in which human activity can reduce local biodiversity.

Which process is required to recycle both carbon and nitrogen?

A Condensation

B Decomposition

C Photosynthesis

D Precipitation

The moisture content in soil affects the growth of plants.

Two students investigate the moisture content of different soils.

This is the method used by student X:

• Measure the mass of each soil sample.

• Place the soil samples in a warm oven to dry for 4 hours.

• Measure the mass of each soil sample again.

The table shows their results.

Calculate the percentage change in mass of soil sample C.

Give your answer to 3 significant figures. Write your answer in the table.

Soil sample A lost less mass than soil sample B.

Why is the percentage change in mass greater for soil sample A ?

The two students compare their results.

• Student Y used a similar method but left the soil in the oven for a different length of time.

• Student Y found the moisture content of soil sample C to be much higher than student X.

Explain why student Y found the moisture content of soil sample C to be higher than student X

What could both students do to check that the moisture content they measured is accurate?

Moisture content is one factor that affects plants.

The amount of microorganisms in the soil can also affect plant growth.

Explain why soil microorganisms are important for plant growth.

Why are microorganisms described as a biotic factor and soil moisture as an abiotic factor?

Bread mould is a type of fungus that decomposes plant material.

A student investigates the effect of temperature on decomposition.

• They leave slices of bread at three different temperatures.

• Each day the student records the area of each slice of bread covered by mould.

Which is a correct statement about these results?

Tick (✓) one box.

Look at the results for 20 °C.

Calculate the increase in area covered by mould between day 5 and day 10.

The diagram shows the water cycle.

Complete the diagram.

Use the words from the list.

Collection Condensation Evaporation Precipitation Respiration

Explain why transpiration is important to the plant communities in an ecosystem.

The diagram shows some of the levels of organisation within the ecosystem.

Complete the diagram using words in the list.

Explain why the carbon cycle is important to plants.

The flowchart in Fig. 12.1 shows bacteria involved in cycling nitrogen.

Identify which of the bacteria in Fig. 12.1, if present in large amounts, would make the soil poor for plant growth.

Tick (✓) one box.

Explain why large amounts of these bacteria would make the soil poor for plant growth.

Abiotic and biotic factors can affect the bacterial communities.

Which is a biotic factor?

Tick (✓) one box.

Plants are an important part of any community.

Fig. 12.2 shows the effect of abiotic factors on the rate of photosynthesis by plants.

Explain why lines X, Y and Z level out at different rates of photosynthesis.

Plant material decomposes to make compost.

Gardeners add compost to their soil to increase crop yield.

Give one reason why compost increases crop yield.

Gardeners use compost activator to speed up the decomposition of plant material.

Compost activator contains bacteria.

Scientists are developing a new compost activator. To do this they need to isolate samples of bacteria.

They prepare agar jelly plates containing streaks of different bacteria. Fig. 14.1 shows a scientist preparing an agar jelly plate.

In Fig. 14.1 the scientist uses a sterile glass rod to transfer the bacteria.

Suggest why this is better than just pouring the liquid directly from the bottle.

Some bacteria grow faster at 37 °C than at 25 °C.

The scientist chooses to grow the bacteria at 25 °C.

Suggest why this would be safer than growing them at 37 °C.

What is the final dilution factor in tube five ?

The scientist puts 1 ml from each tube onto a separate agar plate.

The scientist then leaves the bacteria to grow so that the bacterial colonies become visible.

They use this formula to calculate the number of bacteria in the original sample:

number of bacteria in the original sample = number of CFU in sample × dilution factor

There are 29 CFU grown from the sample taken from tube 5.

Calculate the number of bacteria in the original sample.

Give your answer in standard form.

Number of bacteria in the original sample =........ CFU per ml

Look at the diagram showing parts of the nitrogen cycle.

Which part of the nitrogen cycle involves bacteria as decomposers?