Energy flow and nutrient cycles

खेलकर सीखें

इन सवालों के जवाब देकर एनर्जी कमाएं, फिर मछली पकड़ें और घूमें। कोई अकाउंट नहीं चाहिए।

शिक्षकों के लिए: Energy flow and nutrient cycles (MYP Biology, Year 3) के लिए इस्तेमाल के लिए तैयार लेसन स्लाइड्स, रिवीज़न नोट्स — इन्हें अपने लेसन में इस्तेमाल करें, या टॉपिक को एक इंटरैक्टिव क्लास एक्टिविटी की तरह चलाएं जिसे आपके शिक्षार्थी लाइव गेम की तरह खेलें।

लेसन नोट्स

Big idea: energy flows, matter cycles

Big idea (key concept): Systems. An ecosystem is a system. Living things and their surroundings are linked by flows of energy and cycles of matter.
Related concept: Energy. Energy cannot be made or destroyed, only transferred. Tracking where it goes explains why ecosystems look the way they do.
Global context: Globalization and sustainability. Food supplies, climate and water all depend on these flows, so understanding them helps us plan how to feed people without damaging the planet.
Almost all energy enters an ecosystem as light from the Sun. Producers capture it by photosynthesis and store it as chemical energy in food.
Energy flows one way: Sun, then producers, then consumers, then to the surroundings as heat. It is never recycled, so ecosystems need a constant supply of sunlight.
Matter such as carbon, water and nitrogen cycles. The same atoms are used again and again, passing between living things, the air, water and soil.

Energy and matter moving through a tide pool

Food chains and trophic levels

A food chain shows who eats whom. The arrows point in the direction energy and matter are transferred, from the food to the feeder.
Each step is a trophic level. Level 1 is the producer. Level 2 is the primary consumer (eats producers). Then secondary and tertiary consumers eat other animals.
Example: grass, grasshopper, frog, python, eagle. Grass is level 1 and the eagle is level 5. The eagle is the apex predator because nothing in the chain eats it.
Animals are classed by diet: herbivores eat plants, carnivores eat animals and omnivores eat both. One animal can sit at different levels in different chains.
Decomposers (bacteria and fungi) feed on dead remains and waste from every level, so they link to all of them.
Real ecosystems are food webs, many interlinked chains. If one species falls in number, many others are affected.

Trophic levels from grass to eagle

Energy transfer, efficiency and pyramids

Only about 10% of the energy at one trophic level is passed to the next. The rest is lost. In a pyramid of energy the bars shrink quickly: for example 10,000 J in producers, 1,000 J in primary consumers and 100 J in secondary consumers.
Percentage efficiency = energy passed on ÷ energy available × 100. If primary consumers get 1,000 J from 10,000 J in the producers, the efficiency is 1,000 ÷ 10,000 × 100 = 10%.
Energy is lost as heat from respiration, as movement and other life processes, in faeces and urine, and in parts that are not eaten such as roots, bones and fur. It is not destroyed: it spreads into the surroundings.
This is why food chains rarely have more than four or five levels, and why there are far fewer top predators than herbivores. Eating crops directly also wastes less energy than feeding crops to animals and eating the animals.
A pyramid of biomass shows the dry mass of living material at each level. It is usually pyramid-shaped. Dry mass is used because water content varies. Ocean pyramids can be narrower at the base, because fast-reproducing phytoplankton have a small mass at any moment.
A pyramid of numbers counts organisms and can look odd: one oak tree feeds hundreds of caterpillars. A pyramid of energy over a year is never inverted, because energy is lost at every step.

A pyramid of energy with 10% passed on at each level

The carbon cycle and the water cycle

Carbon dioxide makes up only about 0.04% of the air, but it is the starting point of the carbon cycle. Photosynthesis removes carbon dioxide from the air and turns it into carbon compounds in plants.
Carbon passes along food chains by feeding. All organisms, including plants and decomposers, return carbon dioxide to the air by respiration.
When organisms die, decomposers break them down and release carbon dioxide. Over millions of years, buried remains can become fossil fuels. Burning wood or fossil fuels (combustion) releases the carbon dioxide quickly.
Humans burn fossil fuels and clear forests faster than natural processes remove carbon dioxide, so the amount in the air is rising. Oceans also take in and release carbon dioxide.
The water cycle is powered by the Sun and gravity. Evaporation turns liquid water into vapour, and plants lose vapour from their leaves by transpiration.
Vapour cools and condenses into clouds. Precipitation (rain, snow) brings water to the ground, where it soaks in or flows as runoff into rivers and back to the sea.

The carbon cycle

Decomposers: recycling nutrients

Decomposers are mainly bacteria and fungi. They break down dead plants, dead animals and waste. Detritivores such as earthworms and woodlice help by breaking material into small pieces first.
Decomposers release enzymes onto the dead material. The enzymes break it into small, soluble molecules, and the decomposers absorb them.
As they respire, they release carbon dioxide. They also release mineral ions such as nitrates into the soil, which plants take up through their roots to make proteins.
Without decomposers, dead material would pile up and nutrients would stay locked inside it. Plants would run out of minerals and the whole food web would collapse.
Decay is fastest when it is warm, moist and has plenty of oxygen. It is slow in cold, dry conditions, and in waterlogged, acidic peat bogs where oxygen is scarce.
People use this: compost heaps keep material warm, damp and aerated, so decomposers turn waste into nutrient-rich compost. Food is kept in fridges and freezers to slow decay.

Fungi growing on dead wood and leaf litter

Think like a scientist: what makes things decay?

Investigation. Put equal masses of dried leaf pieces in mesh bags and bury them in moist soil in identical pots. Keep the pots at different temperatures, for example 5, 15, 25 and 35 °C. After two weeks, dry and weigh the leaf pieces again.
The independent variable is the temperature. The dependent variable is the mass lost by the leaf pieces (starting mass minus final mass).
Control variables: the type and starting mass of leaf, the soil type, the amount of water, the size of the pieces, the time and the amount of air. Why must the soil moisture be the same?
Inquiry task: how many bags would you use at each temperature, and why? Repeat so you can calculate a mean and spot an anomaly, and decide how you would dry the leaves to the same level each time.
Evaluate: at 55 °C the decay is likely to slow down again, because heat damages the enzymes and kills the decomposers. What does that tell you about the claim that warmer always means faster?
Data skill: to compare energy transfer between two food chains, calculate the percentage efficiency each time and compare the percentages, not the raw numbers.

स्लाइड्स

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

साइन अप करें — फ्री लॉग इन

प्रैक्टिस सवाल

फ्री प्रीव्यू — 49 में से 8 सवाल। सभी देखने के लिए साइन अप करें।

1.What is the original source of energy for almost all food chains?
Easy
- AFossil fuels
- BThe Sun
- CThe wind
- DThe soil
2.What is a producer?
Easy
- AAn animal that eats other animals
- BAn organism that breaks down dead material
- CAn organism that makes its own food, usually by photosynthesis
- DAn animal that eats only plants
3.A primary consumer eats producers.
Easy
True or false?
4.In the food chain grass → rabbit → fox, which organism is the secondary consumer?
Easy
- AThe grass
- BThe rabbit
- CThe soil bacteria
- DThe fox
5.What do the arrows in a food chain show?
Easy
- AThe direction in which energy is transferred
- BWhich animal is the bigger one
- CWhich organism lives the longest
- DThe direction in which animals migrate
6.Complete the sentence.
Easy
An organism's position in a food chain is called its ____ level.
7.About what percentage of energy is passed on from one trophic level to the next?
Easy
- AAbout 90%
- BAbout 10%
- CAbout 50%
- DAbout 1%
8.Energy is recycled round an ecosystem again and again, like carbon is.
Easy
True or false?

और सवाल

9.What does a pyramid of biomass show?
Easy
- AThe number of species in each habitat
- BThe ages of the organisms in a chain
- CThe mass of living material at each trophic level
- DHow fast each animal can move
10.Which process removes carbon dioxide from the air?
Easy
- ARespiration
- BCombustion
- CDecomposition
- DPhotosynthesis
11.Which process releases carbon dioxide from the cells of all living things?
Easy
- ARespiration
- BPhotosynthesis
- CCondensation
- DTranspiration
12.What does burning fossil fuels add to the air?
Easy
- ANitrogen
- BCarbon dioxide
- CPure oxygen only
- DWater vapour only
13.Match each word in the water cycle to its meaning.
Easy
- Evaporation
- Condensation
- Precipitation
- Transpiration
- Water vapour turning into droplets
- Water vapour lost from plant leaves
- Rain or snow falling to the ground
- Liquid water turning into vapour
14.Which organisms are the main decomposers?
Easy
- APlants and algae
- BInsects and spiders
- CBacteria and fungi
- DBirds and mammals
15.What do decomposers return to the soil?
Easy
- ASunlight that plants can use
- BOxygen that plants can use
- CGlucose that plants can use
- DMineral ions that plants can take up
16.Put this food chain in order, starting with the producer.
Easy
- Frog
- Grass
- Eagle
- Grasshopper
- Python
17.Dead material decays faster in warm, moist conditions than in cold, dry conditions.
Easy
True or false?
18.Complete the sentence.
Easy
Water vapour escaping from the leaves of plants is called ____.
19.In what form is most of the energy lost along a food chain?
Easy
- AHeat from respiration
- BLight given out by the producers
- CSound made by the consumers
- DElectricity produced by the cells
20.A field of grass holds 20,000 kJ of energy. The grasshoppers that eat it hold 2,400 kJ. What is the percentage efficiency of the transfer? Give a whole number.
Medium
21.Why are food chains rarely longer than five trophic levels?
Medium
- APredators are always too small to hunt
- BToo little energy is left to support more levels
- CPlants cannot support more than five types of animal
- DAnimals cannot digest the top predators
22.Which of these is a reason energy is lost between trophic levels?
Medium
- AEnergy is destroyed when an animal eats
- BPlants keep all of the energy they absorb
- CSome energy is released as heat in respiration
- DEnergy cannot be stored in living things
23.Why is a pyramid of energy never inverted?
Medium
- ALarge animals always eat more food than small ones
- BProducers always weigh the most of all organisms
- CConsumers can make their own energy as they grow
- DEnergy is lost at every transfer, so less is available at each higher level
24.A pyramid of numbers for one oak tree, 500 caterpillars and 20 birds is not pyramid-shaped. Why?
Medium
- ANumbers ignore size, and one large tree can feed many caterpillars
- BThe caterpillars are producers
- CThe birds have no energy
- DEnergy is gained between the levels
25.Why is dry mass used when measuring biomass?
Medium
- AWater is the only part that contains energy
- BThe water content varies, so dry mass gives a fairer comparison
- CDry mass is easier to measure from a distance
- DLiving organisms contain no water
26.Which of these are reasons for energy loss along a food chain? (select all that apply)
Medium
- AHeat released in respiration
- BFaeces and urine
- CParts that are not eaten, such as bones
- DEnergy being destroyed
- EEnergy absorbed from the Sun
27.Which process puts carbon from dead organisms back into the air as carbon dioxide?
Medium
- AProducers photosynthesising
- BRain falling on the soil
- CDecomposers respiring
- DAnimals eating plants
28.Over millions of years, buried and compressed dead organisms with little oxygen can become...
Medium
- AFresh soil full of nitrates
- BClouds full of water vapour
- CNew producers
- DFossil fuels such as coal and oil
29.Put these steps in order for a carbon atom moving round the carbon cycle.
Medium
- A rabbit eats the plant
- It is in carbon dioxide in the air
- The rabbit respires and releases it as carbon dioxide
- A plant takes it in during photosynthesis
30.Which two things power the water cycle?
Medium
- AEnergy from the Sun, and gravity
- BEnergy from fossil fuels, and wind
- CPhotosynthesis and respiration
- DThe Moon and the ocean floor
31.Which process mainly carries water from the land back to the sea?
Medium
- ATranspiration
- BRunoff and river flow
- CCondensation
- DEvaporation
32.Why do decomposers release enzymes onto dead material?
Medium
- ATo keep the dead material from drying out
- BTo make the dead material grow again
- CTo break it into soluble molecules that they can absorb
- DTo attract larger animals to eat it
33.Why does dead material decay very slowly in a waterlogged peat bog?
Medium
- AThere are no plants in a bog
- BThe water in a bog is always too hot
- CBogs contain more decomposers than other soils
- DThere is little oxygen and the water is acidic, so decomposers are not active
34.Matter cycles round an ecosystem, but energy flows through it in one direction.
Medium
True or false?
35.A student buries equal masses of leaf in soil at different temperatures and measures the mass lost. What is the dependent variable?
Medium
- AThe mass lost by the leaf pieces
- BThe temperature of the soil
- CThe type of leaf used
- DThe amount of water added
36.In the same investigation, which variable must be kept the same?
Medium
- AThe temperature of the soil
- BThe amount of water in the soil
- CThe mass lost by the leaf pieces
- DThe final mass of the leaf pieces
37.Which way of getting food wastes less energy overall?
Medium
- APeople eating animals fed on the same crops
- BPeople eating the top predators in a chain
- CPeople eating crops directly
- DPeople eating only the very largest animals
38.Complete the sentence.
Medium
Fungi and bacteria that break down dead material are called ____.
39.Complete the sentence.
Medium
A pyramid that shows the dry mass of living material at each level is a pyramid of ____.
40.In one food chain, the producers hold 24,000 kJ, the primary consumers 2,400 kJ and the secondary consumers 120 kJ. What is the percentage efficiency of the transfer from primary to secondary consumers?
Hard
41.
The table shows invented values for one food chain.
Trophic level Energy held (kJ)
Grass 50,000
Grasshopper 4,000
Frog 600
Snake 30
Which transfer is the least efficient?
Hard
- AGrass to grasshopper
- BGrasshopper to frog
- CAll three are equally efficient
- DFrog to snake
42.In some oceans the biomass of phytoplankton at one moment is smaller than the biomass of the zooplankton that eat it. How is this possible?
Hard
- APhytoplankton reproduce very quickly, so a small mass can support a larger mass of consumers
- BZooplankton make their own food by photosynthesis
- CEnergy is gained at each step in the ocean
- DPhytoplankton do not lose energy in respiration
43.The amount of carbon dioxide in the air has risen steadily for 150 years. Which statement best explains this?
Hard
- APlants have stopped taking in carbon dioxide
- BBurning fossil fuels and clearing forests release carbon dioxide faster than it is removed
- CDecomposers have started making more oxygen
- DRespiration has stopped in the oceans
44.A sealed glass garden contains plants, soil, decomposers and small animals. It survives for years if it sits in the light. Which statement is correct?
Hard
- ANeither matter nor energy needs to be supplied
- BIt needs a continuing input of both matter and light
- CMatter is recycled inside it, but it needs a continuing input of light energy
- DEnergy is recycled inside it, but matter must be added
45.If decomposers were removed from an ecosystem, the supply of minerals to plants would not change.
Hard
True or false?
46.
In one experiment, equal masses of leaf were buried at different temperatures for two weeks.
Temperature (°C) Mass lost (g)
5 2
15 8
25 15
35 20
55 1
A student concludes that warmer always means faster decay. How should you evaluate this?
Hard
- AIt is supported, because 35 °C had the highest value
- BIt is supported, because each reading is higher than the first
- CIt cannot be tested, because mass lost is not measurable
- DIt is not supported at 55 °C, where decay almost stopped
47.Explain why energy flows through an ecosystem but nutrients are recycled.
Hard
48.Explain why there are usually far fewer top predators than herbivores in an ecosystem.
Hard
49.Plan an investigation into how the temperature affects the decay of leaves in soil. Include what you change, what you measure, two things you keep the same and how you make your results reliable.
Hard

रिवीज़न नोट्स

## The big idea - An ecosystem is a **system**: **energy flows** through it in one direction (Sun, producers, consumers, heat) while **matter cycles**. ## Food chains and trophic levels - Producer is level 1, then primary, secondary and tertiary consumers. Arrows show the direction of energy transfer. An apex predator has no predators in the chain. ## Energy transfer - About **10%** passes to the next level. Energy is lost as heat from respiration, in movement, in faeces and urine, and in uneaten parts. - **Efficiency = energy passed on ÷ energy available × 100.** - Pyramids: energy is never inverted; biomass uses dry mass; numbers can be odd shapes. ## Cycles - **Carbon:** photosynthesis removes carbon dioxide; respiration, decomposition and combustion return it. Fossil fuels are stores of ancient carbon. - **Water:** evaporation, transpiration, condensation, precipitation and runoff, powered by the Sun and gravity. ## Decomposers - Bacteria and fungi release enzymes, absorb soluble products, and return minerals and carbon dioxide. Fastest when warm, moist and with oxygen.

Producer: An organism that makes its own food, such as a plant or alga.
Consumer: An organism that gets energy by eating other organisms.
Trophic level: An organism's position in a food chain, numbered from the producer upwards.
Apex predator: A predator at the top of a food chain that nothing else in the chain eats.
Food web: Many interlinked food chains in one ecosystem.
Biomass: The mass of living material, measured as dry mass.
Pyramid of energy: A diagram showing the energy at each trophic level, which shrinks at each step up.
Efficiency: The percentage of the energy available that is passed to the next level.
Respiration: The process that releases energy from food, producing carbon dioxide and heat.
Combustion: Burning, which releases carbon dioxide from wood and fossil fuels.
Fossil fuel: A fuel such as coal or oil formed over millions of years from buried dead organisms.
Transpiration: The loss of water vapour from the leaves of plants.
Precipitation: Water falling to the ground as rain, snow or hail.
Decomposer: A bacterium or fungus that breaks down dead material and waste.
Detritivore: An animal such as an earthworm that feeds on dead material and breaks it into pieces.

फ्लैशकार्ड

Where does the energy in most ecosystems come from?

The Sun, captured by producers in photosynthesis.

Does energy flow or cycle through an ecosystem?

It flows one way and is lost as heat. Matter is what cycles.

What do the arrows in a food chain show?

The direction of energy transfer, from the food to the feeder.

What is trophic level 1?

The producer, such as a plant or alga.

What is an apex predator?

A predator at the top of a food chain that no other organism in the chain eats.

What percentage of energy passes to the next trophic level?

About 10%. About 90% is lost.

How is energy lost along a food chain?

As heat from respiration, in movement, in faeces and urine, and in parts not eaten.

How do you calculate percentage efficiency?

Energy passed on ÷ energy available × 100.

Why are food chains short?

So much energy is lost at each step that little remains to support more levels.

Why is a pyramid of energy never inverted?

Energy is lost at every transfer, so each level holds less than the one below.

Why use dry mass for biomass?

Water content varies, so dry mass makes a fair comparison.

Which two processes remove and add carbon dioxide in nature?

Photosynthesis removes it; respiration (and decomposition, combustion) adds it.

What are fossil fuels?

Fuels such as coal and oil made over millions of years from buried dead organisms; burning them releases stored carbon.

What powers the water cycle?

Energy from the Sun, and gravity.

What is transpiration?

The loss of water vapour from the leaves of plants.

What do decomposers do?

They break down dead material, release enzymes, and return minerals and carbon dioxide.

What conditions make decay fastest?

Warm, moist and plenty of oxygen.

Why does decay slow in a peat bog?

There is little oxygen and the water is acidic, so decomposers are not active.

Unlock all 49 questions, flashcards & more

इस टॉपिक के हर सवाल, स्लाइड्स, फ्लैशकार्ड और रिवीज़न नोट्स देखने के लिए फ्री अकाउंट बनाएं।

साइन अप करें — फ्री लॉग इन

पास्ट पेपर

इस टॉपिक के लिए पास्ट-पेपर प्रैक्टिस जल्द आ रही है।

जल्द आ रहा है

Trophic level	Energy held (kJ)
Grass	50,000
Grasshopper	4,000
Frog	600
Snake	30

Temperature (°C)	Mass lost (g)
5	2
15	8
25	15
35	20
55	1