DSE Biology: Ecosystems and Energy Flow — Tutor Lesson Plan (food chains, trophic levels, 10%)

2026-10-27

Tutor lesson-prep guides · Secondary biology

Students draw a food chain but answer why there are fewer tigers with because they get eaten. The real answer is that each level keeps about a tenth of the energy.

Objectives — the student can read trophic levels from a food web, apply the ten per cent rule to energy and biomass, and describe carbon cycling.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Photosynthesis	How producers obtain energy	Light to chemical energy
Respiration	The process releasing energy	Aerobic respiration
Percentages	Ten per cent of 10 000	1000

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-10 min	Chains and webs	Arrows show energy flow	Label three levels
10-26 min	Energy transfer	About ten per cent per level	Four levels
26-42 min	Biomass pyramids	Why the top is narrow	Explain one exception
42-54 min	Carbon cycle	Photosynthesis, respiration, decay, combustion	Draw the cycle
54-57 min	Format	Give reasons, not descriptions	Rewrite one answer
57-60 min	Exit check	Three questions marked	Finish alone

03 Teaching script (read it out)

Scene 1: Arrows show energy flow

Grass, rabbit, snake, hawk: each arrow points from the eaten to the eater.
The first trophic level is always a producer.
One organism can appear in several chains, which makes a web.

Student counts how many chains include the hawk.

Scene 2: Each level keeps about a tenth

Producer 10 000 kJ, primary consumer 1 000, secondary 100, tertiary 10.
The rest is lost to respiration, excretion and uneaten parts.
That is why top predators are few and hold little biomass.

Student computes a tertiary consumer from 50 000 kJ: 50 kJ.

Scene 3: Carbon cycles, energy does not

Photosynthesis fixes carbon dioxide into organic matter; respiration, decay and combustion release it.
Burning fossil fuels upsets that balance and raises atmospheric carbon dioxide.

Note: carbon cycles while energy flows one way.

04 Question types and worked steps

Type	Example	Steps	Answer
Trophic level	grass, rabbit, snake, hawk	Count the arrows	Hawk is fourth
Energy	producer 10 000 kJ	Multiply by 0.1 per level	10 kJ at level four
Biomass	narrow at the top	Energy decreases	Fewer individuals supported
Carbon cycle	role of decomposers	Organic carbon to carbon dioxide	Returned to the air

Sanity check (teach this): Energy must fall at each level; a higher value means the direction or the percentage is wrong.

05 Independent practice (3 questions)

Question	Answer	What to watch
Producer 50 000 kJ, tertiary consumer	50 kJ	Three successive tenths
Snake in a four-level chain	Fourth trophic level	Count from the producer
Does energy cycle?	No, it is lost as heat	Only carbon cycles

06 Common mistakes and what to say

Mistake	Student writes	Say this
Energy and biomass confused	says energy cycles	Energy flows one way.
Levels counted from the consumer	calls the primary consumer level one	Producers come first.
No respiratory loss	assumes full transfer	About a tenth survives.
Arrows reversed	arrow points to the food	Arrows follow energy flow.

07 Homework (paper, section and question numbers)

Secondary biology chapter index — Use the three questions on this page

08 Exit check (last 5 minutes)

Question	Answer	Decision
50 000 kJ to a tertiary consumer	50 kJ	All right: move to balance
Snake in a four-level chain	Fourth level	One wrong: re-teach levels
Does energy cycle?	No, it is lost	Two wrong: repeat scene 2

09 Tutor FAQ

Memorise the ten per cent rule?

Remember about a tenth; numbers are given.

Marine exceptions?

Biomass pyramids can invert, energy pyramids never do.

Link to human impact?

Pollution and habitat loss break the chains.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.