The shape of the lesson
By the end of the lesson, learners can
- Biodiversity and why habitats disappear: Drag the slider to clear the forest, 5% at a time.
- Five effects of deforestation: Deforestation is the clearing of forest, often by cutting and burning.
- Biodiversity: the number of different species in an area.
- Reasons: housing, crops and livestock; extracting natural resources; freshwater and marine pollution.
- Deforestation: biodiversity down, extinction, soil loss, flooding, more carbon dioxide.
- Link each effect to the trees: habitat, roots, water uptake, photosynthesis.
One picture every idea returns to
Biodiversity is the number of different species that live in an area. Habitats are destroyed to provide land for housing, crop plants and livestock, to extract natural resources and by freshwater and marine pollution. By altering food chains and food webs, humans can have a negative impact on habitats. Deforestation reduces biodiversity, can cause extinction, and leads to loss of soil, flooding and an increase of carbon dioxide in the atmosphere.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Clear the forest, lose the species.. Every habitat supports a web of species that depend on each other. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Biodiversity and why habitats disappear | Drag the slider to clear the forest, 5% at a time. Project tab 2 of the lab (Deforestation and its effects) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Five effects of deforestation | Deforestation is the clearing of forest, often by cutting and burning. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 19 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Five effects of deforestation, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Biodiversity is the number of different species, not the number of individual organisms. | A field of a million wheat plants has very low biodiversity. |
| Do not write that deforestation "reduces oxygen so animals suffocate". | The expected effects are lower biodiversity, extinction, soil loss, flooding and more carbon dioxide. |
Habitat destruction: worksheet
6 questions, 19 marks. Written in the style of the papers; no past paper question is reproduced.
Define biodiversity and state two reasons why humans destroy habitats.
Explain the undesirable effects of deforestation.
A survey counted the species of birds in an area of forest and in a nearby area cleared for cattle.
| Area | Number of bird species |
|---|---|
| forest | 64 |
| cattle pasture | 16 |
(a) Calculate the percentage decrease in bird species. (b) Suggest two reasons for the difference.
A hillside forest is cleared and planted with crops. Explain why the crop yield falls after a few years.
Explain how humans can damage a habitat by altering a food web, using an example.
Give two ways in which pollution of fresh water or the sea can destroy habitats.
Answer key and marking notes
- Biodiversity is the number of different species that live in an area.
- To provide land for housing, crop plants or livestock.
- To extract natural resources such as timber or minerals (also accept: freshwater or marine pollution).
- Habitats and food sources are lost, so biodiversity is reduced.
- Species that live only in that forest may become extinct.
- Without roots to hold it, soil is eroded by rain and wind, and the remaining soil loses its mineral ions.
- Water is not absorbed by trees, so it runs off into rivers, causing flooding.
- Fewer trees remove carbon dioxide by photosynthesis, and burning releases carbon dioxide, so atmospheric carbon dioxide increases.
- (a) (64 − 16) ÷ 64 × 100 = 75%.
- (b) The pasture has fewer types of plant, so fewer habitats such as nesting sites.
- There are fewer food sources (fruits, seeds, insects) for different bird species.
- Without tree roots holding the soil, heavy rain washes the topsoil away (soil erosion).
- Topsoil contains most of the mineral ions and humus, so the remaining soil is less fertile.
- Crops therefore have fewer mineral ions such as nitrate and grow less.
- Example: overfishing a predator, hunting, or introducing a new species (such as rats on an island).
- Removing or adding one species changes the numbers of its prey, predators and competitors.
- For example, removing predators lets herbivores increase and overgraze the producers, so the habitat is damaged.
- Excess fertiliser or sewage causes eutrophication, killing fish and other organisms that need oxygen.
- Plastics, oil or toxic chemicals kill or harm organisms and damage habitats such as coral reefs or shorelines.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which statement describes biodiversity?
- AThe number of different species that live in an area
- BThe total number of individual organisms in an area
- CThe number of organisms of one species in an area
- DThe total mass of plants growing in an area
An area has 500 oak trees and 20 birch trees. A second area has 30 trees of each of 12 different species. Which statement is correct?
- AThe second area has the higher biodiversity
- BThe first area has the higher biodiversity
- CBoth areas have the same biodiversity
- DBiodiversity cannot be compared between areas
An open-cast mine is dug in a forest to obtain copper ore. Which reason for habitat destruction does this show?
- AExtraction of natural resources
- BLand for livestock production
- CMarine pollution
- DLand for housing
After a forest on a hillside is cleared, the river below becomes brown and muddy after rain. What is the main cause?
- ASoil is no longer held by tree roots, so it is washed into the river
- BLeaves from felled trees decay and dye the water brown
- CAnimals leaving the forest drink from and stir up the river
- DRain falling on cleared land contains more dissolved minerals
Which of these is an undesirable effect of deforestation?
- AAn increase of carbon dioxide in the atmosphere
- BAn increase in the number of species in the area
- CA decrease in the risk of flooding downstream
- DA decrease in soil erosion on the cleared land
A forest island has a single species of snail found nowhere else. The forest is cleared for palm oil. Why is extinction a particular risk here?
- AThe snail has no other habitat to move to, so the whole species is lost
- BPalm oil plants release a chemical that kills all snails
- CThe snail will evolve too quickly and become a new species
- DClearing the forest increases the snail's food supply too much
Sea otters eat sea urchins, and sea urchins eat kelp seaweed. People hunt the sea otters. What is the most likely effect on the kelp forest?
- AUrchin numbers rise and the kelp forest is destroyed
- BUrchin numbers fall and the kelp forest grows larger
- CKelp is unaffected because otters do not eat kelp
- DKelp grows faster because otters stop releasing waste
Rainforest soils are thin. Farmers clear a forest and grow crops, but within three years the yield has fallen sharply. Which explanation is best?
- ARain washes away topsoil and leaches the mineral ions no longer recycled by the trees
- BCrop plants photosynthesise more slowly in tropical sunlight
- CInsects from the forest die out, so the crops are not protected
- DThe crops take carbon dioxide from the soil instead of the air
Quiz key
Biodiversity is the number of different species living in an area. The total number of organisms ignores variety; the number of one species is a population; plant mass is biomass, not biodiversity.
The second area has 12 species and the first has only 2, so the second has higher biodiversity even though it has fewer trees (360 against 520). Total numbers of trees do not measure biodiversity, and the two areas can be compared by counting species.
Mining removes a natural resource (copper ore) from the environment, destroying the habitat on the surface. Livestock and housing are about using the land surface for people; marine pollution affects the sea.
Without roots to bind it and a canopy to shield it, soil is eroded by heavy rain and carried into rivers, making them muddy. Decaying leaves, animals and dissolved minerals do not explain the large amount of mud carried in after each rainfall.
Fewer trees take in carbon dioxide and burning wood releases it, so atmospheric carbon dioxide increases. Deforestation reduces species numbers, raises flood risk and increases soil erosion, so the other three are the opposite of what happens.
A species living in only one place loses its entire habitat when that place is destroyed, so it can become extinct. There is no evidence of a toxin from palm plants; evolution does not happen fast enough to rescue it; and clearing the forest removes, not increases, its food.
With fewer otters, fewer urchins are eaten, so urchins increase and graze away the kelp, destroying the habitat for many other species. Urchins would rise, not fall. Kelp is affected indirectly through the food chain, and otter waste is not the key factor.
In a rainforest most mineral ions are held in the living plants and recycled quickly by decomposers. When trees are removed, heavy rain erodes the thin topsoil and washes out the remaining ions, so crops soon lack nutrients. Tropical sunlight favours photosynthesis; forest insects do not protect crops; plants take carbon dioxide from the air.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.