The shape of the lesson
By the end of the lesson, learners can
- A trap that snaps: Choose Venus fly trap and press Go once: one hair touched, the trap stays open.
- Auxin and the acid wall: In the auxin view, press Go and watch the yellow H + ions pile up in the walls of the cells behind the shoot tip before the cells begin to stretch upwards.
- Gibberellin wakes a barley grain: In the gibberellin view, press Go.
- Fly trap: two touches in about 20 s, action potentials, turgor change.
- Auxin: H+ pumped into the wall, wall loosens, cell elongates.
- Gibberellin: embryo to aleurone layer, amylase gene switched on.
- Amylase: starch to maltose for the embryo's respiration.
One picture every idea returns to
The Venus fly trap has modified leaves with two lobes, each carrying sensitive trigger hairs. Bending a hair produces a receptor potential; if two hairs are touched within about 20 seconds, action potentials spread across the lobes. These trigger rapid movement of ions and water, changing the turgor of cells in the lobes, so the lobes flip from convex to concave and the trap snaps shut in a fraction of a second. Auxin, made in shoot tips, stimulates elongation growth: it binds to a receptor and stimulates proton pumps to pump H+ into the cell wall; the acidic wall activates expansins, which loosen the links between cellulose microfibrils, so water entering by osmosis stretches the wall and the cell elongates. In a germinating barley grain, the embryo releases gibberellin, which travels to the aleurone layer and switches on the gene for amylase; amylase hydrolyses starch in the endosperm to maltose, providing sugars for the embryo's respiration and growth.
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, Plants respond too.. Plants have no nerves or muscles, yet a Venus fly trap snaps shut in a fraction of a second, shoots grow towards light and a barley grain turns its starch store into sugar on cue. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: A trap that snaps | Choose Venus fly trap and press Go once: one hair touched, the trap stays open. Project tab 8 of the lab (Control and coordination lab, plant responses) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Auxin and the acid wall | In the auxin view, press Go and watch the yellow H + ions pile up in the walls of the cells behind the shoot tip before the cells begin to stretch upwards. | Pairs |
| 21 to 30 min | Teach and check: Gibberellin wakes a barley grain | In the gibberellin view, press Go. | Cooperative Concept Mapping |
| 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, 22 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 Gibberellin wakes a barley grain, 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.
Cooperative Concept Mapping
Teams receive the key terms on cards and arrange them on a large sheet, drawing and labelling the links. Compare maps between teams before showing the model map.
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 |
|---|---|
| The Venus fly trap has no muscles and no nerves. | Its rapid movement comes from action potentials and changes in turgor and cell wall properties, not from contraction. |
| Auxin does not make the cell divide here, and it is the cell wall that becomes acidic, not the cytoplasm. | The key steps are protons pumped into the wall, acidic wall, loosening, then water uptake and elongation. |
Control and coordination in plants: worksheet
6 questions, 22 marks. Written in the style of the papers; no past paper question is reproduced.
Describe the response of a Venus fly trap to an insect landing on its lobes, and explain how closure is achieved.
Explain the role of auxin in elongation growth.
Describe the role of gibberellin in the germination of a barley grain.
Plan an experiment to show that gibberellin stimulates amylase production in barley grains.
Coleoptile segments are placed in buffers. In pH 7 buffer with auxin they grow 2.4 mm in 2 hours; in pH 4.5 buffer without auxin they grow 2.2 mm; in pH 7 buffer without auxin they grow 0.4 mm. Explain what these results suggest.
State two ways in which coordination in plants differs from coordination in mammals.
Answer key and marking notes
- The insect bends trigger hairs on the inner surface of the lobes.
- Ion channels open and a receptor potential is produced in cells at the base of the hair.
- If two hairs are stimulated within about 20 seconds, action potentials travel across the lobes.
- Ions and water move rapidly; cell walls loosen as protons are pumped into them and the turgor of cells in the lobes changes.
- The lobes flip from convex to concave, so the trap snaps shut in a fraction of a second.
- Auxin is made in the shoot tip and moves to the zone of elongation, where it binds to receptors.
- It stimulates proton pumps in the cell surface membrane to actively pump H+ into the cell wall.
- The cell wall becomes acidic (lower pH).
- This activates expansins, which loosen the bonds between cellulose microfibrils, so the wall becomes more extensible.
- Water enters by osmosis and turgor pressure stretches the cell, which elongates.
- The grain absorbs water and the embryo produces gibberellin.
- Gibberellin diffuses to the aleurone layer.
- It causes breakdown of DELLA proteins, allowing a transcription factor to switch on the gene for amylase, so amylase is made.
- Amylase hydrolyses starch in the endosperm to maltose / glucose, which the embryo uses for respiration and growth.
- Cut barley grains in half and keep the halves without embryos; soak them in a range of gibberellin concentrations (including zero as a control).
- Place the cut halves on starch agar for a fixed time, then flood the plates with iodine solution.
- Measure the area of the clear zone (no blue-black colour) around each half as a measure of amylase activity; keep temperature, time and number of grains the same.
- Auxin increases growth from 0.4 mm to 2.4 mm at pH 7.
- An acidic buffer alone (pH 4.5) causes almost as much growth (2.2 mm) as auxin.
- This supports the idea that auxin works by acidifying the cell wall (proton pumping), and low pH itself loosens the wall so cells elongate.
- Plants have no nervous system: no neurones or synapses (although some, like the Venus fly trap, produce action potentials).
- Plant responses are mostly brought about by plant hormones (such as auxin and gibberellin) changing growth, often slowly, rather than by muscles contracting.
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.
In a germinating barley grain, which tissue responds to gibberellin by producing amylase?
- Athe aleurone layer
- Bthe embryo
- Cthe endosperm
- Dthe seed coat
Auxin stimulates proton pumps in cells behind a shoot tip. Where are the protons pumped to?
- Ainto the cell wall
- Binto the vacuole
- Cinto the chloroplasts
- Dinto the nucleus
An insect brushes one trigger hair of a Venus fly trap once, then flies away. What happens?
- Aa receptor potential is produced but the trap stays open
- Bthe trap snaps shut immediately
- Cthe trap closes slowly over the next hour
- Ddigestive enzymes are secreted onto the open lobes
How does a low pH in the cell wall allow a plant cell to elongate?
- Ait activates expansins that loosen the links between cellulose microfibrils
- Bit dissolves the cellulose microfibrils completely
- Cit makes the cell lose water so the wall becomes thinner
- Dit stimulates the cell to divide into two smaller cells
Which enzyme hydrolyses starch in the endosperm of a germinating barley grain, and what product does the embryo receive?
- Aamylase; maltose
- Bamylase; gibberellin
- Cmaltase; starch
- Dprotease; amino acids only
Barley grains were soaked in water and their amylase activity measured. What do the results in the bar chart show?
- Athe embryo is the source of a signal, gibberellin, that stimulates amylase production
- Bthe embryo produces the amylase that breaks down the starch
- Cgibberellin inhibits amylase production when the embryo is present
- Dthe aleurone layer cannot make amylase without the embryo attached
A mutant barley plant has DELLA proteins that cannot be broken down. Its grains are given gibberellin. What would you expect?
- Alittle amylase is made, because the DELLA proteins keep blocking transcription of the amylase gene
- Bmore amylase than normal is made, because DELLA proteins activate the amylase gene
- Camylase is made normally, because gibberellin acts directly on the amylase gene
- Dthe embryo makes no gibberellin, so the added gibberellin is broken down
A trigger hair of a Venus fly trap is touched once, and a second hair is touched 45 seconds later. The trap does not close. Which is the best explanation?
- Athe effect of the first touch fades before the second, so the two are not added together to trigger closure
- Bthe second hair was on the other lobe, and only one lobe can respond
- Cthe first touch used up all the ATP in the lobes
- Dthe trap can close only if three hairs are touched
Quiz key
Gibberellin from the embryo diffuses to the aleurone layer, where it switches on the amylase gene. The embryo produces the gibberellin but not this amylase. The endosperm is the starch store that amylase acts on. The seed coat protects the grain and does not secrete enzymes.
Proton pumps in the cell surface membrane move H+ out of the cytoplasm into the cell wall, lowering its pH so that it loosens. Pumping into the vacuole or chloroplasts would not loosen the wall. Protons are not pumped into the nucleus as part of this response.
A single touch produces a receptor potential, but closure needs a second stimulus within about 20 seconds to set off action potentials. Snapping shut after one touch would waste energy on raindrops. Slow closure over an hour is not how the trap responds. Digestive enzymes are released only after the trap has closed on prey.
Expansins are activated at low pH and break hydrogen bonds between cellulose microfibrils and other wall polysaccharides, so the wall can stretch as the cell takes up water. The cellulose itself is not dissolved, or the cell would burst. Water is taken up, not lost, during elongation. Elongation growth is cell enlargement, not cell division.
Amylase hydrolyses starch to maltose (and then glucose), which the embryo uses for respiration and growth. Gibberellin is the signal, not a product of starch breakdown. Maltase breaks maltose down; it does not produce starch. The aleurone layer may make proteases too, but they do not act on starch.
Removing the embryo (B) stops amylase production; adding gibberellin to grains without an embryo (C) restores it to almost the level of whole grains (A). So the embryo normally supplies gibberellin, which stimulates the aleurone layer. If the embryo made the amylase itself, C would stay low. Gibberellin raises, not lowers, amylase activity. C shows the aleurone layer can make amylase without the embryo, as long as gibberellin is present.
Gibberellin works by causing the breakdown of DELLA proteins, which inhibit a transcription factor needed for the amylase gene. If DELLA proteins cannot be broken down, the gene stays switched off even with gibberellin. DELLA proteins are inhibitors, not activators. Gibberellin does not act directly on the gene. The mutation affects DELLA breakdown, not gibberellin production or stability.
The trap closes only if two stimuli arrive within about 20 seconds; after 45 seconds the effect of the first touch has faded, so the second counts as a first touch again. Hairs on either lobe can contribute. One touch does not use up the lobes' ATP. Two touches, not three, are needed for closure.
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.