The shape of the lesson
By the end of the lesson, learners can
- Cortex and medulla: Extended.
- Filtration in the glomerulus: Extended.
- Reabsorption and urine: Extended.
- Cortex outer, medulla inner.
- Glomerulus filters water, glucose, urea and ions; blood cells and proteins stay in the blood.
- Reabsorbed: all the glucose, some ions, most water.
- Urine: urea, excess water, excess ions; no glucose, no protein.
One picture every idea returns to
Extended: a kidney cut lengthways shows an outer cortex and an inner medulla. In each nephron, blood in the glomerulus is filtered: water, glucose, urea and ions pass into the nephron, while blood cells and proteins stay in the blood. As the filtrate flows along the nephron, all of the glucose, some of the ions and most of the water are reabsorbed into the blood. What is left is urine: urea, excess water and excess ions.
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, Filter everything, keep what you need.. Each kidney holds about a million microscopic tubes called nephrons. 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: Cortex and medulla | Extended. Project tab 2 of the lab (A kidney cut in half) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Filtration in the glomerulus | Extended. Project tab 3 of the lab (Filtration and reabsorption in a nephron) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Reabsorption and urine | Extended. | Jigsaw |
| 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, 17 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 Reabsorption and urine, 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.
Jigsaw
Split the content into expert pieces. Expert groups master one piece each, then regroup so every home team has one expert per piece, and each expert teaches their piece to the team.
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 cortex is the outer layer and the medulla is the inner layer. | The pale space in the middle, joined to the ureter, is the pelvis, not the medulla. |
| Filtration does not pick out the useful substances: glucose is filtered out along with urea, because both are small. | The nephron sorts useful from waste later, by reabsorption. |
| Healthy urine contains no glucose and no protein. | Glucose is filtered, but all of it is reabsorbed; protein is never filtered at all. Keep the two reasons separate. |
The kidney: worksheet
6 questions, 17 marks. Written in the style of the papers; no past paper question is reproduced.
Extended. A kidney is cut in half lengthways. Name the outer region and the inner region that can be seen.
Extended. Describe what happens to blood as it passes through the glomerulus.
The table shows the concentrations of some substances in blood plasma, in the filtrate entering the nephron, and in urine.
| Substance | Plasma / g per dm3 | Filtrate / g per dm3 | Urine / g per dm3 |
|---|---|---|---|
| protein | 75 | 0 | 0 |
| glucose | 1.0 | 1.0 | 0 |
| urea | 0.3 | 0.3 | 20 |
Extended. Explain the figures for (a) protein, (b) glucose, (c) urea.
Extended. The kidneys of an adult form about 180 dm3 of filtrate per day but produce only about 1.5 dm3 of urine. Assuming the filtrate is mostly water, calculate the percentage of the filtered water that is reabsorbed.
Extended. State the substances found in the urine of a healthy person, and name two substances that are filtered in the glomerulus but returned to the blood.
Extended. A urine test shows glucose in a patient’s urine. Using your knowledge of the nephron, suggest what this tells a doctor.
Answer key and marking notes
- Outer region: cortex.
- Inner region: medulla.
- Blood arrives at the glomerulus at high pressure.
- Water, glucose, urea and ions are filtered out of the blood into the nephron (Bowman’s capsule), forming the filtrate.
- Blood cells and proteins are too large to be filtered, so they remain in the blood.
- (a) Protein is in plasma but not in the filtrate because protein molecules are too large to be filtered out of the glomerulus.
- (b) Glucose is filtered, so its concentration in the filtrate equals that in plasma.
- All of the glucose is then reabsorbed into the blood, so there is none in urine.
- (c) Urea is filtered and is not reabsorbed, while most of the water is reabsorbed, so urea becomes much more concentrated in the urine (about 67 times).
- Water reabsorbed = 180 − 1.5 = 178.5 dm3.
- Percentage = (178.5 ÷ 180) × 100 = 99.2% (about 99%).
- Urine contains urea, excess water and excess ions.
- Glucose is filtered and all of it is reabsorbed.
- Water (most of it) and ions (some of them) are also filtered and reabsorbed.
- In a healthy nephron all of the filtered glucose is reabsorbed, so normally urine contains no glucose.
- Glucose in urine means more glucose was filtered than the nephrons could reabsorb.
- This suggests the blood glucose concentration is abnormally high (for example in untreated diabetes), so further tests are needed.
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 blood vessel brings blood containing urea to a kidney?
- Athe renal artery
- Bthe renal vein
- Cthe hepatic portal vein
- Dthe pulmonary artery
Which statement about the kidneys is correct?
- AThey remove urea, excess water and excess ions from the blood
- BThey make urea from excess amino acids
- CThey excrete the carbon dioxide made in respiration
- DThey store urine until it is released from the body
A person produces urine at an average rate of 1.0 cm3 per minute. What volume of urine is produced in one day?
- A1.44 dm3
- B14.4 dm3
- C0.144 dm3
- D0.06 dm3
In one day a person takes in 2500 cm3 of water from food and drink and makes 300 cm3 in respiration. They lose 600 cm3 in sweat, 400 cm3 in exhaled air and 100 cm3 in faeces. What volume must the kidneys excrete in urine to keep the water content of the body constant?
- A1700 cm3
- B1400 cm3
- C2800 cm3
- D1100 cm3
The diagram shows a kidney cut lengthways. Which labelled region is the medulla?
- AQ
- BP
- CR
- DS
Which pair of components of the blood stays in the glomerulus and is not filtered into the nephron?
- Ared blood cells and proteins
- Bglucose and red blood cells
- Curea and proteins
- Dwater and ions
The table shows the concentrations of three substances, X, Y and Z, in the blood plasma, in the filtrate entering a nephron and in the urine of a healthy person. Which row identifies them correctly?
- AX glucose, Y protein, Z urea
- BX urea, Y protein, Z glucose
- CX protein, Y glucose, Z urea
- DX glucose, Y urea, Z protein
The kidneys form filtrate at 120 cm3 per minute and urine at 1.5 cm3 per minute. Assuming the filtrate is mostly water, what percentage of the filtered water is reabsorbed?
- A98.8%
- B1.25%
- C80%
- D98.5%
Quiz key
The renal artery, a branch of the aorta, brings blood containing urea to each kidney. The renal vein carries the cleaned blood away. The hepatic portal vein carries blood from the gut to the liver. The pulmonary artery carries deoxygenated blood from the heart to the lungs.
The kidneys excrete urea, excess water and excess ions, which leave as urine. Urea is made in the liver, not the kidneys. Carbon dioxide is excreted through the lungs. Urine is stored in the bladder, not in the kidneys.
A day has 24 × 60 = 1440 minutes, so the volume is 1440 cm3, which is 1440 ÷ 1000 = 1.44 dm3. 14.4 and 0.144 dm3 come from slipping a power of ten in the unit conversion. 0.06 dm3 is the volume for one hour only (60 cm3).
Total gain = 2500 + 300 = 2800 cm3. Losses other than urine = 600 + 400 + 100 = 1100 cm3. Urine = 2800 − 1100 = 1700 cm3. 1400 cm3 forgets the water made in respiration. 2800 cm3 is the total gain, ignoring the other losses. 1100 cm3 is the total of the other losses, not the urine.
Q is the medulla, the darker inner region that contains the loops of the nephrons and the collecting ducts. P is the cortex, the outer layer. R is the pelvis, the space that collects urine. S is the ureter, carrying urine to the bladder.
Red blood cells and protein molecules are too large to be filtered, so they stay in the blood. Glucose is small and is filtered (then all reabsorbed). Urea is filtered, and that is how it gets into urine. Water and ions are both filtered, and most of the water and some of the ions are later reabsorbed.
X is filtered (same concentration in plasma and filtrate) but absent from urine, so all of it is reabsorbed: glucose. Y is in plasma but not in the filtrate, so it is too large to be filtered: protein. Z is filtered, not reabsorbed and becomes far more concentrated in urine as water is reabsorbed: urea. Each wrong row swaps one of these patterns, for example urea would never be absent from healthy urine, and protein could not appear in the filtrate.
Reabsorbed = 120 − 1.5 = 118.5 cm3 per minute; (118.5 ÷ 120) × 100 = 98.75%, about 98.8%. 1.25% is the percentage that becomes urine, not the percentage reabsorbed. 80 is 120 ÷ 1.5, a ratio, not a percentage. 98.5% wrongly subtracts 1.5 from 100 instead of working out a percentage of 120.
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.