Scientific calculations
The concentrations of different substances in the blood can be measured - for example, the level of water in the blood throughout the day. This gives scientists data that they can analyse, helping them to explain what is going on.
Question
A patient's blood plasma was monitored over a period of hours to see how the water levels changed.
Describe what hormonal change happens at point A.
Explain why the amount of water in the blood decreases.
There is less ADH being released from the pituitary gland and so less water is reabsorbed by the kidney.
More water travels to the bladder and is lost in the urine. The blood water levels return to normal.
Question
Suggest a reason for the trend in the graph at point B.
The person has lost water, which could be to do with sweating if the person is too hot or has been exercising.
Question
A scientist studied a patient's blood plasma and urine. Describe the results shown in the table.
Give an explanation.
| Substance | Concentration in blood plasma (g/100ml) | Concentration in urine (g/100ml) |
| Protein | 8.0 | 0 |
| Urea | 0.03 | 2 |
| Glucose | 0.1 | 0 |
| Substance | Protein |
|---|---|
| Concentration in blood plasma (g/100ml) | 8.0 |
| Concentration in urine (g/100ml) | 0 |
| Substance | Urea |
|---|---|
| Concentration in blood plasma (g/100ml) | 0.03 |
| Concentration in urine (g/100ml) | 2 |
| Substance | Glucose |
|---|---|
| Concentration in blood plasma (g/100ml) | 0.1 |
| Concentration in urine (g/100ml) | 0 |
When you answer a question like this you must make sure that you describe AND explain the results. You shouldn't write 'describe' and 'explain' in your answer, but in the mark scheme the sections have been split up so you can see the difference between in a description and explanation.
Description: There is no protein or glucose in the urine.
There is more urea in the urine than in the blood plasma.
Explanation: Proteins are too large to fit through the capillary wall and so are not filtered out of the blood in the kidney nephron. Glucose is filtered out of the blood in the nephron but then it is all reabsorbed back into the blood again. Therefore no glucose is found in the urine. Glucose is needed for respiration. Urea is a waste product so needs to be removed from the body. It is not reabsorbed back into the blood so is found in the urine.
More guides on this topic
- How do substances get into, out of and around our bodies?
- How does the nervous system help us respond? - OCR 21st Century
- What role do hormones play in human reproduction? - OCR 21st Century
- What can happen when organs & control systems stop working?
- Sample exam questions - the human body - staying alive