What you need to know
- 8.10–8.16Original mixed practice. Night lengths are illustrative.
No doses and no diagnoses.
By the end, you should be able to…
- Place CNS, hormones, scans and phytochromeA plant pigment that exists in two forms, Pr and Pfr, which change into each other in red and far-red light. in the right answers.
- Give night length rather than the common-name trap.
- Keep serotoninA neurotransmitter in the brain involved in mood, sleep and appetite. as a contribution.
Build your understanding
Sort the question before writing
If it names a region, give the function. If it names a scan, say structure or function and whether it uses ionising radiation. If it names a plant, decide whether the answer is auxinA plant growth substance made in shoot tips that promotes cell elongation., gibberellinA plant growth substance that causes stem elongation and switches on amylase genes in germinating seeds. or phytochromeA plant pigment that exists in two forms, Pr and Pfr, which change into each other in red and far-red light.. If it names depression or Parkinson’s, use the transmitter and the limit.
Make your reasoning visible
Pfr
Active form. Short night keeps it. Long night loses it.
Pituitary releases
Hypothalamus controls. Do not swap them.
Avoid this misconception
The claim: CT, MRI and PET are three names for the same X-ray of thoughts.
The correction: CT uses X-rays for structure. MRI uses magnets for structure and does not use ionising radiation. PET uses a radioactive tracer for function. fMRI is the task version of MRI. None of them reads thoughts.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
Name the two organs of the central nervous system.
Show suggested answer
Brain and spinal cord.
Practice question
Retrieval and explanation · suggested answer
Which region coordinates balance, and which controls heart rate?
Show suggested answer
Cerebellum coordinates balance. The medulla oblongata controls heart rate.
Practice question
Retrieval and explanation · suggested answer
A plant flowers only after a long night. What happens if red light flashes in the middle of that night?
Show suggested answer
Pfr is formed, the long night is interrupted, and the short-day plant does not flower.
Practice question
Retrieval and explanation · suggested answer
State the transmitter and the brain region linked to Parkinson’s disease.
Show suggested answer
Dopamine, produced by cells in the substantia nigra that are lost.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Illustrative: nights are 12 hours. Species A flowers only if nights are shorter than 9 hours. Species B flowers only if nights are longer than 9 hours. Neither receives a flash. Which flowers? What single red-flash treatment would reverse both outcomes? Assume usual phytochrome responses.
Show a hint
12 is a long night relative to 9. A flash shortens the night the plant measures.
Explore the reasoning
A does not flower, because the night is longer than 9 hours. B does flower, because it needs a long night. A red flash in the middle creates Pfr and splits the night, so A now responds as if the night were short and flowers, while B loses its long night and does not. Far-red is not in this treatment. The 9 hours is illustrative.
Recall this lesson
Lesson recall questions
Question 1 of 5: Name the plant growth regulator that stimulates transcription of amylase genes in the aleurone of a germinating cereal grain.
Plant growth regulators
Practice question
Retrieval and explanation · suggested answer
Name the plant growth regulator that stimulates transcription of amylase genes in the aleurone of a germinating cereal grain.
Lesson: 8B 5: Chemical Control Systems in Plants
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Use the NIBIB sentence when a question exaggerates
8B · Exam PracticeNIBIB limits fMRI to observing activation during cognitive tasks, as a type of MRI. That is enough to reject a claim that a scanner reads motives. Plant answers…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB limits fMRI to observing activation during cognitive tasks, as a type of MRI. That is enough to reject a claim that a scanner reads motives. Plant answers are a different part of the same exam practice and do not come from that page. 8.10–8.16 mixed. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause. This is an extension to the lesson, not another fact to memorise.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Which scan from the specification uses a radioactive tracer rather than a magnet?
Explore a possible response
PET. MRI and fMRI use magnets. CT uses X-rays.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
Activation during a task is not a thought transcript
8B · Investigating the Human BrainNIBIB describes MRI as magnet-and-radio pictures of soft tissue, and fMRI as a specialised MRI used to observe brain activation during cognitive tasks. That is the source for…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB describes MRI as magnet-and-radio pictures of soft tissue, and fMRI as a specialised MRI used to observe brain activation during cognitive tasks. That is the source for 8.15’s functional MRI. It does not say the scanner reads intentions. CT and PET are separate NHS descriptions: X-rays, and a radioactive tracer. 8.14 and 8.15: know the five regions, and know what each scan can show. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Why is “the fMRI showed the hypothalamus, so the person was thirsty” too strong?
Explore a possible response
Seeing a region, or even activation, is not a labelled thirst. Thirst would be an interpretation that needs the task and other evidence. The hypothalamus does contain water-balance centres, but a scan caption is not that conclusion by itself.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering