Answers · Hormones

A reflex and a fright — answer key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. CQ1 · Practice

Model answer. C. Nervous control has the faster speed of action: impulses act within a fraction of a second. Hormonal control has the longer duration of effect: a hormone keeps acting for minutes while it stays in the blood.

A full answer includes

I chose row C.
I did not choose row A: the faster kind of control is not also the longer-lasting one.

Also accept

Watch for

“Row A: nervous control is faster and also lasts longer.” — Nervous control is faster, but its effect is short: when the impulses stop, the muscle relaxes. The longer-lasting effect is hormonal.
“Row B: hormonal control is faster and also lasts longer.” — A hormone lasts longer, but it is slower to act: it must be carried in the blood to its target organs. Impulses act within a fraction of a second.
“Row D: hormonal control is faster, and nervous control lasts longer.” — Both columns are the wrong way round. Nervous control is faster; hormonal control lasts longer.

2. CQ2 · Practice

Model answer. Adrenaline keeps the heart rate high for as long as it stays in the blood. If it were removed more slowly, it would stay in the blood longer, so the heart rate would stay above the resting rate for longer: the duration of the hormonal effect would increase. The jump in the first second is nervous, so it would not change.

A full answer includes

I chose "would stay above the resting rate for longer".
I did not choose the jump in the first second: that part is caused by nerves, not by adrenaline.

Also accept

it would stay above the resting rate for longer

Watch for

“The heart rate would jump higher in the first second.” — The jump in the first second is caused by nerve impulses, before adrenaline reaches the heart. Slower removal of adrenaline changes the later, longer part.
“The heart rate would fall back to the resting rate sooner.” — That is the wrong way round. Adrenaline that stays in the blood longer keeps acting longer, so the fall is slower.
“The heart rate would not change at all after the fright.” — The nerves still make the heart rate jump, and adrenaline is still released. Only its removal is slower.

3. CQ3 · Practice

Model answer. Nervous control. Within one second only nerve impulses can reach the heart. Adrenaline has to be released into the blood and carried to the heart, which takes longer: it causes the slower climb to 123 over the next two minutes.

A full answer includes

I chose nervous control.
I did not choose adrenaline: a hormone cannot be released and carried to the heart within one second.

Also accept

nervous control

Watch for

“Hormonal control: adrenaline reached her heart.” — Adrenaline causes the slower climb over the next two minutes. In the first second it has not yet been carried to the heart in the blood.
“Neither: the heart speeds up whenever she walks.” — She was already walking before the horn. The sudden rise came just after the horn, so it is a response to that stimulus.
“Both kinds of control, equally and at the same moment.” — Both kinds of control take part in a fright, but not at the same moment: the nerves act first, and adrenaline adds to the rise later.

4. CQ4 · Practice

Model answer. Halfway back is halfway between the peak and the resting rate: (118 + 76) ÷ 2 = 194 ÷ 2 = 97 beats per minute.

Checked automatically

Heart rate halfway back (beats per minute): 97 (within ±0.5)
- Common wrong answer 59 : That is half of the peak. Halfway back is halfway between 118 and 76.
- Common wrong answer 42 : That is the rise above the resting rate. Halfway back is (118 + 76) ÷ 2.
- Common wrong answer 21 : That is half of the rise. Add it to the resting rate of 76.

A full answer includes

I added the peak and the resting rate and halved the total: (118 + 76) ÷ 2.
I wrote 97 beats per minute.
I did not halve the peak on its own.

Also accept

97 beats per minute

Watch for

“59 beats per minute.” — That is half of the peak. The heart rate falls back towards the resting rate of 76, not towards zero.
“42 beats per minute.” — That is the rise above the resting rate, 118 − 76. Halfway back is (118 + 76) ÷ 2.
“21 beats per minute.” — That is half of the rise. Add it to the resting rate to find the heart rate halfway back.

5. CQ5 · Practice

Model answer. A blink is a reflex: nervous control, which starts within a fraction of a second and is over in well under a second. A 0.5-second window holds the whole blink and shows its shape. 0.02 second is too short to hold it; in a 1-minute or 10-minute window it would take up a strip far too narrow to read.

A full answer includes

I chose 0.5 second.
I did not choose 10 minutes: the blink would fill too little of the screen for its shape to be seen.

Also accept

0.5 second

Watch for

“0.02 second, to see it in the most detail.” — A blink lasts a few tenths of a second, so a 0.02-second window would show only the very start of it.
“1 minute, to leave some time to spare.” — The blink would fill less than a hundredth of a 1-minute window: you could not see its shape.
“10 minutes, to be sure of seeing all of it.” — All of it would be there, but in a strip far too narrow to read: you could not see its times.

6. CQ6 · Practice

Model answer. The leg is moved by nerve impulses: when the impulses stop, the leg muscle stops contracting, so the effect is short. The heart rate is kept high by adrenaline, a hormone carried in the blood. It goes on acting for as long as it stays in the blood, which is many minutes, so that effect lasts longer.

A full answer includes

I wrote that the leg is moved by nerve impulses.
I wrote that the leg muscle relaxes when the impulses stop, so that effect is short.
I wrote that the heart rate is kept high by adrenaline, a hormone carried in the blood.
I wrote that adrenaline keeps acting while it stays in the blood, for minutes.
I did not write that the heart takes longer to slow down because it is a bigger muscle.

Also accept

impulses stop, so the leg effect is short; adrenaline stays in the blood, so the heart effect lasts

Watch for

“The heart is a bigger muscle, so it takes longer to slow down.” — Size is not the reason. The heart stays fast because adrenaline is still in the blood.
“The leg jerk is hormonal too, but that hormone is used up faster.” — The leg jerk is a reflex, controlled by nerves. It is short because the impulses stop.

7. CQ7 · Practice

Model answer. Speed of action: X is faster, reaching its full size in 0.08 seconds, while Y takes 2 minutes. Duration of effect: X is shorter, over in under a second, while Y lasts about 25 minutes. Y is slow to build up and long-lasting, so it is mainly hormonal (adrenaline); X is a nervous response.

A full answer includes

I wrote that X acts faster than Y (0.08 seconds compared with 2 minutes).
I wrote that the effect of X is shorter than the effect of Y (under 1 second compared with about 25 minutes).
I identified Y as the mainly hormonal response.
I did not compare only one of the two features.

Also accept

X faster; X shorter; Y hormonal

Watch for

“X is hormonal, because the fly touches the whole ear.” — X reaches its full size in 0.08 seconds and is over in under a second: fast and short, so it is nervous control.
“Y lasts longer, so it is also faster.” — Speed and duration are two different features. Y lasts longer, but it takes 2 minutes to build up: it is slower.

8. CQ8 · Practice

Model answer. The highest point of the trace, 104 beats per minute, is at 2 minutes on the time axis, so the time to the peak is 2 minutes.

Checked automatically

Time to the peak: 2 min (within ±0.25 min)
- Common wrong answer 104 : That is the heart rate at the peak. Go down from the peak to the time axis.
- Common wrong answer 12 : That is the end of the graph. The peak is the highest point of the trace.

A full answer includes

I went straight down from the highest point of the trace to the time axis.
I wrote 2 minutes.
I did not write the heart rate at the peak instead of the time.

Also accept

2 minutes

Watch for

“104 minutes.” — 104 is the heart rate at the peak, on the vertical axis. The time to the peak is read on the time axis.
“12 minutes, at the end of the graph.” — The end of the graph is not the peak. The peak is the highest point of the trace.

9. CQ9 · Practice

Model answer. (a) Halfway between the peak and the resting rate is (104 + 64) ÷ 2 = 84 beats per minute. (b) Going across from 84 on the vertical axis to the falling part of the trace and down to the time axis gives 6 minutes.

Checked automatically

(a) Heart rate halfway back (beats per minute): 84 (within ±0.5)
- Common wrong answer 52 : That is half of the peak. Halfway back is halfway between 104 and 64.
(b) Time halfway back: 6 min (within ±0.5 min)
- Common wrong answer 0.25 : That is where the trace passes 84 on its way up, in the first half minute. Use the falling part, after the peak.

A full answer includes

(a) I added the peak and the resting rate and halved the total: (104 + 64) ÷ 2.
(a) I wrote 84 beats per minute.
(b) I went across from 84 to the falling part of the trace, after the peak.
(b) I wrote 6 minutes.
I did not use the point where the trace passes 84 on its way up.

Also accept

(a) 84; (b) 6 minutes

Watch for

“(a) 52 beats per minute.” — That is half of the peak. Halfway back is halfway between 104 and 64.
“(b) About a quarter of a minute.” — The trace also passes 84 on its way up, in the first half minute. Halfway back is on the falling part, after the peak.

10. CQ10 · Practice

Model answer. The heart rate jumps at once, within the first second: that is nervous control. It then rises more slowly to a peak of 104 at 2 minutes and falls back slowly, still above the resting rate at 12 minutes: that rise and slow fall are caused by adrenaline, so they show hormonal control.

A full answer includes

I wrote that the heart rate jumps at once, at the start.
I identified that first jump as nervous control.
I wrote that the heart rate then rises to a peak at 2 minutes.
I wrote that it falls back slowly.
I wrote that it is still above the resting rate at 12 minutes.
I identified the rise to the peak and the slow fall as hormonal control (adrenaline).
I did not write that the whole trace is hormonal.

Also accept

jump at once nervous; rise to peak and slow fall hormonal

Watch for

“The whole trace is hormonal.” — The first jump, at once, is too fast for a hormone: it is nervous. Adrenaline causes the later rise and the slow fall.
“The slow fall is nervous, because the impulses have stopped.” — The fall lasts for minutes, as adrenaline is slowly removed from the blood: that part is hormonal.

11. CT1 · Apply

Model answer. Q and S are slower to start (several days, and about 10 minutes) and last much longer (the rest of its life, and about 2 hours), as hormonal control does: S is caused by the hormone insulin. P and R start within a fraction of a second and are over within about a second, as nervous control does.

A full answer includes

I chose Q.
I chose S.
I did not choose P or R: they start within a fraction of a second and are over within about a second.

Also accept

Q and S

Watch for

“P, because a colour change involves the whole body.” — P starts within 0.2 seconds and is over in about a second: fast and short, like nervous control.
“R, because the dog moves its whole body.” — R starts within 0.1 seconds and is over in under a second: fast and short, like nervous control.

12. CT2 · Apply

Model answer. The effect of adrenaline lasts for minutes: in the model person, the heart rate was still above resting at 10 minutes. About 15 minutes shows the rise, the peak and the slow fall. 1 second or 10 seconds would show only the very start, and 1 minute would stop near the peak.

A full answer includes

I chose about 15 minutes.
I did not choose a window of seconds: the effect of adrenaline lasts for minutes.

Also accept

about 15 minutes

Watch for

“1 second, because the injection acts at once.” — The adrenaline must be carried in the blood to the heart, and then it acts for minutes. 1 second shows almost nothing.
“10 seconds, because hormones act fast.” — Hormones act more slowly than nerves, and their effect lasts for minutes. 10 seconds would miss the peak and the fall.
“1 minute, to see the rise.” — In 1 minute the heart rate is still rising or near its peak. The slow fall back would be missed.

13. CT3 · Apply

Model answer. Speed of action: the knee jerk is a reflex under nervous control and happens at once, within a fraction of a second; the deeper voice is caused by the hormone testosterone and builds up slowly, over months. Duration of effect: the knee jerk is over within a second, when the impulses stop; the deeper voice lasts for the rest of his life. A hormonal effect is slower to appear, and it can last far longer than minutes.

A full answer includes

Speed: I wrote that the knee jerk acts faster, at once.
Speed: I wrote that the voice change is slower, over months.
Duration: I wrote that the effect of the knee jerk is short: the leg drops back within a second.
Duration: I wrote that the voice change lasts much longer, for the rest of his life.
I did not compare only the speed, or only the duration.

Also accept

knee jerk faster and shorter; voice change slower and much longer

Watch for

“The voice change is faster, because the blood carries testosterone to the throat.” — The blood does carry testosterone, but the voice changes over months: far slower than the knee jerk, which happens at once.
“Both effects are short, because each stops when its signal stops.” — The knee jerk stops when the impulses stop. The deeper voice stays for life: a hormonal effect can last far longer.