Sample Essay Answers: Biological Rhythms, Sleep, and Dreaming
Discuss explanations relating to the functions of sleep. (24 marks)
Chris' answer
There is a lot of disagreement about the functions of sleep, and several theories have been put forward. The first of these is the ecological approach. This says that sleep is related to an animal's lifestyle and habitat. Meddis proposed that animals sleep when it is unsafe to be foraging. It keeps them safe and out of harm's way. But this is contradicted by the Indus dolphin, which sleeps for brief periods over the whole day, or the bottlenose dolphin, which sleeps with only one side of the brain at a time so it never loses consciousness. This is because dolphins have to breathe regularly and if they sleep deeply they would drown. But it would be safest if they didn't sleep at all, so it shows that sleep is very necessary and has more functions than just safety. The ecological approach has also shown that the length of sleep depends on body size, as large animals usually sleep less than smaller animals, and predators sleep for longer than prey animals. But there are lots of exceptions, as sloths are large animals and are not predators but sleep for most of the day. Large animals burn up energy more slowly than small animals, so small animals may sleep more in order to conserve energy.
The restoration approach to sleep says that sleep is necessary to restore the brain and the body after hormones and chemicals have been used up in the day, to make sure that they function properly. Oswald says that slow-wave sleep is for body restoration as growth hormone is released during this period, and REM sleep is for the brain as oxygen consumption is greatest during this stage as the brain makes new transmitters and synapses. On the other hand, Horne says that sleep is only for the brain, as the body restores itself when we are just resting. Horne did many studies on sleep deprivation, and showed that it affects perception and attention more than anything else, so that sleep is necessary for the brain to function properly. When he let people sleep after deprivation, they spent more time in deep slow-wave sleep and REM than anything else, and Horne concluded that these were the important stages of sleep for brain restoration. He called them core sleep.
Horne's theory would explain why babies spend about 80% of their sleep time in REM, as their brains are growing rapidly and they are learning huge amounts. However some studies found that people sleep longer after physical exercise, which would support Oswald as the body is being restored. But Horne found in his study that people don't sleep for longer after exercise, they only go to sleep quicker.
Other ideas about the functions of sleep include resynthesising neurotransmitters, which is very close to Horne's restoration theory. Dreaming in REM sleep might also be an important function of sleep but that is a controversial area as psychologists do not agree on what the functions of dreams are. So sleep is very complicated. It is affected by the animal's lifestyle and also seems to be important for the brain to function properly. As all animals sleep, it must have important functions, but we still don't agree on what those are.
Examiner's comment
A very good essay worthy of a good A grade. The key is organisation; many answers will have similar material but it will be presented in a disorganised way with no overall pattern. This candidate covers two main areas, with reasonable AO1 and impressive AO2. They understand that ecological accounts cover a range of factors and that no one factor is dominant, so there is no point in pretending that there is. The restoration accounts are presented clearly, and using Oswald and Horne is useful as they can be easily compared. Sleep deprivation studies are used effectively and there is a good balance between AO1 and AO2 comment and analysis. This is an area that can benefit from a closing summary, and this candidate produces one that emphasises how complicated the functions of sleep seem to be, and also refers to other work they could have covered given the time. A small picky point is that they could have pointed out that there is no necessary contradiction between ecological and restoration accounts-sleep is necessary for restoration, but where and when animals sleep is influenced by a range of ecological and physiological factors. Overall the key to this answer is effective use of material.
Sam's answer
Meddis said that sleep was to keep animals safe at night, as predator animals sleep for more than animals preyed upon. But Webb called this a waste of time theory. Also some dolphins can't sleep much because they live in rivers and have to avoid branches all the time and have to be alert. This shows that sleep doesn't keep animals safe. Also, the sloth sleeps for 18 hours a day even though it isn't in danger because it sleeps up in trees and doesn't have any predators. So sleep can't be just for safety.
Other theories say that sleep is to keep the body healthy, and this has been studied using sleep deprivation. Randy Gardner, a student, went without sleep for 11 days and suffered few problems, and even though he slept more to catch up, he didn't make up all the sleep he had lost. Peter Tripp, a disc jockey, suffered from hallucinations and delusions after he was sleep deprived. This shows that there are individual differences in how we react to sleep deprivation. But these were case studies and it is hard to generalise, and also they were only on men so cannot be generalised to women. Rats that are deprived of sleep for many days eventually die. This shows that sleep must be necessary, but these experiments were very unethical. Rats were kept awake by dropping them in water when they fell asleep to wake them up. But as it was done on rats it is hard to generalise to humans. A man who had a tumour and couldn't sleep did eventually die, but this might have been due to his tumour and not the sleep deprivation.
Oswald said that slow-wave sleep was for the body. He found that hormones were released in SWS to help the body recover. This is supported because people sleep more after doing ultra marathons. The brain is very active during REM sleep so Oswald says this is to restore the brain. This is supported by studies which show that babies have lots of REM sleep when their brains are growing.
Sleep has lots of functions but there seems to be more evidence for Oswald's theories, that sleep is to restore the brain and the body.
Examiner's comment
This answer would just about get through, with a D grade, on the basis of reasonable AO1 and some attempts at AO2. There are some key misunderstandings, as reflected in the first sentence (why should predators sleep more if sleep is for safety?), but some relevant examples are given, such as the dolphins and the sloth, and some accurate if limited commentary. A weakness throughout is that there is no consistent focus on "explanations", so findings are rarely linked to different theories. Sleep deprivation studies are described, but their full implications for explanations are not brought out and AO2 is restricted to methodology and ethics. The broad range of systematic studies is not referred to but is far more important than these case studies. Oswald is covered more effectively, with findings clearly linked to his theory. Throughout there is little attempt at sustained commentary and analysis, and a general lack of organisation and focus.