Part2

Read the text and answer the questions below.

The Internal Body Clock

From buffalo to bacteria, oaks to algae, all life follows the same relentless 24-hour cycle, which is driven by the rising and setting of the Sun. Or is it? Over 250 years ago, a French scientist performed a simple experiment that blew apart the idea that all life on Earth does the bidding of the Sun. Intrigued by the way some flowers open and close their leaves each day, Jean-Jacques de Mairan put a heliotrope in a darkened room and observed the effect. He was expecting the plant, robbed of sunlight, to cease its daily routine. To his astonishment, its leaves continued to open and close as if in response to some invisible timekeeper.

But what – and where – is this internal timekeeper? And how does it achieve such astonishing regularity? These are the mysteries at the forefront of chronobiology, the study of the effect of time in living organisms. The search for answers is about more than just tying up some scientific loose ends. Internal ‘clocks’ clearly cause a lot of hardship. When an individual’s ‘clock’ is knocked out of synchronization through having to work at night or go on long-haul flights, that person can be left utterly unable to think or act. Yet even when these ‘clocks’ work correctly, the natural rhythms of alertness they generate prove dangerous: traffic accident statistics show two deadly peaks, at 4 a.m. and again twelve hours later when people are at their least alert.

During the 1970s, best-selling books began to emerge claiming such phenomena were manifestations of so-called biorhythms, a set of three cycles governing physical, emotional and intellectual traits. Said to start from the moment of birth and repeat every 23, 28 and 33 days respectively, they were supposed to result in ‘critical days’ when one or more cycles led to sub-optimal performance, with unfortunate consequences.

Scientists have since dismissed biorhythms as pseudoscience, insisting the existence of the three cycles has no basis in fact. In 1998, Dr Terence Hines of Pace University, New York State, published the most comprehensive study of the claims made for biorhythms, reviewing the results of over 130 investigations. He found that three-quarters of them failed to provide any support for biorhythms. Most of the remainder contained blunders ranging from faulty mathematics to basic errors in statistics, while the handful of positive studies were explicable as flukes.

But there is no doubting the existence of 24-hour biological cycles – or, rather, ones roughly 24 hours long. Following de Mairan’s pioneering work, other researchers found that when deprived of the cues provided by sunlight, organisms settle down to ‘free-running’ cycles that are close to, but rarely exactly, 24 hours. In the case of humans, the cycle is typically around 24.5 hours long. This is the so-called ‘circadian’ cycle (from the Latin meaning ‘about a day’), the length of which is generated by the mysterious internal ‘clock’.

F

During the late 1960s, chronobiologists believed they had found the ‘clock’, in the form of the suprachiasmatic nucleus (SCN), a collection of nerves in a region of the brain known as the hypothalamus. Linked to photosensitive cells in the eye, the SCN senses daylight and triggers the release of hormones like melatonin, which keep body functions in synchronization with the time of day. For a few years the SCN was regarded as the ultimate pacemaker – at least in higher organisms such as ourselves. But in 1971, scientists at the California Institute of Technology working with fruit flies found evidence for something truly amazing. Fruit flies appeared to have genes affecting the daily rhythm of their behavior – suggesting that there are ‘clocks’ inside each of their cells. Further evidence for this emerged in 1995, when researchers at Massachusetts General Hospital isolated nerve cells from the SCN, and found they kept up a circadian cycle without help from daylight. Finally, in 1997, scientists at Northwestern University in Illinois found a gene that regulates the daily rhythms of cellular activity in mammals.

G

The details of how this gene, known as CLOCK, actually works are still being investigated, but they could culminate in better ways of coping with shift-work and jet-lag. Professor Takahashi, who led the research, says that now that we know that circadian clocks exist throughout our bodies, we will need new strategies and therapeutics to reset all of our cells. But how do all the biochemical ‘clocks’ inside their cells stay in synchronization and why did organisms bother to acquire a link with sunlight? So far, no one knows, though there are several theories. For example, sunlight might be useful in keeping the myriad cellular ‘clocks’ in lockstep.

H

In the search for answers, researchers are studying the behavior of a microbe called cyanobacterium. In 2005, a team at Nagoya University, Japan, showed that chemical reactions between three proteins produced by this bacterium ebbed and flowed on a 24-hour cycle. Cyanobacterium is the oldest form of life on Earth, so this suggests that cellular ‘clocks’ have existed for over three billion years. All subsequent organisms have followed suit, says Professor Johnson of Vanderbilt University, Tennessee. ‘Bacteria, fungi, plants and animals all appear to have evolved clock systems independently from each other.’ Quite why is still unknown. But one thing is clear: the daily routine of life is certainly not a modern invention.

Questions 14–18

Reading Passage 2 has eight paragraphs.

Which paragraph contains the following information?

14 support for an earlier finding from experiments on insects

15 criticism of the way some research data was analysed

16 reference to a basic test on a plant

17 a statement that the length of natural cycles varies slightly between living things

18 reference to a theory that became popular with the public

Questions 19–22

Complete the summary below.

Write NO MORE THAN TWO WORDS from the passage for each answer.

An overview of research into the existence of the internal ‘clock’

Towards the end of the 1960s, research into the SCN, which is located in the hypothalamus led chronobiologists to believe they had found the internal ‘clock’ at last. Their theory was based on the fact that certain hormones that regulate the timing of physical functions are controlled by the SCN. The SCN is able to perceive 19 __________ as a result of connections to the eye.

Several years later, research involving 20 __________ showed that the timing of their normal actions was regulated by certain 21 __________ or ‘clocks’, in their cells. Thus the internal ‘clock’ is not an individual mechanism, as previously thought, but exists within each cell.

Other scientists went on to conduct experiments in the dark that proved that a 22 __________ was maintained by individual SCN cells.

Questions 23–24

Choose TWO correct answers.

23-24 Which TWO of the following problems are stated as being linked with the internal ‘clock’?

□ a decrease in output in workplaces without windows to let in natural light

□ a failure among workers on night-shifts to perform tasks

□ an increase in casualties on the roads at specific times of day □ a decline in efficiency on certain days in a number of fixed cycles

□ a rise in mood swings dependent on the appearance of the Sun

25-26 Which TWO of the following issues relating to internal ‘clocks’ remain to be solved, according to information in the passage?

□ the precise length of the free-running daily cycle in different animals □ the reason for ‘clocks being temporarily driven out of synchronisation □ the reason for living beings forming a connection with the Sun’s rhythms □ the way in which all ‘clocks’ in a single organism are able to stay in step with one another □ the location of the ‘clocks’ across the whole range of living organisms