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Part 4: You will hear a lecturer talking to a group of biology students about recent plant studies.

First you have some time to look at questions 31 to 40.

Now listen carefully and answer questions 31 to 40.

Good morning, everyone. In the last few weeks, we looked at ways in which different types of animals use their senses. And today, I’m going to introduce the topic of plant behavior. And we’ll look at the reasons why ideas about plants have been changing in the last few years.

So up until fairly recently, plants’ lack of eyes or ears or noses or mouths made them less interesting to many members of the public compared to animal species. And even by scientists, they were generally regarded as organisms which were essentially passive. However, in the last 20 years or so, evidence has started to emerge that plants can sense their surroundings in quite sophisticated ways. But because scientific attitudes towards plants and their capabilities had been fixed for such a long time, this evidence has been met with some disbelief.

So let’s look at some of these recent findings that are starting to change the way some scientists view plant life. It all began with a Canadian study that looked at a species of plant known as the Great Lakes Sea Rocket. This is a wild plant which grows on beaches. In appearance, it’s perfectly ordinary, with little purple flowers and a long stalk. But actually, the plant is far from ordinary. Normally, when the sea rocket detects other plants growing nearby, it quickly grows additional roots. This is so it can compete with these other plants for the available nutrients in the soil by soaking up as many of them as possible. But scientists found that the sea rocket doesn’t do that when the surrounding plants are related to it. And as even animals sometimes find this type of recognition difficult, such a finding was very unexpected. It was an ability that was previously unheard of in any other plant.

Since then, it’s been suggested that two other plants may have a similar ability. These are sagebrush and thornapple. It’s been claimed that these plants can recognise the characteristics of their neighbours by sensing properties of the light that is reflected from them. The reason they are able to do this is that all plant species are slightly different to each other in this respect. So, each plant species has what you could call its own signature. Sagebrush and thornapple are able to recognise these. But scientists point out that this behaviour is very different to the way that animals sense things.

Another type of plant which can sense things in its surroundings is the dodder plant. This plant is different to most other species because it doesn’t have the ability to make sugar by converting nutrients from the soil. This means that as soon as the dodder has sprouted from a seed, it needs to find another plant in order to survive. In other words, it’s a parasite. Dodders infest a variety of food crops around the world as they wrap themselves like string around their target plants and the effect can be devastating for farmers. It’s particularly damaging to alfalfa as well as to potatoes and different varieties of citrus.

At first, scientists were puzzled as to how the dodder knows which plants to prey on. But now they’ve found that the plant can identify a suitable host by sensing the chemicals that other plants release into the soil and air. What really surprised researchers was how extremely quickly and accurately the dodder identifies a possible host. They used time-lapse videos to study the mechanism and saw from these that when the dodder is trying to check out its environment, it rotates in a circle and then, without touching any other plants, it heads directly towards its selected host. It could sense reliably which type of plant it would grow best on. Scientists who were working on the project reported that the dodder sprout resembled a worm as it moved towards the other plant.

Well, those are some examples of the new discoveries about plant characteristics. So which direction is plant science likely to go in next? Many of the phenomena related to plant behaviour that I’ve just described are now quite easy to observe, using up-to-date equipment. So, gradually, scientists are accepting the fact that plants are more capable than we used to believe. But although such plant behaviour is often obvious, to some scientists,

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