Mutual Harm - IELTS Reading Answers & Explanations
From Collins Practice Tests For IELTS 2 Academic Reading Test 1 · Part 1 · Questions 1–14
Reading Passage
You should spend about 20 minutes on Questions 1-14, which are based on Reading Passage 1 below.
Mutual harm
A In forests and fields all over the world, plants are engaged in a deadly chemical war to suppress other plants and create conditions for their own success. But what if we could learn the secrets of these plants and use them for our own purposes? Would it be possible to use their strategies and weapons to help us improve agriculture by preventing weeds from germinating and encouraging growth in crops? This possibility is leading agricultural researchers to explore the effects plants have on other plants with the aim of applying their findings to farming.
B The phenomenon by which an organism produces one or more chemicals that influence the growth, survival and reproduction of other organisms is called allelopathy. These chemicals are a subset of chemicals produced by organisms called secondary metabolites. A plant's primary metabolites are associated with growth and development. Allelochemicals, however, are part of a plant's defence system and have a secondary function in the life of the organism. The term allelopathy comes from the Greek: allelo and pathy meaning 'mutual harm'. The term was first used by the Austrian scientist Hans Molisch in 1937, but people have been noting the negative effects that one plant can have on another for a long time. In 300 BC, the Greek philosopher Theophrastus noticed that pigweed had a negative effect on alfalfa plants. In China, around the first century AD, the author of Shennong Ben Cao Jing described 267 plants that have the ability to kill pests.
C Allelopathy can be observed in many aspects of plant ecology. It can affect where certain species of plants grow, the fertility of competitor plants, the natural change of plant communities over time, which plant species are able to dominate a particular area, and the diversity of plants in an area. Plants can release allelopathic chemicals in several ways: their roots can release chemicals directly into the soil, and their bark and leaves can release chemicals into the soil as they rot. Initially, scientists were interested in the negative effects of allelopathic chemicals. Observations of the phenomenon included poor growth of some forest trees, damage to crops, changes in vegetation patterns and, interestingly, the occurrence of weed-free areas. It was also realised that some species could have beneficial effects on agricultural crop plants and the possible application of allelopathy became the subject of research.
D Today research is focused on the effects of weeds on crops, the effects of crops on weeds, and how certain crops affect other crops. Agricultural scientists are exploring the use of allelochemicals to regulate growth and to act as natural herbicides, thereby promoting sustainable agriculture by using these natural chemicals as an alternative to man-made chemicals. For example, a small fast-growing tree found in Central America, sometimes called the 'miracle tree', contains a poison that slows the growth of other trees but does not affect its own seeds. Chemicals produced by this tree have been shown to improve the production of rice. Similarly, box elder – another tree – stimulates the growth of bluestem grass, which is a tall prairie grass found in the mid-western United States. Many weeds may use allelopathy to become ecologically successful; a study in China found that 25 out of 33 highly poisonous weeds had significant allelopathic properties.
E There may be at least three applications of allelopathy to agriculture. Firstly, the allelopathic properties of wild or cultivated plants may be bred into crop plants through genetic modification or traditional breeding methods to improve the release of desired allelochemicals and thus improve crop yield. Secondly, a plant with strong allelopathic properties could be used to control weeds by planting it in rotation with an agricultural crop and then leaving it to rot and become part of the soil in order to inhibit the growth of weeds. Finally, naturally occurring allelopathic chemicals could be used in combination with man-made chemicals. Boosting the efficiency of man-made herbicides could lead to a reduction in the amount of herbicides used in agriculture, which is better for the environment.
F Despite the promising uses of allelopathic chemicals, agricultural scientists are still cautious. Firstly, allelopathic chemicals may break down and disappear in the soil more easily than artificial chemicals. Secondly, allelopathic chemicals may be harmful to plants other than weeds. Thirdly, allelopathic chemicals could persist in the soil for a long time and may affect crops grown in the same field as the allelopathic plants at a later date. Because the effects of allelopathic chemicals are not yet fully known, agricultural scientists will need to continue to study the biological war between plants.
Questions
Questions 1–5 Matching Headings
Choose the correct heading for paragraphs B-F from the list of headings below.
Write the correct number, i-ix.
i. What are metabolites?
ii. The negative effects of allelopathy
iii. Biological warfare in the plant world
iv. Why we cannot use allelopathic chemicals at present
v. What is allelopathy?
vi. The reasons why plants compete with other plants
vii. The effects of allelopathy and realisation of its possible uses
viii. How could we use allelopathic chemicals in farming?
ix. Specific examples of allelopathic plants
Questions 6–9 Multiple Choice (One Answer)
Choose the correct letter, A, B, C or D.
Questions 10–14 Summary Completion
Complete the summary of paragraphs E and F below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
Scientists can see three potential uses of allelopathic chemicals in farming. Firstly, the ability to produce allelopathic chemicals could be 10 into agricultural crops; secondly, allelopathic plants could be planted in rotation with the 11; finally, naturally produced chemicals could be combined with 12 herbicides. However, agriculturalists are still 13 as allelopathic plants may have negative effects on plants which are not the intended target and the chemicals could remain in the ground for a(n) 14, even after the plants themselves have died.
Answers & Explanations Summary
| # | Answer | Evidence | Explanation |
|---|---|---|---|
| Q1 | v | The phenomenon by which an organism produces one or more chemicals that influence the growth, survival and reproduction of other organisms is called allelopathy | Excerpt/Passage Explanation: The passage clearly defines the term by explaining that allelopathy is a process where a living thing creates chemicals that affect the life and growth of other nearby living things. Answer Explanation: The answer means that the best title for Paragraph B is "What is allelopathy?" Reason For Correctness: The correct answer is "v" because Paragraph B provides the basic definition of the term, explains its Greek origins, and discusses the history of how the concept was first identified. The paragraph focuses on explaining what the phenomenon is rather than how it is used or its specific environmental effects. Keywords such as "called," "term," "meaning," and "first used" indicate that this section is dedicated to defining the subject. |
| Q2 | vii | It can affect where certain species of plants grow, the fertility of competitor plants, the natural change of plant communities over time, which plant species are able to dominate a particular area, and the diversity of plants in an area It was also realised that some species could have beneficial effects on agricultural crop plants and the possible application of allelopathy became the subject of research |
Excerpt/Passage Explanation: The passage shows that allelopathy has many results, like changing which plants live in an area. It also explains that people found out these chemicals can help farmers, so they started studying how to use them. Answer Explanation: The answer means that Paragraph C explains how allelopathy changes things in nature and how scientists started thinking about using it to help farming. Reason For Correctness: The correct answer is vii because the paragraph explains the different ways allelopathy impacts nature, such as where plants grow and how healthy they are. These are the "effects." Then, it mentions that people "realised" (learned or understood) that these effects could be helpful for "agricultural crop plants." This matches the "realisation of its possible uses" part of the heading. |
| Q3 | ix | For example, a small fast-growing tree found in Central America, sometimes called the 'miracle tree', contains a poison that slows the growth of other trees but does not affect its own seeds. Chemicals produced by this tree have been shown to improve the production of rice. Similarly, box elder – another tree – stimulates the growth of bluestem grass, which is a tall prairie grass found in the mid-western United States. Many weeds may use allelopathy to become ecologically successful; a study in China found that 25 out of 33 highly poisonous weeds had significant allelopathic properties | Excerpt/Passage Explanation: The passage lists real names of plants, like the miracle tree and the box elder, and explains what they do to help or hurt other plants around them. Answer Explanation: The answer means Paragraph D provides several real-life examples of plants that use chemicals to affect other plants. Reason For Correctness: The correct answer is ix because Paragraph D describes specific types of plants, such as the 'miracle tree' and the 'box elder,' as well as certain weeds found in China. The paragraph explains exactly how these plants use their chemicals to either hurt or help other growth. By including these names and details, the paragraph serves as a list of specific cases, which matches the heading 'Specific examples of allelopathic plants.' |
| Q4 | viii | There may be at least three applications of allelopathy to agriculture | Excerpt/Passage Explanation: The passage states that there are at least three ways that we can use these special plant chemicals in the business of farming. Answer Explanation: The answer is the heading that describes how people can use plant chemicals to help grow food on farms. Reason For Correctness: The correct answer is viii because Paragraph E outlines three specific ways, or "applications," for using allelopathic chemicals in "agriculture" (farming). It explains how these chemicals can be added to crops through breeding, used to stop weeds when plants rot in the dirt, or mixed with man-made chemicals to help the environment. Common words in the text and the heading that show this connection include "applications" being a synonym for "use," and "agriculture" being a synonym for "farming." |
| Q5 | iv | Despite the promising uses of allelopathic chemicals, agricultural scientists are still cautious Because the effects of allelopathic chemicals are not yet fully known, agricultural scientists will need to continue to study the biological war between plants |
Excerpt/Passage Explanation: The passage explains that even though these plant chemicals could be helpful, experts are acting very carefully. They are not using them yet because they don't have enough information about what will happen if they do, so they need to keep studying them. Answer Explanation: The answer identifies the heading for Paragraph F as 'Why we cannot use allelopathic chemicals at present'. Reason For Correctness: The correct answer is 'iv' because Paragraph F discusses the current limitations and concerns regarding the use of allelochemicals in farming. It explains that although they seem useful, scientists are worried because these chemicals might break down too quickly, harm crops instead of just weeds, or stay in the dirt for too long. Because of these unknown dangers, researchers believe it is not yet safe to use them widely and that more study is needed first. |
| Q6 | C | The phenomenon by which an organism produces one or more chemicals that influence the growth, survival and reproduction of other organisms is called allelopathy | Excerpt/Passage Explanation: The passage explains that allelopathy is a situation where a living thing makes chemicals that change how other living things grow, stay alive, or make new plants. Answer Explanation: The answer means that 'allelopathy' is the name for how chemicals from one plant can change the way another plant grows or lives. Reason For Correctness: The correct answer is based on the definition given in paragraph B. It states that this process involves an organism creating chemicals that affect the growth, survival, and reproduction of other organisms. The text distinguishes these chemicals (allelochemicals) from 'primary metabolites,' which are for the plant's own growth. Therefore, it specifically refers to the external effects of these chemicals on other plants. Keywords to notice are ‘chemicals,’ ‘influence,’ and ‘other organisms.’ |
| Q7 | C | It can affect where certain species of plants grow, the fertility of competitor plants, the natural change of plant communities over time, which plant species are able to dominate a particular area, and the diversity of plants in an area | Excerpt/Passage Explanation: The passage provides a list of things that allelopathy can change, including the places where plants live, how well nearby plants can produce seeds, how the mix of plants changes naturally over long periods, which specific plants take over an area, and how many different types of plants live in one place. Answer Explanation: The answer is 'the nutrients present in the soil'. Reason For Correctness: The correct answer is C because the text specifically lists several ecological factors that allelopathy changes, but it never mentions nutrients (the food or minerals in the ground). According to the passage, allelopathy influences where plants live (location), the reproduction levels of competing plants (fertility), how plant groups change over time, which plants become the most powerful (dominate), and the variety of plants (diversity). While the text describes chemicals being released into the soil, it does not suggest that these chemicals change the actual nutrient levels available to the plants. |
| Q8 | A | Agricultural scientists are exploring the use of allelochemicals to regulate growth and to act as natural herbicides, thereby promoting sustainable agriculture by using these natural chemicals as an alternative to man-made chemicals | Excerpt/Passage Explanation: The passage explains that people who study farming are looking at how to use these natural chemicals to control how plants grow and to kill weeds. This helps farming stay healthy for the earth because it uses nature instead of factory-made sprays. Answer Explanation: The answer means that researchers want to find ways to use these natural plant chemicals to help grow food in a way that does not hurt the environment. Reason For Correctness: The correct answer is A because the text explains that experts are looking for ways to use natural plant poisons to help crops grow better and kill weeds. This is described as 'sustainable agriculture' because it uses natural things instead of man-made chemicals. While the text mentions forests and the negative effects of weeds, these are parts of the background or history, while the 'main' interest today is applying this knowledge to help farmers grow food more naturally. |
| Q9 | A | For example, a small fast-growing tree found in Central America, sometimes called the 'miracle tree', contains a poison that slows the growth of other trees but does not affect its own seeds. Chemicals produced by this tree have been shown to improve the production of rice. Similarly, box elder – another tree – stimulates the growth of bluestem grass, which is a tall prairie grass found in the mid-western United States | Excerpt/Passage Explanation: The passage lists three specific examples: a tree that makes other trees grow slowly (affecting growth), a tree that helps rice grow (making it productive), and a tree that helps grass grow better (stimulating growth). It does not mention a tree that acts as a poison for weeds. Answer Explanation: The answer means that the text does not talk about a tree that is very harmful or deadly to weeds. Reason For Correctness: The correct answer is A because the text mentions several specific trees and their effects, but killing weeds is not one of them. The passage says the 'miracle tree' hurts other trees and helps rice. It says the 'box elder' tree helps grass. While it mentions that some weeds are poisonous, it never mentions a tree that is poisonous to weeds. |
| Q10 | bred | Firstly, the allelopathic properties of wild or cultivated plants may be bred into crop plants through genetic modification or traditional breeding methods to improve the release of desired allelochemicals and thus improve crop yield | Excerpt/Passage Explanation: The passage states that scientists can use special methods to put the natural chemical-making abilities of wild plants into the plants we grow for food. Answer Explanation: The answer means that the specific physical features or chemical abilities of one plant can be added into another plant through special farming or scientific methods. Reason For Correctness: The correct answer is 'bred'—the past participle of 'breed'—applied here in the context of genetics and farming. Paragraph E explains that the ability of some plants to release chemicals that stop competitors can be transferred to farm crops. This can happen through either 'genetic modification' or 'traditional breeding methods'. |
| Q11 | agricultural crop | Secondly, a plant with strong allelopathic properties could be used to control weeds by planting it in rotation with an agricultural crop and then leaving it to rot and become part of the soil in order to inhibit the growth of weeds | Excerpt/Passage Explanation: The passage explains that a plant with the power to stop weeds can be grown in the same field at a different time from the main farm plants. When this special plant dies and turns into dirt, it stops weeds from growing. Answer Explanation: The answer refers to the specific plants that farmers grow to sell or use, such as wheat, corn, or rice. Reason For Correctness: The correct answer is found in the section describing the second way to use plant chemicals in farming. The text says that farmers can grow a special plant (one that makes chemicals to stop weeds) and swap it periodically with their regular farm plants. The term the author uses for these regular farm plants is 'agricultural crop'. This 'rotation' helps keep weeds away without using as many artificial sprays. |
| Q12 | man-made | Finally, naturally occurring allelopathic chemicals could be used in combination with man-made chemicals | Excerpt/Passage Explanation: The passage explains that chemicals that grow in nature can be mixed with chemicals that people make in factories. Answer Explanation: The answer 'man-made' describes things that are produced by humans rather than being found naturally in nature. Reason For Correctness: The correct answer is identified in Paragraph E. The text explains that natural plant chemicals can be used together with 'man-made' chemicals or herbicides to improve their effectiveness. Using natural chemicals this way allows farmers to use fewer artificial substances, making farming more environmentally friendly. |
| Q13 | cautious | Despite the promising uses of allelopathic chemicals, agricultural scientists are still cautious | Excerpt/Passage Explanation: The passage explains that even though these chemicals could be very helpful, the people who study farming are being careful and not moving too fast because they still have concerns. Answer Explanation: The answer means that people are being very careful or showing worry because they are not 100% sure if something is safe or good yet. Reason For Correctness: The correct answer is 'cautious' because the passage explicitly states that agricultural scientists (the 'agriculturalists' mentioned in the summary) remain 'cautious' despite the potential benefits of allelopathic chemicals. This sense of being careful is linked to the concerns listed afterward, such as the chemicals potentially staying in the soil for too long or hurting the wrong plants. |
| Q14 | long time | Thirdly, allelopathic chemicals could persist in the soil for a long time and may affect crops grown in the same field as the allelopathic plants at a later date | Excerpt/Passage Explanation: The passage explains that these natural chemicals can stay in the earth for many months or years, which might cause problems for new crops that are planted in the same place later on. Answer Explanation: The answer "long time" means that these plant chemicals can stay in the dirt for a very long period after the plants are gone. Reason For Correctness: The correct answer is based on paragraph F, which lists reasons why agricultural scientists are careful about using allelopathy. It mentions that these chemicals can 'persist,' which is a synonym for 'remain,' in the 'soil' (ground) for a 'long time.' This matches the summary sentence about how long the chemicals might stay in the ground. |