19. Genetic technology
A section of Biology, 9700
Listing 10 of 107 questions
Food crops like wheat may be improved by selective breeding and genetic modification. Outline how wheat crops have been improved by selective breeding. Variation in height of a strain of wheat plants in a field shows a continuous pattern of variation. Explain what is meant by continuous variation and explain why this type of variation occurs in a population. Wheat and other crops have been genetically modified to be resistant to the herbicide glyphosate since 1996. shows the area of glyphosate-resistant crops grown as a percentage of the total planted hectares (plotted points) and the number of weed species with resistance to glyphosate . percentage of planted hectares number of resistant weed species year area resistant species Describe and explain the relationship between the area of glyphosate-resistant crops grown and the number of resistant weed species. Suggest one social advantage and one environmental advantage of growing glyphosate-resistant wheat. social advantage environmental advantage
9700_s16_qp_42
THEORY
2016
Paper 4, Variant 2
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Weeds reduce crop yields by competing with crop plants for space, light, water and minerals. The modes of action of three different types of herbicide are summarised in Table 4.1. Table 4.1 type of herbicide mode of action year of first widespread use photosystem II inhibitor prevents photophosphorylation ALS inhibitor prevents synthesis of the amino acids isoleucine, leucine and valine glyphosate prevents synthesis of the amino acids phenylalanine, tryptophan and tyrosine shows the cumulative number of species of weeds that have become resistant to these three types of herbicide since 1960. number of species year ALS inhibitor ALS inhibitor photosystem II inhibitor photosystem II inhibitor glyphosate glyphosate Describe how the number of weed species resistant to herbicides has changed since 1960. Explain how a weed species becomes resistant to a herbicide. ALS inhibitor herbicides work by binding to an enzyme present in chloroplasts called acetolactate synthetase (ALS). ALS is a globular protein consisting of four identical polypeptides each composed of 668 amino acids. The primary structure of the ALS polypeptide of each weed species resistant to ALS inhibitor herbicides has been sequenced. Amino acid substitutions at positions as far apart as position 122 and position 574 can result in resistance. The gene that codes for the ALS polypeptide does not contain any non-coding sections . The first amino acid in the final polypeptide is methionine. State the number of base pairs in the gene that codes for an ALS polypeptide. Explain why resistance to ALS inhibitor herbicide can result from substitutions of amino acids that are far apart in the primary sequence. Genetic modification is one method used to develop herbicide resistance in crop plants. Other methods include: method 1: crossing a crop plant with a herbicide-resistant wild plant belonging to the same genus and then applying the herbicide method 2: causing mutations in the crop plants and then applying the herbicide. State two benefits of using method 1 and two benefits of using method 2 to develop herbicide resistance in crop plants. method 1 method 2
9700_s17_qp_42
THEORY
2017
Paper 4, Variant 2
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Bt maize has been genetically engineered to resist insect attack. In 2019, Bt maize formed 83% of the maize grown in the USA. Outline how the genetic engineering process produced Bt maize plants with resistance to insect attack. A proposed conservation benefit of Bt maize is that, unlike chemical insecticide sprays, it should not harm non‑target insects. When Bt maize was first grown in the USA, scientists were concerned that maize pollen containing the Bt toxin might be deposited by the wind on wild plants such as milkweeds, Asclepias spp. Milkweed leaves are the food source of caterpillars of the monarch butterfly, Danaus plexippus. In 1999, a laboratory experiment tested the effects of feeding milkweed leaves treated in different ways to the caterpillars of monarch butterflies. Each group of caterpillars was provided with milkweed leaves to eat throughout the experiment. The three different treatments were: • leaves with no pollen • leaves dusted with pollen from non‑Bt maize • leaves dusted with pollen from Bt maize. shows the results of this laboratory experiment. time / days percentage survival of monarch caterpillars leaves with no pollen Key: leaves with pollen from non-Bt maize leaves with pollen from Bt maize State what can be concluded from . Laboratory results are not always useful in predicting what will happen in real ecosystems. • Some scientists predicted that increasing the area of Bt maize in the USA would decrease the number of monarch butterflies, based on the results in . • More monarch butterflies were counted in 2019 than in 1999, even though the quantity of Bt maize grown more than tripled. Suggest reasons why the predicted decrease in the number of monarch butterflies did not occur in the real ecosystem.
9700_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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Explain the advantages to a plant species of cross-pollination compared to self-pollination. Some of the most important food plants for humans depend on insect pollinators, such as the honeybee, Apis mellifera. shows a honeybee. A study was carried out in 2006 to show how four food crops are pollinated. shows the results of this study. almond apple orange plant peach pollinated by honeybee pollinated by other insects pollinated by birds / wind / rainwater Key number of plants pollinated The populations of honeybees in some parts of the world have declined in recent years. With reference to , explain which crop will be most affected and which crop will be least affected by the decline in honeybees. most affected least affected Suggest reasons why honeybee populations have declined.
9700_w12_qp_43
THEORY
2012
Paper 4, Variant 3
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Atlantic salmon, Salmo salar, is one of the most important fish species farmed for human consumption. shows an Atlantic salmon. Infectious pancreatic necrosis (IPN) is a serious viral disease currently affecting farmed salmon. Describe how artificial selection could be used to produce a population of salmon that is resistant to IPN. Suggest problems that may arise from artificial selection. A laboratory investigation was carried out to compare the artificially selected farmed Atlantic salmon with farmed salmon that had not been artificially selected. Three groups of young fish were set up in carefully controlled conditions as follows: • Group A: artificially selected salmon • Group B: non-artificially selected salmon • Group C: non-artificially selected salmon. During this investigation, only groups A and B were exposed to IPN on day 0. The percentages of salmon that died (percentage mortality) were calculated and are shown in .                    WLPHGD\V JURXS% JURXS$ JURXS& SHUFHQWDJH PRUWDOLW\ Describe and explain the differences in percentage mortality between groups A and B. Suggest a reason for the mortality in group C.
9700_w15_qp_43
THEORY
2015
Paper 4, Variant 3
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Questions Discovered
107