Question
Russian scientists have discovered the fruits of a flowering plant, Silene stenophylla, in the food store in a burrow of a ground squirrel in frozen sediments in Siberia.
Dating techniques suggest that the fruits were stored by the ground squirrel about 32 000 years ago, shortly before the ground became permanently frozen.
Tissue samples were taken from the fruits and grown in a nutrient culture medium. After treatment with plant hormones to stimulate the growth of roots and shoots, 36 complete plants were produced.
These ‘regenerated’ plants, which looked identical to one another, flowered and after cross-pollination, produced seeds that were able to germinate.
(a) Explain why cross-pollination produces more genetic variation among the offspring than self-pollination.[3]
(b) The flowers of modern-day S. stenophylla look similar, but not identical, to the flowers of the ‘regenerated’ plants.
Outline how DNA sequencing could be used to compare the DNA of modern-day and ‘regenerated’ S. stenophylla.[4]
(c) Suggest a simple experiment, using plants of modern-day and ‘regenerated’ S. stenophylla to find out whether, after 32 000 years, they are still the same species[2] [Total: 9]
Answer/Explanation
Ans:
2 (a) idea of cross-pollination involves two (parents)/ self-pollination one (parent) ;
ref. outbreeding/ inbreeding ;
(two parents) have different, genotypes / sets of alleles ;
idea of new combinations of alleles in offspring ;
(b) (total) DNA/ genome, cut into fragments ;
by restriction enzymes ;
DNA, denatured/ made single stranded ;
ref. primers /(modified) PCR ;
ref. dideoxynucleotides / chain termination ;
DNA/Taq, polymerase ;
copies of different lengths produced ;
electrophoresis ; A description
detection, of fluorescence/by laser scanner ;
sequence of, bases /nucleotides, read (by computer) ;
(c) cross(-pollinate) them ; A description
(if same species) offspring, are fertile/ can themselves produce seeds; ora
Question
(a) Wheat, Triticum aestivum, owes its origin to hybridisation involving three different, but related, species of grass, A, B and C.
Each of these species had seven pairs of chromosomes (2n = 14).
The hybridisation process is shown in Fig. 3.1.
(i) Using the symbols in the key, complete Fig. 3.1 by writing in the chromosome sets of T. aestivum. [1]
(ii) At the points labelled Y and Z in the hybridisation process, a fertile hybrid was produced from a sterile hybrid.
Explain why the hybrid (AB) is sterile and what occurred at the point labelled Y in Fig. 3.1.[4]
(b) In 2012, permission was granted for a field trial in the UK of genetically modified T. aestivum. The wheat carries a gene, taken from peppermint plants, that results in the wheat leaves releasing a volatile, non-toxic chemical, (E)-β-farnesene (Eβf), into the
atmosphere.
Eβf is not only produced by various species of plants. It is also secreted by aphids when they are disturbed by a predator.
Two experiments have been performed into the effect of Eβf on the behaviour of aphids feeding on leaves in closed containers.
Experiment 1
Either 10 cm3 of air from a syringe that contained plant leaves that secrete Eβf
or 10 cm3 of air from a syringe with no such leaves
was added to the containers of feeding aphids.
Experiment 2
Either 20 cm3 of air containing 50ng of Eβf
or 20 cm3 of air containing no Eβf
was added to the containers of feeding aphids.
In both experiments, the number of aphids that stopped feeding and moved away from the food leaves was counted. The results are shown in Table 3.1.
(i) Discuss the extent to which the results of these experiments support the idea that Eβf is an alarm signal for aphids.[4]
(ii) Other experiments show that Eβf attracts predators of aphids, such as ladybirds.
Explain how growing genetically modified wheat secreting Eβf could increase the yield of wheat.[3]
(iii) Suggest why growing this genetically modified wheat might be acceptable to people who object to the growth of genetically modified insect-resistant maize or cotton.[3] [Total: 15]
Answer/Explanation
Ans:
3 (a) (i) AABBCC ;
(ii) meiosis unsuccessful (in, sterile hybrid/AB) ;
gametes not formed ;
bivalents cannot form/ chromosomes cannot pair up/ chromosomes are not homologous ;
polyploidy occurs / chromosomes double ; A tetraploid
failure of cell division/ all chromosomes in one daughter cell ; A description
chromosomes can now form pairs / gametes can be formed/ meiosis can be completed ;
(b) (i) in presence of Eβf large number aphids, stop feeding/move ;
in absence of Eβf, few/ no, aphids, stop feeding/ move ;
air in Experiment 1, has other chemicals / not pure Eβf or air in Experiment 2 has only Eβf ;
Eβf concentration in Experiment 2 may be unnaturally high or Eβf concentration unknown in Experiment 1 ;
different volumes of air in Experiment 1 and Experiment 2 ;
comparative data quote ;
e.g.
55% versus 84% or 54 out of 99 versus 111 out of 132
54.5% versus 0.9% or 54 out of 99 versus 1 out of 113
84% versus 0% or 111 out of 132 versus 0 out of 106
(ii) Eβf stops aphids settling ;
Eβf attracts, predators of aphids / ladybirds ;
attacked aphids secrete more Eβf ;
aphids not, eating/ taking nutrients from, wheat ;
(iii) gene/Eβf, already in, peppermint/ various plant species ;
Eβf not, toxic / harmful to human health ;
no new chemical added to human diet ;
does not kill insects (unlike Bt maize or cotton) ;
aphids still available for, predators / food web ;
Question
Fig. 5.1 shows the area of land that was used to grow genetically modified (GM) crops in the USA,
Brazil, India and China from 2004 to 2015.
(a) (I) Suggest reasons why the area of land used to grow GM crops in the USA is greater than
the area of land used to grow GM crops in Brazil.
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. [2]
(ii) Describe the differences in the area of land that was used to grow GM crops in China
and the area of land that was used to grow GM crops in India, over the time shown in
Fig. 5.1.
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. [3]
(b) (I) Genetic modifications in crops can provide resistance to insect pests. Bt maize is one
type of GM crop that has been produced to be resistant to insect pests.
State two benefits to farmers of insect resistance in crops.
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. [2]
(ii) Describe the difference between Bt maize and non-GM maize that explains why Bt maize
is resistant to insects.
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. [2]
(c) (I) State two reasons why people may have objections to the growth of insect-resistant GM
crops.
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. [2]
(ii) In 2015, the percentage of the USA population that objected to the use of GM crops was
lower than in 2005.
Suggest why a smaller percentage of the USA population objected to the use of GM
crops in 2015.
………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. [1]
[Total: 12]
▶️Answer/Explanation
Answer:
5(a)(I) in USA unless otherwise stated
any two from:
1 can afford GM crops ;
2 (technology) developed in USA ;
3 more land available (to grow crops) ;
4 fewer laws restricting GM crops / more widespread (public) approval ;
5 climate conditions more suitable for GM crops ;
5(a)(ii) any three from:
1 initially / in 2004–2006, India uses smaller area (than China) / ora ;
2 area in China remains (almost) constant ;
3 area in India increases (throughout) ;
4 area in India is greater (than China) after 2006 ;
5 comparative figures
(one area from India and one from China for two different years plus units) ;
5(b)(I) any two from:
1 increase yield ;
2 increase quality ;
3 less / no, pesticide / insecticide, needs to be used ;
4 (so) less / no, money spent on, pesticides / insecticides ;
A cheaper
5(b)(ii) 1 contains gene from, Bacillus thuringiensis / bacterium ;
2 produces, (Bt) toxin / compound, harmful to insects ;
5(c)(I) any two from:
1 resistance (to insects) may be transferred to wild plants ;
2 contamination of food marketed as organic ;
3 may kill, useful insects / pollinators ;
4 decrease in biodiversity ;
5 potential health risks of humans (eating GM crops) ;
6 insects may become resistant (to toxin) ;
5(c)(ii) any one from:
1 education / awareness ;
2 reasons for objections have not been proven ;
3 consumption of GM foods shows no ill effects ;
4 entire generation grown up in GM era ;