An investigation was carried out to study the effect of different intensities of blue light on the percentage germination of barley seeds. Barley seeds were exposed to blue light for a period of seven days. All other variables were kept constant. The results are shown in Table 9.1. The effect of blue light on the concentration of abscisic acid (ABA) was also investigated. ABA concentration was measured at intervals over seven days in barley seeds exposed to blue light at an intensity of 57 arbitrary units. The results are shown in Table 9.2. For comparison, in the dark the concentration of ABA in barley seeds fell from 100 au at the start (day 0 ) to 45 au on day 1 and did not increase from day 1 to day 7 . ABA is thought to affect gibberellin synthesis or activity. Using the information in Table 9.1 and Table 9.2, describe the effect of blue light on the germination of barley seeds and suggest an explanation for this effect. ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . .........................................................................................................................................
Exam No：9700_m24_qp_42 Year：2024 Question No：9(a)
Answer:
Knowledge points:
16.1.1 explain the meanings of the terms haploid (n) and diploid (2n)
16.1.2 explain what is meant by homologous pairs of chromosomes
16.1.3 explain the need for a reduction division during meiosis in the production of gametes
16.1.4 describe the behaviour of chromosomes in plant and animal cells during meiosis and the associated behaviour of the nuclear envelope, the cell surface membrane and the spindle (names of the main stages of meiosis, but not the sub-divisions of prophase I, are expected: prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II and telophase II)
16.1.5 interpret photomicrographs and diagrams of cells in different stages of meiosis and identify the main stages of meiosis
16.1.6 explain that crossing over and random orientation (independent assortment) of pairs of homologous chromosomes and sister chromatids during meiosis produces genetically different gametes
16.1.7 explain that the random fusion of gametes at fertilisation produces genetically different individuals
16.2.1 explain the terms gene, locus, allele, dominant, recessive, codominant, linkage, test cross, F1, F2, phenotype, genotype, homozygous and heterozygous
16.2.2 interpret and construct genetic diagrams, including Punnett squares, to explain and predict the results of monohybrid crosses and dihybrid crosses that involve dominance, codominance, multiple alleles and sex linkage
16.2.3 interpret and construct genetic diagrams, including Punnett squares, to explain and predict the results of dihybrid crosses that involve autosomal linkage and epistasis (knowledge of the expected ratios for different types of epistasis is not expected)
16.2.4 interpret and construct genetic diagrams, including Punnett squares, to explain and predict the results of test crosses
16.2.5 use the chi-squared test to test the significance of differences between observed and expected results (the formula for the chi-squared test will be provided, as shown in the Mathematical requirements)
16.2.6.1 TYR gene, tyrosinase and albinism
16.2.6.2 HBB gene, haemoglobin and sickle cell anaemia
16.2.6.3 F8 gene, factor VIII and haemophilia
16.2.6.4 HTT gene, huntingtin and Huntington’s disease
16.2.7 explain the role of gibberellin in stem elongation including the role of the dominant allele, Le, that codes for a functional enzyme in the gibberellin synthesis pathway, and the recessive allele, le, that codes for a non-functional enzyme
Solution:
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