HKDSE 2020: Biology ‘easier than last year' with manageable multiple choice questions

In Paper One, most of the multiple choice questions were manageable. The last two questions were about pedigree and genetics. If candidates paid enough attention to whether inheritance was sex-linked, they should be fine, Ho says.

The slightly more challenging parts could be found in Paper Two, Ho said, in both Q2 and Q4 about Ecology and Biotechnology, respectively.

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Q2 focused a lot on students’ data analysis skills, and apart from the usual textbook materials, like bioaccumulation and biomagnification, it asked something extra.

In class, students only learned that fishermen weren’t allowed to catch baby fish because they had to make sure the fish would grow and carry out reproduction before being captured. Instead of directly asking about that concept, the question showed a tool with a hole in it, and asked why fishermen should let go of the clams that fit through the hole and keep those that can’t go through it.

Some students were surprised by the question. Yet, Ho said they must have learned the ideas and concepts in class, so they just had to think more.

Q4 in Paper Two was about a new diagnosis technique to test for Down syndrome. Although the technique, using the mother’s blood to diagnose Down syndrome in her baby, was not included in the exam syllabus, the concepts asked were nothing new.

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“Candidates should not have been scared by the question; they should just relate the answer to what they’ve learned in class, regarding the polymerase chain reaction and explain how there will be one more chromosome in the 21st pair of chromosomes if the baby has Down syndrome,” says Ho.

Cyrus Chu, 17-year-old student from St Louis School, said that he didn’t find this year’s paper too difficult. “There were so many more diagrams of experimental set-ups, so it tested candidates’ application of knowledge instead of their ability to memorise model answers. The concepts asked, however, were quite simple,” he said,

For example, this year’s diagrams were about transpiration and ecosystem, but one of the questions last year showed a diagram and asked about the adaptive features of xylem, which was much more complex, Cyrus said. Apart from that, he also said the essay on the human circulatory system was much easier than last year’s essay on genetics and hybrid pets.

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He found Paper One B Q9, about the ecosystem and nitrogen cycle, most difficult to answer. It showed a diagram of an ecosystem in which the fish were releasing toxic ammonia, which was being turned into nitrate that the plants eventually absorbed. Part of the question asked why, if there’s more fish food, some of the fish would die.

Ho said since the question had hinted that ammonia was toxic and could kill the fish, candidates should think about how the fish food actually contained a lot of nitrogen because of nutrients like protein. And if there’s more fish food, meaning more nitrogen provided for the fish, they would produce more ammonia. If the speed at which the fish produce ammonia is faster than the speed in which ammonia became nitrate and was absorbed by the plants, then the toxic ammonia would accumulate and kill the fish.

“I think it’s so difficult because it requires you to tie everything together and consider a lot of different factors,” Cyrus said.

But overall, this year’s Biology paper was still similar to what Cyrus had expected, if not easier. “I had enough time to finish the paper so I’d say it was kind of smooth,” he said.