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  • Stage 1

    Answer 4 questions correctly in a row.

This passage describes gill surface area in East African cichlids.
an East African cichlid fish swimming near a lake's sandy bottom
"Haplochromis sp." by Roberto Nistri, Alamy Stock Photo
an East African cichlid
  • East African cichlids (SIK-lids) are fish found in freshwater lakes. Like most animals, cichlids need oxygen to live. Cichlids absorb oxygen from the water using their gills. Gills with a greater surface area can absorb more oxygen.
  • Some cichlids live in polluted water with low levels of oxygen. If these cichlids have gills with smaller surface areas, they may not be able to absorb enough oxygen to survive. But if their gill surface areas are too large, they may absorb too many harmful pollutants or parasites.
The table below describes a possible population of East African cichlids at the start of a period of time and at the end of that period. The table shows gill surface area measurements for a representative sample of the population at the start and for another representative sample at the end.
Complete the table.
Data from representative samples of a population of East African cichlids
Point in timeList of gill surface area measurements
(
mm
2
)
Average gill surface area
(
mm
2
)
Start261, 275, 359, 373, 437, 505, 507, 611416
End250, 251, 329, 346, 389, 391, 424
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