Which of the following organs regulates the levels of water, salts , hydrogen ions and urea in the mammalian blood?

The sequence of the one-way gaseous exchange mechanism in a fish is

The type of asexual reproduction that is common to both Paramecium and protists is

In an experiment to determine the percentage of humus and water in a soil sample, the following results were obtained
Weight of the evaporating basin alone = 80.5g
Weight of basin and soil = 101.5g
Weight after drying the soil in the oven = 99.0g
Weight of basin and roasted soil = 95.5g
The percentage of humus in the soil sample is