Aresearcher is interested in the effects of nitrate and phosphate on plant growth and sets up an experiment in which groups of five plants are given 1, 2, and 3 grams of nitrate and 1, 2, and 3 grams of phosphate in all combinations over a period of one month. the researcher measures plant height and weight at the end of the experiment. what is missing in this experimental design?
a. a control
b. an independent variable
c. a dependent variable
d. a constant

The correct answer will be option-A

Explanation:

A scientific experiment is designed in a way that it tests the predicted hypothesis and so contains the three different types of variables namely: independent (can be modified), dependent (to be studied) and the control (kept constant and unchanged).

In the given question, since the scientists studied the effect of nitrate and phosphate in which he provided the plant samples with nitrate and phosphate but he missed the control sample which should lack the variable to be tested that is nitrate and phosphate. This control variable helps the scientist to study the relationship between other samples.

Thus, option-A is the correct answer.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c