Plants require the smallest amount of which of the following nutrients?a. oxygenb. phosphorusc. carbond. iron

The inorganic nutrient most often lacking in crops isa. carbon.b. nitrogen.c. phosphorus.d. potassium.

Consider the following statements regarding limiting nutrients. Select True or False for each statement.T/F Nitrogen (N), phosphorus (P), and potassium (K) are common examples.T/F Their presence limits the availability of micronutrients.T/F Their availability tends to limit plant growth.T/F Certain macronutrients and micronutrients can be considered limiting nutrients.

Micronutrients are needed in very small amounts becausea. most of them are mobile in the plant.b. most serve mainly as cofactors of enzymes.c. most are supplied in large enough quantities in seeds.d. they play only a minor role in the growth and health of the plant.

Where is the start codon located?a. at the start (5′ end) of the mRNAb. in the DNA just upstream of where transcription startsc. at the downstream end of the 5′ untranslated region (UTR)d. at the upstream end of the 3′ untranslated region (UTR)

Where does most nutrient uptake occur in roots?a. at the root cap, where root tissue first encounters soil away from the zone of nutrient depletionb. at the Casparian strip, where ions must enter the symplast before entering xylem cellsc. in the symplastic and apoplastic pathwaysd. in root hairs, in the zone of maturation

Why are proton pumps in root-hair plasma membranes important?a. They pump protons into cells, generating a membrane potential (voltage).b. They allow toxins to be concentrated in vacuoles, so the toxins do not poison enzymes in the cytoplasm.c. They set up an electrochemical gradient that makes it possible for roots to absorb cations and anions.d. They set up the membrane voltage required for action potentials to occur.

Why is the presence of clay particles important in soil?a. They provide macronutrients—particularly nitrogen, phosphorus, and potassium.b. They bind metal ions, which would be toxic if absorbed by plants.c.They allow water to percolate through the soil, making oxygen-rich air pockets available.d. The negative charges on clay bind to positively charged ions and prevent them from being leached out of the soil.

. A problem with intensive irrigation is (A) overfertilization. (B) aquifer depletion. (C) the long-term depletion of soil oxygen. (D) the clogging of waterways by vegetation debris.