Biology Chapter 37

Topsoil _____.

is a mixture of rock fragments, living organisms, and humus

Humus consists of _____.

decomposing organic material

A major long-term problem resulting from excessive irrigation is the _____.

accumulation of salts in the soil

Mineral nutrients _____.

contribute little to a plant’s overall mass

For an element to be considered a macronutrient _____.

it must be required in relatively large amounts

Which of the following is a symptom of magnesium deficiency in plants?

chlorosis

Nitrogen-fixing bacteria in the soil _____.

convert atmospheric nitrogen to ammonia

Mycorrhizae enhance plant nutrition mainly by

absorbing water and minerals through the fungal hyphae.

We would expect the greatest difference in plant health between two groups of plants of the same species, one group with mycorrhizae and one group without mycorrhizae, in an environment

in which the soil is relatively deficient in mineral nutrients.

How do plants obtain organic molecules?

Plants synthesize their own organic molecules.

The relationship between legumes and Rhizobium is _____.

mutualistic (Both the legume and the Rhizobium benefit from this relationship. The legume gains a supply of fixed nitrogen from Rhizobium, and Rhizobium gains organic nutrients from the legume.)

Mutualistic associations between roots and soil fungi are called _____.

mycorrhizae

The sundew plant has to digest insects because _____.

it obtains nitrogen from their bodies that it cannot get from the soil

The inorganic nutrient most often lacking in crops is __________.

nitrogen

Micronutrients are needed in very small amounts because

most serve mainly as cofactors of enzymes.

Epiphytes are

plants that grow on other plants.

Some of the problems associated with intensive irrigation include all but

overfertilization

A mineral deficiency is likely to affect older leaves more than younger leaves if

the mineral is very mobile within the plant.

Two groups of tomatoes were grown under laboratory conditions, one with humus added to the soil and one a control without humus. The leaves of the plants grown without humus were yellowish (less green) compared with those of the plants grown in humus-enriched soil. The best explanation for this difference is that

the humus contained minerals such as magnesium and iron, needed for the synthesis of chlorophyll.

Identify the components of the rhizosphere, the soil layer that surrounds plant roots.

dirt, bacteria, fungi

Select the correct statement(s) about plant nutrition.

Mineral deficiency symptoms vary with the mobility of the mineral within the plant.