Plant Physiology & Growth Flashcards

Apical dominance occurs when the apical bud suppresses the growth of lateral buds. Which hormone is primarily responsible for this effect?

Answer: Auxin produced in the apical meristem

High auxin concentrations from the apical meristem inhibit lateral bud development; removing the apex releases lateral buds from this suppression.

Which plant hormone primarily promotes root initiation on stem cuttings?

Answer: Auxin

Auxins (often IBA or NAA in rooting powders) stimulate root initiation on stem cuttings by promoting cell division in the cambium region.

The Casparian strip, found in root endodermis cells, functions to:

Answer: Force water and ions to pass through cell membranes rather than between cells, allowing selective uptake

The Casparian strip is a band of waxy suberin that blocks apoplastic movement, forcing ions through the symplast where selective transport occurs.

A day-neutral plant will flower:

Answer: Regardless of photoperiod, when mature enough

Day-neutral plants flower based on developmental maturity rather than day length; tomatoes and cucumbers are common examples.

Phototropism is the directional growth of a plant in response to:

Answer: Light direction

Phototropism causes shoots to bend toward light (positive) and roots to grow away from it (negative), mediated by uneven auxin distribution.

Magnesium is an essential macronutrient in plants primarily because it:

Answer: Is the central atom in the chlorophyll molecule

Magnesium is the central metal ion in the chlorophyll molecule; deficiency causes yellowing, particularly on older leaves first, as it is a mobile nutrient.

Biological nitrogen fixation, the conversion of atmospheric N2 into plant-available ammonia, is carried out by:

Answer: Nitrogen-fixing bacteria such as Rhizobium in root nodules of legumes

Rhizobium bacteria form symbiotic nodules on legume roots and convert atmospheric nitrogen into ammonia that the plant can use.