Plant Nutrition

Chapter 38

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 35.2

Roots would starve without the sugar produced in the photosynthetic tissues of the shoot.

The shoot system depends on water and minerals absorbed from the soil by the roots.

PlantsShoots - above groundRoots - below grounddependent on each other.

• Shoots - stems and leaves.

• vegetative (leaf bearing) or reproductive (flower bearing).

• Stem has nodes, leaves attached, and internodes, segments between nodes.

• Growth of a young shoot is at its terminal bud

• axillary bud - branch.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 35.2

The presence of a terminal bud inhibits the growth of axillary buds, a phenomenon called apical dominance.

A plant is capable of indeterminate growth because it has perpetually embryonic tissues called meristems in its regions of growth.

Apical meristems, - elongation for primary growth of roots and shoots

Woody plants also show secondary growth, thickening of roots and shoots due to lateral meristems

Indeterminate growth vs. Determinate growth

• Modified shoots stolons, rhizomes, tubers, and bulbs, are often mistaken for roots. Asexual reproduction.

• Leaves are the main photosynthetic organs of most plants, but green stems are also photosynthetic.

– leaves consist of a flattened blade, the petiole, which joins the leaf to a stem node.

Monocots have parallel major veins length of the blade

Dicot have a multibranched network of major veins.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 35.2

Roots anchor the plant in the soil, absorb minerals and water, and store food.

Monocots have fibrous root systems. Dicots have taproots.

• Most absorption of water and minerals in bothsystems occurs near the root tips, where vastnumbers of tiny root hairs increase the surfacearea enormously.

• Root hairs are extensionsof individual epidermalcells on the root surface.

Cop yright © 2002 Pear son Education, Inc., pub lishing as B enjamin Cummings

Fig. 35.3

Roots, through root hairs, absorb water and minerals from the soil.

Carbon dioxide diffuses into leaves from the surrounding air through stomata.

Plants, photosynthetic autotrophs transform inorganic compounds into organic ones.

A plant needs sunlight as its energy source for photosynthesis and CO2 and inorganic ions, to synthesize organic molecules.

Essential nutrientsIf the absence of a particular mineral causes a plant to become abnormal when compared to controls grown in a complete medium, then that element is essential.

Macronutrients - Elements required by plants in relatively large quantities • There are 9 macronutrients : carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, and magnesium.

• Micronutrients - Elements that plants need in very small amounts • The 8 micronutrients are iron, chlorine, copper, zinc, magnanese, molybdenum, boron, and nickel.Most of these function as cofactors of enzymatic reactions.

• Loams, equal amounts of sand, silt and clay.Loamy soils provide a large surface area for retaining minerals and water provide air spaces(oxygen) to the root for cellular respiration.

• Cation exchange The soil pH affects cation exchange and influences the chemical form of all minerals.

• Even though an essential element may be abundant in the soil, plants may be starving for that element because it is bound too tightly to clay or is in a chemical form that the plant cannot absorb.

Nitrogen is lost from this local cycle when soil microbes called denitrifying bacteria converts NO3

- to N2 which diffuses to the atmosphere.Other bacteria, nitrogen-fixing bacteria, restock nitrogenous minerals in the soil by converting N2 to NH3 (ammonia), via nitrogen fixation.

The atmospheres is nearly 80% nitrogen, but plants cannot use nitrogen in the form of N2.It must first be converted to ammonium (NH4

+) or nitrate (NO3-).

A legume’s roots have swellings called nodules, composed of plant cells that contain nitrogen-fixing bacteria of the genus Rhizobium.

Inside the nodule, Rhizobium bacteria assume a form called bacteriods, which are contained within vesicles formed by the root cell.

Parasitic plants extract nutrients from other plants

Carnivorous plants supplement their mineral nutrition by digesting animals• Living in acid bogs and other habitats where soil conditions are poor are plants that fortify themselves by occasionally feeding on animals.