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Mader: Biology 8th Ed.

Nutrition and Transport in Plants

Chapter 26

1


Outline

• Essential Inorganic Nutrients

• Soil Formation

• Soil Profiles

• Soil Erosion

• Mineral Uptake

• Transport Mechanisms

– Water

– Organic Nutrients

2


Plant Nutrition and Soil


– About 95% of a plant’s dry weight is carbon, hydrogen, and oxygen.

!Carbon dioxide and water

– Essential nutrients have identifiable role, and a deficiency causes a plant to die.

!Macronutrients

!Micronutrients

3

Table 26.1

4


Overview of Plant Nutrition

5

Mader: Biology 8th Ed. Fig. 26.26


Nutritional Function of Soil

• Soil is defined as a mixture of soil particles, decaying organic material, living organisms, air, and water.

– Roots take up oxygen from air spaces.

• Soil Particles

– Sand

– Clay

– Silt

7


Absorbing Minerals

8


9


Soil Profiles

• Soil profile is a vertical section from ground surface to unaltered rock below.

– Parallel layers - Horizons.

!A (topsoil) - Litter and humus.

!B (subsoil) - Inorganic nutrients.

!C (weathered rock)

– Because parent material and climate differ, soil profile varies according to particular ecosystem.

10


Generalized Soil Profile

11


Soil Erosion

• Soil erosion occurs when water or wind carry soil away to a new location.

– Worldwide, removes about 25 billion tons of topsoil annually.

!Deforestation

!Desertification

!Agricultural contaminants

12


Adaptation of Roots for Mineral Uptake

• Symbiotic Relationships

– Rhizobium bacteria fix atmospheric nitrogen.

!Live in root nodules.

– Mycorrhizal association between fungi and plant roots.

!Ectomycorrhizas

!Endomycorrhizas

13


Fig. 26.5

14


Root Nodules

15


Mycorrhizas

16


Transport Mechanisms in Plants

• Leaves carry on photosynthesis.

– Xylem transports water.

!Two types of conducting cells.

"Tracheids

"Vessel Elements

!Water flows passively from an area of higher water potential to an area of lower water potential.

17


18


Conducting Cells of Xylem

19


Transport Mechanisms in Plants

– Phloem transports organic materials.

!Conducting cells are sieve-tube members.

"Have companion cells to provide proteins.

"End walls are sieve plates.

# Plasmodesmata extend through sieve plates.

20


Plant Transport System

21


Water Transport

• Water entering roots creates a positive pressure (root pressure).

– Pushes xylem sap upward.

– May be responsible for guttation.

!Water forced out vein endings along edges of leaves.

22


Cohesion-Tension Model

• Cohesion-tension model of xylem transport suggests a passive xylem transport.

– Water molecules tend to cling together.

– Polarity of water allows interaction with molecules of vessel walls.

– Water column moves passively upward due to transpiration.

!Column must be continuous.

!Waxy cuticle prevents water loss.

23

Mader: Biology 8th Ed.Fig. 26.11

24


Opening and Closing of Stomata

• Each stomata in leaf epidermis is bordered by guard cells.

– Increased turgor pressure opens stomata.

!Active transport of K+ into guard cells.

25


26


Organic Nutrient Transport

• Role of Phloem

– Girdling of tree (removing strip of bark) below the level of majority of leaves causes bark to swell just above the cut.

!Sugar accumulates in the swollen tissue.

"Phloem transports sugar

27


Pressure-Flow of Phloem Transport

• Positive pressure drives sap in sieve tubes.

– Sucrose is actively transported in sieve tubes, and water flows by osmosis.

!Increase in pressure creates flow that moves water and sucrose to a sink.

28


Pressure-Flow of Phloem Transport

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30


31


32


Review


• Soil Formation

• Soil Profiles

• Soil Erosion

• Mineral Uptake

• Transport Mechanisms

– Water

– Organic Nutrients

33

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