Principles of Biology ______Lake Tahoe Community College



Principles of Biology - Biology 102 Lake Tahoe Community College

Spring Quarter Instructor: Ralph Sinibaldi

Written by: Sue Kloss

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Ch. 37 - Plant Nutrition

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Intro – some plants are heavy metal accumulators – e.g brake fern – 200x higher than soil, and thrives in these conditions.

A. brake fern takes up arsenic.

1. Sunflowers and Italian mustard take up lead

2. Help clean up contaminated soils -phytoremediation

3. Radioactive metals – taken up by sunflowers – 2000 times higher than water levels – chernobyl

4. Problem – plants must then be disposed of, animals may consume them, long time to work

5. Plants evolved these abilities from uptake of compounds that reduce herbivory

I. Uptake and transport of nutrients

Intro- Jan Baptiste van Helmont- planted a willow in a pot w/ 090.9 kg of soil. After 5 yrs, the willow

weighed 76.8 kg, but the pot had only lost .06 kg of soil.

A. Plants acquire nutrients from soil and air (Fig. 37.2)

1. leaves take in CO2 - about 95% of plant’s dry weight is organic material built

mainly from Carbon acquired in CO2

2. Plants get water, minerals and O2 from the soil.

3. Sugars made by plant- composed of CHO

a. CO come from CO2, H comes from H2O

b. Plants use these sugars to make everything else they need, e.g. wood

made from sugar derivatives

c. by weight, most of the plant’s organic material comes from CO2

d. organic substances account for 96% of the dry weight, inorganic 4%

4. Cell respiration breaks down some sugar to provide energy for plant, consuming O2.

5. Plants are net producers of O2, though they also consume some.

a. during Ps, H2O is split, and O2 is released through leaves

b. O2 taken up by roots used in root cellular respiration

6. Plants take up minerals

a. nitrogen becomes part of hormones, coenzymes and ATP, nucleic acids, proteins.

b. N and Mg - components of chlorophyll, light absorbing molecule

c. P - nucleic acids, phospholipids, ATP

7. Plants take up water - 3 functions

a. water in plants allows turgor and 3D aspect, and growth

b. provides most of volume for cell elongation

c. acts as a solvent for plant to acquire other necessary substances

II. Plant Nutrients and Soil

A. Plant health requires essential inorganic nutrients

1. essential plant nutrients- required for plant to complete life cycle

2. studied hydroponically (Fig. 37.3)

3. macronutrients CHOPKiNS Ca Fe Mg

a. CHO structural

b. Calcium - cell walls, glue holding cells together

c. K - cofactor, main solute for osmotic regulation

d. Mg- component of chlorophyll

e. N, P, S - important in organic compounds plants make and use (example?)

4. micronutrients -chlorine, copper, zinc, molybdenum, manganese, boron and nickel

minute amounts, but can kill a plant if absent, most act as cofactors of enzymes

a. e.g. iron acts as a metallic component of cytochromes, proteins in the electron

transport chain of chloroplasts and mitochondria

b. Mb is so rare that there is only 1 molecule of it for every 60 million atoms of H in

dried plant material but deficiency of this micronutrient will kill plant

c. mineral deficiencies cause various symptoms (Fig. 37.4, Table 37.1)

1. chlorosis - yellowing of leaves - in mineral is mobile, will occur in old leaves

if not mobile will occur in young leaves, which typically act as sinks and have

drawing power for substances in the plant

2. symptoms of plant are usually enough for a plant pathologist to identify the

deficiency, usually caused by local soil characteristics

3. testing plants and soils for nutrient content is usually the way to confirm the

deficiency

4. moderation is important in correcting deficiencies bc overdoses of many

nutrients is toxic to plants

II. Soil Quality is a major determinant of plant distribution and growth

A. Along with climate, soil texture and composition are major factors that determine whether a plant can

grow in a particular area

1. texture is the soil’s general structure, referring to various sized particles and their relative amts

2. composition is soil’s organic and inorganic chemical components

B. Texture and composition of soils

1. soil formation - PaTTCO

a. Pa - parent material

b. T - time

c. T- topography

d. C - climate

e. O- organisms

2. soil horizons- layers of soils with distinct characteristics (Fig. 37.5)

a. A horizon (topsoil) - organic inputs

1. loams - approx. equal amts. of sand, silt clay - 3 particle sizes - contain

ability to hang onto water and nutrients, also have air spaces

2. organisms - 1 tsp of A horizon has 5 billion bacteria in addition to protists,

algae, fungi, roots, insects, nematodes, earth and other worms

3. Humus - decomposing organic material - formed by fungus and bacteria -

builds a crumbly soil and maintains a well of nutrients

4. film of water around soil particles; some water can be absorbed by roots, not

all (Fig. 37.6);

a. called soil water and contains dissolved ions (minerals, nutrients)

b. Negatively charged ions (anions) such as Nitrate NO3-, Phosphate

(H2PO4-), and sulfate (SO42-) are not bound tightly to negatively

charged soil particles and are easily released, but are also easily leached

away into ground water in rain

c. Positively charged ions Potassium K+, Calcium (Ca2+) and

magnesium (Mg2+) are held tightly to negatively charged soil particles;

these can be displaced from soil particles by replacing them with H+,

called Cation exchange, and is a process stimulated by roots, which add

H+ to soil water

b. B horizon - less organic material, less weathered

c. C horizon - similar chemically to parent material but has soil structure, not rock

3. Soil Conservation - must be managed bc of intensive resource and crop harvest to maintain

nutrient pool and structure (Dust Bowl of 1930s)

a. fertilization, irrigation and prevention of erosion all top goals in soil conservation

b. more than 30% of world’s farmland suffers from low productivity stemming from poor

soil conditions (pollution, salinity, mineral deficiency, acidity, poor drainage)

III. Nitrogen and Plants

A. Most plants get nitrogen from bacteria (Fig. 37.9)

1. atmospheric N unusable

2. need ammonium (NH4+) or nitrate (NO3-)

3. supplied by bacteria called nitrogen fixers; convert N2 to ammonium

4. also by ammonifying bacteria- decompose humus

5. only a little ammonia used by plants, remains bound to clay in soil

6. nitrifying bacteria turns ammonium into nitrates; plants mostly use this and convert it to

ammonium for amino acids. What are these used for?

a. proteins, nucleic acids, chlorophyll and other important molecules

IV. Nutritional adaptations of plants involve relationships with other organisms

A. Legumes and some other plants have nodules with N fixing bacteria (Fig. 37.10)

1. nodules on roots = plant cells w/ N fixing bacteria

2. legumes = peanuts, peas, beans, etc.

3. most N fixing bacteria from genus Rhizobium

4. some non-legumes fix N- alders

5. beneficial relationship - plant provides CHO and other compounds; root nodule bacteria may

secrete excess NH4+, increasing soil fertility;

a. each legume as its own Rhizobium species (Fig. 37.11)

6. crop rotation - soybeans or alfalfa reduce need for industrial fertilizers

B. Fungi help plants absorb nutrients - mycorrhizae - beneficial association (Fig. 37.12)

1. especially helpful for plants in poor soils

2. helps increase uptake of water, nutrients, esp. phosphate

a. endomycorrhiza- enter cell wall, not plasma membrane - 85% of plants, esp. grains

and legumes

1. form root hairs, look normal

b. ectomycorrhizae - extracellular - provide huge surface area for plant absorption

15% of plants including many gymno and tree families - pine, spruce, oak, walnut birch

1. don’t form root hairs, unnecessary given enormous surface area

3. transfers some to plants

4. may secrete acid increasing solubility of minerals

5. protect plant against pathogen

6. Plant’s Ps may help fungus

7. citrus trees require less fertilizer if they have mycorrhiza

8. organisms interconnected- plants not independent

C. Plants and other organisms - epiphytes, parasites and carnivores

1. Epiphytes- orchids, ferns

2. Parasites

a. dodder - roots pierce vascular tissue of host

b. mistletoe - Ps, also parasite- root pierces vascular tissue

3. Carnivores - acidic soils- little nitrogen - slow decomposition

a. sundew and Venus f lytrap get N from insects

b. trap insects, secrete digestive enzymes

ch 37 Study Questions:

1. Describe the ecological role of plants in transforming inorganic molecules into organic compounds.

2. Define the term essential nutrient.

3. Explain how hydroponic culture is used to determine which minerals are essential nutrients.

4. Distinguish between macronutrient and micronutrient.

5. Name the nine macronutrients required by plants.

6. List the eight micronutrients required by plants and explain why plants need only minute quantities of these elements.

7. Explain how a nutrient’s role and mobility determine the symptoms of a mineral deficiency.      

8. Define soil texture and soil composition.

9. Explain how soil is formed.

10. Name the components of topsoil.

11. Describe the composition of loams and explain why they are the most fertile soils.

12. Explain how humus contributes to the texture and composition of soils.

13. Explain why plants cannot extract all of the water in soil.

14. Explain how the presence of clay in soil helps prevent the leaching of mineral cations.

15. Define cation exchange, explain why it is necessary for plant nutrition, and describe how plants can stimulate the process.

16. Explain why soil management is necessary in agricultural systems but not in natural ecosystems such as forests and grasslands. Describe an example of human mismanagement of soil.

17. List the three mineral elements that are most commonly deficient in agricultural soils.

18. Describe problems resulting from farm irrigation in arid regions.

19. Define nitrogen fixation and write an overall equation representing the conversion of gaseous nitrogen to ammonia.

20. Explain the importance of nitrogen-fixing bacteria to life on Earth.

21. Explain why a symbiosis between a legume and its nitrogen-fixing bacteria is considered to be mutualistic. 22. Explain why a symbiosis between a plant and a mycorrhizal fungus is considered to be mutualistic.

23. Distinguish between ectomycorrhizae and endomycorrhizae.      

24. Name one modification for nutrition in each of the following groups of plants:

a. epiphytes

b. parasitic plants

c. carnivorous plants

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