Chapter 37 Reading Quiz 1.What is the general name for elements that plants require in large amounts? 2.What are the most fertile soils called? 3.What is found in soil that is capable of nitrogen fixation? 4.What are “mycorrhizae”? 5.Plants that grow on the surface of another plant but are not parasitic are called…?

1. Describe the chemical composition of plants and explain how this leads to plants’ nutritional needs. Carbohydrate (carbon, hydrogen, oxygen) Nitrogen, sulfur, and phosphorus A plant’s nutritional needs are met with water, minerals, and sunlight

2. Explain how a hydroponic culture is used to determine which minerals are essential nutrients. In a hydroponic culture, the roots of a plant are bathed in certain nutrients only to find out what is really necessary for plant growth Water is aerated to provide oxygen to the roots

3. Distinguish between macronutrient and micronutrient. Macronutrient  elements that are required by plants in relatively large amounts Micronutrient  elements that plants need in very small amounts

4. List the nine macronutrients required by plants. 1.Carbon 2.Oxygen 3.Hydrogen 4.Nitrogen 5.Sulfur 6.Phosphorus 7.Potassium 8.Calcium 9.Magnesium

5. List eight micronutrients required by plants and explain why plants need only minute quantities of these elements. 1.Chlorine 2.Iron 3.Boron 4.Manganese 5.Zinc 6.Copper 7.Molybdenum 8.Nickel These elements function in plants mainly as cofactors of enzymatic reactions Any deficiency can weaken or kill a plant

6. Explain how a nutrient’s role and mobility determine the symptoms of a mineral deficiency. The symptoms of a mineral deficiency depend partly on the function of the nutrient in the plant Ex: magnesium is necessary in the function of chlorophyll, and when it is deficient, the leaves turn yellow Mobility  deficiency will show up in older tissues because younger tissues have a stronger “pulling” power

7. Explain what determines the texture of topsoil and list the type of soil particles from coarsest to smallest. Topsoil  mixture of decomposed rock of varying texture, living organisms and humus (decomposing organic material) Depends on particle size: 1. Coarse sand 2. Sand 3. Silt 4. Clay

8. Describe the composition of loams and explain why they are the most fertile soils. Loams  equal amounts of sand, silt, and clay  fine particles retain water and minerals  Coarser particles provide air spaces with oxygen for cellular respiration

9. Explain how humus contributes to the texture and composition of soil. It prevents clay from packing together Builds a crumbly soil that retains water but is porous for root aeration Helps to act as a reservoir of mineral nutrients

10. Explain why plants cannot extract all of the water in soil. Some water adheres so tightly to hydrophilic soil particles that it cannot be extracted by plants This happens because the soil has electrically charged particles

11. Explain how the presence of clay in soil prevents the leaching of mineral cations. Many minerals in soil (Ca 2+, K +, Mg 2+ ) adhere by electrical attraction to the negatively charged surfaces of clay particles This clay prevents the draining away of mineral nutrients during heavy rain or irrigation Nitrates, phosphates, and sulfates do not bind and tend to drain away

12. Define cation exchange, explain why it is necessary for plant nutrition, and describe how plants can stimulate the process. Cation exchange  positively charged minerals are made available to the plant when hydrogen ions in the soil displace the mineral ions from the clay particles This is stimulated by the roots themselves, which secrete H + and compounds that form acids in the soil solution

13. Explain why soil management is necessary in agricultural systems but not in natural ecosystems such as forests and grasslands. Agriculture is unnatural and depletes the mineral content of the soil, making soil less fertile Crops use more water than natural vegetation Leads to “crop rotation” in farms Also “contour tillage”

14. List the three mineral elements that are most commonly deficient in farm soils. 1.Nitrogen 2.Phosphorus 3.Potassium Mainly because they are leached away in rains and irrigation

15. Describe the environmental consequence of overusing commercial fertilizers. Excess minerals from chemical fertilizers may be leached from soil and may pollute streams and lakes Often causes “algal blooms” and choke off life in lakes 

16. Explain how soil pH determines the effectiveness of fertilizers and a plant’s ability to absorb specific mineral nutrients. Acidity affects cation exchange and the chemical form of the minerals A change may make one essential element more available while causing another to adhere to soil and is not available

17. Describe problems resulting from farm irrigation in arid regions and list several current approaches to solving these problems. Huge drain of water resources Can gradually make soil salty and infertile  use of drip irrigation (slow watering)  use plant varieties that require less water

18. Describe precautions that can reduce wind and water erosion. Rows of trees to divide fields can act as windbreaks Terracing hillsides helps prevent water erosion Planting alfalfa and wheat provides good ground cover and protection

19. Define nitrogen fixation and write the overall equation representing conversion of gaseous nitrogen to ammonia. NH 3 + H  NH 4 Nitrogen fixation  the process of converting atmospheric nitrogen to nitrogenous compounds that can be directly used by plants (nitrate or ammonia)

20. Distinguish between nitrogen fixing bacteria and nitrifying bacteria. Nitrogen-fixing  restock nitrogenous minerals in the soil by converting N 2 to NH 3 (ammonia) Nitrifying  convert NO 3 - to N 2 which diffuses from the soil to the atmosphere

21. Explain why the symbiosis between a legume and its nitrogen-fixing bacteria is considered to be mutualistic. Symbiotic nitrogen fixation results from intricate interactions between roots and bacteria Nodules form with the bacteria which supplies fixed nitrogen and the plant supplies carbohydrates and other organic compounds

22. Discuss the relationships between root nodule formation and mycorrhizae development. Mycorrhizae are modified roots consisting of symbiotic associations of fungi and roots Lots of evolutionary similarities between nodule formation and mycorrhizae (gene activation, signal-transduction pathways)

23. Describe modifications for nutrition that have evolved among plants including parasitic plants, carnivorous plants, and mycorrhizae. Mycorrhizae  helps plants absorb water and minerals Parasitic  haustoria taps in to obtain xylem or phloem Carnivorous  live in poor soil conditions, obtain nitrogen and minerals by killing and digesting insects