Exam I - Ch. 37 – WS 6
Chapter 37: Soil and Plant Nutrition
1. How do roots absorb inorganic minerals from the soil?
 Cation Exchange – roots pump out H+ to get other positive ions that
the plant needs (Ca2+, K+, Mg2+)
- Remember that soil particles are negatively charged, so positively
charged ions (cations) form ionic bonds with the soil particles
- Cation exchange depends on two things:
a) Number of cation adhesion sites on the soil particles
b) Soil pH
2. What are the two types of essential elements required for a plant to complete its
life cycle and produce another generation?
 Macronutrients – needed in large amounts (Magnesium)
 Micronutrients – need in small amounts (Iron)
3. Can you describe the various bacteria that participate in the nitrogen cycle?
 Nitrogen-fixing bacteria: Atmospheric Nitrogen → Ammonia
 Ammonifying bacteria: Organic material in soil → Ammonia
 Nitrifying bacteria: Ammonium → Nitrate
 Denitrifying bacteria: Nitrate → Atmospheric Nitrogen
4. In what two forms can nitrogen be absorbed by plants?
 Ammonium (NH4+) and nitrate (NO3-)
5. Which enzyme helps to convert nitrogen for plants to use?
 Nitrogenase
6. Can you explain another relationship between plants and bacteria involving
nitrogen fixation.
 Symbiotic relationship between Rhizobium bacteria and Legume
roots.
- Plant roots send out Flavonoid into the soil
- Flavonoid activates transcription genes in bacteria
- Bacteria releases nod factor
- Activates nodulin genes which allow bacteria to enter plant roots
7. How do nodules form on the plant roots?
 Bacteria enter plant roots via root hairs (infection threads)
 Pericycle cells (surrounding the vascular bundle) divide and form
nodules
 Bacteria inside nodules are referred to as Bacteroids
Exam I - Ch. 37 – WS 6
8. What is the role of Leghemoglobin?
 Protein formed by both the plant and bacteria
 Binds to O2 preventing the deactivation of the nitrogenase enzyme
9. How does fungus play a role in plant nutrition?
 Fungus attaches to plant roots forming Mycorrhizae (fungus roots)
- Increased surface area for water absorption
- Fungus sends out digestive enzymes to break down organic material
- Fungus can grow factors and antibiotics to aid the plant
10. Carnivorous plants eat insects in order to obtain what nutrient?
 Nitrogen found in chitin which comprises the exoskeleton of the insect