BIOL 205 Module 1 quiz

What are the three major building blocks required to make plant tissue?

Carbon (CO2)

Which elements make up most of plant biomass?

Carbon

Where do plants obtain carbon?

From atmospheric CO2

Where do plants obtain mineral nutrients?

From soil

What are mineral nutrients?

Essential elements obtained from soil

Why are mineral nutrients also found in animals?

Plants are the base of food webs

How are plant nutrients classified?

Macronutrients and micronutrients

What distinguishes macro- from micronutrients?

Amount required

Why is nitrogen a macronutrient?

Required in very large quantities

Which biomolecules contain nitrogen?

Proteins

Why are fertilizers labeled NPK?

Nitrogen

What is Liebig’s Law of the Minimum?

Growth is limited by the scarcest resource

What analogy explains Liebig’s Law?

Shortest plank in a barrel

Which nutrients most commonly limit growth?

Nitrogen and phosphorus

What is global nutrient limitation?

Growth below climatic potential due to nutrients

Why are many old soils nutrient-poor?

Leaching and lack of renewal

Why are Australian soils infertile?

Very old geology

How do clay soils affect nutrients?

Strong binding

How do sandy soils affect nutrients?

Poor retention

What is nutrient homeostasis?

Regulated balance of uptake and use

What is chelation?

Binding toxic elements to reduce reactivity

What are heavy metals?

Non-essential toxic elements

Give examples of heavy metals

Mercury

Why are heavy metals toxic?

Enzyme inhibition and ROS generation

How can heavy metals enter plants?

Mimic nutrients

What determines metal availability?

Soil pH

Why does liming reduce toxicity?

Raises pH

What is symbiosis?

Close association between organisms

Does symbiosis imply benefit?

No

What symbioses affect plant nutrition?

Nitrogen fixation and mycorrhizae

What do plants provide symbionts?

Carbon and habitat

What do symbionts provide plants?

Nutrients and water

How old are mycorrhizal symbioses?

~400 million years

Why were mycorrhizae important for land plants?

Improved nutrient uptake

What nutrient limits most terrestrial ecosystems?

Nitrogen

Why is nitrogen abundant but limiting?

Exists as inert N2 gas

What bond makes N2 inert?

Triple bond

Which organisms can fix nitrogen?

Some prokaryotes

Can plants fix nitrogen directly?

No

What enzyme fixes nitrogen?

Nitrogenase

How much ATP does fixation require?

~16 ATP per N2

Why is nitrogenase anaerobic?

Oxygen inactivates it

Which plant family contains most nitrogen fixers?

Fabaceae

What are legumes?

Members of Fabaceae

Give examples of legumes

Peas

What bacteria fix nitrogen in legumes?

Rhizobia

Where are rhizobia housed?

Root nodules

Do rhizobia fix nitrogen freely?

No

What is traded in legume symbiosis?

Carbon for nitrogen

Why is signaling specific?

Avoid pathogens

What plant signal attracts rhizobia?

Flavonoids

What bacterial signal triggers nodulation?

Nod factors

What plant structure curls during infection?

Root hair

What is an infection thread?

Guided bacterial tunnel

What are bacteroids?

Differentiated rhizobia in nodules

What is facultative fixation?

Plants can regulate fixation

What are costs of fixation?

Carbon

Why is oxygen a problem?

Inhibits nitrogenase

What molecule manages oxygen?

Leghemoglobin

Why are nodules pink?

Leghemoglobin

How do plants sanction cheating rhizobia?

Smaller

When is fixation favored?

Low N

Why doesn’t fixation dominate ecosystems?

High cost and shared benefits

What is autoregulation of nodulation?

Systemic suppression of nodules

When is fixation highest in succession?

Rapid growth phase

What are mycorrhizal fungi?

Root-associated fungi

What do mycorrhizae increase?

Effective root surface area

Why are hyphae effective?

Thin and extensive

Which nutrient commonly moves via fungi?

Phosphorus

What are ectomycorrhizae?

External root fungi

Do ectomycorrhizae enter cells?

No

What are endomycorrhizae?

Intracellular fungi

What structures increase exchange?

Arbuscules

Which plants are ectomycorrhizal?

Conifers

Which plants are endomycorrhizal?

Most flowering plants

What special ability do ectomycorrhizae have?

Break down organic matter

How do mycorrhizae increase P availability?

Organic acids

How do mycorrhizae affect drought tolerance?

Increase water uptake

What hormone attracts mycorrhizae?

Strigolactones

What fungal signal confirms compatibility?

Myc factors

Why are mycorrhizae reduced in agriculture?

Tillage and fertilizers

What are biofertilizers?

Microbial inoculants

Why is regulation important?

Products vary in quality

What traditional system uses fixation?

Three Sisters

Which crop fixes nitrogen there?

Beans

What are endophytes?

Microbes living inside plants

Where were leaf N-fixers found?

Sugarcane

How was leaf fixation shown?

Radioactive N2 uptake

What is the rhizosphere?

Root-influenced soil

How do plants shape microbes?

Exudates and pH

What does PCA show?

Distinct communities

What are plant growth-promoting bacteria?

Beneficial rhizosphere microbes

What is a common mycorrhizal network?

Shared fungal connections

Is resource sharing proven?

Evidence inconclusive

Why are nutrient trade-offs important?

Limited resources

Why are nutrients key for climate models?

Limit carbon uptake