chapter 6 ecology

Why is water essential to life?

Water makes up 50–90% of organisms and serves as the medium for biochemical reactions; for example, enzymes function in aqueous environments

Where did life evolve?

Life evolved in water; early cells depended on aquatic environments for stability and chemical reactions

What must organisms maintain regarding water?

Organisms must maintain proper internal water concentrations to avoid dehydration or swelling; for example, desert animals must prevent water loss

What determines water movement between organism and environment?

Concentration gradients determine water movement; for example, water leaves an organism in dry air due to a steep gradient

Which direction does water move?

Water moves down its concentration gradient from high to low concentration; for example, from moist tissues to dry air

What affects whether an organism gains or loses water?

The magnitude of the concentration gradient; for example, hot dry air increases water loss

What is diffusion?

Diffusion is the movement of substances from high to low concentration; for example, oxygen moving into cells

What is osmosis?

Osmosis is the diffusion of water across a semipermeable membrane; for example, water entering plant roots

What causes most water loss in terrestrial organisms?

Evaporation is the main cause; for example, sweating or transpiration

What is relative humidity?

Relative humidity is the percentage of water vapor in air compared to its maximum capacity; for example, 100% means fully saturated air

What happens to evaporative loss when humidity increases?

It decreases because the gradient is reduced; for example, sweating is less effective in humid climates

What is vapor pressure deficit?

The difference between actual and maximum water vapor pressure; for example, high deficit = dry air and high evaporation

What does isosmotic mean?

Internal and external solute concentrations are equal; for example, many marine invertebrates

What does hypoosmotic mean?

Lower solute concentration than environment, causing water loss; for example, marine bony fish

What does hyperosmotic mean?

Higher solute concentration than environment, causing water gain; for example, freshwater fish

What is water potential (ψ)?

Water potential is the capacity of water to do work and move; for example, water flows through plants due to potential differences

What is the water potential of pure water?

Zero; this serves as the reference point

What is water potential in nature usually?

Negative due to solutes and pressure; for example, plant tissues have negative ψ

Which direction does water move in plants?

From higher (less negative) to lower (more negative) water potential; for example, soil → roots → leaves → air

What contributes to plant water potential?

Solutes, matric forces, and pressure; for example, evaporation creates negative pressure pulling water upward

What challenges do terrestrial organisms face?

Water loss through evaporation and limited access to water; for example, desert environments

How do animals regulate water?

By balancing intake (drinking, food) with loss (evaporation, excretion); for example, producing concentrated urine

How do plants regulate water?

By balancing root uptake with transpiration loss; for example, closing stomata to reduce loss

Main ways animals get water?

Drinking, food, and metabolic water; for example, animals eating moist plants

What is metabolic water?

Water produced during cellular respiration; for example, kangaroo rats rely on it

Example of animals that don't need to drink?

Kangaroo rats survive entirely on metabolic water from food oxidation

How do plants adapt roots in dry environments?

They grow deeper roots to access groundwater; for example, desert shrubs

What affects root development?

Water availability and microclimate; for example, plants in dry soil grow deeper roots

Animal water conservation strategies?

Producing concentrated urine, reducing activity, reclaiming water from breath; for example, nocturnal desert animals

Plant water conservation strategies?

Reduced leaf area, thick leaves, fewer stomata, dormancy; for example, cacti

How do camels conserve water?

They store water, tolerate dehydration, and reduce heat gain; for example, allowing body temperature to rise

How do saguaro cacti conserve water?

They store water, have shallow roots, and close stomata during the day; for example, opening stomata at night

How do scorpions survive desert conditions?

They have low metabolism and stay in humid burrows; for example, avoiding daytime heat

How do cicadas survive desert conditions?

They use evaporative cooling despite high water loss; for example, feeding on plant fluids to compensate

How do aquatic organisms regulate water?

By balancing drinking, excretion, and osmotic exchange; for example, fish adjusting salt levels

Most marine organisms are?

Isosmotic, meaning little energy spent on osmoregulation; for example, many invertebrates

Marine bony fish are?

Hypoosmotic, so they lose water and drink seawater; for example, tuna

How do marine fish remove excess salt?

Through gill chloride cells and kidneys; for example, excreting sodium and chloride

Freshwater fish are?

Hyperosmotic, so they gain water from surroundings; for example, trout

What problem do freshwater fish face?

Excess water entering their bodies; for example, swelling risk

How do freshwater fish solve this problem?

Excrete dilute urine and actively absorb salts; for example, via gill cells

What is stable isotope analysis?

The study of isotope ratios to understand ecological processes; for example, tracking nutrient sources

What is deuterium (D)?

A heavy stable isotope of hydrogen; used as a tracer in ecological studies

How is deuterium used in plants?

It helps identify water sources; for example, distinguishing summer vs winter rainfall uptake