frst 303: water movement

What is the overall formula for photosynthesis?

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

What is converted during photosynthesis?

Inorganic carbon (CO₂) → Organic carbon (glucose)

What is the byproduct of photosynthesis?

Oxygen (O₂)

Where do light reactions occur?

In the thylakoids of chloroplasts

What do light reactions require?

Light + H₂O

What do light reactions produce?

ATP + NADPH + O₂

What is the key pigment for photosynthesis?

Chlorophyll (absorbs light, except green)

How does water reach the leaves?

Via xylem

How does O₂ exit the plant?

Through stomata

Where do dark reactions (Calvin Cycle) occur?

In the chloroplast stroma

What do dark reactions require?

CO₂ + ATP + NADPH

What do dark reactions produce?

Glucose

What enzyme fixes carbon in the Calvin Cycle?

Rubisco

How does higher CO₂ affect growth?

Increases growth (unless limited by other factors)

What is the main role of leaves?

Photosynthesis

What leaf layer is the main site of photosynthesis?

Palisade mesophyll

What are stomata and their function?

Adjustable pores that regulate gas exchange and water loss

Where are stomata mostly located?

On the underside of leaves

What is the function of chloroplasts?

Perform photosynthesis; contain chlorophyll

What is the origin of chloroplasts (evolutionarily)?

Evolved from cyanobacteria (endosymbiosis theory)

What is photoinhibition?

Damage to photosystems from too much light; light and dark reactions fall out of sync.

Why can shade leaves get sunburned?

Sudden full-sun exposure damages their photosystems.

Difference between sun and shade leaves?

Sun leaves: thicker, more photosynthetic layers; Shade leaves: thinner, low-light adapted.

What is evapotranspiration?

Combined water loss from evaporation (non-living) + transpiration (plants).

Define evaporation.

Water loss from soil or bark.

Define transpiration.

Water vapor loss through stomata or lenticels.

Main functions of water in plants?

Photosynthesis, nutrient transport, turgor maintenance, cooling via evaporation.

How much water is lost through stomata?

~92%

What are lenticels?

Gas pores in bark allowing gas exchange; minor water loss.

What is the cuticle?

Waxy layer reducing evaporation.

Why is so much water lost through stomata?

CO₂ must dissolve on wet leaf surfaces for photosynthesis; evaporation drives gas exchange.

What controls stomatal opening and closing?

Abscisic acid (ABA).

Why do stomata close?

To prevent water loss and wilting.

Why do stomata open?

To allow CO₂ intake → enables photosynthesis.

What causes water cohesion and surface tension?

Hydrogen bonding between H₂O molecules.

What does ψ (water potential) measure and in what units?

Water potential in MPa (megapascals).

Direction of water movement (ψ)?

From higher ψ (less negative) → lower ψ (more negative).

What drives water movement in trees?

Transpiration pull + cohesion + adhesion + surface tension.

Describe the water pathway in plants.

Soil → root hairs → root xylem → stem xylem → leaf veins → leaf cells → stomata → air.

Difference between angiosperms and conifers in water transport?

Angiosperms use vessels; conifers use tracheids.

What is osmosis?

Water moves from low solute (high ψ) → high solute (low ψ).

Why must roots have higher solute concentration than soil?

To absorb water by osmosis.

How does water move in herbaceous plants?

Through primary xylem.

How does water move in woody plants?

Through secondary xylem (sapwood).

What is sapwood?

Conducts water; sometimes still alive.

What is heartwood?

Non-conductive, dead, provides support.