Horticulture Photosynthesis Study Guide

Be able to tell the difference between photosystem 1 and 2, what they do, how it happens

PSII generates the oxygen and electron flow necessary for the process, while PSI is responsible for creating NADPH, both of which are crucial for the plant to produce energy-rich molecules (ATP and NADPH) used in the Calvin cycle to synthesize glucose.

On a typical sunny day, when would the stomata be open day or night? Why?

During the day: Stomata are open to take in CO₂ for photosynthesis and release O₂.

At night: Stomata are closed to conserve water since there's no photosynthesis happening.

This way, the plant optimizes its use of resources and prevents water loss when it's not actively using CO₂ for photosynthesis.

And if it was a brutally hot day, how and why would the stroma change?

On a hot day, stomata close to prevent excessive water loss through transpiration.

What % of water can be lost through stomata on a typical day?

90%

What are the structures that control the opening and closing of the stomata and how does the plant control these structures?

Guard cells and stomata

guard cells control the opening and closing of the stomata by regulating water movement.

When guard cells take in water, they become turgid (swollen) and open the stomata.

When guard cells lose water, they become flaccid and the stomata close.

This process is influenced by factors like light, CO₂ levels, water availability, hormones (especially abscisic acid), and temperature.

Were plants the first photosynthesizers on Earth? Are they the biggest producers of oxygen today?

No, Plants (both land plants and aquatic plants) are among the major producers of oxygen today

Do plants use oxygen for respiration?

Yes

Parts of a Chloroplast

Outer Membrane

Inner Membrane

Stroma

Thylakoid Membranes

Granum (Plural: Grana)

Lumen

Light-dependent Reactions (Occur in the thylakoid membranes)

These reactions require light to occur and take place in the thylakoid membranes. During these reactions, light energy is absorbed by chlorophyll, and water molecules are split to release oxygen. This process also produces ATP and NADPH, which are used in the next stage.

Calvin Cycle (Light-independent Reactions) (Occur in the stroma)

The Calvin cycle occurs in the stroma, the fluid-filled space surrounding the thylakoids. It doesn't directly require light but uses the ATP and NADPH generated in the light-dependent reactions to convert carbon dioxide into glucose (or other sugars) through a series of enzyme-driven steps.

How do pigments look to us and why, light waves, etc.

The color of a pigment is determined by the wavelengths of light it absorbs and reflects. Pigments do not "emit" color; instead, they absorb certain wavelengths and reflect or transmit others, and our eyes interpret those reflected wavelengths as color.

Chlorophyll appears green because it absorbs blue and red light and reflects green.

Equation for photosynthesis

6CO2+6H2O→C6H12O6+6O2

Reactants

CO₂ provides carbon atoms to make glucose.

H₂O provides electrons and protons and produces oxygen as a byproduct.

Light energy powers the entire process by providing the energy needed to drive the light-dependent reactions.

Products

Glucose is the energy-rich product that the plant uses for growth, development, and energy.

Oxygen is a byproduct of splitting water during the light-dependent reactions.

PSII

Splits water to release oxygen and generates electrons, which pass through the electron transport chain.

PSI

Further excites electrons and ultimately helps form NADPH, which is essential for the Calvin cycle to produce glucose.

Water (H₂O)

Supplies electrons, protons, and produces oxygen.

Carbon Dioxide (CO₂)

Provides carbon atoms for glucose production in the Calvin cycle.

ATP

Provides energy to drive reactions in the Calvin cycle.

NADPH

Provides high-energy electrons for the reduction of 3-PGA to G3P in the Calvin cycle.

RuBP

Accepts CO₂ in the Calvin cycle to begin carbon fixation.

G3P

The 3-carbon sugar that is synthesized in the Calvin cycle, used to make glucose and other carbohydrates.

Rubisco

The enzyme that catalyzes the fixation of CO₂ with RuBP in the Calvin cycle.

ATP Synthase

Enzyme that synthesizes ATP using the proton gradient created in the light-dependent reactions.

3 Phases of the Calvin Cycle

carbon fixation, reduction, regeneration of RuBP

Carbon Fixation

CO₂ is fixed to RuBP by rubisco, creating two molecules of 3-PGA.

Reduction

ATP and NADPH convert 3-PGA into G3P (a 3-carbon sugar).

Regeneration of RuBP

G3P molecules are rearranged to regenerate RuBP, allowing the cycle to continue.

Where does the mass of the plant come from?

The mass of a plant primarily comes from carbon dioxide (CO₂) in the air, which is absorbed through the plant's stomata during photosynthesis.

Why is the pH different inside and outside of the thylakoid when light is present?

nside the thylakoid (lumen): The proton concentration is high due to the pumping of protons across the membrane during electron transport, making the pH lower (more acidic).

Outside the thylakoid (stroma): The proton concentration is lower because the protons are pumped into the thylakoid lumen, making the pH higher (more basic).

What is photorespiration? Under what conditions does it occur?

Photorespiration happens when plants use oxygen instead of carbon dioxide by mistake, wasting energy and slowing growth.

In what type of plants does photorespiration most often occur?

It's most common in C₃ plants (like wheat and rice) when it's hot and dry or when CO₂ is low.

What are some adaptations to avoid photorespiration that plants have evolved?

C₄ plants (like corn) and CAM plants (like cacti) have special ways to avoid photorespiration and are more efficient in hot, dry conditions.

Carbon Dioxide (CO₂)