Photosynthesis & Plant Processes
Honors Biology – Interactive Study Set (Click each blue card to reveal the answer)
Energy & Nutrition
What is energy?
the ability to do cellular work (life functions). Chemical energy comes from glucose/food.
Heterotrophic Nutrition
Organisms consume food (glucose). Ex. Animals, fungi, amoeba, paramecia & some bacteria
Autotrophic Nutrition
Organisms make own food (glucose). Conduct Photosynthesis or Chemosynthesis. Ex. Plants, green algae, moss, euglena, phytoplankton & cyanobacteria
Why can’t glucose be used as a DIRECT energy source?
If all the energy were released at once most would be lost as heat/light; a living cell must release chemical energy in food molecules a little bit at a time and trap those bits by using them to make ATP.
ATP (Adenosine Triphosphate)
Briefly stores chemical energy! When a phosphate (Pi) is broken off of ATP…the energy released powers life functions, active transport, cell division, organelle movement, etc.
Photosynthesis – Overview
Purpose of Photosynthesis
transform Light Energy into Chemical Energy stored in glucose (food).
Photosynthesis Equation
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
(light energy over enzymes)
(light energy over enzymes)
Who performs photosynthesis?
Autotrophs/Producers
When does photosynthesis occur?
When Light Energy is present
Where does photosynthesis occur in the cell?
Occurs in chloroplasts!
Role of chlorophyll
green pigment that absorbs light energy inside chloroplasts
What do plants do with glucose after it is made?
• Broken down during Cellular Respiration → energy to ATP
• Used to build di- & polysaccharides by dehydration synthesis
• Hydrocarbon backbone rearranged to build lipids, amino acids, proteins, nucleic acids
• Extra N & P absorbed from soil
• Used to build di- & polysaccharides by dehydration synthesis
• Hydrocarbon backbone rearranged to build lipids, amino acids, proteins, nucleic acids
• Extra N & P absorbed from soil
Factors & Leaf Structure
Factors that Affect the Rate of Photosynthesis
Light intensity, Water availability, Amount of CO₂, Time of year/season, Temperature (optimal for enzyme activity)
Best wavelengths for photosynthesis
Blue, violet & red (absorbed the most by chlorophyll)
Worst wavelength for photosynthesis
Green (reflected, not absorbed by chlorophyll)
Stroma
fluid-filled area inside the chloroplast
Thylakoids
contain chlorophyll & photosystems
Granum / Grana
stacks of thylakoids
Cuticle
waxy, clear layer prevents water loss & allows light absorption
Palisade Mesophyll
closely packed cells that conduct LOTS of photosynthesis
Spongy Mesophyll
air spaces trap gases for photosynthesis, cellular respiration & transpiration
Xylem
transports water & minerals from roots to the leaves
Phloem
transports sugar from the leaves to anywhere it is needed
Stomata (stoma)
microscopic holes for gas exchange & transpiration
Guard Cells
regulate the opening & closing of stomata
Transpiration
evaporation of water through leaf stomata
Transpirational Pull
the upward movement of water through the xylem vessels, driven by the evaporation of water from the stomata during transpiration
Stomata Regulation
How do guard cells open stomata?
Actively pump K⁺ into central vacuoles → water follows by osmosis → guard cells become turgid, swell & push apart → stomata open
How do guard cells close stomata?
K⁺ diffuses out of vacuoles → water follows by osmosis → guard cells collapse & close stomata
When are stomata open?
Water is plentiful, daytime
When are stomata closed?
Drought, nighttime (to conserve water)
Photosynthesis Stages
Light-Dependent Reactions – Location
Thylakoid membranes
Light-Dependent Reactions – Purpose
Convert light energy into chemical energy (ATP & NADPH); release O₂
Light-Dependent Reactions – Inputs
Light energy, H₂O
Light-Dependent Reactions – Outputs
ATP, NADPH, O₂
Light-Independent Reactions (Calvin Cycle) – Location
Stroma
Light-Independent Reactions – Purpose
Carbon fixation: bonding CO₂ to organic molecules to build glucose (building more bonds = storing more energy)
Light-Independent Reactions – Inputs
CO₂, ATP, NADPH
Light-Independent Reactions – Output
Glucose (C₆H₁₂O₆)
Electron carrier used in photosynthesis
NADP⁺ → NADPH (carries high-energy electrons to Calvin Cycle)
Carbon Fixation
the process of building complex ORGANIC compounds (like glucose) from inorganic carbon compounds (CO₂). Building more bonds = storing more energy
Step 1 – Light Dependent Reactions
Chlorophyll in Photosystem II absorbs light → energizes electrons
Step 2 – Light Dependent Reactions
High-energy electrons fall down ETC → energy pumps H⁺ inside thylakoid → electrochemical gradient
Step 3 – Light Dependent Reactions
H⁺ diffuses through ATP synthase → produces ATP
Step 4 – Light Dependent Reactions
Electrons re-energized in Photosystem I → picked up by NADP⁺ → NADPH
Step 5 – Light Dependent Reactions
H₂O split → O₂ released, electrons replace those lost in PSII, H⁺ stays inside thylakoid
Calvin Cycle Step 1
CO₂ bonds to RuBP → PGA formed (carbon is fixed)
Calvin Cycle Step 2
ATP & NADPH provide energy & electrons → PGA converted to G3P (3-carbon sugars)
Calvin Cycle Step 3
Leftover G3P regenerates RuBP so cycle can continue; 2 G3P combine → one glucose