Biology 1: Photosynthesis, Chloroplast Structure, and Carbon Fixation Pathways

Comprehensive Question and Answer flashcards reviewing Biology 1 topics including the history of photosynthesis, leaf and chloroplast structures, light-dependent reactions, the Calvin cycle, photorespiration, and comparisons of C3, C4, and CAM pathways.

What is photosynthesis and what is its general balanced chemical equation?

Photosynthesis is the process by which plants use light energy to produce food in the form of sugars from carbon dioxide and water. Its general chemical equation is: $6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$.

What three main inputs do plants require for photosynthesis, and where does each come from?

1. Water ($H_2O$): Absorbed from the soil by the roots.
2. Carbon dioxide ($CO_2$): Enters leaves through stomata.
3. Light energy: Usually comes from the Sun and is absorbed by chlorophyll.

What are the Greek origins and meanings of the word "photosynthesis"?

"Photo" means light, and "synthesis" means putting together or combining. Together, it means using light energy to combine raw materials and produce food.

What key discovery regarding photosynthesis is credited to Jan van Helmont?

He investigated plant growth and the role of water in the growth of plants.

What was Joseph Priestley's contribution to the understanding of photosynthesis?

He demonstrated that plants could restore air that had been affected by burning.

What did Jan Ingenhousz demonstrate regarding plant air restoration?

He showed that light is necessary for plants to restore air.

What was Julius von Sachs's primary contribution to the study of photosynthesis?

He demonstrated the formation of starch in green plant tissues.

What major photosynthetic process did Melvin Calvin help explain?

He helped explain the reactions of carbon fixation in the Calvin cycle.

Based on this transport diagram, what are the key differences between xylem and phloem?

Xylem features one-way flow, transports water and minerals from roots upward, has no end walls between cells, and is stiffened with lignin. Phloem features two-way flow, transports water and food (sugars/organic nutrients), and has end walls with perforations.

Identify the major structural components of the chloroplast shown in this diagram.

The diagram shows the outer membrane, intermembrane space, inner membrane, stroma, thylakoids organized into grana, thylakoid lumen, ribosomes, chloroplast DNA, and starch granules.

What is the difference between a thylakoid, a granum, and the stroma?

• Thylakoid: A flattened membrane sac where light-dependent reactions take place.
• Granum (plural: grana): A stack of thylakoids.
• Stroma: The fluid-filled region surrounding the grana where the Calvin cycle occurs.

What are stomata and guard cells, and what are their functions?

Stomata are tiny openings in leaves that allow gas exchange. Guard cells are specialized cells that surround the stomata and control their opening and closing.

What is the leaf cuticle and what is its primary function?

A waxy protective layer covering the leaf surface that helps reduce water loss.

What stage of photosynthesis is depicted here, where does it occur, and what are its main inputs and outputs?

It depicts the light-dependent reactions occurring in the thylakoid membrane. Inputs: light, water ($H_2O$), ADP + $P_i$, and $NADP^+$. Outputs: oxygen ($O_2$), ATP, and NADPH.

What is photolysis in the context of photosynthesis?

The process by which water molecules are split using light energy, releasing oxygen as a by-product.

Where does the Calvin cycle take place, and why does it depend on the light-dependent reactions?

It takes place in the stroma of the chloroplast. Although it does not directly require light, it requires the ATP and NADPH generated during the light-dependent reactions.

What photosynthetic cycle is shown here, and what are its three numbered phases?

The Calvin Cycle. Its three phases are: Phase 1: Carbon Fixation (catalyzed by RuBisCO), Phase 2: Reduction (forming G3P using ATP and NADPH), and Phase 3: Regeneration of RuBP (using ATP).

What are the roles of RuBisCO and RuBP in carbon fixation?

RuBisCO is the enzyme that combines carbon dioxide ($CO_2$) with RuBP (ribulose 1,5-bisphosphate), a five-carbon acceptor molecule, to produce an unstable compound that splits into two molecules of 3-PGA.

What is G3P and what happens to it at the end of the Calvin cycle?

G3P (glyceraldehyde-3-phosphate) is a three-carbon sugar product. Most G3P molecules are recycled to regenerate RuBP, while some exit the cycle to form glucose and other organic compounds.

How do the light-dependent reactions and the Calvin cycle compare in terms of location, light requirement, and primary function?

• Light-dependent reactions: Located in the thylakoid membrane; directly require light; convert light energy into chemical energy (ATP and NADPH).
• Calvin cycle: Located in the stroma; do not directly require light; fix carbon dioxide to synthesize organic molecules (G3P).

What is photorespiration and why does it occur?

Photorespiration is a process where RuBisCO binds to oxygen ($O_2$) instead of carbon dioxide ($CO_2$). It occurs under hot or dry conditions when stomata close to conserve water, decreasing internal $CO_2$ levels and raising the relative concentration of $O_2$.

Which three organelles are involved in the photorespiratory pathway, and what 2-carbon compound is associated with it?

The three organelles are the chloroplast, peroxisome, and mitochondrion. The two-carbon compound formed is 2-phosphoglycolate, which is processed through glycolate and related intermediates.

What are the key characteristics and examples of C3 plants?

Their first stable product of carbon fixation is the 3-carbon compound 3-PGA; initial fixation and the Calvin cycle occur in the same cells (mesophyll); photorespiration can be high in hot, dry conditions. Examples: rice, wheat, and soybeans.

What photosynthetic pathway is illustrated here, and how does it separate carbon fixation?

The C4 pathway. It separates carbon fixation spatially: initial fixation occurs in mesophyll cells via PEP carboxylase to produce oxaloacetate (4C) and malate, which transfers $CO_2$ to bundle-sheath cells where the Calvin cycle takes place.

What photosynthetic pathway is shown here, and how does its temporal separation operate?

Crassulacean Acid Metabolism (CAM) photosynthesis. Stomata open at night to fix $CO_2$ into oxaloacetate and malic acid stored in vacuoles; during the daytime, stomata close to conserve water, and malic acid releases $CO_2$ to the Calvin cycle.

What are representative plant examples of the C4 and CAM pathways?

• C4 examples: corn, sugarcane, and many tropical grasses.
• CAM examples: cacti, pineapple, and many succulents.

How do C3, C4, and CAM plants compare in their first stable product, stomatal opening schedule, and photorespiration levels?

• C3: 3-carbon compound (3-PGA); stomata open during the day; photorespiration can be high.
• C4: 4-carbon compound (oxaloacetate); stomata open during the day; photorespiration is usually low.
• CAM: Organic acids (malic acid); stomata open at night; photorespiration is usually low.

What is a photon in the context of plant biology?

A discrete packet of light energy.

What is the function of root hairs in plant transport?

They are extensions of root epidermal cells that increase surface area for the absorption of water and minerals from the soil.