Photosynthesis Core Concepts and Vocabulary

Vocabulary flashcards covering core concepts, leaf and chloroplast anatomy, light reactions, Calvin cycle, and key biochemical processes of photosynthesis.

Autotroph

An organism (such as plants, algae, cyanobacteria) that produces organic food from inorganic raw materials using external energy (e.g., sunlight).

Heterotroph

An organism that must consume organic nutrients made by other organisms.

Photosynthesis

The chemical process by which autotrophs convert solar energy into chemical energy stored in carbohydrates like glucose, taking in $CO_2$ from the air and $H_2O$ from soil.

Mesophyll

Inner leaf tissue rich in chloroplasts.

Stomata

Microscopic pores on the leaf epidermis for gas exchange ($CO_2$ in, $O_2$ out); singular form is stoma.

Leaf Veins

Leaf structures that transport water and nutrients from roots.

Cuticle / Epidermis

The outer protective layer of a leaf that reduces water loss.

Stroma

The fluid-filled interior space and matrix of a chloroplast surrounding thylakoids; site of the Calvin cycle.

Thylakoid

A flattened, sac-like membrane compartment inside a chloroplast containing chlorophyll; site of the light reactions.

Granum

A stacked column of thylakoid membrane discs inside a chloroplast; plural form is grana.

Thylakoid Space

The inner lumen of a thylakoid where $H^+$ builds up.

Light Reactions

The primary stage of photosynthesis occurring in thylakoid membranes that splits $H_2O$ using light energy to produce $ATP$, $NADPH$, and $O_2$.

Calvin Cycle

The primary stage of photosynthesis occurring in the stroma that uses $ATP$ and $NADPH$ to reduce $CO_2$ into G3P/glucose.

Photosynthesis Chemical Equation

$6CO_2 + 6H_2O + \text{Solar Energy} \rightarrow C_6H_{12}O_6 + 6O_2$, wherein $H_2O$ is oxidized into $O_2$ (loses $e^-$ and $H^+$) and $CO_2$ is reduced into $C_6H_{12}O_6$ (gains $e^-$ and $H^+$).

Chlorophyll a & b

Photosynthetic pigments in thylakoids that absorb blue and red light while reflecting green light.

Carotenoids

Photosynthetic pigments in thylakoids that absorb blue-green light while reflecting yellow, orange, and red light.

Absorption Spectrum

A graph showing the percentage of light absorbed by different photosynthetic pigments (e.g., Chlorophyll a, Chlorophyll b, Carotenoids) across various wavelengths of visible light.

Light Reactions Inputs

Inputs: Solar energy, $H_2O$, $\text{ADP} + \text{P}_i$, $NADP^+$;

Light Reaction Outputs

Outputs: $O_2$ , $ATP$, $NADPH$.

Calvin Cycle Inputs

Inputs: $CO_2$, $ATP$, $NADPH$;

Calvin Cycle Outputs

Outputs: G3P (3-carbon sugar derivative), $\text{ADP} + \text{P}_i$, $NADP^+$.

Electron Transport Path

The sequential flow of an electron in photosynthesis: $H_2O\text{ (split at PS II)}\rightarrow\text{PS II}\rightarrow\text{Electron Transport Train}\rightarrow\text{PS I}\rightarrow\text{NADPH}\rightarrow\text{Calvin Cycle (G3P)}\rightarrow\text{Glucose}$ .

Photosystem II (PS II)

A protein-pigment complex in the thylakoid membrane that absorbs light, splits water, and feeds $e^-$ to the initial ETC to drive $ATP$ chemiosmosis.

Photosystem I (PS I)

A protein-pigment complex in the thylakoid membrane that re-energizes $e^-$ to pass them to $NADP^+$ reductase to yield $NADPH$.

Photolysis

The light-driven splitting of a water molecule ($H_2O$) at Photosystem II, producing electrons to replenish PS II, hydrogen protons ($H^+$), and oxygen gas ($O_2$).

NADP+ / NADPH

A major coenzyme that acts as an electron carrier in photosynthesis; oxidized $NADP^+$ accepts 2 high-energy $e^-$ and 1 proton ($H^+$) during light reactions to become reduced $NADPH$.

ATP Synthase

An enzyme and channel protein complex located in thylakoid/mitochondrial membranes that synthesizes $ATP$ from ADP and inorganic phosphate as protons ($H^+$) flow through it down their gradient.

Chemiosmosis

The mechanism of $ATP$ production wherein energy stored in a transmembrane electrochemical gradient of hydrogen ions ($H^+$) is used by $ATP$ synthase to phosphorylate ADP into $ATP$.

Carbon Dioxide Fixation

The chemical process of capturing inorganic atmospheric carbon dioxide ($CO_2$) and covalently bonding/fixing it into an organic compound (RuBP) at the beginning of the Calvin cycle.

RuBP (Ribulose-1,5-bisphosphate)

The 5-carbon acceptor molecule that binds atmospheric $CO_2$ during carbon fixation in the Calvin cycle. Without its regeneration, the Calvin cycle stops and no continuous sugar synthesis can occur

G3P Versatility

The synthetic capacity of plants to convert G3P into glucose/sucrose, starch, cellulose, fatty acids & glycerol, and amino acids. It is when RuBP is fixed with carbon and when it is reduced. After that six more times, it becomes glucose

Calvin Cycle Step 1

$CO_2$ Fixation ($CO_2$ attaches to RuBP via RuBisCO),

Calvin Cycle Step 2

$CO_2$ Reduction (3PG converted to G3P using $ATP$ and $NADPH$),

Calvin Cycle Step 3

RuBP Regeneration (5 G3P use $ATP$ to regenerate 3 RuBP)

Upper Right Hand Box

Photosynthesis

Right Middle Box

Glucose and O2

Lower Middle Box

Heterotroph

Lower Left Box

Cellular Respiration

Left Side Box

H20 and CO2

Upper Middle Box

Autotroph