Unit 3 Biology Study Guide: Energy, Photosynthesis & Cellular Respiration

Vocabulary flashcards covering the key terms, locations, structures, and pathways of photosynthesis and cellular respiration from Unit 3 Biology.

Autotrophs

Organisms that make their own food.

Photoautotrophs

Organisms that use sunlight as their energy source to make organic compounds; plants are an example.

Chemoautotrophs

Organisms that use chemical energy, such as energy from sulfide or methane, to make organic compounds.

Heterotrophs

Organisms that obtain energy from outside sources because they cannot make their own food.

Chloroplast

The organelle surrounded by a double membrane where photosynthesis occurs.

Thylakoids

Flattened membrane sacs inside chloroplasts where the light-dependent reactions occur.

Grana

Stacks of thylakoids located inside the chloroplast.

Stroma

The fluid-filled space surrounding the grana where the Calvin cycle occurs.

Chlorophyll a

The most important light-absorbing pigment found in thylakoids; absorbs the most light.

Chlorophyll b

A light-absorbing pigment in thylakoids that absorbs slightly different wavelengths from chlorophyll a.

Carotenoids and xanthophylls

Accessory pigments in thylakoids that absorb additional wavelengths of light; include red, orange, and yellow pigments.

Photolysis

The splitting of water during the light-dependent reactions, replacing electrons lost by PSII and releasing oxygen ($\text{O}_2$) and protons ($\text{H}^+$).

ATP synthase

An enzyme that uses the energy of $H^+$ flowing down its concentration gradient to convert ADP into ATP.

Calvin cycle

Light-independent reactions occurring in the stroma that use $\text{CO}_2$, ATP, and NADPH to make 3-carbon sugar molecules (G3P).

Rubisco

The enzyme that attaches $\text{CO}_2$ to RuBP (a 5-carbon molecule) during the carbon fixation stage of the Calvin cycle.

G3P

A 3-carbon sugar produced during the Calvin cycle that can be used to make glucose and other organic compounds.

C3 photosynthesis

Photosynthesis pathway common in moderate light and rainfall where the first stable compound formed after $\text{CO}_2$ fixation is a 3-carbon compound, occurring entirely in mesophyll cells.

C4 photosynthesis

An adaptation to hot, dry conditions that separates steps spatially by fixing $\text{CO}_2$ into a 4-carbon compound in mesophyll cells before moving it to bundle-sheath cells for the Calvin cycle.

CAM photosynthesis

An adaptation to desert conditions that separates steps by time: stomata open at night to fix $\text{CO}_2$ into 4-carbon molecules stored in vacuoles, and close during the day for photosynthesis.

ATP (adenosine triphosphate)

The cell's energy source; composed of adenine, ribose sugar, and three phosphate groups.

Coupled reactions

Reactions in which an energy-releasing reaction drives an energy-requiring reaction, commonly powered by ATP breakdown.

Cellular respiration

The process that transforms chemical energy in food into chemical energy cells can use (ATP), represented by $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$.

Oxidation

The removal of hydrogen/electrons from a molecule.

Reduction

The gain of hydrogen/electrons by a molecule.

Glycolysis

The first stage of cellular respiration occurring in the cytoplasm; splits one 6-carbon glucose into two 3-carbon pyruvate molecules with a net gain of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Preparatory reaction

Stage 2 of aerobic cellular respiration occurring in the mitochondrial matrix; oxidizes pyruvate, releases $\text{CO}_2$, reduces $\text{NAD}^+$ to NADH, and forms acetyl-CoA.

Krebs cycle (Citric Acid Cycle)

Stage 3 of cellular respiration occurring in the mitochondrial matrix; completes glucose breakdown, releases $\text{CO}_2$, forms NADH and $\text{FADH}_2$, and produces $2\,\text{ATP}$ per glucose.

Electron Transport Chain (ETC)

Stage 4 of cellular respiration in the inner mitochondrial membrane; uses electrons from NADH and $\text{FADH}_2$ to pump $H^+$ and make $34\,\text{ATP}$, with oxygen as the final electron acceptor.

Fermentation

An anaerobic pathway occurring without oxygen whose main purpose is to regenerate $\text{NAD}^+$ so glycolysis can continue, yielding a total of $2\,\text{ATP}$ per glucose.

Lactic acid fermentation

A form of anaerobic pathway that occurs in muscle cells and produces lactic acid.

Alcoholic fermentation

A form of anaerobic pathway occurring in single-celled fungi such as yeast that produces ethanol and $\text{CO}_2$, and is used in bread-making.