AQA A Level Biology Topic 5 Vocabulary Flashcards

Vocabulary flashcards covering key terms, processes, and structural concepts from A Level Biology Topic 5 Energy Transfers in and Between Organisms.

Chloroplast structure

A double-membrane organelle containing stroma (with small/70S ribosomes, circular DNA, starch granules, and lipid droplets), grana (stacks of thylakoids), and lamellae (thylakoid membranes linking grana).

Photoionisation

The process by which chlorophyll absorbs light energy, exciting its electrons to a higher energy level so they are released from chlorophyll, leaving it positively charged.

Photolysis of water

The light-driven reaction in which water splits to produce protons, electrons, and oxygen according to the equation $\text{H}_2\text{O} \rightarrow \frac{1}{2}\text{O}_2 + 2\text{e}^- + 2\text{H}^+$.

Ribulose bisphosphate (RuBP)

A 5-carbon compound that reacts with carbon dioxide in the light-independent stage of photosynthesis to form two molecules of glycerate 3-phosphate.

Rubisco

The enzyme that catalyses the reaction between carbon dioxide and ribulose bisphosphate (RuBP) during the Calvin cycle.

Glycerate 3-phosphate (GP)

A 3-carbon compound formed in the light-independent reaction when carbon dioxide combines with ribulose bisphosphate (RuBP).

Triose phosphate (TP)

A 3-carbon sugar produced in the Calvin cycle when glycerate 3-phosphate (GP) is reduced using reduced NADP and energy from ATP hydrolysis.

Rf value

A comparative measure in chromatography calculated as distance moved by spot divided by distance moved by solvent front.

Dehydrogenase

An enzyme in photosynthesis that catalyses the reduction of NADP in the light-dependent reaction by transferring electrons gained from photoionisation or photolysis.

DCPIP

A redox indicator dye and electron acceptor that changes from blue when oxidised to colourless when reduced.

Mitochondrion structure

A double-membraned organelle containing an outer membrane, cristae (folds of the inner membrane), and a matrix with small (70S) ribosomes and circular DNA.

Glycolysis

An anaerobic process in the cytoplasm where glucose is phosphorylated using inorganic phosphate from $2$\,ATP, split into two triose phosphate molecules, and oxidised to two pyruvate molecules with a net gain of $2$\,ATP and $2$\,reduced NAD.

Link reaction

The process in the mitochondrial matrix where pyruvate is oxidised and decarboxylated to acetate, producing $\text{CO}_2$ and reduced NAD, before acetate combines with coenzyme A to form acetyl coenzyme A.

Krebs cycle

A cyclic series of oxidation-reduction reactions in the mitochondrial matrix where acetyl coenzyme A (2C) reacts with a 4C molecule to form a 6C molecule, regenerating the 4C molecule while producing reduced NAD, reduced FAD, ATP, and $\text{CO}_2$.

Substrate level phosphorylation

The direct transfer of a phosphate group from an intermediate compound to ADP to form ATP.

Oxidative phosphorylation

The formation of ATP from ADP and inorganic phosphate driven by energy released as electrons pass down an electron transfer chain and protons diffuse down an electrochemical gradient via ATP synthase.

Gross primary production (GPP)

The chemical energy store in plant biomass in a given area or volume in a given time, representing the total energy transferred into chemical energy from light energy during photosynthesis.

Net primary production (NPP)

The chemical energy store in plant biomass remaining after respiratory losses ($R$) to the environment are deducted from gross primary production, given by $\text{NPP} = \text{GPP} - R$.

Saprobionts

Organisms that decompose organic compounds in dead matter or waste by secreting enzymes for extracellular digestion (saprobiotic nutrition) and absorbing needed nutrients while releasing mineral ions.

Mycorrhizae

Symbiotic associations between fungi and plant roots where fungal hyphae extend root surface area to increase water and inorganic ion uptake in exchange for organic compounds.

Nitrogen cycle

The biogeochemical pathway by which nitrogen is recycled through ecosystems via nitrogen fixation, ammonification, nitrification, and denitrification.

Nitrogen fixation

The process by which nitrogen-fixing bacteria convert atmospheric nitrogen gas ($\text{N}_2$) into ammonia ($\text{NH}_3$), forming ammonium ions ($\text{NH}_4^+$) in the soil.

Ammonification

The breakdown and decomposition of nitrogen-containing compounds (such as proteins or urea) from dead matter or waste into ammonia and ammonium ions by saprobionts.

Nitrification

A two-step oxidation reaction performed by nitrifying bacteria in aerobic conditions that converts ammonium ions in soil into nitrites and then nitrates.

Denitrification

The reduction of nitrates in soil into nitrogen gas by denitrifying bacteria under anaerobic conditions.

Eutrophication

The process where excess dissolved nutrients leach into water bodies causing an algal bloom, blocking light, killing submerged plants, and promoting aerobic respiration by saprobionts that depletes oxygen and causes aquatic animals to die.