AQA A Level Biology Topic 5: Energy Transfers in and Between Organisms

Vocabulary flashcards covering photosynthesis, respiration, energy transfers in ecosystems, and nutrient cycles based on the AQA A Level Biology Topic 5 specification.

Photoionisation

The process where chlorophyll absorbs light energy, exciting its electrons to a higher energy level until they are released, leaving the chlorophyll positively charged.

Chemiosmotic theory (in LDR)

The process where energy from electrons moving along the electron transfer chain is used to pump protons into the thylakoid, creating a gradient that drives ATP synthesis via ATP synthase as protons move back into the stroma.

Photolysis of water

The light-driven splitting of water into protons, electrons, and oxygen, represented by the equation: $H_2O \rightarrow \frac{1}{2} O_2 + 2e^- + 2H^+$.

Ribulose bisphosphate (RuBP)

A 5-carbon compound that reacts with $CO_2$ in the light-independent reaction, catalyzed by the enzyme rubisco.

Glycerate 3-phosphate (GP)

The 3-carbon intermediate formed when $CO_2$ reacts with RuBP; it is subsequently reduced to triose phosphate using ATP and reduced NADP.

Triose phosphate (TP)

A 3-carbon sugar produced in the Calvin cycle that can be converted into useful organic substances like glucose or used to regenerate RuBP.

Rf value

A calculated ratio used in chromatography to identify pigments, defined as: $Rf = \frac{\text{distance moved by spot}}{\text{distance moved by solvent front}}$.

DCPIP

A redox indicator dye used in photosynthesis experiments that turns from blue (oxidized) to colourless (reduced) when it accepts electrons.

Dehydrogenase

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

Glycolysis

The first stage of respiration occurring in the cytoplasm where glucose is phosphorylated and eventually oxidized to two molecules of pyruvate, yielding a net gain of $2$ ATP and $2$ reduced NAD.

Link reaction

The process in the mitochondrial matrix where pyruvate is oxidized and decarboxylated to acetate, which then combines with coenzyme A to form Acetyl Coenzyme A.

Krebs cycle

A series of oxidation-reduction reactions in the mitochondrial matrix that regenerates a 4-carbon molecule, producing $CO_2$, ATP via substrate-level phosphorylation, and reduced NAD and FAD.

Oxidative phosphorylation

The final stage of aerobic respiration where energy from electrons passed down the electron transfer chain is used to synthesize ATP, with oxygen acting as the final electron acceptor to form water.

Biomass

The total mass of living or organic material, measured in terms of mass of carbon or dry mass of tissue per given area.

Gross primary production (GPP)

The total chemical energy store in plant biomass in a given area or volume, in a given time, resulting from photosynthesis.

Net primary production (NPP)

The chemical energy store in plant biomass after respiratory losses ($R$) are subtracted, calculated as: $NPP = GPP - R$.

Net production of consumers (N)

The chemical energy stored in consumer biomass calculated using the formula: $N = I - (F + R)$, where $I$ is ingested energy, $F$ is energy lost in faeces/urine, and $R$ is respiratory loss.

Saprobionts

Organisms that decompose organic compounds by secreting enzymes for extracellular digestion and absorbing the needed nutrients while releasing mineral ions.

Mycorrhizae

Symbiotic associations between fungi and plant roots that increase the surface area for the absorption of water and inorganic ions.

Nitrogen fixation

The conversion of atmospheric nitrogen gas ($N_2$) into ammonia ($NH_3$) by nitrogen-fixing bacteria.

Nitrification

The two-step oxidation of ammonium ions into nitrites and then nitrates by nitrifying bacteria in aerobic conditions.

Denitrification

The process where nitrates in the soil are converted back into nitrogen gas by denitrifying bacteria, typically occurring in anaerobic conditions like waterlogged soil.

Ammonification

The process by which saprobionts break down nitrogen-containing compounds from dead organisms or waste into ammonia, forming ammonium ions in the soil.

Eutrophication

The process where excess nutrients cause an algal bloom, blocking light and leading to the death of plants, subsequent decomposition by aerobic saprobionts, and the depletion of oxygen for aquatic life.