Photosynthesis (Edexcel International A Level (IAL) Biology): Flashcards

ATP is a nucleotide, structurally similar to the nucleotides that make up DNA and RNA. It is a phosphorylated nucleotide.

An ATP molecule consists of adenine, a ribose sugar, and three phosphate groups.

Photophosphorylation is the production of ATP using energy from light during photosynthesis.

The enzyme ATPase catalyses the hydrolysis of ATP.

The removal of a phosphate group from ATP is known as dephosphorylation.

True.

ADP and inorganic phosphate produced by ATP hydrolysis can be recycled to make more ATP.

Photolysis is the splitting of water molecules using light energy during the light-dependent reactions of photosynthesis.

The light-dependent reactions occur across the thylakoid membrane, while the light-independent reactions take place in the stroma of the chloroplast.

During the light-dependent reactions, light is converted into chemical energy in the form of ATP and reduced NADP.

Photolysis of one water molecule produces 2 hydrogen ions (2H⁺), 2 electrons (2e⁻), and one oxygen atom (O).

NADP is a coenzyme that can transfer hydrogen from one molecule to another.

Photophosphorylation is the production of ATP using light energy during the light-dependent reactions of photosynthesis.

False.

Cyclic photophosphorylation produces ATP only, not NADPH.

During non-cyclic photophosphorylation, electrons are excited in photosystem II and passed along an electron transport chain to photosystem I.

ATP synthase is an enzyme that catalyses the production of ATP as hydrogen ions diffuse through it across the thylakoid membrane during the light-dependent reactions.

In photosynthesis, reduction is the gain of electrons, gain of hydrogen, or loss of oxygen, while oxidation is the loss of electrons, loss of hydrogen, or gain of oxygen.

The Calvin cycle is the set of light-independent reactions in photosynthesis where carbon dioxide is fixed to produce organic molecules such as glucose, using ATP and reduced NADP.

The enzyme rubisco catalyses the reaction between carbon dioxide and RuBP in the Calvin cycle.

ATP and reduced NADP from the light-dependent reactions are required for the Calvin cycle.

When carbon dioxide combines with RuBP, it produces glycerate 3-phosphate (GP).

The reduction of GP to GALP requires energy from ATP and hydrogen from reduced NADP.

False.

The Calvin cycle is a light-independent reaction, so it does not require light, but it does require ATP and reduced NADP from the light-dependent reactions.

A hexose sugar is a type of sugar molecule that contains six carbon atoms, such as glucose.

The main transport sugar in plants is sucrose, which is produced from hexose sugars like glucose.

Polysaccharides such as starch and cellulose are made from hexose sugars produced in the Calvin cycle.

Phosphates are required to make nucleic acids and nitrates are required to make amino acids when combined with Calvin cycle products.

GALP from the Calvin cycle is used to produce glucose, sucrose, starch, cellulose, lipids, nucleic acids, and amino acids.

The Calvin cycle provides acetyl groups for acetyl coenzyme A, an important coenzyme in respiration.

A chloroplast is an organelle found in plant cells where photosynthesis occurs.

The chloroplast envelope is a double membrane that encloses the chloroplast, keeping all components needed for photosynthesis close together.

Each chloroplast is surrounded by a double membrane called the chloroplast envelope.

The stroma is a cytoplasm-like, gel-like fluid inside the chloroplast that contains enzymes, sugars, ribosomes, and chloroplast DNA.

The stroma contains enzymes and sugars, as well as ribosomes and chloroplast DNA.

When thylakoids stack up, they form structures called grana (singular: granum).

Lamellae are membranous channels that connect grana within the chloroplast.

Proteins called photosystems contain photosynthetic pigments such as chlorophyll a, chlorophyll b, and carotene.

True.

Grana create a large surface area for photosystems and ATP synthase enzymes, maximising light absorption and ATP production.

Photosystem I absorbs light at a wavelength of 700 nm, while photosystem II absorbs light at 680 nm. They contain different combinations of photosynthetic pigments.

A photosynthetic pigment is a molecule in chloroplasts that absorbs light energy at specific wavelengths for use in photosynthesis.

Chloroplasts contain several different photosynthetic pigments within photosystems embedded in the thylakoid membranes.

Chlorophylls absorb wavelengths in the blue-violet and red regions of the light spectrum, reflecting green light.

β Carotene is a carotenoid pigment and appears orange.

The absorption spectrum of a pigment shows the amount of light absorbed at different wavelengths.

False.

Each type of photosynthetic pigment absorbs light at different wavelengths, giving each pigment a unique absorption spectrum.

An action spectrum shows how the rate of photosynthesis varies with the wavelength of light available.

Having several different pigments with different absorption spectra allows plants to photosynthesise under a wider variety of light wavelengths and maximise rates of photosynthesis.

A photosynthetic pigment is a molecule in chloroplasts that absorbs specific wavelengths of light for photosynthesis.

Different photosynthetic pigments are different colours because they absorb different wavelengths of light and reflect others. For example, chlorophylls absorb red and blue light but reflect green, so they appear green.

The colour of a pigment is due to the wavelengths of light reflected by that pigment.

Chromatography is a technique used to separate mixtures based on the different speeds at which their components move through a material.

A pencil is used because pen ink contains pigments that would separate during chromatography and obscure the results.

Acetone is used in pigment extraction because it is a(n) organic solvent and can dissolve phospholipid membranes in plant cells.

True.

The formula for R_f value is distance travelled by pigment ÷ distance travelled by solvent.

In chromatography, carotenoids have the highest R_f values, while chlorophyll b has the lowest.

A limiting factor in photosynthesis is an external factor, such as light intensity, carbon dioxide concentration, or temperature, that is below its optimum level and reduces the rate of photosynthesis even if other factors are optimal.

The three main external factors that affect the rate of photosynthesis are light intensity, carbon dioxide concentration, and temperature.

For photosynthesis to occur, plants require photosynthetic pigments, carbon dioxide, water, light energy, and a suitable temperature.

If any of the main factors is below the optimum level, the rate of photosynthesis will be reduced, even if the other two are optimal.

False.

Water shortages usually affect other processes in the plant before photosynthesis, so water is not generally considered one of the main limiting factors for photosynthesis.

Increasing light intensity increases the rate of photosynthesis, as more energy is supplied for the light-dependent stage, producing more ATP and reduced NADP. However, at a certain point, the rate plateaus and light intensity is no longer the limiting factor.

When light intensity is increased, the rate of photosynthesis eventually reaches a plateau, above which it does not increase further.

Increasing carbon dioxide concentration increases the rate of photosynthesis, as it is needed for carbon fixation in the Calvin cycle, up to the point where another factor becomes limiting.

Carbon dioxide is required for the light-independent stage of photosynthesis, where it is fixed in the Calvin cycle.

As temperature increases, the rate of photosynthesis increases up to an optimum, due to increased enzyme activity. Above the optimum temperature, enzymes denature and the rate decreases.

Most reactions in photosynthesis are catalysed by enzymes, which explains the effect of temperature on the rate.

True.

Aquatic plants produce oxygen during photosynthesis, which can be collected and measured as bubbles underwater to investigate the rate of photosynthesis.

The light-dependent stage of photosynthesis is the phase where light energy is used to produce ATP and reduced NADP, which are then used in the Calvin cycle.