Photosynthesis Lecture Notes

Vocabulary-style flashcards covering the process of photosynthesis, leaf structure, chloroplast components, light-dependent and independent reactions, and limiting factors.

Photosynthesis

The process by which plants, some bacteria, and some protistans use energy from sunlight to produce glucose from carbon dioxide and water.

ATP (Adenosine triphosphate)

A molecule released by cellular respiration from pyruvate that provides energy for cellular processes.

Chlorophyll

A complex green pigment molecule associated with the conversion of usable sunlight energy into chemical energy.

Chlorophyll a

A type of chlorophyll present in all photosynthetic organisms that absorbs energy primarily from violet-blue and reddish orange-red wavelengths.

Accessory pigments

Pigments that absorb energy that chlorophyll a does not absorb, including chlorophyll b, c, d, e, xanthophylls, and carotenoids.

Chlorophyll tail

A lipid-soluble hydrocarbon tail represented by the formula $C_{20}H_{39}- $.

Chlorophyll head

A flat hydrophilic head with a magnesium ion at its centre, linked to the tail by an ester bond.

Xylem vessels

Specialized plant cells that transport water from the roots up to the leaves.

Stomata

Specialized structures (singular: stoma) flanked by two guard cells that allow gases like carbon dioxide and oxygen to enter and leave the leaf.

Cuticle

A protective waxy layer covering the leaf that carbon dioxide cannot pass through.

Thylakoid

The structural unit of photosynthesis consisting of flattened sacs or vesicles containing photosynthetic chemicals.

Grana

The name for collective stacks of thylakoids within a chloroplast.

Stroma

The fluid-filled areas between the grana within a chloroplast where light-independent reactions occur.

Photoactivation

The process where chlorophyll a absorbs light energy, resulting in an excited electron and the splitting of water molecules.

Phosphorylation

The addition of a phosphate group to an organic compound.

Light-dependent reactions

A series of reactions occurring in the grana that require direct light energy to produce ATP and NADPH.

Photolysis

The splitting of water into oxygen, hydrogen ions, and free electrons by light energy, represented by $2H_2O \rightarrow 4H^+ + O_2 + 4e^- $.

NADPH

The reduced state of nicotinamide adenine dinucleotide phosphate (NADP+), formed when NADP+ reacts with electrons and hydrogen ions.

Light-independent reactions

A series of reactions occurring in the stroma using ATP and NADPH to make carbohydrates from carbon dioxide.

Photoionisation

The process where sufficient light energy ionises a chlorophyll molecule by freeing an electron, leaving a positively charged ion.

Photosystem

A core comprising a chlorophyll molecule, an electron acceptor, and an electron donor.

Photosystem II (PSII)

Also known as P680, this is the first photosystem to occur in the light-dependent reactions.

Photosystem I (PSI)

Also known as P700, this photosystem absorbs energy most efficiently at $700\,nm $.

Z scheme

The name given to the electron transfer process due to the Z shape of the accompanying energy changes.

Non-cyclic phosphorylation

A pathway involving both PSII and PSI that produces both ATP and NADPH.

Chemiosmosis

The process where H+ ions diffuse from high to low concentration across an electrochemical gradient to drive ATP production.

Cyclic phosphorylation

A process involving only PSI that generates extra ATP for light-independent reactions without forming NADPH.

Carbon fixation

The incorporation of carbon dioxide into organic compounds.

Ribulose 1,5-biphosphate (RuBP)

A five-carbon sugar that combines with carbon dioxide at the beginning of the Calvin cycle.

Glycerate 3-phosphate (GP)

The molecule formed when the unstable six-carbon sugar produced from RuBP and $CO_2 $ breaks down.

Glyceraldehyde 3-phosphate (GALP)

A 3-carbon molecule formed by the reduction of phosphorylated GP by NADPH.

Limiting factors

Environmental factors such as light intensity, carbon dioxide concentration, and temperature that determine the rate of photosynthesis.