BIO103 - CH10 VOCAB - photosynthesis

energy

The capacity to cause change, especially to do work (to move matter against an opposing force).

photosynthesis

The conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes.

autotroph

An organism that obtains organic food molecules without eating other organisms or substances derived from other organisms. They use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones.

heterotroph

An organism that obtains organic food molecules by eating other organisms or substances derived from them.

mesophyll

Leaf cells specialized for photosynthesis. In C3 and CAM plants, these cells are located between the upper and lower epidermis; in C4 plants, they are located between the bundle-sheath cells and the epidermis.

stomata

A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant.

chlorophyll

A green pigment located in membranes within the chloroplasts of plants and algae and in the membranes of certain prokaryotes. Form "a" of this substance participates directly in the light reactions of photosynthesis, which convert light/solar energy to chemical energy.

adenosine triphosphate

An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells. Abbreviated as ATP.

oxidation

The complete or partial loss of electrons from a substance involved in a redox reaction.

reduction

The complete or partial addition of electrons to a substance involved in a redox reaction (opposite of oxidation!!!).

NADP+

The oxidized form (= hydrogens were stripped/taken) of nicotinamide adenine dinucelotide phosphate, an electron carrier that can accept electrons, becoming NADPH. NADPH temporarily stores electrons produced during the light reactions.

NADPH

The reduced form (= electrons added) of nicotinamide adenine dinucelotide that temporarily stores electrons produced during light reactions.. It acts as a "reducing power" that can be passed along to an electron acceptor, reducing it.

light reactions

The first of two major in photosynthesis (preceding the Calvin Cycle). Also called the "water splitting" reactions. These reactions, which occur on the thylakoid membranes of the chloroplast (or on membranes of certain prokaryotes), convert light/solar energy to the chemical energy of ATP and NADPH, releasing oxygen in the process.

photophosphorylation

The process of generating ATP from ADP and phosphate by means of chemiosmosis, using a proton-motive force generated across the thylakoid membrane of the chloroplasts (or the membrane of certain prokaryotes) during the light reactions of photosynthesis. [NOTE: similar to oxidative phosphorylation in mitochondria during cellular respiration]

electron transport chain

A sequence of electron carrier molecules (membrane proteins) that shuttle electrons down a series of redox reactions that release energy used to make ATP.

chemiosmosis

An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient (HIGH to LOW) across a membrane to drive cellular work, such as the synthesis of ATP. [the perfect analogy for this process is a hydroelectric dam... the water "gradient" turns the turbines which generates electricity]

absorption spectrum

The range of a pigment's ability to absorb various wavelengths of light.

chlorophyll a

A photosynthetic pigment that participates directly in light reactions, which convert light/solar energy to chemical energy. Chlorophyll b and carotenoids serve as accessory photopigments that transfer energy to this pigment.

ATP synthase

A complex of several membrane proteins that functions in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion (=proton) concentration gradient (HIGH to LOW) to make ATP. [analogy.... these are the turbines generating electricity in a hydroelectric dam]

carbon fixation

The initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (e.g. plant). It is the first step of the Calvin Cycle and typically involves the enzyme rubisco.

electromagnetic spectrum

The entire spectrum of electromagnetic radiation, ranging in wavelength from less than a nanometer to more than a kilometer.

photon

A quantum, or discrete quantity (a "packet"), of light energy that behaves as if it were a particle.

Calvin cycle

The second of two major stages in photosynthesis (following the light reactions), involving (a) carbon fixation (of atmospheric CO2) and (b) reduction (remember, in a redox reaction, what is reduction???) of the fixed carbon into carbohydrate.

redox reaction

A phrase/idea that many students have problems conceptualizing. A chemical reaction involving the complete (or partial) transfer of one or more electrons from one reactant to another. Remember, it's all about the electrons... make sure to review electronegativity!!!

rubisco

Ribulose byiphosphate (RuBP) carboxylase-oxygenase, the enzyme that normally catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP). When excess O2 is present or CO2 levels are low, this enzyme can bind to oxygen, resulting in photorespiration.

photosystem

A light-capturing unit located in the thylakoid membrane of the chloroplast (or in the membrane of certain prokaryotes), consisting of a reaction-center complex surrounded by numerous light-harvesting complexes. There are two types, I and II, and they absorb light best at different wavelengths.

photosystem I

A light-capturing unit located in the thylakoid membrane of the chloroplast (or in the membrane of certain prokaryotes); it has two molecules of P700 chlorophyll a at its reaction center.

photosystem II

A light-capturing unit located in the thylakoid membrane of the chloroplast (or in the membrane of certain prokaryotes); it has two molecules of P680 chlorophyll a at its reaction center.

reaction-center complex

A complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor. Located centrally in a photosystem, this complex triggers the light reactions of photosynthesis. Excited by light energy, the pair of chlorophyll a molecules donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain.

light-harvesting complex

A complex of proteins associated with pigment molecules (chlorophyll a, chorophyll b, and carotenoids) that capture light energy and transfer it to reaction-center pigments in a photosystem.

C3 plant

A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound (glyceraldehyde 3-phosphate, G3P) as the first stable intermediate.

C4 plant

A plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin Cycle.

CAM plant

A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. In this process, CO2 entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.