Photosynthesis: The Light-dependent Reactions

Explanation
Exothermic reactions release energy by transferring it from the system to the surroundings. These reactions involve breaking of chemical bonds, resulting in the release of heat. The energy released can be in the form of light, heat, or sound. Examples of exothermic reactions include combustion, such as burning wood or gasoline, where energy is released in the form of heat and light. Another example is the reaction between acids and bases, where heat is generated. In contrast, endothermic reactions absorb energy from the surroundings, resulting in a decrease in temperature.

Explanation
A catalyst is a substance that increases the rate of a reaction that would otherwise be too slow. It does this by providing an alternative pathway with a lower activation energy, allowing the reaction to occur more quickly. Catalysts are not consumed in the reaction and can be used repeatedly, making them highly efficient in speeding up chemical reactions.

Explanation
The active site is the region on the enzyme where the reaction takes place. It is a specific pocket or cleft on the enzyme's surface that is complementary in shape and charge to the substrate molecule. The active site provides a favorable environment for the reaction to occur by bringing the substrate molecules into close proximity and orienting them in the correct position. It also facilitates the formation and breakage of chemical bonds during the reaction. The active site plays a crucial role in catalyzing the reaction and determining the specificity of the enzyme for its substrate.

Explanation
A coupled reaction refers to the process in which enzymes link reactions that release energy (exothermic reactions) to reactions that require energy (endothermic reactions). This coupling allows the energy released from one reaction to be used to drive the energy-requiring reaction. This mechanism is essential for maintaining energy balance and efficient utilization of energy in biological systems.

Explanation
Enzymes are proteins that act as catalysts in biological reactions, including the steps of photosynthesis and respiration. They facilitate and speed up these processes by lowering the activation energy required for the reactions to occur. Enzymes are specific to the reactions they catalyze, and they play a crucial role in the regulation and efficiency of both photosynthesis and respiration.

Explanation
Oxidation is a chemical reaction in which a substance loses electrons. This is consistent with the statement "loss of electrons" in the given answer. Additionally, oxidation often involves the formation of more C-O bonds, as oxygen atoms tend to bond with carbon atoms during oxidation reactions. Therefore, the statement "more C-O bonds" is also a characteristic of oxidation.

Explanation
During oxidation, an electron is removed from an atom or molecule, resulting in a positive charge. In order to balance the charge, a proton may follow and be added to the system, forming a hydrogen ion. During reduction, on the other hand, an electron is added to an atom or molecule, resulting in a negative charge. In this case, a proton may be removed from the system, leading to the removal of a hydrogen ion. Therefore, the correct answer is "removed; added".

Explanation
Carbon dioxide is a gas that is required for photosynthesis in plants. Stomatal pores are small openings on the surface of leaves that allow for gas exchange. Carbon dioxide molecules diffuse through these stomatal pores and dissolve in the thin film of water that surrounds the mesophyll cells. This dissolved carbon dioxide is then used by the plant for photosynthesis. Therefore, the statement is true.

Explanation
Water is the source of electrons used in photosynthesis. During the light-dependent reactions of photosynthesis, water molecules are split by sunlight, releasing oxygen and hydrogen ions. The electrons from the hydrogen ions are then used to convert carbon dioxide into glucose during the light-independent reactions. Therefore, water serves as the initial source of electrons that are crucial for the production of glucose, the main energy source for plants.

Explanation
The stroma is the colorless fluid matrix in the chloroplast that contains enzymes. It is responsible for various metabolic reactions, such as the synthesis of glucose during photosynthesis. The grana and thylakoids, on the other hand, are structures within the chloroplast where the light-dependent reactions of photosynthesis occur.

Explanation
thylakoid; grana are stacks of thylakoid disks

Explanation
The thylakoid membrane is a membrane system found in chloroplasts, which are responsible for photosynthesis in plants. This membrane contains green chlorophyll and other light capturing pigments, such as carotenoids. These pigments are essential for capturing light energy and converting it into chemical energy during the process of photosynthesis. Therefore, the statement that the thylakoid membrane contains green chlorophyll and other light capturing pigments is true.

Explanation
visible light

Explanation
This statement is true because according to the electromagnetic spectrum, shorter wavelengths correspond to higher energy photons, while longer wavelengths correspond to lower energy photons. This relationship is observed across various forms of electromagnetic radiation, such as visible light, ultraviolet light, and X-rays.

Explanation
Red has the longest wavelength among the given colors, while violet has the shortest wavelength. This is because different colors of light have different wavelengths, with red light having a longer wavelength and violet light having a shorter wavelength. The color red is associated with longer wavelengths and lower frequencies, while violet is associated with shorter wavelengths and higher frequencies.

Explanation
T.W. Engelmann demonstrated in 1882 that oxygen production is directly related to the type of light that chlorophyll absorbs.

Explanation
Each chlorophyll molecule contains a long lipid tail which is anchored into the interior of a thylacoid membrane and one atom of magnesium. The long lipid tail helps to anchor the chlorophyll molecule into the thylacoid membrane, which is where photosynthesis takes place in plant cells. The magnesium atom is a central component of the chlorophyll molecule and is essential for its ability to absorb light energy during photosynthesis.

Explanation
Chlorophyll a reflects green light; chlorophyll b reflects bluish green light

Explanation
There is 3x more chlorophyll a than b in a chlorplast

Explanation
Carotenoids are the yellowish-orange pigments found in all plants. They are responsible for the vibrant colors of fruits, vegetables, and flowers. Carotenoids play a crucial role in photosynthesis by absorbing light energy and transferring it to chlorophyll molecules. They also act as antioxidants, protecting plants from harmful effects of light and oxygen.

Explanation
The maximum absorption of chlorophylls is in the blue and green wavelength; the max absorption of carotenoids is in the blue-green parts of the spectrum

Explanation
The correct answer is "non-cyclic" because in light-dependent photosynthesis, electrons flow in a linear pathway from water to NADP+ through photosystem II, the electron transport chain, and photosystem I. This pathway is called non-cyclic because the electrons do not cycle back to the original molecule (chlorophyll) after passing through the electron transport chain. In contrast, cyclic photosynthesis involves a circular pathway where electrons cycle back to the original molecule, resulting in the production of ATP but no NADPH or oxygen.

Explanation
The individual units of both photosystems involved in the non-cyclic pathway are mostly composed of chlorophyll a. They also contain much smaller amounts of chlorophyll b and carotenoid pigments. Additionally, each unit has a reaction-center molecule of chlorophyll a.

Explanation
The given statement is true because the reaction-center molecule is specifically designed to receive and transfer electrons during a chemical reaction. It has a unique structure and composition that allows it to absorb energy and raise an electron to an excited state. This excited state is crucial for the molecule to carry out its function in the reaction. Therefore, it is correct to say that the reaction-center molecule is the only molecule in the unit where an electron can be raised to an excited state.

Explanation
Antenna pigments are the other pigments in the unit that gather light energy and transfer it to the reaction-molecule. These pigments act as light-harvesting molecules, absorbing light of different wavelengths and funneling the energy to the reaction-center pigment, which initiates the chemical reactions of photosynthesis. Antenna pigments expand the range of light that can be absorbed and increase the efficiency of energy transfer within the photosynthetic system. UV pigments, on the other hand, are not mentioned in the question and do not play a role in light energy transfer.

Explanation
P700 is the reactin-molecule for photosystem I

Explanation
Photosystem I is the correct answer because even though it was discovered first, it is not the first in line in the process of photosynthesis. Photosystem II actually comes before Photosystem I in the sequence of events during photosynthesis. Photosystem II is responsible for capturing light energy and generating high-energy electrons, which are then passed on to Photosystem I. Therefore, while Photosystem I may have been discovered earlier, it is not the first step in the overall process of photosynthesis.