SBI4U Biology Final Exam Master Review

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy. The overall equation illustrates that carbon dioxide (CO₂) and water (H₂O) are utilized in the presence of light energy to produce glucose (a form of sugar) and oxygen (O₂). This transformation is essential for life on Earth, as it provides the primary source of organic matter for nearly all organisms and releases oxygen into the atmosphere, which is crucial for respiration.

Insertion or deletion mutations alter the number of nucleotides in a DNA sequence, leading to a shift in the reading frame during protein synthesis. This shift changes how subsequent codons are read, potentially resulting in a completely different and often nonfunctional protein. In contrast, substitution mutations (including silent and missense mutations) only change one nucleotide without affecting the overall reading frame, thereby not causing a frameshift.

During translation, the P site of the ribosome is responsible for holding the growing polypeptide chain. The ribosome has three sites: A (aminoacyl), P (peptidyl), and E (exit). The P site specifically accommodates the tRNA carrying the nascent polypeptide, allowing for the formation of peptide bonds with incoming amino acids from the A site. This process is crucial for protein synthesis, as it ensures the correct sequence of amino acids is linked together, ultimately forming functional proteins.

Ligase is the enzyme responsible for joining Okazaki fragments on the lagging strand during DNA replication. As DNA is synthesized discontinuously in short segments called Okazaki fragments, ligase catalyzes the formation of phosphodiester bonds between these fragments, sealing the gaps and creating a continuous DNA strand. This process is crucial for maintaining the integrity of the DNA molecule, ensuring that the genetic information is accurately replicated and passed on during cell division.

DNA replication is termed semi-conservative because, during the process, each of the two resulting DNA molecules retains one original strand from the parent DNA and incorporates one newly synthesized strand. This ensures that genetic information is accurately passed on during cell division, as each daughter cell receives a mix of the old and new DNA, maintaining the integrity of the genetic code while allowing for potential variations. This mechanism is crucial for evolution and adaptation in living organisms.

RuBisCO, or ribulose bisphosphate carboxylase/oxygenase, is the key enzyme in the Calvin cycle that catalyzes the fixation of carbon dioxide (CO₂) into organic molecules. It facilitates the reaction between CO₂ and ribulose bisphosphate (RuBP), leading to the production of 3-phosphoglycerate, which is then used to synthesize glucose and other carbohydrates. This process is essential for photosynthesis, allowing plants to convert inorganic carbon into a form that can be utilized for energy and growth.

Enzymes act as catalysts in biochemical reactions, facilitating the conversion of substrates into products by providing an alternative reaction pathway with a lower activation energy. This means that less energy is required for the reaction to occur, increasing the reaction rate. Importantly, enzymes are not consumed or permanently altered during the reaction, allowing them to be reused multiple times. Their ability to lower activation energy without being depleted is a key characteristic that distinguishes them from other chemical substances.

Polar molecules have a significant difference in electronegativity between their atoms, leading to an uneven distribution of electron density. This results in partial positive and negative charges, allowing them to interact favorably with water, which is also a polar solvent. Consequently, polar molecules tend to be hydrophilic, meaning they can dissolve in water, as the positive and negative regions of the polar molecules are attracted to the opposite charges in water molecules. This property is essential for many biological processes and chemical reactions.

Denaturation of a protein involves the disruption of its higher-order structures, such as secondary, tertiary, and quaternary structures, usually due to changes in temperature, pH, or chemical exposure. However, the primary structure, which consists of the linear sequence of amino acids linked by peptide bonds, remains intact during denaturation. This is because the covalent bonds that hold the amino acids together are not broken in the process, thus preserving the primary sequence despite the loss of the protein's functional shape.

Dehydration synthesis is a chemical reaction that links smaller molecules, such as monomers, to form larger molecules, like polymers. During this process, a water molecule is removed as a byproduct. The removal of water allows the reactive groups of the monomers to bond together, creating a covalent bond and resulting in a larger, more complex structure. This process is fundamental in forming biological macromolecules, including carbohydrates, proteins, and nucleic acids.

An exergonic reaction is characterized by the release of energy as it proceeds, making it spontaneous. Cellular respiration is a prime example, where glucose is broken down to release energy stored in its bonds. This process is essential for cellular functions, providing the energy needed for various biological activities. In contrast, endergonic reactions require energy input and lead to increased order, which is not the case for exergonic reactions.

Active transport is a cellular process that requires energy in the form of ATP to move substances against their concentration gradient, from areas of lower concentration to areas of higher concentration. This mechanism is essential for maintaining cellular homeostasis and allowing cells to accumulate necessary nutrients, ions, and other molecules, despite their lower concentration outside the cell. Unlike passive transport methods such as simple diffusion, facilitated diffusion, and osmosis, which rely on concentration gradients and do not require energy, active transport is vital for various physiological functions.

In competitive inhibition, an inhibitor competes with the substrate for binding to the active site of an enzyme. When more substrate is added, it increases the likelihood of substrate molecules binding to the enzyme instead of the inhibitor. This can effectively outcompete the inhibitor, allowing the reaction to proceed at a higher rate. Therefore, the effects of the inhibitor can be mitigated by increasing the substrate concentration, demonstrating that competitive inhibition can be overcome in this manner.

When a cell is placed in a hypertonic solution, the concentration of solutes outside the cell is higher than inside. This difference in concentration causes water to move out of the cell through osmosis in an attempt to balance the solute levels. As water leaves the cell, it loses volume, leading to the cell shrinking. This process can result in cellular dehydration and potentially impair cell function if the exposure to the hypertonic environment is prolonged.

The Calvin cycle occurs in the stroma of the chloroplast because this is the site where carbon fixation takes place. The stroma contains the necessary enzymes, substrates, and energy from ATP and NADPH produced in the light-dependent reactions. This environment allows for the conversion of carbon dioxide into glucose, making it essential for photosynthesis. The stroma's fluid matrix supports the biochemical reactions involved in synthesizing organic compounds, highlighting its crucial role in plant metabolism.

A covalent bond is formed when two atoms share electrons, allowing them to achieve stability by filling their outer electron shells. This sharing creates a strong attraction between the positively charged nuclei of the atoms and the shared electrons, resulting in a stable molecule. Covalent bonds can involve single, double, or triple pairs of shared electrons, depending on the number of electrons each atom needs to achieve a full valence shell. This type of bond is fundamental in the formation of organic compounds and is essential for the structure of many biological molecules.

The carboxyl group (-COOH) is responsible for the acidic properties in amino acids and fatty acids. This functional group can donate a proton (H⁺) to a solution, thereby increasing the concentration of hydrogen ions and lowering the pH, which characterizes acidity. In amino acids, the carboxyl group is one of the two functional groups present, contributing to their zwitterionic nature and overall behavior in biological systems. Fatty acids also possess carboxyl groups, which define their acidic characteristics and influence their solubility and reactivity.

Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing a small amount of energy. During this process, a total of four ATP molecules are generated; however, two ATP molecules are consumed in the initial steps. Therefore, the net yield of ATP from glycolysis is two ATP molecules. This process occurs in the cytoplasm and does not require oxygen, making it a crucial energy source for cells, especially under anaerobic conditions.

During fermentation, the regeneration of NAD⁺ is crucial for maintaining glycolysis, the metabolic pathway that breaks down glucose to produce energy. Glycolysis requires NAD⁺ to accept electrons during the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate. Without sufficient NAD⁺, glycolysis would halt, leading to a lack of ATP production. Fermentation processes, such as lactic acid fermentation or alcoholic fermentation, serve to convert pyruvate into other products, allowing NADH to be oxidized back to NAD⁺, thus facilitating the continuation of glycolysis in anaerobic conditions.

Cohesion refers to the attraction between molecules of the same substance. In the case of water, hydrogen bonds form between water molecules, causing them to stick together. This property is crucial for various biological processes, such as water transport in plants and the formation of water droplets. Cohesion contributes to surface tension, allowing small objects to float on water and enabling various ecological interactions.