IGCSE Biology Questions And Answers

Enzymes are biological catalysts that speed up chemical reactions in the body without being consumed in the process. They work by lowering the activation energy required for reactions to occur, which allows essential biological processes to proceed quickly and efficiently at relatively low temperatures. This catalytic activity is crucial for digestion, metabolism, and many other regulatory and signaling pathways.

Leaves are the primary site of photosynthesis in plants. This process involves converting light energy, usually from the sun, into chemical energy stored in glucose. Leaves are well-suited for this task due to their broad, flat surfaces which maximize light absorption. They contain chloroplasts, which are organelles that hold chlorophyll. Chlorophyll captures light energy, which is then used to convert carbon dioxide from the air and water from the soil into sugars and oxygen.

Insulin is a hormone produced by the pancreas that regulates blood sugar levels. It facilitates the uptake of glucose from the blood into cells, where it can be used for energy, thereby lowering blood glucose levels. Insulin's role is critical in preventing hyperglycemia, a condition characterized by excessively high blood sugar levels that can lead to serious health problems, including diabetes type 2.

The mitochondrion is known as the powerhouse of the cell because it produces adenosine triphosphate (ATP), the cell’s main energy currency. This process, known as cellular respiration, involves the conversion of the energy stored in glucose into ATP. Mitochondria have their own set of DNA and are involved in several other essential functions, including the regulation of the cell cycle and cell growth.

Transpiration is the process through which water moves through plants from roots to leaves, then evaporates into the atmosphere primarily from the stomata in the leaves. This movement of water is crucial for the transport of nutrients from the soil, maintaining the structure of the plant, and cooling the plant on hot days. The process is driven by the evaporation of water at the leaf surface, creating a negative pressure that pulls water up from the roots through the xylem vessels.

Ribosomes are essential cellular organelles responsible for protein synthesis. They read messenger RNA (mRNA) sequences that have been transcribed from DNA and use the information to assemble amino acids into polypeptide chains. These chains fold into functional proteins that perform numerous tasks within the cell and throughout the body. Ribosomes can be found floating freely within the cytoplasm or attached to the endoplasmic reticulum, facilitating the production of proteins that are needed both inside and outside of the cell.

Prokaryotic cells, unlike eukaryotic cells of animals, plants, and fungi, do not have a defined nucleus. Instead, their genetic material is contained in a single, circular strand of DNA that floats freely within the cell in a region called the nucleoid. This lack of a membrane-bound nucleus and other organelles allows prokaryotes to have faster growth rates and simpler cellular organization, which are advantages in many environments.

Nucleic acids are the molecules that make up genetic material, which includes DNA and RNA. These molecules are vital for storing and transmitting genetic information from one generation to the next and are crucial for the synthesis of proteins. DNA molecules are composed of two strands forming a double helix, whereas RNA is typically single-stranded.

Meiosis is a specialized type of cell division that results in four daughter cells, each with half the number of chromosomes of the parent cell. This process is essential for producing gametes in sexually reproducing organisms. It introduces genetic diversity through phases like crossing over and independent assortment, where different traits are mixed before the gametes are formed, contributing to genetic variation in populations.

Vitamin K is crucial for the synthesis of proteins required for blood coagulation. Without Vitamin K, the blood clotting process is severely impaired, leading to increased bleeding and bruising. This vitamin acts as a cofactor for an enzyme that catalyzes the carboxylation of specific protein residues, which is essential for activating the proteins that mediate clotting.