Topic 2 - Keystone Sample Quiz

The cellular organelle labelled C is the mitochondria. The mitochondria are double-membraned organelles found in most eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they generate most of the cell's energy in the form of ATP through cellular respiration. The mitochondria have their own DNA and can replicate independently of the cell. They are involved in various metabolic processes, including the breakdown of carbohydrates and fatty acids to produce energy.

The main function of a vacuole in a cell is storage. Vacuoles are membrane-bound organelles that store various substances such as water, ions, nutrients, and waste products. They help maintain the cell's shape and provide support. In plant cells, vacuoles are particularly large and play a crucial role in maintaining turgor pressure, which helps the plant stand upright. Additionally, vacuoles can also store pigments, toxins, and defense compounds to protect the cell from external threats. Overall, the storage function of vacuoles is essential for maintaining the cell's homeostasis and carrying out various metabolic processes.

The cell membrane acts as a barrier and selectively regulates the movement of substances in and out of the cell. It allows essential molecules, such as nutrients and oxygen, to enter the cell while preventing the entry of harmful substances. Similarly, waste products and excess molecules are expelled from the cell through the membrane. This regulation of substance movement helps maintain the internal environment of the cell and ensures its proper functioning.

Genes, hormones, and cell location play the most direct role in controlling the events shown in the diagram because genes provide the instructions for the development and differentiation of cells, hormones regulate various physiological processes and can influence cell behavior, and cell location determines the interactions between cells and their surrounding environment, which can influence their development and function. These factors collectively determine the specific events and processes that occur during embryonic development.

This sequence represents a decrease from the greatest number of structures to the least number of structures present in a cell. The gene is the smallest unit of genetic information and is present in every cell. The chromosome is made up of many genes and is present in the nucleus of a cell. The nucleus is the largest structure in a cell and contains the chromosomes and genes. Therefore, the sequence gene → chromosome → nucleus represents a decrease in the number of structures present in a cell.

Stem cells have the ability to develop into different types of specialized cells due to the different environments they are exposed to and the functioning of different parts of their genetic code. This means that the specific conditions and signals in the cell's environment, as well as the activation or suppression of certain genes within the genetic code, play a role in determining the type of mature cell that the stem cell will differentiate into.

The diagrams show groups of cells, which indicates that they are working together in a coordinated manner. This suggests that they are part of a larger structure or unit, rather than individual cells carrying out different functions. Therefore, the most appropriate explanation is that these groups of cells represent tissues in which similar cells function together. Tissues are collections of similar cells that work together to perform a specific function in the body.

Genes involved in the production of abnormal red blood cells have an abnormal sequence of bases. The sequence of bases, which are adenine (A), thymine (T), cytosine (C), and guanine (G), determine the genetic code within a gene. Any alteration or abnormality in the sequence of bases can lead to changes in the structure or function of the protein encoded by that gene. In the context of abnormal red blood cells, a mutation or abnormal sequence of bases in the genes responsible for red blood cell production can result in the production of defective or dysfunctional red blood cells.

Both mitosis and meiosis involve DNA replication before the division of the nucleus. In both processes, the DNA is duplicated during the interphase stage, which occurs before the actual division takes place. This ensures that each resulting cell receives a complete set of genetic information. Asexual reproduction is not a characteristic shared by both mitosis and meiosis, as mitosis can also occur in multicellular organisms for growth and tissue repair. The statement that both occur only in reproductive cells is incorrect, as mitosis can occur in various somatic cells throughout the body. The statement that the number of chromosomes is reduced by half is specific to meiosis, not mitosis.

During development, cells go through a process called differentiation, where they specialize and express different parts of their identical genetic instructions. This allows them to perform specific functions and form different types of cells in the human body. Mutations can occur during development, but they are not the main explanation for the observation mentioned. Additionally, while cells may have different genetic material, this is not the primary reason for the variety of cell types in a human. Lastly, the statement that some cells develop before others is true, but it does not fully explain the observation of different cell types at birth.

Down syndrome is caused by an error in meiotic cell division. Meiosis is the process by which gametes (sperm and egg cells) are formed. During meiosis, the chromosomes are supposed to separate properly, with each gamete receiving one copy of each chromosome. However, in the case of Down syndrome, an error occurs during meiotic cell division, leading to the presence of an extra chromosome (specifically, an extra copy of chromosome 21) in the resulting gamete. When this gamete combines with another gamete during fertilization, the resulting individual will have three copies of chromosome 21 instead of the usual two, leading to the characteristics and symptoms of Down syndrome.