Which statement best describes how genes are expressed in an organism?

• A. Gene expression is solely determined by the organism's age and not by external factors.
• B. Genes are expressed at constant levels in all cells regardless of environmental conditions.
• C. All genes in an organism are expressed simultaneously to maintain homeostasis.
• D. Gene expression is regulated and can vary depending on the cell type and environmental signals.

Answer: (D)

Verified step by step guidance

1. Understand that gene expression refers to the process by which information from a gene is used to synthesize a functional gene product, typically proteins.
2. Recognize that gene expression is not constant; it is regulated and can vary depending on several factors, including cell type, developmental stage, and environmental signals.
3. Consider how different cells in an organism have different functions and therefore express different sets of genes. For example, liver cells express genes related to detoxification, while muscle cells express genes related to contraction.
4. Explore how environmental signals, such as temperature, light, and nutrients, can influence gene expression. For instance, certain genes may be upregulated in response to stress or changes in nutrient availability.
5. Conclude that gene expression is a dynamic process that allows organisms to adapt to their internal and external environments, ensuring proper function and homeostasis.