Question

what causes cells in living organisms to be different from one another?
a. an organism evolves new cell types in response to its environment.

b. the brain of an organism sends a signal to its cells to differentiate when the organism is in danger.

c. the dna of an organism moves from one cell to another, allowing different cells to have different functions.

d. an organism expresses different genes at different times in development, causing cells to be specialized.

Explanation:

• Option A: Evolution of new cell types in response to environment is not the main cause of cell differentiation in an organism's lifetime; evolution occurs over generations.
• Option B: Not all organisms have a brain, and cell differentiation is not triggered by brain signals in danger; it's a developmental process.
• Option C: DNA does not move from one cell to another in a multicellular organism to cause cell differences; each cell has the same DNA (except in some cases like immune cells, but that's not the main mechanism for general cell specialization).
• Option D: Cell differentiation (specialization) occurs because different genes are expressed at different times during development. This is the correct mechanism for cells to become different (e.g., muscle cells, nerve cells, etc. express different genes from the same genome).

Answer:

D. An organism expresses different genes at different times in development, causing cells to be specialized.