Question

which structure acts as a semi - permeable barrier, protecting the cell and regulating what enters and exits?
a. cell membrane
b. nucleus
c. cytoplasm
d. cytoskeleton

where is dna housed in a eukaryotic cell?
a. golgi apparatus
b. mitochondria
c. cytoplasm
d. nucleus

Explanation:

• First question: The cell membrane is a semi - permeable barrier. It is made of a phospholipid bilayer with embedded proteins. The phospholipids have hydrophilic heads and hydrophobic tails. Small non - polar molecules (like oxygen) can pass through the lipid bilayer, while polar molecules (like ions) usually need transport proteins. This selective permeability allows the cell to maintain its internal environment, protect itself from the external environment, and regulate the entry and exit of substances.
• Second question: In eukaryotic cells, the nucleus is the organelle that houses the DNA. The DNA is organized into chromosomes. The nucleus has a nuclear envelope (a double - membrane) with nuclear pores that regulate the movement of molecules (such as RNA and proteins) in and out of the nucleus. The DNA in the nucleus contains the genetic information that controls the cell's activities, growth, and reproduction.

Answer:

1. A. Cell membrane
2. D. Nucleus