The cell membrane functions as a selective barrier that controls the movement of substances in and out of the cell, maintaining homeostasis. It is essential for protecting cellular integrity.

The nucleus contains the cell's DNA and regulates all cellular activities, which makes it the control center. Its role is fundamental in directing protein synthesis and overall cell function.

Prokaryotic cells do not have a membrane-bound nucleus, which is a defining feature distinguishing them from eukaryotic cells. This fundamental difference affects how cellular processes are organized.

Mitochondria generate energy in the form of ATP through cellular respiration, earning them the nickname 'powerhouses of the cell'. Their role is central to energy production in both plant and animal cells.

The cytoplasm is the gel-like substance inside the cell that houses the organelles and supports various cellular processes. It plays an essential role in maintaining the cell's structure and function.

Ribosomes are the molecular machines that translate mRNA into proteins by linking amino acids together. They can be found either free-floating in the cytoplasm or attached to the endoplasmic reticulum.

The rough ER is characterized by the presence of ribosomes and is primarily involved in protein synthesis. In contrast, the smooth ER lacks ribosomes and is important for lipid synthesis and detoxification.

The Golgi apparatus receives proteins from the endoplasmic reticulum, modifies them, and then packages them into vesicles for secretion or transport to other parts of the cell. This process is critical for proper protein functioning.

Lysosomes contain hydrolytic enzymes that break down waste materials and cellular debris. Their function is crucial for digesting macromolecules and recycling cellular components.

The cell wall, composed primarily of cellulose, provides structural support and rigidity to plant cells. This rigid structure defines the shape of the cell and protects it from external stress.

The nucleolus is the site within the nucleus where ribosomal RNA is produced and combined with proteins to form ribosomes. This process is essential for initiating protein synthesis.

Phospholipids form the fundamental bilayer of the cell membrane and their structure allows the membrane to remain fluid. Their amphipathic nature is key to the dynamic movement within the membrane.

The semi-permeable cell membrane permits selective transport, allowing necessary molecules to enter or exit while blocking others. This selective permeability is critical for maintaining a controlled internal environment.

Actin filaments are a key component of the cytoskeleton involved in cellular movements and maintaining cell shape. Their dynamic assembly and disassembly facilitate processes like cell migration and division.

Chloroplasts are responsible for photosynthesis, the process that converts light energy into chemical energy stored in sugars. This function is vital for plant growth and energy supply.

During apoptosis, mitochondria release cytochrome c, which activates caspases and triggers cell death. This mechanism is central to the intrinsic pathway of programmed cell death.

Vesicles are small, membrane-bound sacs that carry molecules between different organelles within a cell. Their role in intracellular transport is crucial for maintaining cellular organization and communication.

Spindle fibers, composed of microtubules, attach to chromosomes and pull them apart during mitosis. This ensures that each daughter cell receives the correct number of chromosomes.

Peroxisomes contain enzymes that oxidize fatty acids and detoxify harmful byproducts such as hydrogen peroxide. Their activity is essential for maintaining cellular metabolic balance and preventing oxidative damage.

Cholesterol molecules interspersed within the phospholipid bilayer modulate membrane fluidity by preventing phospholipids from packing too tightly. This mechanism helps maintain membrane stability across different temperature conditions.