AP Biology: Cell Structure & Function

What is the primary difference between prokaryotic and eukaryotic cells regarding their genetic material?

Prokaryotic cells have a nucleoid region where their circular DNA is located, but lack a membrane-bound nucleus. Eukaryotic cells possess a true nucleus enclosed by a nuclear envelope, containing their linear DNA.

Describe the main function of the plasma membrane.

The plasma membrane regulates the passage of substances into and out of the cell, maintains cellular integrity, and facilitates cell-to-cell communication and adhesion. It exhibits selective permeability.

What is the role of ribosomes in a cell?

Ribosomes are responsible for protein synthesis (translation), assembling amino acids into polypeptide chains according to genetic instructions from mRNA. They can be free in the cytoplasm or bound to the endoplasmic reticulum.

Differentiate between the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER).

RER has ribosomes on its surface and synthesizes proteins destined for secretion or insertion into membranes. SER lacks ribosomes and is involved in lipid synthesis, detoxification of drugs and poisons, and calcium ion storage.

What is the primary function of the Golgi apparatus?

The Golgi apparatus modifies, sorts, and packages proteins and lipids synthesized in the ER, then ships them to other destinations inside or outside the cell. It acts as the cell's "post office."

Explain the endosymbiotic theory as it relates to mitochondria and chloroplasts.

The endosymbiotic theory proposes that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells. Evidence includes their own circular DNA, ribosomes, and double membranes.

What is the main role of mitochondria in a eukaryotic cell?

Mitochondria are the sites of cellular respiration, where organic molecules are broken down to produce ATP, the primary energy currency of the cell. They have a highly folded inner membrane called cristae to increase surface area.

What are lysosomes, and what is their primary function?

Lysosomes are membrane-bound sacs containing hydrolytic enzymes that digest macromolecules, old organelles, and foreign substances. They are the cell's "recycling centers."

How does water typically move across a cell membrane, and what is this process called?

Water moves across a cell membrane from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration) through a process called osmosis. This can occur directly or via aquaporins.

Describe facilitated diffusion.

Facilitated diffusion is a type of passive transport where specific transport proteins help hydrophilic molecules or ions move across the cell membrane down their concentration gradient, without the expenditure of cellular energy.

What is active transport, and why is it necessary?

Active transport is the movement of substances across a cell membrane against their concentration gradient, requiring energy (usually ATP) and specific transport proteins. It is necessary to maintain specific internal concentrations of ions and molecules.

What is the primary role of the cell wall in plant cells?

The cell wall in plant cells provides structural support, maintains cell shape, and prevents excessive water uptake, protecting the cell from osmotic lysis. It is composed primarily of cellulose.

How does the surface area to volume ratio limit cell size?

As a cell grows, its volume increases faster than its surface area, decreasing the surface area to volume ratio. A low ratio can make it difficult for the cell to transport nutrients in and waste out efficiently, limiting its size.

What are plasmodesmata, and what is their function?

Plasmodesmata are narrow channels that pass through the cell walls of adjacent plant cells, connecting their cytoplasm. They allow for the direct intercellular exchange of water, small solutes, and some larger molecules.

What are the three main components of the cytoskeleton, and what is their general function?

The three main components are microtubules, microfilaments (actin filaments), and intermediate filaments. Together, they provide structural support, facilitate cell motility, and organize organelles within the cell.