Ap Biology Unit 2

Plasma Membrane

The plasma membrane is the outer envelope of the cell, made up mostly of phospholipids and proteins. It is semipermeable which is important because it regulates the movement of substances into and out of the cell. Meaning it alllows small or non-charged molecules through (like oxygen, carbon dioxide, water).

The Nucleus

The nucleus directs what goes on in the cell and is responsible for the cell’s ability to reproduce

Ribosomes

The ribosomes are sites of protein synthesis. Their job is to manufacture all the proteins required by the cell or secreted by the cell. Ribosomes are round structures composed of two subunits, the large subunit and the small subunit. The structure is composed of ribosomal RNA (rRNA) and proteins. Ribosomes can be either free floating in the cell or attached to another structure called the endoplasmic reticulum (ER)

Endoplasmic Reticulum (ER)

The ER is a continuous channel that extends into many regions of the cytoplasm and provides mechanical support and transportation. The rough ER compartmentalises the cell.The region of the ER that lacks ribosomes is called the smooth ER. The smooth ER makes lipids, hormones, and steroids and breaks down toxic chemicals.

Golgi Complex

After the ribosomes on the rough ER have completed synthesizing proteins, the Golgi complex modify, process, and sort the products.They’re the packaging and distribution centers for materials destined to be sent out of the cell. They package the final products in little sacs called vesicles, which carry products to the plasma membrane.The Golgi complex processes proteins and lipids synthesized in the ER, modifying them as necessary before packaging them into vesicles for transport within or outside the cell.

Mitochondria

They’re power stations responsible for converting energy from organic molecules into useful energy for the cell. The most common energy molecule in the cell is adenosine triphosphate (ATP).

Lysosomes

They have sacs that carry digestive enzymes, which they use to break down old, worn-out organelles, debris, or large ingested particles.

Vacuoles

They are fluid-filled sacs that store water, food, wastes, salts, or pigments

Peroxisomes

Peroxisomes are organelles that detoxify various substances, producing hydrogen peroxide (H2O2) as a byproduct. They have enzymes that break down hydrogen peroxide into oxygen and water.

Cytoskeleton

The shape of a cell is determined by a network of protein fibers called the cytoskeleton. It provides structural support, aids in cell movement, and plays a role in cell division.

Cilia and Flagella

Cilia and flagella have locomotive properties in single-celled organisms. The beating motion of cilia and flagella structure allows it to move.

Aquaporins

Aquaporins are proteins in the cell membrane that act like water channels — they help water move in and out of cells quickly. Even though water is small and can pass through the cell membrane on its own, it moves too slowly when there’s a lot of water to move. So the cell uses aquaporins to speed things up.

diffusion

If there is a high concentration of something in one area, it will move to spread out and diffuse into an area with a lower concentration. The substance moves down a concentration gradient

simple diffusion

When the molecule that is diffusing is hydrophobic, the diffusion is called simple diffusion because the small non-polar molecule can just drift right through the membrane without trouble.This process does not require the assistance of transport proteins.

facilitated diffusion.

When the diffusion requires the help of a channel-type protein

Osmosis

Osmosis is the movement of water molecules across a semipermeable membrane from an area of high water concentration to an area of low water concentration, until both sides are balanced. Water moves to dilute the more concentrated side (where there are more solutes like salt or sugar). No energy is needed — it’s a type of passive transport. Important in cells to maintain balance and prevent shrinking or bursting.

Active Transport

Movement against the natural flow is called active transport.It requires energy, usually from ATP, to move molecules from an area of low concentration to an area of high concentration, helping to maintain concentration gradients within cells.

the sodium-potassium pump.

The sodium-potassium pump is a special protein found in the cell membrane that moves sodium (Na⁺) ions out of the cell and potassium (K⁺) ions into the cell. It uses energy from ATP to do this, which means it's a type of active transport (because it goes against the concentration gradient). The pump works by moving 3 sodium ions out of the cell and 2 potassium ions in each time it runs. This helps create a difference in charge and ion concentration between the inside and outside of the cell.

Endocytosis

When the particles that want to enter a cell are just too large, the cell uses a portion of the cell membrane to engulf the substance. The cell membrane forms a pocket, pinches in, and eventually forms either a vacuole or a vesicle. This process is called endocytosis.

Pinocytosis

the cell ingests liquids.This process involves the uptake of extracellular fluid and small soluble molecules through small vesicles.

Phagocytosis

the cell takes in solids.It is a type of endocytosis where large particles or cells are engulfed by the cell membrane, forming a phagocytic vesicle.

Exocytosis

In exocytosis, a cell ejects waste products or specific secretion products, such as hormones, by the fusion of a vesicle with the plasma membrane, which then expels the contents into the extracellular space. Exocytosis is basically reverse endocytosis.