Other Cell Concepts

Passive transport processes move ions or molecules across the plasmalemma without any energy expenditure by the cell whereas active transport processes involve the cell spending energy.

During diffusion a molecule moves from an area of high concentration to an area of low concentration. Movement is achieved following the concentration gradient and no energy is spent by cell.

Bacterial cells have cell membranes, cell walls, chromosomes, cytoplasm, and ribosomes. They may have flagella or cilia as well. They do not contain any membrane-bound organelles, such as the nucleus, endoplasmic reticulum, or mitochondria.

There are two fundamental sections of the cell cycle: mitosis and interphase. The M phase denotes mitosis, during which the cell divides. Interphase is composed of several subsections during which the cell grows, organelles replicate, and the cell prepares for division.

Interphase can be divided into the subsections G1, S, and G2. While G1 and G2 are dedicated to the growth of the cell and organelle replication, the S phase is when cellular DNA is replicated.

A cell does not have to have a nucleus. Prokaryotic cells are characterized by the fact that they don't have a nucleus nor any other membrane-bound organelles. However the rest of the statements are true of all cells and comprise cell theory.

Receptor-mediated endocytosis is a process that resembles pinocytosis but is far more selective and only allows the entry of specific molecules into the cell. Target substances are bound to receptors on the membrane surface and brought into the cell via coated vesicles.