Foundational Concept 2: Highly-organized assemblies of molecules, cells, and organs interact to carry out the functions of living organisms
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All content in “Cells”

Cell membrane overview

2A: Not all shall pass! Yards have fences, and cells have membranes. You don’t want just anybody waltzing into your backyard. Similarly, a healthy cell doesn’t just let in any random molecule - this is the concept of selective permeability. Some molecules (e.g. steroids) more easily cross the barrier whereas others (e.g. charged ions) have a more difficult time getting inside the cell without a little help from transporters in the membrane.

Cell-cell interactions

2A: The human body is composed of about 100 trillion cells (this is not counting your bacterial buddies, who actually outnumber your cells 10 to 1!) Your cells must speak to each other to coordinate this massive symphony of life. In this tutorial, you will learn about the molecular basis of cellular signaling that makes this vast network speedy and efficient.

Transport across a cell membrane

2A: Each cell in your body has a “membrane potential.” Think of it like rolling a ball to the top of a hill - once the ball is at the top, it is smooth sailing down. Similarly, this electric membrane potential allows ions to flow down a gradient of electrical energy (the inside of the cell is negative relative to the outside). We will discuss this concept as well as other mechanisms for movement of ions, water, and other molecules across cellular membranes.

Cell theory

Let’s go on a journey that starts with Robert Hooke and Anton van Leeuwenhoek hunched over their microscopes looking at cork and bacteria, respectively. These videos will guide you through the events that led us to the knowledge we have today about cells.

Eukaryotic cells

Unlike prokaryotes, eukaryotic cells have a nucleus and other membrane-bound organelles that allow the cell to compartmentalize different functions. These videos will provide an overview of eukaryotic cells and will take you through the structures and functions of the various organelles found within the plasma membrane.


The cytoskeleton provides an internal framework for the cell, much like our skeleton helps support our body. In these videos, you will learn about the different filaments that comprise the cytoskeleton, and how these filaments provide structural support, create roadways for intracellular transport, and generate cellular motion.


When you think about prokaryotes, disease-causing bacteria might come to mind. However, most prokaryotes are not harmful. Prokaryotes live symbiotically with many plants and animals and are key players in the global ecosystem. They are incredibly diverse and are found in the most extreme of environments. These videos will take you through a general overview of these amazing organisms.


Viruses can cause sickness and disease, however they are not living entities. If they are not alive, then what are they? In this section, you will learn about the different types of viruses and how they survive, replicate, and spread inside a host organism.

Cellular development

What is the difference between a heart cell and a liver cell? Not only do they look different, but they obviously have different roles in our bodies. Yet, both of these cells have the same 23 chromosomes in their nuclei, so shouldn’t they be similar? These videos explain why a heart cell becomes a heart cell and not a liver cell.


Do you remember when you were just a sperm and an egg, or when you were just made up of 32 cells, or when you were a blastocyst attaching to your mom’s uterus? These videos should help jog your memory about the nine months before you came into this world as an human being.