[LS1-2] Cellular Differentiation and Organ Systems

This standard focuses on the hierarchy of cells, tissues, and organs that function cooperatively to fulfill the needs of an organism, broadly looking at how sensory information is transformed through interacting systems to create behaviors that help an organism survive and reproduce.

Resources for this Standard:

For Teachers Only

Here’s the Actual Standard:

Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

Standard Breakdown

This standard essentially starts at the concept of cellular differentiation – the idea that cells express different sets of proteins, and therefore have different functions. From this, the idea of the hierarchy of cells to body systems can be introduced.

Specialized cells differentiate from the original zygote cell through the processes of gene expression and regulation. As a fetus develops, cells in different parts of the fetus are exposed to different environments, allowing them to express different portions of the DNA. This creates different sets of proteins. Some cells differentiate into endocrine cells, which express hormones. Hormones can further cellular differentiation, leading to a wide variety of cell types in each organism.

Groups of cells with a common function form tissues, such as muscle tissue or nervous tissue. An organ is a collection of different tissues, again serving a common function. A system is a collection of organs with a common purpose. An organism is a collection of systems with the common goal of survival and reproduction of the DNA.

The main idea behind this standard is that all behaviors and processes in an organism are the result of more than one body system, and many different types of cell. For instance, consider eating. Cells in the eyes send information to the brain. The brain processes the information, considering whether the image contains food. If it does, the nervous system sends signals to the muscular system allowing the organism to obtain the food. Food then enters the digestive system, where it is broken down into nutrients. The nervous system is connected to the digestive system as well and monitors the amount of nutrients in food in order to better inform the next feeding opportunity.

A little clarification

The standard contains this clarification statement:

Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.

This clarification statement points out that there are many, many examples of how the organizational hierarchy of body systems allows an organism to survive and reproduce. The breadth of this subject makes for a great opportunity for students to do their own research and synthesize a model of almost any biological process and the systems an organism uses to carry out that process.

What to Avoid

The NGSS standard HS-LS1-1 also contains the following assessment boundary:

Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.

So, students do not need to understand the biochemical basis of any process, only the hierarchy of cells to organ systems that allows a process to occur. Here’s what you should avoid, more specifically:

Molecular and Chemical Reactions

When talking about any hierarchical system, behavior, or process, the scope starts at a specialized cell and ends at the organism level. For example, if discussing the action of the kidneys, it is sufficient to know that kidney cells specialize in removing waste products out of the bloodstream. Students do not need to dive into the complexities of urea production, water balance, active and passive diffusion, or any of the other specific biochemical processes that make kidney function possible.

However, you can show how kidney function plays into the entire excretory system and why organisms need to remove nitrogenous wastes created by the utilization and degredation of proteins as they grow. Other systems and processes should be viewed with the same focus on cells to organism survival.