Sucrose and Heart Rate

Students use what they know about cellular structure and how cells extract energy from food molecules to investigate how the body is made up of smaller interacting systems that are made up of different combinations of cells. They do this by testing how the circulatory system of daphnia is affected by consumed sugar.

• The human body is complex, with multiple interacting systems.
• All of the systems depend on one another to function properly because they are all interconnected.
• There are trillions of cells in the human body, which make up all of the structures in an organism.
• When you eat different kinds of food, all of your systems are involved in breaking down the food molecules and transporting them where they need to go.

• Why is the immune system important?
• How does the immune system work?
• What are some of the ways that scientists believe bacteria help our immune systems?
• How do the nervous system and the immune system interact?
• How does the circulatory system contribute to the overall functioning of the organism?
• What is the relationship between molecules, cells, tissues, and organs?
• Why are nutrients important for an organism’s structures?
• How does the digestive system contribute to breaking down food molecules and getting them where they need to go?
• Why do you sometimes get a sugar “high” when you eat sweets such as candy or cake?

Misconception: Cells are completely separate from atoms and molecules.

Fact: Cells are matter, which means they are made up of atoms and molecules. For example, proteins are part of every cell. 

Misconception: Animal cells do not carry out essential life functions, such as obtaining energy and eliminating waste, themselves.

Fact: 

Organ : a structure composed of two or more tissue types in a multicellular organism that work together to carry out a specific function

Organ system : a group of closely interacting organs in a multicellular organism that carry out a specific function

Tissue : a group of similar cells in a multicellular organism that perform a specific function

Microbes and Us

For many people, when they think about bacteria, they think about microscopic organisms that make us sick. There is a reason for this. Many bacteria do cause illness, which is why it’s important to wash your hands frequently.

However, our health actually depends on the many trillions of bacteria that live within our bodies. Over the last decade, scientists have been learning about the many ways that bacteria and other microorganisms help our bodies function. Sarkis Mazmanian is one scientist who has been studying interactions between microbes within the human body and the body’s immune system. The immune system is the body system responsible for fighting off infections, and Mazmanian has been investigating how certain bacteria actually help the immune system function.

The immune system is highly complex, and it can recognize those substances that belong in the body and those that do not belong. The immune system works because the body’s cells carry “markers” that tell the immune system they belong. When a substance in the body has a different marker, the immune system launches an attack.

Scientists have found that some bacteria help to stimulate the immune system, making it work more effectively. Other bacteria help protect our bodies from disease-causing bacteria by releasing toxins that kill the harmful cells. For example, in 2005, Mazmanian discovered that a particular kind of bacteria helps the human body fight off infections.

In recent years, Mazmanian has expanded his research to investigate connections between microbes, the immune system, and the nervous system. The human body is incredibly complex, and it is constantly performing a wide range of functions, from the steady beating of your heart to the never-ending communication between your brain and the rest of your body, the contraction of muscle cells so you can move, and the protection against potentially disease- causing microbes. In order to carry out all of these functions efficiently and constantly, the human body is organized into different systems, each with a different but essential role to play in keeping the entire body healthy and functioning as it should. The immune system is one system, and the nervous system is another.

The nervous system is the body system that acts as the control center for an organism’s entire body. It does this with cells called neurons that send messages throughout the body and interact with the environment. Mazmanian decided to expand his research because he realized there are many parallels between the immune and nervous systems.

The Nervous System

Like the immune system, the nervous system is an organ system because it’s a group of organs in a multicellular organism that closely interact together to carry out specific functions. Organs are structures in multicellular organisms made up of two or more types of tissues that work together to carry out a specific function, and tissues are similar groups of specialized cells. Nervous tissues are found in the brain, spinal cord, and nerves. Their role is to stimulate muscle contraction, respond to the environment, and communicate with the entire body. The cells in nervous tissue are neurons.

Neurons are highly specialized and therefore look unlike any other cell in the body. Their job is to carry messages throughout the body, making muscles move, responding to the environment, and communicating with the entire body. Nerve cells have long, threadlike branches that allow cells to receive and transmit messages throughout the body. The human body has approximately 100 billion neurons, which you have had since before you were born.

When he started his research, Mazmanian had a hypothesis. His past research told him that microbes affected the immune system, so he predicted that microbes would interact with the brain through the immune system because he knew that the immune system and the nervous system interact in ways both big and small. The nervous system sends signals to keep the immune system functioning properly, and the immune system protects the nervous system from harmful microbes. After conducting experiments and gathering data, Mazmanian thinks his hypothesis might not be entirely correct. His data so far suggests that the microbes can interact with the brain without going through the immune system. He and other scientists are continuing this area of research.

For the hands-on activity in this lesson, students carry out an experiment to analyze the effect of sugar on the heart rate of daphnia. Students use the daphnia heart rate experiment to analyze the role of carbohydrates in increasing the heart rate phenomena of an organism and also to consider science phenomena related to the interconnectedness of the body systems when accessing and using the energy in food.