Human Body Systems and Cellular Energy Processes

Circulatory and Lymphatic Systems

Key Components and Functions

• Platelets: A small, irregularly shaped, disk-like cytoplasmic body found in blood plasma that promotes blood clotting. It has no definite nucleus, no DNA, and no hemoglobin. Also called a blood platelet or thrombocyte.
• Lymphatic System: Responsible for the removal of interstitial fluid, the extracellular fluid that bathes most tissue. It also acts as a highway, transporting white blood cells to and from the lymph nodes.
• Heart’s Natural Pacemaker: The sinoatrial (SA) node.
• Dialysis: Provides an artificial replacement for lost kidney function.

Common Questions

How are lymph vessels and veins similar?

Just as blood flows through veins, lymph fluid flows through lymph vessels.

What structure develops lymphocytes?

Lymphocytes develop in the bone marrow.

What determines molecule diffusion into or out of the blood?

This is determined by concentration gradients. Gases diffuse from an area of high concentration to an area of low concentration.

The Digestive System

The human digestive system is a series of organs that converts food into essential nutrients that are absorbed into the body and moves the unused waste material out of the body. It is essential to good health because if the digestive system shuts down, the body cannot be nourished or rid itself of waste.

Key Components and Processes

• Enzymes: Specific enzymes break down macronutrients:
  • Proteins: Broken down by proteases.
  • Carbohydrates: Broken down by carbohydrases.
  • Lipids: Broken down by lipases.
• Villi: Any of numerous minute, elongated projections set closely together on a surface, typically increasing its surface area for the absorption of substances.
• Movement of Food: Food moves in one direction, controlled by smooth muscles and sphincters.

Common Questions

Where are starches digested?

The digestion of starches begins in the mouth.

What does a cell use for energy?

Cells convert glucose into ATP (adenosine triphosphate) for energy.

What is the most common food source for energy?

Plants are the most common food source for energy in most ecosystems.

Photosynthesis and Cellular Respiration

Photosynthesis is the process used by plants and other organisms to convert light energy into chemical energy. In contrast, chemosynthesis is the biological conversion of one or more carbon molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic molecules (e.g., hydrogen gas, hydrogen sulfide) or methane as a source of energy, rather than sunlight.

The Process of Photosynthesis

Water molecules enter the thylakoids. They are broken up by an enzyme, which results in oxygen atoms from the water molecules forming oxygen gas and hydrogen ions.

Common Questions

What are the reactants for photosynthesis?

The reactants are light energy, carbon dioxide, and water.

What happens to the sugars made during photosynthesis?

The sugars are used to provide energy for the organism.

Where does cellular respiration occur?

Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. It occurs in the mitochondria.

When is lactic acid formed?

Lactic acid is a product of fermentation, which occurs during anaerobic exercise (exercise without sufficient oxygen).