Unit

1. Unit Animal Science

2. Problem Area Growth and Development of Animals

3. Lesson Absorption of Nutrients

4. Student Learning Objectives • 1. Identify end products of food which are capable of being absorbed and how they are utilized by animals. • 2. Describe the role of the plasma membrane in animal cells and explain how a selectively permeable membrane functions. • 3. Explain how nutrient absorption is affected by food digestibility.

5. Terms • Diffusion • Digestibility • Osmosis • Plasma membrane • Semi-permeable membrane • Total digestible nutrients • Absorption • Active transport • Apparent digestibility • Assisted diffusion • Carrier molecules • Concentration gradient

6. What are the end products of food which are capable of being absorbed and how are they utilized by animals? • Proteins, carbohydrates, and fats must be broken down into their ‘end products’ in order to be digested. • A. These end products, mostly amino acids, move from the digestive canal into cells that line the digestive tract, and then into the bloodstream. • B. Vitamins, minerals, and water are also absorbed from the digestive tract and transported by the blood throughout the body. • C. These end products are used by individual cells to carry out daily processes of life, growth, and reproduction.

7. What is the role of the plasma membrane in animal cells and how does a selectively permeable membrane function? • Absorptionis the movement of food nutrients from the digestive canal into the bloodstream though the cell wall of the digestive system. • A. Absorption is aided by three processes: diffusion, assisted diffusion, and active diffusion.

8. 1. Diffusionis the movement of a substance from a high concentration to a low conentration. Diffusion occurs when the concentration of nutrients outside a cell is greater than the concentration of nutrients inside the cell. • This difference creates what is known as a concentration gradient. Whenever a concentration gradient exists, molecules will naturally move from high to low concentrations, in a slow movement.

9. 2. Assisted diffusionis when the rate of diffusion is increased by the use of carrier molecules, or molecules that ‘carry’ nutrient molecules from a high to low concentration. • 3. Nutrients may sometimes move against a concentration gradient (from a low to high concentration) in a process called active transport. Active transport requires the input of additional energy from inside the cell. Active transport is important for the movement of cells through the intestinal lining.

12. B. Absorption in animals takes place because of a selectively permeable membrane surrounding cells, called the plasma membrane. • 1. The plasma membrane is a semi-permeable membrane, meaning some molecules are allowed to pass through, while others are not. • 2. Osmosisis the process of diffusion through a semi-permeable membrane.

13. C. Nutrients are absorbed in the digestive tract at specific locations. The location of absorption is influenced by where nutrient digestion to end products occur. • 1. Minerals, such as calcium, magnesium, and iron are absorbed in the upper-most region of the small intestine. • 2. Water soluble vitamins and simple sugars are absorbed from the alkaline environment of the small intestine. • 3. Fats and proteins are absorbed in the lower small intestine. • 4. Water is primarily absorbed from the colon.

14. How is absorption affected by food digestibility? • Sources of nutrients for livestock feed can vary greatly in their digestibility. • A. Digestibilityrefers to the ability of the animal to digest the food into useful end products that can be absorbed and utilized. Producers must consider the digestibility of a food source as well as the nutrient content when planning a balanced ration.

15. B. Apparent digestibilityis the difference in the total nutrients consumed and the nutrients remaining in the feces. The goal of an animal nutritionist is to formulate feed with high apparent digestibility. • C. Total digestible nutrients, abbreviated TDN, represents the relative energy value of feed to livestock. There are four factors that will affect TDN: • 1. Percentage of dry matter. • 2. Digestibility of dry matter. • 3. Amount of mineral matter. • 4. Amount of fat.

18. Review/Summary • What are the end products of food which are capable of being absorbed and how are they utilized by animals? • What is the role of the plasma membrane in animal cells and how does a selectively permeable membrane function? • How is absorption affected by food digestibility?