Animal Structure, Function, and Nutrition: Energy and Biomolecules

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Animal Structure and Function: Nutrition and Energy

Importance of Animals in Ecosystems and Human Life

Animals play crucial roles in ecosystems and human society. They serve as sources of food and other products, and are essential for maintaining the health and balance of natural ecosystems.

Food Sources: Animals provide meat, dairy, eggs, and other products essential for human nutrition.
Ecosystem Roles: Animals contribute to pollination, seed dispersal, pest control, and nutrient cycling.

Illustration of animal food sources: cow, pig, chicken, fish

Why We Need to Eat: Nutrients and Energy

Functions of Food

Food is required for both growth and maintenance of the body, as well as for providing the energy necessary for all life processes.

Nutrients: Raw materials and chemicals needed for growth, tissue repair, and energy production. Major classes include carbohydrates, proteins, lipids (fats), water, minerals, and vitamins.
Energy: Chemical energy from food is used to perform basic life functions such as movement, growth, and cellular processes.

Diagram of major nutrient classes: carbohydrate, protein, fat, vitamin, mineral, water Diagram showing how food is converted to ATP, heat, and waste in the body

Factors Affecting Energy Requirements

Endothermy vs. Ectothermy

Animals differ in their energy needs based on how they regulate body temperature:

Endothermic (warm-blooded): Maintain constant body temperature internally; require more energy/food (e.g., mammals, birds).
Ectothermic (cold-blooded): Rely on external sources for body heat; require less food (e.g., reptiles, amphibians, fish).

Comparison of endotherms and ectotherms

Other Factors Influencing Energy Needs

Body Size: Larger animals generally require more energy.
Physical Activity: More active animals need more energy.
Sex: Males often require more energy due to greater muscle mass.
Age: Metabolic rate decreases with age.
Hereditary Factors: Some individuals have naturally higher or lower metabolic rates.

Illustration of factors affecting metabolism: activity, sleep, genetics, etc.

Measuring Energy Requirements

Basal Metabolic Rate (BMR): The minimum energy required to maintain vital body functions at rest.
Daily Energy Requirement: Depends on BMR and activity level; varies from day to day.

Type of Activity	Energy required (kJ/kg/h)
Sleeping	4.1
Sitting	5.2
Walking (6.4 km/h)	20.6
Climbing stairs, running (8.8 km/h)	63.0
Competitive cross-country skiing	73.6

Table of average energy requirements for various activities

Essential Nutrients: What and How Much We Need to Eat

Major Nutrient Classes

There are six major classes of nutrients required for human health:

Carbohydrates
Proteins
Lipids (Fats)
Water
Vitamins
Minerals

Diagram of 6 major nutrients: carbohydrates, fats, minerals, proteins, vitamins, water

Carbohydrates

Types and Functions

Carbohydrates are the main source of energy for the body. They are classified by the number of sugar units:

Monosaccharides: Single sugar molecules (e.g., glucose, fructose).
Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose).
Polysaccharides: Many monosaccharides joined (e.g., starch, cellulose in plants; glycogen in animals).

Glycogen: Energy-storing carbohydrate in animals, stored in liver and muscle.
Starch and Cellulose: Plant carbohydrates; cellulose provides dietary fiber and structural support in plants.

Proteins

Structure and Dietary Importance

Proteins are complex molecules made up of amino acids. There are 20 different amino acids, 9 of which are essential and must be obtained from food.

Animal Proteins: Contain all essential amino acids.
Plant Proteins: Often lack one or more essential amino acids; must be combined for a complete profile.

Diagram of amino acid structure

Functions of Proteins

Build and repair cell structures
Enzymes: Catalyze chemical reactions
Hormones: Act as chemical messengers
Transport: Carry molecules (e.g., hemoglobin transports oxygen)
Defense: Antibodies in the immune system
Source of energy (when in excess)

Function	Example
Control of chemical reactions	Digestive chemicals
Movement	Myosin in muscle cells
Transporting oxygen	Hemoglobin in red blood cells
Structure	Collagen in muscles and connective tissue; keratin in hair and nails
Hormones (chemical messengers)	Human growth hormone
Defence	Antibodies produced by the immune system
Source of energy	Excess proteins from diet

Table of protein functions and examples

Lipids (Fats)

Functions and Types

Lipids are essential for long-term energy storage, absorption of fat-soluble vitamins (A, D, E, K), insulation, and as components of cell membranes.

Triglycerides: Composed of three fatty acids bonded to a glycerol molecule.
Saturated Fats: Solid at room temperature (e.g., butter).
Unsaturated Fats: Liquid at room temperature (e.g., oils); considered healthier.

Diagram of triglyceride structure Comparison of saturated and unsaturated fatty acid chains

Other Lipids

Steroids: Include sex hormones (testosterone, estrogen) and cholesterol.
Essential Fatty Acids: Cannot be synthesized by the body; must be obtained from diet (e.g., omega-3 fatty acids).

Diagram of glycerol, free fatty acid, and triglyceride

Summary Table: Carbohydrates, Lipids, and Proteins

Nutrient	Main Function	Examples
Carbohydrates	Primary energy source	Bread, rice, fruits
Proteins	Build/repair tissues, enzymes, hormones	Meat, beans, eggs
Lipids	Long-term energy, cell membranes, hormones	Oils, butter, nuts

Additional info: For a complete understanding, students should also review the roles of vitamins, minerals, and water in metabolism and health, as well as the consequences of nutrient deficiencies and excesses.