Shanghai Edition Junior High School English, Grade 9, Semester 1: The Foundation of Life: Physiological Functions of the Seven Essential Nutrients

Imagine the human body as a factory that is actively operating and continuously expanding:Carbohydratesserve as the factory’s daily power reserve; approximately 70% of the energy required for life activities comes from this source. In the warehouse,Fatsact as reserve fuel for the generator, with energy content roughly twice that of an equivalent mass of carbohydrates. As the steel framework of the factory, it isProteins, which not only form the fundamental building blocks of cells but also repair damaged tissues.

Core Functions and Key Components

Trace Regulation: Vitamins are small organic molecules that do not provide energy but play a crucial regulatory role in metabolic processes. The reducing property of vitamin C can decolorize purple potassium permanganate solution.
Mineral Homeostasis: For example, calcium (1,300 g) and phosphorus (650 g) jointly support bone structure; iron (4 g–5 g) is responsible for oxygen transport.
Dietary Fiber: Known as the 'Seventh Essential Nutrient,' it promotes intestinal motility, but daily intake should not exceed 20 g, or it may interfere with nutrient absorption.

Scientific Alert

Although proteins can be broken down for energy, they are 'prioritized' for tissue construction when carbohydrates and fats are sufficient, serving only as a secondary energy source during extreme starvation. Additionally, excessive intake of certain trace elements can have toxic side effects.

QUESTION 1

Approximately 70% of the energy required for human life activities comes from which of the following substances?

Fats

Proteins

Carbohydrates

Vitamins

QUESTION 2

Which of the following descriptions accurately reflects the physiological function of fats?

Is the basic substance that constitutes cells

Contains about twice the energy per unit mass compared to carbohydrates

Plays a major role in regulating life activities

QUESTION 3

Xiao Lin noticed frequent gum bleeding while brushing his teeth. According to nutritional advice, which foods should he eat more of?

Meat and eggs

Fresh vegetables and fruits

Dairy products and legumes

QUESTION 4

Which of the following statements about dietary fiber is incorrect?

Known as the 'Seventh Essential Nutrient'

Promotes intestinal motility

The more consumed, the healthier, with no upper limit

QUESTION 5

The fundamental substance forming human cells and the primary source of energy for life activities are respectively:

Proteins and fats

Proteins and carbohydrates

Minerals and vitamins

Nutrition and Digestive Physiology: Integrated Analysis

Exploring mechanisms of nutrient absorption through clinical cases and experimental design

A biology interest group is studying the transformation of nutrients within the body. They collected food packaging labels, analyzed the chemical properties of vitamin C, and are preparing to observe intestinal structure through dissection.

1. What are digestive glands, digestive fluids, and digestive enzymes? On what does the site of digestion of food components in the digestive tract depend?

Answer:
Digestive glands (such as salivary and pancreatic glands) are organs that secrete digestive fluids; digestive fluids (such as saliva and gastric juice) contain digestive enzymes that catalyze the breakdown of food. The location where each food component is digested primarily depends on whether specific digestive enzymes capable of breaking down that component are present at that site (for example, if pepsin is present in the stomach, protein digestion begins there).

2. Is it suitable to use the upper segment of the duodenum as material to observe intestinal villi? Why?

Answer:
Not ideal. The upper duodenum's primary function is to receive acidic chyme emptied from the stomach and to receive bile and pancreatic juice. Its intestinal wall contains numerous duodenal glands that secrete mucus to protect the mucosa. The typical structure of intestinal villi—designed to maximize absorption area—is most prominent and characteristic in the jejunum and ileum.

3. Based on the 'Balanced Diet Pyramid,' analyze what major aspects the term 'balance' should include?

Answer:
‘Balance’ should include three aspects: first, balance among nutrient types (appropriate proportions); second, diversification of food sources (avoiding selective eating); third, balance between energy intake and expenditure (maintaining a healthy weight).

4. Match the following diseases with the appropriate foods/substances to supplement: (A) Scurvy (B) Endemic goiter (C) Rickets (D) Anemia.

Answer:
(A) Scurvy – Supplement vitamin C / fresh fruits and vegetables; (B) Endemic goiter – Supplement iodine / seaweed and laver; (C) Rickets – Supplement vitamin D and calcium / dairy products and sun exposure; (D) Anemia – Supplement iron and protein / pork liver and red meat.