📚 Food and The Stages of Digestion | 食物与消化的各个阶段
Digestion is the process by which large, insoluble food molecules are broken down into small, soluble substances that the body can absorb and use.
消化是将大分子、不溶性的食物分解为身体可以吸收和利用的小分子可溶性物质的过程。
In KS3 CIE Science, understanding food groups and the stages of digestion helps explain how nutrients power every cell.
在 KS3 CIE 科学课程中，了解食物种类和消化阶段有助于解释营养物质如何为每个细胞提供能量。
1. Why We Need Food | 我们为什么需要食物
Food gives the body energy for daily activities, growth, repair and all the chemical reactions that keep us alive.
食物为身体提供日常活动、生长、修复以及维持生命所需的全部化学反应的能量。
Energy in food is released during respiration, which takes place in every living cell and produces heat to keep the body warm.
食物中的能量在呼吸作用中释放，呼吸作用发生在每个活细胞中，并产生热量以保持体温。
A shortage of food or a poorly balanced diet can lead to tiredness, poor growth and a weak immune system.
食物不足或饮食不均衡会导致疲劳、发育不良和免疫系统虚弱。
The body also needs food to make new cells, especially during childhood, pregnancy and after injury.
身体还需要食物来制造新细胞，尤其是在儿童期、孕期和受伤后。
2. Macronutrients: Carbohydrates, Proteins and Fats | 宏量营养素：碳水化合物、蛋白质和脂肪
Carbohydrates are the body’s main source of quick energy and are found in foods such as bread, rice, pasta and potatoes.
碳水化合物是身体快速供能的主要来源，存在于面包、米饭、面食和土豆等食物中。
Proteins are needed to build and repair muscles, skin, hair and enzymes; good sources include meat, fish, eggs and beans.
蛋白质用于构建和修复肌肉、皮肤、毛发和酶；优质来源包括肉类、鱼类、蛋类和豆类。
Fats provide a concentrated store of energy, protect organs and help keep the body warm; they are found in oils, butter, nuts and cheese.
脂肪提供浓缩的能量储备，保护器官并帮助身体保温；它们存在于油、黄油、坚果和奶酪中。
| Nutrient | Main function | Food examples |
|---|---|---|
| Carbohydrates | Quick energy supply / 快速供能 | Bread, rice, pasta / 面包、米饭、面食 |
| Proteins | Growth and repair / 生长和修复 | Meat, fish, eggs, beans / 肉类、鱼类、蛋类、豆类 |
| Fats | Stored energy and insulation / 储存能量和隔热 | Oils, butter, nuts / 油、黄油、坚果 |
3. Micronutrients and Water | 微量营养素和水
Vitamins and minerals are needed only in small amounts, but they are essential for healthy body functions.
维生素和矿物质只需要很少的量，但它们对健康的身体功能至关重要。
For example, vitamin C helps keep skin and gums healthy, calcium strengthens bones and teeth, and iron is needed to make haemoglobin in red blood cells.
例如，维生素C有助于保持皮肤和牙龈健康，钙能强化骨骼和牙齿，铁是制造红细胞中血红蛋白所必需的。
Water makes up about 60% of body mass and is essential for digestion, transporting nutrients, removing waste and controlling body temperature.
水约占人体质量的60%，对消化、运输营养、排出废物和调节体温至关重要。
Many chemical reactions in cells happen in solution, so water is the medium in which life processes occur.
细胞中的许多化学反应在溶液中进行，因此水是生命过程发生的介质。
4. The Digestive System: An Overview | 消化系统概览
The digestive system is a long, continuous tube called the alimentary canal, running from the mouth to the anus.
消化系统是一条长而连续的管道，称为消化道，从口腔延伸到肛门。
The main stages of digestion are ingestion, digestion, absorption and egestion.
消化的主要阶段是摄入、消化、吸收和排遗。
Ingestion is taking food into the body, digestion is breaking food down mechanically and chemically, absorption is moving nutrients into the blood, and egestion is removing undigested waste.
摄入是将食物摄入体内，消化是机械性和化学性地分解食物，吸收是将营养物质送入血液，排遗是排出未消化的废物。
Several organs help with digestion, including the liver, gall bladder and pancreas, which release substances into the digestive tube.
多个器官协助消化，包括肝脏、胆囊和胰腺，它们向消化道释放物质。
5. Stage 1: Ingestion and Chewing in the Mouth | 第一阶段：口腔中的摄入与咀嚼
Digestion begins in the mouth when food is taken in and chewed by the teeth.
消化从口腔开始，食物入口后由牙齿咀嚼。
Teeth cut, tear and grind food into smaller pieces, which increases the surface area for enzymes to work on later.
牙齿将食物切碎、撕裂和磨细，这增加了稍后酶作用的表面积。
Saliva is released from salivary glands and contains the enzyme salivary amylase, which starts breaking down starch into smaller sugars such as maltose.
唾液由唾液腺分泌，含有唾液淀粉酶，开始将淀粉分解成更小的糖，如麦芽糖。
Chewing also mixes food with saliva to form a soft, moist lump that is easier to swallow.
咀嚼还将食物与唾液混合，形成一个柔软湿润的食团，使其更容易吞咽。
6. Stage 2: Swallowing and the Oesophagus | 第二阶段：吞咽与食道
After chewing, the tongue pushes the food into a soft ball called a bolus and moves it to the back of the mouth for swallowing.
咀嚼后，舌头将食物推成一个柔软的食物团，称为食团，并将其移到口腔后部准备吞咽。
The bolus passes into the oesophagus, a muscular tube that connects the throat to the stomach.
食团进入食道，食道是连接咽喉和胃的肌肉管道。
Waves of muscle contraction called peristalsis squeeze the bolus along the oesophagus towards the stomach.
称为蠕动的肌肉收缩波推动食团沿食道向胃移动。
A flap of tissue called the epiglottis closes over the windpipe during swallowing so food does not enter the lungs.
吞咽时会厌软骨覆盖气管，防止食物进入肺部。
7. Stage 3: Digestion in the Stomach | 第三阶段：胃中的消化
The stomach is a muscular bag that churns food and mixes it with gastric juice to form a liquid called chyme.
胃是一个肌肉袋，搅动食物并将其与胃液混合，形成一种称为食糜的液体。
Gastric juice contains hydrochloric acid, which kills harmful bacteria and provides the right acidic pH for the enzyme pepsin to work.
胃液中含有盐酸，可以杀死有害细菌，并为胃蛋白酶发挥作用提供适宜的酸性pH值。
Pepsin begins the chemical digestion of proteins, breaking them down into shorter chains called peptides.
胃蛋白酶开始对蛋白质进行化学消化，将其分解成较短的肽链。
Food usually stays in the stomach for a few hours before being released slowly into the small intestine.
食物通常在胃中停留数小时，然后缓慢释放进入小肠。
8. Stage 4: Digestion and Absorption in the Small Intestine | 第四阶段：小肠中的消化与吸收
The small intestine is the main site of chemical digestion and nutrient absorption in the digestive system.
小肠是消化系统中化学消化和营养物质吸收的主要场所。
It receives bile from the liver and gall bladder, which emulsifies fats by breaking large fat droplets into smaller ones to increase surface area.
小肠接收来自肝脏和胆囊的胆汁，胆汁通过将大脂肪滴分解成小脂肪滴来乳化脂肪，增加表面积。
Pancreatic juice from the pancreas contains enzymes that complete the breakdown of starch, proteins and fats into simple sugars, amino acids, fatty acids and glycerol.
来自胰腺的胰液含有酶，完成淀粉、蛋白质和脂肪的分解，生成单糖、氨基酸、脂肪酸和甘油。
The inner lining of the small intestine is covered with tiny finger-like projections called villi, which absorb digested nutrients into the blood.
小肠内壁覆盖着称为绒毛的微小指状突起，将消化后的营养物质吸收进入血液。
Villi have a large surface area and a rich blood supply, so absorption happens quickly and efficiently.
绒毛具有较大的表面积和丰富的血液供应，因此吸收迅速而高效。
9. Stage 5: Water Absorption in the Large Intestine | 第五阶段：大肠中的水分吸收
By the time food reaches the large intestine, most nutrients have already been absorbed; what remains is mostly water, fibre and undigested waste.
当食物到达大肠时，大部分营养物质已被吸收；剩余的主要是水分、纤维和未消化的废物。
The large intestine absorbs water and mineral salts from this material, turning it into semi-solid faeces.
大肠从这些物质中吸收水分和矿物盐，将其转变为半固体的粪便。
Fibre, such as cellulose from plant cell walls, cannot be digested by human enzymes, but it adds bulk and helps food move through the gut.
纤维（如植物细胞壁中的纤维素）不能被人体酶消化，但它增加粪便体积并帮助食物在肠道中移动。
Millions of harmless bacteria live in the large intestine and help break down some remaining food substances.
大肠中生活着数百万无害细菌，帮助分解一些剩余的食物物质。
10. Stage 6: Egestion | 第六阶段：排遗
Egestion is the removal of undigested waste material from the body through the anus in the form of faeces.
排遗是未消化的废物以粪便形式通过肛门排出体外的过程。
Egestion is different from excretion, which is the removal of metabolic waste products such as carbon dioxide and urea.
排遗不同于排泄，排泄是清除代谢废物，如二氧化碳和尿素。
If too little water is absorbed or material moves too slowly, a person may have diarrhoea or constipation.
如果吸收的水分太少或物质移动过慢，人可能会出现腹泻或便秘。
The final stage of egestion completes the journey of food through the digestive system.
排遗作为最后阶段，完成了食物在消化系统中的旅程。
11. Enzymes: The Body’s Chemical Tools | 酶：身体的化学工具
Enzymes are biological catalysts made of protein that speed up chemical reactions without being used up themselves.
酶是由蛋白质构成的生物催化剂，能加速化学反应而自身不被消耗。
Each enzyme is specific to one type of substrate, like a lock and key: amylase digests starch, protease digests proteins, and lipase digests fats.
每种酶对某一类底物具有专一性，就像锁与钥匙一样：淀粉酶消化淀粉，蛋白酶消化蛋白质，脂肪酶消化脂肪。
Digestive enzymes work best at a particular temperature and pH; for example, stomach protease works best in acidic conditions, while intestinal enzymes prefer alkaline conditions.
消化酶在特定的温度和pH值下活性最高；例如，胃蛋白酶在酸性条件下活性最高，而肠道酶则偏好碱性条件。
| Enzyme | Substrate | Products |
|---|---|---|
| Amylase / 淀粉酶 | Starch / 淀粉 | Maltose and simple sugars / 麦芽糖和单糖 |
| Protease / 蛋白酶 | Proteins / 蛋白质 | Amino acids / 氨基酸 |
| Lipase
Published by TutorHao | KS3 Revision Series | aleveler.com 更多咨询请联系16621398022（同微信） CommentsMore posts |
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply