IGCSE OCR Biology: Last-Minute Revision Notes | IGCSE OCR 生物：考前冲刺笔记

📚 IGCSE OCR Biology: Last-Minute Revision Notes | IGCSE OCR 生物：考前冲刺笔记

As the IGCSE OCR Biology exam approaches, these last-minute revision notes will help you focus on the most important concepts. From cell structure to ecosystems, these summaries cover key points you need to recall quickly.

随着IGCSE OCR生物考试的临近，这份考前冲刺笔记将帮助你聚焦最重要的概念。从细胞结构到生态系统，这些总结涵盖了你需要快速回忆的关键点。

1. Cell Structure | 细胞结构

Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells have all these plus a cell wall made of cellulose, a large permanent vacuole, and chloroplasts for photosynthesis.

动物细胞含有细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞除了这些，还具有由纤维素构成的细胞壁、一个大的中央液泡以及用于光合作用的叶绿体。

The nucleus controls cell activities and contains DNA. The cell membrane is selectively permeable, controlling what enters and leaves. Mitochondria are the site of aerobic respiration, producing ATP. Ribosomes are where proteins are synthesised.

细胞核控制细胞活动并含有DNA。细胞膜是选择透过性的，控制物质的进出。线粒体是有氧呼吸的场所，产生ATP。核糖体是蛋白质合成的场所。

2. Movement of Substances | 物质进出细胞

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It is a passive process (no energy required). Examples include oxygen diffusing into cells from capillaries and carbon dioxide diffusing out.

扩散是粒子从高浓度区域向低浓度区域的净移动，沿着浓度梯度进行。这是一个被动过程（无需能量）。例子包括氧气从毛细血管扩散进入细胞，二氧化碳扩散出细胞。

Osmosis is the diffusion of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution. In plant cells, water enters by osmosis, causing the vacuole to swell and the cell to become turgid. In animal cells, too much water intake can cause lysis (bursting).

渗透是水分子通过部分透性膜从稀溶液向浓溶液的扩散。在植物细胞中，水通过渗透进入，使液泡膨胀，细胞变得坚挺。在动物细胞中，过多水分进入会导致细胞溶解（破裂）。

Active transport is the movement of particles against a concentration gradient, using energy from respiration. This requires carrier proteins. An example is the uptake of mineral ions by root hair cells from soil.

主动运输是粒子逆浓度梯度的移动，利用呼吸作用提供的能量。这需要载体蛋白。例如根毛细胞从土壤中吸收矿物离子。

3. Enzymes | 酶

Enzymes are biological catalysts that speed up chemical reactions without being used up. They are proteins with a specific active site that fits a specific substrate, like a lock and key.

酶是生物催化剂，加速化学反应而自身不被消耗。它们是蛋白质，具有特定的活性位点，与特定底物契合，如同锁和钥匙。

The rate of an enzyme-controlled reaction increases with temperature up to an optimum (around 37°C in humans). Beyond the optimum, the enzyme denatures: the active site loses its shape, and the substrate can no longer bind. pH also affects enzyme activity; each enzyme has an optimum pH. For example, pepsin works best at pH 2 in the stomach, while amylase works best around pH 7.

酶促反应的速率随温度升高而增加，直到最适温度（人类约37°C）。超过最适温度，酶会变性：活性位点失去形状，底物不再能结合。pH也影响酶活性；每种酶都有最适pH。例如，胃蛋白酶在胃中pH 2时活性最佳，而淀粉酶在pH 7左右活性最佳。

Digestive enzymes break down large food molecules: amylase breaks starch into maltose; protease breaks protein into amino acids; lipase breaks lipids into fatty acids and glycerol. Bile, produced in the liver, emulsifies fats and neutralises stomach acid to provide an alkaline pH for lipase.

消化酶分解大分子食物：淀粉酶将淀粉分解为麦芽糖；蛋白酶将蛋白质分解为氨基酸；脂肪酶将脂质分解为脂肪酸和甘油。肝脏分泌的胆汁能乳化脂肪，并中和胃酸，为脂肪酶提供碱性pH。

4. Nutrition and Digestion | 营养与消化

A balanced diet includes carbohydrates for energy, proteins for growth and repair, lipids for energy storage and insulation, vitamins and minerals for various functions, dietary fibre to aid digestion, and water.

均衡饮食包括提供能量的碳水化合物、用于生长和修复的蛋白质、用于能量储存和绝缘的脂质、具有多种功能的维生素和矿物质、帮助消化的膳食纤维以及水。

Food tests: Iodine solution turns blue-black in the presence of starch. Benedict’s solution turns brick-red when heated with reducing sugars such as glucose. Biuret reagent turns purple for proteins. The emulsion test: ethanol is added to a sample, then poured into water; a cloudy white emulsion indicates lipids.

食物测试：碘液遇淀粉变蓝黑色。本尼迪克特

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