CHAPTER 1 Cells: The Fundamental Units of Life

1.1 UNITY AND DIVERSITY OF CELLS

1.2 CELLS UNDER THE MICROSCOPE

1.3 THE PROKARYOTIC CELL

1.4 THE EUKARYOTIC CELL

1.5 MODEL ORGANISMS

• Eukaryotic cells are generally larger and more complex than bacteria and archaea.真核細胞通常比細菌和古細菌更大、更復雜。
• Eukaryotic cells can be single-celled organisms or part of multicellular organisms.真核細胞可以是單細胞生物或多細胞生物的一部分。
• All complex multicellular organisms, including plants, animals, and fungi, are formed from eukaryotic cells.所有復雜的多細胞生物，包括植物、動物和真菌，都是由真核細胞形成的。
• Eukaryotic cells have a nucleus and other membrane-enclosed organelles common to all eukaryotes.真核細胞具有所有真核生物共有的細胞核和其他膜封閉細胞器。

Eukaryotic cells are generally larger and more elaborate than bacteria and archaea. They can exist as single-celled organisms, such as amoebae and yeasts, or as part of more complex multicellular organisms, including plants, animals, and fungi. By definition, all eukaryotic cells possess a nucleus, which is accompanied by a variety of other organelles. These organelles are typically membrane-enclosed and common to all eukaryotic organisms.真核細胞通常比細菌和古細菌更大、更精細。它們可以作為單細胞生物存在，例如變形蟲和酵母，或作為更復雜的多細胞生物的一部分，包括植物、動物和真菌。根據定義，所有真核細胞都擁有一個細胞核，並伴隨著各種其他細胞器。這些細胞器通常是膜封閉的，並且是所有真核生物共有的。

This section focuses on the main organelles found in eukaryotic cells, discussing their functions and examining how they came to serve their specific roles in the life of eukaryotic cells. The presence of a nucleus and other specialized organelles allows eukaryotic cells to carry out complex processes and efficiently perform their functions within a multicellular organism.本節重點介紹真核細胞中發現的主要細胞器，討論它們的功能並研究它們如何在真核細胞的生命中發揮其特定作用。細胞核和其他專門細胞器的存在使真核細胞能夠執行復雜的過程並在多細胞生物體內有效地發揮其功能。

The Nucleus Is the Information Store of the Cell

細胞核是細胞的信息存儲

• The nucleus is usually the most prominent organelle in a eukaryotic cell.細胞核通常是真核細胞中最突出的細胞器。
• It is enclosed within two concentric membranes forming the nuclear envelope.它被包圍在兩個形成核膜的同心膜內。
• The nucleus contains DNA, which encodes the genetic information of the organism.細胞核包含 DNA，它編碼生物體的遺傳信息。
• DNA molecules become visible as individual chromosomes during cell division.DNA 分子在細胞分裂過程中變成可見的單個染色體。
• Prokaryotic cells also contain DNA but do not have a distinct nucleus or nuclear envelope.原核細胞也含有 DNA，但沒有明顯的細胞核或核膜。

The nucleus is typically the most prominent organelle in a eukaryotic cell and is enclosed within two concentric membranes that form the nuclear envelope. The nucleus contains DNA, extremely long polymers that encode the genetic information of the organism. When viewed under a light microscope, these giant DNA molecules become visible as individual chromosomes when they compact before a cell divides into two daughter cells.細胞核通常是真核細胞中最突出的細胞器，並被包裹在形成核膜的兩個同心膜內。細胞核含有 DNA，一種極長的聚合物，編碼生物體的遺傳信息。當在光學顯微鏡下觀察時，當細胞分裂成兩個子細胞之前，這些巨大的 DNA 分子會壓縮，從而以單個染色體的形式可見。

細胞核包含真核細胞中的大部分DNA。（A）這張典型的動物細胞圖顯示瞭其廣泛的膜封閉細胞器系統。細胞核呈棕色，核包膜為綠色，細胞質（細胞核外的細胞內部）為白色。（B）哺乳動物細胞核的電子顯微照片。單個染色體是不可見的，因為在細胞分裂周期的這個階段，DNA分子作為細線分散在整個細胞核中。

In contrast, prokaryotic cells also carry genetic information in the form of DNA but lack a distinct nucleus. This is because prokaryotic cells do not enclose their DNA within a nuclear envelope, and their genetic material is not segregated from the rest of the cell contents. The presence of a nucleus in eukaryotic cells allows for efficient organization and management of genetic information, contributing to the complexity and diversity of eukaryotic organisms.相比之下，原核細胞也攜帶 DNA 形式的遺傳信息，但缺乏明顯的細胞核。這是因為原核細胞不會將它們的 DNA 包裹在核膜中，並且它們的遺傳物質不會與其他細胞內容物分離。真核細胞中存在細胞核可以有效地組織和管理遺傳信息，從而增加真核生物的復雜性和多樣性。

當細胞即將分裂時，染色體變得可見。 當真核細胞準備分裂時，其DNA分子逐漸變得更加緊湊（濃縮），形成可以在光學顯微鏡中區分的蠕蟲樣染色體。這裡的照片顯示瞭蠑螈肺培養細胞中染色體凝結過程中的三個連續步驟;請註意，在右邊的最後一個顯微照片中，核包膜已經分解。

Mitochondria Generate Usable Energy from Food Molecules

線粒體從食物分子中產生可用能量

要點（無序/句子）：

• Mitochondria are present in essentially all eukaryotic cells and are prominent organelles in the cytoplasm.線粒體基本上存在於所有真核細胞中，是細胞質中的重要細胞器。
• They are enclosed in two separate membranes, with the inner membrane folded and projecting into the organelle's interior.它們被包裹在兩個獨立的膜中，內膜折疊並伸入細胞器內部。
• Mitochondria generate chemical energy for the cell by producing adenosine triphosphate (ATP) through the oxidation of food molecules.線粒體通過食物分子的氧化產生三磷酸腺苷 (ATP)，從而為細胞產生化學能。
• This process, called cell respiration, consumes oxygen and releases CO2.這個過程稱為細胞呼吸，消耗氧氣並釋放二氧化碳。
• Mitochondria contain their own DNA and reproduce by dividing, and are thought to derive from engulfed bacteria in a symbiotic relationship with an ancestral eukaryotic cell.線粒體包含它們自己的 DNA 並通過分裂繁殖，並且被認為源自與原始真核細胞存在共生關系的吞噬細菌。

Mitochondria are present in virtually all eukaryotic cells and are among the most conspicuous organelles in the cytoplasm. They appear as worm-shaped structures that often form branching networks when observed with a fluorescence microscope. Electron microscopic examination reveals that mitochondria are enclosed in two separate membranes, with the inner membrane forming folds that project into the organelle's interior.線粒體幾乎存在於所有真核細胞中，是細胞質中最顯眼的細胞器之一。它們呈蠕蟲狀結構，在熒光顯微鏡下觀察時通常會形成分支網絡。電子顯微鏡檢查表明，線粒體被封閉在兩個獨立的膜中，內膜形成折疊，伸入細胞器內部。

線粒體的形狀和大小各不相同。這種出芽的酵母細胞在其線粒體中含有綠色熒光蛋白，在超分辨率共聚焦熒光顯微鏡中觀察。在這個三維圖像中，線粒體形成復雜的分支網絡。

The primary function of mitochondria is to generate chemical energy for the cell. They do this by harnessing the energy from the oxidation of food molecules, such as sugars, to produce adenosine triphosphate (ATP), the basic chemical fuel that powers most cellular activities. This process, known as cell respiration, consumes oxygen and releases CO2, effectively functioning as "breathing" at the cellular level.線粒體的主要功能是為細胞產生化學能。他們通過利用食物分子（例如糖）的氧化產生的能量來產生三磷酸腺苷 (ATP)，這是為大多數細胞活動提供動力的基本化學燃料。這個過程稱為細胞呼吸，消耗氧氣並釋放二氧化碳，在細胞水平上有效地起到“呼吸”的作用。

線粒體具有獨特的內部結構。（A）線粒體橫截面的電子顯微照片揭示瞭內膜的廣泛折疊。 （B）線粒體膜排列的三維表示顯示瞭光滑的外膜（灰色）和高度卷曲的內膜（紅色）。內膜含有負責真核細胞能量產生的大部分蛋白質;它高度折疊，為這項活動提供瞭很大的表面積。（C）線粒體的最內側隔室是橙色的。

Mitochondria contain their own DNA and reproduce by dividing. Their similarity to bacteria in many aspects has led to the hypothesis that they originated from bacteria engulfed by an ancestor of present-day eukaryotic cells. This event is thought to have created a symbiotic relationship in which the host eukaryote and the engulfed bacterium helped each other survive and reproduce, leading to the evolution of mitochondria as essential organelles in eukaryotic cells.線粒體含有自己的 DNA 並通過分裂繁殖。它們在許多方面與細菌的相似性導致瞭這樣一種假設，即它們起源於被現代真核細胞的祖先吞噬的細菌。這一事件被認為創造瞭一種共生關系，在這種關系中，宿主真核生物和被吞噬的細菌相互幫助生存和繁殖，導致線粒體進化為真核細胞中的必需細胞器。

線粒體被認為是從吞噬的細菌進化而來的。幾乎可以肯定的是，線粒體是從需氧細菌進化而來的，這些細菌被古細菌衍生的早期厭氧真核細胞吞噬，並在其中存活下來，與宿主共生。如該模型所示，當今線粒體的雙膜被認為來自被吞噬細菌的質膜和外膜; 源自吞噬祖先細胞質膜的膜最終丟失。

Chloroplasts Capture Energy from Sunlight

葉綠體從陽光中捕獲能量

• Chloroplasts are large, green organelles found in plant and algae cells, but not in animal or fungal cells.葉綠體是大型綠色細胞器，存在於植物和藻類細胞中，但不存在於動物或真菌細胞中。
• They have a complex structure with two surrounding membranes and internal stacks of membranes containing chlorophyll.它們具有復雜的結構，有兩個周圍的膜和包含葉綠素的膜的內部堆棧。
• Chloroplasts perform photosynthesis, capturing sunlight energy and using it to produce energy-rich sugar molecules while releasing oxygen as a by-product.葉綠體進行光合作用，捕獲陽光能量並利用它產生能量豐富的糖分子，同時釋放氧氣作為副產品。
• Plant cells can extract the stored chemical energy by oxidizing sugars and their breakdown products, mainly in the mitochondria.植物細胞可以通過氧化糖及其分解產物（主要在線粒體中）來提取儲存的化學能。
• Like mitochondria, chloroplasts contain their own DNA, reproduce by dividing, and are thought to have evolved from engulfed photosynthetic bacteria.像線粒體一樣，葉綠體含有它們自己的 DNA，通過分裂繁殖，並且被認為是從被吞噬的光合細菌進化而來的。

Chloroplasts are large, green organelles found in the cells of plants and algae, but not in the cells of animals or fungi. They possess a complex structure, with two surrounding membranes and internal stacks of membranes containing the green pigment chlorophyll.葉綠體是大型綠色細胞器，存在於植物和藻類的細胞中，但不存在於動物或真菌的細胞中。它們具有復雜的結構，有兩個周圍的膜和包含綠色色素葉綠素的內部膜堆。

植物細胞中的葉綠體捕獲陽光的能量。（A）從開花植物的葉子中分離的單個細胞，在光學顯微鏡下看到，顯示出許多綠色葉綠體。（B）其中一種葉綠體的圖，顯示瞭內膜和外膜，以及含有吸收光能的綠色葉綠素分子的高度折疊的內膜系統。

Chloroplasts are responsible for carrying out photosynthesis—trapping the energy of sunlight in their chlorophyll molecules and using this energy to drive the production of energy-rich sugar molecules. During this process, they release oxygen as a molecular by-product. Plant cells can then extract this stored chemical energy when needed, similar to how animal cells do, by oxidizing these sugars and their breakdown products, primarily in the mitochondria. Chloroplasts enable plants to directly obtain energy from sunlight and produce the food molecules and oxygen that mitochondria use to generate chemical energy in the form of ATP.葉綠體負責進行光合作用——將陽光的能量捕獲在其葉綠素分子中，並利用這種能量來驅動富含能量的糖分子的產生。在此過程中，它們釋放氧氣作為分子副產品。然後，植物細胞可以在需要時提取這種儲存的化學能，就像動物細胞所做的那樣，主要是在線粒體中氧化這些糖及其分解產物。葉綠體使植物能夠直接從陽光中獲取能量，並產生線粒體用來產生 ATP 形式的化學能的食物分子和氧氣。

Like mitochondria, chloroplasts contain their own DNA and reproduce by dividing. They are also thought to have evolved from bacteria—specifically, photosynthetic bacteria that were engulfed by an early aerobic eukaryotic cell.像線粒體一樣，葉綠體含有自己的 DNA 並通過分裂繁殖。它們也被認為是從細菌進化而來的——特別是被早期好氧真核細胞吞沒的光合細菌。

葉綠體幾乎可以肯定是從被吞噬的光合細菌進化而來的。這種細菌被認為已被已經含有線粒體的早期真核細胞吸收。

Internal Membranes Create Intracellular Compartments with Different Functions

內膜產生具有不同功能的細胞內區室

• Eukaryotic cells contain various membrane-enclosed organelles with different functions.真核細胞包含各種功能不同的膜封閉細胞器。
• The endoplasmic reticulum (ER) produces cell-membrane components and materials for export.內質網產生用於出口的細胞膜成分和材料。
• The Golgi apparatus modifies and packages molecules made in the ER for secretion or transport.高爾基體修飾和包裝在內質網中產生的分子以用於分泌或運輸。
• Lysosomes break down unwanted molecules and release nutrients from ingested food particles.溶酶體分解不需要的分子並從攝入的食物顆粒中釋放營養物質。
• Peroxisomes provide an environment for reactions involving hydrogen peroxide to neutralize toxic molecules.過氧化物酶體為涉及過氧化氫的反應提供環境以中和有毒分子。
• Transport vesicles ferry materials between organelles and participate in endocytosis and exocytosis.運輸囊泡在細胞器之間運送物質並參與胞吞和胞吐。

Eukaryotic cells contain a variety of membrane-enclosed organelles with different functions, including nuclei, mitochondria, and chloroplasts. Most of these structures are involved in the cell's ability to import raw materials and export both useful substances and waste products.真核細胞含有多種功能不同的膜封閉細胞器，包括細胞核、線粒體和葉綠體。這些結構中的大多數都與細胞輸入原材料和輸出有用物質和廢物的能力有關。

The endoplasmic reticulum (ER) is an irregular maze of interconnected spaces enclosed by a membrane and is the site where most cell-membrane components and materials for export are made. Cells specialized for protein secretion have an enlarged ER. The Golgi apparatus consists of stacks of flattened, membrane-enclosed sacs that modify and package molecules made in the ER for secretion or transport to another cell compartment.內質網是一個不規則的迷宮，由膜包圍的相互連接的空間組成，是制造大多數細胞膜成分和出口材料的場所。專門用於蛋白質分泌的細胞具有擴大的內質網。高爾基體由一堆扁平的、膜封閉的囊組成，這些囊修飾和包裝在內質網中產生的分子，用於分泌或運輸到另一個細胞室。

內質網產生真核細胞的許多成分。（A）動物細胞示意圖以綠色顯示內質網。（B）哺乳動物胰腺細胞薄切片的電子顯微照片顯示瞭內質網的一小部分，其中ER在這種細胞類型中存在大量，專門用於蛋白質分泌。請註意，內質網與核包膜的膜是連續的。這裡顯示的散佈在內質網（和核包膜）區域的黑色顆粒是核糖體。高爾基體裝置由一堆扁平的膜封閉盤組成。（A）帶有紅色高爾基體裝置的動物細胞示意圖。（B）更逼真的高爾基體圖。附近看到的一些囊泡已經從高爾基體堆中捏掉瞭;其他人註定要與它融合。此處僅顯示一個堆棧，但一個單元格中可以存在多個堆棧。 （C）顯示典型動物細胞高爾基體的電子顯微照片。

Lysosomes are small, irregularly shaped organelles where intracellular digestion occurs, releasing nutrients from ingested food particles and breaking down unwanted molecules for recycling or excretion. Peroxisomes are small, membrane-enclosed vesicles that provide an environment for reactions involving hydrogen peroxide to neutralize toxic molecules.溶酶體是一種形狀不規則的小細胞器，在細胞內進行消化，從攝入的食物顆粒中釋放營養物質，並分解不需要的分子以進行回收或排泄。過氧化物酶體是一種小的、被膜包裹的囊泡，可為涉及過氧化氫的反應提供環境，以中和有毒分子。

膜封閉的細胞器分佈在整個真核細胞細胞質中。（一）膜封閉細胞器的各種類型，顯示不同的顏色，每個類型都特化以執行不同的功能。（二）填充這些細胞器外空間的細胞質（顏色為藍色）。

Transport vesicles move materials between organelles, such as the endoplasmic reticulum, the Golgi apparatus, and lysosomes, and participate in endocytosis and exocytosis. Endocytosis involves the formation of vesicles at the cell surface that carry material from the external medium into the cell, while exocytosis sees vesicles from inside the cell fuse with the plasma membrane and release their contents into the external medium. This process is responsible for the secretion of hormones and signal molecules that enable cellular communication.運輸囊泡在內質網、高爾基體和溶酶體等細胞器之間運輸物質，並參與胞吞和胞吐。內吞作用涉及在細胞表面形成囊泡，這些囊泡將物質從外部介質帶入細胞，而胞吐作用則看到細胞內部的囊泡與質膜融合並將其內容物釋放到外部介質中。這個過程負責激素和信號分子的分泌，從而實現細胞通訊。

真核細胞在其質膜上參與持續的內吞作用和胞吐作用。它們通過內吞作用導入細胞外物質，並通過胞吐作用分泌細胞內物質。內吞物質首先被遞送到稱為內體的膜封閉細胞器

The Cytosol Is a Concentrated Aqueous Gel of Large and Small Molecules

細胞質溶膠是大分子和小分子的濃縮水凝膠

• The cytosol is the part of the cytoplasm not contained within intracellular membranes.胞質溶膠是不包含在細胞內膜內的細胞質的一部分。
• It is the largest single compartment in most cells.它是大多數牢房中最大的單個隔間。
• The cytosol is a concentrated aqueous gel of large and small molecules.胞質溶膠是大分子和小分子的濃縮水性凝膠。
• Many fundamental chemical reactions occur in the cytosol, such as nutrient breakdown and protein synthesis by ribosomes.許多基本的化學反應發生在胞質溶膠中，例如核糖體的營養分解和蛋白質合成。

The cytosol, which is the part of the cytoplasm not contained within intracellular membranes, makes up the largest single compartment in most cells. It is a concentrated aqueous gel consisting of various large and small molecules that are closely packed together. The cytosol is the site of many essential chemical reactions for the cell, such as the early steps in nutrient molecule breakdown and protein synthesis by ribosomes. As a crucial part of cellular function, the cytosol serves as the location for numerous vital processes that support the cell's existence.胞質溶膠是細胞質中不包含在細胞內膜中的部分，它構成瞭大多數細胞中最大的單個隔室。它是一種濃縮的水性凝膠，由各種大小分子緊密堆積而成。胞質溶膠是細胞許多基本化學反應的場所，例如營養分子分解的早期步驟和核糖體合成蛋白質的過程。作為細胞功能的重要組成部分，胞質溶膠充當支持細胞存在的眾多重要過程的位置。

細胞質非常擁擠。這種大腸桿菌細胞質的原子詳細模型基於細菌中存在的50個最豐富的大分子的大小和濃度。RNA、蛋白質和核糖體以不同的顏色顯示

The Cytoskeleton Is Responsible for Directed Cell Movements

細胞骨架負責定向細胞運動

• The cytosol contains a system of protein filaments called the cytoskeleton.胞質溶膠包含稱為細胞骨架的蛋白質絲系統。
• The cytoskeleton is composed of three major filament types: actin filaments, microtubules, and intermediate filaments.細胞骨架由三種主要的絲類型組成：肌動蛋白絲、微管和中間絲。
• The cytoskeleton provides mechanical strength, controls cell shape, and drives and guides cell movements.細胞骨架提供機械強度，控制細胞形狀，並驅動和引導細胞運動。
• Both plant and animal cells rely on the cytoskeleton for internal organization, cell division, and organelle movement.植物和動物細胞都依賴細胞骨架進行內部組織、細胞分裂和細胞器運動。

The cytosol in eukaryotic cells contains a system of protein filaments called the cytoskeleton, which is composed of three major filament types: actin filaments, microtubules, and intermediate filaments. These filaments, along with other proteins that attach to them, form a structure that provides mechanical strength, controls cell shape, and drives and guides cell movements. Both plant and animal cells depend on the cytoskeleton for internal organization, cell division, and organelle movement.真核細胞中的胞質溶膠包含稱為細胞骨架的蛋白質絲系統，它由三種主要的絲類型組成：肌動蛋白絲、微管和中間絲。這些細絲連同附著在其上的其他蛋白質一起形成一種結構，可提供機械強度、控制細胞形狀並驅動和引導細胞運動。植物和動物細胞都依賴細胞骨架進行內部組織、細胞分裂和細胞器運動。

細胞質非常擁擠。這種大腸桿菌細胞質的原子詳細模型基於細菌中存在的50個最豐富的大分子的大小和濃度。RNA、蛋白質和核糖體以不同的顏色顯示

Actin filaments are abundant in all eukaryotic cells, especially muscle cells, where they play a crucial role in muscle contraction. Microtubules, the thickest filaments, are involved in chromosome separation during cell division, while intermediate filaments strengthen most animal cells. The cytoskeleton is essential for both plant cells, which are encased in a rigid cell wall, and animal cells that exhibit more flexible movements. The cytoskeleton's role in cell division may be its most ancient function, as even bacteria contain proteins related to eukaryotic cytoskeletal elements involved in cell division.肌動蛋白絲在所有真核細胞中都很豐富，尤其是肌肉細胞，它們在肌肉收縮中起著至關重要的作用。微管是最粗的細絲，參與細胞分裂過程中的染色體分離，而中間細絲則加強大多數動物細胞。細胞骨架對於包裹在堅硬細胞壁中的植物細胞和表現出更靈活運動的動物細胞都是必不可少的。細胞骨架在細胞分裂中的作用可能是其最古老的功能，因為即使是細菌也含有與參與細胞分裂的真核​​細胞骨架元件相關的蛋白質。

微管有助於分離分裂動物細胞中的染色體。透射電子顯微照片和示意圖顯示瞭附著在有絲分裂紡錘體微管上的重復染色體（在第18章中討論）。當細胞分裂時，它的核包膜分解，它的DNA凝結成可見的染色體，每個染色體都復制形成一對連體染色體，最終將被紡錘形微管拉開成單獨的子細胞。

The Cytosol Is Far from Static

細胞質遠非靜態

• The cell interior is in constant motion.細胞內部在不斷運動。
• The cytoskeleton is a dynamic structure that assembles and disassembles rapidly.細胞骨架是一種動態結構，可以快速組裝和分解。
• Motor proteins use ATP energy to move organelles and proteins throughout the cytoplasm.馬達蛋白使用 ATP 能量在整個細胞質中移動細胞器和蛋白質。
• Molecules in the cell are constantly colliding due to random thermal motion.由於隨機熱運動，細胞中的分子不斷碰撞。

The cell interior is far from static, with constant motion occurring throughout. The cytoskeleton, composed of protein filaments, is a dynamic structure that assembles and disassembles rapidly, often within minutes. Motor proteins utilize energy stored in ATP molecules to move along these filaments, transporting organelles and proteins throughout the cytoplasm at rapid speeds. Furthermore, large and small molecules within the cell are subject to random thermal motion, causing them to constantly collide with each other and other structures in the crowded cytosol. The intricate details of cell structure and the dynamic nature of the cell's interior were not immediately understood and have accumulated gradually through scientific discovery.細胞內部遠非靜止的，始終在不斷運動。由蛋白質絲組成的細胞骨架是一種動態結構，可以快速組裝和分解，通常在幾分鐘內完成。運動蛋白利用儲存在 ATP 分子中的能量沿著這些細絲移動，以快速的速度將細胞器和蛋白質輸送到整個細胞質中。此外，細胞內的大分子和小分子會受到隨機熱運動的影響，導致它們不斷地相互碰撞，並在擁擠的細胞質中與其他結構發生碰撞。細胞結構的復雜細節和細胞內部的動態特性並沒有立即被理解，而是通過科學發現逐漸積累起來的。

Eukaryotic Cells May Have Originated as Predators

真核細胞可能作為捕食者而起源

• Eukaryotic cells are larger and more complex than prokaryotic cells.真核細胞比原核細胞更大、更復雜。
• The origin of eukaryotes remains a mystery.真核生物的起源仍然是個謎。
• One theory suggests the ancestral eukaryotic cell was a predator that fed by capturing other cells.一種理論認為，祖先的真核細胞是一種捕食者，通過捕獲其他細胞來進食。
• The nuclear compartment may have evolved for more delicate and complex control of genetic information.核室可能已經進化為對遺傳信息進行更精細和復雜的控制。
• Primitive eukaryotic cells likely engulfed free-living bacteria, which eventually became mitochondria.原始真核細胞可能吞沒瞭自由生活的細菌，最終變成瞭線粒體。
• A subset of these cells later acquired chloroplasts by engulfing photosynthetic bacteria.這些細胞的一部分後來通過吞噬光合細菌獲得瞭葉綠體。
• Some present-day protozoans provide evidence of predatory behavior in single-celled eukaryotes.一些現代原生動物提供瞭單細胞真核生物捕食行為的證據。

Eukaryotic cells, larger and more complex than prokaryotic cells, possess features such as a nucleus, a versatile cytoskeleton, mitochondria, and other organelles. The origin of eukaryotes is still a mystery, but one theory suggests that the ancestral eukaryotic cell was a predator that captured other cells. This lifestyle would require a large size, a flexible membrane, and a cytoskeleton for movement and feeding. The nuclear compartment may have evolved to protect DNA and allow for more complex control of genetic information.真核細胞比原核細胞更大、更復雜，具有細胞核、多功能細胞骨架、線粒體和其他細胞器等特征。真核生物的起源仍然是個謎，但有一種理論表明，真核細胞的祖先是一種捕食其他細胞的捕食者。這種生活方式需要大尺寸、柔韌的膜和用於運動和進食的細胞骨架。核室可能已經進化到可以保護 DNA 並允許對遺傳信息進行更復雜的控制。

真核生物從何而來？真核生物、細菌和古菌的譜系在30多億年前就彼此分道揚鑣——這是地球生命進化的早期。 一段時間後，真核生物被認為已經獲得瞭線粒體;後來，一部分真核生物獲得瞭葉綠體。 線粒體在植物、動物和真菌中基本相同，因此可能是在這些品系在大約 15 億年前分化之前獲得的。

A primitive eukaryotic cell with a nucleus and cytoskeleton likely engulfed free-living bacteria that eventually became mitochondria. Around 1.5 billion years ago, a subset of these cells acquired chloroplasts by engulfing photosynthetic bacteria. The behavior of some present-day protozoans supports the idea of predatory behavior in single-celled eukaryotes. Protozoans display a wide variety of anatomical features and behaviors, and studying these organisms can provide valuable insights into fundamental cell biology.具有細胞核和細胞骨架的原始真核細胞可能吞噬瞭最終成為線粒體的自由生活細菌。大約 15 億年前，這些細胞的一部分通過吞噬光合細菌獲得瞭葉綠體。一些現代原生動物的行為支持單細胞真核生物捕食行為的觀點。原生動物顯示出各種各樣的解剖學特征和行為，研究這些生物可以為基本細胞生物學提供有價值的見解。

一種原生動物吃另一種原生動物。 （A）掃描電子顯微照片顯示Didinium本身，其周向環狀跳動的纖毛和頂部的“鼻子”。（B）看到Didinium攝入另一種纖毛原生動物，一種草履蟲，人工著色為黃色。各種各樣的原生動物說明瞭這類單細胞真核生物的巨大多樣性。 這些圖紙是按照不同的比例完成的，但在每種情況下，比例尺代表 10 μm。（A）、（C）和（G）中的生物是纖毛蟲;（B）是日生動物;（D）是變形蟲; （E） 是甲藻;（F）是裸藻。

Reference:

• Alberts, B., Hopkin, K., Johnson, A.D., Morgan, D., Raff, M., Roberts, K. and Walter, P., 2019.Essential cell biology: Fifth edition. WW Norton & Company.