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Kinds of Angles
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Each angle of a rectangle is a right angle.
Two right angles have a total of 108 degrees.
Each angle of a rectangle is a right angle.
Two right angles have a total of 108 degrees.
A right angle is both an acute angle and an obtuse angle.
When two lines meet at a point an angle is formed.
An angle greater than 45 degrees is called an obtuse
angle.
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Describing and illustrating different kinds of anglesBasic Concepts in Geometry and Kinds of AnglesKINDS AND PARTS OF ANGLESSpeedtest 3.2 - Kinds of lines and anglesThe cytoskeleton is a network of thin tubes and filaments that crisscrosses the cytosol. The tubes and filaments give shape to the cell from the inside in the same way that tent poles support the shape of a tent. The cytoskeleton also acts as a system of internal tracks, shown in Figure 4-18, on which items move around inside the cell. The cytoskeleton’s functions are based on several struc- tural elements. Three of these are microtubules, microfilaments, and intermediate filaments, shown and described in Table 4-2. Microtubules Microtubules are hollow tubes made of a protein called tubulin. Each tubulin molecule consists of two slightly different subunits. Microtubules radiate outward from a central point called the centrosome near the nucleus. Microtubules hold organelles in place, maintain a cell’s shape, and act as tracks that guide organelles and molecules as they move within the cell. Microfilaments Finer than microtubules, microfilaments are long threads of the beadlike protein actin and are linked end to end and wrapped around each other like two strands of a rope. Microfilaments con- tribute to cell movement, including the crawling of white blood cells and the contraction of muscle cells. Intermediate Filaments Intermediate filaments are rods that anchor the nucleus and some other organelles to their places in the cell. They maintain the inter- nal shape of the nucleus. Hair-follicle cells produce large quantities of intermediate filament proteins. These proteins make up most of the hair shaft. 84 CHAPTER 4 TABLE 4-2 The Structure of the Cytoskeleton Property Microtubules Microfilaments Intermediate filaments Structure hollow tubes made of two strands of intertwined protein fibers coiled into coiled protein protein cables Protein subunits tubulin, with two subunits: å actin one of several types of and ∫ tubulin fibrous proteins Main function maintenance of cell shape; cell maintenance and changing of maintenance of cell shape; motility (in cilia and flagella); cell shape; muscle contraction; anchor nucleus and other chromosome movement; movement of cytoplasm; cell organelles; maintenance of organelle movement motility; cell division shape of nucleus Shape Microtubules provide a path for organelles and molecules as they move throughout the cell. FIGURE 4-18 Microtubules Nucleus Endoplasmic reticulum Mitochondrion Ribosomes Copyright © by Holt, Rinehart and Winston. All rights reserved. Copyright © by Holt, Rinehart and Winston. All rights reserved. CELL STRUCTURE AND FUNCTION 85 1. Explain how the fluid mosaic model describes the plasma membrane. 2. List three cellular functions that occur in the nucleus. 3. Describe the organelles that are found in a eukaryotic cell. 4. Identify two characteristics that make mitochon- dria different from other organelles. 5. Contrast three types of cytoskeletal fibers. CRITICAL THINKING 6. Relating Concepts If a cell has a high energy requirement, would you expect the cell to have many mitochondria or few mitochondria? Why? 7. Analyzing Information How do scientists think that mitochondria originated? Why? 8. Analyzing Statements It is not completely accurate to say that organelles are floating freely in the cytosol. Why not? SECTION 3 REVIEW During cell division, centrioles organize microtubules that pull the chromosomes (orange) apart. The centrioles are at the center of rays of microtubules, which have been stained green with a fluorescent dye. FIGURE 4-20 Cilia and Flagella Cilia (SIL-ee-uh) and flagella (fluh-JEL-uh) are hairlike structures that extend from the surface of the cell, where they assist in movement. Cilia are short and are present in large numbers on certain cells, whereas flagella are longer and are far less numerous on the cells where they occur. Cilia and flagella have a membrane on their outer surface and an internal structure of nine pairs of micro- tubules around two central tubules, as Figure 4-19 shows. Cilia on cells in the inner ear vibrate and help detect sound. Cilia cover the surfaces of many protists and “row” the protists through water like thousands of oars. On other protists, cilia sweep water and food particles into a mouthlike opening. Many kinds of protists use flagella to propel themselves, as do human sperm cells. Centrioles Centrioles consist of two short cylinders of microtubules at right angles to each other and are situated in the cytoplasm near the nuclear envelope. Centrioles occur in animal cells, where they organize the microtubules of the cytoskeleton during cell division, as shown in Figure 4-20. Plant cells lack centrioles. Basal bodies have the same structure that centrioles do. Basal bodies are found at the base of cilia and flagella and appear to organize the devel- opment of cilia and flagella.ANIMAL SKELETONS The bones in your body make up your skeleton. You have 206 bones. Bones give your body shape and support. They keep the soft parts inside you safe. Bones come in many shapes and sizes. Your arms and legs are long bones. Your pelvis and shoulder blades are flat bones. The bones in your wrists, hands, ankles, and feet are small. This is what your skeleton looks like. Look at the many kinds of bones in your body. Other animals have skeletons, too. Each animal's skeleton is different. Some are short, some are tall, some are light, and some are strong. Look at this skeleton. How is it different from your skeleton? Do you know what it is? CLUE: This animal flies. It's an eagle. Its bones are hollow and light. Wing feathers attach to the wing bones. Look at this skeleton. How is it different from your skeleton? Do you know what it is? CLUE: This animal hops. It's a frog. It has long back legs for hopping. 10 Its back legs are longer than its body. Look at this skeleton. How is it different from your skeleton? Do you know what it is? CLUE: This animal swims. It's a blue whale. It has no leg bones. Its arms are flippers. Whales are supported by the water. If a whale lived on land, its skeleton would have to be much stronger. Look at this skeleton. How is it different from your skeleton? Do you know what it is? CLUE: This animal runs well. It's a horse. It has long legs for running. A horse has a large rib cage to keep its large lungs safe. It needs large lungs to take in lots of air when it runs. Look at this skeleton. How is it different from your skeleton? Do you know what it is? CLUE: This animal slithers. It's a snake. It has no arms or legs. Its skeleton is one long backbone with ribs. Look at these skulls, or head bones. These are the skulls of the animals in this book. Look at how their shapes and parts are different. Each animal's skeleton is perfect for the way it lives. It has the right kind of skeleton for the support it needs. It has the right kind of skeleton for the way it moves. And so do you.Solving Problems on Different Kinds of Proportion好的，根據您提供的表格 [NEW SOURCE]，以下是表格中例句的中文意思： * **1. all** * **全部的**：**All** my friends were here with me. (我所有的朋友當時都在這裡。) * **全部**：**All** of us enjoyed the movie. (我們所有人都很喜歡這部電影。) * **都**：He got **all** wet. (他全身都濕透了。) * **2. along** * **沿著**：We walked **along** the river yesterday evening. (我們昨天傍晚沿著河邊散步。) * **帶……一起**：When my mother goes out, she takes my little brother **along**. (我媽媽外出時，會帶著我的小弟弟一起去。) * **3. angle** * **觀點**：We should look at the problems from different **angles**. (我們應該從不同的觀點來看待這些問題。) * **角度**：The picture is hanging at an **angle** of 45°. (這張畫以 45 度的角度懸掛著。) * **4. answer** * **答案**：Do you know the **answer** to the question? (你知道這個問題的答案嗎？) * **回答；回應**：Could you **answer** the phone for me? (你可以幫我接一下電話嗎？) * **5. back** * **後面**：She wrote her cellphone number down on the **back** of the paper. (她把她的手機號碼寫在紙的背面。) * **後面的**：Open the **back** door, please. (請打開後面的門。) * **回原處**：It’s time to go **back** home. (該回家了。) * **6. bat** * **蝙蝠**：Did you ever see a **bat** flying quickly in the sky at night? (你曾經看過蝙蝠在夜空中快速飛行嗎？) * **球棒**：Swing the **bat** higher. (把球棒揮高一點。) * **擊**：It’s your turn to **bat**. (輪到你打擊了。) * **7. bite** * **一口的量**：Jane took a **bite** of the guava. (珍咬了一口芭樂。) * **咬**：The dog **bit** the woman’s leg. (那隻狗咬了那個女人的腿。) * **8. book** * **書**：I’ve just started reading a **book** by Stephen King. (我剛開始讀一本史蒂芬·金的書。) * **預訂；預約**：They **booked** two seats at the theater. (他們在劇院預訂了兩個座位。) * **9. block** * **街區**：Nancy and I live on the same **block**. (南希和我住在同一個街區。) * **阻擋**：Those heavy boxes **blocked** my way to the restroom. (那些沉重的箱子擋住了我去洗手間的路。) * **10. bow** * **蝴蝶結**：David chose a gray **bow** tie to go with his black suit. (大衛選擇了一個灰色蝴蝶領結來搭配他的黑色西裝。) * **鞠躬**：The actor **bowed** to everyone before he left the stage. (那位演員在離開舞台前向大家鞠躬。) * **11. break** * **暫停；休息**：I’m tired. Can we take a **break**? (我累了。我們可以休息一下嗎？) * **分解**：These plastic forks are hard to **break** down. (這些塑膠叉子很難分解。) * **打破**：The glass is very expensive. Don’t **break** it. (這個玻璃很貴。不要打破它。) * **12. bright** * **晴朗的**：It’s a **bright** morning. Why not take a walk along the river? (這是個晴朗的早晨。何不沿著河邊散步呢？) * **明亮的**：The room isn’t **bright** enough. Let’s not read here. (這個房間不夠明亮。我們不要在這裡閱讀。) * **13. call** * **打電話**：I got a **call** from my old friend last night. (我昨晚接到我老朋友的電話。) * **打電話**：Tina **called** me last night. We talked a lot about music. (蒂娜昨晚打電話給我。我們聊了很多關於音樂的事。) * **呼喊**：Listen! Is that a **call** for help? (聽！那是求救的呼喊嗎？) * **呼喊**：Why did you **call** my name then? (那你當時為什麼喊我的名字？) * **14. camp** * **營隊**：Patrick joined a science **camp** this summer. (派屈克今年夏天參加了一個科學營隊。) * **露營**：They **camped** by the river yesterday. (他們昨天在河邊露營。) * **15. case** * **箱；盒**：The kids drank the whole **case** of Coke. (孩子們喝掉了一整箱可樂。) * **實例；情況**：The number of new **cases** of Covid-19 is growing. (新冠肺炎的新增病例數正在增加。) * **16. catch** * **接球**：Nice **catch**! My good dog. (接得好！我的好狗狗。) * **罹患（病）**：My head hurts. I may **catch** a cold. (我頭痛。我可能感冒了。) * **抓住**：I didn’t **catch** the ball. (我沒有接到那個球。) * **17. change** * **零錢；找零**：I think you’ve given me the wrong **change**. (我想你找錯錢了。) * **改變；交換**：The leaves **change** (in color) from green to red in the fall. (秋天時，樹葉的顏色從綠色變成紅色。) * **18. clean** * **打掃；清理**：Tom **cleans** the toilet once a week. (湯姆一週打掃一次馬桶。) * **乾淨的**：The water isn’t **clean**. Don’t drink it. (這水不乾淨。不要喝。) * **19. close** * **關；闔**：**Close** your books, students. Let’s have a pop quiz. (同學們，把你們的書闔上。我們要進行隨堂測驗。) * **靠近地**：Jane sat **close** to her husband at the party. (在派對上，珍緊挨著她的丈夫坐著。) * **20. cold** * **感冒**：I had a **cold** a week ago. (我一個星期前感冒了。) * **寒冷的**：It was **cold** last night. (昨晚很冷。)