Loading...
Paroh's plan against the Jews
Quiz by Sara Taib
Customize this quiz to suit your class
Instantly translate to 100+ languages
Tag the questions with any skills you have. Your dashboard will track each student's mastery of each skill.
Give this quiz to my class
Cell Size Cells differ not only in their shape but also in their size. A few types of cells are large enough to be seen by the unaided human eye. For example, the nerve cells that extend from a giraffe’s spinal cord to its foot can be 2 m (about 6 1/2 ft) long. A human egg cell is about the size of the period at the end of this sentence. Most cells, how- ever, are only 10 to 50 μm in diameter, or about 1/500 the size of the period at the end of this sentence. The size of a cell is limited by the relationship of the cell’s outer surface area to its volume, or its surface area–to-volume ratio. As a cell grows, its volume increases much faster than its surface area does, as shown in Figure 4-5. This trend is important because the materials needed by a cell (such as nutrients and oxygen) and the wastes produced by a cell (such as carbon dioxide) must pass into and out of the cell through its surface. If a cell were to become very large, the volume would increase much more than the surface area. Therefore, the surface area would not allow materials to enter or leave the cell quickly enough to meet the cell’s needs. As a result, most cells are microscopic in size. Comparing Surface Cells Materials microscope, prepared slides of plant (dicot) stem and ani- mal (human) skin, pencil, paper Procedure Examine slides by using medium magnification (100). Observe and draw the sur- face cells of the plant stem and the animal skin. Analysis How do the surface cells of each organism differ from the cells beneath the surface cells? What is the function of the surface cells? Explain how surface cells are suited to their function based on their shape. Quick Lab Small cells can exchange substances more readily than large cells because small objects have a higher surface area–to-volume ratio. FIGURE 4-5 mb06se_csfs02.qxd 5/18/07 10:54 AM Page 73 74 CHAPTER 4 BASIC PARTS OF A CELL Despite the diversity among cells, three basic features are common to all cell types. All cells have an outer boundary, an interior sub- stance, and a control region. Plasma Membrane The cell’s outer boundary, called the plasma membrane (or the cell membrane), covers a cell’s surface and acts as a barrier between the inside and the outside of a cell. All materials enter or exit through the plasma membrane. The surface of a plasma mem- brane is shown in Figure 4-6a. Cytoplasm The region of the cell that is within the plasma membrane and that includes the fluid, the cytoskeleton, and all of the organelles except the nucleus is called the cytoplasm. The part of the cytoplasm that includes molecules and small particles, such as ribosomes, but not membrane-bound organelles is the cytosol. About 20 percent of the cytosol is made up of protein. Control Center Cells carry coded information in the form of DNA for regulating their functions and reproducing themselves. The DNA in some types of cells floats freely inside the cell. Other cells have a mem- brane-bound organelle that contains a cell’s DNA. This membrane- bound structure is called the nucleus. Most of the functions of a eukaryotic cell are controlled by the cell’s nucleus. The nucleus is often the most prominent structure within a eukaryotic cell. It maintains its shape with the help of a protein skeleton called the nuclear matrix. The nucleus of a typical animal cell is shown in Figure 4-6b. Most animal cells have a cell membrane, a nucleus, and a variety of other organelles embedded in a watery substance. The surface of the cell membrane can be seen in (a). The organelles inside the cell are labeled in the diagram (b). FIGURE 4-6 (a) (b) Mitochondrion Microfilaments Lysosome Golgi apparatus Smooth ER Ribosomes Cell membrane Microtubules Rough ER Nuclear pore Nuclear envelope Nucleolus Nucleus Copyright © by Holt, Rinehart and Winston. All rights reserved. Cell wall Ribosome Cell membrane Peptidoglycan Pili Flagellum DNA CELL STRUCTURE AND FUNCTION 75 A prokaryotic cell lacks a membrane- bound nucleus and membrane-bound organelles. Most prokaryotic cells are much smaller than eukaryotic cells are. FIGURE 4-7 A white blood cell (eukaryotic) changes shape as it attacks purple- stained bacterial cells that are much smaller (prokaryotic). FIGURE 4-8 TWO BASIC TYPES OF CELLS Fossil evidence suggests that the earliest cells on Earth were simple cells similar to some present-day bacteria. As cells evolved, they differentiated into two major types: prokaryotes and eukaryotes. Prokaryotes Prokaryotes (proh-KAR-ee-OHTS) are organisms that lack a membrane- bound nucleus and membrane-bound organelles. Although prokaryotic cells lack a nucleus, their genetic information—in the form of DNA—is often concentrated in a part of the cell called the nucleoid. Figure 4-7 shows a typical prokaryotic cell. Prokaryotes are divided into two domains: Bacteria and Archaea (ahr-KEE-uh). The domain Bacteria includes organisms that are similar to the first cellular life-forms. The domain Archaea includes organisms that are thought to be more closely related to eukaryotic cells found in all other kingdoms of life. Eukaryotes Organisms made up of one or more cells that have a nucleus and membrane-bound organelles are called eukaryotes (yoo-KAR-ee-OHTS). Eukaryotic cells also have a variety of subcellular structures called organelles, well-defined, intracellular bodies that perform specific functions for the cell. Many organelles are surrounded by a mem- brane. The organelles carry out cellular processes just as a person’s pancreas, heart, and other organs carry out a person’s life processes. Eukaryotic cells are generally much larger than prokary- otic cells, as seen in Figure 4-8, which shows a white blood cell (eukaryote) destroying tiny bacterial cells (prokaryotes).Paros de emergencia Paro CardiorrespiratorioPagsasanay: Poyen Paru-paroReview of Parah AdumahStructure de la paroi cellulaire bactériennePencemaran sudah terjadi sejak kehidupan prasejarah yaitu saat manusia pertama kali menemukan api dan semakin parah ketika logam ditemukan. Pencemaran terus terjadi hingga kini seperti pencemaran udara yang disebabkan oleh beragam kegiatan manusia contohnya membakar sampah, merokok, menggunakan kendaraan bermotor, serta asap pabrik. Akibat pencemaran udara tersebut adalah kualitas udara yang memburuk, banyak terjadi penyakit infeksi saluran pernapasan bahkan jika semakin parah akan mengakibatkan hujan asam. Pencemaran juga terjadi pada air, kegiatan manusia yang menyebabkan pencemaran air seperti membuang sampah ke laut, membuang limbah industri ke laut, menggunakan bahan peledak. Akibatnya kualitas air semakin menurun dan hewan-hewan mati serta banjir jika musim hujan. Selain itu pencemaran juga terjadi pada tanah, kegiatan yang mengakibatkan pencemaran tanah seperti membuang sampah yang tidak bisa terurai oleh tanah, penggunaan pestisida. Akibatnya kualitas tanah menurun dan tidak bagus jika ditanami tumbuhan. Selain itu kualitas air tanah juga berdampak, seperti berwana keruh dan berbau yang tidak sehat jika dikonsumsi oleh manusiaA főérintkezők egy számjeggyel kerülnek jelölésre, a segédérintkezőket két számjegy jelöli. A páratlan számú a betáplálást, a páros a fogyasztói oldalt jelöli. Az NO (normally open) jelölés nyugalmi állapotban nyitott érintkezőt jelent (záró kontaktus). Az NC (normally closed) jelölés nyugalmi állapotban zárt érintkezőt jelent (bontó kontaktus). Alapkivitelben a mágneskapcsolók általában egy záró segédérintkezővel rendelkeznek, hogy az öntartás megvalósítható legyen. A mágneskapcsolókhoz számos (a gyártó által meghatározott számú) további segédérintkező külön egységként csatlakoztatható akár homloklapra, akár oldalra. Az egységek a felhasználó igényei szerint záró és/vagy nyitó kontaktusokat tartalmaznak. A rajzon a segédérintkezőket két szám jelöli. Az első az áramkör érintkező sorszámára, a második az érintkező funkciójára utal (például 21-22 bontó érintkező; 33-34 záró érintkező). Egy adott mágneskapcsoló segédérintkezőinek a működésekor a nyitó érintkező hamarabb bont, mint ahogy a záró érintkező zár. A segédérintkezők hamarabb működésbe lépnek, mint a főérintkezők.