Cell Theory Objectives Explain the Cell Theory. April 27, 2022 1 Cells and the Cell Theory Robert Hooke was the first person to describe cells. In 1665, he built a microscope to look at tiny objects. One day, he looked at a thin slice of cork. Cork is found in the bark of cork trees. The cork looked like it was made of little boxes. Hooke named these boxes cells, which means “little rooms” in Latin. Hooke’s cells were really the outer layers of dead cork cells. Hooke’s microscope and
Transcript
Cell TheoryObjectivesExplain the Cell Theory.
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Cells and the Cell Theory
Robert Hooke was the first person to describe cells. In 1665, he built a microscope to look at tiny objects. One day, he looked at a thin slice of cork. Cork is found in the bark of cork trees. The cork looked like it was made of little boxes. Hooke named these boxes cells, which means “little rooms” in Latin. Hooke’s cells were really the outer layers of dead cork cells. Hooke’s microscope and his drawing of the cork cells.
The Cell Theory Almost 200 years passed before scientists concluded
that cells are present in all living things. Scientist Matthias Schleiden (mah THEE uhs SHLIE duhn) studied plants. In 1838, he concluded that all plant parts were made of cells. Theodor Schwann (TAY oh dohr SHVAHN) studied animals. In 1839, Schwann concluded that all animal tissues were made of cells. Soon after that, Schwann wrote the first two parts of what is now known as the cell theory.
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Later, in 1858, Rudolf Virchow (ROO dawlf FIR koh), a doctor, stated that all cells could form only from other cells. Virchow then added the third part of the cell theory.
All organisms are made up of 1 or more cells.
The Cell is the basic unit of all living things.
Cells come from existing Cells
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Many Small Cells
There is a physical reason why most cells are so small. Cells take in food and get rid of wastes through their outer surface. As a cell gets larger, it needs more food and produces more waste. Therefore, more materials pass through its outer surface.
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Cell Size Continues….As the cell’s volume increases, its surface area grows too. But the cell’s volume grows faster than its surface area. If a cell gets too large, the cell’s surface area will not be large enough to take in enough nutrients or pump out enough wastes. So, the area of a cell’s surface—compared with the cell’s volume—limits the cell’s size. The ratio of the cell’s outer surface area to the cell’s volume is called the surface area–to-volume ratio, which can be calculated by using the following equation:
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Two Kinds of Cells
All cells have cell membranes, organelles, cytoplasm, and DNA. But there are two basic types of cells—cells without a nucleus and cells with a nucleus. Cells with no nucleus are prokaryotic (proh KAR ee AHT ik) cells. Cells that have a nucleus are eukaryotic (yoo KAR ee AHT ik) cells. Prokaryotic cells are further classified into two groups: bacteria (bak TIR ee uh) and archaea (AHR kee uh).
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Objective:Identify the different parts of a eukaryotic cell.Explain the function of each part of a eukaryotic cell.
Even though most cells are small, cells are still complex. A eukaryotic cell has many parts that help the cell stay alive.
Plant cells and animal cells are two types of eukaryotic cells. These two types of cells have many cell parts in common. But plant cells and animal cells also have cell parts that are different. Compare the plant cell in Figure 1 and the animal cell in Figure 2 to see the differences between these two types of cells.
a cell is the smallest unit that can perform all life processes.
Cells are covered by a membrane that separates the inside of the cell and the cytoplasm from the outside.
All cells have DNA, and many store the DNA in a nucleus.
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Plant
Objectives:1. List three advantages of being multicellular.2. Describe the four levels of organization in living things.3. Explain the relationship between the structure and function of a part of an organism
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The Benefits of Being MulticellularYou are a multicellular organism. This means that you are made of many cells. Multicellular organisms grow by making more small cells, not by making their cells larger. For example, an elephant is bigger than you are, but its cells are about the same size as yours.
Benefits of Larger Cells Larger size Longer Life Specialization
Read page 20 in the textbook and provide an explanation to each one.
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Tissues A tissue is a group of cells that work together to
perform a specific job. The material around and between the cells is also part of the tissue. The cardiac muscle tissue, shown in Figure 2, is made of many cardiac muscle cells. Cardiac muscle tissue is just one type of tissue in a heart.
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Tissues Working Together
A structure that is made up of two or more tissues working together to perform a specific function is called an organ. For example, your heart is an organ. It is made mostly of cardiac muscle tissue. But your heart also has nerve tissue and tissues of the blood vessels that all work together to make your heart the powerful pump that it is.
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Organs Working Together
A group of organs working together to perform a particular function is called an organ system. Each organ system has a specific job to do in the body.
For example, the digestive system is made up of several organs, including the stomach and intestines. The digestive system’s job is to break down food into small particles. Other parts of the body then use these small particles as fuel. In turn, the digestive system depends on the respiratory and cardiovascular systems for oxygen.
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Organs working together
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Structure and Function
Structure and FunctionIn organisms, structure and function are related. Structure is the arrangement of parts in an organism. It includes the shape of a part and the material of which the part is made. Function is the job the part does. For example, the structure of the lungs is a large, spongy sac. In the lungs, there are millions of tiny air sacs called alveoli. Blood vessels wrap around the alveoli, as shown in Figure 4. Oxygen from air in the alveoli enters the blood. Blood then brings oxygen to body tissues. Also, in the alveoli, carbon dioxide leaves the blood and is exhaled.
The structures of alveoli and blood vessels enable them to perform a function. Together, they bring oxygen to the body and get rid of its carbon dioxide.
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Objectives• Explain the process of diffusion.• Describe how osmosis occurs.• Compare passive transport with active transport.• Explain how large particles get into and out of cells.
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Diffusion
What happens if you pour dye on top of a layer of gelatin? At first, it is easy to see where the dye ends and the gelatin begins. But over time, the line between the two layers will blur, as shown in Figure 1. Why? Everything, including the gelatin and the dye, is made up of tiny moving particles. Particles travel from where they are crowded to where they are less crowded. This movement from areas of high concentration (crowded) to areas of low concentration (less crowded) is called diffusion (di FYOO zhuhn). Dye particles diffuse from where they are crowded (near the top of the glass) to where they are less crowded (in the gelatin). Diffusion also happens within and between living cells. Cells do not need to use energy for diffusion.
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Figure 1 The particles of the dye and the gelatin slowly mix by diffusion.
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Diffusion of WaterThe cells of organisms are surrounded by and filled with fluids that are made mostly of water. The diffusion of water through cell membranes is so important to life processes that it has been given a special name—osmosis (ahs MOH sis).
Water is made up of particles, called molecules. Pure water has the highest concentration of water molecules. When you mix something, such as food coloring, sugar, or salt, with water, you lower the concentration of water molecules. Figure 2 shows how water molecules move through a membrane that is semipermeable (SEM i PUHR mee uh buhl). Semipermeable means that only certain substances can pass through. The picture on the left in Figure 2 shows liquids that have different concentrations of water. Over time, the water molecules move from the liquid with the high concentration of water molecules to the liquid with the lower concentration of water molecules.Figure Page 35 in text.
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The Cell and OsmosisOsmosis is important to cell functions. For example, red blood cells are surrounded by plasma. Plasma is made up of water, salts, sugars, and other particles. The concentration of these particles is kept in balance by osmosis. If red blood cells were in pure water, water molecules would flood into the cells and cause them to burst. When red blood cells are put into a salty solution, the concentration of water molecules inside the cell is higher than the concentration of water outside. This difference makes water move out of the cells, and the cells shrivel up. Osmosis also occurs in plant cells. When a wilted plant is watered, osmosis makes the plant firm again.
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Moving Small Particles
Small particles, such as sugars, cross the cell membrane through passageways called channels. These channels are made up of proteins in the cell membrane. Particles travel through these channels by either passive or active transport. The movement of particles across a cell membrane without the use of energy by the cell is called passive transport, and is shown in Figure 3. During passive transport, particles move from an area of high concentration to an area of low concentration. Diffusion and osmosis are examples of passive transport.
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Figure on page 36 in textbook.
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Active TransportA process of transporting particles that requires the cell to use energy is called active transport. Active transport usually involves the movement of particles from an area of low concentration to an area of high concentration.
Moving Large ParticlesSmall particles cross the cell membrane by diffusion, passive transport, and active transport. Large particles move into and out of the cell by processes called endocytosis and exocytosis.
EndocytosisThe active-transport process by which a cell surrounds a large particle, such as a large protein, and encloses the particle in a vesicle to bring the particle into the cell is called endocytosis (EN doh sie TOH sis). Vesicles are sacs formed from pieces of cell membrane.
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Exocytosis
When large particles, such as wastes, leave the cell, the cell uses an active-transport process called exocytosis (EK soh sie TOH sis). During exocytosis, a vesicle forms around a large particle within the cell. The vesicle carries the particle to the cell membrane. The vesicle fuses with the cell membrane and releases the particle to the outside of the cell.
