Cells, 2024 Grade 8, Cells, PDF

# Chapter 6 Organizing Cells ## Key Question: How do cells work together? ### Looking Ahead - Organisms can be made up of one cell (unicellular organisms) or many cells (multicellular organisms). - Unicellular organisms perform all of the processes necessary for life using a single cell. - The sk...

# Chapter 6 Organizing Cells ## Key Question: How do cells work together? ### Looking Ahead - Organisms can be made up of one cell (unicellular organisms) or many cells (multicellular organisms). - Unicellular organisms perform all of the processes necessary for life using a single cell. - The skills of analysis can be used to study organisms. In multicellular organisms, cells organize into tissues, tissues into organs, and organs into organ systems. Multicellular plants and animals depend on systems of organs to carry out life processes. - When cells are not able to perform their functions, the health of the organism is affected. ## Vocabulary - organism - unicellular organism - multicellular organism - vertebrate - invertebrate - fungi - protist - bacteria - movement - locomotion - cellular differentiation - tissue - organ - organ system - xylem vessel - phloem vessel # 6.1 Classifying Organisms - Living things are often called *organisms*. - Organisms are living systems composed of smaller parts working together to carry out the processes of life. - An organism that is made up of only one cell is called a *unicellular organism*. - Almost all unicellular organisms are so small that they can only be seen using a microscope. - Organisms can also be made up of many cells working together. An organism that is made up of more than one cell is called a *multicellular organism.* - Most of the living things that you see every day are multicellular organisms. - Scientists classify living things into groups based on their characteristics. ## Smaller Groups * **Plants**: Plants are multicellular organisms. Trees, grasses, flowers, bushes, vines, mosses, and herbs are examples of plants. All plants make their own food by *photosynthesis*. Plants can live on land or in water. Water lilies and Elodea are examples of plants that live in the water. * **Animals**: Animals are also multicellular organisms. Animals may be further divided into vertebrates and invertebrates. - *Vertebrates* are animals with a backbone, such as a moose, salmon, or blue jay. - *Invertebrates* are animals without a backbone, such as a spider, shrimp, or snail. * **Fungi**: Fungi (singular, fungus) are organisms that usually obtain nutrients by absorbing them from dead or decaying matter and cannot carry out photosynthesis. Most fungi are multicellular, though some are unicellular. Field mushrooms and baker's yeast are both examples of fungi. * **Protists**: Protists are a diverse group of organisms that are commonly found in wet or moist environments such as ponds, rivers, and mud. Protists can be unicellular or multicellular and have all of the organelles of a typical animal cell. Some protists, like the Volvox shown in Figure 5, are plant-like organisms that have chloroplasts and can perform photosynthesis. Common plant-like protists include diatoms and algae. Other protists are more like animals and cannot perform photosynthesis. They must obtain food from their environment. Common animal-like protists include amoebas and paramecia. * **Bacteria**: Bacteria (singular, bacterium) are the simplest and most abundant unicellular organisms on Earth. Bacteria do not have a nucleus. Although they are unicellular, some types of bacteria gather into groups called bacterial colonies. The bacterium that causes strep throat is an example of a bacterium that forms colonies. Figure 6 shows a common bacterium, Escherichia coli (E. coli). # 6.2 Unicellular Organisms - Unicellular organisms perform the same life processes as multicellular organisms. - Individually, these cells can only be seen using a microscope. - Unicellular organisms are often called "micro-organisms". - Unicellular organisms include bacteria and some protists and fungi. ## Nutrition - Many unicellular organisms live in bodies of water and must move around to find food. - Most often, they must obtain nutrients by eating other organisms. - Plant-like protists, and some types of bacteria, can make their own food through *photosynthesis*. - The Euglena is a protist that has both plant and animal characteristics, which it uses for obtaining nutrients. - Other micro-organisms, such as fungi and bacteria, interact with one another to obtain nutrients. - Lichens are organisms that form from the interaction of a fungus with an alga (Figure 2). ## Paramecia - Paramecia are unicellular organisms that are found in aquatic environments. - These animal-like protists feed on bacteria and algae. - Paramecia are covered with *cilia* that beat in unison, creating water currents that move the paramecium toward a food source. - The *oral groove* of the paramecium also contains cilia that create currents that draw the food into a cavity. - Once this cavity is filled, the food is enclosed in a vacuole where it is slowly digested. - As the food vacuole travels through the cell, nutrients diffuse through the vacuole's membrane into the cytoplasm. - Any remaining waste materials are eliminated through an anal pore. ## Amoeba - The amoeba is another animal-like protist that must move about to find food. - The amoeba uses *phagocytosis* to feed on organisms. - The pseudopods extend around the food material and form a food vacuole. - The vacuole acts as a site of both storage and digestion. - When the amoeba needs nutrients, chemicals are released into the vacuole to break down the stored food. - The food particles are then able to diffuse into the cytoplasm of the cell. - Once digestion is complete, wastes are released out of the cell by *exocytosis*. ## Gas Exchange - Most organisms also need oxygen to survive. The chemical reactions that allow organisms to obtain energy from food use oxygen and release carbon dioxide as a waste product. - This means that there must be a steady exchange of oxygen and carbon dioxide into and out of the cell. - In unicellular organisms, oxygen diffuses across the cell membrane into the cell. Carbon dioxide diffuses out of the cell once the concentration of carbon dioxide is higher inside the cell than it is outside of the cell. - Some micro-organisms, including some bacteria and fungi, can survive without oxygen. - Yeast is a unicellular fungus that can survive without oxygen. - This characteristic makes yeast useful in many industries. ## Responding to the Environment - Humans are able to detect changes in the environment using the five senses. - Unicellular organisms do not have this ability. - They must sense their surroundings in other ways. - Some bacteria can detect chemicals, such as sugar, in their environment and move toward them. Photosynthetic protists, like Euglena, can detect light using special sensors. - All organisms are able to sense their environment in some way and respond to it. ## Movement and Locomotion - Unicellular organisms sometimes move toward or away from things in their environment. - This includes food, light, and predators. - Unicellular organisms can move in two distinct ways - movement and locomotion. ## Movement - Movement enables an organism to change its form or shape. - This is achieved using pseudopods. - Protists, such as the amoeba, use pseudopods to obtain nutrients or to get rid of wastes. - Some cells in multicellular organisms, such as white blood cells, use pseudopods to engulf invading organisms by phagocytosis. ## Locomotion - Locomotion enables an organism to change its position in the environment. - Unicellular organisms achieve locomotion using cilia and flagella. - By creating currents in the surrounding environment, cilia and flagella can move the cell in one direction or another. ## 6.3 Performing Unicellular Organisms - The paramecium is one of the most complex of the unicellular organisms. - Paramecia are commonly found in bodies of water, and are covered in cilia, which they use to swim from place to place in their environment. ## Purpose - To observe prepared slides of unicellular organisms and of *Paramecium* culture using the compound microscope. ## Equipment and Materials - apron - microscope - prepared slides of unicellular organisms, including *Paramecium* - 2 eyedroppers - slide and cover slip - *Paramecium* culture - 10% glycerine ## Procedure 1. Put on your apron and obtain a microscope. 2. Place a prepared slide of *Paramecium* on the stage of the microscope. With your microscope on low power, observe the slide. Move the slide around on the stage until you find some cells. Now, using the medium- or high-power objective lens, focus on one cell and create a biological drawing of what you observe. Label all visible structures. 3. Repeat step 2 for prepared slides of two other microorganisms. For each organism you view, be sure to include the name of the organism and the total magnification used. 4. Use a clean eyedropper to place a drop of *Paramecium* culture onto the centre of a clean slide. Gently lower a cover slip from a 45° angle to cover the sample. Tap the slide gently to remove any air bubbles. 5. Place the slide on the microscope stage and observe under low power (Figure 1). Use the coarse-adjustment knob to focus on the cells. Switch to medium power and use the fine-adjustment knob to bring the cells into focus once more. Create a biological drawing of what you observe. 6. Prepare a second wet mount by combining one drop of *Paramecium* culture and one drop of glycerine on the centre of a new slide. Be sure to use a clean eyedropper for each solution. 7. Repeat step 5, taking care to examine the locomotion of the paramecia while focusing on the movement of the cilia. Describe your observations and create biological drawings of the paramecia locomotion. ## Analyze and Evaluate - Summarize how a *paramecium* moves. - Why do you think glycerine was added to the slide in step 6? - Using your knowledge from Section 6.2, select two of the structures that you observed and explain their importance in meeting the needs of the micro-organism. - Compare your observations of live and prepared *paramecia*, and describe the benefits and drawbacks of using both types of slides ## Apply and Extend - Microbiologists are scientists that specialize in the study of micro-organisms. Use the internet to research some of the techniques that "professional" microbiologists use to prepare slides of micro-organisms. Write a brief report describing two different methods. Include a summary of how these methods have helped the study of microbiology. # 6.4 Multicellular Organisms - Multicellular organisms have more working parts (cells) than unicellular organisms. - The Douglas fir tree is one of the largest organisms on Earth. - This giant tree is made up of many cells, which form the trunk, branches, leaves, and so on. - Multicellular organisms use all of their cells to perform life processes and meet their needs. ## Specialization and Differentiation - All multicellular organisms start as a single cell. - When the cell divides, the new cells do not move away from each other, but stay close to one another. - The number of cells formed determines the size of the organism. - As the number of cells increases, each cell becomes better able to perform one particular function within the organism. ## Tissues, Organs, and Organ Systems - Within multicellular organisms, differentiated cells are organized according to the function they perform. ## Tissues - A group of cells that is similar in shape and function is called a tissue. - In animals, four basic types of tissue are epithelial tissue, muscle tissue, connective tissue, and nervous tissue. Blood is an example of connective tissue. In humans, epithelial tissue can be found covering the external surfaces of the body, and lining the surfaces of structures such as the mouth, heart, liver, and eyes. - In plants, tissues made from thin-walled plant cells are commonly found in the parts of the plant that carry water and nutrients. Tissues made from thick-walled plant cells are found in the parts of the plant that provide structure. ## Organs - Different tissues assemble to form larger structures, such as the skin, stomach, and heart. These structures are called organs. - Organs are made up of different types of tissue that work together to achieve one or more functions within the organism. - Skin, for example, is the largest organ in the human body and is made up of epithelial tissue, connective tissue, nerve tissue, and fat tissue. - Skin provides both structural support and a barrier that protects internal structures from the outside environment. - Other animal organs include the heart, stomach, brain, lungs, intestines, eyes, and liver. - In plants, stems, leaves, flowers, and roots are all organs. ## Organ Systems - Organs never work alone. - Two or more organs working together to perform a related function are known as an organ system. - In humans, the digestive system is an organ system made up of several organs: the mouth, esophagus, stomach, liver, pancreas, small and large intestines, and anus. - Organ systems often overlap and share organs. Both the circulatory system and the respiratory system include the lungs. - Organ systems are also interdependent. For example, all organs need contact with the brain to function properly. - Organ systems in animals include the circulatory system, respiratory system, digestive system, musculoskeletal system, and nervous system (Figure 4). - Plants have two major organ systems: the root system and the shoot system (Figure 5). ## Human Organ Systems - Humans are multicellular organisms made up of several tissues, organs, and organ systems. - Human organ systems work together to perform all of the processes necessary for life. - Table 1 summarizes the structures and functions of five important human organ systems. | Major function | Circulatory system | Respiratory system | Digestive system | Musculoskeletal system | Nervous system | |---|---|---|---|---|---| | | transports nutrients, dissolved gases (oxygen and carbon dioxide), and wastes to and from individual cells in the organism | exchanges oxygen and carbon dioxide between blood and the external environment | breaks food down into small particles, called nutrients, that can be transported by the circulatory system to all cells of the body | provides structural support to the body protects internal structures from the outside environment plays a role in movement and locomotion bones muscles | responds to changes in the internal and external environment of the body coordinates the function of all other organ systems brain spinal cord sensory organs (eyes, ears, nose, taste buds) | | Major organs | heart blood vessels | lungs windpipe | mouth esophagus stomach liver pancreas small and large intestines anus | bones muscles | brain spinal cord sensory organs (eyes, ears, nose, taste buds) | | Major tissues | epithelial muscle nerve connective | epithelial muscle nerve connective | epithelial muscle nerve connective | epithelial muscle nerve connective | epithelial nerve connective | ## 6.5 Multicellular Organisms Meeting Their Needs - As a living thing, you have needs that must be met every day. - You need to eat and breathe. - You also need to respond to things in your environment. - You answer your teacher when she calls your name in class and you pull your hand away from something that feels hot. - You also need to be able to move from place to place. - Almost all multicellular organisms, from small to large, have these needs. ## Systems Working Together - It is important that all systems within a multicellular organism work together. - For example, oxygen and nutrients are materials that cells need to survive. - The respiratory, digestive, and circulatory systems work together to meet this need. - The respiratory system supplies oxygen to blood cells and the digestive system supplies nutrients. - The circulatory system then pumps the oxygen- and nutrient-rich blood to all the cells of the body. - Cells use the nutrients and oxygen to produce energy. - During this process, cells release carbon dioxide as a waste product. - The carbon dioxide diffuses out of the cells of the body and into blood cells. - The blood cells are then transported to the lungs by the circulatory system, where carbon dioxide can be exhaled from the body. - Like a chain, which is only as strong as its weakest link, an organism is only as strong as its weakest system. - For example, the circulatory system depends on at least two other organ systems (respiratory and digestive systems) in order to do its job properly. - If one of these organ systems is not doing its job well, the whole organism can be affected. ## Nutrition - Animals are unable to make their own food and must survive either by consuming living things (such as fruits, vegetables, and meat) or by consuming products that come from living things (such as eggs and honey). - Food material must be broken down into nutrients that the cells of the body can absorb and use for energy. ## Nutrition in Humans - In humans, food is taken into the body and broken down by a digestive system made up of specialized organs and tissues. - Food enters the mouth, where it is broken down into smaller pieces by the teeth. - Cells in the mouth release chemicals that help with this breakdown. - Swallowing moves the food into the esophagus. - Muscle cells lining the walls of the esophagus help push food down into the stomach. - Cells in the stomach release chemicals that further break down the food. - Stomach muscles contract and relax, moving food into the intestines. In the intestine, the nutrients are absorbed into the blood vessels of the circulatory system and are transported to other parts of the body. - Undigested food is passed out of the anus as waste. - The cells of the body use these nutrients for energy and pass wastes into the blood for removal from the body. These wastes pass through the kidneys and are eliminated as urine. - Each cell involved in this process has a unique task that is necessary for digestion. ## Nutrition in the Earthworm - The earthworm has a small mouth leading to a pharynx. - Earthworms "suck" in food using the pharynx. - The esophagus then pushes food into the crop, an organ that moistens and stores food. - A specialized stomach called the gizzard contains particles of sand and gravel that help break down tough foods. - In the intestine, chemicals further break down the food into nutrients that can be absorbed into the cells of the body. - Undigested food is passed through the anus as waste. ## Nutrition in Plants - Plants cannot hunt for nutrients as animals do. - Instead, they obtain nutrients directly from their environment. - Plants use roots to absorb water and nutrients from the soil. - Special tube-like tissues called *xylem vessels* then transport the water and minerals from the roots to other parts of the plant. - When water is absorbed by the roots, it is carried up through the shoot system to the leaves of the plant. - The plant leaves use sunlight, carbon dioxide, and water to make food by *photosynthesis*. - Other tube-like tissues called *phloem vessels* located outside the xylem transport food from the leaves to the rest of the plant. - Excess sugars are transported to the stems and roots for storage. Figure 4 shows xylem and phloem tissues in a plant. ## Gas Exchange - Small multicellular organisms use diffusion to obtain oxygen. - For example, the earthworm uses its moist skin to exchange gases with the outside air. - Some aquatic organisms, like fish, pass oxygen-rich water through gills, where it diffuses into blood capillaries. - Most land animals use lungs for gas exchange. - In all cases, oxygen is absorbed from the environment, and carbon dioxide is removed from the blood. - The dissolved gases are transported in the blood. ## Gas Exchange in Vertebrates - In humans, air is inhaled through the mouth and nose and passes into the trachea. - A flap-like structure in the trachea opens when you breathe, but closes when you swallow food. - This prevents food from entering the trachea and lungs. - Air travels down the trachea into the lungs. - In the lungs, tubes called bronchi branch off into smaller tubes called bronchioles. - At the end of the bronchioles are round sacs of alveoli, where gas exchange occurs. - The walls of the alveoli are only one cell thick. - This allows oxygen to diffuse out of the cells of the alveoli and into the blood cells. - The circulatory system transports the oxygen-rich blood cells to the rest of the body. - As blood circulates throughout the body, oxygen diffuses out of the blood cells and into the cells of the body. - In the same way, carbon dioxide diffuses out of the body cells and into the blood cells. - Blood cells are carried to the alveoli. - Carbon dioxide diffuses out of the blood cells and into the alveoli. - The carbon dioxide then travels through the bronchioles, bronchi, and trachea. - It is removed from the body when you exhale. ## Gas Exchange in Plants - Plants have special tissues containing stomates, which they use for gas exchange. - Stomates are microscopic pores that control the movement of gases and water vapour into and out of the plant. - Stomates are mainly found on the bottom surface of a leaf but can also be found in other parts of the plant, including the stems (Figure 7). ## Responding to the Environment - All vertebrates and some invertebrates have a complex nervous system. - Nerve cells are highly specialized to process and transmit information. - Nervous systems respond to factors in the environment (such as temperature) by sending signals through the nerve cells, or neurons, to organs. - These signals are sent to the brain where they are processed, and a response is initiated. - For example, a cat may see a saucer of milk. Information from the cat's eyes travels along nerve cells to the brain, where the brain processes the information. - If the brain decides it wants the milk, the brain sends a signal to the muscles in the cat's limbs, and the cat moves to the saucer of milk and drinks it. ## Plant Responses to the Environment - Plants are also able to respond to their environment. - For example, specialized cells in the leaves of trees detect the decrease in sunlight as winter approaches. - Chloroplasts then reduce production of green chlorophyll. - As existing chlorophyll is broken down, other coloured particles are revealed, creating the beautiful red- and orange-coloured leaves we see during autumn. - The leaves eventually die and fall off. - In the spring, increased sunlight and warmer temperatures promote the production of new leaves containing large amounts of chlorophyll, and the green colour returns to the leaves. ## Locomotion and Movement - Muscles and bones work together to allow vertebrates to move around. - The human musculoskeletal system is made up of more than two hundred bones that support the hundreds of muscles in the body. - The muscles are attached to the bones in ways that move the bones when the muscles contract. - Muscle contractions are controlled by signals from the nervous system. - Muscles also play an important role in the functioning of organs. - For example, muscle cells in the walls of the heart contract to move blood into and out of the heart. - Muscle cells use a lot of energy. - For this reason, they have many mitochondria that convert food energy into motion. - Invertebrate animals also use muscles to achieve locomotion, but most do not have bones. - The earthworm, for example, uses muscle contractions for locomotion. - The earthworm anchors itself to the soil with tiny hair-like projections, and then muscles in the body contract and expand to pull the body through the soil. # 6.6 Interactions Between Unicellular and Multicellular Organisms - You see and interact with many multicellular organisms every day-trees, flowers, cats, birds, and other humans, just to name a few. - You may not see unicellular organisms, but many of them affect your life every day! - You would not have most types of bread to eat without unicellular organisms, nor would you be able to digest certain foods. - Some unicellular organisms also cause disease, while some help you fight disease. - Cells are an important part of your life. ## The Importance of Unicellular Organisms - Unicellular organisms can be found in nearly every environment on Earth. - Some are dangerous to humans, but many are important to human health and the environment. - Many unicellular organisms play an important role in recycling nutrients. - Fungi and bacteria, for example, are decomposers. - They break down dead plant and animal material, releasing usable nutrients and carbon dioxide back into the environment. - Some bacteria are able to change nitrogen in the air into a material that acts as a plant fertilizer. - Other micro-organisms are used in the food industry. - Yeast, for example, is used to produce breads and pastries. - Yogurt is produced by bacterial action on milk. - Some micro-organisms produce antibiotics that we use to treat infections. - For example, *penicillin*, a common antibiotic used to treat bacterial infections, is made from a fungus. ## Cells Gone Wrong - Sometimes, cells are not able to function properly. - This may happen for several reasons. - An organism may inherit damaged genes that cause cells to fail, or environmental factors may damage cells. ## Diabetes - In the chapter narrative, we met Keiko. - Keiko has diabetes, a disease caused by dysfunctional cells. - Cells in the pancreas normally produce *insulin*, a chemical that helps other cells in the body absorb sugars from the blood. - There are two types of diabetes, type 1 and type 2. - In a person with type 1 diabetes, cells in the pancreas do not produce insulin (or do not produce enough insulin). - Insulin must be injected into the body. - In type 2 diabetes, cells in the body do not respond to insulin, and sugar cannot be absorbed. - People with type 2 diabetes must regulate their blood sugar with exercise and diet. - In the past, this disease was rarely seen in people under the age of 40. - Recently, there have been a growing number of cases reported in teens and children in Canada. - These cases appear to be caused by obesity and lack of physical activity. - Many health care professionals consider type 2 diabetes an epidemic in developed countries. - Fortunately, it may be prevented by eating a healthy diet and leading an active lifestyle. - Both types of diabetes, if uncontrolled, can lead to heart disease, blindness, and kidney failure. # 6.6 Interactions Between Unicellular and Multicellular Organisms Continued ## Cells Gone Wrong - Sometimes, cells are not able to function properly. This may happen for several reasons. An organism may inherit damaged genes that cause cells to fail, or environmental factors may damage cells. ## Diabetes - In the chapter narrative, we met Keiko. Keiko has diabetes, a disease caused by dysfunctional cells. Cells in the pancreas normally produce insulin, a chemical that helps other cells in the body absorb sugars from the blood. There are two types of diabetes, type 1 and type 2. In a person with type 1 diabetes, cells in the pancreas do not produce insulin (or do not produce enough insulin). Insulin must be injected into the body. In type 2 diabetes, cells in the body do not respond to insulin, and sugar cannot be absorbed. People with type 2 diabetes must regulate their blood sugar with exercise and diet. In the past, this disease was rarely seen in people under the age of 40. Recently, there have been a growing number of cases reported in teens and children in Canada. These cases appear to be caused by obesity and lack of physical activity. Many health care professionals consider type 2 diabetes an epidemic in developed countries. Fortunately, it may be prevented by eating a healthy diet and leading an active lifestyle. Both types of diabetes, if uncontrolled, can lead to heart disease, blindness, and kidney failure. ## Cancer - Cancer is caused by dysfunctional cells. Cancerous cells divide quickly and uncontrollably and form masses called tumors. However, not all tumors are cancerous. Benign tumors, for example, stay in one place and do not normally affect the function of tissues and organs. In malignant tumors, cancerous cells break away from the tumor, enter the bloodstream, and move to other parts of the body. Malignant tumors interfere with blood supply to healthy cells, causing the healthy cells around the tumor to die. Cancer can be caused by chemicals (such as those found in cigarette smoke) or by infectious diseases, or it can be inherited.