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What does your heart have in common with your eyeball? They are both made of cells. There are over two hundred different types of cells in the human body. Cells for everything in your body from bone to blood. Each cell type is unique in its structure and function. Although these cells are different, they have many characteristics in common. In this lesson, you will learn about cell theory, the differentiation of cells, and the two basic categories into which all cells can be organized.
In 1663, a scientist named Robert Hooke discovered cells. While observing a piece of cork through a microscope, Hooke viewed tiny shapes similar to a honeycomb. The shapes reminded him of the rooms at a monastery, and he called them cells. What Hooke had observed were the dead, empty cells of a plant. Ten years later, Anton van Leeuwenhoek became the first person to view a live cell under a microscope. During the nineteenth century, two biologists named Theodor Schwann and Matthias Jakob Schleiden, developed cell theory. This theory states that the basic, or smallest, unit of life is the cell and that all living organisms are composed of cells.
According to cell theory, all cells reproduce to create new cells. The genetic material of the parent cell is passed to daughter cells. During a type of asexual reproduction called mitosis, a parent cells splits into two identical daughter cells. During sexual reproduction, an egg cell and a sperm cell unite, creating a non-identical daughter cell. The new cell contains half of the mother's genetic material half of the father's, this is how you were created and why you make look somewhat like your mom and somewhat like your dad. Cell theory also states that cells are similar in their chemical make up. For example, all cells, no matter where they are in the body, contain carbon. All cells also change food into energy, which is used to carry out the functions needed to sustain life.
All cells fall into one of the two major classifications – prokaryotes and eukaryotes. Prokaryotes are the largest group of organisms on the planet. They are unicellular organisms with simple internal structures lacking a nucleus and membrane-bound organelles. The nucleus of a cell contains genetic information and controls cellular activity. It is sometimes referred to as the brain of the cell. Prokaryotes do not have a nucleus. Their genetic material forms ring-like strands dispersed throughout the cytoplasm of the cell. Prokaryotes are the most primitive type of cell on earth. Scientists believe they appeared almost four billion years ago. Most prokaryotes are bacteria, such as esherichia coli (E. coli) and staphylococcus, which causes staph infections. Prokaryotes reproduce by mitosis.
Eukaryotes are usually more advanced than prokaryotes. They can be over ten times the size of prokaryotes and have a much larger volume. Although eukaryotes can be unicellular, most are multicellular. Eukaryotes have a true nucleus, membrane-bound organelles, and complex internal structures. Scientists believe eukaryotes appeared approximately one billion years ago. Many hypothesize that eukaryotic cells evolved from prokaryotes. Fungi, plants, animals, and small organisms called protists are all eukaryotes. Reproduction in eukaryotes may occur by mitosis or the fertilization of an egg cell by a sperm cell.
Both prokaryotes and eukaryotes have a cell membrane, cytoplasm, and DNA. Cytoplasm makes up most of the cell volume. DNA contains hereditary information that is passed from parent to child during reproduction. The cell membrane controls the movement of all material into and out of the cell. The cell membrane is semi-permeable, which means it allows some substances to pass through, but not others. It is made of a double layer of lipids (fat-like molecules) and phosphorous molecules. Proteins embedded within the membrane act as passageways into and out of the cell.
The first person to view a cell through a microscope was:
All cells _____.
Are you alive? Is the chair you are sitting on alive? What does it mean to be alive? How are living organisms different from nonliving objects? Although there may be numerous philosophical and theological answers to these questions, the scientific community has come to a consensus on what characteristics all living organisms have in common. To be classified as "living," seven basic characteristics must be displayed. In this lesson, you will learn about the basic characteristics of life.
All organisms are composed of cells. A cell is the fundamental unit of life. Though you might not think it, most organisms are unicellular, meaning they are made of only one cell. Bacteria and protozoa, such as the paramecium, are examples of unicellular organisms. Other organisms, like humans, cats, and trees, are multicellular. This means they are made of more than one cell. In unicellular organisms, all of the processes necessary for life are carried out within one cell. In multicellular organisms, cells are differentiated. The cells in multicellular organisms have different functions. For example, your skin cells carry out different activities than your heart cells. Plants, animals, and fungi are multicellular organisms
Most multicellular organisms have complicated structures. Their cells are organized into different levels. A group of similar cells working together will form tissue. Similar tissues will form an organ, which works together with other organs in a system. For example, your heart is made of individual cells called cardiac myocytes. Together, the myocytes form a type of tissue called cardiac muscle. This tissue forms the heart, which is part of the circulatory system.
Have you ever been outside with a dog on a hot summer day? As the temperature rises, the dog begins to pant. When our bodies get too warm, glands in our skin release a mixture of water and salt called sweat. As sweat evaporates, it cools the skin and lowers body temperature. Sweating is our body's way of maintaining a stable internal temperature. Dogs have only a few sweat glands in their paws, which is not adequate for lowering body temperature. Panting allows fresh air to cool the blood vessels in the dog's nose. This cooler blood is then circulated to the rest of the body.
Living organisms use energy gained from metabolism to keep their internal conditions balanced. Although changes continually occur in the external environment, the internal environment remains the same. This maintenance of internal conditions is called homeostasis. Sweating and panting are examples of temperature homeostasis. Individual cells in an organism also maintain homeostasis. The cell membrane controls the passage of materials into and out of the cell. Waste products must be removed from the cell, while nutrients must be brought in. This balance between incoming and outgoing chemicals is an example of homeostasis in a cell.
Are you the same size as when you were born? After birth, all living organisms increase in cell size or in cell number. A change either in cell size or cell number is called growth. Growth occurs in a predictable pattern predetermined by an organism's genes. For example, the life cycle of a butterfly includes four distinct stages – egg, larva, pupa, and adult. All butterflies will begin life as an egg, grow into a caterpillar, create a cocoon, and complete a metamorphosis. The growth pattern and life cycle for butterflies is predictable and predetermined.The growth of an organism does not just refer to an increase in size. Usually, growth also increases the complexity and internal organization of the organism. For example, tadpoles have tails and gills. As they grow, they develop specialized cells that become arms, legs, and lungs. The same growth occurs in plants. The a apple seed is very simple in comparison to the roots, trunk, branches, bark, leaves, flowers, and fruit of a full-grown tree. Growth is controlled by chemical substances, such as hormones and auxins.
Can two snakes have a baby turtle? Can two turtles have baby alligators? Of course not. The ability to produce exact or close copies of the original organism is important for the continuation of life. Reproduction is an important characteristic of all living organisms. Most unicellular organisms reproduce by a type of asexual reproduction called mitosis. During mitosis, a single parent cell splits into two identical daughter cells. Multicellular organisms, on the other hand, usually reproduce sexually. A female egg is united with a male sperm during fertilization. The new organism that grows from this union has half of the father's genes and half of the mother's.
What happens if you prick your finger on a needle? You pull your hand back, right? If you go out in the sun, you will squint your eyes. Living organisms show responses to changes in temperature, light, chemicals, and other aspects of the environment. The response may be either internal or external. Responses are displayed in several ways. The contraction of a unicellular organism when touched is an example of response. A response are the flight response of an animal when it senses danger from a predator. A plant turning toward sunlight is another example of response.
Have you ever noticed the similarities between a wooly mammoth from the Ice Age and the elephants of today? An elephant resembles the wooly mammoth but they are not the same. The ability to change over a period of time in response to the environment is called adaptation, or adaptability. Living organisms adapt to changes in the environment. Adaptations can be physical, behavioral, or mental. They contribute to an organism's ability to survive and reproduce in certain environments. Adaptation is often linked with natural selection and evolution. In natural selection, organisms that are best adapted to the environment, survive and reproduce. The favorable traits are passed down through generations. Over time, these adaptive traits can cause the evolution of an organism.
The Peppered moth is white with black spots, which helps it blend in with the bark on beech trees. The burning of coal in Great Britain caused many beech trees to become black with soot. Over time, the Peppered moth became all black in order to blend in with the new bark color. What type of example is this? adaption
Take a deep breath. As you inhale, air enters your nose and travels down your windpipe into your lungs. Blood vessels in your lungs carry oxygen from the air to your heart, where it is pumped to the rest of your body. Our bodies are made of different organs that work together to performance specific functions. Individual cells also have different structures calledorganelles. Each type of organelle performs a different function, but they work together to carry out cellular activity. In this lesson, you will learn about some of the main organelles in an animal cell.
What organ in your body do you think is the most important? Your heart? Your brain? What about your skin? The skin is the largest organ in the human body. It protects the body and holds it together. The membrane of a cell is like the skin on your body. It protects the other organelles and encases the cell's cytoplasm. Like skin, the cell membrane is semi-permeable, which means it allows the transfer of some materials, but not others. The membrane keeps harmful materials out and lets beneficial materials in.
The cell membrane is made of special phosphorous molecules and lipids called phospholipids. Phospholipids are shaped like a balloon with two strings. The rounded part of the phospholipid is called the head and the two strings are called the tails. Two layers of phospholipids form the cell membrane. The cell membrane is sometimes called a phospholipid bilayer (bi- meaning two). Embedded within the membrane are special proteins that open and close tiny holes. These holes allow the movement of materials into and out of the cell.
Right now, your eyes are moving to read this sentence. What controls your eye muscles? The brain is the control center for everything in your body. It is the headquarters for all body functions, such as breathing, sleeping, and reading. The nucleus is like the "brain" of a cell. It controls all cell activity, including eating, movement, and reproduction. The nucleus also contains cell DNA. In eukaryotes, the nucleus is enclosed by a double membrane called the nuclear envelope. Like the cell membrane, the nuclear envelope has special openings that allow the passage of material into and out of the nucleus.
When you ride in a car, what makes the car move? Where does the car get its power? Division and other cellular activities require energy. The mitochondriaare the power plants of the cell, like the engine of a car. These organelles convert chemical energy from food into ATP, the main energy source for cellular work. Mitochondria take in nutrients, break them down, and create energy through the process of cellular respiration. One cell has many mitochondria. The number depends on the function of the cell. For example, a nerve cell needs less energy than a muscle cell, and will have fewer mitochondria. Kind of like a fast car needs a bigger engine than a slower car.
The mitochondria are enclosed by two membranes. The outer membrane covers the organelle, while the inner membrane forms a compartment filled with a special fluid called the mitochondrial matrix. The inner membrane contains many folds called cristae, which increase the surface area inside the organelle. This increases the efficiency of the chemical reactions, allowing
If the mitochondria are the cell's power plant and the nucleus is the command center, then the endoplasmic reticulum (ER)is the cell's factory. This organelle is like a packaging and storage facility. The ER is divided into two types – rough and smooth. The rough ER looks like sheets of bumpy membrane. The bumps are ribosomes attached to the organelle. The function of the rough ER is protein synthesis, in other words it's where the proteins are made. Ribosomes create the amino acids that are assembled into proteins inside the ER. Some of the proteins are used by the cell, while others are packaged and sent out through the cell membrane for use elsewhere. The smooth ER is a network of tubes attached to the rough ER. It is called smooth ER because it lacks ribosomes. The smooth ER is responsible for the production and storage of steroids and lipids, also known as fats. It also stores calcium ions used by muscle tissue.
What do you think happens to products once they are manufactured? When a television or pair of sneakers is created, how do they make it from the factory to the store? Manufactured products are picked up by trucks and transported to other locations. In a cell, the Golgi body is like the truck that picks up products from the factory. This organelle (sometimes called the Golgi apparatus or Golgi complex) works closely with the endoplasmic reticulum. It receives simple molecules manufactured by the ER and combines them into more complex molecules. These larger molecules are either shipped out of the cell or stored for later use. The Golgi body also creates lysosomes, sacs of digestive enzymes that break down the cell's food and waste.
One of these things is not like the other one. Have you ever played a game where you had to list the differences between two pictures? Maybe the flower in one picture has more petals than the flower in the other picture. Or maybe the flower is missing and there is a cactus in the picture instead. Comparing plant and animal cells is very similar. Plant cells have some organelles that animal cells do not, and vice versa. Both plant and animal cells have a nucleus, mitochondria, cell membrane, cytoplasm, endoplasmic reticulum, and Golgi body. Only animal cells have lysosomes. In this lesson, you will learn about the main organelles unique to plant cells.
Cell walls are much thicker than cell membranes. When Robert Hooke used a microscope to view cells for the first time in 1665, he saw the thick cell walls of a cork sample, which comes from trees. Most plant cells have both a primary and secondary cell wall. The primary cell wall is thinner and more flexible than the secondary cell wall. Its elasticity allows the cell to grow. Once the cell stops growing, the secondary wall forms inside the primary wall. The secondary wall is thicker and more rigid than the primary wall. The main chemical component of cell walls is a complex carbohydrate called cellulose. Cellulose is made of thousands of sugar molecules linked end to end. It is extremely durable, which makes it useful for paper, linen, and cotton products.
Close your eyes and concentrate. Focus all your energy on making food with your body. Did it work? No matter how hard you try, your body will never be able to make its own food. Unlike plants, humans are not autotrophs. Our cells are unable to make food by using photosynthesis. What makes plant cells so different? They contain special organelles calledchloroplasts that capture sunlight and use it to combine carbon dioxide and water into sugar and oxygen. Organisms without chloroplasts cannot create their own food.
Chloroplasts look like flat, oval disks. Like mitochondria, they have two membranes. The outer membrane encases the entire organelle. The inner membrane contains a thick fluid called stroma, which makes up most of the chloroplast's volume. Spaced throughout the stroma are stacks of hollow disks called grana. The grana contain chlorophyll, which traps solar energy for use during photosynthesis. Plants are not the only organisms containing chloroplasts. Certain bacteria and algae also have this organelle, which enables them to make their own food.
Where do you store things in your room? Do you have a special chest at the foot of your bed or a designated drawer in your dresser? Maybe you just use your closet. In a plant cell, food, waste, and water are stored in special organelles calledvacuoles. Both plant and animal cells have vacuoles, but only plants have a large central vacuole. The central vacuole is like a walk-in closet. It is able to store a large amount of chemicals for the cell, primarily salts, minerals, proteins, and water.
In addition to storage, the central vacuole also helps the cell maintain its shape. When a plant is fully hydrated, the central vacuole is filled to capacity with water. The fluid-filled organelle presses against the cell wall, creating a special type of pressure called turgor. A plant with high turgor has healthy cells with a good deal of rigidity. When a plant is dehydrated, its central vacuole is only partially full. It does not press against the cell wall, which reduces turgor and causes the plant to wilt. If the plant receives water in time, the central vacuole will re-fill and turgor will increase.
The middle lamella _____.
Think about trying to lift a car. Could you do it alone? How many of your friends would you need to actually lift a car? You are like a cell. A cell by itself cannot do all the things that can be done by a group of cells. A group of similar cells that perform a unified function is called tissue. Cells in a tissue have similar structures, shapes, and responsibilities. The tissue level is the second tier of organization. It is more complex than the cell level because it involves several cells working together. In this lesson, you will learn about plant tissues.
Do plants have skin? Although it is very different from animal skin, plants do have a special outer covering made of dermal tissue. The outer dermal layer of a plant is called the epidermis. Like animal skin, the epidermis is the first line of defense against damage and disease. In trees and other woody-stemmed plants, the epidermis is replaced by another dermal tissue called periderm. The periderm, commonly called bark, is made of hard, dead, cork cells. Dermal tissue has four important functions. First, it protects the plant against physical damage and illness. Second, it helps the plant retain water. Third, it regulates the exchange of oxygen and carbon dioxide with the atmosphere. Finally, dermal tissue, particularly in the roots, absorbs water and minerals from the environment.Have you ever touched wax paper? The epidermis of many plant leaves and stems have a similar waxy coating called thecuticle. Like animals, plants "sweat" when they are hot. Plants release water into the air through a process calledtranspiration. The cuticle helps keep the plant from losing too much water. The cuticle also prevents the plant from absorbing much water through its leaves or stems. Since plant roots need to absorb water and nutrients from the soil, their dermal tissue does not have a cuticle.
Have you ever used a straw to drink a milkshake or glass of apple juice? When you use your mouth to suck, liquid from the bottom of the glass moves up the straw. Vascular tissue in plants works like a straw. It pulls water and nutrients from the soil and transports it up the stem to the leaves. Vascular tissue also carries food from the leaves to the rest of the plant. There are two types of vascular tissue - xylem and phloem. Xylem is made of dead cells that form microscopic tubes. These tubes transport water and dissolved minerals from the roots to the rest of the plant. Like xylem, phloem cells form microscopic tubes, but phloem is living. The tubes transport sugars and nutrients from the leaves to the rest of the plant. Together, xylem and phloem form a vascular bundle.
Have you ever eaten celery, carrots, or lettuce? If so, you have eaten ground tissue. Plants are made mostly of ground tissue, which fills the spaces between the epidermis and vascular tissue. Ground tissue is responsible for photosynthesis, food storage, and plant support. In roots and stems, ground tissue forms a food storage area called the cortex. Food is also stored in stems in a central area called the pith. In leaves, ground tissue is found in the mesophyll layer that contains photosynthetic cells. Ground tissue is made primarily of three types of cells - parenchyma, collenchyma, and sclerenchymaParenchyma cells are the most abundant type in plants. They have thin walls, many chloroplasts, and can differentiate into other cell types if necessary. If a plant is injured, parenchyma cells can change into other types to help repair the damage. The primary job of parenchyma cells is food storage and photosynthesis. Collenchyma cells have thick wall that provide the plant with flexibility and support. These cells are mainly found in young plants that are still growing. They are able to elongate and stretch as the plant grows. Sclerenchyma cells have the thickest walls. These cells are only found in older plants that have stopped growing. Most sclerenchyma cells are dead.
Ground tissue _____.
In which of the following locations would you most likely find parenchyma cells?
What did you have for dinner last night? Chicken? Salmon? Steak? If you ate poultry, fish, or meat, you ate the muscle tissue of an animal. Depending on the amount of fat on your food, you may have eaten connective tissue, too. Add epithelial tissue to the menu if your piece of chicken had skin on it. Animals have four main types of tissue: epithelial, connective, nervous, and muscle. In this lesson, you will learn about these types of tissue.
Squamous cells are flat and irregularly shaped. The thinness of these cells allows easy passage of material, which is why they are found in the lungs, kidneys, and blood vessels. Cuboidal cells are shaped like cubes. Their nuclei are usually found in the center of the cell. Columnar cells are longer than they are wide, which allows for a greater amount of surface area. Columnar cells are found in the digestive tract where surface area for absorption is important.
What do you think bones and blood have in common? Since bone is solid and blood is liquid, it may not seem like they have any common characteristics, but they are both types of connective tissue. As its name suggests, connective tissue has a "connecting" function. It supports and connects other tissues. Without this type of tissue you would be unable to stand and the organs in your body would simply float around. Connective tissue can be liquid, solid, or semi-solid.
Unlike epithelial tissue, connective tissue is made of cells scattered throughout a web of fibers. The most common type of connective tissue is loose connective tissue, which holds organs and other tissue in place. Adipose tissue contains fat cells and their purpose is to cushion, insulate, and store energy. Fibrous connective tissue is denser than loose connective tissue. It forms tendons, which connect muscle to bone, and ligaments, which join bones together. Cartilage is a flexible, rubbery type of connective tissue. It is found at the ends of bones and in the ears and nose. Bone is made of hard connective tissue embedded in calcium salts. Blood is liquid connective tissue.
What would happen if you couldn't tell if things were too hot? You could easily burn your skin picking up a hot pan from the stove or washing your hands in scalding water. We need to be able to feel the world around us. We can do this because of nervous tissue. The main function of nervous tissue is communication between different parts of the body. It is found in the brain, spinal cord, and nerves. Signals from nervous tissue control a variety of body processes, such as moving, thinking, and remembering.
The cells in nervous tissue are called neurons. Each neuron has a cell body, which contains the nucleus, a long fiber called an axon, and a dendrite. Neurons do not connect to one another. They transmit signals across a space called a synapse. Chemical changes in the synapses cause the messages, or impulses, to move from nerve cell to nerve cell. Nerve impulses move like electric signals moving through wires. They move at almost the speed of light. Some neuron messages travel at a speed of about 450 miles per second. This speed enables us to react quickly to danger. Dendrites receive the signals, while axons transmit the signal to other neurons. Nervous tissue forms the brain, spinal cord, and nervous system.
Imagine trying to run, skip, swim, or play the violin without any muscles. How would you move your body? Muscle tissue is responsible moving your body and organs, such as pumping your heart. Since it has so much work to do, muscle tissue is usually the most abundant tissue in an animal. It is made of long cells called muscle fibers, which are able to contract. During a contraction, the muscle fibers shorten and a part of the body moves. When the fibers relax, they elongate and return to their resting position. You can see muscle contractions in your arm by "making a muscle" with your bicep. Notice how your bicep gets shorter and rounder when you bring your fist toward your shoulder. When you relax your arm, the bicep elongates and is at rest.
There are three types of muscle tissue - skeletal, smooth, and cardiac. Skeletal muscle is attached to bones by fibrous connective tissue. It is often called voluntary muscle because it can be controlled. When you type on the computer, you decide which keys your fingers strike and how your hand moves. Skeletal muscle is also called striated muscle because it has alternating bands of dark and light stripes. Smooth muscle is found in the inner lining of organs, such as the digestive tract and arteries. The cells in smooth muscle are long and spindle shaped. They contract more slowly than skeletal muscle, but can hold the contraction for a longer period of time. Smooth muscle is involuntary because it cannot be controlled. Cardiac muscle is found only in the heart. It is striated, like skeletal muscle, but it is involuntary like smooth muscle.
Epithelial tissue _____.
Connective tissue _____.
Choose all that apply. Which of the following can be found in nerve cells?
Do you play an instrument? Imagine you play the violin. When you play by yourself, you are like a cell. When you get together with another violin player, you are acting like tissue. If you add a cello and a viola to your group, you form a group of four string instruments called a string quartet. With the help of other instruments, you can play more complicated music.An organ is like a string quartet. It is the third level of cell organization in which groups of similar tissue work together to perform specific functions. Organs are more complex than the tissues they are made from, which enables them to perform functions that tissues cannot carry out on their own. In this lesson, you will learn about three major organs in the human body.
Have you ever made a promise by crossing your heart? Have you ever doodled someone's name inside a heart on a piece of scrap paper? When you hear the Star Spangled Banner before a baseball game, where do you place your hand? The heart is an important symbol of trust, romance, and patriotism. It is also an important organ in your body. Without the heart, you would be unable to pump blood, which means the trillions of cells in your body would never receive oxygen, water, nutrients, or food.
The heart is the main organ in the cardiovascular system. Its job is to pump oxygen-rich blood to the body and oxygen-poor blood to the lungs. The heart is the hardest working organ in the body. it pumps all day, every day, for your entire life without ever pausing to rest. With an average rate of 70 beats per minute, the heart pumps the equivalent of 2,000 gallons of blood around your body every day. Over the course of a 70-year life, the heart will beat approximately 2.5 billion times. Lucky for us, the heart is made of cardiac muscle. Unlike smooth or skeletal muscle, cardiac muscle does not get tired.
With such an important responsibility, you might think the heart is a large organ. The average adult heart weighs only 9 ounces. It is about the size of two clenched fists. The heart is divided into four hollow chambers. The upper chambers are called atria (singular atrium), and the lower chambers are called ventricles. Atria receive blood and ventricles pump it out of the heart. Special one-way valves between chambers keep blood from flowing backwards. The thumping sound known as the "heartbeat" is actually the noise made by valves as they close.
Take a minute to relax and focus on your breathing. Concentrate on the movement of your lungs as you inhale and exhale. What do you feel? As you breathe in, your lungs expand and fill with air. You can feel your chest move when you inhale. As you breathe out, your lungs release carbon dioxide into the air. You feel your chest fall when you exhale because your lungs are deflating. The lungs are the second largest organ in the body. They absorb oxygen from the air and remove carbon dioxide from your blood.
Inhaling brings oxygen-rich air into the lungs and exhaling sends carbon dioxide out into the air. What happens in between breaths? From the outside, your lungs look like pink sponges, but inside, they are more like trees. The windpipe in your throat, called the trachea, splits into two tubes called bronchi. One bronchus enters the right lung, and the other enters the left lung. Inside each lung, the bronchus splits off into smaller tubes, like the branches of a tree. The smallest tubes, calledbronchioles, are the thickness of a strand of hair. Each lung has about 30,000 bronchioles.
Do you have a favorite memory from your childhood? What about a favorite food or song? Is there a book or movie you enjoy more than any other? All of these things have one thing in common - your brain. Without the brain, you would be unable to remember a memory, taste a meal, hear a song, or see a movie. The brain is the main organ in the nervous system. It controls the body and interprets signals from sense organs, like the eyes, ears, and tongue.
The average adult brain weighs about three pounds. It is pale gray in color and has a wrinkled, folded appearance. There are three main areas of the brain: the cerebrum, cerebellum, and brain stem. The cerebrum is the largest part of the brain. It is responsible for speech, thought, emotion, sensations, and memory. Whenever you talk, think, remember, cry, or imagine, you are using your cerebrum.The second largest part of the brain is the cerebellum. It sits below the cerebrum and is responsible for muscle coordination and balance. Using a computer to type requires a lot of coordination between eye muscles and the muscles in your hands. The cerebellum keeps track of all these muscle movements. The brain stem is the smallest part of the brain. It is located below the cerebellum and connects the brain to the spinal cord. The brain stem is in charge of involuntary muscles, such as the heart and stomach.
Oxygen is _____.
Marissa is adding numbers in her head. Which part of her brain is she using?
The heart _____.
Which of the following statements is true?
When you inhale _____.
Plant leaves _____. contains many parenchyma cells
Which of the following statements is true?
Have you ever watched a professional basketball game on television? Each player on the team has a job to do. Generally, the point guard organizes offense, the shooting guard shoots the ball, the center protects the basket, and the forwards do a little of everything. Every player can dribble, shoot, and block shots, but the team is not effective unless all the players cooperate with one another. The same is true of our bodies. There are several organ systems that have their own jobs to do, but the body does not work effectively unless the systems cooperate. In this lesson, you will learn about organ systems and how they depend on one another.
Imagine a classroom. There are lots of different pieces that make up that classroom like students, a teacher, desks and chairs, books and so on. The classroom as a whole would be considered a system. A system is an organized group or related objects that form a whole. The individual pieces of a system work together to complete certain tasks, just like all of the pieces of a classroom work together to create learning. The output from one part of a system becomes the input for another part. This output can be material, energy, or information. A system relies on the correct function of all its parts. Could your classroom work if one of the pieces wasn't there? If there were no students would the classroom function? Improper functioning in one area can result in complete system failure.
In biology, a system is a group of organs that work together to perform a specific function. The system level is the fourth level of cellular organization. Systems are more complex than the organs and tissues that they are composed from. Like other systems, biological systems rely on the proper functioning of all organs and tissues. Failure in one area can seriously affect the function of the system as a whole. Infection, disease, and injury are factors that can damage a system and cause failure. For example, hepatitis can cause severe liver damage. Left untreated, hepatitis can cause life-threatening liver failure.
When food is chewed in the mouth, enzymes in saliva break down starch into sugar. Swallowed food travels down the esophagus into the stomach, where it is further broken down by stomach acids. The liver secretes special enzymes that help the stomach digest fats. Nutrients and water from digested food is absorbed by the intestines before it is passed out of the body as waste.
Have you ever held your breath while swimming underwater? Maybe you have held your breath to rid yourself of hiccups. The scientific term for holding your breath is apnea, which literally means "without air." When you hold your breath, your respiratory system is unable to obtain fresh oxygen from the air. Since the human body cannot store much oxygen, it is not a good idea to hold your breath for longer than a minute and a few seconds. Once you start breathing again, your lungs fill with air to absorb oxygen into the blood.
Biceps, quadriceps, and triceps. Do these words sound familiar? They are major muscles in the human body. Biceps are attached to the front of your arm bones, while triceps are attached to the back. Quadriceps are the large muscles in your thigh. All three of these muscles are part of your body's muscular system. The main job of this system is body movement. It is made of all the skeletal muscles in the body. Skeletal muscle is voluntary, which means it can be controlled and directed. It is attached to bones by tendons.
The respiratory system _____.
Imagine a soccer team without a coach. How would the players know which plays to run? An organ system is like a sports team. Individual players, or organs, have specific jobs. When everyone works together, the system functions properly. The nervous system is like the coach of a sports team. It directs the other organ systems and controls body activities. In this lesson, you will learn about the nervous system, immune, excretory, endocrine, reproductive, and cardiovascular systems.
The nervous system is the body's command center. It controls and coordinates the body's activities, which means it interacts with all the other organ systems. After a large meal, nerves in your stomach send signals to your brain indicating you are full. The brain sends signals to the endocrine system, which decreases hunger. When you exercise, your nervous system sends signals to the cardiovascular and respiratory systems to increase heart rate and breathing rate. When you are resting, your nervous system sends signals to decrease heart rate and breathing rate. Nerves in muscles send information to the brain about the body's and movement. The brain combines this information with signals from sense organs to coordinate movement. Even the joints between your bones have special sensory neurons that send signals about the body's position to the brain.
The endocrine system is made of all the organs that secrete hormones. This includes the pituitary gland, thyroid, thymus, adrenal glands, pancreas, testes, and ovaries. The endocrine system works closely with the nervous system to regulate body functions, such as digestion and temperature. Like the nervous system, the endocrine system interacts with nearly every other organ system. The cardiovascular system transports hormones throughout the body via blood. These hormones can affect the function of all the organs in the body.
Hormones are important chemicals in the body. They can influence the body's growth, cell reproduction, immune system activity, and emotional responses. In a frightening situation, hormones can cause a heightened awareness. Adrenal glands located on top of each kidney are also important for the release of adrenaline. This hormone gives you the "rush" associated with intense situations and the tingly feeling when you are scared. The reproductive glands, called gonads, are in the pelvic area. A woman's gonads are called ovaries; a man's are called testes or testicles. Gonads are responsible for producing reproductive cells, eggs and sperm.
The reproductive system is unlike other body systems in that it is not essential for keeping an individual alive, but it is essential for keeping a species alive. As mentioned in the section on the endocrine system, the reproductive system produces hormones. The reproductive system also produces the reproductive cells. The male gamete is called sperm and the female gamete is called ovum. Conception or fertilization occurs when the female gamete (egg cell) is fertilized by the male gamete (sperm cell). Both the female and the male reproductive systems are necessary for reproduct
Since female egg cells and male sperm cells meet in the female body in order to reproduce, the task of nurturing developing offspring is unique to the female reproductive system.
Each sex, male and female, has its own distinctive reproductive system; meaning they are different in shape and structure. The female's reproductive organs are located entirely in the pelvis. The main organs of the female system are the vagina, uterus, fallopian tubes, and ovaries. The ovaries produce the egg cells that are necessary for reproduction. When an egg is produced in an ovary, it migrates through the fallopian tubes toward the uterus. If an egg cell is fertilized by a sperm cell, it is implanted in the uterus. This is where a fetus grows and develops. When a baby is ready to be born, muscular contractions push it from the uterus, through the vagina, and into the world!
Have you ever cooked pasta and used a colander to separate the water from the noodles? The colander filters out the water as waste. Kidneys are like colanders in your body because they filter waste from your blood. Kidneys and the organs in the urinary tract make up the excretory system. This system works together with the cardiovascular and endocrine systems to remove liquid waste from the body. Dissolved waste is carried through the kidneys by blood. Hormones released by the endocrine system regulate urine production. When you are dehydrated, less urine is produced to keep as much water in the body as possible.
Think back to the last time you were sick. Did you have a fever? Although it may be uncomfortable, a mild fever is actually good for your body when it is ill. When foreign invaders, such as bacteria or viruses, enter the body, the immune system increases the internal temperature. Most germs can only survive and reproduce within a certain temperature range. Fever is an effective defense mechanism for fighting illness, which is the main responsibility of the immune system. Unlike other organ systems, the immune system is not a group of linked organs, but a collection of body responses. The immune system is often associated with white blood cells, but these germ-fighting cells are actually part of the lymph system.
The lymph system is made of bone marrow, lymph nodes, the thymus, and spleen. Bone marrow is a thick, jelly-like substance found in the center of bones. It creates white blood cells, the primary defender against foreign intruders. Lymph nodes are clusters of white blood cells found through the body. When you are sick, your lymph nodes swell with extra white blood cells. Sometimes, you can feel the swollen nodes on the outside of your throat beneath your jaw. The thymus and spleen are special organs that store white blood cells. These organs also produce lymph fluid, a clear liquid used to transport white blood cells into the blood.
Put your hand on your heart. Do you feel your heartbeat? Each time your heart beats, blood is pumped through blood vessels to your entire body. The heart and blood vessels make up the cardiovascular system. This system supplies the body with nutrients and oxygen. It also carries cellular waste to other organs, where they are removed from the body. The cardiovascular system is often called the circulatory system. It works with almost all the body's organ systems. In addition to carrying oxygen for the respiratory system, blood transports nutrients from the digestive system to cells all over the body. It carries hormones for the endocrine system, waste for the excretory system, and white blood cells for the immune system.
The heart is made of involuntary cardiac muscle. It has two upper chambers called atria and two lower chambers called ventricles. The left atrium receives oxygen-rich blood from the lungs. The blood passes into the left ventricle through a heart valve, where it is pumped to the rest of the body. Oxygen-poor blood from the body flows into the right atrium. It passes into the right ventricle, where it is pumped to the lungs. Once in the lungs, blood drops off carbon dioxide and picks up fresh oxygen. The oxygen-rich blood flows into the left atrium, and the cycle begins again.
Fertilization occurs when:
Choose all that apply. The main organs of the female reproductive system include:
A fever is a useful defense mechanism because it limits the ability of germs to reproduce their cells.
The cardiovascular system transports material for the _____.
Which of the following statements is true?
Think back to the last time you were sick. Did you have a fever? Normally, your body maintains a constant temperature of about 98.6°F. When you get sick, the immune system sends white blood cells to fight the germs in your body. Your body also turns up the heat. This increase in body temperature is called a fever. Mild fevers are actually helpful in fighting an illness. Many bacteria and viruses cannot survive in above-normal body temperatures. Once the germs have been destroyed, your body turns down the heat and your fever goes away. Your internal temperature balance is restored. In this lesson, you will learn about maintaining an internal balance.
To qualify as living, an organism must be able to maintain a stable internal condition. The environment is always changing, but the internal state of an organism must remain constant. The process by which internal environments are regulated is called homeostasis. Although homeostasis usually refers to regulation at the organism level, it also occurs at the cellular level. The cell membrane regulates the movement of materials into and out of the cell. Nutrients and food move into the cell, while waste is moved out. The nutrients taken into the cell balance the waste removed from the cell, and homeostasis is achieved.
Temperature is an important internal condition for all organisms. Body temperatures must be kept within a certain range, or the organism will not survive. For example, the normal body temperature range for humans is 97.6°F (36.4°C) to 99.6°F (37.6°C). Hypothermia occurs when body temperature falls a few degrees below 97.6°F. Hypothermia is a life-threatening condition in which the body loses heat faster than it can generate it. Sometimes the body has too much heat. Fever occurs when body temperature rises a few degrees higher than 99.6°F. Like hypothermia, a very high fever can be life threatening.
The maintenance of internal temperatures within an acceptable range is called thermoregulation (thermo meaning "heat"). Warm-blooded animals generate their own heat through metabolism, while cold-blooded animals must absorb heat from the external environment. A lizard basking in the sun raises its body temperature by absorbing heat. Similarly, a frog submerged in water lowers its body temperature by surrounding itself with a cooler environment.
Have you ever "seen" your breath on a cold day? Animals and plants lose water during respiration. When you breathe out, water vapor in your breath forms a misty cloud. Like temperature variations, small changes in water levels can cause life-threatening problems for an organism. Water lost from respiration other body functions, such as sweating, must be replaced. Animals replace water by drinking and eating, while plants absorb water from the environment. If the amount of water lost is greater than the amount of water gained, the organism becomes dehydrated. Its cells shrivel and eventually die. Too much water can also be a problem. If the amount of water gained is greater than the amount of water lost, the organism's cells can swell and burst. It is important for organisms to maintain a balance.
Homeostasis requires the ability to sense and respond to changes in the environment. When a change is detected, a homeostatic response will ensure regulation of the organism's internal conditions. Many environmental changes are sensed by an organism's nervous system. For example, changes in temperature are picked up by the skin. Other changes are detected at a chemical level. When muscles increase their oxygen use, they also increase their carbon dioxide production. This increase in carbon dioxide causes blood vessels to enlarge, allowing more oxygen-rich blood to reach the muscles.
An organism is a system. Within all successful systems is a mechanism called feedback. When part of the output of a system is fed back into the system as part of its input, a feedback loop is created. Feedback loops can be either negative or positive. Negative feedback occurs when the output of a system is reduced or completely stopped. When your body temperature rises, your skin releases a liquid mixture of salt and water called sweat. As it dries, sweat cools your skin and lowers your body temperature. Sweating is a type of negative feedback because the rise in temperature is slowed or stopped. Think of negative feedback like the air conditioner in your home. You set the thermostat for 75 degrees and when the house gets too hot, the air conditioner kicks in until the room is back down to 75 degrees.
The homeostasis control center in vertebrate animals is the hypothalamus. This region of the brain regulates body temperature, blood pressure, heartbeat, metabolism, and blood sugar. The hypothalamus links the nervous system to the endocrine system through a connection to the pituitary gland. This gland is often called the "master gland" because it controls all the other glands in the endocrine system. Hormones are special chemicals secreted by organs in the endocrine system. In animals, hormones are released directly into the blood. In plants and other organisms, hormones are released by special tissues.
Which of the following conditions are regulated by homeostasis?
When calcium blood levels fall, a gland in the body releases a special hormone. This is a positive feedback loop, which means _____.
The endocrine system _____.
Which of the following systems use the cardiovascular system for the transport of materials?
Which of the following statements is true?
Digestion begins when starch is broken down in the _____.
When you are sick, extra white blood cells are created by the _____.
What is the lowest level of organism organization?
The nervous system _____.
Which of the following statements is true?
Connective tissue _____.
How are plant and animal cells different?
What does the cardiovascular system do?
The cell membrane _____.
Without a cuticle, a plant _____.
The lungs _____.
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