Science Review 2 PDF

# Unit 2.0: Cell - A- Brate ## Overview: Through this unit, students will explore how cells contribute to the function of living organisms. Students will gather information and use this information to support explanations of the "structure and function" relationship of cells. They will communicate...

# Unit 2.0: Cell - A- Brate ## Overview: Through this unit, students will explore how cells contribute to the function of living organisms. Students will gather information and use this information to support explanations of the "structure and function" relationship of cells. They will communicate their understanding of cell theory through models and analogies. They will gain a basic understanding of the role of cells in body systems and how those systems work to support the life functions of the organism. ## Enduring Understanding: - All living things are composed of cells. - The ways cells function are similar in all living organisms. - Many basic functions of organisms occur in cells. - Within the cell are specialized parts for the transport of materials, energy capture and release, protein building, waste disposal, information feedback and movement. - Different body tissues and organs are made of different kinds of cells. ## Essential Questions: - How do we know if something is alive? - How do the structures of organisms contribute to life's functions? - How can one explain the ways in which cells contribute to the function of living organisms? ## Topic/Content In this unit, we will learn about: - Introduction to cell - Cell Theory - Plant and Animal cells - Cell structure and Function - Cell Model ## Essential Vocabulary: Cells, Cell Wall, Cell Membrane, Nucleus, Mitochondria, Chloroplast, Ribosome, Plasma Membrane, Vacuole, Lysosome, Plastids, Structure, Function, Levels of Organization, Interdependence, Golgi Body, Chlorophyll, Endoplasmic Reticulum, Cytoplasm # Microscopes: Unlocking the Hidden World Microscopes are powerful tools that allow us to see and explore the incredibly small world that is usually invisible to the naked eye. They play a vital role in scientific research, healthcare, and various other fields. Let's delve into the fascinating world of microscopes: ## What is a Microscope? A microscope is an optical instrument that magnifies tiny objects, making them appear larger and more detailed. It achieves this by using lenses and various optical components to bend and focus light. ## Parts of an Optical Microscope: - Eye piece - Body tube - Nose piece - Objective lens - Stage - Condenser - Mirror - Base - Course adjustment knob - Fine adjustment screw - Handle - Pillars **Descriptions:** - **Eyepiece**: This is where you look through the microscope. It contains a magnifying lens. - **Objective Lenses**: These are the lenses closest to the specimen and come in various magnifications. - **Stage**: The stage holds the specimen being observed. - **Illuminator**: The illuminator is a light source that shines light through the specimen. - **Coarse and Fine Adjustment Knobs**: These knobs help you focus on the specimen by adjusting the distance between the objective lens and the specimen. ## How Microscopes Work: 1. **Magnification**: Microscopes use multiple lenses to magnify objects. The eyepiece lens typically magnifies 10 times, and the objective lens can be switched to different magnifications. The total magnification is calculated by multiplying the eyepiece magnification by the objective lens magnification. 2. **Illumination**: Light from the illuminator passes through the specimen and into the objective lens, allowing you to see the specimen. ## What Microscopes Can Reveal: Microscopes are used to observe and study various tiny objects and organisms, including: - **Cells**: Microscopes have been crucial in understanding the structure and function of cells, the basic building blocks of life. - **Microorganisms**: Microscopes allow us to study bacteria, viruses, and other microorganisms that are invisible to the naked eye. - **Tissues and Organs**: They help in the examination of tissues and organs for medical diagnoses and research. - **Nanoparticles**: In materials science, microscopes are used to investigate and manipulate nanoparticles with precision. ## Research: Choose a specific kind of microscope and research how it is used, whether it is used to view live or dead samples and its range of magnification. # Introduction to Cells: The Building Blocks of Life Cells are the basic structural and functional units of all living organisms. They are often referred to as the "building blocks of life" because they are the smallest entities that can perform all the functions required for life. The study of cells is fundamental to biology, as it provides insights into the complexity and diversity of life forms on Earth. This introduction will explore the significance of cells, their structure, and their role in the living world. # Types of Cells in the Body - Stem Cells - Bone Cells - Blood Cells - Muscle Cells - Fat Cells - Skin Cells - Nerve Cells - Endothelial Cells - Sex Cells - Pancreatic Cells - Cancer Cells # Significance of Cells: Cells are crucial to life for several reasons: 1. **Fundamental Units**: Cells are the smallest units of living organisms. Every living thing, whether it's a bacterium, a plant, an animal, or a human, is composed of one or more cells. Understanding cells is essential for comprehending the biology of all life forms. 2. **Structural and Functional Diversity**: Cells exhibit remarkable diversity in structure and function. Different types of cells are specialized for various tasks within an organism. For example, nerve cells transmit signals, muscle cells contract, and red blood cells carry oxygen. 3. **Basis of Health and Disease**: Many diseases and health conditions result from problems at the cellular level. Understanding cellular biology is critical for diagnosing, treating, and preventing diseases. # Cell Structure: While cells come in various shapes and sizes, they share common structural components: 1. **Cell Membrane**: The outer boundary of a cell that separates its internal environment from the external surroundings. It regulates the passage of substances in and out of the cell. 2. **Cytoplasm**: The gel-like substance that fills the interior of the cell, where various cellular organelles and structures are suspended. 3. **Nucleus**: Often referred to as the cell's control centre, the nucleus contains genetic material (DNA) that governs the cell's activities and heredity. 4. **Organelles**: These are specialized structures within the cell, each with specific functions. Common organelles include mitochondria (energy production), endoplasmic reticulum (protein synthesis), and Golgi apparatus (packaging and shipping). 5. **Cytoskeleton**: A network of protein filaments that provides structural support to the cell and facilitates intracellular transport. 6. **Ribosomes**: Tiny structures responsible for protein synthesis, where amino acids are assembled into proteins. # Types of Cells: Cells can be broadly categorized into two main types: - **Prokaryote:** These are simpler and lack a true nucleus. Bacteria and archaea are examples of organisms with prokaryotic cells. - **Eukaryote**: More complex, eukaryotic cells have a defined nucleus and membrane-bound organelles. All multicellular organisms, including plants, animals, and humans, consist of eukaryotic cells. # Animal Cells: ## Structure of Animal Cells: - Cell Membrane: The outer boundary that separates the cell’s interior from its external environment, regulating the passage of substances in and out of the cell. - Nucleus: The central control centre of the cell, housing the genetic material (DNA) responsible for directing cellular activities. - Cytoplasm: A gel-like substance that fills the cell’s interior, containing various organelles. - Mitochondria: Organelles responsible for energy production through cellular respiration. - Endoplasmic Reticulum (ER): A network of membranes involved in protein synthesis and lipid metabolism. Rough ER has ribosomes on its surface, while smooth ER does not. - Golgi Apparatus: Responsible for modifying, sorting, and packaging proteins and lipids for transport within or outside the cell. - Ribosomes: Tiny structures that assemble amino acids into proteins. - Lysosomes: Organelles containing enzymes that break down waste materials and cellular debris. - Centrioles: Structures involved in cell division (mitosis and meiosis) in animal cells. - Cytoskeleton: A network of protein filaments (microfilaments and microtubules) that provides structural support and facilitates intracellular transport. - Vesicles: Membrane-bound sacs involved in various cellular processes, such as transport and storage. ## Functions of Animal Cells: - Animal cells are highly adaptable and can perform a wide range of functions, including cellular respiration, secretion, movement, and responding to stimuli. - They make up the tissues, organs, and organ systems of animals, enabling them to carry out complex life processes. # Plant Cells: ## Structure of Plant Cells: - Cell Wall: A rigid outer layer made of cellulose that provides structural support and protection to the cell. - Cell Membrane: Similar to animal cells, it regulates the passage of substances in and out of the cell. - Nucleus: The control centre containing DNA. - Cytoplasm: Like in animal cells, it surrounds the organelles. - Mitochondria: Responsible for energy production. - Chloroplasts: Unique to plant cells, chloroplasts are involved in photosynthesis, where they convert light energy into chemical energy (glucose). - Endoplasmic Reticulum (ER): Involved in protein and lipid metabolism. - Golgi Apparatus: Responsible for modifying and packaging proteins and lipids for transport within or outside the cell. - Ribosomes: Synthesise proteins - Lysosomes: Involved in waste breakdown, though less common in plant cells. - Central Vacuole: A large, central sac that stores water, nutrients, and waste materials, providing turgor pressure for structural support. - Plasmodesmata: Channels that connect plant cells, facilitating communication and transport between them. - Cytoskeleton: Provides structural support. - Vesicles: Used for transport and storage, similar to animal cells. ## Functions of Plant Cells: - Plant cells, through photosynthesis, convert light energy into glucose, a vital source of energy for the plant and other organisms. - They form the building blocks of plant tissues, enabling the growth and development of the plant. - Plant cells, collectively organised into tissues, make up the various structures of plants, including roots, stems, leaves, and flowers. **"If plant and animal cells had personalities, what do you think they would be like? Imagine and describe their character traits, hobbies, and even jobs these cells might have. Additionally, predict how their unique personalities could affect their roles in living organisms. Get creative and have fun!"** # Cell Theory: The Foundation of Modern Biology Cell theory is one of the most fundamental principles in biology, providing a framework for understanding the structure, function, and organisation of all living organisms. It represents a cornerstone of biological knowledge and has been refined and expanded upon over centuries. Cell theory comprises three main principles that collectively explain the significance of cells in the living world: 1. **All living organisms are composed of cells:** - Cell theory asserts that every living organism, regardless of its size or complexity, is made up of one or more cells. This principle suggests that cells are the basic structural and functional units of life. - This idea was first proposed by the German scientist Matthias Schleiden, who observed that plant tissues were composed of cells, and the Italian scientist Giuseppe Francesco Bonaventura Balsamo-Crivelli (better known as Camillo Golgi) extended this concept to animals. 2. **The cell is the basic unit of life:** - The cell is the smallest unit that exhibits all the characteristics of life, such as growth, reproduction, metabolism, and response to stimuli. It is the fundamental building block of life. - This principle was put forward by the German physiologist Theodor Schwann, who, along with Schleiden, formulated the first two parts of the cell theory. Schwann observed that animal tissues were also composed of cells. 3. **All cells arise from pre-existing cells:** - Cell theory proposes that new cells are generated through cell division, and they inherit genetic material from the parent cell. This concept contradicts the earlier belief in spontaneous generation, which posited that life could arise spontaneously from non-living matter. - The principle that all cells arise from pre-existing cells was proposed by the German physician Rudolf Virchow. Virchow’s work emphasized that cell division is responsible for the growth, repair, and reproduction of cells. # Cell Theory Timeline: - **1660s**: Robert Hooke: In 1665, he coined the term "cellulae" which was shortened to "cell" after he observed the box-like structures - when he viewed the cork tissues through a microscopic lens. - **1670s**: Anthon van Leeuwenhoek: Observed protists in 1660s (single-celled organisms) that he called animalcules from pond water, in 1670s he also observed the bacteria from his teeth (dental scrapings), Red Blood Cells and Sperm cells using magnifying tools which consists of 2 flat thin metals and biconvex lenses. - **1830s**: Matthias Schleiden (1838): A German botanist who concluded that all plants are made of cells. Theodor Schwann (1839): A German physiologist who founded modern histology by defining that animals consists of cells and cells product (basic unit of animal structure). - **1840s**: Robert Remak: In 1842, a German embryologist and neurologist discovered and named the three germ layers of the early embryo: the ectoderm, mesoderm and endoderm. - **1850s**: Rudolf Virchow: In 1855, a German pathologist and statesman, also one of the most prominent physicians of the 19th century, pioneered the modern concept of pathological processes by his application of the cell theory to explain the effects of disease in the organs and tissues of the body. He emphasized that diseases arose primarily in their individual cells. And lastly, he also concluded "omnis cellula e cellula"; all cells develop only from pre-existing cells. # Germ Theory: Revolutionizing Our Understanding of Disease Germ theory is a foundational concept in the field of microbiology that has transformed our understanding of the causes of infectious diseases. It proposes that microorganisms, known as germs or pathogens, are responsible for many diseases, challenging centuries-old beliefs about the origins of illness. Germ theory has had a profound impact on public health, medicine, and sanitation practices, leading to significant advancements in disease prevention and treatment. ## Key Principles of Germ Theory: 1. **Microorganisms as Pathogens**: Germ theory asserts that microscopic organisms, such as bacteria, viruses, fungi, and protozoa, can cause diseases in humans, animals, and plants. These microorganisms are commonly referred to as pathogens. 2. **Transmission of Diseases**: It emphasizes that diseases are not spontaneous or caused by "bad air" or supernatural forces, as previously believed. Instead, infections are often spread through the transmission of germs from one individual to another. **"If germs had a secret society, what do you think their initiation process would be like? Imagine and describe how germs might recruit new members and what kind of activities they would do together. How would their secret society affect their ability to make people sick? Use your imagination and come up with a fun and creative story!"** # Unit 2.1: You Can't Sneeze on this Tissue ## Overview: The unit will introduce students to the level of organisation within organisms include cells, tissues, organs, organ systems and whole organisms. Emphasis will be placed on the function and coordination of these components. Students will observe how the vascular tissue of a plant transports materials through the plant stalks. ## Enduring Understanding: - Many basic functions of organisms occur in cells. - Different body tissues and organs are made of different kinds of cells. - Living systems at all levels of organisation demonstrate the complementary nature of structure and function. - Organisms seek to maintain homeostasis at all biological levels of organisation. - The level of organisation within organisms includes cells, tissues, organs, organ systems and whole organisms. ## Essential Questions: - How do we know if something is alive? - How can one explain the ways in which cells contribute to the function of living organisms? - How do the structures of organisms contribute to life’s functions? - What are the advantages of multicellularity? ## Topic/Content In this unit, we will learn about: - Plant Tissues - Animal Tissues - Levels of Organization - Organ Systems in Human Body - Defend an Organ - Nutrients ## Essential Vocabulary: Xylem, Phloem, Connective Tissue, Disposal of Wastes, Epithelial Tissue, Muscle Tissue, Nervous Tissue, Organ, Organ System, Tissue, artery, body system, circulatory system, digestive system, nervous system, respiratory system # Introduction In the world of biology, living organisms are composed of smaller structures that work together to maintain life. These structures are like building blocks that form the foundation of life. In this lesson, we’ll explore cells, tissues, organs, and organ systems to understand how they function in the human body. 1. **Cells: The Basic Units of Life** - What is a Cell? Cells are the smallest units of life. They are like tiny factories that perform various tasks to keep an organism alive. - Types of Cells: There are many types of cells, including blood cells, nerve cells, muscle cells, and skin cells, each with its unique functions. - Parts of a Cell: A cell has various parts like the nucleus (control centre), cytoplasm (where chemical reactions occur), and cell membrane (barrier that surrounds the cell). 2. **Tissues: A Group of Cells** - What is a Tissue? Tissues are groups of similar cells working together for a common purpose. They are like teams of specialized workers in the body. - Types of Tissues: There are four main types of tissues: epithelial (covering), connective (support), muscle (movement), and nervous (control). 3. **Organs: Made of Tissues** - What is an Organ? Organs are structures made up of different types of tissues that work together to perform specific functions. They are like machines with various parts working in harmony. - Examples of Organs: The heart (pumping blood), lungs (breathing), and stomach (digesting food) are examples of organs in the human body. - Interactions: Organs often rely on other organs to function correctly. For instance, the heart and blood vessels work together to circulate blood throughout the body. 4. **Organ Systems: Teams of Organs** - What is an Organ System? Organ systems are groups of organs that work together to perform more complex functions necessary for survival They are like departments within a company, each with a specific role. - Examples of Organ Systems: Some major organ systems in the human body include the circulatory system (heart, blood vessels), the respiratory system (lungs, airways), and the digestive system (stomach, intestines). - Integration: Organ systems must work together seamlessly. For instance, the digestive system breaks down food, and the circulatory system transports nutrients from digested food to cells. ## What are vascular plants? Trees, bushes, grass, and plants with vegetables or fruits are all vascular plants. A vascular plant has special tissues that form thin tubes inside the plant. These tubes carry water and other materials up and down the plant. These tubes connect the three main parts of a vascular plant: roots, stems, and leaves. - **Roots:** have several functions: anchor plants to the ground, take in water and minerals from the soil, store food made by the plant (in some plants) - **Stems:** Stems have several jobs: support the plant above ground; move materials from the roots to the leaves and from the leaves to the roots; provide support for the plant. - **Leaves:** have one main job: make food for the plant ## Classifying Vascular Plants: There are two ways vascular plants reproduce, that is, form offspring (more of their own kind). Plants such as ferns do not have seeds. They grow from spores. A spore is a single cell that can develop into a new plant. The new plant is exactly like the plant that produced the spore. Most familiar vascular plants make and grow from seeds. A seed contains an undeveloped plant and stored food inside a protective coat. Some seed plants produce flowers. Some do not. ## Classifying Seed Plants: Most seed plants produce flowers. Some do not. Seed plants that produce flowers are called angiosperms. There are over 235,000 kinds of angiosperms, from rose plants to orange trees. Seed plants that do not produce flowers are called gymnosperms. Gymnosperms produce seeds inside a cone. When the cone falls, the seeds are released. Evergreens are gymnosperms. These trees lose their leaves slowly all year. When a leaf is lost, a new one grows back. So, these trees look green all year. # Plant Tissues Plants are multicellular eukaryotes with tissue systems made of various cell types that carry out specific functions. Plant tissue systems fall into one of two general types: meristematic tissue, and permanent (or non-meristematic) tissue. Cells of the meristematic tissue are found in meristems, which are plant regions of continuous cell division and growth. Meristematic tissue cells are either undifferentiated or incompletely differentiated, and they continue to divide and contribute to the growth of the plant. In contrast, permanent tissue consists of plant cells that are no longer actively dividing. - **Meristematic tissues:** consist of three types, based on their location in the plant. Apical meristems contain meristematic tissue located at the tips of stems and roots, which enable a plant to extend in length. Lateral meristems facilitate growth in thickness or girth in a maturing plant. Intercalary meristems occur only in monocots, at the bases of leaf blades and at nodes (the areas where leaves attach to the stem). This tissue enables the monocot leaf blade to increase in length from the leaf base; for example, it allows lawn grass leaves to elongate even after repeated mowing. - **Meristems:** produce cells that quickly differentiate, or specialize, and become permanent tissue. Such cells take on specific roles and lose their ability to divide further. They differentiate into three main types: dermal, vascular, and ground tissue. Dermal tissue covers and protects the plant, and vascular tissue transports water, minerals, and sugars to different parts of the plant. Ground tissue serves as a site for photosynthesis, provides a supporting matrix for the vascular tissue, and helps to store water and sugars. - **Secondary tissues:** are either simple (composed of similar cell types) or complex (composed of different cell types). Dermal tissue, for example, is a simple tissue that covers the outer surface of the plant and controls gas exchange. Vascular tissue is an example of a complex tissue, and is made of two specialised conducting tissues: xylem and phloem. Xylem tissue transports water and nutrients from the roots to different parts of the plant, and includes three different cell types: vessel elements and tracheids (both of which conduct water), and xylem parenchyma. Phloem tissue, which transports organic compounds from the site of photosynthesis to other parts of the plant, consists of four different cell types: sieve cells (which conduct photosynthates), companion cells, phloem parenchyma, and phloem fibres. Unlike xylem conducting cells, phloem conducting cells are alive at maturity. The xylem and phloem always lie adjacent to each other. In stems, the xylem and the phloem form a structure called a vascular bundle; in roots, this is termed the vascular stele or vascular cylinder. # Tissues: A tissue is a group of connected cells that have a similar function within an organism. The simplest living, multicellular organisms, sponges, are made of many specialised types of cells that work together for a common goal. Such cell types include digestive cells, tubular pore cells, and epidermal cells. Though the different cell types create a large organised, multicellular structure-the visible sponge-they are not organised into true tissues. If a sponge is broken up by passing it through a sieve, the sponge will reform on the other side. More complex organisms, such as jellyfish, coral, and sea anemones, have a tissue level of organisation. For example, jellyfish have tissues that have separate protective, digestive, and sensory functions. There are four basic types of tissues in the bodies of all animals including the human body. These make up all the organs, structures, and other contents of the body. The four basic types of tissues are epithelial, muscle, nervous, and connective. ## Four Types of Tissues - **Epithelial Tissue:** Epithelial tissue is made up of a layer or layers of tightly packed cells that line the surfaces of the body. The largest example of epithelial tissue (also the largest organ in the human body) is the skin. Mammalian skin consists of stratified epithelium, which has several layers of cells. The outermost layers of cells, called squamous cells, are flat plate-like cells, while the deeper layers are roughly cube-shaped and called cuboidal cells. Epithelial tissue has multiple functions, but it serves primarily to protect, absorb, and secrete. As you probably already know, our skin organ covers our entire body and protects underlying tissues from bacteria, chemicals, and other injury. Epithelial cells also line the small intestine where they absorb nutrients, and similar cells in the glands secrete enzymes and hormones. - **Muscle Tissue:** Muscle tissue encompasses not only the muscles, such as those in our legs or fingers, that we actively control but also the tissue that forms most of our internal organs. There are three types of muscle tissue: skeletal, cardiac, and smooth. Skeletal muscle tissue forms what we think of as our muscles; it is attached to our bones by our tendons and can be relaxed or contracted voluntarily. Similar in structure to skeletal muscle, cardiac muscle is found exclusively in the walls of the heart. The major difference, however, is that cardiac muscle is involuntary and cannot be actively controlled. Similarly, smooth muscle, which forms the muscle layers in internal organs such as the digestive tract and bladder, is an involuntary tissue. Smooth muscle tissue controls slow involuntary movements such as stomach wall contractions and the contractions of arteries to regulate blood flow. - **Muscles at work:** Unlike many things that wear out with use, our muscles actually get stronger the more often they are used. Doing different kinds of exercises helps different groups of muscles. But how can you tell if you are improving? - **Nervous Tissue:** Nervous tissue is made up of the nerve cells (neurons) that form the nervous system, including the brain and spinal cord. These cells are especially responsive to stimuli, allowing nervous tissue to transmit stimuli from the brain to the body extremely rapidly. - **Connective Tissue:**Connective tissue connects, supports, or separates other tissues and organs. Connective tissue proper can be either loose or dense. Adipose tissue, or fat, is an example of loose connective tissue, while tendons and ligaments, composed of collagen, are examples of dense connective tissue. Other forms of connective tissue include blood (fluid connective tissue) and cartilage and bone (both forms of supporting connective tissue). - **Your Skeleton**: How important is your skeleton? Can you imagine your body without it? You would be a wobbly pile of muscle and internal organs, and you would not be able to move. - **The Adult Human Skeleton**: The adult human skeleton has 206 bones, some of which are named below. Bones are made up of living tissue. They contain many different types of tissues. Cartilage, a dense connective tissue, is found at the end of bones and is made of tough protein fibres. Cartilage creates smooth surfaces for the movement of bones that are next to each other, like the bones of the knee. - **Ligaments**: Ligaments are made of tough protein fibres and connect bones to each other. Your bones, cartilage, and ligaments make up your skeletal system. ## Functions of Bones: Your skeletal system gives shape and form to your body, but it also plays other important roles. The main functions of the skeletal system include: - **Support**: The skeleton supports the body against the pull of gravity, meaning you don’t fall over when you stand up. The large bones of the lower limbs support the rest of the body when standing. - **Protection**: The skeleton supports and protects the soft organs of the body. For example, the skull surrounds the brain to protect it from injury. The bones of the rib cage help protect the heart and lungs. - **Movement**: Bones work together with muscles to move the body. - **Making blood cells**: Blood cells are mostly made inside certain types of bones. - **Storage**: Bones store calcium. They contain more calcium than any other organ. Calcium is released by the bones when blood levels of calcium drop too low. The mineral, phosphorus, is also stored in bones. ## Structure of Bones: Bones come in many different shapes and sizes, but they are all made of the same materials. Bones are organs, and recall that organs are made up of two or more types of tissues. The two main types of bone tissue are compact bone and spongy bone. - **Compact bone:** makes up the dense outer layer of bones. - **Spongy bone:** is found at the centre of the bone and is lighter and more porous than compact bone. ## Early in Human Development: Early in human development, the skeleton consists of only cartilage and other connective tissues. At this point, the skeleton is very flexible. As the foetus develops, hard bone begins to replace the cartilage, and the skeleton begins to harden. Not all of the cartilage, however, is replaced by bone. Cartilage remains in many places in your body, including your joints, your rib cage, your ears, and the tip of your nose. A baby is born with zones of cartilage in its bones that allow growth of the bones. These areas, called growth plates, allow the bones to grow longer as the child grows. By the time the child reaches an age of about 18 to 25 years, all of the cartilage in the growth plate has been replaced by bone. This stops the bone from growing any longer. Even though bones stop growing in length in early adulthood, they can continue to increase in thickness throughout life. This thickening occurs in response to strain from increased muscle activity and from weight-lifting exercises. ## Joints: A joint is a place where two or more bones of the skeleton meet. With the help of muscles, joints work like mechanical levers, allowing the body to move with relatively little force. The surfaces of bones at joints are covered with a smooth layer of cartilage that reduces friction at the points of contact between the bones. ## Types of Joints: There are three main types of joints: immovable, partly movable, and movable. - **Immovable joints:** allow no movement because the bones at these joints are held securely together by dense collagen. The bones of the skull are connected by immovable joints. - **Partly movable joints :** allow only very limited movement. Bones at these joints are held in place by cartilage. The ribs and sternum are connected by partly movable joints. - **Movable joints:** allow the most movement. Bones at these joints are connected by ligaments. Movable joints are the most common type of joints in the body, so they are described in more detail next. ## Movable Joints: - **Ball and Socket**: - **Pivot**: - **Hinge”:** **Relate**: How might a suit of armour be a good analogy for a function of the skeletal system? # The Circulatory System ## Introduction The first system you’ll be examining in this learning package is the circulatory system. The circulatory system transports substances around our bodies; it delivers essential nutrients to every one of our cells, and it helps to transport waste products to waste-disposal sites - the lungs, the skin, and the kidneys. The circulatory system is an organ system that includes the heart, the blood vessels, and the blood itself. It has three functions: - To transport materials (i.e., nutrients and oxygen) and cells from one place to another - To defend the body against invasion by harmful organisms by taking white blood cells to an area of injury or infection - To maintain a constant body temperature Your body has a closed network of blood vessels-hollow tubes-that move blood and nutrients. A pumping organ-the heart-pushes blood through this network of vessels. ## What is Blood? Blood circulates through the body delivering nutrients and removing waste materials. Blood is made up of red blood cells, white blood cells, and platelets all suspended in plasma. - **Plasma:** About 55% of your blood is made up of plasma. Plasma is a liquid made up of proteins, minerals, dissolved salts, and water. - **Red Blood Cells:** Your body produces two million red blood cells every second. Red blood cells are responsible for carrying oxygen from your lungs to your cells and for carrying carbon dioxide from your cells to your lungs where it is exhaled. - **White Blood Cells:** White blood cells defend the body against attack from foreign organisms, such as bacteria and some viruses, and form antibodies that protect the body from future attacks. - **Platelets and Clotting:** Platelets contain the enzymes needed to turn clotting agents into fibrin-fibrous strands that heal wounds. Platelets collect around the edges of a wound, break themselves open, and release enzymes that promote the chemical reaction needed to heal the wound. ## Blood Vessels: The Highways and Byways of the Blood: The body’s transportation network is a lot like a road system with highways, streets, and small winding back alleys. The major difference is that the roads in the body are all one way. Three types of blood vessels make up this network: - **Arteries:** - **Veins:** - **Capillaries:** - **Arteries:** Arteries are blood vessels that carry blood away from the heart. They have muscular walls that send the blood on its journey to the outer regions of the body. **So, exactly how does an artery work?** Think about squeezing that last bit of toothpaste from the tube. You squeeze from the bottom to the top, pushing the toothpaste ahead of your fingers. Arteries work in a similar way. - **Arterial Function:** Each time the heart contracts, it sends out a gush of blood under high pressure. As high-pressure blood enters the main artery, the artery wall expands and balloons out. Between each heartbeat or contraction, the pressure decreases, and the arteries return to their normal shape. Each time the artery expands and contracts, it pushes the blood along. - **Pulse Rate:** The rhythm of arterial expansion and contraction is called the pulse. Your pulse rate is the same as your heartbeat rate because it’s a single beat of the heart that causes each expansion and contraction of the artery. - **Arterial Characteristics:** Arteries are much thicker than veins and most are located deep within our bodies. There’s a good reason for this. Arterial blood is under high pressure. If a large artery is cut, blood literally spurts out in great gushes, and the victim can bleed to death very quickly. The chances of an artery being cut are reduced because it’s located deep inside the body rather than near the skin. - **Veins:** Veins are blood vessels that carry blood toward the heart. Veins don’t have muscles of their own, but they do have valves. Valves are folds or flaps of skin that prevent blood from backing up in the vein. Since the blood in your veins is at a much lower pressure, veins are located closer to our body’s surface. Blood doesn’t spurt from a cut vein, so clotting can easily stop the flow. - The way blood moves through the veins is similar to the way air is forced out of the lungs. In both instances, an external set of muscles squeezes the organ, reduces its volume, and increases its pressure. The pressure difference causes the flow of blood (or air) from a region of high pressure to one of low pressure. One difference is that veins have valves to prevent the backflow of blood. Lungs don’t need valves because there is nowhere for the air to flow back to. - **Capillaries:** Capillaries are the tiny blood vessels that join arteries to veins. Their walls are usually no more than one cell thick. Nutrients and gases diffuse into the cells through the capillary walls. Wastes diffuse from the cells to the capillaries. **Research:** Doctors often use an electrocardiogram (EKG) reading to see if there is something wrong with how a person’s heart is beating. An EKG is a type of graph that draws the pumping activity of the heart. How might graphing the heartbeat help a doctor tell if there is a problem? **“If you were a doctor specialising in cardiovascular health, how would you explain the importance of arteries, veins, and capillaries to a group of young students? What analogies or metaphors would you use to make the topic easier to understand?”** # The Digestive System ## Function of the Digestive System: Nutrients in the foods you eat are needed by the cells of your body. How do the nutrients in foods get to your body cells? What organs and processes break down the foods and make the nutrients available to cells? The organs are those of the digestive system. The processes are digestion and absorption. The digestive system is the body system that breaks down food and absorbs nutrients. It also gets rid of solid food waste. The digestive system is mainly one long tube from the mouth to the anus, known as the gastrointestinal tract (GI tract). The main organs of the digestive system include the oesophagus, stomach, and the intestine. The intestine is divided into the small and large intestine. The small intestine has three segments. The ileum is the longest segment of the small intestine, which is well over 10 feet long. The large intestine is about 5 feet long. ## Digestion: Digestion is the process of breaking down food into nutrients. There are two types of digestion, mechanical and chemical. In mechanical digestion, large chunks of food are broken down into small pieces. Mechanical digestion begins in the mouth and involves physical processes, such as chewing. This process continues in the stomach as the food is mixed with digestive juices. In chemical digestion, large food molecules are broken down into small nutrient molecules. This is a chemical process which also begins in the mouth as saliva begins to break down food and continues in the stomach as stomach enzymes further digest the food. ## Absorption: Absorption is the process that allows substances you eat to be taken up by the blood. After food is