AS Biology Edexcel Unit 1 PDF

# AS Biology Edexcel: Unit 1 ## Molecules, Diet, Transport and Health ### Cell Structure A diagram depicting a typical cell, broken in half, showing the following components: * **Cell Membrane** * **Mitochondria** * **Cytoplasm** * **Rough ER** * **Nucleus** * **Ribosomes** * **Vacuole** ### P...

# AS Biology Edexcel: Unit 1 ## Molecules, Diet, Transport and Health ### Cell Structure A diagram depicting a typical cell, broken in half, showing the following components: * **Cell Membrane** * **Mitochondria** * **Cytoplasm** * **Rough ER** * **Nucleus** * **Ribosomes** * **Vacuole** ### Problems with Genetic Testing **Ethical** 1. Risk of false positive or negative result 2. Healthy fetus may be aborted if false positive result 3. May result in miscarriage/ spontaneous abortion of fetus 4. Ethical concerns as its a potential life(killing unethical) 5. Who has the right to decide if a test should be done and terminating life of fetus/fetus has the right to life **Social** 1. Social stigma of having a disabled child 2. Cost implications to health service or individuals 3. Social pressure 4. Religion Issues ### Genetic Testing **Prenatal Screening** * **Amniocentesis**: * Remove about 20 cm^3 of amniotic fluid at about 16 week of pregnancy * Cells from fluid cultured for several weeks before analysis * **Chorionic villus sampling**: * Sample taken from developing placenta between 8 and 12 weeks of pregnancy * Then DNA analysed for recessive faulty allele **Preimplantation Genetic Diagnosis** * A parent already have a family history or child affected by genetic disease. * So they can carry preimplantation genetic diagnosis based on the technique of IVF. * After few cell divisions, a single cell is removed from each embryo * Genetic make up is checked and only those embryos free of the problem alleles are placed in the mothers uterus to implant and grow ### The Reproductive System **Female** * Egg produced but yet has a less/ weak chance of fertility due to: * Thick mucus which can block the cervix, so sperm can't reach to the egg * Thick mucus blocks the oviduct * Implanted impaired **Male** * Lack of the vas deference which is the tube carrying sperm out of testes into the deferens semen. * Vas deference is present but is partly/totally blocked by thick sticky mucus. #### The Sweat Glands * **Normal**: * CFTR allows Cl ions to move into the cell. * So less Cl ions are lost in sweat. * Reducing water loss, preventing dehydration. * **Cystic Fibrosis**: * CFTR mutation so less Cl ions move into the cell. * So more salts(chloride and sodium) are lost in sweat. * So water moves by osmosis out of epithelial cells, increasing chance of dehydration. ### Genetic Screening * When whole population (large number of people) are tested for genetic disease. * To be able to identify carriers. #### Process * If one member of a family is born with genetic disease such as cystic fibrosis, other family members will be offered testing. * Diploid somatic cells are used and analysed, as gametes are not used as it has half the DNA, which might be missed. * All possible CFTR mutations are tested as its a large gene. * If one partner in a couple knows he is a carrier, the other partner is advised to be tested as well. #### Value * It is much cheaper than caring for severely affected children. * Carriers to faulty allele have the option to decide on having a child. ### Cystic Fibrosis (Genetic Disease) * Serious genetic disorder caused by faulty recessive allele (due to mutation in the gene coding for CFTR protein) on an autosome. * Affects the production of mucus by epithelial cells. #### Normal Airway Epithelium * Normal CFTR gene. * Cl ions leaves the cells through CFTR protein and into the mucus. * Sodium Channels are inhibited by CFTR, so Na ions remain outside the cells in mucus. * Sa NaCl causes the mucus to be hypertonic. * Water moves out of the cell by osmosis. * Resulting in watery thinner mucus * Cilia can beat. * Cilia can move mucus away from airways. #### Airway Epithelium Affected by Cystic Fibrosis * Mutation in the CFTR gene (faulty CFTR allele) leads to changes in the primary structure of the CFTR channel protein. * CFTR can’t function properly. * Cl ions build up inside cells (not exported out of cell). * Water doesn't move out of the cell by osmosis or water moves out of the mucus and into the cell by osmosis. * Resulting in sticky mucus. * Cilia can’t beat effectively. * Cilia can’t move mucus away, as it’s too thick. * Accumulates in the airways/bronchi/bronchioles. * Reduces rate of gas exchange. * Mucus traps dust and bacteria. * Bacteria have ideal growth conditions in the mucus, so can cause infections. #### Symptoms **Respiratory** 1. Thick sticky mucus 2. Build up in airways, narrowing airways. 3. Reduces air flow into alveoli. 4. Smaller concentration gradient between blood and alveoli. 5. Reducing gas exchange. 6. Sever coughing. 7. Mucus fill up the lungs, increasing susceptibility to lung infections. **Digestive** 1. Blockage of the pancreatic duct. 2. Thick sticky mucus, so no enzymes reach the duodenum. **Reproductive** * May not be functional in both sexes **Sweat Glands** * Thick sweat ### Four Types of Proteins **1. Globular Proteins** * Spherical, they are water soluble. * This is because the amino acids with hydrophilic polar R groups are facing outwards. * So hydrogen bonds can form with water. * While amino acids with hydrophobic R groups point towards the inside of the molecule. * The molecule curl up into a spherical shape (globular shape) and have tertiary structure. Some have quaternary structure. * Many have metabolic functions. * If their shape is altered slightly by changing conditions, they lose their ability to function. * They don't dissolve in water to make a solution. * Instead, the molecules are so big, forming a colloid. * The protein molecules act as colloid being suspended in cytoplasm (water), where they don’t settle and can’t be easily separated.. * They are important as they hold molecules in position in the cytoplasm. **2. Fibrous Proteins** * Have a simpler structure. * Polypeptides lie parallel to each other. * More stable to changes in temperature and pH. * They don't curl up but form long strands with many amino acids. * Water insoluble. * Large number of repeating amino acid sequences. * Have structural function (being very tough thus giving strength). **3. Glycoproteins** * A protein molecule with a short carbohydrate chain attached to it. * The carbohydrate chain can help stabilise the membrane. * It can also help with the glycoproteins also acting as receptor molecules. * These can recognize messenger molecules, as hormones. * Act as cell receptors. * They are important for binding cells together. * They act as cell markers or antigen. * They can allow cell-cell recognition. * They also function as transport proteins. **4. Glycolipids** * Similar to glycoproteins. * The carbohydrate chain helps stabilize the membrane. * It also helps with the glycolipids also acting as receptor molecules. ### Importance of Ring Structure * More stable in a solution. * Occupies less space. * Can easily add more rings to make a polymer. ### Importance of Carbohydrates * They are the main source of energy for living organisms. * They are the building blocks of cell walls in plants. ### Importance of Water * Excellent solvent * It is dipolar. * It contributes to the stability of cell membranes. * Plays an important role in transport systems. ### Importance of Lipids * They are the main source of energy in the body. * They play an important role in cell structure. ### The Human Gas Exchange System **Structure** 1. Nasal Passage 2. Pharynx 3. Epiglottis 4. Larynx 5. Trachea 6. Alveoli 7. Diaphragm 8. Internal Intercostal Muscles 9. External Intercostal Muscles **How Alveoli are Adapted for Gaseous Exchange** 1. Thin alveolar wall (squamous epithelium) 2. Many alveoli 3. Surrounded by many capillaries (capillary network) #### Role of the Respiratory System in Gas Exchange 1. Ventilation - removal of Carbon dioxide and bringing of Oxygen, thus maintaining steep concentration gradient. 2. Alveoli have adaptations: * large surface area * surfactant * thin wall * rich in blood capillaries 3. Overcoming the limitation of diffusion. #### Breathing (Ventilation) 1. Inhalation is an active process. 2. Exhalation is a passive process. ### The Structure of DNA * 2 polynucleotide strands * Held together by Hydrogen bonds between the nitrogenous bases. * Each strand has a sugar phosphate backbone with phosphodiester bonds * The two strands twist forming a double helix (3D shape). * Each full turn in a DNA molecule has 10 base pairs, 3.4 nm length. ### The Structure of RNA * Single stranded * Contains sugar Ribose * Contains Uracil instead of Thymine. * No H-bonds between bases. ### DNA Replication 1. DNA double helix unwinds. 2. Hydrogen bonds between complementary bases are broken. 3. Free activated nucleotides line up along both strands. 4. DNA polymerase enzyme lines up the new nucleotides along the DNA template strand, step by step. 5. DNA ligase is an enzyme that catalyse the formation of phosphodiester bonds between adjacent mononucleotides. 6. Process continues along whole DNA molecule, producing two genetically identical DNA molecules 7. DNA replication is semi conservative, where each newly formed DNA molecule contains one original and one newly synthesised DNA strand ### The Genetic Code * A sequence of 3 bases in the template strand of the DNA codes for one amino acid. * The sequence of bases that codes for all the amino acids in a protein is a gene. * Triplets are called a genetic code, made up of 3 nucleotides that code for one amino acid in a protein. #### Properties of the Genetic Code * **Triplets**: Each sequence of three bases is called a codon. There 64 possible codons, which is more enough to specify the 20 different amino acids that occur in proteins. * **Universal**: The same triplet genetic code codes for the same amino acid in all living organism. * Strong evidence for the idea that all living organism originate from one group. * **Degenerate**: Some amino acids have more than one genetic code. * There are more codons than the number of amino acids. * Arranging the 4 bases in triplets gives 64 possible combinations, 61 possible codons for 20 amino acids, so more than one codon specifies an amino acid. * This minimizes the effect of mutation. * **Not Overlap**: No base of a given triplet enters to be a part of the adjacent triplet. ### Protein Synthesis * The process of protein synthesis takes place in two stages: * Transcription - formation of mRNA from the gene in the nucleus. * Translation - formation of polypeptide chain using mRNA and tRNA in the cytoplasm ### The Importance of Transport Systems * Large organisms have a small surface area to volume ratio, making simple diffusion insufficient due to: * High metabolic rate * Long distances of diffusion. * Concentration gradient. ### Features of Mass Transport Systems * They are found in all organisms with a mechanism for moving substances around the body. * They are composed of vessels and a pump to move the fluid. * They make use of pumps to generate pressure, creating a pressure gradient. * They are often found in conjunction with a large gas exchange surface. ### Types of Circulatory Systems **Open** * The blood is not enclosed in blood vessels and is pumped into the cavities of the body. **Closed** * The blood is pumped through the vessels separate from the interstitial fluid. #### The Mammalian Heart * Made of 4 chambers: * 2 upper thin walled atria * 2 lowered thicker walled ventricles. * The right side of the heart receives blood from systemic circulation and pumps it to the lungs. * The left side of the heart receives blood from lungs and pumps it around the rest of the body. * **Arteries** carry blood under relatively high pressure, away from the heart to all body cells. * **Veins** return blood from body organs to the heart. * **Coronary Arteries**: supply the heart muscle. * **Septum** divides the human heart. * **Myoglobin** is a respiratory pigment which has a stronger affinity for oxygen than haemoglobin. #### The Structure of Arteries and Veins **Layers** 1. Tunica intima: endothelium- a single layer of flat cells. 2. Tunica media: smooth muscle and elastic tissue. 3. Tunica externa: elastic fibres and collagen fibres. **Capillaries** * The thin, porous wall of a capillary allows for the exchange of molecules between the blood and the surrounding tissue. * They are found in all tissues and allow for the transport of oxygen, nutrients, and waste products. #### The Cardiac Cycle * The cardiac cycle is the sequence of events which make up one heartbeat. * It involves Atrial systole, Ventricular systole and Diastole. * **Atrial Systole**: Both atria contract, increasing pressure. * **Ventricular Systole:** The ventricles contract, pushing blood into the arteries. * **Diastole**: The heart relaxes. **How the Heart Works** * The Lub is caused when ventricles contract and the blood is forced against atrioventricular valves causing them to close. * The Dub is caused when ventricles relax and a back flow of blood hits the semilunar valves, causing them to close. **How the Heartbeat is Initiated and Controlled** * The heart is myogenic. This means that it contracts and relaxes naturally, without needing impulses from a nerve. * The heartbeat is initiated by the Sinoatrial Node (SAN), which is located in the wall of the right atrium. * The SAN sends out electrical impulses that cause the atria to contract. * The impulses then pass to the Atrioventricular Node (AVN), which is located in the septum between the atria and the ventricles. * The AVN delays the impulses slightly, allowing the atria to finish contracting before the ventricles begin. * From the AVN, the impulses travel down the Bundle of His, a group of specialized muscle fibers that are located in the septum. * The Bundle of His divides into the Purkinje fibers, which spread throughout the ventricles and cause them to contract. ### Transport of Oxygen * **Haemoglobin** plays a role in the transport of both oxygen and carbon dioxide. * Haemoglobin combines reversibly with oxygen in a 1:4 ratio, forming oxyhaemoglobin. * The Bohr Shift describes the effect of carbon dioxide on haemoglobin. * It indicates that the amount of oxygen the haemoglobin carries is affected by both partial pressure of oxygen pO2 and partial pressure of carbon dioxide pCO2. * This results in the release of more oxygen in active tissues. * **Fetal Haemoglobin** has a higher affinity for oxygen than adult haemoglobin. ### The Different Types of Transport **1) Simple Diffusion** * Non-polar molecules move down the concentration gradient from areas of higher concentration to areas of lower concentration. * No metabolic energy needed (passive). **2) Facilitated Diffusion** * Polar molecules move down the concentration gradient. * They use transport proteins (carriers) to move across the membrane. * No metabolic energy needed (passive). **3) Active Transport** * Molecules move against the concentration gradient (from an area of lower concentration to an area of higher concentration). * They use transport proteins (carriers) to move across the membrane. * Requires metabolic energy from ATP (active). **4) Bulk Transport** * The movement of very large molecules, like proteins or polysaccharides. * Includes: * Endocytosis: The taking in of materials by the cell surface membrane. * Exocytosis: The release of materials from the cell. ### The Functions of Cell Membranes 1. Barrier between inside and outside of cell. 2. Selectively permeable. 3. Have receptors for signaling substances. 4. Allow cell recognition by acting as cell surface antigens, so as to prevent cell destruction. 5. They form hydrogen bonds with water, leading to stability. 6. Allow for the flexibility of the cell, which is important for processes such as phagocytosis. 7. They act as the sites of enzymes. 8. They provide a surface for chemical reactions to occur. 9. They can be damaged by: * High temperatures: this disrupts the tertiary structures of proteins, which damages functionality of protein carriers and leads to loss of the membrane's partially permeable nature. * Alcohol: denatures (alters the 3D shape) proteins and phospholipids. ### The Functions of Blood Plasma * It carries all your blood cells and everything that needs transporting around your body including: * Digested food particles. * Nutrient molecules. * Excretory products. * Hormones. * It helps to maintain a steady temperature. * It acts as a buffer to regulate pH changes. ### The Roles of Blood * Red Blood Cells * Transport oxygen from lungs to tissues. * Also transport carbon dioxide. * White Blood Cells * Protect the body against infection. * Platelets * Prevent blood loss and prevent entry of pathogens. ### Cell Structure * **Cell Membrane:** Controls and selects what enters and leaves the cell. * **Nucleus:** Contains the cell’s DNA. * **Cytoplasm:** The gel-like substance that fills the cell. * **Mitochondria:** Responsible for cellular respiration, so as to provide energy for the cell. * **Rough Endoplasmic Reticulum (RER):** Network of membranes involved in protein synthesis * **Ribosomes:** Small organelles involved in protein synthesis. * **Smooth Endoplasmic Reticulum (SER):** Involved in lipid synthesis and detoxification. * **Golgi Apparatus:** Processes and packages proteins for transport. **Why do cells have this structure?** * Different organelles carry out different functions, allowing for a greater degree of specialization. * The cell membrane acts as a barrier, preventing the contents of the cell from spilling out. * The structure of the cell membrane ensures controlled transport of substances. ### Different Processes for Transporting Substances Across Cell Membranes * **Simple Diffusion:** * The movement of small, non-polar molecules from an area of higher concentration to an area of lower concentration. * Passive (doesn’t require energy). * Occurs across phospholipid bilayers. * **Facilitated Diffusion:** * The movement of larger, polar molecules, using transport proteins (carriers or channels). * Passive (doesn't require energy). * Occurs across phospholipid bilayers. * **Active Transport:** * The movement of molecules against the concentration gradient. * Requires energy from ATP (active). * Occurs across phospholipid bilayers. * **Bulk Transport:** * The movement of very large molecules or whole cells into or out of the cell. * Includes: * **Endocytosis:** The taking in of materials by the cell surface membrane. * **Exocytosis:** The release of materials from the cell. * Requires energy from ATP. #### Osmosis * The passive movement of water molecules from an area of higher water potential to an area of lower water potential. * Occurs across partially permeable membranes. * No metabolic energy required (passive). #### Water Potential * The tendency for water to move out of a solution. * The higher the concentration of solutes in a solution, the lower the water potential. * Water will move from an area of high water potential to an area of low water potential. #### Turgor * The state of a plant cell is perfectly balanced by the forces of osmosis and the wall pressing back. * It is caused by a high pressure potential within. #### Plasmolysis * The process where the cell membrane pulls away from the wall, creating a gap between the plasma membrane and the cell wall. * Incipient plasmolysis is the point at which the cell membrane begins to pull away from cell wall as the protoplasm shrinks. * It occurs when a cell is placed in a hypertonic solution. ### The Different Types of Carbohydrates * **Monosaccharides:** * The simplest carbohydrates. * Contain one sugar molecule. * Examples: glucose, fructose, galactose. * **Disaccharides:** * Formed from two monosaccharides joined together by a glycosidic bond. * Examples: sucrose, lactose, maltose. * **Polysaccharides:** * Formed from many monosaccharides joined together by glycosidic bonds. * Examples: starch, glycogen, cellulose. ### The Difference Between Reducing and Non-Reducing Sugars * **Reducing Sugars:** * Have a free functional group (an aldehyde or ketone group) that can react with Benedict’s reagent. * They give a positive result in Benedict’s test, changing the color of the solution from blue to brick red. * They include all monosaccharides and disaccharides. * **Non-Reducing Sugars:** * They have no free functional groups that can react with Benedict’s reagent because both their functional groups are occupied by the glycosidic bonds. * They give a negative result in Benedict’s test. * They include sucrose. ### The Tests for Sugars * **Benedict’s Test:** * Used to test for reducing sugars * A reducing sugar reacts with Benedict’s reagent to form a colored precipitate. The concentration of reducing sugar determines the intensity of the red precipitate. * Heat the test tube with the unknown solution, and Benedict’s reagent. * Observe any color changes. * **Iodine Solution:** * Used to test for starch. * If starch is present, the iodine solution will turn blue-black in color. ### Testing for Starch and Reducing Sugars in Fruit Juice * **Procedure:** * Prepare a range of known concentrations of glucose solution using serial dilution using the stock solution of 2% glucose (4%, 2%, 1%, 0.5%, 0.25%). * Use Benedict’s reagent to test the known concentrations of glucose and create a calibration curve. * Prepare a range of known concentrations of starch solution using serial dilution using the stock solution of 2% starch (2%, 1%, 0.5%, 0.2%, 0.1%). * Use iodine solution to test the known concentrations of starch and create a calibration curve. * Use Benedict’s reagent to test the fruit juice, and compare your results to your calibration curve for glucose. * Use iodine solution to test the fruit juice, and compare your results to your calibration curve for starch. ### Other Methods to test for Starch and Reducing Sugars * **Colorimeter:** * Measure the intensity of the blue color of the unreacted iodine solution or Benedict’s reagent using a colorimeter. * **Weighting the Precipitate:** * If using the Benedict’s test, precipitate the copper oxide and weigh it. ### Importance of the Properties of Water * **Solvent**: * Water has high surface tension. * Water is an excellent solvent for ions and polar molecules. * **High Specific Heat Capacity**: * Water is very resistant to change in temperature due to the presence of hydrogen bonds. * **High Latent Heat of Vaporization**: * Water absorbs a lot of heat to change from a liquid to a gas. * **Density Change at 4°C**: * Water is most dense at 4°C, so ice is forms on the top of the water. * **Cohesion and Adhesion**: * Water molecules stick together by hydrogen bonds. * Adhesive forces between water molecules and other molecules are strong due to hydrogen bonds. ### Importance of Lipids * **Energy Storage** * Lipids are rich in carbon-hydrogen bonds, which release a lot of energy when they are broken. * **Insulation** * They act as a thermal insulator, preventing heat loss. * **Protection** * They protect vital organs. * **Metabolic source of water** * In animals like the desert kangaroo rat, they are metabolized to produce water. ### The Four Types of Lipids * **Triglycerides:** * Formed from glycerol and three fatty acids. * They are insoluble in water due to their non-polar nature. * **Phospholipids:** * Similar to triglycerides. * However, one of the fatty acids is replaced by a phosphate group. * They contain both hydrophilic (polar) heads and hydrophobic (non-polar) tails. * The hydrophilic heads face the watery environment of the cytoplasm. * The hydrophobic tails face toward the center of the bilayer. * **Steroids:** * Have a ring structure. * They are not polymers. * Examples include cholesterol. * **Waxes:** * They’re long chain fatty acids and alcohols. * They are waterproof and can be used for structural purposes. ### The Difference between Saturated and Unsaturated Fatty Acids * **Saturated Fatty Acid:** * The fatty acid tail has no carbon-carbon double bonds. * **Unsaturated Fatty Acid:** * The fatty acid tail has at least one carbon-carbon double bond. ### The Four Types of Polysaccharides * **Starch:** * A polysaccharide made from a-glucose. * It is an energy storage molecule in plants. * It is made up of two components: * **Amylose:** linear chains of a-glucose molecules, linked by 1-4 glycosidic bonds. * **Amylopectin:** branched chains of a-glucose molecules. * **Glycogen:** * Also made of a-glucose. * It is an energy storage molecule in animals. * It is more highly branched than amylopectin. * **Cellulose:** * Made from β-glucose. * It is a structural component of cell walls in plants * **Chitin:** * Made from N-acetylglucosamine. * It is a structural component of the exoskeletons of arthropods. ### The Properties of Amino Acids * Amino acids are the monomers of proteins. * They have a central carbon atom that is attached to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R group. * They contain a mix of hydrophilic and hydrophobic groups. * The properties of the amino acids are determined by the R group. ### The Structure of Proteins * **Primary :** * Linear sequence of amino acids is a polypeptide or protein. * Held by a peptide bonds. * **Secondary:** * Regular folding or coiling of polypeptide chains. * Held by hydrogen bonds. * *a-Helix*: the polypeptide chain is coiled into a spiral shape. * *β-pleated sheet*: polypeptide chains are held into regular parallel pleats. * **Tertiary:** * Overall folding of the polypeptide chain in a specific 3D shape. * Held by a combination of hydrogen bonds, ionic bonds, disulfide bonds, and hydrophobic interactions. * **Quaternary:** * The three-dimensional arrangement of two or more polypeptides or proteins in a protein. * Held together by the same interactions as in the tertiary structure. ### The Importance of Enzymes * Enzymes are biological catalysts. * Most enzymes are globular proteins, with a specific 3D shape. * This shape gives them a specific active site, to which a substrate can bind. * This interaction between the enzyme and the substrate lowers the activation energy needed by the reaction. ### The Four Mechanisms to Control Enzyme Activity * **Temperature:** * Enzyme activity increases with temperature until a certain point, as the molecules gains kinetic energy and collide more frequently. * Above a certain temperature, the enzyme denatures. * **pH:** * Each enzyme has an optimum pH. * At pH levels above or below this optimum pH, enzyme activity decreases. * This is because pH levels can alter the tertiary structure of the protein, which affects the shape of the active site. * **Substrate Concentration:** * Increase the rate of reaction until saturation is reached. * At saturation, the active sites of all the enzymes are occupied, and the rate of reaction will not increase. * **Enzyme Concentration:** * Increase the rate of reaction. ### Types of Enzyme Inhibitors * **Competitive Inhibitors:** * They have similar shapes to the substrate. * They compete with the substrate for the active site of the enzyme. * They increase the Km value of the reaction. * **Non-Competitive Inhibitors:** * They bind to a site on the enzyme other than the active site. * They change the 3D shape of the enzyme and prevent its activity. * They decrease the Vmax value of the reaction. ### The Importance of Blood * It transports oxygen to cells to allow for respiration. * It transports carbon dioxide from cells to the lungs to be removed. * It delivers nutrients to cells. * It transports waste products from cells to be removed from the body. * It is regulated by: * Liver: this detoxifies the blood and breaks down toxins and drugs. * Kidneys: this filter waste products such as excess urea from the blood. * Lungs: this oxygenates the blood. ### The Structure of the Human Heart 1. It has four Chambers: * **Atria:** two upper chambers, receiving blood. * **Ventricles:** two lower chambers, pumping blood. 2. The right atrium receives deoxygenated blood from the body. 3. The right ventricle pumps deoxygenated blood to the lungs. 4. The left atrium receives oxygenated blood from the lungs. 5. The left ventricle pumps the oxygenated blood around the body 6. The heart has four valves that control the direction of blood flow: * **Atrioventricular Valves** (AV-valves): * The tricuspid valve (right AV valve) * The bicuspid valve (left AV valve) * Prevent backflow from the ventricles to atria. * **Semilunar Valves:** * The pulmonary valve * The aortic valve * They prevent backflow from the pulmonary artery and aorta to the ventricles. #### The Cardiac Cycle * **Atrial Systole:** * Both atria contract at the same time, squeezing blood into the ventricles. * The semilunar valves are closed, and the AV valves are open. * The pressure in the atria is higher than the pressure in the ventricles. * **Ventricular Systole:** * Both ventricles contract at the same time, forcing blood into the pulmonary artery and the aorta. * The AV valves are closed, and the semilunar valves are open. * The pressure in the ventricles is higher than the pressure in the arteries. * **Diastole:** * The heart relaxes. * The semilunar valves close, and the AV valves open. * The pressure in the atria is higher than the pressure in the ventricles. ### The Structure and Functions of Blood Vessels * **Arteries:** * Carry blood away from the heart under high pressure. * They have a thick, strong wall lined with three layers: * **Tunica Intima:** Endothelium - single layer of flat cells. * **Tunica media:** Smooth muscle and elastic tissue. * **Tunica externa:** Elastic fibres and collagen fibers. * They help to maintain blood pressure and allow for the elastic recoil of arteries. * They have a narrow lumen to maintain blood pressure. * **Veins:** * Carry blood back to the heart under low pressure. * They have a thin wall with three layers. * **Tunica Intima:** Endothelium - single layer of flat cells. * **Tunica media:** Smooth muscle and elastic tissue. * **Tunica externa:** Elastic fibres and collagen fibers. * They have a wider lumen to reduce resistance to blood flow. * They have valves to prevent blood from flowing back. * **Capillaries:** * Tiny blood vessels that connect arteries and veins, allowing for the exchange of substances between blood and the surrounding tissues. * They have very thin walls and a narrow lumen, allowing for the rapid diffusion of substances. #### The Adaptation of Blood Vessels to their Functions * **Arteries**: * They have thick, strong walls that can withstand high pressure. * The narrow lumen helps to maintain blood pressure. * The elastic tissue allows them to stretch and recoil as the blood flows. * **Veins:** * They have thin walls that allow for the contraction of the surrounding skeletal muscles to help propel blood towards the heart. * They have valves to prevent backflow. * **Capillaries:** * They have thin walls and a narrow lumen to facilitate the exchange of substances between blood and the surrounding tissues. ### Importance of the Blood Supply to the Heart * The heart is the most metabolically active organ in the body. * It can't receive its oxygen supply from the blood in the heart chambers. * The coronary arteries supply the heart muscle with a constant supply of oxygen and nutrients so that it can function properly. * The coronary arteries are very narrow, so any build-up of atheroma can lead to a reduction in blood flow, which can cause angina or a heart attack. ### The Causes and Effects of Atherosclerosis * **Atherosclerosis:** * It is a condition where plaque (atheroma) builds up on the lining of the arteries, causing narrowing. * It can lead to a variety of cardiovascular problems, including angina, heart attack, and stroke. * **How Atherosclerosis Develops:** 1. Damage to the endothelial lining of the arteries. 2. Inflammation of the artery walls. 3. Build-up of cholesterol and other lipids in the walls. 4. Formation of plaques. 5. Hardening of the arteries. * **The Effects of Atherosclerosis**: * **Angina**: When a plaque blocks a coronary artery. * **Heart attack:** When a plaque blocks a coronary artery, leading to a heart attack. * **Stroke:** When a plaque blocks a cerebral artery, leading to a stroke. * **Aneurysm:** When a plaque weakens the wall of an artery, making it bulge. * **Increased Blood Pressure:** When the arteries are narrowed. ### The Importance of Exercise * Regular exercise can help to reduce your risk of cardiovascular disease by: * Lowering blood pressure * Improving cholesterol levels * Increasing the efficiency of your heart * Reducing stress