Organisation and the Vascular Structures.docx

**[Organisation and the Vascular Structures]** **[Plants]** [Structure of flowering plant] (1) [Seeds]*\ *Most flowering plants arise from a seed which consists of an embryo surrounded by a testa (seed coat). The embryo consists of one or two cotyledons (seed leaves), a plumule, a radicle, and s...

**[Organisation and the Vascular Structures]** **[Plants]** [Structure of flowering plant] (1) [Seeds]*\ *Most flowering plants arise from a seed which consists of an embryo surrounded by a testa (seed coat). The embryo consists of one or two cotyledons (seed leaves), a plumule, a radicle, and sometimes an endosperm.\ If seeds have a healthy supply of water, oxygen, and a suitable temperature, they will germinate. [Roots\ ]*Structure\ *- If the radical persists, it will give rise to a tap root whose branches will form lateral roots. Tap roots are normally large obvious, e.g., carrots and parsnips.\ - If the radical does not persist, adventitious fibrous roots arise from the base of the young stem e.g., grass.\ - Adventitious roots are roots that develop from any part of the plant that is not derived from the radicle e.g., Ivy. *Root Growth\ *- The apical meristem, near the tip of the root, divide by mitosis. The cells produced at the front of the meristem produce a structure called the root cap. This becomes slimy and lubricates the passage of the root through the soil. It protects the apical meristem of the root from abrasion.\ - The cells formed at the rear of the apical meristem acquire vacuoles and elongate, pushing the tip of the root forwards. This is called the zone of elongation.\ - Once fully elongates, the cells on the outside of the root produce root hairs. These have a large surface area to absorb water and minerals.\ - Cells near the core of the root differentiate into vascular tissue, xylem and phloem. This is called the zone of differentiation.\ - The cells mature in the zone of maturation.\ A diagram of a structure Description automatically generated(2) *Functions of the Root\ *- Anchorage: The root anchors the plant in the ground, preventing it from being blown over or washed away.\ - Uptake of minerals: Roots absorb water and minerals from the soil.\ - Food storage: Any excess food produced by the leaves is transported to the roots through the phloem to be stored for later use. This process is called translocation. Food can be stored in the form of sugars or starch. The stored food can be used at night when the plant is no longer photosynthesising. It can also be used so that they can grow quickly in the spring. Parsnips use this type of storage.\ - Vegetative propagation: Roots can be used to produce new plants that are identical to the parent plant. [Stem\ ]*Structure\ *The stem is a cylinder that rises vertically from the ground. Most stems are solid, but a few are hollow. Some stems also twine around other plant stems. Leaves arise from various points on the stem called nodes. The length of stem between successive leaves is called the internode. Buds are miniature compressed stems and are found at various places on the stem. There are two types of buds;\ - Terminal buds: Often called apical buds, found at the ends of stems and are responsible for elongation. Sometimes they are directed by hormones to form flowers instead of new stems.\ - Axillary buds: Found in the axils of leaves. The axil is the angle between the petiole and the stem. Axillary buds are usually dormant. They can grow into side stems or branches when they are far enough away from the terminal bud, or if the terminal bud is removed. *Functions of the Stem\ *- Support: The stems hold the leaves and flowers in place so that they can carry out their functions efficiently\ - Transport: The stem transports water and minerals upwards in a tissue called xylem. Transports food and other materials up and down the stem in a tissue called phloem\ - Food storage: Some plants store food in their stems e.g., potato\ - Vegetative reproduction: In strawberries, some stems grow across the surface of the ground. These are called runners and form new plants where a bud touches the ground [Leaf\ ]*Structure\ *- Most leaves consist of a stalk called the petiole, and a flattened blade-like portion called the lamina. The veins of the leaf are raised areas, usually on the underside, caused by the vascular bundles.\ - In monocots, these run parallel to each other. In dicots, they are branched.\ - In many leaves there is a larger vein running up the centre called the midrib.\ - The angle formed between the petiole and the stem is called the axil. The bud on this is called the axillary bud. *Function of the Leaf\ *- Photosynthesis: The primary function of leaves. Most leaves have a large surface area to capture the maximum amount of light.\ - Food storage: Some plants, such as cabbage and onion, store food.\ - Excretion: The waste products of metabolism are stored in the leaves, and then discarded when the leaves fall. [Flowers\ ]*Structure and Function\ *- Flowers are the organ of sexual reproduction. Large, brightly coloured, and scented flowers attract pollinators. Small and dull flowers are pollinated by the wind. [Plant Tissue Types] [Dermal Tissue\ ]- Protective outer covering of the plant.\ - In older plants, can have a layer of cork that acts as an insulating and protective layer. Called the epidermis in young plants.\ - Pores in the epidermis of leaves called stomata allow for gaseous exchange and transpiration.\ - The stem of woody plants have pores for gaseous exchange called lenticels. [Ground Tissue\ ]Ground tissue has a variety of functions including:\ - Photosynthesis: In leaves, ground tissue form the cells of the spongy mesophyll layer and palisade mesophyll. These cells contain chloroplasts and his is where most photosynthesis occurs\ - Storage: In stems and roots, ground tissue is used for storage of food and water. In stems, it forms the endosperm\ - Protection: Ground tissue fills space and provides protection\ - Support: In non-woody plants, ground tissue contributes to rigidity when it is turgid [Vascular Tissue\ ]Vascular tissues are complex and are composed of several types of cells. Two of these are Xylem and Phloem. [Xylem\ ]*Structure -- Xylem Vessels\ *- Found in angiosperms\ - Narrow so that capillary action is at a maximum\ - Heavily lignified and therefore dead when mature\ - Lignin gives them strength to withstand the negative tension of water transport\ *Structure -- Tracheids\ *- When mature, are thickened with a polymer called lignin, which is both waterproof and strong. These are described as lignified.\ - Lignified cells are dead and contain no cell contents\ - Have tapered ends and are perforated to allow the easy movement of water and dissolved minerals from one cell to the next\ - Pits contain no lignin, pits allow the lateral movement of water within the stem *Function of Xylem\ *- Xylem transports water and dissolved minerals up the stem\ - Lignin supports the plant by holding up the plant against the pull of gravity [Phloem\ ]*Structure -- Sieve Tube Cells\ *- Have no nucleus, ribosomes, cytoskeleton, and no large vacuoles. The lack or organelles makes transport through them easier.\ - Sieve tube cells end in perforated sieve plates, and these can transport dissolved substances in either direction.\ *Structure -- Companion Cells\ *- Have a nucleus and control the adjoining sieve tube element through special pores called the plasmodesmata.\ - Companion cells pump sugar into the phloem in leaves *Function of Phloem\ *- Transport of food and hormones (auxins) to all plant cells from the leaves\ - Companion cells controls the activities of the sieve tubes [Meristematic Tissue\ ]The areas of the plant where there is rapid cell division by mitosis to produce new tissue in the form of unspecified cells. There are two types of meristematic tissue. [Apical Meristems\ ]- Responsible for growth in length of stems, shoots, and roots\ - Found at the tips of shoots in the apical bud and in axillary buds\ - In roots, they are found immediately behind the root cap in the zone of division [Lateral Meristems\ ]- Responsible for growth in width of stem. They are known as cambium and there are three different types:\ - Vascular Cambium\ - Inter-fascicular Cambium\ - Cork Cambium [Differences between Monocotyledons and Dicotyledons] A monocot is a plant whose seed contains one seed leaf e.g., daffodils. A dicot is a plant whose seed contains two seed leaves e.g., geraniums. Monocot Dicot -------------------------------------------------------------------------------- ----------------------------------------------------------------------------- Have strap-shaped leaves Leaves ae broader than they are long and are irregular in shape The veins in the leaf run parallel to the sides Veins are spread out in different directions and are branches When flowers are present, they usually have floral parts in multiples of three Floral parts in multiples of four or five Most are herbaceous Both herbaceous and woody species Vascular bundles are scattered throughout the stem Vascular bundles are arranged in a ring around the outer region of the stem [Mandatory Practical -- Prepare and examine microscopically the transverse section of a dicotyledonous stem] \- Collect a herbaceous stem\ - Trap the stem between two pieces of carrot to hold it steady\ - Wet the stem to lubricate the movement of the backed blade and make it easier to slice without damaging the structure of the stem\ - Using a backed blade, cut away from yourself for safety\ - Cut the sections as thinly as possible\ - Place the thinly cut slices in water to keep the cells turgid\ - Lift the thinnest sections you can find with a paintbrush\ - Place the section on a clean slide and add a drop of iodine stain\ - Lower a coverslip onto the section at an angle to prevent air bubbles\ - Turn on the microscope light\ - Examine the slide at low power, focusing with the coarse focus knob\ - Examine at high power, focusing with the fine focus knob\ - Draw what you see. **[Humans]** [The Circulatory System and Blood] A circulatory is needed to ensure all cells can obtain enough oxygen and nutrients, and that their metabolic waste is remove before it can cause damage. There are two types of circulatory systems, Open systems, and Closed systems. [Open Systems\ ]In open systems, the heart pumps a fluid called haemolymph into an open central cavity called the haemocoel. As the haemolymph moves across the haemocoel, it exchanges materials with the surrounding cells. It then reaches collecting vessels at the other side, through which it is returned to the heart and pumped back into the other side of the haemocoel. This is found in animals like snails and insects. [Closed Systems\ ]**Blood is always enclosed in blood vessels. Tissue fluid bathes the cells and acts as a medium through which substances are exchanged between the blood and the cells e.g., earthworms and vertebrates. The closed circulatory systems are more efficient than open ones because:\ - The blood can be pumped around the body faster and therefore the exchange of food and oxygen is faster. This allows the animal to be more active.\ - It allows the flow of blood to different organs to be increased or decreased** **[Two-circuit Circulatory system\ ]In advanced animals, like mammals, a two-circuit system is used. A pulmonary system driven by the right side of the heart pumps deoxygenated blood from the heart to the lungs, where it gets rid of CO~2~ and collects oxygen before returning to the other side of the heart.\ A systemic circuit driven by the left side of the heart pumps oxygen-rich blood to all the cells of the body and delivers CO~2~ rich blood back to the opposite side of the heart. Both sides are interconnected but separated by the septum of the heart.** **[Blood Vessels]** **There are three main types of blood vessel: Arteries, Capillaries and Veins**  **(3)** **[Arteries]** **[Veins]** **[Capillaries]** ----------------------------- ----------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------ **Lumen** **Small** **Large** **Tiny** **Wall** **Thick Wall -- Outer layer of collagen and inner layer of smooth muscle and elastic fibres** **Thin Wall** **1 cell thick -- Endothelium allows the exchange of materials between blood and cells** **Valves** **None (blood under pressure)** **Present (prevents backflow)** **None** **Direction of blood flow** **Transports blood away from the heart** **Transport blood to heart** **Link arteries to veins** **Blood Type** **Carries Oxygenated Blood (except pulmonary artery)** **Carries deoxygenated blood (except pulmonary vein)** **Oxygenated and deoxygenated** **Blood Flow** **Rapid flow under high pressure** **Slow flow under low pressure - assisted by squeezing action of nearby arteries and muscles** **Slow, pressure falling (allows time for exchange of substances to occur)** **Pulse** **Blood flows in pulses** **Blood flows at a steady rate** **No pulse** [Arterioles\ ]Arterioles are branches of arteries or small arteries. They have the same structure as arteries but are smaller. The muscle layer surrounding the arterioles can contract, causing the lumen of the arteriole to constrict. This can reduce blood flow.\ [Venules]*\ *Venules are small veins that are formed when capillaries start to join again. The blood in venules is under low pressure and does not pulse. It is also rich in CO~2~ and low in O~2~. The blood is moving back towards the heart. [Blood Flow through the body] A diagram of a human body Description automatically generated(4) \- Deoxygenated blood (dark red) leaves the right ventricle of the heart under high pressure through the semilunar valves into the pulmonary artery. This is the only artery that carries deoxygenated blood. It passes through the capillaries of the lungs, losing CO~2~ and collecting oxygen\ - Oxygen rich blood (bright red) leaves the lungs through the pulmonary vein and enters the left atrium. This is the only vein that carries oxygenated blood\ - The blood passes through the bicuspid valve into the left ventricle. It is pumped through the semilunar valves into the aorta. Some goes to the head through the carotid artery, the rest passes downwards to the body through the aorta\ - The hepatic artery goes to the liver and the mesenteric artery goes to the intestines The renal artery supplies blood to the kidneys where it is purified. The rest goes to the gonads and the legs\ - In each of these organs, the blood passes through capillaries and loses all its pressure and most of its oxygen before it starts its journey back to the heart through the interior vena cava (5) \- Deoxygenated blood from the head and arms enters the heart through the superior vena cava. Deoxygenated blood from the rest of the body enters the heart through the inferior vena cava.\ - Both vessels empty into the right atrium. The contraction of the atrium causes this blood to flow through the tricuspid valve into the right ventricle. When the ventricle contracts, it forces the blood out through the semilunar valve into the pulmonary artery, which goes into the lungs, where the blood loses CO~2~ and collects oxygen\ - Oxygenated blood leaves the lungs through the pulmonary veins and enters the heart at the left atrium. The contraction of the atrium causes this blood to flow through the bicuspid valve into the left ventricle. When the left ventricle contracts, it forces the oxygenated blood into the aorta, through the semilunar valve. Blood from the aorta travels around the whole body [Hepatic Portal System\ ]Veins that do not return to the heart but go to a second capillary bed are called portal veins. The vein leading from the intestines to the liver is called the hepatic portal vein. The hepatic portal vein brings blood rich in digested food, but lacking in oxygen, from the intestine directly to the liver. The blood is modified in the liver and then transported back to the heart. (6) [Heartbeat\ ]The heart muscle is a specialised tissue. It is strong, branched, and never tires. The normal rate of the human heart when resting is about 75 beats per minute. CO~2~ levels in the blood are monitored by the Medulla Oblongata in the brain and this information is used to control the heartbeat.\ Each beat of the heart sends a pulse of pressure along the artery. This is most easily detected at the wrist or neck and is normally taken at the wrist using the first two fingers of the left hand.\ The heartbeat is the sound made by the valves of the heart closing. It is often described as a 'lub-dub' sound. The 'lub' is made when the bicuspid and tricuspid valves shut under the backpressure from the blood in the contracting ventricles. The 'dub' sound is made when the semilunar valves of the aorta and pulmonary artery slam shut at the backpressure from the arteries.\ Heart-muscle tissue is auto-rhythmic and will beat on its own. However, there is a pacemaker in place to coordinate the contraction of cells in sequence. It consists of a group of cells in the wall of the right atrium, called the sino-atrial (SA) node which initiates the actual contraction, and a relay station in the wall between the left and right atria near the ventricles, called the atrioventricular (AV) node. [The Cardiac Cycle] The Cardiac cycle is one complete sequence of blood filling and emptying the heart.\ - Diastole is the period of relaxation during which the heart fills\ - Systole is the period of contraction during which the heart empties\ - Both sides of the heart beat in unison\ During diastole, the muscles of the atria and ventricles relax, allowing blood to flood from the vena cava and pulmonary veins into the atria and ventricles.\ - Once the chambers are full, the SA node initiates contraction, which forces the last of the blood from the atria into the ventricles. Once the atria is completely empty, the AV node initiates systole.\ - This contraction slams the cuspid valves shut, preventing blood being forced back into the atria and forcing blood out of the heart through the semilunar valves into the aorta and pulmonary arteries\ - Both atria and ventricles relax, and diastole starts again. The semilunar valves prevent backflow of blood under pressure from the arteries [Blood pressure\ ]***- Blood pressure is the force exerted by the blood on the walls of the arteries due to the contracting of the heart. It depends on the volume of blood within the system and the space available within the blood vessels\ - Blood pressure is measured in an artery of the upper arm using a sphygmomanometer.\ - An inflatable cuff is used to measure the pressure required to stop the blood flow at this point. Two pressures are measured: systolic and diastolic pressures of the ventricles (120/80 mm Hg -- for a healthy adult).\ - These values normally rise with age. If the lower of the two is above 95 the person is suffering from high blood pressure (hypertension). High blood pressure is often caused by blockages in arterioles or small arteries.*** ***[A healthy circulatory system\ ]- Smoking: Smoking can cause cancer, emphysema, atherosclerosis, and high blood pressure which can lead to heart attacks and strokes\ - Diet: A diet rich in saturated fats can lead to obesity which can cause high blood pressure and a blockage of coronary arteries, leading to heart disease\ - Exercise: Regular exercise improves the efficiency of the circulatory system and reduces the risk of heart disease*** **[Blood Composition]** [Plasma\ ]Plasma makes up 55% of blood. Plasma is a straw-coloured liquid matrix composing of 90% water and 10% dissolved proteins, salts, foodstuffs and waste materials.\ *Functions of Plasma Proteins\ *- A series of proteins prevent blood loss and the entry of pathogens by clotting\ - Antibodies mark pathogens and infected or damaged cells for attack by phagocytic white blood cells\ - Albumen maintains the osmotic balance within the organism\ *Functions of Dissolved Salts\ *- Maintain osmotic balance\ - Essential for the proper functioning of cells [Red Blood Cells\ ]-Red blood cells are the most abundant cells and are produced in the red bone marrow of long bones.\ - Red blood cells do not contain a nucleus or mitochondria when they are mature, which allows them to carry out their role of transporting oxygen around the body with maximum efficiency\ - Biconcave discs\ - Filled with the red respiratory pigment haemoglobin\ - Survive for approximately 120 days before being broken down and recycled by the spleen and liver to make bile pigments [White Blood Cells\ ]White blood cells are made in the bone marrow. Their numbers can increase when an infection is present. White blood cells defend the body from attack. There are many different types of white blood cells including:\ - Monocytes: The largest white blood cell and account for about 7% of all white blood cells. They form part of the innate immune system, attacking and engulfing anything they consider not to be part of the body itself. Monocytes have a large bean shaped nucleus; they move by amoeboid motion and engulf cells by phagocytosis. After engulfing the cells, they present antigens from the destroyed cell to T-Cells.\ - Lymphocytes: Have a large spherical nucleus and they make up 20-40% of all white blood cells. They are stored in the lymphatic system. Most are short lived, surviving for only a few weeks. There are many types of lymphocytes including T Cells (attack invaders), and B-Cells (make antibodies). [Platelets\ ]- Cellular fragments that play a major role in blood clotting\ - They gather at the site of a wound and start a series of chemical reactions that result in the production of fibrin\ - Fibrin forms a network of strands across the wound, trapping blood cells and forming a scab. This prevents blood loss and the entry of pathogens [Blood Groups\ ]- Blood groupings are based on antigens that occur on the outer surface of blood cells. An antigen is a substance that produces an immune response, which is essentially the production of a protein called an antibody.\ - Blood groups determine which blood groups can be safely received in blood transfusions.\ - If someone is given the wrong blood group in a transfusion there may be a sever allergic reaction, which can kill. Blood Group O A B AB ------------- --------- ----- ----- --------- Antigens Neither A B A and B Antibodies A and B B A Neither Population 55% 31% 11% 3% [Rhesus Factor\ ]- The Rhesus protein was first discovered in Rhesus Monkeys\ - Blood with the rhesus antigen on the surface is said to be Rhesus positive (RhD+), and blood without it is said to be Rhesus negative (RhD-)\ *Importance in pregnancy*\ - If the mother is Rhesus negative, and the unborn child is Rhesus positive, then some of the baby's Red blood cells with Rhesus antigens may cross into the mother's bloodstream at the end of pregnancy.\ - The mother will recognise these rhesus antigens as 'foreign' and produce antibodies against them. Usually there is no danger to the baby during the first pregnancy, though the mother is now sensitised to the rhesus antigen.\ - The antibodies produced by the mother will destroy the baby's red blood cells in subsequent Rhesus positive babies because antibodies pass into baby.\ - This may cause the baby to be anaemic, brain damaged or stillborn\ - To prevent this happening, the mother may be injected with Rhesus antibodies immediately after the birth of her first child. These will destroy the baby's red blood cells before they cause a natural build-up of anti-Rhesus antibodies in her blood [Mandatory Practical -- Dissect, Display and identify a sheep's or ox's heart] \- Place the heart on a dissecting board with the front facing upwards\ - Identify the blood vessels: aorta, pulmonary artery, vena cava and pulmonary vein.\ - Make a shallow cut in the left ventricle and the left atrium.\ - Push open the chambers and examine the internal structure.\ - Locate the bicuspid valve and note the chordae tendinae -- anchoring the cusps of the valve\ - Repeat the previous steps for the right side of the heart.\ - Locate the tricuspid valve and note the chordae tendinae anchoring the cusps\ - **Note the difference between the walls of the left ventricle and the right ventricle\ - Locate the septum separating the left from the right side of the heart.\ - Insert a forceps under the moderator band in the right ventricle\ - Identify the opening at the base of the aorta, above the semi-lunar valves, leading to the coronary arteries\ - To highlight the coronary arteries: Using a dropper, pump air into the opening at the base of the aorta** **[Mandatory Practical -- Investigate the effect of exercise on the pulse rate of a human\ ]- Measure your resting pulse rate at the wrist, using your second finger. Count the number of beats in 15 seconds and multiply this figure by 4. Repeat twice more and take an average\ - Take some gentle exercise, like walking, for three minutes and then sit down\ -Record your new pulse rate three times and take an average\ Note the time taken for the pulse to return to its resting rate\ - Take some strenuous exercise, like running, for three minutes and sit down\ - Record the new pulse rate three times and take an average\ - Once again, note the time it takes for your pulse to return to its resting rate\ - Document the results as follows\ ** **Activity** **Pulse Rate 1** **Pulse Rate 2** **Pulse Rate 3** **Average Pulse Rate** **Time taken to return to resting rate** -------------- ------------------ ------------------ ------------------ ------------------------ ------------------------------------------ **Resting** **Running** **Walking** **- Heart rate increases with level of exercise\ - The faster the heart rate is after exercise, the longer it takes to return to normal\ - A fit person's heartbeat is slower at rest, and returns to resting rate faster than that of an unfit person** **[The Lymphatic System]** [Structure of The Lymphatic System]  (7) \- Lymphatic capillaries: Narrow, blind-ending tubes that collect excess tissue fluid from around cells and return it to the blood\ - Lymph nodes: Concentrated in the neck, groin, and armpit. Contain phagocytic white blood cells which filter foreign particles, cancer, and bacteria from the lymph. They produce and store B-lymphocytes and T-lymphocytes which detect antigens such as viruses and produce antibodies against them\ - Lymph vessels: Capillaries drain the lymph into larger tubes called lymph vessels. The lymph moves along vessels very slowly. The lymph reaches the thoracic duct where it enters the bloodstream through the left subclavian vein\ - Spleen: Destroys defective red blood cells and recognises antigens to help prevent disease\ - Thymus: Responsible for the development and training of T-cells [Functions of The Lymphatic System\ ]*Transport\ *- To absorb and transport fatty acids and glycerol via lacteals from the small intestine to skin or other organs for storage\ - Tissue fluid and plasma proteins that have leaked from capillaries are returned into the blood in the subclavian veins\ *Defence\ *- Phagocytic white blood cells in the lymph nodes filter the lymph, removing pathogens, cell debris and cancer cells\ - Lymph nodes produce and export B-lymphocytes and T-lymphocytes **[Exam Questions]** [2014 -- HL -- Section A -- Question 3] 3\. The diagram shows a region of tissue that includes body cells and parts of the circulatory and lymphatic systems. A diagram of a nervous system Description automatically generated \(a) Name part C -- Lymph Vessel\ (b) What type of blood vessel is A? Arteriole\ (c) If a transverse section of A were viewed under the microscope state one way in which it would differ from a transverse section through B. A has a thicker wall than B\ (d) Give two functions of the lymphatic system.\ 1. Collect excess tissue fluid and return it to the bloodstream.\ 2. Maturation of lymphocytes\ (e) Give one way in which lymph differs from blood. Lymph does not have any red blood cells\ (f) Name a major blood vessel that returns the blood in B to the heart. Vena Cava [2014 -- HL -- Section B -- Question 9] \(b) Answer the following in relation to investigations that you carried out in the laboratory.\ (i) 1. When dissecting a mammalian heart where, precisely, did you locate the tricuspid valve? Between the right atrium and the right ventricle\ 2. Briefly describe how you carried out the dissection to expose this valve. Using a scalpel, an incision was made into the right hand side of the heart\ 3. Where did you find the semilunar valves during the dissection? At the base of the aorta\ (ii) 1. When you investigated the effect of exercise on the human pulse rate or breathing rate what did you first establish? Resting pulse rate\ 2. How did you measure pulse rate or breathing rate?\ - Felt for pulse on the wrist using index and middle finger\ - Counted the number of pulses for one minute. [2014 -- HL -- Section C -- Question 9] \(c) Answer the following questions in relation to carbon dioxide.\ (i) Name a structure found in cells in which carbon dioxide is produced. Mitochondrion\ (ii) Give a feature of a capillary which allows the rapid uptake of carbon dioxide. Wall is one cell thick\ (iii) Carbon dioxide levels are usually higher in venous blood than in arterial blood. Why is this the case? Venous blood has collected carbon dioxide from the body cells that produce carbon dioxide as a result of respiration\ (iv) Name a blood vessel which is an exception to the situation outlined in (iii) above. Give a reason for the exception. Pulmonary vein - Carries blood from the lungs that has had carbon dioxide excreted\ (v) Briefly outline the role of carbon dioxide in the control of the human breathing rate.\ - Medulla oblongata senses the amount of carbon dioxide in the blood\ - High levels of carbon dioxide stimulates increased breathing rate [2014 -- HL -- Section C -- Question 14] \(i) Draw a diagram of a transverse section through a young dicotyledonous stem as seen under the low power lens of a microscope. Indicate on your diagram a location for each of the following: dermal tissue, ground tissue, vascular tissue. \(ii) 1. Which of the above tissue types has a different location in a young root? Vascular tisses\ 2. Where precisely is the tissue type referred to in 1. found in the root? Centre of the root\ 3. Give one function of ground tissue. Photosynthesis\ (iii) Draw labelled diagrams to show the detailed structure of the two vascular tissues of plants. \(iv) Which of the tissues referred to in (iii) is composed of living cells? Phloem\ (v) What is the function of meristematic tissue? Mitosis **[References]** 1. Leavingbio.net 2. Bio1152.nicerweb.com 3. Biology-igcse.weebly.com 4. Thealevelbiologust.co.uk 5. Istockphoto.com 6. Nagwa.com 7. Nurselabs.com