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Revision notes on cells, life processes and living organisms CHARACTERISTICS OF LIVING ORGANISMS 1.1 recall that living organisms share the following basic characteristics (ch1) Movement Muscles in animals, directional growth in plants, flagella in bacteria Respiration Release energy from food Sensitivity Responding to changes in the environment Growth Increase in size and mass Reproduction Producing offspring (more of the same kind of organism) Excretion Getting rid of toxic waste Nutrition Taking in or producing their own food Control of internal conditions Keeping internal conditions constant, e.g body temperature VARIETY OF LIVING ORGANISMS 1.2 Describe common features shared by organisms within the groups: plants, animals, fungi, bacteria, protoctists and viruses, and describe examples and their features in each group (ch2) Plants Plants are multicellular organisms Examples include flowering plants, such as a cereal (for example maize) and a herbaceous legume (for example peas or beans). Plants contain chloroplasts and are able to carry out photosynthesis Plants have cellulose cell walls. The cell wall and the vacuole together give the cell its shape and maintain turgor (stiffness) to support the plant (see point 2.14) Plants store carbohydrates as starch or sucrose. Starch is stored in the leaf and the root; sucrose is transported in the phloem (see point 2.51) Animals Animals are multicellular organisms Examples include mammals (e.g. humans) and insects (e.g. housefly and mosquito). Mammals keep a constant body temperature and are vertebrates (have a backbone) Insects are invertebrates Animals do not contain chloroplasts and are not able to carry out photosynthesis: animals are heterotrophic – they consume other organisms for their nutrition Animals usually have nervous coordination and are able to move from one place to another Animals have no cell walls and they often store carbohydrate as glycogen Revision notes on cells, life processes and living organisms Fungi Fungi are not able to carry out photosynthesis; many are multicellular; some, like yeast, are single-celled. Their body is usually organised into a mycelium of threadlike structures called hyphae, which contain many nuclei; the hyphae feed by excreting digestive enzymes onto food material and absorbing the organic products; this is known as saprotrophic nutrition Fungi have cell walls made of chitin; they may store carbohydrate as glycogen. Examples include mucor (green-blue mould) which reproduces using spores, and yeast, used to make bread or beer. Bacteria Bacteria are microscopic single-celled organisms with no nucleus (are prokaryotes). Examples: Lactobacillus bulgaricus, a rod-shaped bacterium used to make yoghurt from milk, and Pneumococcus, a spherical bacterium that causes pneumonia. Bacteria have a cell wall, cell membrane, cytoplasm and plasmids (rings of extra DNA: see points 5.12, 5.13). Bacteria DNA is in a large loop called the chromosome. Most bacteria feed off other living or dead organisms (saprotrophic nutrition). A few bacteria can carry out photosynthesis. Protoctists Protoctists are microscopic single-celled organisms. They are complex cells with a nucleus and other organelles. They are not animals or plants because each cell is an individual organism, not part of a multicellular organism. Some protoctists, like Amoeba, have features like an animal cell. Others, like Chlorella, have chloroplasts and are more like plants. A pathogenic protoctist, Plasmodium, is responsible for causing malaria (see point 1.30) Viruses Viruses are small particles, smaller than bacteria; they are parasites and can reproduce only inside living cells; they infect every type of living organism. Examples include the tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, the influenza virus that causes ‘flu’ and the Revision notes on cells, life processes and living organisms HIV virus that causes AIDS (see point 1.30). 1.3 Viruses have a variety of shapes and sizes; they have no cellular structure but have a protein coat and contain genetic material - either DNA or RNA. Apart from reproduction, viruses do not perform any of the life processes (MRSGRENC) Recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria, protoctists or viruses. Pathogen: an organism that causes disease like a virus, fungus or bacterium. Viruses are responsible for AIDS and 'flu; bacteria can cause pneumonia; malaria is caused by a protoctist; Athlete's foot (Fusspilz) is a fungal infection (see point 1.2) NB white blood cells provide defence against pathogens: phagocytes are non-specific, lymphocytes are specific (see point 2.61) SECTION 2: STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS A) LEVELS OF ORGANISATION 2.1 Describe the levels of organisation within organisms: organelles, cells, tissues, organs and systems. (ch1) ORGANISM < ORGAN SYSTEM < ORGAN < TISSUE < CELL < ORGANELLE < BIOLOGICAL MOLECULE Biological molecule – molecule made by organisms and used in life processes, e.g. respiration Examples: DNA, proteins, lipids, starch, glucose, amino acids, haemoglobin, enzymes Organelles - structures within a cell that carry out specific functions Examples: nucleus, chloroplast, mitochondria (see point 2.20, 2.30) Cells - the basic structural and functional unit from which all biological organisms are made Examples of specialized cells include nerve cells, sperm cells, root hair cells and palisade mesophyll cells Tissues - a group of specialized cells, which are adapted to carry out a specific function Examples include muscle tissue, nerve tissue, palisade mesophyll tissue (in leaves) Organs - a collection of two or more tissues, which carries out a specific function or functions Examples include the heart, brain, spinal cord, liver, kidneys, lungs, bladder, small intestine, pancreas and stomach; in a plant the leaf is an example of an organ. Organ Systems - a group of two or more organs Examples include the circulatory system, nervous system, endocrine system and digestive system. Revision notes on cells, life processes and living organisms B) CELL STRUCTURE 2.2 Recognise cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole (ch1) 2.3 Describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole (ch1) 2.4 Nucleus structure: at the centre of the animal cell and between the vacuole and cell membrane in a plant cell. Contains DNA Nucleus function: Controls cell activities Cell membrane structure: selectively permeable boundary of the cell Cell membrane function: Controls what substances go in and out of cell Cytoplasm structure: a jelly-like substance that fills the cell and contains enzymes Cytoplasm function: site of most of the chemical reactions in the cell. Chloroplast structure: contain a green pigment called chlorophyll. (Only plant cells) Chloroplast function: Absorb light energy to make (food)glucose by photosynthesis Cell wall structure: made of cellulose or chitin which surrounds the cell membrane (Only plant cells) Cell wall function: rigid structure that gives the cell support and strengthens it. Vacuole structure: largest part of plant cell, in the centre; contains cell sap, a store of dissolved sugars and minerals. (Only in plants) Vacuole function: fills with water and maintains turgor to support the plant Describe the differences between plant and animal cells. (ch1) Both contain a nucleus, cytoplasm and a cell membrane Animal cells do not have a cell wall, central vacuole or chloroplasts (see point 2.30) Revision notes on cells, life processes and living organisms BIOLOGICAL MOLECULES AND ENZYMES 2.5 Recall the chemical elements present in carbohydrates, proteins and lipids (fats and oils) (ch4) Carbohydrates and lipids: C,H,O; Proteins also have nitrogen so their elements are C,H,O,N 2.6 C = carbon, H = hydrogen, O = oxygen; N = nitrogen Describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units: (ch4) starch and glycogen from simple sugar (glucose); protein from amino acids; lipid from fatty acids and glycerol 2.7 Describe the tests for glucose and starch (ch4) Glucose: Benedict's solution, heated Colour of solution changes from blue to yellow/orange with a brick red precipitate if glucose is present. Starch: Iodine solution Colour change from yellow-brown to blue-black if starch is present 2.8 Understand the role of enzymes as biological catalysts in metabolic reactions (ch1) (there is more about specific enzymes in the notes about nutrition and digestion) 2.9 Understand how the functioning of enzymes can be affected by changes in temperature (ch1) All enzymes have an optimum temperature where they work fastest Low temperatures: less kinetic energy means fewer collisions between enzyme and substrate High temperature: the enzyme is denatured (changes shape making the enzyme inactive) 2.10 Understand how the functioning of enzymes can be affected by changes in pH (ch1) All enzymes have an optimum pH where they work fastest At high or low pH, the enzyme is denatured so is inactive or less active 2.11 Describe how to carry out simple controlled experiments to illustrate how enzyme activity can be affected by changes in temperature (ch1) The experiment in the syllabus is using amylase to break down starch. Iodine (on a spotting tile) is used to test whether starch is still present (see point2.70), The amylase / starch mixture is tested at different temperatures, e.g. 20°C, 30°C, 40°C, 50°C Revision notes on cells, life processes and living organisms D) MOVEMENT OF SUBSTANCES INTO AND OUT OF CELLS 2.12 2.13 recall simple definitions of diffusion, osmosis and active transport (ch1) understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport (ch1) Diffusion: Movement of particles from a region of higher concentration to a region of lower concentration. It is passive – it does not need energy from respiration as it depends on the movement energy of the particles themselves (their kinetic energy) Osmosis: net movement of water molecules from an area of higher water concentration (water potential) to an area of lower water concentration (or water potential) across a semipermeable membrane Alternatively, osmosis can be described as the net movement of water molecules from a more dilute (or hypotonic) solution to a more concentrated (hypertonic) solution across a semipermeable membrane. Active transport: movement of particles from a region of lower concentration to a region of higher concentration using energy from respiration Can also be described as movement against the concentration gradient (whereas passive diffusion moves substances down their concentration gradient) 2.14 understand the importance in plants of turgid cells as a means of support The vacuole fills with water and puts pressure on the cytoplasm, which presses against the cell wall and makes the cell turgid (stiff) 2.15 understand the factors that affect the rate of movement of substances into and out of cells the rate of movement of substances increases when the surface area to volume ratio is high, temperature is high, and concentration gradient is steep (big difference in concentration) the distance that a substance has to move is also important in root hair cells (see point 2.53), in the small intestine (see point 2.31), and in gas exchange between the alveoli and capillaries ( 2.46) 2.16 describe simple experiments on diffusion and osmosis using living and non-living systems. Diffusion: Absorption of coloured substances by cubes of agar gel (small cubes => fast diffusion as SA:Volume ratio is higher) Osmosis: Potato stick experiment (increased mass when in distilled water) Factors investigated: SA:Volume ratio, temperature; concentration gradient Revision notes on cells, life processes and living organisms (2.17-2.22 Nutrition, Flowering plants) 2.23 understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre macronutrients (the main part of the diet) are carbohydrate, protein and lipids; micronutrients (necessary in small amounts) are vitamins and minerals; water and fibre are not nutrients but are necessary in the diet NB diet means all the food and drink you ingest, not special foods or restrictions 2.24 recall sources and describe functions of macronutrients: carbohydrate, protein, lipid (fats and oils) carbohydrates are the main form of fuel for respiration so are important for energy production in a healthy diet carbohydrate is mainly starch, the storage form of sugar in plants carbohydrates are digested into single sugars (mainly glucose) by enzymes; simple sugars are quickly absorbed, so eating them can cause obesity starch is found in potatoes, rice and cereals; sugars are found in fruits, desserts and sweets proteins are made of amino acids, and are found in meat, fish, eggs, milk and beans We need less protein than carbohydrate. Protein is used for growth and repair. lipids are fats and oils (oils are liquid at room temperature; fats are usually saturated and are soft solids at room temperature) lipids are used to store energy and to make body fat that provides cushioning and heat insulation. They also build cell membranes. lipids are very high in energy and so a limited amount should be taken in a calorie-controlled diet. Saturated fats are generally thought to increase the risk of heart disease. Recall sources and describe functions of (micronutrients) vitamins A, C and D, and the mineral ions calcium and iron Vitamin A is found in leafy vegetables and in liver Vitamin A prevents night-blindness Vitamin C is found in (especially citrus) fruits Vitamin C is necessary for wound healing and sticking cells together Vitamin D is found in milk products and is made by the skin exposed to sunlight. Vitamin D enables us to absorb calcium for healthy bones and teeth iron is found in green leafy vegetables and particularly in red meat Iron is needed to make haemoglobin that transport oxygen in red blood cells Calcium is found in milk and nuts Calcium is necessary for the growth of healthy bones and teeth, and prevents rickets Revision notes on cells, life processes and living organisms Recall sources and describe functions of water and dietary fibre as components of the diet Dietary fibre is necessary to prevent constipation and keep the large intestine healthy Fibre is in wholegrain cereals and in whole fruits and vegetables Water is involved in all metabolic reactions in the body. It is part of all drinks (yes, really!) 2.26 recognise the structures of the human alimentary canal and describe in outline the functions of the organs: mouth mainly mechanical digestion (teeth bite, grind and chew and saliva moistens) but also chemical digestion of starch, using salivary amylase oeesophagus mechanical digestion: a bolus of food is swallowed and pushed to the stomach using peristalsis stomach mechanical digestion: the stomach churns the food, increasing its surface area chemical digestion: mixing it with a protease (pepsin) and HCl acid; chemical digestion: acid kills bacteria, pepsin begins the digestion of protein in to peptides pancreas Chemical digestion: the pancreas produces many digestive enzymes including amylase, proteases and lipase. liver produces bile, which emulsifies lipids and neutralises stomach acid small intestine Most chemical digestion and all absorption takes place here Reference: http://bio1151b.nicerweb.net/Locked/media/ch41/41_19HumanDuodenum.jpg large intestine absorbs water from the undigested food 2.27 understand the processes of ingestion, digestion, absorption, assimilation and egestion ingestion taking food into the mouth digestion mechanical and chemical processes that break down large insoluble molecules into small soluble molecules absorption small, soluble molecules are absorbed into the bloodstream from the small intestine (see point2.31) assimilation absorbed nutrient molecules are used by cells for respiration or to make new substances egestion undigested food passes out of the body via the anus Revision notes on cells, life processes and living organisms 2.28 explain how and why food is moved through the gut by peristalsis Peristalsis: all parts of the digestive tract are surrounded by circular and longitudinal muscle when the circular muscle contracts, it squeezes the food along 2.29 understand the role of digestive enzymes amylase digestion of starch to maltose maltase digestion of maltose to glucose proteases digestion of proteins to peptides/amino acids lipases digestion of lipids to fatty acids and glycerol 2.3 recall that bile is produced by the liver and stored in the gall bladder understand the role of bile in neutralising stomach acid and emulsifying lipids 2.31 emulsifying: splitting lipids up into droplets to increase the surface area for lipase to act on neutralising stomach acid to provide optimum pH for digestive enzymes explain how the structure of a villus helps absorption of the products of digestion in the small intestine Remember factors in diffusion: concentration gradient, surface area and short distance 1. large surface area: villi (finger-like shape) with microvilli on their surface 2. short distance: - the wall of the villi is one cell thick and - blood vessels are close to the surface 3. concentration gradient: many blood vessels taking away absorbed nutrients 4. a lacteal at the centre of a villus transports glycerol and fatty acids from lipid digestion 2.25 understand that energy requirements vary with activity levels, age and pregnancy Energy requirements decrease in old age. Teenagers need quite a high energy intake as fuel for growth and activity. Athletes or people doing heavy manual work use a lot of energy and need to replace it In pregnancy, extra energy is required for the foetus to grow 2.32 recall how to carry out a simple experiment to determine the energy content in a food sample a calorimeter tests the energy content of food by combusting (burning) a sample and measuring how much heat energy is released (the heat is absorbed by water) a simple experiment: burn a food sample (e.g. a nut) on a needle and use it to heat water in a test tube above it – record mass of nut, temperature increase + volume of water Revision notes on cells, life processes and living organisms f) Respiration 2.33 recall that the process of respiration releases energy in living organisms the energy is stored in the form of a chemical called ATP energy from respiration is needed for all life processes; in the end, it is all released as heat. 2.34 describe the differences between aerobic and anaerobic respiration NB. All types use glucose and release some energy. Aerobic is the most efficient. 1. aerobic: uses and needs oxygen; 2. anaerobic: when oxygen is not available – produces lactic acid 3. anaerobic respiration in bacteria / yeast is called fermentation and produces ethanol and carbon dioxide (how beer is produced) NB Why we breathe hard after strenuous exercise (the oxygen debt) 1. we can’t get enough oxygen to the muscles for them to get all the energy for hard exercise just from aerobic respiration, so they use anaerobic respiration 2. anaerobic respiration produces lactic acid 3. this lactic acid can cause cramps and we need to break it down 4. lactic acid is broken down by oxygen, so we need to breathe harder until all the lactic acid is broken down (the amount of oxygen needed = the oxygen debt) 2.35 2.36 2.37 recall the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms Word equation: glucose plus oxygen => carbon dioxide plus water . Symbol equation: C6H12O6 + 6O2 => 6H20 + 6CO2 recall the word equation for anaerobic respiration in plants and in animals anaerobic respiration in animals: glucose => lactic acid fermentation in plants, bacteria and yeast: glucose => ethanol + carbon dioxide describe simple controlled experiments to demonstrate the evolution of carbon dioxide and heat from respiring seeds or other suitable living organisms Heat from respiration: use peas, for example, in a vacuum flask closed with cotton wool so that gases can enter and leave. The temperature will rise as the peas respire. Control: compare with peas that have been boiled and so are dead and cannot respire; Standardize: sterilise the peas so bacteria cannot grow on their surface; same amount of peas, same size vacuum flask Carbon dioxide from respiration: put small organisms into a tube on a wire mesh above some hydrogencarbonate indicator, and seal the tube (put a bung in). The indicator will change from orange/red to yellow. Control: do the same experiment without organisms, or using dead organisms; Revision notes on cells, life processes and living organisms Standardize: same size tube, same volumeof hydrogencarbonate indicator, same temperature g) Gas exchange 2.38 understand the role of diffusion in gas exchange. in the tissues, carbon dioxide diffuses from the cells, where it is at a high concentration because it has been produced by cell respiration, into the capillaries, where it has a lower concentration. in the lungs, carbon dioxide diffuses from the blood, where it is at a high concentration, into the alveoli, where it has a lower concentration and oxygen diffuses from the alveoli, where it is at a high concentration, into the capillaries where it has a lower concentration (Remember factors in diffusion: concentration gradient, surface area and short distance e.g. the capillaries are very fine so have a large surface area, and have a thin wall) 2.44 Breathing in humans: describe the structure of the thorax Structure: ribs intercostal muscles diaphragm trachea bronchi bronchioles alveoli pleural membranes Your notes Revision notes on cells, life processes and living organisms 2.45 understand the role of the intercostal muscles and the diaphragm, in ventilation (external) intercostal muscles diaphragm rib cage volume in the thorax pressure in the thorax air is forced 2.46 1. 2. 3. 4. inhalation contract exhalation relax contracts and flattens pulled upwards and outwards increases relaxes and becomes tent-shaped moves down and inwards decreases decreases increases into the lungs out of the lungs explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries alveoli have thin walls (short distance for diffusion) and a large surface area (they are small and there are many of them) capillaries are close to alveoli (short distance for diffusion) and the rich blood supply maintains the a steep concentration gradient by bringing CO2 to the lungs and removing oxygen Revision notes on cells, life processes and living organisms 2.47 understand the biological consequences of smoking in relation to the lungs and the circulatory system tar in cigarette smoke sticks to and irritates bronchioles which fill up with mucus causing lung infections (bronchitis) and emphysema (enlarged air spaces and less surface area) tar also contains mutagens (see point 3.34) which cause lung cancer carbon monoxide in cigarette smoke binds to haemoglobin and prevents it from carrying oxygen; the heart needs to work harder, leading to heart disease 2.48 describe a simple experiment to investigate the effect of exercise on breathing in humans. Use a treadmill or steps; stopwatch; Measure: count the breaths per minute at rest and immediately after exercise. Standardize: same age, sex, conditions (temperature of surroundings, time of day, size of step, length of exercise...) h) Transport 2.49 understand why simple, unicellular organisms can rely on diffusion for movement of substances in and out of the cell small organisms have a large surface area to volume ratio so diffusion is fast enough to support the organism's needs for nutrition and gas exchange for respiration 2.50 understand the need for a transport system in multicellular organisms large organisms have a lower surface area to volume ratio so diffusion is too slow to support life processes (nutrition and respiration) to support respiration the lungs provide a large surface area for gas exchange, and the circulatory system transports oxygen to the tissues and removes waste carbon dioxide (2.51-2.56 Transport in flowering plants) 2.57 recall the composition of the blood: red blood cells, white cells, platelets and plasma 2.58 understand the role of plasma in the transport of carbon dioxide, digested food, urea, hormones and heat energy 2.59 describe the adaptations of red blood cells for the transport of oxygen, including shape, structure and the presence of haemoglobin biconcave shape increases the surface area for faster diffusion of oxygen into the cell (in the lungs) and out (into the tissues) haemoglobin binds to oxygen in the lungs (oxyhaemoglobin) and releases it in the tissues; the cell carries more haemoglobin because it has no nucleus. shape makes it flexible; small size + flexibility help it pass through narrow capillaries Revision notes on cells, life processes and living organisms 2.60 describe how the immune system responds to disease using white blood cells, illustrated by phagocytes ingesting pathogens and lymphocytes releasing antibodies specific to the pathogens. phagocytes engulf and digest pathogens. (they are non-specific) lymphocytes produce specific antibodies that attach to pathogens and destroy them either directly or make them stick together 2.61 understand that vaccination results in the manufacture of memory cells, which enables future antibody production to the pathogen to occur sooner, faster and in greater quantity Normally, it takes time for the body to produce the specific lymphocyte to produce the antibody that will attach to a new pathogen (1st exposure to antigen). The pathogen can make you ill before the immune system responds effectively; Some of the lymphocytes remain in the blood as memory cells . (2nd exposure to antigen)Memory cells make the immune response fast if a familiar pathogen enters the body, memory cells produce antibody SOONER, FASTER and in GREATER QUANTITY. 2.62 2.63 Recall that platelets are involved in blood clotting, which prevents blood loss and the entry of microorganisms When exposed to air or blood vessel damage, Platelets cause: soluble fibrinogen to be converted to insoluble fibrin threads. The fibrin threads form a mesh that catches red blood cells to form a clot. The clot prevents excessive blood loss and stops pathogens entering the body. describe the structure of the heart and how it functions The heart is a double pump (mammals have a double circulation), so both sides are very similar, consisting of muscle walls, valves, some nervous tissue and its own blood vessels, the coronary circulation The muscle walls on the left side of the heart are thicker to provide enough pressure to pump the blood through all the arteries of the body; the right side has to pump it through the lungs only Revision notes on cells, life processes and living organisms 1. oxygenated blood enters the left atrium from the lungs through the pulmonary vein deoxygenated blood enters the right atrium from the body through the vena cava 2. when the atria are full, the atrial muscles contract, increasing the pressure in the atria 3. high pressure in the atria opens the tricuspid and bicuspid valves 4. blood flows through the valves (tricuspid on the right, bicuspid on the left) into the ventricles 5. the ventricles fill with blood and the ventricle muscle contracts, increasing the pressure in the ventricles 6. high pressure in the ventricles closes the tricuspid and bicuspid valves, preventing blood flowing backwards, 7. high pressure in the ventricles opens the semilunar valves 8. blood flows through the semilunar valves into the pulmonary artery and the aorta 9. the pulmonary artery transports deoxygenated blood to the lungs to pick up oxygen; the aorta transports oxygenated blood to the body 2.64 understand that the heart rate changes during exercise and under the influence of adrenaline receptors in the aorta monitor the amount of carbon dioxide in the blood if the blood has a high level of carbon dioxide (e.g. during exercise), the medulla sends a signal to the SA node (pacemaker) to increase heart rate. The SA node is also sensitive to adrenaline, so the heart rate increases when the blood contains a lot of adrenaline 2.65 describe the structure of arteries, veins and capillaries and understand their roles Arteries: narrow lumen thick wall containing muscle and elastic fibres elastic fibres and muscle in the wall make the artery flexible so the arteries stretch and recoil to help push the blood along. the thick muscular walls of arteries also maintain the pressure on the blood Revision notes on cells, life processes and living organisms Veins: wider lumen thinner wall than arteries, o the blood flows more slowly and at lower pressure. contain valves o The valves mean that blood in veins can only flows one way Capillaries: 2.66 have walls that are just one cell thick, have pores and they are adapted for exchange between the blood and the tissue fluid by diffusion (oxygen, carbon dioxide, glucose) recall the general plan of the circulation system to include the blood vessels to and from the heart, the lungs, the liver and the kidneys pulmonary artery aorta renal artery, hepatic artery carries deoxygenated blood from the heart to the lungs, carries oxygenated blood from the heart to the body carries oxygenated blood to the kidneys carries oxygenated blood to the liver pulmonary vein carries oxygenated blood from the lungs to the heart to the lungs vena cava renal vein carries deoxygenated blood from the body back to the heart carries deoxygenated blood from the kidney hepatic vein carries deoxygenated blood from the liver hepatic portal vein carries absorbed nutrients to the liver from the small intestine (2.67 excretion in flowering plants, 2.68-2.76 excretion in humans, 2.77-279, general coordination, 2.80-2.82- flowering plants) Humans 2.83 describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems endocrine system: nervous system: chemical messages travel in the blood and… electrical signals* travel along neurones and … … have a widespread effect …communicate directly with other neurones so have a local effect* the response is slower and … nervous responses are usually fast … …lasts longer than nervous signals …but only short-lasting. Revision notes on cells, life processes and living organisms *Chemicals are released in the synapses, the small gaps between neurones – a chemical transmitter from the first neurone diffuses to the membrane of the next neurone, which starts a new electrical signal 2.84 recall that the central nervous system (CNS) consists of the brain and spinal cord and is linked to sense organs by nerves The cerebral cortex is responsible for conscious responses and memory. Coordination happens in the spine, too. The cells in the CNS are relay neurons. 2.85 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses 2.86 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object Automatic responses are known as reflexes. Examples are blinking, the pupillary response to bright light, and the knee jerk (patellar) reflex. They are important for protecting us from injury. The pathway of a reflex is called a reflex arc: the parts of the reflex arc are… stimulus -> receptor -> sensory neurone -> relay neurone/s in CNS -> motor neurone -> effector -> response In the example of withdrawing the finger from a hot object, the stimulus is heat, detected by a temperature receptor in the finger, and the effector is a muscle in the arm. There are also reflexes that involve the brain rather than the spinal cord, e.g. the blink reflex or the pupil reflex. 2.87 describe the structure and function of the eye as a receptor the cornea transparent outer layer at front that refracts (bends) light entering the eye the iris coloured area around pupil, controls how much light enters eye (see 2.88) the sclera protective white outer layer lens, ciliary muscle and suspensory ligaments focuses light rays on the retina (“accommodation”: see point 2.87) the retina and the optic nerve the retina detects light; the signal passes to the brain (the visual cortex) via the optic nerve Revision notes on cells, life processes and living organisms 2.88 understand the function of the eye in focusing near and distant objects responding to changes in light intensity ACCOMMODATION: the lens refracts the light more when focusing on a near object - it becomes fatter because the ciliary muscle contracts and the suspensory ligaments become slack THE PUPILLARY REFLEX: The iris controls how much light enters the eye. In bright conditions, the circular muscle of the iris contracts and the radial muscle relaxes to constrict (make smaller) the pupil, so the retina is not damaged by too much light. 2.90 In dim light the circular muscle relaxes, the radial muscle contracts and the pupil dilates (gets bigger) understand the sources, roles and effects of the following hormones: ADH, adrenaline, insulin, testosterone, progesterone and oestrogen ADH is released from the pituitary ADH causes the kidney to reabsorb more water into the gland- its target organ is the kidney (the blood when the blood is too concentrated (osmoregulation) collecting ducts) (see point2.68 and 2.74) adrenaline is released from the adrenal glands in a "fight or flight" response to situations that cause fear or excitement; target organs include the heart, lungs, liver, brain, eye and muscles the heart pumps more blood, the breathing rate increases, the liver releases glucose, so more glucose and oxygen are supplied to the muscles for energy from respiration; more light enters the eye and mental alertness increases insulin is released by the pancreas when the blood sugar is high; the liver is the target organ testosterone is released by the testes, and oestrogen by the ovaries; the liver converts glucose to glycogen, lowering the blood sugar. The glycogen is broken down again when blood glucose is low they are responsible for secondary sexual characteristics in adolescent boys (testosterone) and girls (oestrogen) Progesterone is produced by the ovaries, like oestrogen: target organ is the uterus Progesterone prepares the lining of the uterus for pregnancy Revision notes on cells, life processes and living organisms 2.89 (CHAPTER 8) describe the role of the skin in temperature regulation, with reference to sweating, vasoconstriction and vasodilation the hypothalamus detects changes in temperature of the blood when the blood becomes cool: blood vessels under the skin constrict (vasoconstriction), so less blood flows to the skin, and less heat is radiated from the skin. Hairs stand up to trap an insulating layer of air. when the hypothalamus detects a rise in the temperature of the blood blood vessels under the skin widen (vasodilation) so more blood flows under the skin and more heat is radiated by the skin; and sweat glands produce sweat, which causes the skin to lose heat energy when the water in the sweat evaporates