HL IB Biology Transport PDF

Head to www.savemyexams.com for more awesome resources HL IB Biology Your notes Transport Contents Blood Vessels Identify Blood Vessels: Skills Measuring Pulse Rate: Skills Coronary Heart Disease: Ski...

Head to www.savemyexams.com for more awesome resources HL IB Biology Your notes Transport Contents Blood Vessels Identify Blood Vessels: Skills Measuring Pulse Rate: Skills Coronary Heart Disease: Skills The Transpiration Stream Adaptations of Xylem Vessels Drawing Root & Stem Structure: Skills Tissue Fluid (HL) Circulatory Systems (HL) The Mammalian Heart (HL) The Cardiac Cycle: Skills (HL) The Roots & Water Transport (HL) Translocation in Plants (HL) Page 1 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Blood Vessels Your notes Capillaries Introduction to blood vessels The circulatory system of the human body contains several different types of blood vessel: Arteries Arterioles Capillaries Venules Veins Each type of blood vessel has a specialised structure that relates to the function of that vessel Blood vessels diagram Page 2 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The circulatory system includes several blood vessels, each specialised to carry out its function Adaptations of capillaries for exchange of materials Capillaries provide the exchange surface in the tissues of the body through a network of vessels called capillary beds The wall of a capillary is made from a single layer of endothelial cells Being just one cell thick reduces the diffusion distance for oxygen and carbon dioxide between the blood and the tissues of the body The thin endothelium cells of some capillaries have gaps between them called fenestrations which allow blood plasma to leak out and form tissue fluid Page 3 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Tissue fluid surrounds the cells, enabling exchange of substances such as oxygen, glucose, and carbon dioxide Tissue fluid contains oxygen, glucose and other small molecules from the blood plasma Your notes Large molecules such as proteins usually can't fit through the fenestrations into the tissue fluid The permeability of capillaries can vary depending on the requirements of a tissue Capillaries form branches in between the cells; this is the capillary bed These branches increase the surface area for diffusion of substances to and from the cells Being so close to the cells also reduces the diffusion distance Capillaries have a lumen with a small diameter Red blood cells squeeze through capillaries in single-file This forces the blood to travel slowly which provides more opportunity for diffusion to occur It also reduces the diffusion distance as red blood cells are brought in close contact with the capillary wall Capillary structure diagram Page 4 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Capillaries have a narrow lumen and walls that are one cell thick to increase the rate of diffusion between the blood and cells Your notes Page 5 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Arteries Adaptations of arteries Your notes Arteries transport blood away from the heart at high pressure Blood travels from the ventricles to the tissues of the body Remember; arteries carry blood away from the heart Artery walls consist of three layers: The innermost layer is an endothelial layer, consisting of squamous epithelium The endothelium is one cell thick and lines the lumen of all blood vessels. It is very smooth and reduces friction for free blood flow The middle layer contains smooth muscle cells and a thick layer of elastic tissue This layer is very thick in the walls of arteries The layer of muscle: Strengthen the arteries so they can withstand high pressure Can contract or relax to control the diameter of the lumen and regulate blood pressure The elastic tissue helps to maintain blood pressure in the arteries; it stretches and recoils to even out fluctuations in pressure when the heart beats Further from the heart there is more smooth muscle and less elastic tissue due to smaller fluctuations in blood pressure The outer layer covers the exterior of the artery and is mostly made up of collagen and elastic fibres Collagen is a strong protein and protects blood vessels from damage by over-stretching Along with elastic fibres, it prevents the arterial wall from rupturing as blood surges from the ventricles Arteries have a narrow lumen which helps to maintain high blood pressure Artery structure diagram Page 6 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Arteries have thick muscular walls and a narrow lumen Arterial blood pressure Arteries, and to a slightly lesser extent arterioles, must be able to withstand high pressure generated by the contracting heart, and both must maintain this pressure when the heart is relaxed Muscle and elastic fibres in the arteries help to maintain the blood pressure as the heart contracts and relaxes Systolic pressure is the peak pressure point reached in the arteries as the blood is forced out of the ventricles at high pressure At this point the walls of the arteries are forced outwards, enabled by the stretching of elastic fibres Diastolic pressure is the lowest pressure point reached within the artery as the heart relaxes At this point the stretched elastic fibres recoil and force the blood onward through the lumen of the arteries This maintains high pressure throughout the heart beat cycle Page 7 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Vasoconstriction of the circular muscles of the arteries can increase blood pressure by decreasing the diameter of the lumen Vasodilation of the circular muscles causes blood pressure to decrease by increasing the diameter of Your notes the lumen Exam Tip Be careful with the language you use to describe the roles of muscle and elastic tissue; muscle can contract and relax, while elastic tissue can stretch and recoil. Page 8 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Veins Adaptations of veins Your notes Veins transport blood to the heart at low pressure Remember; veins carry blood into the heart They receive blood that has passed through capillary networks, across which pressure has dropped due to the slow flow of blood The capillaries converge to form venules, which deliver blood to veins The structure of veins differs from arteries: The middle layer is much thinner in veins There is no need for a thick muscular and elastic layer as veins don't have to maintain or withstand high pressure The walls of veins are flexible, allowing surrounding muscles and tissues to compress them This facilitates the movement of blood back to the heart Veins contain valves These prevent the back flow of blood that can result under low pressure, helping return blood to the heart Movement of the skeletal muscles pushes the blood through the veins, and any blood that gets pushed backwards gets caught in the valves; this blood can then be moved forwards by the next skeletal muscle movement Veins have a wide lumen This maximises the volume of blood that can flow at any one time Vein structure diagram Page 9 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Veins have thin walls and a wide lumen Exam Tip For “explain” questions, remember to pair a description of a structural feature to an explanation of how it helps the blood vessel to function. For example, “capillaries have walls that are one-cell thick, enabling quick and efficient diffusion of substances due to a short diffusion distance." Page 10 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Identify Blood Vessels: Skills Your notes Structure of Arteries & Veins Distinguishing arteries and veins in micrographs Arteries The arterial walls are much thicker and stronger than those of veins This is due to the presence of more collagen and elastic fibres, as well as a thicker layer of smooth muscle The lumen of arteries is relatively narrow compared to the thickness of the wall This maintains the blood pressure inside the arteries Veins The walls of veins are much thinner than those of arteries They do not need to withstand the high pressure present in arteries The lumen of veins is much wider in diameter compared to the thickness of the wall A larger lumen helps to ensure that blood returns to the heart at an adequate speed A large lumen reduces friction between the blood and the endothelial layer of the vein The rate of blood flow is slower in veins but a larger lumen means the volume of blood delivered per unit of time is equal These characteristics can be used to distinguish arteries and veins in micrographs Artery and vein micrograph diagrams Page 11 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Arteries and veins can be distinguished from each other by the thickness of their walls and the diameter of the lumen; arteries (left) have thick walls and a narrow lumen while veins (right) have thin walls and a wide lumen Note that you do not need to know the scientific names for the different tissue layers in the walls of the blood vessels Page 12 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Measuring Pulse Rate: Skills Your notes Measuring Pulse Rate The contraction of the ventricles forces a large volume of blood through the arteries, which expand to accommodate this This can be felt as a pulse, especially in places where an artery is close to the skin surface or passes over a bone For this reason, the carotid artery or radial artery can be used to measure pulse rate The carotid artery runs down the side of the neck and a pulse can be felt just below the jaw The radial artery passes over the wrist bones where a pulse can be felt just below the base of the thumb A pulse can be taken as follows: Place two fingers on the radial or carotid artery and gently compress the blood vessel Count the number of pulses felt for 60 seconds Alternatively, you could count for 30 seconds and multiply by 2 Do not use your thumb when taking a pulse, since it also has a pulse that can lead to inaccurate results There are many digital devices that can also be used to determine pulse rate These include data loggers, smartwatches or fitness bands They scan the blood flow through the radial artery to measure pulse rate Measuring pulse diagram The radial or carotid artery can be used to measure the pulse rate Page 13 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Coronary Heart Disease: Skills Your notes Coronary Heart Disease Occlusion of the arteries can be defined as The narrowing of the arteries due to a blockage The arteries can be blocked by the process of atherosclerosis Atherosclerosis begins when there is damage to the walls of the arteries due to high blood pressure This damage can lead to the build-up of fatty deposits known as atheromas under the endothelium These fatty deposits narrow the lumen of the artery, reducing the space for blood flow Atherosclerosis can lead to an increase in blood pressure within the artery, which causes further damage to the artery wall Fibrous tissue is produced to repair the damage to the artery wall This type of tissue is not elastic, so the overall elasticity of the artery wall is reduced The smooth lining of the arteries breaks down and forms lesions called plaques This further damage can lead to the rupturing of blood vessel walls, which results in blood clotting Clots formed within a blood vessel are called a thrombus Once it circulates in the blood clots are known as an embolus Consequences of atherosclerosis of the arteries When an embolus blocks a small artery or arteriole, tissues further down from the blockage do not receive the required level of oxygen and nutrients This can inhibit cell functions and cause the cells to die If this happens in the coronary arteries then parts of the heart muscle die This may stop the heart from pumping blood and lead to a myocardial infarction, or heart attack Blockages in the coronary arteries may be bypassed by undergoing heart bypass surgery Blood vessels from the patient's leg are removed and used to create an alternative route for blood to flow past the blockage Atherosclerosis & coronary heart disease diagram Page 14 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Atherosclerosis leads to narrowing of the arteries; this can lead to coronary heart disease Page 15 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Buildup of plaque in the coronary arteries narrows the lumen, and can lead to a heart attack Evaluating epidemiological data relating to the incidence of coronary heart disease Claims about the importance of different risk factors and coronary heart disease, e.g. a diet high in saturated fats, are based on: Epidemiological studies on human populations The evidence provide correlation data and so do not provide a definite causal link between coronary heart disease and risk factors such as saturated fat intake Clinical studies of individual patients Page 16 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Such studies are small, e.g. they may focus on just a few individuals, so they may not provide representative data Studies will not include a suitable controlled experiment so it is not possible to make a Your notes definite causal link from the results A controlled experiment would involve. e.g. one group of participants eating a normal diet while another group eats a diet high in saturated fat Ethical considerations would prevent such controlled experiments from being carried out, due to the risk of harm to a group consuming a high fat diet over a long period When evaluating data from studies on coronary heart disease you could consider the following: The sample group used must be representative of the population Larger sample sizes are more likely to be representative as they cover a larger cross-section of the population Samples must not all come from the same demographic group, e.g. not all white men who are over 60 and live in London Samples must be human; results from animal trials do not perfectly represent human physiology Statistical analysis should be used to check that any differences between results are statistically significant E.g. the use of error bars in graphical data or the comparison of mean values from different trial groups Some studies need to have a control with which to compare the results E.g. when testing a drug to treat heart disease, a control group that is not given the drug should be included in the study to ensure that any effect shown is due to the drug and not any other factor Studies should be repeated, or there should be many studies that show the same result, before conclusions can be drawn The study should be designed to control any variable that is not being tested; this increases the validity of the results Controlled factors might include, e.g. prior health of participants, other lifestyle factors of participants such as exercise and stress levels, age of participants, and biological sex of participants Results are considered to be valid if they measure what they set out to measure, i.e. they are not influenced by external variables or poor experimental design, and have been analysed correctly Researchers should not be biased, i.e. looking for a particular outcome This could be a problem if someone is being paid to come up with a particular result Data collection methods must be accurate, e.g. participants may not tell the truth in a questionnaire about diet or exercise Page 17 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes A study was carried out into the relative risk of heart disease (CVD) in non-smoking adults exposed to a range of levels of cigarette smoke from a smoking partner. The study looked at 523 non-smoking partners of smokers. The results are shown in the graph below Evaluate the validity of the data A commentary on the validity of the data could include The study included 523 people; this is a fairly small sample size and may not represent an entire population This is only one study; more studies would need to be carried out to back up these results Being able to replicate the results of a study shows that the results are reliable There is no information on how other risk factors might be interacting with smoking to influence the risk of CVD Risk factors such as age, diet, biological sex, or exercise levels may be playing a role, as these factors may be interacting with the smoking variable e.g. Smokers are often older More men may smoke than women Smokers may be less likely to exercise Page 18 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The data doesn't comment on the use of any statistical tests so we cannot state the significance of the differences between the different levels of smoke exposure Your notes NOS: Correlation coefficients quantify correlations between variables and allow the strength of the relationship to be assessed Sometimes correlation between two variables can appear in the data Correlation is an association, or relationship, between variables There is a clear distinction between correlation and causation: a correlation does not necessarily imply a causative relationship Causation occurs when one variable has an influence on, or is influenced by, another In order to get a broad overview of the correlation between two variables the data points for both variables can be plotted on a scatter graph Correlation can be positive or negative Positive correlation: as variable A increases, variable B increases Negative correlation: as variable A increases, variable B decreases The correlation coefficient (r) can be calculated; this indicates the strength of the relationship between variables Perfect correlation occurs when all of the data points lie on a straight line with a correlation coefficient of 1 or -1 Remember that even strong correlations do not imply a causal relationship between the variables The closer the correlation coefficient is to 1 or -1, the stronger the relationship If there is no correlation between variables the correlation coefficient will be 0 Low correlation coefficients or no correlation between variables may provide evidence against a hypothesis Page 19 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Scatter graphs can be used to show the correlation between variables Your notes Page 20 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Transpiration Stream Your notes The Transpiration Stream When water evaporates from the surfaces of cells inside a leaf during transpiration, more water is drawn from the nearest xylem vessels to replace the water lost by evaporation Water molecules adhere to the cell walls of plant cells in the leaf, enabling water to move through the cell walls Here the water moves through the cell walls of the xylem into other cells of the leaf This movement of water that occurs due to adhesion to the walls of a narrow tube is capillary action The loss of water from the xylem vessels generates tension (negative pressure) within the xylem The tension generated in the xylem when water moves into the cells in the leaves creates a pulling force throughout the xylem vessels that is transmitted, via cohesion between water molecules, all the way down the stem of the plant and to the ends of the xylem in the roots This is known as transpiration pull and it allows water to be moved upwards through the plant, against the force of gravity This is sometimes known as the cohesion-tension theory of transpiration This continuous upwards flow of water in the xylem vessels of plants is known as the transpiration stream Water transport in plants diagram Page 21 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The movement of water through xylem vessels is due to the evaporation of water vapour from the leaves and the cohesive and adhesive properties exhibited by water molecules Transpiration is important to the plant in the following ways It provides a means of cooling the plant via evaporative cooling The transpiration stream is helpful in the uptake of mineral ions The turgor pressure of the cells (due to the presence of water as it moves up the plant) provides support to leaves (enabling an increased surface area of the leaf blade) and the stem of non- woody plants Page 22 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Adaptations of Xylem Vessels Your notes Adaptations of Xylem Vessels The transport of water occurs in xylem vessels, one of the vascular tissues found within plants Along with water, xylem vessels are also responsible for the transport of mineral ions from the roots The cohesive property of water, together with the structure of the xylem vessels, allows water to be transported under tension from the soil to the leaves Xylem vessel adaptations Xylem vessels are formed from long lines of cells that are connected at each end Mature xylem vessels are non-living cells As the xylem cells develop the cell walls between the connected cells degrade and the cell contents are broken down This forms mature xylem vessels that are long, continuous, hollow tubes that lack cell content and end walls This allows for unimpeded flow through the xylem vessels The walls of xylem vessels are thickened with cellulose and strengthened with a polymer called lignin This means xylem vessels are extremely tough and can withstand very low internal pressures, i.e. negative pressure (tension), without collapsing in on themselves Xylem vessel walls contain tiny pores called pits which allow water to enter and move sideways between vessels This means that if a vessel is damaged, the water can flow into another vessel and still reach the leaves Xylem structure diagram Page 23 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Xylem vessels are adapted to transport water from the roots to the leaves in plants Page 24 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Drawing Root & Stem Structure: Skills Your notes Dicotyledonous Stem Structure Distribution of tissues in a transverse section of a dicotyledonous stem The stem in a dicotyledonous plant contains several different types of tissues, which include: The epidermis which forms the outer layer of the stem This prevents water loss and provides protection from herbivores Parenchyma which forms the cortex and pith of the stem These cells act as storage structures for starch and other substances The cortex is the region located directly beneath the epidermis while the pith is the central region of the stem Vascular tissue arranged in a ring of vascular bundles Xylem transports water and dissolved mineral ions from the roots to the leaves Phloem transports organic solutes from the leaves to other parts of the plant The distribution of tissues in a transverse section of a dicotyledonous stem can be represented as a plan diagram There are a few things to keep in mind when drawing plan diagrams: Do not draw individual cells; only the outline of different tissues are drawn Draw clear, continuous lines; do not sketch Avoid shading parts of your drawing Pay attention to the size and proportions of different parts visible in a micrograph Make sure the different parts are clearly labelled Add a scale bar or the estimated size of your drawing Include annotations that give the functions of the labelled sections Page 25 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A plan diagram (bottom right) showing the distribution of different tissues in a dicotyledonous stem Note that a hand-drawn plan diagram should not contain shading Exam Tip You are expected to annotate your drawing with the main functions of these structures; this is not shown above Page 26 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Dicotyledonous Root Structure Distribution of tissues in a transverse section of a dicotyledonous root Your notes The arrangement of the vascular tissues differ in a root compared to a stem The xylem is centrally located in a root in a cross-shaped structure, while it forms the outer part of the ring of vascular bundles in a stem Remember, x = a cross = xylem Phloem bundles are arranged between the cross "arms" of xylem in a root, while it forms the inner part of the ring of vascular bundles in a stem The cortex consists of parenchyma cells that store starch and other substances while the epidermis forms the outer layer of the root Specialised epidermal cells called root hairs are present in roots to absorb water and mineral ions from the soil The endodermis forms the boundary between the vascular tissue and cortex in a root You should be able to draw a plan diagram of the tissues in a dicotyledonous root; see above for the features of a plan diagram drawing Page 27 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A plan diagram (bottom right) of a dicotyledonous root showing the distribution of different tissues Note that hand-drawn plan diagrams should not contain any shading Page 28 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Exam Tip Your notes Don't forget to draw your plan diagrams large enough to fill at least half of the available space on a page. Making a drawing that is too small will make it difficult to label structures accurately and may cost you marks Page 29 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Tissue Fluid (HL) Your notes Release & Reuptake of Tissue Fluid Plasma is a straw-coloured liquid that constitutes around 55 % of the blood Plasma is largely composed of water (95 %) and, because water is a good solvent, many substances can dissolve in it, allowing them to be transported around the body As blood passes through capillaries some plasma is forced out through gaps in the walls of the capillary to surround the cells of the body; this results in the formation of tissue fluid The composition of plasma and tissue fluid are very similar, although tissue fluid contains fewer proteins and cells Proteins are too large to fit through gaps in the capillary walls and so remain in the blood Red blood cells and platelets are not present in the tissue fluid as they are also too large to leave the capillaries Tissue fluid bathes almost all the cells of the body that are outside the circulatory system Exchange of substances between cells and the blood occurs via the tissue fluid For example, carbon dioxide produced in aerobic respiration will leave a cell, dissolve into the tissue fluid surrounding it, and then move back into the capillary The effect of blood pressure on tissue fluid Tissue fluid formation at the arterial end When blood is at the arterial end of a capillary the blood pressure is high enough to force fluid out of the capillary The process by which tissue fluid is forced out of the capillaries at high pressure is known as pressure filtration Reuptake of tissue fluid at the venous end At the venous end of the capillary the blood pressure within the capillary is reduced due to increased distance from the heart and the slowing of blood flow as it passes through the capillaries Tissue fluid drains back into the capillaries from the tissues Roughly 90 % of the fluid lost at the arterial end of the capillary is reabsorbed at the venous end The other 10 % remains as tissue fluid and is eventually collected by vessels known as lymph vessels From the lymph vessels the fluid is eventually returned to the circulatory system The effect of solute concentration on tissue fluid Pressure filtration occurs due to the outward force exerted by high blood pressure at the arterial end of capillaries, but high blood pressure isn't the only factor that affects tissue fluid: After pressure filtration has occurred, proteins remain in the blood as they are too large to pass through the pores in the capillary wall Page 30 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The increased protein concentration of the capillary creates a solute gradient between the capillary and the tissue fluid The solutes in this case are the proteins in the blood Your notes The solute gradient exerts an inward pull on the tissue fluid which draws water back into the capillary This is due to osmosis, which is the movement of water from a dilute solution (the tissue fluid) to a solution with a higher solute concentration (the capillary) At the arterial end the outward force generated by the high blood pressure is greater than the inward force of the solute gradient so the net movement of water is out of the capillaries into the tissue fluid At the venous end the inward force of the solute gradient is greater than the outward force of the blood pressure and fluid moves back into the capillaries At the arterial end the hydrostatic pressure (blood pressure) has a greater effect than the solute gradient so the tissue fluid is forced out of the capillaries At the venous end the hydrostatic pressure has less effect than the solute gradient so most of the fluid is drawn back into the capillary Page 31 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Exam Tip Your notes Remember that tissue fluid is formed by pressure filtration of plasma in capillaries, which is promoted by the higher blood pressure from arterioles. Lower pressure in venules allows tissue fluid to drain back into capillaries. Note that the specification does not require knowledge of the effect of solute concentration on tissue fluid, but this has been included here to better explain the draining of tissue fluid at low blood pressure. Page 32 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Composition of Plasma & Tissue Fluid Blood plasma and tissue fluid are similar in their composition, although there are some differences Your notes between them Water and solutes form an important part of both plasma and tissue fluid Substances that are too large to filter out through the capillary wall, such as plasma proteins and red blood cells will not be found in tissue fluid Some white blood cells, which are very flexible cells, are able to squeeze out of the capillaries, so are present in the tissue fluid Substances such as glucose, amino acids and oxygen are absorbed by cells, so tissue fluid will contain less of these substances Glucose and oxygen are requirements of aerobic respiration while amino acids are needed for protein synthesis Cells produce carbon dioxide as a waste product during cell respiration which will diffuse into the tissue fluid Composition of blood plasma and tissue fluid table Substance Blood plasma Tissue fluid Red blood cells, phagocytes, Blood cells Phagocytes lymphocytes and platelets Proteins Many large plasma proteins Fewer, smaller proteins Glucose Higher concentration Lower concentration Amino acids Higher concentration Lower concentration Oxygen Higher concentration Lower concentration Carbon dioxide Lower concentration Higher concentration Page 33 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Drainage Into Lymph Ducts Formation of lymph Your notes Some tissue fluid re-enters the capillaries while some enters the lymph capillaries The lymph capillaries are separate from the circulatory system and form part of the lymphatic system They have closed ends and large pores that allow large molecules to pass through They contain fluid known as lymph Larger molecules that are not able to pass through the capillary wall enter the lymphatic system Small valves in the vessel walls are the entry point to the lymphatic system Lymph fluid moves along the larger vessels of this system by compression caused by body movement. Any backflow is prevented by valves These larger vessels are known as lymph ducts People who have been sedentary on planes may experience swollen lower limbs due to the lack of movement which causes lymph to accumulate in these parts Lymph nodes are present in the lymph ducts These contain macrophages which will engulf bacteria present in the lymph Other cells of the immune system can also be found in the lymph nodes The lymph eventually re-enters the bloodstream through veins located close to the heart Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries If plasma proteins are not removed from tissue fluid they could increase the solute concentration of the tissue fluid and prevent the reabsorption of water into the blood in the capillaries After digestion lipids are transported from the intestines to the bloodstream by the lymph system, so lymph fluid contains lipids Tissue fluid and lymph vessels diagram Page 34 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 35 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Some components of tissue fluid drain into the lymph vessels Your notes Page 36 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Circulatory Systems (HL) Your notes Comparing Single & Double Circulation Differences between single circulation in bony fish and double circulation in mammals Both fish and mammals have a closed circulatory system This means blood is contained within a system of blood vessels Bony fish have single circulation Blood moves through the heart once during each complete circuit The heart has two chambers It enters the heart from the body before being pumped to the gills Here blood is oxygenated before moving to the rest of the body Single circulation diagram Page 37 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Bony fish have single circulation Mammals have double circulation This means blood flows through the heart twice for each complete circuit of the body The heart has four chambers; two on the right and two on the left The right side of the heart pumps deoxygenated blood to the lungs for gas exchange; this is pulmonary circulation Blood then returns to the left side of the heart, so that oxygenated blood can be pumped at high pressure around the body; this is systemic circulation Double circulation diagram Page 38 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 39 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Mammals have double circulation The main advantages of the mammalian double circulation system include: Keeping oxygenated and deoxygenated blood separate, so that cells can receive blood with high oxygen levels for aerobic respiration Maintaining a high pressure for the transport of oxygenated blood to every part of the body Pumping blood at a lower pressure in the lungs so that delicate blood vessels are not damaged Page 40 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Mammalian Heart (HL) Your notes The Mammalian Heart Adaptations of the mammalian heart to deliver blood to the arteries The heart muscle is known as cardiac muscle; a specialised form of muscle tissue that is able to contract repeatedly and continuously without becoming fatigued The heart is divided into four chambers; the two top chambers are atria and the bottom two chambers are ventricles The atria These chambers receive blood from the veins that return from the lungs and the body They are surrounded by a thin layer of muscle, allowing them pump blood over a short distance into the ventricles below The ventricles These chambers receive blood from the atria They have thick muscle walls which can generate high pressures for pumping blood to the lungs and to the body The left ventricle has thicker muscle than the right ventricle, as it must pump blood all around the body The left and right sides of the heart are separated by a wall of muscular tissue, called the septum. The septum is very important for ensuring blood doesn’t mix between the left and right sides of the heart The wall of the right atrium contain a small region of tissue known as the pacemaker, or sinoatrial node (SAN) The pacemaker initiates the heart beat by sending a wave of excitation across the atria This causes atrial contraction The electrical impulse travels down to the base of the ventricles From the base, it spreads upwards across the ventricular walls This causes ventricular contraction There are two blood vessels bringing blood to the heart; the vena cava and pulmonary vein There are two blood vessels taking blood away from the heart; the pulmonary artery and aorta Valves in the heart Valves are important for keeping blood flowing forward in the right direction and stopping it flowing backwards Valves in the heart: Open when the pressure of blood behind them is greater than the pressure in front of them Close when the pressure of blood in front of them is greater than the pressure behind them The valves between the atria and the ventricles are the atrioventricular valves; they prevent blood from flowing back from the ventricles into the atria Page 41 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The right atrium and right ventricle are separated by the tricuspid valve The left atrium and left ventricle are separated by the bicuspid valve The valves between the ventricles and the arteries are the semilunar valves Your notes The right ventricle and the pulmonary artery are separated by the pulmonary valve The left ventricle and aorta are separated by a valve called the aortic valve Heart structure diagram Deoxygenated blood flows into the right atrium from the body, from which it flows downwards into the right ventricle, and then upwards to the pulmonary artery which carries it to the lungs Oxygenated blood from the lungs enters the left atrium, flows down into the left ventricle, and then upwards to the aorta which carries it to the rest of the body Page 42 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Coronary arteries The heart is a muscle and so requires its own blood supply; blood supplies the cells with oxygen and Your notes glucose for aerobic respiration The heart receives blood through arteries called coronary arteries These arteries are visible on the front of the heart Coronary arteries diagram The coronary arteries supply the heart muscle with oxygenated blood Exam Tip When looking at the heart, remember that the right side of the heart will appear on the page as being on the left. This is because the heart is labelled as if it were in your body and flipped around. Page 43 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Cardiac Cycle: Skills (HL) Your notes The Cardiac Cycle Control of the cardiac cycle Control of the basic heartbeat is myogenic, which means the heart will beat without any external stimulus from the nervous system This intrinsic rhythm means the heart beats at around 60 times per minute The sinoatrial node (SAN) is a group of cells in the wall of the right atrium; it controls the cardiac cycle as follows: The SAN initiates a wave of depolarisation that spreads across the atria and causes the atria to contract A region of non-conducting tissue prevents the depolarisation spreading straight to the ventricles This delays the wave of depolarisation for long enough to allow the atria to finish contracting The depolarisation is instead carried to the atrioventricular node (AVN); this is a region of conducting tissue between atria and ventricles Conducting fibres carry the wave of excitation down the septum and out around the walls of the ventricles The bundle of His is a collection of conducting tissue located in the septum The Purkyne fibres spread around the ventricles The ventricles depolarise from the base upwards, and the ventricles contract Stages in the cardiac cycle table Stage in sequence Event 1 Sinoatrial node sends out a wave of excitation 2 Atria contract 3 Atrioventricular node sends out a wave of excitation 4 Purkyne tissue conducts the wave of excitation 5 Ventricles contract Page 44 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Control of cardiac cycle diagram Your notes The wave of depolarisation spreads across the heart in a coordinated manner The events of the cardiac cycle The cardiac cycle is the series of events that take place in one heart beat, including muscle contraction and relaxation The contraction of the heart is called systole, while the relaxation of the heart is called diastole One cardiac cycle is followed by another in a continuous process There is no gap between cycles where blood stops flowing The events of the cardiac cycle occur simultaneously in the left and right sides of the heart Volume and pressure changes Contraction of the heart muscle causes a decrease in volume in the corresponding chamber of the heart, which then increases again when the muscle relaxes Page 45 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Volume changes lead to corresponding pressure changes When volume decreases, pressure increases When volume increases, pressure decreases Your notes Throughout the cardiac cycle heart valves open and close as a result of pressure changes in different regions of the heart Valves open when the pressure of blood behind them is greater than the pressure in front of them They close when the pressure of blood in front of them is greater than the pressure behind them Valves are an important mechanism to stop blood flowing backwards Atrial systole The heartbeat is initiated by the sinoatrial node The walls of the atria contract Atrial volume decreases Atrial pressure increases The pressure in the atria rises above that in the ventricles, forcing the atrioventricular (AV) valves open Blood is forced into the ventricles There is a slight increase in ventricular pressure and chamber volume as the ventricles receive the blood from the atria The ventricles are relaxed at this point; ventricular diastole coincides with atrial systole Ventricular systole The walls of the ventricles contract Ventricular volume decreases Ventricular pressure increases The pressure in the ventricles rises above that in the atria This forces the AV valves to close, preventing back flow of blood The pressure in the ventricles rises above that in the aorta and pulmonary artery This forces the semilunar (SL) valves open so blood is forced into the arteries and out of the heart During this period, the atria are relaxing; atrial diastole coincides with ventricular systole The blood flow to the heart continues, so the relaxed atria begin to fill with blood again Diastole The ventricles and atria are both relaxed The pressure in the ventricles drops below that in the aorta and pulmonary artery, forcing the SL valves to close The atria continue to fill with blood Blood returns to the heart via the vena cava and pulmonary vein Pressure in the atria rises above that in the ventricles, forcing the AV valves open Blood flows passively into the ventricles without need of atrial systole The cycle then begins again with atrial systole Page 46 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Cardiac cycle diagram Your notes Valves during the cardiac cycle table Page 47 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Stage in cardiac cycle Atrioventricular valves Semilunar valves Your notes Atrial systole Open Closed Ventricular systole Closed Open Diastole Open Closed Pressure changes during the cardiac cycle graph Page 48 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The pressure changes during the cardiac cycle can be used to determine the events taking place Analysing the cardiac cycle The lines on the graph represent the pressure of the left atrium, aorta, and the left ventricle Page 49 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The points at which the lines cross each other are important because they indicate when valves open and close Point A - the end of diastole Your notes The atrium has filled with blood during the preceding diastole Pressure is higher in the atrium than in the ventricle, so the AV valve is open Between points A and B - atrial systole Left atrium contracts, causing an increase in atrial pressure and forcing blood into the left ventricle Ventricular pressure increases slightly as it fills with blood Pressure is higher in the atrium than in the ventricle, so the AV valve is open Point B - beginning of ventricular systole Left ventricle contracts causing the ventricular pressure to increase Pressure in the left atrium drops as the muscle relaxes Pressure in the ventricle exceeds pressure in the atrium, so the AV valve shuts Point C - ventricular systole The ventricle continues to contract Pressure in the left ventricle exceeds that in the aorta Aortic valve opens and blood is forced into the aorta Point D - beginning of diastole Left ventricle has been emptied of blood Muscles in the walls of the left ventricle relax and pressure falls below that in the newly filled aorta Aortic valve closes Between points D and E - early diastole The ventricle remains relaxed and ventricular pressure continues to decrease In the meantime, blood is flowing into the relaxed atrium from the pulmonary vein, causing an increase in pressure Point E - diastole The relaxed left atrium fills with blood, causing the pressure in the atrium to exceed that in the newly emptied ventricle AV valve opens After point E - late diastole There is a short period of time during which the left ventricle expands due to relaxing muscles This increases the internal volume of the left ventricle and decreases the ventricular pressure At the same time, blood is flowing slowly through the newly opened AV valve into the left ventricle, causing a brief decrease in pressure in the left atrium The pressure in both the atrium and ventricle then increases slowly as they continue to fill with blood Page 50 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes The graph below shows pressure changes during the cardiac cycle. Calculate the heart rate of this person. Give your answer in beats per minute. Step 1: Work out the length of one heart beat It takes 0.7 seconds for completion of one cardiac cycle, which is one heart beat So there is 1 cycle in 0.7 seconds Step 2: Calculate how many heart beats occur per second Divide by 0.7 to find out how many cycles in 1 second 1 ÷ 0.7 = 1.43 beats in 1 second Step 3: Calculate how many heart beats occur per minute Multiply by 60 to find out how many cycles in 60 seconds Page 51 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.43 × 60 = 85.71 beats in 60 seconds So the heart rate is 85.71 beats / min Your notes Exam Tip You might be asked to interpret the graph of the cardiac cycle so it is important you understand it and can analyse where each stage of the cycle is happening. Common areas of assessment include Pressure and volume changes, Timings of valves opening and closing When blood starts flowing in or out of specific chambers Note that the specification refers to events 'in the left side of the heart', while this pages does not distinguish between left and right. The events of the cardiac cycle occur simultaneously in the left and right sides of the heart, so anything on this page can be applied equally to the left or right sides. Page 52 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Roots & Water Transport (HL) Your notes Generation of Root Pressure Loss of water at the leaves by transpiration creates a negative pressure inside xylem vessels which pulls water up the stem of plants, but plants can also push water up from the roots by generating root pressure Root pressure is generated as follows: Minerals are actively transported into the cells of the roots from the soil, lowering the water potential of the root cells Note that a low water potential is the result of a high solute concentration This creates a water potential gradient between the soil and the cells of the roots and water moves into the root cells by osmosis Minerals are then actively transported from cell to cell across the root, eventually reaching the xylem As minerals enter the cells and the xylem the water potential is reduced and water follows by osmosis Water enters the xylem and generates a positive pressure potential; this pushes the column of water upwards; this is root pressure Root pressure is important in driving the movement of water up xylem vessels when the rate of transpiration is low E.g. in conditions of high humidity or before the leaves of deciduous plants develop in spring Root pressure diagram Page 53 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Water moves into the xylem by osmosis due to the water potential gradient created when minerals are actively transported into roots from the soil Water that enters the xylem in this way generates root pressure Page 54 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Translocation in Plants (HL) Your notes Translocation in Plants Translocation is the biological term used to describe the transport of organic solutes in the phloem tissue The liquid that is being transported within the phloem can be referred to as phloem sap This phloem sap consists of sugars in the form of sucrose, along with water and other dissolved substances such as amino acids These dissolved substances are sometimes referred to as assimilates Translocation within phloem tissue transports these organic compounds from regions known as ‘sources’ to regions known as ‘sinks’ Sources and sinks Sources are the regions of plants in which organic solutes originate; they can include Mature green leaves and green stems Photosynthesis in these regions produces glucose which is converted into sucrose before being transported Storage organs, e.g. tubers and tap roots, unloading their stored substances at the beginning of a growth period Food stores in seeds which are germinating Sinks are the regions of plants where organic compounds are required for growth; they can include Meristems that are actively dividing Roots that are growing or actively taking up mineral ions Young leaves in bud Any part of the plant where organic compounds are being stored, e.g. developing seeds, fruits, or storage organs Note that sources can become sinks and vice versa, depending on the time of year and the processes taking place inside the plant Sources and sinks diagram Page 55 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Organic compounds are moved through a plant, by the process of translocation, from source(s) to sink(s). Phloem adaptations The function of phloem tissue in a plant is to transport organic compounds, particularly sucrose, from sources to sinks The cells that make up the phloem tissue are highly specialised, meaning that their structure aids their function Phloem is a complex tissue made up of different cell types; it is mainly made up of sieve tube elements and companion cells Sieve tube cells, or elements, line up end-to-end to form a continuous tube through which phloem sap flows The cells are separated by perforated sieve plates which allow the passage of assimilates Page 56 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Sieve tube cells have reduced cytoplasm and few organelles to allow the free flow of phloem sap Companion cells are closely associated with the sieve tube and aid with the loading and Your notes unloading of dissolved substances, or assimilates Companion cells contain many mitochondria which generate ATP for the active loading of sucrose into the sieve tube Sieve tubes and companion cells are linked by bridges of cytoplasm known as plasmodesmata Phloem adaptations diagram Page 57 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Phloem tissue contains sieve tube cells and companion cells Sieve tube structure and function table Structure Function Page 58 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Allows for the continuous movement of the Sieve plates organic compounds between cells Your notes Strengthens the wall to withstand the Cellulose cell wall hydrostatic pressures that move the assimilates No nucleus, vacuole or ribosomes in Maximises the space for the translocation of mature cells assimilates Reduces friction to facilitate the movement of Thin cytoplasm assimilates Companion cell structure and function table Structure Function Provides metabolic support to sieve tube Nucleus and other organelles elements Moves assimilates into and out of the sieve Transport proteins in plasma membrane tube elements Provide ATP for the active transport of Many mitochondria assimilates into or out of the companion cells Link with sieve tube elements to allow Plasmodesmata assimilates to move from the companion cells into the sieve tubes Translocation The loading and unloading of sucrose and other organic compounds from the source to the phloem, and from the phloem to the sink is an active process, meaning that it requires energy in the form of ATP A summary of the process is 1. Active transport is used to load organic compounds into the phloem at the source 2. The high concentrations of solutes in the phloem at the source lower the water potential and cause water to move into the phloem vessels by osmosis Water can move in from the neighbouring xylem vessels 3. This results in a raised hydrostatic pressure and generates a hydrostatic pressure gradient between the source and the sink; this causes the contents of the phloem to flow towards the sink down a pressure gradient Hydrostatic pressure refers to the pressure exerted by a fluid on the walls of its container; in this case the walls of the phloem Page 59 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4. At the same time sucrose is being unloaded from the phloem at the sink, lowering the water potential of the cells of the sink 5. Water follows by osmosis, maintaining the hydrostatic pressure gradient between the source Your notes and the sink Page 60 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Exam Tip Your notes Remember that direction of movement in the phloem is determined by the locations of the source and the sink, so can be either upward or downward. Understand the difference between sieve tube elements and companion cells, and make sure that you can describe how the structure of sieve tube cells is related to their function Page 61 of 61 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers