Volume And Water Potential Of The Blood example essay topic

Gas Exchange 3.1 Surface area to volume ratio Exchange of gases occurs by diffusion at surface Whereas Production of wastes and use of resources occurs in the volume Therefore, as organisms increase in size they have proportionately less surface area compared to volume Adaptations flat, thin, ribbed bodies increase exchange surfaces 3.2 As organisms get larger they must have exchange surfaces within them all are moist, thin permeable, large surface area Plants Spongy / Palisade Mesophyll Air directly contacts cells Insects Ends of tracheoles Air directly contacts cells Fish Gill Lamellae O 2 absorbed by blood pigments then delivered to cells Mammals Alveoli O 2 absorbed by blood pigments then delivered to cells Ventilation Aim maintain concentration gradient Remove CO 2 rich O 2 poor air Supply O 2 rich CO 2 poor air Move respiratory medium over exchange surface Insects larger insects make pumping movements of the abdomen, which crushes the air sacs and helps to move air Fish move operculum out, buccal cavity up therefore one way flow of water over the gill lamellae counter current flow of water against the direction of blood flow Mammal Tidal flow of air movement of diaphragm and ribs Control of Breathing Involuntary Respiratory centre is bundle of nerves in medulla oblongata Impulses are sent to the diaphragm and external intercostal muscles causing them to contract As lungs expand stretch receptors in airway sense and send back info Meeting Demand CO 2 levels vary according to exercise As CO 2 goes up pH goes down Chemoreceptors sense this Receptors in the medulla oblongata Carotid bodies in the carotid arteries Aortic bodies in the aortic arch As chemoreceptors sense increase in CO 2 o decrease in pH, impulses are sent to the respiratory centre, this sends impulses to the diaphragm and intercostal muscles increase the rate of ventilation. Oxygen / Haemoglobin Dissociation Curves 3.7 (part). Red blood cells contain haemoglobin (Hb) which transports all of the oxygen around your body and most of the CO 2. Each Hb molecule can carry up to four O 2 molecules.

However, . The relationship between O 2 concentration (partial pressure of O 2 - p O 2) and how much is taken up by Hb (% saturation) is not linear, it is 'S's hoped (sigmoid). This is because a completely 'empty' Hb molecule takes up the first O 2 rather 'reluctantly', then takes up the remaining three rapidly, and finally it is 'full' and won't take up any more... Loading: In the lungs the pO 2 is very high, so Hb is 'filled up' (saturated) with O 2, represented by the flat 'top' of the curve.

Carrying: As the Hb travels through arteries and arterioles, pO 2 drops, but not enough for the Hb to give up any oxygen, we are still in the flat region at the top... Unloading: When the Hb reaches capillaries which are next to actively respiring cells, pO 2 is much lower, due to oxygen being consumed to make ATP. Here, Hb is 'emptied' of its oxygen, which diffuses to the cells. This is represented by the steep part of the curve in the middle of the 'S'... The relationship between p O 2 and Hb saturation is not fixed, the shape of the curve alters in response to various conditions: Condition Effect on curve Overall result Increased pCO 2 Shifts to the right (Bohr shift) At any given pO 2, Hb will be less saturated, so oxygen will be given up more easily Increased temperature Shifts to the right At any given pO 2, Hb will be less saturated, so oxygen will be given up more easily Increased pH (alkaline) Shifts to the left At any given pO 2, Hb will be more saturated, so oxygen will be given up less easily. This makes good sense, if cells are actively respiring they produce CO 2, heat up and become more acidic (due to dissolved CO 2, and production of lactic acid), all these things cause the curve to move to the right, so oxygen is given up easily.

This oxygen is precisely what actively respiring cells need! Other examples: Foetal Hb is to the left of its mother's (so it can 'steal' oxygen from her blood via the placenta). Myoglobin, in muscles has a curve to the left of Hb (it also 'steals' oxygen from Hb, and retains it as a store and only gives it up at very low pO 2)... Finally, Hb carries CO 2 by means of a series of reactions (catalyzed by carbonic anhydrase) which result in the production of hydrogen ions and hydrogencarbonate ions. The hydrogen ions are taken up by Hb, meaning that Hb acts as a buffer, absorbing excess acid. The hydrogencarbonate diffuses into the plasma, in exchange for chloride ions (the chloride shift).

CARDIAC CYCLE AND ITS CONTROL. The heart muscle is myogenic (contracts without stimulation). The sino-atrial node coordinates the heart beat so that the muscle cells contract together... The SAN is in the right atrium next to the vena cava. Specialised muscle (Purkinje) fibres radiate out from the node and cause atrial contraction (systole). These stimulate the AVN, on the septum at the junction of the atria & ventricles.

The AVN causes a time delay which ensures the ventricle contracts after the atria. The bundle of His (Purkinje fibres) pass down the septum to the apex of the ventricles. These first cause contraction of the papillary muscles which tension the cuspid valves. Ventricular systole radiates upwards from the apex. Once the electrical stimulation has died away the heart chambers relax (diastole) CONTROL OF HEART RATE.

The SAN sets a resting heart rate. Blood O 2 & CO 2 levels are detected by chemoreceptors of the Aortic & Carotid bodies. These send nerve impulses to the cardiovascular centre of the medulla. The medulla has chemoreceptors which also detect CO 2.

If CO 2 drops the CV centre sends nerve impulses along parasympathetic nerves to the SAN, which reduces heart rate (vagus nerve). If CO 2 goes up the CV centre sends nerve impulses along sympathetic nerves to the SAN, which increases heart rate (accelerator nerve). Adrenaline can also act directly on the SAN, mirroring the effect of sympathetic nerves. CO 2 dissolves in water to release hydrogen ions which decrease the pH and increase the acidity.

The heart rate is controlled so that the demands of the body are met with the minimum cardiac output. PRESSURE & VOLUME CHANGES & VALVES. Valves stop the backflow of blood within the heart and as blood exits the heart. Muscular contraction (systole) causes an increase in hydrostatic pressure in the heart... When the valves open the volume of the heart chamber decreases. Blood always attempts to flow from high to low pressure unless valves stop it.

Valves open or close when pressure lines cross (on graph). The heart empties from the bottom up. ELECTRICAL ACTIVITY. P is the trace produced by stimulation of atrial systole. QRS is the trace produced by ventricular systole CIRCULATION AND BLOOD VESSELS. Blood leaves the heart in spurts when the ventricle contacts.

In arteries, this is first pushed along by elasticity and then by a peristaltic pulse. In the tissue capillaries this is smoothed out to a constant flow by the arterioles, in the lungs, the blood continues to flow in pulses. Throughout circulation there is a pressure drop. Fluid leaves the arterioles and bathes the tissues, because the hydrostatic pressure outwards exceeds the difference in water potential (osmotic pressure).

Most is drawn back into the venules by the solute potential of the blood proteins (osmotic potential), some returns via the lymph. Blood flow is the fastest where the total cross sectional area is least... The same volume of blood must enter and leave the heart per minute but the pressure is different Digestion q Mammals have a gut to digest then absorb food q The generalised structure of the mammalian gut wall q Epithelium q Lumen q Muscle layers q How different parts of alimentary canal are adapted for their function Movement of food through peristalsis q How q Sites of production and action of Amylase's Mouth Starch to Maltose Endopeptidases Stomach / Pancreas Pepsin / Trypsin Polypeptides into smaller chains Exo peptidases Pancreas and intracellular (small intestine epithelial cells) Cuts di and tri peptides into individual amino acids Lipase Pancreas Fats into mono glycerides and fatty acids Maltase intracellular (small intestine epithelial cells) Breaks maltose into glucose Bile Liver Not an enzyme emulsifies fats into smaller droplets q Mechanisms for absorption in the ileum q Structure of a liver lobule q Control of Digestive Secretions q Nervous sight smell q Hormonal Gastrin Presence of food in the stomach Stomach secretes pepsin and hydrochloric acid begins muscular movement of stomach Cholecystokinin Presence of acidified chyme in duodenum causes cells in the mucosa of duodenum to secrete hormone into bloodstream Pancreas secretes enzymes Gall bladder secretes bile Secretin Presence of acidified chyme in duodenum causes cells in the mucosa of duodenum to secrete hormone into bloodstream Effects liver (bile) and Pancreas fluid non enzymic components of pancreatic juice q Liver q Blood sugar q Glycogenesis making glycogen from glucose q Glycogenolysis breaking up glycogen into glucose q Gluconeogenesis making glucose from non-carbohydrate sources (fats and proteins) q Roles of insulin (going down) and glucagon (going up) in controlling blood sugar levels Transamination changing one amino acid into another not possible to synthesis essential amino acids (must be obtained from diet 3.8 Excretion and OsmoregulationMost questions in the exam ask about some, or all, of the following: . The kidney, specifically: . which substances move, . in which direction and why, . how this is controlled... What other animals do, particularly single-celled animals, fish (which both excrete ammonia directly into water) and insects (which excrete solid uric acid) and why... Delamination and the ornithine cycle (learn and regurgitate!

). The Kidney. Everything the kidney does is done in the nephrons (about a million per kidney). First, the blood is filtered at the glomerulus. All the components of the blood are squeezed through the filter into Bowman's capsule, except proteins and cells. Reabsorption.

Glucose, amino acids and mineral ions are actively reabsorbed into the blood in the proximal convoluted tubule... Water, by osmosis is also reabsorbed to balance the concentration... Varying amounts of salts and water are reabsorbed from the distal convoluted tubule... Varying amounts of water are reabsorbed from the collecting ducts... Some poisonous substances are secreted, actively, into the proximal convoluted tubule.

Generating Concentrated Urine. ascending limb impermeable to water but actively pumps out sodium chloride (salt) so the fluid in the ascending limb gets more and more dilute... tissue fluid surrounding loop has sodium chloride pumped into it from ascending loop and therefore becomes more concentrated... descending limb loses water to the surrounding tissue fluid, passively, by osmosis, but is impermeable to sodium chloride, so salt doesn't follow... The high sodium chloride concentration in the tissue fluid around the loop draws water out of the nearby collecting duct, by osmosis. Anti diuretic Hormone (ADH) controls the volume and water potential of the blood. Osmoreceptors in hypothalamus are sensitive to water potential of the blood.

Drop in water potential (more concentrated) results in release of ADH from pituitary gland. ADH causes the normally impermeable collecting duct and distal tubule walls to become more permeable resulting in more water being reabsorbed into the blood and the urine becoming more concentrated and of a smaller volume Aldosterone controls the volume and sodium (Na+) content of the blood. Drop in blood volume detected by cells in the kidney (juxtaglomerular cells), which is generally associated with low blood Na+... A complex chain of events causes aldosterone to be released from the cortex of the adrenal gland... Aldosterone causes the distal tubule to reabsorb more Na+, which increases blood Na+ and volume... Finally, the kidney helps to control blood pH, by secreting excess acid or alkali into the distal convoluted tubule (so the pH of urine can vary, but blood pH remains the same).

Revision notes on Xylem and Phloem (3.7 part) Stem structure A transverse section of a stem shows that the vascular tissues occur in bundles at regular intervals around the outer part of the stem. The centre of a stem is filled with pith. The outermost layer of the stem is waterproof with lenticel's for gas exchange. Each bundle consists of phloem on the outside and xylem on the inside with the cambium in between. There may also be sclerenchyma fibres exterior to the phloem to give extra strength.

The cambium is meristem atic producing new xylem and phloem as the stem increases in girth. At the nodes of the stem branches in the vascular bundles occur so that the vascular bundles enter the petioles of leaves as well as continuing up the stem. In woody plants the vascular tissue forms a complete ring around the stem and the centre of the stem becomes filled with xylem (wood) as the plant gets bigger. Xylem structure Xylem consists of xylem vessels and tracheids as well as parenchyma tissue. The vessels are made from columns of cells in which the end walls have broken down to leave a long tube. These cells die as they become specialised because their walls become impregnated with lignin which is not permeable.

The net result is a tube of xylem elements in which there is no cytoplasm. Xylem vessels remain in contact via pits in their lateral (side) walls. Tracheids are also dead but each tracheid has a pointed end and overlaps the ones above and below, the tracheids also have connections via pits. Between the vessels and tracheids is xylem parenchyma. Xylem function Xylem carries water and ions from the roots to the stem, leaves, flowers and fruits. Water travels upwards in the xylem because of the transpiration pull caused by evaporation of water from the cells of the leaf followed by diffusion of water vapour through the stomata i.e. transpiration (also get some transpiration through the cuticle).

The continuous column of water in the xylem does not separate due to forces of cohesion between the water molecules. These forces are made possible because water is a polar molecule and water molecule have hydrogen bonds between them and they also adhere to the walls of the xylem vessel. This is known as the COHESION TENSION THEORY of water movement. Transport in the xylem is an example of MASS FLOW. Because the cytoplasm has gone from the xylem and the end walls of the vessels have disintegrated then there is no barrier to the flow of water up the xylem.

Water can leave the xylem through the pits to move into adjacent tissues. Ions absorbed in the roots also move upward in the xylem dissolved in the water Water enters the xylem after it has been absorbed and has travelled across the root to the central vascular bundle of the root. Capillarity and Root pressure also play a part in water movement in plant but neither can explain how water can travel to the top of trees. Evidence Evidence for the cohesion tension theory of water movement comes from the fact that water in the xylem is under tension so air enters the xylem if the xylem is damaged and by the variation in the girth of trees at different times of the day. Water can be shown to move up the xylem by allowing a stem to take up dye.

Movement of water in the xylem is entirely passive (it continues if the plant is poisoned so that it cannot make ATP), that means that no chemical energy is expended in water movement through the xylem. Phloem Structure The phloem in a plant forms only a very this layer about the same thickness as a piece of paper. Phloem tissue consists of sieve tubes, companions cells and phloem parenchyma. All phloem tissue is living (unlike xylem) although the cytoplasm of the sieve tubes is highly specialised and has a reduced number of cell organelles. The sieve tubes consist of a column of cells formed end to end.

Between each cell the cell wall has a number of holes so that it has the appearance of a sieve and this is known as the sieve plate. The cytoplasm of the sieve tubes is modified and contains no mitochondria. Adjacent to each sieve tube is a companion cell which has a very dense cytoplasm and which supplies energy for the sieve tubes. The sieve tubes carry sugar up and down the plant.

They are loaded with sugars in the leaves and then the sugar moves in solution either up or down the plant to where it is needed. Theories of Phloem Transport 1. Pressure flow 2. Cytoplasmic streaming 3. Electro-osmotic flowN o one theory provides a totally satisfactory explanation to flow.

The most accepted theory is the pressure flow theory that states that sugars are loaded into the phloem in an area of high concentration, the source, and are then transported by mass flow to an area of low concentration, the sink, where they are unloaded. This theory allows for substances to move both up and down the plant. Movement of substances in the phloem is an active process requiring ATP. Evidence for 1.

The contents of the phloem have a positive pressure- they exude fluid when cut and aphid stylets exude fluid when they penetrate the phloem. 2. Experiments have shown a concentration in the phloem contents with the highest concentration near the source-analysis of exudates from aphid stylets 3. A physical model of this theory functions 4. Viruses can be moved in the phloem. This must be mass flow as they are nor in solution and are therefore not able to move by diffusion.

Evidence against 1. Sugars and amino acids have been found to move in different directions in the same vascular bundle. 2. Phloem transport may not occur in the direction of the deepest sink.

3. The sieve plate is an impediment to mass flow Experiments used to investigate mass flow Radioactive tracers. These are introduced via radioactive carbon dioxide and photosynthesis and the path traced by autoradiography. Ringing experiments. The phloem is removed in a ring around the stem and this stops flow in the phloem. Shows that sugars, amino acids and salts are transported in the phloem.

Use of Aphids for sampling 3.6 Exchange of Water and Ions in Plants Most questions in the exam ask about some, or all, of the following: . Root structure and function (particularly mineral absorption). Stomata and transpiration (and factors affecting transpiration). Features of xerophytes (plants that live in very dry conditions) Root structure and function: .

Root structure learn the typical layout of tissues in roots (Support Booklet p. 20) and how it differs from stems... Root function: . Water and minerals are absorbed through root hairs and pass through the cells of the cortex... These substances can move through the porous cell walls in the cortex, rather like water soaking through paper, this is called the apo plast pathway... Water and minerals can also pass through the living part of these cells (cell membrane, cytoplasm etc.) the symplast pathway... The cells of the cortex also contain large vacuoles, and substances can pass through these (as well as the cytoplasm etc.) the vacuolar pathway...

Between the cells of the cortex and the xylem and phloem is a layer of cells called the endodermis. These cells have a special waterproof layer in part of their cell walls, forming the Caspar ian strip. This forces water and minerals to take the symplast pathway through the endodermis... Because all cell membranes are selectively permeable, this allows the cells of the endodermis to control the amount of each mineral taken into the xylem: Substance Method of transport across endodermis Reason Water Osmosis Water is drawn up xylem in transpiration stream (see 3.7) Minerals at a higher concentration in soil than plant cells Facilitated diffusion These can flow down their concentration gradient into the plant Minerals at a lower concentration in soil than plant cells Active transport (requires ATP) These must be moved against their concentration gradient into the plant Toxins Transport blocked or inhibited Mechanism unknown (Water and minerals then pass up the stem in the xylem - see 3.7 and enter the leaves) Stomata and transpiration. 99% of the water that goes up the xylem evaporates into air spaces in the leaves, and diffuses out through the stomata as water vapour, this is transpiration... Anything that affects the concentration gradient of water vapour from plant to air will therefore affect the rate of transpiration: Factor Effect on rate of transpiration Reason Increased light intensity Increases Stomata open wider in light (see below) Increased humidity Decreases Decreased concentration gradient (humid air around leaves) Increased air movement Increases Increased concentration gradient (humid air around leaves blown away) Increased temperature Increases More rapid evaporation from leaves Dry soil around roots or high salt concentration (e.g. sea water) Decreases Decreased uptake of water into roots, therefore less available in leaves (The rate of transpiration can be measured with a photometer)...

Clearly, stomata are very important in transpiration, as most of the water vapour passes through them. They usually open in the light and close in the dark; they also close when water supply to the roots is very poor... Stomatal opening is controlled by the two guard cells which surround each stoma. The cell wall on the inner surface is much thicker than on the outer surface. As these cells become turgid (swell) they bend outwards, causing the stoma to open (you can demonstrate this by sticking sellotape on one side of a sausage-shaped balloon then blowing it up, it bends away from the sellotape)... There are two hypotheses to explain how guard cells change their shape: .

The potassium movement hypothesis states that potassium ions (K+) are pumped into the guard cells, by active transport. This lowers their water potential, water flows in by osmosis, the guard cells become turgid and stomata open. The reverse process closes stomata. This hypothesis is the most widely accepted... The starch-sugar hypothesis states that there is a balance between sugars (soluble) and starch (insoluble) controlled by two enzymes with different optimum pH's. The enzyme which converts starch into sugar has a high optimum pH (alkaline), which is produced in the day, because acidic CO 2 is used up in photosynthesis.

Therefore, sugar accumulates, water potential drops, water enters, cells become turgid, stomata open. The enzyme which converts sugar to starch has a low optimum pH (acidic), which is produced at night, because CO 2 is produced by respiration (no photosynthesis). Starch accumulates, but because starch is insoluble water potential rises, water leaves, guard cells lose turgidity, stomata close. This hypothesis is not widely accepted. Xerophytes. These are plants that are adapted to live in very dry conditions by having some, or all, of the following features: .

A very thick, waxy cuticle to reduce evaporation of water through this part of the leaf (cuticular transpiration)... Stomata sunk into pits, which trap a layer of humid around them, so reducing transpiration... Hairs around stomata, again trapping a layer of humid air... Few, small leaves; often rolled into a tube. This reduces surface area for transpiration, and humid air is also trapped inside the in rolled leaf... Closing stomata in the day, when it is hot, and opening them at night, reducing evaporation. (such plants take in CO 2 at night, store it as an organic acid and then break the acid down in the day to release the CO 2, internally, for photosynthesis.

This is called CAM photosynthesis)... Storage of water in thick stems and leaves (these plants are called succulents)... Deep, tap roots to draw up water from deep soil layers... Roots very close to the soil surface, to absorb condensation which forms at night.