Exchange of substances

• SA:V ratio

  • Exchange surfaces in organisms have many similar adaptations to make transport across the surface more efficient
  • surface area:volume ratio = The relationship between the size of an organism of structure and its surface area to volume ratio plays a significant role in the types of adaptations an organism will have
• Small organisms

  • Small organisms such as amoeba, have very large SA:V ratio
  • This means that there is a big surface for exchange of substances, but also there is a smaller distance from the outside of the organisms to the middle of it
  • As a result, very small organisms can simply exchange substances across their surface
• Larger organisms

  • The larger an organism is, the smaller its surface area compared to its volume and the larger the distance from the middle to the outside
  • Larger organisms will typically have a higher metabolic rate too, which demands efficient transport of waste out of cells and reactants into the cells
  • As a result, they have adaptations that help make the exchange across surfaces more efficient
• Adaptations to increase SA:V ratio

  • Villi and microvilli- Absorption of digested food
  • Alveoli and bronchioles - Gas exchange
  • Spiracles and tracheoles - Gas exchange
  • Gill filaments and lamellae - Gas exchange
  • Thin wide leaves - Gas exchange
  • Many capillaries - Capillary network
• During digestion, large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes
• Carbohydrates

  • Carbs require more than one enzyme to hydrolyse them into monosaccharides: amylases
  • Amylase is produces by the pancreas and salivary glands it hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds
  • Begins in the mouth
  • Continues in the duodenum
  • Completed in the ileum
  • Sucrose and lactose are membrane bound enzymes that hydrolyse sucrose and lactose into monosaccharides
• Proteins

  • Proteins are large polymer molecules that can be hydrolysed by three enzymes:

  1. Endopeptidases (hydrolyse peptide bonds between amino acids in the middle of a polymer chain)
  2. Exopeptidases (hydrolyse peptide bonds between amino acids at the end on a polymer chain)
  3. Membrane bound dipeptidase (Hydrolyse peptide bonds between two amino acids)

  • Starts in the stomach, continues in the duodenum and if fully digested in the ileum
• Lipids

  • Digested by lipase and the action of bile salts
  • Produces in the pancreas and it can hydrolyse the ester bond in triglycerides to form the fatty acids and monosaccharides
  • Bile salts - produced in the liver - can emulsify lipids to form tiny droplets, micelles - so increases surface area
• Lipid digestion

  • Physical - lipids are coated in bile salts to create an emulsion
  • Many small droplets of lipids provide a larger SA to enable the faster hydrolysis action by lipase
  • Chemical - Lipase hydrolysis lipids into glycerol and fatty acids.
• Lipid absorption

  • Lipids are digested into monoglycerides and fatty acids by the action of lipase and bile salts - form micelles
  • When the micelles encounter the ileum epithelial cells due to the non-polar nature of the fatty acids and monoglycerides, they can simply diffuse across the cell surface membrane to enter the cells of the epithelial cells
  • Once in the cell these will be modified back into triglycerides inside of the endoplasmic reticulum and Golgi body
  • Micelles - Water soluble vesicles
• Cardiac muscle

  • The walls of the heart have thick muscular layer. This muscle is called cardiac muscle and it has unique properties
  • It is myogenic, meaning it can contract and relax without nervous or hormonal stimulation
  • It never fatigues, as long as it have a supply of oxygen
• Coronary arteries

  • Supple the cardiac muscle with oxygenated blood
  • These branch off from the aorta
  • If they become blocked the cardiac muscle won't receive oxygen, therefore will not be able to respire and the cells will die. This results in myocardial infarction (a heat attack)
• Four chambers

  2 Atria

  • Left atrium
  • Right atrium

  2 ventricle

  • Left atrium
  • Right atrium
• Atria

  • Thinner muscular walls
  • Do not need to contract as hard as not pumping blood as far
  • Elastic walls to stretch when blood enters
• Ventricles

  • Thicker muscular walls to enable bigger contraction
  • This creates a higher blood pressure to enable blood to flow longer distances
• Right ventricle

  • Pumps blood to the lungs this needs to be at a lower pressure to prevent damage to capillaries in the lungs and slow blood flows slowly to allow time for gas exchange
  • Therefore, thinner muscular wall in comparison to the left ventricle
• Left ventricle

  • Pumps blood to the body. This needs to be at a higher pressure to ensure blood reaches all the cells in the body
  • Therefore, much thicker muscular wall in comparison to the right ventricle to enable larger contractions of the muscle to create higher pressure
• Veins

  • Vena cava - carries deoxygenated blood from the body into the right atrium
  • pulmonary vein - carries oxygenated blood from the lungs to the left atrium
• Arteries

  • Pulmonary artery - Carries deoxygenated blood from right ventricle to the lungs to become oxygenated
  • Aorta - Carries oxygenated blood from the left ventricle to the rest of the body
• Valves

  • Semi-layer valves - In aorta and pulmonary artery
  • Atrio ventricular valves - Between atria and ventricles
  • Bicuspid (Left)
  • Tricuspid (Right)
  • Open when pressure is high behind
  • Closed when pressure in high in front
• Septum

  • Separates the deoxygenated and oxygenated blood
  • Maintains high concentration of oxygen in oxygenated blood to maintain concentration gradient to enable diffusion at respiring cells
• Cardiac cycle equation

  $Cardiac.Output=$$Heart.Rate*$$Stroke.Volume$

  
  

  Heart rate = Beats of the heart per minute

  Stroke volume = Volume of blood that leaves the heart each beat
• Diastole

  • The atria and ventricular muscles are relaxed this is when blood will enter the atria via the pulmonary vein
  • The blood flowing into the atria increasing the pressure within the atria
  • The volume of the blood which leaves one ventricle in one minuet is the cardiac output
• Atrial systole

  • The atria muscular walls contract, increasing the pressure further. This causes the atrioventricular valves to open and blood to flow into the ventricles
  • The ventricular muscular walls are relaxed
• Ventricular systole

  • After a short delay, the ventricle muscular walls contract, increasing the pressure beyond that of the atria. this causes the atrioventricular valves to close and the semi-lunar valves to open
  • The blood is pushed out of the ventricles into the arteries
• In mammals their circulatory system is a closed, double circulatory system

  Closed = The blood remains withing the blood vessels
• Double circulatory system

  • The blood passes through the heart twice in each circuit. There is one circuit which delivers blood to the lungs and another circuit which delivers blood to the rest of the body
  • Mammals require a D.C.S to manage the pressure of blood flow
  • The blood flows through the lungs at a lower pressure this prevents damage to the capillaries in the alveoli and also reduces the speed at which the blood flows, enabling more time for gas exchange
  • The oxygen blood form the lungs then goes back through the heart to be pumped out at a higher pressure to the rest of the body
• Key blood vessels

  • There are many blood vessels within the circulatory system, but the only ones you need to be able to name are:
  • Heart (Vena cava, aorta, pulmonary artery and pulmonary vein)
  • Lungs (Pulmonary artery and pulmonary vein)
  • Kidneys (renal artery and renal Vein)
  • The coronary arteries and the following blood vessels attached to these organs
  • These major blood vessels are connected within the circulatory system via the arteries, arterioles, capillaries and veins
• Blood vessels

  • Arteries carry blood away from the heart and into arterioles
  • The arterioles are smaller than arteries and connect to the capillaries
  • The capillaries connect the arterioles to the veins
  • The veins carry blood back into the heart
• Capillaries form capillary beds as exchange surfaces which are many branched capillaries these all have a narrow diameter to slow blood flow Red blood cells can only just fit through and are squashed against the walls, and this maximises diffusion
• Arteries

  Muscle layer - Thicker than veins so that constriction and dilation can occur to control volume of blood

  Elastic layer - Thicker than veins to help maintain blood pressure. The walls can stretch and recoil in response to the heart beat

  Wall thickness - Thicker walls than veins to help prevent the vessels bursting due to the high pressure

  Valves - No
• Veins

  Muscle layers - Relatively thin so it can't control the blood flow

  elastic layer - Relatively thin as the pressure is much lower

  Wall thickness - Thin as the pressure is much lower so there is low risk of bursting the thinness means the vessels are easily flattened, which helps the flow of blood up to the heart

  Valves - Yes
• Arterioles

  Muscle layer - Thicker than in arteries to help restrict blood flow into the capillaries

  Elastic layer - Thinner than in arteries as the pressure is lower

  Wall thickness - Thinner as pressure is slightly lower

  Valves - No
• Capillaries

  Muscle layer - No muscle layer

  Elastic layer - No elastic layer

  Wall thickness - One cell thick consisting of only a lining layer. This provides a short diffusion distance for exchanging materials between the blood and cells

  Valves - No
• Haemoglobin

  • Haemoglobins are groups of proteins found in different organisms. Haemoglobin is a protein with a quaternary structure. Haemoglobin are red blood cells transport of oxygen
• Oxyhaemoglobin dissociation curve

  • Oxygen is loaded in regions with a high partial pressure of oxygen and is unloaded in regions of low partial pressure of oxygen. This is shown on the oxyhaemoglobin dissociation curve
• Cooperative binding

  • The cooperative nature of oxygen binding to haemoglobin is due to the haemoglobin is due to the haemoglobin changing shape when the first oxygen binds. This then makes it easier further oxygens to bind
• The Bohr effect

  • The Bohr effect is when a high carbon dioxide concentration cause the oxyhaemoglobin curve to shift to the right the affinity for oxygen decreases because the acidic carbon dioxide changes the shape of haemoglobin slightly
• Key phrases

  • Affinity of haemoglobin for oxygen = The ability of haemoglobin to attract or bind oxygen
  • Saturation of haemoglobin with oxygen = When haemoglobin is holding the max amounts of oxygen can bind
  • Loading/association of haemoglobin = The binding of oxygen to haemoglobin
  • Unloading/association of haemoglobin = When oxygen detaches or unbinds from haemoglobin
• What is tissue fluid

  • Fluid containing water glucose, amino acids, fatty acids, ions and oxygen which bathes the tissues