U3: Exchange

Why is diffusion alone not sufficient for most organisms?

• Most cells are too far away from exchange surfaces for diffusion to be fully efficient

• Efficient exchange mechanisms require the SA: volume ratio to be large

What is the correlation between size and SA:volume ratio?

• Bigger size = smaller SA:volume ratio

• Smaller size= bigger SA: volume ratio

What are the requirements of an efficient exchange surface?

• Large SA: volume ratio for speed of gas exchange

• Very thin to keep diffusion pathway short to allow materials to cross rapidly

• Partially permeable membrane to allow selected materials to easily diffuse

• Moist because gases have to diffuse in water so they can enter cells

What are the requirements for efficient exchange in larger organisms?

• Efficient transport system to move internal environment (blood) and maintain diffusion gradient

• Ventilation mechanism to ensure air finds its way to the exchange surface quickly

What is ficks law?

• The relationship between factors

• Diffusion= SA x difference in concentration/thickness of membrane

What factors is diffusion affected by?

• SA

• Difference in concentration

• Thickness of membrane

How does exchange work in single-celled organisms?

• There is a large SA:volume ratio

• O2 diffuses in, CO2 diffuses out across cell membrane

• This is efficient

What is the main problem facing animals on land?

• Dehydration as the increase in SA required for gas restricts conserving water as the water will evaporate from it

• This is fought by insects having a waterproof covering

What is the structure of the respiratory system in insects?

• A series of tubes called tracheae which are supported by strengthened rings to stop them from collapsing

• The trachea connect to the atmosphere by openings called spiracles

• The tracheae divide into smaller tubes called tracheoles

• Air diffuses through the spiracles and tracheae to all parts of the body supplying organs directly with air

How is the breathing system of larger insects different to that of small insects?

Larger insects pump their abdomens to quicken the movement of gases

What are the benefits of the spiracle mechanism?

• They can open/close for certain situations

• This can prevent water from enteriong the trachae meaning that it traps air in the body, causing the insects to float.

How does the the ventilation system of insects work?

• Oxygen is used in aerobic respiration

• An oxygen gradient is established

• So oxygen diffuses in

How does an insect respire during flight?

• A little water leaks across the cell membranes of the muscle cell

• The end of the tracheoles fill with this water

• The wing muscles respire anerobically and produce lactate which is a soluble waste product

• This lowers the water potential of the muscle cells

• Water passess from the tracheole to the muscle cells

• This draws air into the tracheoles closer to the muscle cells and reduces the diffusion distance for oxygen

Name the structure that gases enter/leave the body of an insect.

Spiracles

How is an insects tracheal system adapted for efficient gas exchange?

• Highly branched/large number of tracheoles so short diffusion distance to cells

• Tracheoles have thin walls so short diffusion distance to cells

• Tracheae are tubes full of air so fast diffusion

• Fluid in the end of the tracheoles move out into tissues during exercise so larger SA for gas exchange

How are fish adapted for efficient exchange?

• They have a gas tight waterproof covering which prevents water loss

• Small SA:volume ratio so their body structure is not adequate to supply and remove respiratory gases

How does the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water?

• Llamale which increases the SA: volume ratio

• Gill plates and secondary lamellae

• Large number of capillaries to remove oxygen and maintain a gradient

• Thin epithelium so short diffusion pathway

• Pressure changes to bring in more water

• Countercurrent flow so the diffusion along the whole length of the fish and the gradient is maintained

How does the counter-current system work?

• Bony arches support gills

• Water enters via the fishes mouth, goes through gills and out through the operculum

• Blood enters through the back of gills

• The most oxygen rich blood meets the most oxygen rich water

• Oxygen diffuses from water to the blood throughout the entire length of the fish as there is constantly a gradient

Why is the counter-current system beneficial?

There is constantly a diffusion gradient meaning diffusion is constantly happening amd gas exchange can be maximised across the whole length of the fish.

How is the gas exchange of a plant similar to that of an insect?

• No living cell is far from the external air so they constantly have a source of oxygen and carbon dioxide

• Diffusion takes place in the gas phase (air) which makes it faster than if it were in water

How are plants adapted for gas excahnge?

• Many small pores (stomata) so diffusion pathway is short

• Many interconnecting air spaces that occur throughout the mesophyll for easy gas exchange

• Large SA of mesophyll cells for rapid diffusion

Why are stomata important?

They control the rate of gaseous exchange by opening and closing their pores

How do terrestrial organisms limit their water loss?

• A thick cuticle which forms a waterproof barrier

• Rolling up of leaves to protect the lower epidermis from the outside

• Hairy leaves to trap still, moist air next to the leaf surface and reduce the water potential gradient

• Stomata in pits/grooves to trap still, moist air near to the leaf surface and reduce the water potential gradient

• A reduced surface area to volume ratio of the leaves

Label the diagram

What is the role of the cartilage rings on the trachea?

• C shape so they can expand

• Provides strength and support to trachea to prevent a collapse

What is the function of the plueral membrane?

Lubricates area between lungs and ribcage

What is the function of the plueral fluid?

• Prevents friction during breathing between membrane and lung

• Causes the outer surface of the lungs to adhere closely to the inside of the thoracic cavity during inspiration

How does the body protect us from dust and inhaled microorganisms?

• Filtration of inhaled air by the nose

• Cough reflex

• Cilia and mucus in larger airways

• Alveolar macrophages in the blood

What is the function and names of the lining cells in the trachea?

• Ciliated Epithelium

• Have hairs preventing trapping of cells

• Goblet cells

• Secrete muccus which serves as a lubricant

What is a bronchi?

Divisions of the trachea that lead into the lungs

What is a bronchiole?

• Subdivisions of the bronchi

• Walls made if muscle so they can constrict to contract air in and out of the alveoli

Label this image

How is the rate of diffusion maximised in the alveoli?

• Good ventilation and efficient circulatory system to maintain a steep concentration gradient

• Large number of alveoli to provide a large surface area

• Alveolar and capillary walls are very thin and close together to minimize the diffusion path

How does inspiration work?

• Contraction of muscles flattens diaphragm

• Contraction of intercostal muscles raises ribcage

• Iscrease in volume of thorax, lungs and alveoli decreases pressure below the pressure of air

• So air is taken into the lungs to equalise the pressure

How does expiration work?

• Diagrgam relaxes and curves upwards

• External intercostal muscles relax allowing the ribs to fall

• Thorax, lung and alveoli volume decreased

• Pressure in alveoli increased above pressure of external air

• Air flows out to equalise pressure

What is the equation for rate of diffusion?

SAx difference in conentration/length of diffusion pathway

What is ventilation rate?

Number of breaths taken in 1 minute

What is tidal volume?

Volume of air breathed in or out during quiet breathing at rest

What is expiratory reserve volume?

Maximum volume of air which can be forcibly expired after a tidal expiration

What inspiratory reserve volume?

Volume of air which can be inspired above tidal respiration

What is residual volume?

Air which remains in the lungs after forced expiration

What is vital capacity?

The total of inspiratory reserve volume, expiratory reserve volume and tidal volume

What is the equation for pulmonary ventilation?

Pulmonary ventilation (dm3min-1) = tidal volume (dm3) x ventilation rate (min-1)

What happens during forced expiration?

• Abdominal muscles contract, pushing diaphragm upwards

• Internal intercostal muscles contract, pulling ribs downward

What is dead space?

The amount of air that remains in the trachea and bronchial tubes where no gas exchange takes place (150cm3)

What parts of the body control breathing rate?

• Chemoreceptors in carotid and aortic arteries

• Chemoreceptors in medulla

• Stretch receptors in muscles

• Cortex (voluntary control)

What are some risk factors to lung disease?

• Smoking

• Air Pollution

• Genetics

• Chest Infections

• Occupation (gas, dust ext)

What are chemoreceptors stimulated by?

• Rise in CO2 levels

• Fall in PH

• Rise in O2 conc in blood

What are stretch receptors?

• Sensitive to stretch

• Found in walls of bronchi, bronchioles and alveoli

• Detects inhalation and sends inhibitory signals to the respiratory centre to cause exhalation

• Continuous negative feedback system

What is digestion

Large biological molecules are hydrolysed into smaller molecules tat can be absorbed across cell membranes

Label the diagram

What is the function of the osephagus?

Carries food from the mouth to the stomach

What is the function of the stomach?

Produces enzymes, stores and digests food, muscles churn to mix the food with digestive juicesAbsor

What is the function of the ileum?

Absorption of digested food molecules into the bloodstream

What is the function of the large intenstine?

Reabsorption of water

What is the function of the rectum?

Feces are stored

What is the function of the anus?

Faeces are removed from the body in a process called egestion

What is the function of the salivary gland?

Secrete amylase to convert starch to maltose

What is the function of the pancreas?

Pancreatic juice contains protease which hydrolyse proteins, lipases to hydrolyse lipids and amylase to hydrolyse starch

Where does physical breakdown of food occur?

• The mouth: teeth break down food into smaller pieces to increase the surface area upon which enzymes can act

• The oesophagus: peristalsis keeps the moves the food moving towards the stomach

• The stomach:muscles of stomach move about the food particles and produce chyme

How are carbohydrates digested?

• Salivary amylase breaks down the glycosidic bonds in the starch

• Food is passed into the stomach, stomach acid denatures amylase so it can no longer hydrolyse starch

• Food passess into the small intestine where it mixes with pancreatic juice

• Pancreatic amylase continues hydrolysis of any remaining starch into maltose

• Lining of the ileum produces maltase, maltase breaks down the disaccharide maltose into the monosaccharide alpha glucose

• Sucrase hydrolyses the single glycosidic bond in sucrose to form the monosaccharides glucose and fructose

• Lactase hydrolyses the single glycosidic bond in lactose into its monosaccharides glucose and galactose

How are lipids broken down?

• Lipids are coated in bile salts to create an emulsion

• Many small droplets of lipids provide a large surface area

• Lipases hydrolyse the ester bond in the triglyceride which breaks the triglyceride into 1 glycerol molecule and 3 fatty acids

What is a micelle?

• Water soluble vesicles formed of fatty acids, glycerol, monoglycerides and bile salts

• Deliver fatty acids, glycerol and monoglycerides to the epithelial cells of ileum for absorption

How are proteins broken down?

• Endopeptidases hydrolyse the peptide bonds between the amino acids to form a series of smaller peptide molecule

• Exopeptidases act to hydrolyse the peptide bonds between the terminal amino acids at the outer region of the peptide molecule, releasing dipeptides

• Dipeptidases hydrolyse the bond between the dipeptides, resulting in single amino acids

How do villi increase the efficiency of absorpsion?

• Increase surface area for diffusion

• Thin walls reduce diffusion distance

• Muscles that allow them to move to mix the contents of the ileum and ensures when digested molecules are absorbed, new nutrient rich material replaces it

• Well supplied with blood vessels so blood can carry away absorbed molecules, which maintains the diffusion gradient

• Epithelial cells covered in microvilli to further increase surface area

How are monosaccharides and amino acids absorbed?

• Co-transport

• Sodium ions are actively transported out the epithelial cell into the blood

• This reduces the sodium ion concentration in the epithelial cell

• The protein the sodium ions diffuse through is a cotransporter protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient

How are lipids absorbed?

• Micelles come into contact with epithelial cells lining the vill of the ileum

• They are broken down and release the monoglycerides and fatty acids which diffused across the cell surface membrane into the epithelial cells

• In the cells, monoglycerides and fatty acids and transported to the endoplasmic reticulum

• They move to the golgi apparatus where they recombine

• The recombined triglycerides combine with cholesterol and lipoproteins to form chylomicrons

• Chylomicrons move out of the epithelial cells by exocytosis

• They move into lacteals in the centre of each villus, where they ,,ove into the bloodstream

CO TRANSPORT