Exchange and transport systems

• What substances need to be exchanged with the environment?

  Oxygen, Carbon dioxide and Heat
• How does a mouse have a larger surface to volume ratio that a hippo?

  The mouse is smaller in volume so relative to its own volume has a large surface area. A hippo has a larger volume so relative to its own volume it has a smaller surface area.
• How do single-celled organisms exchange substances with their environment?

  Simple diffusion due to a short diffusion pathway
• Why is diffusion across the outer membrane too slow for multicellular organisms?


  Cells are deep within the body creating a long diffusion pathway

  Large animals have low surface area to volume ratio which makes it difficult to exchange enough substances to supply the volume over a relatively small surface area
• How do multicellular organisms exchange substances?

  Specialised exchange organs i.e Lungs, and mass transport i.e circulatory system.
• How is heat exchanged?

  Body size - Small surface area to volume ratio to retain heat. Small animals such as mice have a large surface area to volume ratio so need a high metabolic rate to generate enough heat.

  
  

  Body shape - Compact shape to minimise heat loss, large shapes to increase heat loss i.e elephant ears are large and thin increasing surface area to lose heat

  
  

  Adaptations for heat exchange - Body shape is adapted to suit its environment i.e arctic fox adapted with small ears round head to reduce surface area and reduce heat loss, African bat-eared fox has large ears and long face to increase surface area and increase heat loss.
• Name behavioral adaptations


  Small mammals eating high energy food to support fast metabolic rates to generate heat

  Hippos stay in the water most the day to lose heat
• Name physiological adaptations


  Animals with high SA:V ratios, which live in hot areas, have developed kidney structures to minimize water loss and produce less urine

  Elephants have large flat ears to increase heat loss by increasing SA:V ratio
• What is a gas exchange surface?

  A boundary between the outside environment and the internal environment of an organism
• What do gas exchange surfaces have in common?

  Large surface area

  Thin to provide a short diffusion pathway

  Steep concentration gradient to increase rate of diffusion
• Describe and explain the structure of gills in a fish

  Gills have an artery of deoxygenated blood to the gill, vesseled of oxygenated blood from the gills, gill filaments and lamellae

  
  

  Each gill is made of thin plates ( gill filaments ) which give a large surface area for exchange of gases, increasing rate of diffusion

  Gill filaments are covered in lamellae which further increase rate of diffusion by increasing surface area. Lamellae have many blood capillaries and a thin layer of cells creating a short diffusion pathway between water and the blood
• Explain the counter-current system

  In gills of fish, blood flows through the lamellae in one direction and water flows over them in the opposite direction

  This means that water with relatively high oxygen concentration always flows next to the blood with a low oxygen concentration forming a steep concentration gradient. This means as much oxygen as possible diffuses from water into the blood

  
• Explain gas exchange in dicotyledonous plants

  Mesophyll cells are the main gas exchange surface in the leaf

  They have a large surface area as they are well adapted to their function

  Gases moves in and out through stomata in the epidermis, they are controlled by guard cells, stomata can open and close to control exchange gases and water loss.
• What is the structure of a dicotyledonous plant leaf?

  Waxy cuticle

  Upper epidermis cells

  Palisade mesophyll cell

  Xylem and phloem

  air space

  Spongy mesophyll cells

  lower epidermis cell

  Guard cell

  Stomata

  Waxy cuticle

  
• How is gas exchanged in insect?

  Terrestrial in insects have tracheae which they use for gas exchange.

  Air moves through spiracles, oxygen travels down the concentration gradient towards the cells. Tracheae branch into smaller tracheoles which have thin permeable walls which go to individual cells so oxygen diffuses directly into respiring cells.

  CO2 from the cells move down its own concentration gradient towards spiricales to be released into the atmosphere. Rhythmic abdominal movements move air in and out of spiracles.

  
• How is water loss controlled in insects?

  When too much water is being lost, they use muscles to close the spiriciales.

  They have a waterproof, waxy cuticle all over the body and tiny hairs around the spiracles to reduces evaporation
• How is water loss controlled in plants?

  Stomata are open in the day to allow gas exchange, water enters guard cells to make them turgid opening stomata pore

  When plants start to get dehydrated, guard cells lose water and become flaccid, closing the pore
• Give examples of xerophytic adaptations

  Explain each each adaptation

  Stomata in sunken pits to trap water vapour, reducing concentration of water gradient between the leaf and the air, reducing rate of evaporation from the leaf

  Layer of hairs on the epidermis to trap water vapour around the stomata

  Curled leaves with the stomata inside protecting them from wind which would increase rate of evaporation as the concentration gradient between the air and the leaf would steepen

  Reduced number of stomata so there are less places for water to escape

  Thicker waxy waterproof cuticles on leaves and stems to reduce evaporation
• What organ do humans use for gas exchange?

  Lungs
• What are the structures in the human gas exchange system?

  Trachea

  Rib cage

  Intercostal muscles

  Lung

  Bronchus

  Bronchioles

  Alveoli

  Diaphragm

  
• Describe how structures in the gas exchange system are linked


  When you breathe in, air enters the trachea which splits into two bronchi. One bronchus leading into each lung which branches off into smaller tubes, bronchioles, which end in alveoli. This is where gases are exchanged. The rib cage, intercostal muscles and diaphragm work together to move air in an out of the lungs.
• What is ventilation


  Inspiration and expiration which controlled by the internal and external intercostal muscles and ribcage
• What happens during inspiration?


  External intercostal and diaphragm muscles contract causing the ribcage to move upwards and outwards and diaphragm to flatten.

  This increases the volume of the thoracic cavity. As it increases, lung pressure decreases below atmospheric pressure so air flows into the lungs. Inspiration is an active process.

  
• What happens during expiration?

  External intercostal muscles and diaphragm relax. The ribcage moves downwards and outwards, volume of the thoracic cavity decreases, causing air pressure to increase above atmospheric pressure. Air is forced out if the lungs down the concentration gradient. Expiration is a passive process
• What happens during forced expiration?

  External intercostal muscles relax and internal intercostal muscles contract, pulling the ribcage further down and in. In this movement the set of intercostal muscles are said to be antagonising pairs.
• What is the structure of alveoli?


  The wall of each alveolus is made of alveolar epithelium which and single layer thin ( of cells ) and flat. The walls of capillaries which surround the alveoli are made of capillary endothelium which is also a single layer thin of cells

  Alveoli also contain the protein elastin which helps the alveoli recoil and retain shape after inhaling and exhaling
• How does gas move through the exchange system?

  oxygen moves down the trachea, bronchi, bronchioles, into the alveoli down the pressure gradient. Oxygen moves into the blood down the diffusion gradient and is carried around the body.

  Carbon dioxide moves down its own pressure and diffusion gradient in the opposite way to oxygen and is breathed out
• How is gas exchanged in the alveoli?

  Oxygen diffuses out of the alveoli, across the alveolar endothelium and the capillary endothelium into a haemoglobin in the blood.

  Carbon dioxide diffuses into the alveoli from the blood.
• What features of alveoli speed up the rate of diffusion?

  Thin exchange surface area - Short diffusion pathway speeds up rate of diffusion as alveolar endothelium is only one cell thick

  A large surface area - millions of alveoli mean large surface area for gas exchange

  Steep concentration gradient of oxygen and carbon dioxide between the alveoli and capillaries, increasing rate of diffusion.

  This steep gradient is maintained by the flow of blood and ventilation.

  
• What are the four measures of lung function?

  Tidal volume - volume of air in each breath

  Ventilation rate - number of breaths per minute

  Forced expiratory volume ( FEV ) - Maximum volume of air that can be breathed out in one second

  Forced vital capacity ( FVC ) - Maximum volume of air that can be can be breathed out of the lungs forcefully after a deep breath
• Explain Tuberculosis


  TB is a lung disease caused by bacteria.

  When infected with TB bacteria the immune system cells build a wall around the bacteria in the lungs, forming small hard lumps known as tubercles. Infected tissue within the tubercles dies and gaseous exchange surface is damaged, Tidal volume decreases. TB also causes fibrosis which further decreases tidal volume

  
  

  Reduced tidal volume means less air can be inhaled with each breath, to receive enough oxygen you need to breathe faster so ventilation rate increases.

  
  

  Symptoms include persistent cough, coughing up blood and mucus, chest pains, shortness of breath and fatigue
• Explain Fibrosis


  Fibrosis is the formation of scar tissue in the lungs. This can be the result of infection or exposure to substances like dust.

  Scar tissue is thicker and less elastic, so cannot expand like normal. Tidal volume and FVC is reduced and diffusion is slower across the scar tissue due to increased diffusion pathway.

  
  

  Patients have a faster ventilation rate

  
  

  Symptoms include shortness of breath, dry cough, fatigue, weakness, chest pain
• Explain Asthma


  Asthma is a respiratory condition where airways become inflamed and irritated. Can be caused by pollen, dust or allergic reaction.

  In an attack, smooth lining in the bronchioles contract and large amounts of mucus is produced. Airways constrict causing difficulty breathing, air flow in and out of the lungs is severely reduced, reducing FEV

  
  

  Symptoms include wheezing, tight chest, shortness of breath.

  During an attack symptoms are sudden and can be relieved with drugs i.e an inhaler which cause the muscle in the bronchioles to relax, opening airways
• Explain Emphysema


  Lung disease caused by smoking or long term exposure to air pollution. Foreign particles become trapped in the alveoli. This causes inflammation, attracting phagocytes to the area. The phagocytes produce an enzyme which breaks down elastin.

  
  

  Elastin helps aleoli return to their normal shape after inhaling and exhaling, loss of elastin means alveoli can't recoil to expel air. Destruction is caused to the walls reducing surface area so rate of gaseous exchange decreases.

  
  

  Symptom include shortness of breath and wheezing and increased ventilation rate
• What happens when gas exchange is reduced?

  Less oxygen is able to diffuse into the blood, body cells receive less oxygen and rate of aerobic respiration is reduced. Sufferers may feel tired and weak.
• What does a spirometer do?


  Measures volume of air inspired and expired by the respiratory system
• How do you calculate percentage change?

  difference / original x 100
• What are the dissection tools?

  Scalpel - sharp blade for fine cuts

  Dissecting scissors - precise cuts, won't snap under pressure or damage tissue

  Dissecting pin - pin a specimen during dissection

  Tweezers or forceps - holding or moving specimen
• What are the Ethical issues with dissecting animals?

  Unnecessary killing - sometimes animal already dead, organs used in schools from dead animals

  If animal was raised in a humane way - i.e overcrowding

  If animal was killed humanely
• What happens during digestion?

  Large food molecules like starch and proteins are broken into glucose and amino acids so the can move across membranes and be absorbed to be transported around the body.