3A Exchange and transport systems

• why does every organism need to exchange substances?

  • take in oxygen and nutrients• excrete waste products e.g. by carbon dioxide and urea • maintain body temp
• do smaller organisms have a higher or lower SA:V?

  higher
• how are substances exchanged in single-celled organisms?

  diffuse directly across cell membranes
• why can multicellular organisms not exchange substances through diffusion across cell surface membrane?

  • some cells are deep within the body - large diffusion path• large animals have a small SA:V and cannot exchange substances that quickly across a relatively small area
• how do multicellular organisms exchange surfaces?

  they use specialised exchange organs and mass transport systems
• what is the mass transport system in animals?

  circulatory system
• what is the mass transport system in plants?

  xylem and phloem
• what else is created in cells that needs to be regulated?

  heat
• what two factors influence the rate of heat exchange?

  • body size • body shape
• how does body size influence the rate of heat exchange?

  • large organisms find it harder to loose heat due to high SA:V• small organisms need a high metabolic rate in order to generate enough heat to stay warm
• does a large SA:V increase or decrease the rate of heat exchange?

  increase
• does a small SA:V ratio increase or decrease the rate of heat exchange?

  decrease
• give an example of an animal who has adapted to cold environments.

  artic foxes have small ears and round heads to minimise SA:V ratio and therefore heat loss
• give an example of an animal who has adapted to hot environments.

  african bat eared foxes have large ears and pointy faces to maximise SA:V ratio and therefore increase heat loss
• name 2 behavioural and physiological adaptations of animals who live in cold environments.

  • small mammals eat large amounts of high energy foods to support high metabolic rates.• small mammals develop thick layers of fur and hibernate to avoid the cold.
• name 3 behavioural and physiological adaptations of animals who live in hot environments.

  • kidney adaptations to produce less urine to compensate for high levels of water loss• elephants have large flat ears to increase SA:V• hippos spend most of their day in water to help lose heat
• what is the main form of gas exchange in single celled organisms?

  diffusion.
• why do single celled organisms not need specialised gas exchange surfaces?

  Because they have a high SA:V and have developed a thin surface to shorten the diffusion pathway.
• Why have fish adapted to maximise oxygen intake?

  They require oxygen for respiration and there is a lower oxygen concentration in water than air.
• Describe gill structure?

  Each gill is made of gill filaments, and each filament is covered in lamellae. Lamellaes contain lots of capillaries and a thin surface layer of cells. This is to increase SA:V.
• What adaptation do fish have to improve gas exchange efficiency?

  Counter current system Water flows through the lamellae in the opposite direction to the water flowing over the fish. This means high oxygen concentrated water always flows next to blood with low conc of oxygen. This maintains a steep concentration gradient.
• What is the main gas exchange in dicotyledonous plants?

  Mesophyll cell surface in the leaf.
• Describe the process of gas exchange in dicotyledonous plants.

  gases move in and out through pores called stomata. Stomata opening and closing is controlled by guard cells.
• What is the gas exchange surface in insects?

  Trachea which branches into tracheoles.
• Describe the process of gas exchange in insects.

  Air moves into the tracheoles through pores called spiracles. Oxygen travels down the conc gradient directly into respiring cells. They use rhythmic abdominal movements to move air in and out of the spiricles.
• What substance is usually lost when exchanging gas?

  Water.
• How do insects minimise water loss when exchanging gas?

  They use muscles to close spiracles when not in use. Water proof waxy cuticle and tiny hairs all over the body reduce evaporation.
• How do plants minimise water loss during gas exchange?

  Water in the guard cells is what opens the stomata, so when there is not enough water in the plant, the guard cells close.
• What are xerophytes?

  Plants that are adapted to living in areas where water is in short supply.
• What adaptations do xerophytes have?

  Thick waxy cuticle to limit transpiration. Reduced number of stomata. Hairs on the epidermis to retain water.
• Describe the structure of the gas exchange organs in humans.

  Air enters through the trachea which splits into two bronchi (leading to each lung). Each bronchi branches into bronchioles that lead to smaller air sacs called alveoli.
• What are intercostal muscles?

  Muscle between ribs.
• What are the two stages of gas exchange in humans?

  inspiration, expiration.
• Describe the process of inspiration.

  External intercostal muscles and diaphragm contract.Rib cage moves up and out and diaphragm flattens. Volume of thoracic cavity increases. Lung pressure decreases to below atmospheric pressure. Air travels down pressure gradient into the lungs.
• Is inspiration active or passive?

  Active.
• Describe the process of expiration.

  external intercostal and diaphragm relaxes. Rib cage moves down and in and diaphragm curves.Volume of thoracic cavity decreases. Lung pressure increases to above atmospheric pressure. Air travels down the pressure gradient out of the lungs.
• Is expiration passive or active?

  Passive.
• Describe the process of forced expiration.

  External intercostal muscles relax.Internal intercostal muscles contract. Diaphragm moves down and in.
• Is forced expiration active or passive?

  active.
• Where does gas exchange in the lungs occur?

  alveoli.