mass transport

• haemoglobin

  • has a specific tertiary structure
  • made of 4 polypeptide chains
  • 2 alpha and 2 beta chains
  • each chain has a 'haem' group- carbon molecule with Fe2+ ion attached
• oxygen association

  • haemoglobin that loads/ associates with O2 easily are found in organisms that live in environments with low O2 availability- eg, deep sea, high altitude
  • O2 not easily/ readily released
• Low affinity

  where haemoglobin does not bind to O2 easily and dissociates readily- due to tightness of haemoglobin
• Role of haemoglobin

  • association with O2 at gas exchange surface
  • dissociates oxygen readily to respiring tissues - happens due to difference in PH altering the tertiary structure, therefore is function
• Cooperative binding- binding of O2

  • when the first O2 binds it changes the proteins tertiary structure
  • it exposes the sites/region of the other haem group, making it easier for O2 to bind
• BOHR effect

  when curve shifts to the right because there is low affinity

  meaning O2 is being dissociated
• when there is high partial pressure of oxygen, haemoglobin will load more O2, because there is high affinity- alveoli

  when there is a low partial pressure, more O2 will unload, because there is low affinity- respiring tissue
• Factors affecting Bohr effect

  • CO2 increase
  • Acidic
  • Decrease in PH
  • Exercise
  • Temp increase
• Circulatory system in mammals

  • closed- blood remains in vessels
  • double- blood passes through the heart twice
• mammals require double system to manage pressure of blood flow

  In pulmonary circuit:

  • low pressure applied to slow blood, which provides more time for diffusion of O2 and prevent damage of capillaries
• In systematic circuit:

  high pressure is applied to ensure oxygenated blood reaches every cell in the body
• Blood flow through the heart

  1. Deoxygenated blood from the body returns to the heart via the vena cava entering the right atrium

  2. The right atrium contracts, pushing blood through the tricuspid valve into the right ventricle

  3. The right ventricle contracts, pumping deoxygenated blood through the pulmonary valve and into the pulmonary artery

  4. The pulmonary artery carries the deoxygenated blood to the lungs, where it releases carbon dioxide and picks up oxygen through the process of gas exchange

  5. Oxygenated blood from the lungs returns to the heart via the pulmonary veins, entering the left atrium

  6. The left atrium contracts, pushing blood through the bicuspid valve into the left ventricle

  7. The left ventricle contracts, pumping oxygenated blood through the aortic valve and into the aorta then to the body
• Cardiac cycle

  1. atrial systole
  2. ventricular systole
  3. diastole
• Atrial systole- is the contraction of the atria, pushing blood into the ventricles

  increasing pressure in atria and decreasing volume, causing the atrioventricular valves open
• ventricular systole is the contraction of the ventricles, pushing blood out of the heart

  phase 1- AV valves shut, ventricle walls contract increasing pressure

  phase 2- due to increase in pressure it forces the semilunar valves to open
• Diastole

  • The ventricles and atria relax.
  • The semi-lunar valves close.
  • Blood flows passively into the atria.
• tissue fluid contains:

  • water
  • amino acid
  • glucose
  • fatty acids
  • ions
  • O2
  • it bathes tissue
• how is it formed

  At the arteriole end of capillaries:

  1. A high hydrostatic pressure, exerted by the force of the heart pumping, forces fluid out of capillaries.
  2. This forms tissue fluid surrounding body cells.
• At the venule end of capillaries:

  1. The hydrostatic pressure is lower.
  2. Proteins in blood exert a high oncotic pressure, a type of osmotic pressure, in capillaries.
  3. The water potential is lower in capillaries than in tissue fluid due to fluid loss.
  4. Some tissue fluid moves back into capillaries by osmosis.
• The composition of lymph

  Lymph is the fluid that flows around the lymphatic system via lymph vessels.
• Lymph has a similar composition to tissue fluid, except:

  • Lymph has less oxygen and nutrients.
  • Lymph has more fatty acids.
  • Lymph has more white blood cells (lymphocytes).
• The formation and transport of lymph

  Lymph is formed from tissue fluid.

  It is formed and transported around the body as follows:

  1. Some tissue fluid doesn't re-enter capillaries from tissue fluid.
  2. This fluid instead drains into lymph vessels (lymph capillaries) forming lymph.
  3. Lymph is transported through lymph vessels by muscle contractions.
  4. Lymph is passed through lymph nodes to filter pathogens.
  5. Lymph is eventually returned to the blood.
• Plants need transport systems because:

  • They are multicellular with a low surface area to volume ratio.
  • Diffusion is too slow to meet their metabolic needs.
  • Substances must be moved over long distances.
• xylem tissue

  Xylem tissue transports water and mineral ions around plants. It also provides structural support. It is mostly made up of xylem vessels.
• Adaptations of xylem vessels:

  • They are elongated, hollow tubes without end walls.
  • They lack organelles.
  • Their walls are thickened with lignin for support.
  • They have non-lignified pits that allow movement of water and ions into and out of vessels.
• phloem tissue

  Phloem tissue transports sugars and amino acids (assimilates) around plants. It is mostly made up of sieve tube elements and companion cells.
• Adaptations of sieve tube elements:

  • They are connected end-to-end to form sieve tubes.
  • They have sieve plates with pores at their ends to allow flow of sugars and amino acids.
  • They lack nuclei and most organelles.
  • They have only a thin layer of cytoplasm.
• Adaptations of companion cells:

  • They are connected to sieve tube elements through pores (plasmodesmata).
  • The cytoplasm contains a large nucleus, many mitochondria to release energy for the active transport of substances through the sieve tube elements, and many ribosomes for protein synthesis.
• Mass flow hypothesis

  The mass flow hypothesis proposes that translocation occurs due to pressure gradients.
• Phloem transport


  1. At the source, solutes like sucrose are actively loaded into sieve tube elements from companion cells

  2. This decreases the water potential in sieve tube elements

  3. Water enters the sieve tube elements from the xylem and companion cells by osmosis

  4. This increases hydrostatic pressure in the sieve tube elements at the source

  5. At the sink, solutes are actively removed from the sieve tube elements

  6. This increases the water potential in sieve tube elements at the sink

  7. Water leaves the phloem by osmosis, decreasing the hydrostatic pressure at the sink

  8. This creates a pressure gradient, pushing solutes from the source to areas of lower pressure at the sink