organisms exchange substances with their environment

• what is osmosis?


  the net movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane
• what is water potential?

  water potential is the pressure created by water molecules
• what can water potential tell us ?

  it is used to measure how likely osmosis is to occur between 2 solutions
• what is the water potential for pure water?

  0KPa
• water potential is always in the form of..

  a negative (-) number
• how would you describe the net movement of osmosis?

  water molecules move from the least negative KPa to the most negative KPa. high-> low
• describe a hypertonic cell

  the water potential is higher inside the cell than outside the cell
• describe a hypotonic cell

  water potential is higher outside the cell than inside the cell
• describe an isotonic cell

  the water potential is the same inside and out
• Name two features that helps to reduce water loss?

  1. Waterproof covering (in insects this is a rigid outer skeleton with waterprof cuticles

  2. Small surface area to volume ratio (minimise area of water loss)
• What does the features reducing water loss mean for gas exchange?

  They cannot use their body surface to diffuse respiratory gases
• What do insects have instead of using their body surface for gas exchanges?

  An internal network of tubes called tracheae
• How are the tracheae supported?

  Strengthened rings (chitin) to prevent it from collapsing
• What do the tracheae divide into?

  Smaller tubes called tracheoles
• Where do the tracheoles go? What does this mean?

  Tracheoles extend throughout all body tissue of insect so atmospheric air (with O2) is brought directly to respiring tissues
• How do respiratory gases move in and out of the tracheal system along a diffusion gradients?

  - oxygen used up by cells

  - concentration towards ends of tracheoles falls

  - diffusion gradient so O2 diffuses from atmosphere through tracheae and tracheoles to cells

  - CO2 produced at cells during respiration

  - diffusion gradient going opposite way

  - CO2 diffuses along tracheoles and tracheae to atmosphere

  - diffusion in air more rapid than water so bases exchanged quickly
• How do respiratory gases move in and out of the tracheal system through ventilation?

  - movement of muscles in insects

  - mass movements of air in and out of tracheae

  - further speeds up exchange of respiratory gasesSee an expert-written answer!We have an expert-written solution to this problem!
• Where do gases enter and leave tracheae?

  Tiny pores called spiracles on body surface
• How are spiracles opened and closed?

  By a valve
• What happens when a spiracle is open?

  Water can evaporate from the insect
• Are the spiracles opened or closed most of the time?

  Closed to prevent water loss
• What limitations does the tracheal system have?

  - relies of diffusion for exchange of gases between cels and environment

  - diffusion pathway needs to be short

  - limits the size insects can attain
• How is gas exchanged in single-called organisms?

  - large SA:V ratio

  - oxygen diffuses across body surface (covered by a cell-surface membrane)

  - carbon dioxide diffuses out across body surface
• What happens when a living cell is surrounded by a cell wall?

  The cell wall is completely permeable so there is no barrier to diffusion of gases
• Do fish have a large or small surface area to volume ratio? Explain why and what does this mean for its gas exchange system?

  Small surface area to volume ratio as there bodies are not adequate to supply and remove their respiratory gasses therefore they have a specialized gas exchange surface: Gills
• gill filaments


  Fingerlike projections through which gases enter and leave the blood system-used for respiration and they are stacked up in a pile
• gill lamellae


  At right angle to gill filaments, which increase the surface area of the gills.
• What is it called when water and blood flow in opposite directions?

  Countercurrent flow
• Why does the opposite flow of blood and oxygen maintain a concentration gradient?

  Blood that is well loaded with oxygen meets water

  Water has a maximum concentration of oxygen

  Therefore diffusion of oxygen from water into the blood takes place along a concentration gradient

  Blood with little oxygen meets water which has the most but not all oxygen removed

  Again diffusion of oxygen from water to blood takes place

  Therefore diffusion concentration of oxygen is maintained across the entire width of the gill lamellae
• Explain why water is always lost from the gas exchange surface of terrestrial organisms

  Gas exchange surfaces are permeable

  Higher concentration gradient of water molecules inside than out

  So water will diffuse out
• Explain how the relationship between the direction of flow of the water and of the blood is useful to the fish

  As there is a countercurrent flow which maintains the concentration gradient across the whole gill so MORE oxygen will enter the blood so there is MORE aerobic respiration
• Explain how the gills of a fish are adapted for efficient gas exchange?

  Gills have lamellae which increase surface area for increased diffusion of oxygen

  Thin epithelium walls which decreases diffusion distance into capillaries which increases the rate of diffusion

  Water and blood flow in opposite directions which maintains a concentration gradient as blood always has a lower oxygen concentration

  Circulation of blood by capillaries replaces saturated blood with oxygen
• Concentration of oxygen is higher in the surface waters than it is in water close to the seabed. Explain Why?

  As there is mixing of air and water on the surface water and air has a higher concentration of oxygen than water so oxygen diffuses into water

  Plants/seaweed near surface photosynthesize which produces oxygen
• explain why parallel flow would not achieve the same rates of oxygen extraction ( fish gas exchange)

  the concentrations across the gill would quickly equalise
• define the term zerophyte?

  plants with adaptations that allow them to survive in dry conditions and conserve water
• distinguish between obstructive and restrictive lung diseases

  • obstructive - prevents air reaching the alveoli
  • restrictive - affects the gas exchange tissue itself
• What is the main focus of Lesson 6?

  Mass flow hypothesis
• What does translation refer to in the context of mass flow?

  Transport of assimilates in plants
• What is the structure that runs from leaves to roots?

  3D network of phloem
• How are phloem tissues adapted for translation function?

  Arranged in end-to-end formation