exchange

• what are the exoskeletons of insects made of and what is their purpose?

  -chitin, for protection

  - lipid layer, prevents water loss
• name the system that insects have for gases to enter and leave their body

  tracheal system
• what adaptations do insects have to prevent water loss?

  1. small surface area: volume ratio - where water can evaporate from

  2. insects have a waterproof exoskeleton

  3. spiracles - gases enter and water can evaporate - open and close to reduce water loss
• name and describe the three structures within the tracheal system

  1) spiracles - round openings through which oxygen and carbon dioxide enter and leave

  2) trachea - internal tubes, kept open with spirals of chitin

  3) tracheoles - they extend throughout all tissue to deliver oxygen to respiring cells
• How do gases use diffusion to move in and out of the tracheal system?

  - when cells respire they use oxygen and produce CO2

  - this creates a concentration gradient from the tracheoles to the atmosphere
• How do gases use mass transport to move in and out of the tracheal system?

  - muscles within the abdomen contract and relax which helps gases enter and leave by raising the pressure
• How do gases use water to move in and out of the tracheal system?

  - lactate is produced when the insects are flying as they respire anaerobically

  - this lowers the water potential so water moves into cells by osmosis

  - as the water moves out of the tracheoles, more air from the atmosphere is drawn in due to the drop in volume and pressure
• how are insects adapted for efficient diffusion?

  1) lots of tracheoles - large surface area

  2) walls of tracheoles are thin and there is a short diffusion pathway

  3) use of oxygen and production of CO2 = steep concentration gradients
• briefly describe the anatomy of fish gills

  - gills are made up of stacks of gill filaments

  - each filament is covered in gill lamellae

  - creates a large surface area
• How are fish adapted for efficient gas exchange?

  - large surface area: volume ratio - many gill filaments covered in many lamellae

  - short diffusion distance - capillary network in every lamellae + lamellae are thin

  - maintain concentration gradient by concurrent flow
• what is counter current flow in relation to fish gills?

  when water flows over the gills in the opposite direction to the flow of blood in the capillaries
• why is concurrent flow important in fish gills?

  it ensures equilibrium isn't reached which means a diffusion gradient is maintained across the entire lamellae;

  therefore more oxygen diffuses from water to the blood
• what is the diffusion pathway like in leaves


  short and fast
• what three substances move in and out of the stomata?

  - oxygen

  - carbon dioxide

  - water VAPOUR
• Why is the stomata closed at night?

  At night there is no photosynthesis, so no demand for CO2 inside the leaf

  Stomata closed to prevent water loss
• how are leaves adapted for easy movement of gases?

  air spaces;

  allows gases to move around the leaf;

  come into contact with photosynthesising cells

  OR

  large sa of mesophyll cells;

  for rapid diffusion
• state two similarities between gas exchange in a plant leaf and gas exchange in a terrestrial insect

  ANY TWO:

  - diffusion takes place in the gas phase

  - need to avoid excessive water loss

  - diffuse air through pores in outer covering

  - no living cell is far from external air
• stae two differences between gas exchange in a plant leaf and gas exchange in a terrestrial insect

  ANY TWO:

  - insects may create mass air flow - plants never do

  - insects have a smaller SA:V ratio than plants

  - insects have special structures along which gases diffuse - plants don't

  - insects don't interchange gases between respiration and photosynthesis but plants do
• explain the advantage of a plant being able to control the opening and closing of its stomata

  reduces water loss by evaporation
• name the process that produces CO2 in plants

  respiration
• name the process that uses up CO2 in plants

  photosynthesis
• Some herbicides cause the stomata of plants to close. Suggest how these herbicides might lead to the death of a plant

  - stomata closed = little/no gas exchange with the environment

  - in the absence of gas from the environment, photosynthesis and respiration will eventually cease and the plant will die
• Why is one-way flow an advantage to fish?

  - requires less energy

  - as flow doesn't have to be reversed
• explain why there is a conflict in terrestrial insects between gas exchange and conserving water

  - gas exchange requires a thin, permeable surface with a large area

  - conserving water requires thick, waterproof surfaces with a a small area
• explain how the tracheal system limits the size of insects

  - it relies on diffusion to bring oxygen to respiring tissues

  - if insects were larger, it would take too long for oxygen to reach respiring tissues
• What is a xerophytic plant?

  A plant that is adapted to live in dry climates
• name 3 ways that xerophytes are adapted to reduce water loss

  ANY THREE:

  - curled leaves trap moisture

  - hairs to trap moisture

  - sunken stomata to trap moisture

  - thicker cuticle to prevent evaporation

  - longer root to reach more water supply
• how is the trachea adapted to its role

  has tough c-shaped cartilage rings that support the trachea and keep it open
• describe the process of inspiration

  1. External intercostal muscles + diaphragm contract

  2. Ribs lift up and out sternum forward

  3. Diaphragm forced down

  5. Overall increase in volume of thoarcic cavity an decrease in pressure in the lungs

  6. Pressure in lungs lower then the atmosphere

  7. Air is drawn into lungs down the pressure gradient
• describe the process of expiration

  1. External intercostal muscles + diaphragm relax

  2. Ribs and sternum moves down and in

  3. Decreased volume of thoarcic cavity

  4. Pressure in lungs is increased

  5. Pressure in lungs greater then the atmosphere

  6. Air is forced out of lungs down the pressure gradient