Gas exchange Flashcards
Gas exchange in an insect
Branched chitin lined system of trachea with openings called spiracles. Oxygen diffuses in, down a concentration gradient, through the open spiracles and into tubes called trachea. The trachea are lined with rings of chitin to prevent them from collapsing during ventilation, the trachea split into many branches called tracheoles. The tracheoles are not lined with chitin and so are permeable, this makes them the site of gas exchange in insects
Features of gas exchange in insects
Short diffusion pathways:
Tracheoles are in direct contact with the insect body cells
Insects are small maintaining an overall short diffusion pathway from spirackes to respiring tissue
The walls of the tracheoles are thin
Concentration gradient
The cells respire using the oxygen so the concentration of oxygen at the cells remains low
Body can be moved by muscles to move air so maintain concentration gradient for oxygen and carbon dioxide
Large surface area
Tracheoles are very branched
How do insects prevent water loss ?
Insects are coated in an exoskeleton that is made out of chitin this is impermeable so reduced the loss of water by evaporation from the insects tissues. To aid this the exoskeleton is also covered in waxy cuticle which is impermeable
When the spiracles are open water vapour can diffuse out of them to reduce this the loss spiracles are lined with hairs which trap the water vapour around the spiracles
Insects can also close the spiracles to further prevent loss of water
What happens when the tracheoles are resting ?
Food diffuses into the tracheoles and the tissue is hypotonic
What happens when the tracheoles are active ?
Activity causes metabolites (lactic acid) to accumulate in tissues making them hypertonic so water moves into tissue by osmosis
Fluid diffuse back into tissues
Fluid in the end of the tracheoles moves into tissues during exercise
Cells produce lactate by anaerobic respiration
Reduces water potential
Water moves in down water gradient by osmosis
This increases volume in tracheoles and reduces pressure to draw more in
Diffusion through air is faster
Fish exchange at the gills
Short diffusion pathway
Gills have a single layer of epithelial cells and the capillaries within the gills have a single layer of endothelial cells
Large surface area
The gills are folded into filaments and these are folded into lamellae
Concentration gradient
The gills have lots of blood capillaries
Blood in the capillaries flows in the opposite direction to the flow of water over the gills
This is called counter current flow
What is counter current flow ?
Water and blood flow in opposite directions so the diffusion gradient between the adjacent t flows is maintained over the whole lamella surface
Where does gas exchange occur in a plant ?
At the surface of the mesophyll cells
How does gas exchange occur in plants?
Plants need CO2 for photosynthesis and produce oxygen as a waste gas
Carbon dioxide diffuses into the leaves down a concentration gradient through pores in the surface of the leaf called stomata
The mesophyll cells are where most of the photosynthesis occurs particularly mesophyll cells as they are tall and long shape which increases the surface area for gas exchange
What do plants have that makes them adapted for plants
Large surface area
Large flat leaf
Tall long palisade mesophyll cells
Short diffusion pathway
Thin leaf
Air spaces
Concentration gradient
Mesophyll cels use the carbon dioxide maintaining a low concentration at the mesophyll cells
How do the stomata work ?
They can open and close and the two guard cells control the opening and closing of the stomata
What happens to the guard cells when the stomata open and close
Open-guard cells are turgid
Close-guard cells are flaccid
How do plants reduce water loss ?
Stomata close when guard cells lose water and become flaccid
Leaf is covered in a hydrophobic waxy cuticle which reduces water loss by evaporation
Most stomata are on the lower surface of the leaf
How can xerophytes reduce water loss
Xerophytes have a rolled leaf shape as upper epidermis is facing inwards to trap humid air
Reduced leaf surface area for transpiration
Sunken stomata humid air is trapped reducing water potential gradient between inside leaf and humid trapped air
No stomata exposed lower surface
Hairs trap moist air
Thick cuticle
What is the pathway of oxygen in the human gas exchange system ?
Air enters the trachea, into the bronchus, then the bronchioles, then into the alveoli (this is down the pressure gradient), then the alveoli epithelium, then the capillary endothelium, then into the blood ( this is diffusion down a concentration gradient)
What are the adaptations of the alveoli ?
Large surface area
Alveolar epithelium and capillary endothelium are just one cell thick. Short diffusion distance for oxygen and carbon dioxide between air and blood
Many capillaries close to alveoli to maintain good blood supply and maintain steep concentration gradient
Well ventilated to bring oxygen to the surface and take carbon dioxide away and maintain steep concentration gradient for oxygen and carbon dioxide
What is the purpose of ventilation ?
To maintain the diffusion of gases across the alveolar epithelium air must constantly move in and out of the lungs
Cause and effect of breathing in and breathing out
Breathing in:
The external intercostal muscles contract so the rib cage moves up and out
Diaphragm contracts do it flattens
Increases the volume of the thorax so pressure decreases
Breathing out:
External intercostal muscles relax so rib cage moves down and in
Diaphragm relaxes so it becomes dome shaped
Decreases the volume of the thorax so pressure increases
What is forced expiration and how does it work ?
Internal intercostal muscles contract pulling the ribcage further down and in
External intercostal muscles relax
Lung disease and example effect on lung function
Pulmonary tuberculosis- volume breathed in decreases
Fibrosis- volume breathed in decreases as does the volume exhaled per breath. Gas exchange is reduced as diffusion distance across scar tissue is longer
Asthma- air flow is severely reduced so volume of air exhaled per second reduces
Emphysema- destruction of the alveolar walls which reduces surface area and increase ventilation for compensation
