Gas exchange in a leaf, single celled organisms, terrestrial insects Flashcards
What is the structure of a leaf?
- Waxy cuticle= Prevents water loss= - Upper epidermis = Layer of tightly packed cells that are transparent
- Palisade mesophyll = Layer of elongated cells containing chloroplast
- Spongy mesophyll = Layers of cells containing air spaces
- Stomata = Pores on underside of leaf (less water) allowing air to entre
- Guard cells = control opening and closing of stomata
- Lower epidermis = layer of tightly packed cells
When does gas exchange in a leaf happen and where
Gas exchange happens when guard cells are turgid so the stomata remains open allowing air to entre the leaf down conc gradient
Spongy mesophylls air space allows carbon dioxide to rapidly diffuse into cells to be used up rapidly in photosynthesis
What is the diffusion pathway like in a leaf and how
Stomata and thinness of plant tissue create a short diffusion pathway.
No active ventilation is therefore required
What are xerophytes
Where water is scares and plants need effective adaptations to conserve water
plants with these adaptations are called xerophytes
adaptations include
. few stomata
. needle shaped, curled or small leaves
. waxy cuticle
. Hairs surrounding stomata
How does gas exchange happen in singled celled organisms and why
Gas exchange occurs via simple diffusion due to single celled organisms having a high SA:V ratio
why is having a high SA:V ratio good in single celled organisms
-Large surface area allows max absorption of nutrience, gases and excretion of waste
- Small volume means the diffusion distance to all organelles is short
what happens to the SA:V ratio if an organism increases and why
what happens if the diffusion distance increases
Size of organism is inversely proportional to it surface are to volume ratio
- Less surface are so less area to allow absorption of nutrience, gases and excretion of waste
- Larger volume so a larger diffusion distance
If diffusion distance increases the diffusion time decreases
Why do large multicellular plants and animals need a specialised system for gas exchange/mass transport
Because they have a Low SA:V ratio meaning diffusion alone would be insufficient to meet the metabolic demand
describe a method on how to find the surface area of a leaf
- Draw around the leaf on a piece of graph paper
- count the squares
- then X by 2
What do organisms have for effective gas exchange
- Large SA
- Short diffusion distance
- Concentration gradient (maintained)
- good blood supply (if needed)
How does the tracheal system of a terrestrial insect work
- Exoskeleton is impermeable to gases
- A spiracle which is an opening in the exoskeleton which has valves
. Allows oxygen to diffuse and flow to the trachea
. Mostly closed to reduce water loss - Trachea are tubes in the breathing system which lead to tracheoles (narrower tubes)
. Walls have reinforcement to keep them open as air pressure inside fluctuates - Large number of tracheoles run between cells and into muscle fibre (site of gas exchange/respiration)
- co2 then moves back through down conc gradient
What are the adaptations of the trachea is good for gas exchange in terrestrial insects
- Has a large surface area due to being highly branched
- Has a short diffusion distance due to thin walls
- large number of tracheoles increase SA
How do spiracles in terrestrial insects reduce water loss
By closing using muscles until all the oxygen is diffused out into the muscle fibre
They also have waterproof waxy cuticle all over their bond and tiny hairs reducing evaportation
What is the benefit of the waxy cuticle on the body of terrestrial insects?
It prevents water loss
