OCRA Biology, OCR ALevel Biology OCR AS Level Biology. Module 3 (3.1) Exchange +Transport Summary notes. Revision notes.
H020 and H420. OCR, Breadth and depth of biology. Featured in Paper 1,2,3.
Chapter 5 – Breathing rate and gas exchange - Weaknesses per chapter.
In insects: have a head, thorax, and abdomen. Gas exchange that occurs in insects starts
with:
1) Spiracle: a hole which allows gases and water vapour to come in and out. They open when
active – allowing O2 into the insect and they close when they are at rest – allowing H2O out
of the spiracle.
2) Trachea: main tube about 1 mm wide and lined with chitin. Chitin is impermeable to gases
and is a tough chemical to support the trachea (stops trachea from collapsing)
3) Tracheoles: are individual elongated cells to increase the surface area. They are responsible
for gas exchange.
Other key definitions and involvements in the gas exchange system of an insect:
- Tracheal fluid: surrounds the tracheoles and limits the air penetration and no gas exchange
occurs here. This is because they are resting and so there is no major reason for O2. There is
very high water potential
Resting tracheal fluid Active tracheal fluid
Surrounds the tracheoles and limits the air Surrounds the tracheoles and due to the lack of
penetration. oxygen, anaerobic respiration occurs.
No gas exchange occurs here. Increasing respiration, increases lactic acid and
The insect is resting and so there is no major so decreases water potential of the tracheal
reason for O2. cells.
There is very high-water potential here. The tracheole fluid then moves into the cells
and leave the tracheoles by osmosis.
There is a higher SA for efficient diffusion of
gases.
This means more gases can then move in.
Gas exchange in bony fish:
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