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2. Structure & Function in Living Organisms / 2.7 Gas Exchange /
2.7.1 Diffusion in Gas Exchange
2.7.1 Diffusion in Gas
Exchange
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Diffusion in Gas Exchange
Diffusion is the movement of molecules
from a region of its higher concentration to
a region of its lower concentration
Molecules move down a concentration
gradient, as a result of their random
movement
Diffusion across the cell membrane
Diffusion is the process by which gas
exchange occurs
Single celled organisms, such as amoeba,
can exchange gases sufficiently by simple
diffusion through the cell membrane
Gas exchange in single-celled organisms (such
as amoeba) occurs through diffusion
Multicellular organisms (such as plants and
animals), however, have exchange surfaces
and organ systems that maximise the
exchange of materials
Gills are the gas exchange organs in
fish, lungs in humans and leaves or
roots in plants
These organs increase the efficiency of
exchange in a number of ways:
Having a large surface area to
increase the rate of transport
A short diffusion distance for
substances to move across. This short
distance is created because the
barrier that separates two regions is
as thin as possible
In addition, animals have:
Gas exchange surfaces that are well
ventilated to maintain steep
concentration gradients
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NEXT TOPIC
1. THE NATURE & VARIETY OF LIVING
ORGANISMS
2. STRUCTURE & FUNCTION IN
LIVING ORGANISMS
2.1 Levels of Organisation
2.2 Cell Structure
2.3 Biological Molecules
2.4 Movement of Substances into & out
of Cells
2.5 Nutrition
2.6 Respiration
2.7 Gas Exchange
2.7.1 Diffusion in Gas Exchange
2.7.2 Leaf Structure
2.7.3 Plants: Gas Exchange in
Photosynthesis & Respiration
2.7.4 Practical: The Effect of Light on
Gas Exchange in Plants
2.7.5 Human Gas Exchange System
2.7.6 Smoking & the Human Gas
Exchange System
2.7.7 Practical: The Effect of Exercise on
Breathing
2.8 Transport Systems
2.9 Excretion
2.10 Co-ordination & Response
3. REPRODUCTION & INHERITANCE
4. ECOLOGY & THE ENVIRONMENT
5. USE OF BIOLOGICAL RESOURCES
Author:
Lára
Lára graduated from Oxford University in
Biological Sciences and has now been a science
tutor working in the UK for several years. Lára
has a particular interest in the area of infectious
disease and epidemiology, and enjoys creating
original educational materials that develop
confidence and facilitate learning.
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