OCR F211 Exchange Surfaces and Breathing

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Module 2: Exchange and Transport
1.2.1 Exchange Surfaces and Breathing
(a) Explain, in terms of surface area: volume ratio, why multicellular organisms need specialised exchange
surfaces and singlecelled organisms do not
Multicellular Organisms Singlecelled Organisms
Small surface area: volume ratio their outer surface Large surface area: volume ratio diffusion alone is
is not large enough to make sure all cells have met enough to meet their needs
their sufficient needs
Higher demand for supplies e.g. oxygen, water, Small demand for supplies e.g. oxygen, water,
minerals minerals
Greater diffusion distances less efficient Small diffusion distances more efficient
(b) Describe the features of an efficient exchange surface, with reference to diffusion of oxygen and carbon
dioxide across an alveolus
(c) Describe the features of the mammalian lung that adapt it to efficient gaseous exchange
Feature How Mammalian Lungs
Blood Supply Gives a diffusion gradient for efficient There are capillaries running over the
exchange surface of the alveoli to maintain a steep
concentration gradient
Large Surface A greater area for the substances to diffuse The lungs contain many alveoli increasing
Area the surface area for which oxygen and
carbon dioxide can diffuse across
Thin A shorter distance means a shorter diffusion Alveolar walls and capillary walls are only
time one cell thick
Moist Allows oxygen and carbon dioxide to diffuse Squamous epithelium cells secrete moisture
(d) Describe, with the aid of diagrams and photographs, the distribution of cartilage, ciliated epithelium, goblet
cells, smooth muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli of the mammalian
gaseous exchange system
Cartilage Regular Cshape rings in the trachea and less regular in the bronchi
Ciliated Epithelium and Make up the epithelial tissue in the trachea , bronchi and bronchioles. The
Goblet Cells goblet cells are found between the ciliated cells
Smooth Muscle Found in the trachea, bronchi and bronchioles
Elastic Fibres Found in the trachea, bronchi, bronchioles and alveoli
(e) Describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the mammalian
gaseous exchange
Cartilage Holds open tubes so that they won't collapse when air pressure is too low/ keeps airways
Cilia They're covered in many cilium which sweeps and moves the mucus away from the lungs
Goblet Cells Secrete mucus to stop the cells drying out and traps particles to stop them from damaging
the alveoli
Smooth Muscle Changes the diameter of the alveoli by contracting and constricting the airways

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Module 2: Exchange and Transport
Elastic Fibres Prevents the alveoli from bursting , returns them to their original size and shape and expels
air by recoiling and decreasing volume
(f) Outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function
of the rib cage, intercostal muscles and diaphragm
Inspiration Expiration
Intercostal muscles contract causing the ribcage to Intercostal muscles relax causing the ribcage to move
move upwards and outwards downwards and inwards
Diaphragm contracts pulling the diaphragm lower and Diaphragm…read more


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