Concise A-level OCR Biology Notes covering all the content required by the 2015 specification for Exchange & Transport (Module 3)

1. EXCHANGE
AND
TRANSPORT
BIOLOGY
NOTES
MODULE 3
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3. 3
INDEX
TOPIC 1: EXCHANGE SURFACES. . . . . . . . . . . . . . . . . . . . . 5
1. The Need for Specialised Exchange Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Efficient Exchange Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Components of the Mammalian Gaseous Exchange System. . . . . . . . . . . . . . . . . . 6
4. Ventilation in Mammals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. The Relationship Between Vital Capacity,
Tidal Volume, Breathing Rate & Oxygen Uptake. . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Ventilation and Gas Exchange in Bony Fish and Insects. . . . . . . . . . . . . . . . . . . . . 9
TOPIC 2: TRANSPORT IN ANIMALS. . . . . . . . . . . . . . . . . . 12
1. Transport Systems in Multicellular Animals. . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2. Types of Circulatory Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3. Arteries, Arterioles, Capillaries, Venules and Veins. . . . . . . . . . . . . . . . . . . . . . . 13
4. The Formation of Tissue Fluid from Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. The Structure of the Mammalian Heart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6. The Cardiac Cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7. The Use and Interpretation of Electrocardiograms (ECG) . . . . . . . . . . . . . . . . . . . 19
8. The Role of Haemoglobin in Transporting Oxygen and Carbon Dioxide. . . . . . . . . . 20
9. The Oxygen Dissociation Curve for Fetal and Adult Human Haemoglobin . . . . . . . . . 22
TOPIC 3: TRANSPORT IN PLANTS. . . . . . . . . . . . . . . . . . . 24
1. The Need for Transport Systems in Multicellular Plants. . . . . . . . . . . . . . . . . . . . 24
2. The Vascular System in the Roots,
Stems and Leaves of Herbaceous Dicotyledonous Plants . . . . . . . . . . . . . . . . . . 24
3. Transpiration and & Transpiration Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4. The Movement of Water & Plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5. Adaptations of Plants & The Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6. The Mechanism of Translocation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4. TOPIC 1
Exchange
Surfaces

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Exchange Surfaces
1 The Need for Specialised
Exchange Surfaces
Exchange surfaces are specialised areas that are adapted to make it easier for molecules to
cross from one surface to another. All lining cells need:
•• Oxygen
•• Glucose
•• Proteins
•• Fats
•• Water
•• Minerals
These may be absorbed through surfaces or made in cell cytoplasm, but it is essential that cells
take up these substances some way or another.
•• Single Celled Organisms
○○ Small, single celled organisms have a very large surface area to volume ratio
○○ They are able to exchange gases, nutrients and waste across surface
•• Multicellular Organism
○○ Small surface area to volume ratio
○○ Cells need more supplies
○○ Outer surface not large enough to enable gases and nutrients to enter body fast enough
to keep cells alive
○○ Gases must travel greater distance to reach cells at centre of organism
○○ Require specialised exchange surface
○○ Transport systems help to move nutrients to all parts of the bodyEXAM TIP
EXAM TIP
Surface area:volume ratio is an important concept throughout biology so be sure to
understand its implications. Mice have a small surface area:volume ratio, while elephants
have a large surface area:volume ratio. This means that, among other things, mice lose
heat more rapidly per unit volume than elephants.

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2 Efficient Exchange Surface
Large surface
•• Provides more space for molecules to pass through
•• Often achieved by folding walls of membranes
Thin barrier
•• Reduce diffusion distance
•• Often only one cell thick
Maintain steep diffusion gradient
•• Fresh supply of molecules on one side, keeping concentration high
•• Removal of required molecules on other side keeps concentration low
3 Components of the
Mammalian Gaseous Exchange System
Airways
•• Larger airways allow sufficient flow of air
•• Divide into smaller airways, delivering air to alveoli
•• Strong airways withstand low and high pressure
•• Flexible
•• Able to stretch and recoil
Lungs
•• Air passes through trachea, bronchi and bronchioles
•• Each specifically adapted
•• Air reaches alveoli
•• These are specialised for gas exchange
•• Protected by ribs
•• Movement of ribs and diaphragm help in ventilation
Trachea and Bronchi
•• Bronchi and trachea very similar
•• Bronchi narrower than trachea
•• Walls consist of cartilage
•• Cartilage form C-shaped rings
•• Layers of loose tissue on inside of cartilage
•• Inner lining is ciliated epithelium

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Bronchioles
•• Much narrower than bronchi
•• Smaller ones have no cartilage wall made from smooth muscle and elastic fibres
•• Smallest have clusters of alveoli at the ends
Components of an efficient gaseous exchange surface:
Cartilage
•• Structural role
•• Supports trachea and bronchi
•• Holds them open
•• Prevents collapse when air pressure is low
•• Allows for movement
Cilia
•• Move in a synchronised pattern waft mucus up airway to back
of throat
•• Mucus is then swallowed and bacteria killed in the acidic
stomach
Goblet cells
•• Lie under epithelium
•• Secrete mucus
•• Mucus traps tiny particle sin the air
•• Traps bacteria and pollen, reducing the risk of infection
Smooth Muscle
•• Able to contract
•• Contraction arrows lumen, restricting air flow
•• This is important if harmful substances are present
•• Contraction involuntary
Elastic Fibres
•• Contraction of airways deforms elastic fibres in tissue
•• As smooth muscle relaxes, elastic fibres recoil to original size
•• Help to dilate airway
4 Ventilation in Mammals
Ventilation in mammals is an intricately synchronised mechanism that relies on the movement
of air from an area of high pressure to an area of low pressure. During inhalation, the volume
of the lungs and thoracic cavity increases, decreasing the pressure of the air inside the lungs
and essentially creating a weak vacuum into which air moves in from outside the body. During
exhalation, the cavity constricts, the air inside the lungs is put under a higher pressure and
forced out.

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