notes for unit 2 on F211 OCR

I tutor in biology and I made these notes on exchange surfaces (lungs) and transport in humans (circulation) for my student. Covers everything will need to know in your exam.

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  • Created by: Rachel
  • Created on: 20-12-12 12:11
Preview of notes for unit 2 on F211 OCR

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Single celled organisms, such as Amoeba, have a high surface area to volume ratio. This means that
they don't need a specialized exchange surface because they're so thin that gases are able to
diffuse in and out of them because it is a relatively short distance to cross over.
However, this is not the case for multicellular organisms as the distances that diffusion would have to
take place over (the diffusion paths) are too great. They have a low surface area to volume ratio
(SA:vol), so they require a specialized exchange surface in order to get enough oxygen around the
body and to remove carbon dioxide from the body as the distance is too great for the gases to
diffuse in and out of the body. In mammals the specialized exchange surface is the lungs. This is
because as the size of an organism increases its volume will increase as a much faster rate (cubic)
than its surface area (squared).
Features of an Efficient Exchange Surface
Thin barrier - reduce diffusion path
Large Surface Area to provide more space for molecules to pass through (this is often
achieved by folding the walls and membranes of the surface for exchange).
A fresh supply of molecules on one side of the barrier to keep the concentration high
Removal of required molecules on the other side to keep the concentration low
These last three help to maintain a steep concentration gradient.
The aveloi have several features that provide an efficient exchange surface:
Alveoli produce a large surface area for the diffusion of O2 and CO2 into/out of the blood.
The squamous epithelium of the alveoli is very thin providing a short diffusion distance
The alveoli have capillaries running over their surface delivering CO2 to be removed and
allowing O2 to be carried away

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Page 2

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Gaseous exchange in the lungs
The lungs are a large pair of inflatable
structures lying in the chest cavity. Air can pass
into the lungs through the nose and along the
trachea, bronchi and bronchioles. Each part
of this airway has adapted to its function of
allowing the passage of air. Finally the air
reaches tiny, air-filled sacs called alveoli. The
walls of the alveoli are the surface where the
exchange of gases takes place.…read more

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A thin layer of moisture lines the alveoli. The moisture passes through the cell membranes from the
cytoplasm of the alveolus cells. As we breathe out, it evaporates and is lost. The lungs must produce
a product called a surfactant to reduce the cohesive forces between the water molecules. Without
the surfactant, the alveolus would collapse due to the cohesive forces between the water molecules
lining the air sac.…read more

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The lungs are in the chest cavity and are protected by the ribs which surround them. Each lung is
covered by pleural membranes which secrete a lubricating fluid, allowing the lungs to inflate and
deflate without rubbing against the walls of the ribcage. There are intercostal muscles in between
the ribs. The external intercostal muscles can contract to raise the ribcage, and the internal muscles
can contract to lower the ribcage.…read more

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The cartilage is in the form of incomplete rings or C-rings in the trachea, but is less regular in
the bronchi.
On the inside surface of the cartilage is a layer of glandular tissue, connective tissue, elastic
fibers, smooth muscle and blood vessels. This is often called the `loose tissue'.
The inner lining is an epithelial layer that has two types of cell. Most of the cells have cilia. This
is called ciliated epithelium. Among the ciliated cells are goblet cells.…read more

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The cartilage plays a structural role. It supports the trachea and bronchi, holding them open. This
prevents collapse when air pressure inside is low during inhalation. The cartilage does not form a
complete ring (c-ring) so that there is some flexibility. This allows you to move your neck without
constricting the airways. It also allows the oesophagus to expand during swallowing.
Smooth Muscle
The smooth muscle can contract. When the smooth muscle contracts, it will constrict the airway.…read more

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Inspiration (breathing in)
If the air is to enter the lungs, then the pressure inside them must be lower than the
atmospheric pressure.
The external intercostal muscles contract and the internal intercostal muscles relax,
raising the ribs upwards and outwards.
At the same time, the muscular diaphragm contracts and flattens.
Both of these actions increase the volume inside the thorax, causing the pressure inside
the thorax to decrease.
Since atmospheric pressure is greater, air rushes into the lungs as the lungs.…read more

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A spirometer consists of a chamber filled with oxygen that floats on a tank of water. A person
breathes from a disposable mouthpiece attached
to a tube connected to the chamber of oxygen.
Breathing in takes oxygen from the chamber,
which then sinks down. Breathing out pushes air
into the chamber, which then floats up.
The movements of the chamber are recorded
using a data logger so that a spirometer trace can
be produced (spirogram).…read more

Page 10

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Residual volume is the volume of air that always remains in the lungs, even after the biggest
exhalation possible. Usually around 1.5 dm3
Dead space is the air in the bronchioles, bronchi and trachea. There is no gas exchange between this
air and the blood.
Inspiratory reserve volume is how much more air can be breathed in over and above the normal
tidal volume when you take in a big breath. You call on this reserve while exercising.…read more



amazing, really useful! thanks


do you have these kind of notes for unit 2?


These are a superbly written set of notes with coloured annotated diagrams on the respiratory system and the circulatory system. Although written for the OCR specification they would be useful to any biology student needing to study these topics for their specification. Team these up with a set of flashcards and a quiz or two for a complete set of resources.

Ross Bonnel Loves Kids and You

"These are a superbly written set of notes with coloured annotated diagrams on the respiratory system and the circulatory system. Although written for the OCR specification they would be useful to any biology student needing to study these topics for their specification. Team these up with a set of flashcards and a quiz or two for a complete set of resources."

- Cunt, 2014

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