First 592 words of the document:
Revision for AS OCR Biology Topic 4 (Exchange Surfaces and Breathing)
Organisms exchange substances such as carbon dioxide, oxygen, nutrients and urea.
In singlecelled organisms, these substances can easily diffuse into and out of the cell. They have a small
surface area to volume ratio.
However, in multicellular organisms, some cells are deep inside the body there is a big distance between
them and the outside environment. Large organisms have a large surface area to volume ratio they have to
deliver substances to an organism with a large volume through a small surface area.
Features of an efficient gas exchange:
Large surface area More molecules can diffuse through the gas exchange surface if it has a larger
surface area. This increases the rate of diffusion.
Thin walls The gas exchange surface has thin walls to reduce the diffusion pathway. The molecules
that diffuse through the gas exchange have a short diffusion distance increasing the rate of diffusion.
Steep concentration gradient Organisms can maintain a steep concentration gradient. This helps
molecules to diffuse faster if there are less of them on the other side.
Features of the lung:
Lots of alveoli Large surface area Lots of alveoli increases the surface area from where oxygen
and carbon dioxide diffuse through. This increases the rate of diffusion.
Alveoli have moist and thin walls Thin permeable cell membrane Alveoli have a flat layer of
squamous cells which are only one cell thick. This creates a short diffusion pathway for Oxygen and
Carbon dioxide molecules to travel through.
Steep Concentration Gradient Good network of capillaries nearby Both the alveoli and capillaries
are only one cell thick. The capillaries take away oxygen into the body and bring back carbon dioxide
to maintain the steep concentration gradient.
Rings of cartilage: Present in the walls of the trachea and bronchi and give it support. It is strong but flexible.
It prevents the lungs from collapsing when the pressure of the lungs drop when we exhale.
Goblet Cells: Present in the trachea, bronchi, bronchioles. Secrete mucus which traps unwanted bacteria and
dust particles that are present when we breathe in.
Ciliated epithelium: Present in the trachea, bronchi and bronchioles. Waft the mucus away from the lungs
and towards the throat to be swallowed. This prevents lung infection.
Smooth muscle: Present in the trachea, bronchi and bronchioles. Control the diameter of it. Help to keep
them open when inspiration occurs. During exercise, the smooth muscle relax causing the lumen to open
wider, this reduces the resistance on airflow and more oxygen can enter the lungs.
Elastic fibres: Present in the trachea, bronchi, bronchioles and alveoli. Stretch when we breathe in and recoil
to help push the air out.
Intercostal muscles and Diaphragm contract.
The intercostal muscle raises the ribcage up and out and the diaphragm flattens out.
This increases the volume and decreases the pressure in the lungs.
This draws air in.
Intercostal muscles and diaphragm relax.
The intercostal muscles lowers the ribcage down and in and the diaphragm pushes up.
This decreases the volume and increases the pressure.
This forces air out.
The volume of air in each breath when you are at rest.
The maximum volume of air breathed in or out in any one breath.
Other pages in this set
Here's a taster:
A spirometer records the tidal volume, vital capacity, breathing rate and oxygen consumption of a person.
A spirometer consists of an oxygenfilled chamber with a moveable lid.
A person breathes through a tube which is connected to the oxygenfilled chamber.
As the person breathes in an out, the lid moves up an down.
These movements are recorded by a pen attached to the lid the pen writes on a rotating drum making
a spirometer trace.…read more