OCR GCE Biology - Exchange and Transport

Why do cells need to take in oxygen?
-Aerobic respiration



Name 2 waste products of cells


-Carbon dioxide


What does the ease of exchanging substances depend on?

-Surface area to volume ratio


Smaller animal have h***** SA:V ratio



How do you calculate SA:V ratio?
-Divide surface area by volume


What sort of SA:V ratio do large organisms have in comparison to small organisms?



What do large organisms need, due to their small SA:V ratio?

-Exchange organs


Give examples of substances that must be supplied to cells for respiration

-Oxygen, glucose


Why do waste products need to be removed from a cell?

-Stop it damaging itself


In single-celled organisms, substances can ******* directly into or out of the cell across the cell surface membrane



The diffusion rate is q**** for single-celled organisms



Why is the diffusion rate for single-celled organisms quick?
-Substances have to travel small distances only


In what sorts of organisms/animals is the diffusion rate slow? Why?

-Multicellular animals/organisms

-Some cells are deep within the body – there’s a big distance between them and the outside environment

-Larger animals have a low surface area to volume ratio – it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface

Give an example of a specialised exchange organ?

-Lungs etc.


Describe the route of air in the lungs?


-2-Air splits into two bronchi – one bronchus leading to each lung

-3-Bronchus branches off into smaller tubes called bronchioles

-4-Bronchioles end in small ‘air sacs’ called alveoli, where gases are exchanged

-5-Ribcage, intercostal muscles and diaphragm work together to move air in and out


Where does gas exchange happen?



What is an alveolus made of?

-Single layer of thin, flat cells called the alveolar epithelium


Describe the alveoli

-Arranged in bunches at the end of bronchioles

-Surrounded by a network of capillaries, giving each alveolus its own blood supply


Is it epithelial tissue common in the body? Where is it found?


-Exchange surfaces


What is the name of the tissue that makes the capillary?

-Capillary endothelium


Briefly describe deoxygenate blood being oxygenated at the capillary

-O2 diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into haemoglobin in the blood

-CO2 diffuses into the alveoli from the blood, crossing the capillary endothelium then the alveolar epithelium. After entering the alveolar space, it’s breathed out


Name 2 things most gas exchange surfaces have in common

-Large surface area, which increases the rate of diffusion

-Thin (often just 1 layer of epithelial cells) – provides a short diffusion pathway across the gas exchange surface, which increases the rate of diffusion


Outline how large surface area and thin wall are shown in the lungs

-Alveoli (large surface area)

-Thin wall (alveolar epithelium and capillary endothelium) one cell thick giving


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