Exchange Surfaces

Exchange Surfaces

Monday 8th February 2021

Exchange surfaces

Prokaryotic cells, such as bacteria, can rely solely on diffusion to get the nutrients that they need.

However, multicellular organisms (such as humans) cannot rely on diffusion. Humans require sophisticated exchange systems with adapted exchange surfaces in order to get all the nutrients that we need to survive.

Multiple Choice

What process does a cell have to go through in order to become specialised?

• specialisation

• adaptation

• differentiation

Surface Area to Volume Ratio

• A smaller organism (bacteria) have a small SA and a small volume.

• Their SA:vol ratio will be large.

• Larger organisms have larger SA but will have an even larger volume.

• Their SA:vol ratio will be small.

• SA / vol

Multiple Choice

If a cube has a surface area of 60 cm² and a volume of 20 cm³, what would the surface area to volume ratio be?

• 2:1

• 3:1

• 4:1

• 5:1

Multiple Choice

If a leaf has a surface area of 8 cm² and a volume of 6 cm³, what is its SA:vol ratio?

• 0.75:1

• 1:1.33

• 1.33:1

• 1:0.75

Open Ended

Why do large mammals, like humans, require specialised exchange systems?

Exchange surfaces

• Larger mammals cannot rely on diffusion as they have a small SA:vol ratio.

• Diffusion is not quick enough to occur due to how far substances would need to travel.

• They also do not have a large enough SA to accomodate for how much diffusion they would need to happen.

Multiple Choice

Why do bacteria not need a specialised exchange system?

• they have a large SA:vol ratio so can rely on diffusion alone

• they have a small SA:vol ratio so can rely on diffusion alone

• They aren't big enough to have a specialised system

youtube video

Features of a good exchange system

A large surface area - to maximise diffusion

A short diffusion pathway - to reduce the distance substances need to travel during diffusion.

A rich blood/vascular network that surrounds the system - maintaining a concentration gradient

Open Ended

Why is it important in an exchange system to maintain a concentration gradient?

Villi of the Small Intestines

The small intestine absorbs the majority of the nutrients from our meals.

There are around 30 villi per mm² of the SI (so there are lots and lots of villi!). This increases the surface area.

The epithelium (outer layer which surrounds the villi) is only one cell thick. This reduces the diffusion distance.

The villi has a rich blood supply which maintains a steep concentration gradient.

Lets have a go at some questions!

Remember if you don't know the answer - just guess! You might know more than you think you do :)

Multiple Select

Today, we have only looked at animal examples of exchange surfaces, but plants also have them! What two gases do plants need to carry out photosynthesis?

• oxygen

• carbon monoxide

• hydrogen

• carbon dioxide

Multiple Select

Which of these features makes the alveoli a good exchange system?

• There are many of them.

• They are only one cell thick

• They carry out an important process

• They are surrounded by a rich network of capillaries

• oxygen moves from the alveoli and into the blood

Open Ended

What is a feature of a good exchange system?

Open Ended

The small intestine contains villi which are specialised structures to help with absorbing nutrients. Explain how the villi is adapted as an exchange surface. HINT: you will need to explain each of your points/features.