Diffusion in Multicellular Organisms Flashcards

All 8 cards in this deck

What are the steps to calculate the surface area to volume ratio of a cube-shaped model organism?

e.g. a cube of side $2$ cm

1. Find the surface area: $6\times2\times2=24$ cm$^2$
2. Find the volume: $2\times2\times2=8$ cm$^3$
3. Divide surface area by volume and write as a ratio: $24:8=3:1$

What is the relationship between the size of an organism and its surface area to volume ratio?

As size increases, the surface area to volume ratio decreases.

Why can a single-celled organism rely on diffusion alone across its surface?

It has a relatively large surface area to volume ratio, so enough molecules can be transported in and out to meet its needs.

Why do multicellular organisms need exchange surfaces and a transport system?

They have a small surface area to volume ratio and long diffusion distances, so diffusion across the body surface is too slow to meet their needs.

List the four features that increase the effectiveness of an exchange surface.

Large surface area; thin membrane (short diffusion path); efficient blood supply (in animals); being ventilated (for gas exchange in animals).

How is the small intestine adapted for exchanging materials?

It is very long with villi and microvilli giving a large surface area, a thin wall and a good blood supply.

How are fish gills adapted for exchanging materials?

Many gill filaments covered in lamellae give a large surface area, with thin surfaces and a rich blood supply; water flows over them constantly.

How are plant roots and leaves adapted for exchanging materials?

Root hair cells give roots a large surface area for water and mineral ions; leaves are flat and thin with internal air spaces for gas exchange.