Far apart, so transport

The idea

When roots and leaves are far apart, diffusion cannot supply raw materials to leaves and energy to roots, so plants need transport; being immobile with many dead cells, plants have low energy needs and use slow transport.

Roots and leaves

In a tall tree the roots are deep in the soil and the leaves are high in the air.

Could materials simply spread from the roots to the leaves by themselves?

• No, the distance is too large
• Yes, easily
• They do not need to

Near and far

Press Next step.

Distance decides

Diffusion works well over a short distance. When the soil-contacting roots and the chlorophyll-containing leaves are far apart, it cannot supply raw materials to the leaves and energy to the roots, so the plant needs a transport system. Plants do not move and have many dead cells, so their energy needs are low and the transport can be slow.

When roots and leaves are far apart, diffusion cannot supply raw materials to leaves and energy to roots, so plants need transport; being immobile with many dead cells, plants have low energy needs and use slow transport.

Notes

Roots and leaves far apart: diffusion cannot supply raw materials to leaves and energy to roots, so plants need transport; immobile, with dead cells, they have low energy needs and use slow transport.

Check yourself

When do plants need a transport system?

In a tall tree, diffusion alone cannot supply ...

Why can plants use relatively slow transport systems?

Over which plants can the distance that transport systems cover be very large?

• When the distance between them is very small. If the distances are small, energy and raw materials can easily diffuse to all parts of the plant.
• When roots and leaves are far apart — correct. Yes!
• When the plant is a single cell. A single cell needs no special organs, since its whole surface is in contact with the environment.
• sunlight to the roots. Sunlight is the energy source absorbed by chlorophyll; the problem is moving raw materials and energy.
• blood to the leaves. The problem is supplying raw materials to the leaves and energy to the roots.
• raw materials to the leaves and energy to the roots — correct. Yes!
• They do not move and have many dead cells, so their energy needs are low — correct. Yes!
• They need a great deal of energy. Plants have low energy needs, which is why slow transport is enough.
• They have a heart to pump the sap. The book gives low energy needs as the reason; it does not mention a heart in plants.
• Small herbs close to the ground. In small plants the distances are short and diffusion can do the job.
• Very tall trees — correct. Yes!
• Single-celled organisms. Single-celled organisms need no transport system, since the whole surface is in contact with the environment.