Surafce area-to-volume ratios and constraints on cell size

Why is cell size limited?

Because surface area to volume ratio must allow efficient exchange of materials.

What substances must enter and leave cells?

Oxygen, nutrients, water, energy, carbon dioxide, waste products, and heat.

What does the cytoplasm represent in SA:V terms?

The volume of the cell.

What does the cell membrane represent in SA:V terms?

The surface area of the cell.

How does increasing cell size affect surface area and volume?

Volume increases faster than surface area.

What happens to SA:V ratio as cell size increases?

It decreases.

Why is a low SA:V ratio problematic?

Exchange of materials and heat becomes inefficient.

How do cells overcome low SA:V ratio?

By dividing or forming multicellular organisms.

Why do small animals lose heat quickly?

They have a high SA:V ratio.

How do small animals compensate for heat loss?

By increasing metabolic rate.

Why must metabolic rate decrease as organism size increases?

Surface area cannot meet metabolic demands of large volume.

Give examples of structures that increase SA:V ratio.

Root hair cells, villi, microvilli, cactus spines, dividing yeast cells.

How do root hair cells increase SA:V ratio?

By extending long projections for absorption.

How do villi and microvilli increase SA:V ratio?

By folding the surface to maximise absorption.

How do cactus spines help SA:V ratio?

They increase surface area for heat exchange while reducing water loss.