The Need for a Transport System

This set covers (from the spec): (a)- The need for transport systems in multicellular plants. To include an appreciation of size, metabolic rate and surface area to volume ratio (SA:V). References: CGP OCR A book Oxford OCR A book

Why do multicellular plants need transport systems

Plants are multicellular and have:

• High Metabolic demands/ rate

• Large size

• Small SA:Volume ratio

Transport & metabolic demands

• plants have high metabolic rate which can’t be met by direct diffusion

• Many parts don’t photosynthesis which require a supply of oxygen and glucose and removal of waste products

Transport & size

• Plants need a transport system to move water, nutrients, and other essential substances over long distances due to their large size. This system ensures all parts of the plant receive what they need for growth and survival.

Transport & SA

• Plants overall have a low SA:V ratio as they are multicellular

• They can’t rely on diffusion to supply cells with the substances they need

• Leaves though, are adapted to have a large SA:V ratio

e.g. of nutrients/ substances that plants need

• Glucose and oxygen to the parts that don’t photosynthesis

• Hormones made in one part of the plant → site of action

• Water. Mineral ions absorbed by the root → transported to cells making proteins required for enzymes and structure of the cell

• They also need to remove waste products of metabolism

Why are substances not exchanged through direct diffusion?

It’s too slow to meet plant’s metabolic demands