Form 5 · Paper 2 essay guide

Transport in Plants, Paper 2 essay guide

How Transport in Plants appears in Paper 2 essays: themes, a planning grid, a model answer structure and the keyword list.

Book a Trial Class

One-hour paid trial · Same-day reply

Essay themes this chapter supports

Compare the structure and function of xylem and phloem: Define the role of each tissue: xylem carries water and minerals upward; phloem carries dissolved food (translocation) in both directions. → Xylem structure: dead cells end to end, cross-walls broken down, hollow tube, lignified walls, pits - link each to water transport and support. → Phloem structure: living sieve tube elements, sieve plates, companion cells with mitochondria - link to active loading of sugar. → Summary contrast of living/dead, content, direction and energy requirement.
Explain how water travels from the soil to the leaves: Uptake at the root: root hairs increase surface area; water by osmosis; minerals by active transport. → Movement across the root cortex to the xylem down a water potential gradient. → Transpiration at the leaf: evaporation and diffusion through stomata create tension. → Cohesion-tension theory: continuous column held by cohesion and adhesion, pulled up; mention root pressure as a minor push.
Describe translocation and relate it to sources and sinks: Define translocation, source and sink, with examples of each. → Loading at the source: companion cells actively load sugar, lowering water potential. → Water enters by osmosis, raising pressure; mass flow to the sink; unloading and pressure fall. → Explain why the direction of flow can change with the season or stage of growth.
Discuss phytoremediation as a use of plant transport: Define phytoremediation and its advantage as a low-cost, low-disturbance method. → Phytoextraction: uptake, accumulation in shoots, harvesting. → Phytostabilisation: binding pollutants in soil to limit spread. → Role of hyperaccumulators and the need to match plant to pollutant.

How to structure your essay

Open with one or two sentences that define the topic and set the scope.
Devote one paragraph to each key concept, in a logical order.
Use precise biological terms and, where relevant, a labelled diagram.
Give an example or state where the process happens in the body or plant.
Close by linking the ideas back to the question.

Planning grid

Question	Answer
Introduction	Name the two transport tissues and state that structure suits function in each.
Point 1	Xylem: dead lignified vessels, hollow tube, pits - carry water and minerals up and give support.
Point 2	Phloem: living sieve tubes and companion cells - carry food both ways by translocation.
Point 3	Water pathway: root hair osmosis, minerals by active transport, transpiration pull up the xylem.
Point 4	Translocation: pressure-flow from source to sink, loading and unloading of sugar.
Conclusion	Link both tissues back to keeping the whole plant supplied with water and food.

Key terms to include

xylem
phloem
lignin
sieve tube
companion cell
transpiration
cohesion
adhesion
water potential
osmosis
active transport
translocation
source
sink
phytoremediation
hyperaccumulator
root hair
stomata

A model essay outline

Vascular tissues, Xylem is made of dead, hollow, lignified vessels; phloem is made of living sieve tubes and companion cells.
Transport of water and minerals, Water travels up the xylem in the transpiration stream, driven by evaporation from the leaves.
Transpiration, The loss of water vapour from the leaves through the stomata, which creates the pull that draws water up.
Factors affecting transpiration, Light, temperature, humidity and air movement change the rate of transpiration.
Translocation, The movement of sugars in the phloem from sources (leaves) to sinks (growing or storage tissues).

Frequently asked questions

What is the difference between xylem and phloem?

Xylem is made of dead, hollow, lignified vessels that carry water and dissolved mineral salts upward from the roots to the leaves. Phloem is made of living sieve tubes with companion cells that carry sugars made in photosynthesis from the leaves to other parts of the plant, in a process called translocation. Xylem carries water; phloem carries food.

How does water move up a tall plant?

Water is lost from the leaves as vapour through the stomata by transpiration. This creates a pull, or tension, at the top of the xylem. Because water molecules stick together (cohesion) and to the xylem walls (adhesion), this pull draws a continuous column of water up the xylem from the roots, the transpiration stream.

Which factors affect the rate of transpiration?

Higher light intensity opens the stomata and speeds transpiration; higher temperature increases evaporation; moving air (wind) removes water vapour and speeds it up; higher humidity slows it down because the surrounding air already holds a lot of water vapour, reducing the gradient.