Plant Tissues and Plant Structures

Rachel Hurst
Mar 31
4 min read

HSC Biology | Revision Notes

This topic matters because Module 2 asks students to investigate the structure of autotrophs, the function of structures in plants, and plant vascular systems as part of understanding how multicellular organisms exchange nutrients, gases and wastes.

In this lesson

the main functions of roots, stems and leaves
what xylem and phloem are
how plant tissues support transport
how plant structures relate to function

Why plant structures matter

Plants are multicellular organisms, so different parts of the plant have different jobs.

To survive, a plant must:

absorb water and mineral ions
support itself
carry out photosynthesis
transport substances around the plant
exchange gases with the environment

That is why plants have specialised structures and tissues.

Roots

Roots are the structures that usually grow below the ground.

Main functions of roots

anchor the plant in the soil
absorb water
absorb mineral ions
sometimes store food

How roots are adapted

Roots often have:

many branches, which increase surface area
root hairs, which further increase surface area for absorption
close contact with the soil

Why roots matter

Roots are essential because plants need a constant supply of water and mineral ions for growth, photosynthesis and transport.

Stems

Stems are the structures that support leaves, flowers and other plant parts above the ground.

Main functions of stems

support the plant
hold leaves up to the light
transport substances between roots and leaves
sometimes store food or water

How stems are adapted

Stems contain vascular tissues, especially:

xylem
phloem

These tissues allow transport through the plant.

Why stems matter

Without stems, leaves would not be held in a good position for light absorption, and water and food transport would be much less efficient.

Leaves

Leaves are the main organs for photosynthesis in most plants.

Main functions of leaves

absorb light
carry out photosynthesis
allow gas exchange
lose water by transpiration

How leaves are adapted

Leaves usually have:

a broad surface area to absorb light
thin structure to reduce diffusion distance
stomata for gas exchange
veins containing xylem and phloem

The syllabus specifically includes leaf structure as an example of plant gas exchange structures.

Why leaves matter

Leaves are where most glucose is produced, so they are central to the plant’s energy supply.

Xylem

Xylem is a plant vascular tissue that transports water and mineral ions.

What xylem carries

Xylem transports:

water
dissolved mineral ions

These substances move mainly from the roots upwards to the stems and leaves.

Features of xylem

Xylem cells are adapted for transport because they are:

long and tube-like
hollow at maturity
strengthened with thick walls

Why xylem matters

Xylem is essential because photosynthesis in the leaves depends on water, and the whole plant depends on mineral ions absorbed by the roots.

Phloem

Phloem is a plant vascular tissue that transports organic substances made by photosynthesis.

What phloem carries

Phloem transports:

sugars, especially sucrose
other dissolved organic substances

These products move from the leaves to other parts of the plant where they are needed or stored.

Features of phloem

Phloem is made of living cells adapted for transport of food substances through the plant.

Why phloem matters

Phloem allows the products of photosynthesis to be distributed from the leaves to the roots, stems, fruits and growing tissues. This links directly to the Module 2 focus on tracing the development and movement of the products of photosynthesis.

Xylem and phloem compared

Tissue	Main substance transported	Direction at this level	Main role
Xylem	Water and mineral ions	Mostly roots to leaves	Water transport and support
Phloem	Sugars and other organic substances	From leaves to other parts	Food transport

How the structures work together

Plant structures do not work on their own.

Example of coordination

roots absorb water and mineral ions
xylem carries them up through the stem
leaves use water in photosynthesis
phloem transports sugars made in the leaves to the rest of the plant

This shows how roots, stems, leaves, xylem and phloem form a coordinated transport system.

Plant tissues and transport

Module 2 also includes comparing transport systems in plants and animals, including plant vascular systems and the changes in transport media as they move around an organism. Plant tissues such as xylem and phloem are therefore central to the whole transport section of the module.

Worked example

Exam-style question

Explain how xylem and phloem have different functions in a plant.

Worked answer

Xylem transports water and mineral ions from the roots to the stems and leaves. Phloem transports sugars made during photosynthesis from the leaves to other parts of the plant. This means xylem mainly supplies raw materials, while phloem distributes food substances.

Why this works

This answer:

names both tissues
explains what each transports
clearly compares their functions

Common mistakes

Mixing up xylem and phloem.
Saying roots only anchor the plant and do not absorb substances.
Forgetting that leaves are the main site of photosynthesis.
Saying phloem transports water.
Describing stems only as support structures and not transport structures.

Quick quiz

What are the two main functions of roots?
Why are leaves important in plants?
What does xylem transport?
What does phloem transport?
How do stems help plant transport?