What Do Roots Do?
Roots are the underground parts of most plants. They are hidden from view, but they perform some of the most important jobs in the plant's life. There are three main functions of roots:
- Anchorage — Roots hold the plant firmly in the soil so it is not blown over or washed away.
- Absorption — Roots absorb water and dissolved mineral salts from the soil.
- Storage — In some plants (e.g., carrots, turnips), roots store starch and sugars made by the leaves.
Types of Root Systems
Taproot system — One large central root (the taproot) grows straight down, with smaller lateral roots branching off it. This gives strong anchorage and can reach deep water. Examples: carrots, dandelions, oak trees.
Fibrous root system — Many thin roots of similar size spread out widely near the soil surface. This is efficient for absorbing surface moisture and helps prevent soil erosion. Examples: grasses, wheat, most cereals.
Carrots and parsnips are swollen taproots filled with stored food (starch and sugars). When you eat a carrot, you are eating the plant's energy store.
Root Hairs: Maximising Absorption
The ends of roots are covered in tiny root hair cells — thin, thread-like extensions of individual cells that project into the spaces between soil particles. Root hairs dramatically increase the surface area of the root in contact with the soil, allowing far more water and minerals to be absorbed.
Water enters root hair cells by osmosis — it moves from the soil (where there is relatively more water) into the root cell (where the cell sap is more concentrated). Minerals are absorbed by active transport, which requires energy.
The Root's Inner Structure
Inside a root, specialised tissues transport water upward:
- Xylem vessels — carry water and dissolved minerals from the root up to the stem and leaves.
- Phloem — carries dissolved sugars made in the leaves down to the root for storage or use.
- The root cap at the very tip protects the delicate growing cells as the root pushes through the soil.
Some plants, like orchids, have aerial roots that grow above the ground and can absorb moisture directly from the air. Mangrove trees have prop roots that grow sideways from the trunk to support the plant in waterlogged soil.
Roots and Soil Health
Roots do much more than feed the plant. They bind soil particles together, preventing erosion by wind and rain. When roots decay, they add organic matter to the soil, improving its fertility. Many plant roots also form partnerships with fungi (mycorrhizae), which help the plant access extra minerals in exchange for glucose.
Real world: Carrots and parsnips at the dinner table
A carrot is a swollen taproot filled with stored sugars and starch that the plant built up during its first year of growth. The orange colour comes from beta-carotene — a pigment the carrot plant stores in its root cells. Parsnips, radishes, and beetroot are also edible taproots. When you eat these vegetables, you are consuming the plant's underground energy reserve.
Real world: Grass preventing soil erosion
After heavy rain, you may notice that bare soil washes away but grassy areas remain intact. Grasses have dense fibrous root systems spreading widely through the top 10–20 cm of soil. Millions of fine roots and root hairs bind soil particles together, preventing them from being washed away by rain or blown away by wind. This is why grass is planted on motorway embankments and riverbanks.
Real world: Orchid aerial roots in the home
Phalaenopsis (moth orchids), sold in supermarkets and garden centres, often grow thick greenish roots that protrude out of the pot and even climb up the windowsill. These are aerial roots — they absorb moisture and some nutrients directly from the humid air and from rain splashing on them. The green colour comes from chlorophyll, allowing them to photosynthesise slightly.
Practice Problems
Explain how water enters a root hair cell.
Show answer
What is the advantage of a fibrous root system compared to a taproot system?