Plant structure
Plants feed nearly every food web on land. Their bodies are built to capture light, take up water, and stay upright without a skeleton.
The plant body
A typical flowering plant has roots below ground and a shoot system above: stems, leaves, and flowers. Roots anchor the plant and absorb water and minerals; stems support leaves and transport materials; leaves carry out most photosynthesis.
Plant tissues
Dermal tissue forms the protective outer layer, coated in a waxy cuticle that reduces water loss. Ground tissue fills the interior and does photosynthesis and storage. Vascular tissue transports water and food. Meristems, regions of dividing cells at root and shoot tips, let plants grow throughout their lives.
Xylem and phloem
Xylem carries water and dissolved minerals up from the roots; its cells are dead and hollow when mature, forming pipes. Phloem carries sugars made in the leaves to wherever they are needed or stored, such as roots, fruits, and growing tips. Together they form vascular bundles, the veins you see in leaves.
Roots
Root hairs, tiny extensions of root surface cells, vastly increase the surface for absorbing water and minerals. Taproots, like carrots, plunge deep and store food; fibrous roots, like grasses, spread widely and hold soil. Many roots partner with fungi (mycorrhizae) that extend their reach in exchange for sugars.
Leaves
A leaf's flat shape captures light. Inside, palisade cells packed with chloroplasts do most photosynthesis, and spongy tissue with air spaces lets gases circulate. Pores called stomata, mainly on the underside, let carbon dioxide in and water vapour and oxygen out; guard cells open and close them.
Transpiration
Water evaporating from leaves through stomata is transpiration. It pulls a continuous column of water up the xylem, held together by water molecules' attraction to each other (cohesion) and to xylem walls (adhesion). A large tree can move hundreds of litres of water a day this way, with no pump.
Plant adaptations
Cacti store water in thick stems, have spines instead of leaves to cut water loss, and open stomata at night. Water lilies have stomata on the top of floating leaves. Conifers' needle-like leaves with thick wax resist cold and drought. Each adaptation balances gaining carbon dioxide against losing water.
Worked example
On a hot, dry, windy day, transpiration speeds up, and the plant risks wilting. Guard cells respond by closing the stomata to save water. The cost is that carbon dioxide intake falls, so photosynthesis slows. Plants constantly trade off these two needs.
Key takeaways
Plants have roots, stems, and leaves, built from dermal, ground, and vascular tissues, and grow from meristems. Xylem carries water up; phloem carries sugars around. Root hairs and fungal partners boost absorption. Stomata control gas exchange and water loss. Transpiration pulls water up by cohesion and adhesion.
Flashcard
Anchors and absorbs water and minerals
Check your understanding
Which tissue carries sugar from the leaves to the roots?