MAVO Year 4 · Plants · Section 9.6

Germination, growth and development

Structure of a seed

A bean seed contains the start of a new plant. Its protective outer covering is the seed coat. Inside are two cotyledons, storing food such as starch and proteins. The embryo includes the young root and shoot. Other kinds of seed may have one cotyledon or store much of their food in a separate tissue called endosperm.

Germination

Germination begins under suitable conditions, usually requiring water, oxygen and an appropriate temperature. The seed takes up water and swells. The seed coat opens and the embryonic root emerges. Root hairs later help take up water and minerals. The shoot grows towards the light. In a bean, cotyledons may be carried above the ground, supplying reserves until leaves can produce sufficient food by photosynthesis. Reserves supply material and energy through respiration; they do not create energy from nothing.

Plant growth

Cell division involving mitosis produces new cells. The cells make additional cytoplasm and other components: cell growth. During cell elongation, water uptake into vacuoles helps cells enlarge while their walls expand. Root and shoot growing points, or meristems, are important regions of length growth. Some plants also increase in thickness, especially woody species.

Development

Development means changes in structure and functioning. As a plant develops, it forms new organs such as leaves and, later, flowers, fruits and seeds. Cellular respiration provides energy for these processes. The life cycle therefore links a seed to a mature reproducing plant and a new generation of seeds.

Surviving winter

Annuals complete their life cycle within one growing season and survive unfavourable periods mainly as seeds. Biennials typically grow and store reserves in their first season, then flower and produce seeds in the second. Some form a basal rosette, with leaves close to the ground.

Perennials live for several years. Herbaceous perennials may survive through underground organs such as bulbs, tubers or rhizomes and produce new shoots in spring. Woody perennials retain persistent stems and protect their growing buds.