Chapter 26

Plant Growth and Development

Section 1: How Plants Grow and Develop

Section 2: Regulating Growth and Development

Section 1

How Plants Grow and Develop

Objectives:•Compare seed germination in beans and corn.•Contrast annuals, biennials, and perennials.•Explain how primary and secondary growth are produced.•Describe several traits of bread wheat.•Contrast development in plants and animals.

Section 1

How Plants Grow and Develop

Seeds Sprout•Germination Germination is the resumption of growth by the embryo in a seed. Water and oxygen must penetrate the seed coat before germination can occur. •Plant Life Spans Annuals complete their life cycle in one growing season. Biennials complete their life cycle in two growing seasons. Perrenials live several years and may reproduce many times.

Section 1

How Plants Grow and Develop

Meristems•Primary Growth Apical meristems located at the tips of shoots and roots produce primary growth. The tissues that result from primary growth are known as primary tissues.•Secondary Growth Secondary growth increases a plant’s stem and root width. In woody stems, secondary growth is produced by the cork cambium and vascular cambium, two meristems near the outside of the stem.

Section 1

How Plants Grow and Develop

Plant Development•Patterns of Plant Development Plants develop throughout their lives. Plant development is reversible. Many mature plant cells can divide to form masses of undifferentiated cells, which can develop into a new plant.

Section 2

Regulating Growth and Development

Objectives:•Identify the major nutrients plants need to grow.•Describe how plant hormones control plant growth.•Relate environmental factors to plant growth.

Section 2

Regulating Growth and Development

Nutrients•Mineral Nutrients Plants need at least 14 mineral nutrients for growth. They also need carbon dioxide and water for and oxygen for cellular respiration.

Section 2

Regulating Growth and Development

Hormonal Control of Growth•Auxin Hormones such as auxin regulate plant growth and development. Auxin is a hormone that causes shoots to elongate and inhibits the growth of lateral buds.•Hormones in Agriculture Hormones such as ethylene, gibberellins, and cytokinins, are used in agriculture.

Section 2

Regulating Growth and Development

Environmental Influences on Growth•Tropisms Plants modify their growth in response to the direction of light, gravity, and touch. Such growth responses are called tropisms.•Photoperiodism In many plants, seasonal patterns of flowering and other aspects of growth and development are caused by changes in the length of days and nights, and this plant response is called photoperiodism.•Responses to Temperature Seeds and many mature plants survive periods of unfavorable environmental conditions by becoming dormant.