3.1- Plant Life Cycle and Growth

Overview

This lecture covers the life cycle of a plant from seed to fruit, focusing on growth stages, primary vs. secondary growth, and bud differentiation.

The plant life cycle follows the sequence: seed → seedling → young plant → mature plant → flower → fruit.
Seeds consist of a seed coat (protective outer layer), endosperm (nutrient storage), and embryo (future plant).
Examples of seeds: rice, wheat (durum for pasta, aestivum for bread), beans, and pecans.

Germination requires water, oxygen, and the right temperature.
The seed germinates into a seedling, starting with the emergence of the radicle (first root).
Sunlight becomes important after initial germination stages.

The apical meristem is a tissue at root and shoot tips responsible for cell division and elongation (primary growth).
Meristematic tissues continuously divide, enabling plant growth and development.
Primary growth increases plant height and root depth.
Secondary growth increases plant girth (diameter), common in woody species.

Primary growth occurs at the apical meristems; secondary growth occurs from the cambium.
Vascular cambium and cork cambium add new tissue, resulting in tree rings and bark formation.
Not all plants exhibit secondary growth; it is mostly found in woody plants.

The root cap protects the growing root tip and secretes mucilage to aid soil penetration.
The meristematic zone above the root cap is where active cell elongation occurs.
Lateral roots arise from the pericycle, not the epidermis, to stay connected with the vascular system.

Bud differentiation determines whether a bud becomes a leaf (vegetative) or a flower (reproductive).
Factors influencing bud differentiation include photoperiod, temperature, water, hormones, and pruning.
Temperate plants often require chilling to induce flowering; subtropical plants may be triggered by water changes.

Seed coat — the protective outer covering of a seed.
Endosperm — nutrient-rich tissue inside seeds that supports early growth.
Embryo — the part of a seed that develops into a new plant.
Apical meristem — tissue at shoot and root tips responsible for primary (lengthwise) growth.
Meristematic tissue — plant cells that actively divide, enabling growth.
Primary growth — increase in plant height and root length.
Secondary growth — increase in plant stem/root thickness.
Cambium — a meristematic tissue driving secondary growth in girth.
Root cap — a structure protecting the root tip as it grows.
Bud differentiation — process where buds develop into either leaves or flowers.