1 Review the introduction to Lab topic 15 Plant Diversity I

1. Review the introduction to Lab topic 15, Plant Diversity I, and describe the major trends in the evolution of land plants.

Exercise 21.1 – Factors Influencing Seed Germination

1. What is the function of the seed coat? From what does it develop?

2. What has happened to the endosperm that formed in the embryo sac of the developing ovule in Lab Topic 16, Plant Diversity II?

3. How have the cotyledons developed and from what? (Check your text; see, for example, Campbell and Reece, 2005, Chapter 38)

4. How does the structure of the seed facilitate the dispersal and survival of the plant?

Table 15.5 Fruit Types and Dispersal Mechanisms plantName Fruit Type Dispersal Method

Solution

1. The seed is a fertilized mature ovule which contains an embryonic plant with usually stored food material and a protective coat. After fertilization ovule changes into a seed. The zygote develops into embryo, primary endosperm nucleus forms into endosperm and the integuments develops into protective seed coat. It is made up of two layers the outer layer is thick, reddish-black testa and the inner softer layer is membranous and whitish called tegmen.

Seed coat protects the embryo in its dormancy stage and maintains a conducive environment for its proper growth. It weakens and break down during germination and provides exposure to the embryo to develop resistance against abiotic and biotic stress. It also aids in directing the nutrient supply during the growth and development of the embryo.

4. The seeds are the containers of miniature future plants therefore their dissemination, for their establishment over a wide geographical area is of utmost importance. Seeds have thus structured in a way that in favourable conditions they can germinate and can fully grow into a matured plant or tree.

Seeds dispersed by wind have adopted various characteristics for its survival in the wild e.g. seeds of orchids are light and minute in size to be easily carried away by wind. Fruits of coconut can float to a long distance because of large mesocarp. Some seeds are sticky (Loranthus) and they stick to the beaks of birds. Mechanical dispersion of seeds is well known in squirting cucumber (Ecballium elaterium) where due to the build-up of internal pressure the fruit along with the seed is ejected out.