Life Sciences Grade 12: Biodiversity of Plants and Reproduction

Significance of Seeds

• All seed-bearing plants belong to the phylum Spermatophyta, including Gymnosperms (naked-seed bearing plants) and Angiosperms (flowering plants).
• Seeds are adapted for dispersal, leading to well-distributed species.
• Seeds store reserve food, enabling survival in harsh conditions.
• The testa (seed cover) protects the embryo against unfavorable conditions.
• Cotyledons provide food for developing seedlings.

Seed Structure

• The seed is surrounded by a seed coat or testa.
• The testa protects the seed's contents from drying out.
• The cotyledon stores food for the embryo.
• The embryo is found within the seed and consists of the radicle, plumule, and axis.

Advantages of Seeds for Plants

• Seeds possess a dispersal mechanism, like the parachute on pine seeds for wind dispersal.
• Dispersal mechanisms allow seeds to be widely distributed, reducing competition among plants.
• The testa prevents the embryo from drying out, and the cotyledons provide food.
• The testa and cotyledons protect the embryo in early development.
• The cotyledons supply energy for seedling growth until leaves develop and photosynthesis begins.

Seeds as a Source of Food

• Plants with edible seeds are a major food source, categorized into grains, legumes, and nuts.
• Grains (rice, wheat, maize): Important source of energy-rich carbohydrates (starch). The testa of whole grains provides fiber.
• Legumes: Important source of protein, low in fat, high in fiber, and easily cultivated, transported, and stored.
• Nuts: High in protein, fiber, antioxidants, and mono-unsaturated fatty acids.

Seed Banks

• Seed banks are facilities used to store seeds of various plants and crops to maintain biodiversity.
• Many countries have seed banks; notable ones include Kew’s Millennium Seed Bank Project (UK) and the International Seed Vault (Sweden).
• Seed banks maintain specific conditions: very cold temperatures ($-20^{\circ}C$$) and a dry environment.

Maintaining Biodiversity with Seed Banks

• Seed banks protect against the loss of species due to habitat destruction, climate change, and overuse of species.
• Uses for seed banks:
  • Re-establish endangered or extinct plants.
  • Rehabilitate damaged or destroyed plants.
  • Cultivate overexploited plants.
  • Cultivate new, hardier, disease-resistant hybrids.
  • Conserve endemic species.
  • Produce plant material for research.

Terminology

• Spermatophyta: Phylum of seed-bearing plants.
• Endemic: Species occurring only in a specific area.
• Mitochondrial DNA: DNA found in the mitochondria.
• Plastid DNA: DNA found in the chloroplast.
• Nuclear DNA: DNA found in the nucleus.
• Indigenous species: Species that occur naturally in an area.

Review Questions

• Question 1: The radicle grows into the first root.
• Question 2: The part of the seed that protects the embryo in its early stages are the testa and cotyledon.
• Question 3: The seedling obtains its food from the cotyledon until it is able to produce its own food.
• Question 4: The phylum that produces seed-bearing plants is called Spermatophyta.
• Question 5: The phylum that produces naked seeds is called Gymnosperm.
• Question 6: The phylum that bears seeds within fruit is Angiosperm.