One function of a plant's seed is to (1) perform photosynthesis (2) provide food for early development (3) decompose dead organisms or (4) reproduce sexually?

(2) Provide food for early development 

Some functions of seeds include protecting the embryo, providing food, and allowing for easy dispersal. A tissue in seeds stores carbohydrates, fats, and proteins that provide food for a young plant, and this tissue can be found in the endosperm, perisperm, and/or cotyledons of the seed.

An egg, or a sack of flour

Glucose, also called grape sugar, blood sugar or corn sugar, is among the simplest and one of the primary naturally occurring sugars. produced naturally by plants as the primary photosynthesis product, it is heavily used by living beings as a main energy source and is necessary for cellular respiration. chemically, it is a monosaccharide carbohydrate and serves as a building block for complex sugars like starch.