Each part of a plant has a very important function.  All plants produce flowers for the same reason: to make seeds so another plant can grow.

 Leaves: These are the parts of the plant where food is made by  photosynthesis.  Leaves take in carbon dioxide from the air, water  

from the soil, and energy from the sunlight.  During photosynthesis, the leaves use light energy to change carbon dioxide and water into food. (sugar)

Flowers: These are the reproductive parts of a plant.  Flower petals and the flowers smell attract insects and bees to pollinate the flower.  After pollination, the petals fall off and seeds develop in the part of a flower called the ovary.  The ovary itself usually becomes what we call the fruit.

Stems:  These support the upper parts of plants.  Water and dissolved nutrients from the soil travel up the stem in a system of tubes.  Food from the leaves travel down stems to the roots.  Stems also store food for the plant.

Roots: These anchor plants in the soil.  Water and minerals are taken from the soil through the roots.  Many plants such as carrots, store food in their roots.

Seeds: these contain a tiny embryo of a plant inside.  The seed halves contain food which supplies energy and materials for growth until the plant grows its first leaves above the ground.