The stem is the highway of a plant. It holds up the leaves so they can catch sunlight, and inside it are tiny tubes. One set of tubes carries water and minerals up from the roots to every leaf, and another set carries the sugary food made in the leaves down to the roots and fruits. You can prove that stems carry water with a simple experiment using coloured water and a white flower or a celery stalk. Some stems also store food: potato is a swollen underground stem, and sugarcane stores sugar in its stem. Ginger and turmeric, used in both Indian and Thai kitchens, are underground stems too. The stem also bears buds, flowers and fruits.
A flower is the reproductive part of a plant, and its parts are arranged in rings. On the outside are the sepals, usually small and green, which protect the bud before it opens. Inside them are the petals, often brightly coloured and scented to attract insects, birds and bats. Inside the petals stand the stamens, the male parts. Each stamen has a thin stalk called the filament with an anther on top that makes powdery pollen. At the centre is the pistil, the female part, made of a sticky stigma at the top, a tube called the style and a swollen base called the ovary containing ovules. When pollen reaches the stigma, pollination has happened. The ovary grows into the fruit and the ovules become seeds. Hibiscus, which grows all over Thailand, is a perfect flower to study because its parts are large and easy to see. Mustard, rose, jasmine and datura are used in Indian classrooms.
Example: Take a hibiscus flower and carefully pull off the parts from the outside inward, laying each ring on a sheet of paper. Count the sepals and petals. Look at the long central column: the many small yellow knobs are anthers on the stamens, and the five red sticky tips at the very end are the stigmas. Use a hand lens to see pollen grains on the anthers, and slice open the base with adult help to find the ovary with tiny ovules. Expected result: five sepals, five petals, many stamens joined into a tube around the style, and a five-lobed stigma. Then place a white flower or celery stalk in water coloured with food dye. Expected result: after a few hours the petals or leaf veins turn the colour of the dye, showing that the stem carried the water up.