By Angie Papple Johnston

The General Science subtest of the ASVAB contains a variety of questions, including about living organisms such as plants, their components, and what those components do.

Plants sustain themselves by pulling nutrients and water from the soil, capturing energy from the sun, and taking carbon dioxide from the air. The following table shows how plants use their organs to stay alive and well.

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This figure shows the basic anatomy of a plant.

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The anatomy of a plant.

A plant’s stem is technically part of its shoot system, but it has several big jobs. It moves water and nutrients between roots and leaves, holds the plant upright so it can grow taller (and access more sun so it can grow even taller), and redirects the plant’s growth.

Plants make their own food through photosynthesis, which takes place in the leaves. All they need are carbon dioxide, water, and sunlight. Photosynthesis occurs in two stages: light-dependent reactions and the Calvin cycle.

Light-dependent reactions happen when chlorophyll and other pigments absorb energy from sunlight. The energy splits water molecules into hydrogen and oxygen, and the oxygen evaporates into the atmosphere when temperatures heat up. The hydrogen that’s left behind combines with carbon dioxide the plant absorbs to form glucose—that’s what plants “eat.”

The Calvin cycle is a series of chemical reactions that take place during photosynthesis. These reactions can only happen after the plant has captured energy from sunlight.