This chapter explains how plants make their own food, transport materials, and respire. Experiments show that plants need both sunlight and water to grow: a plant kept in sunlight with water grows best, one without water dies, and one in the dark with water grows poorly. Plants store food as starch, made in the leaves — the food factories of plants — which are broad, flat, and green because of the pigment chlorophyll. The iodine test (turning blue-black) detects starch and shows that starch forms only in green, sunlit parts of a leaf, confirming the need for chlorophyll and sunlight. A further experiment with caustic soda absorbing carbon dioxide shows that carbon dioxide from the air is also essential. The process by which plants make food using sunlight, chlorophyll, carbon dioxide, and water is photosynthesis, producing glucose (stored as starch) and releasing oxygen, summarised as Carbon dioxide + Water giving Glucose + Oxygen in the presence of sunlight and chlorophyll. Gases enter and leave the leaf through tiny pores called stomata. Plants transport water and dissolved minerals upward from the roots through tube-like structures called xylem (shown by red ink rising up a stem), while the food made in leaves is carried to all parts through phloem. Plants also respire: an experiment with germinating seeds turns lime water milky, proving they release carbon dioxide. During respiration, glucose is broken down using oxygen to release carbon dioxide, water, and energy (Glucose + Oxygen giving Carbon dioxide + Water + Energy), and all parts of a plant, green or non-green, carry out respiration to power their growth.
Requirements for plant growthPhotosynthesis and chlorophyllStomata and gas exchangeTransport through xylem and phloemRespiration in plants
Key terms
Photosynthesis
The process by which plants make food in the form of glucose using sunlight, chlorophyll, carbon dioxide, and water, releasing oxygen.
Chlorophyll
The green pigment in leaves that captures sunlight and is essential for the preparation of starch.
Stomata
Tiny pores on the surface of leaves that help in the exchange of gases during photosynthesis and respiration.
Xylem
The tube-like structures that transport water and dissolved minerals from the roots to other parts of the plant.
Phloem
The tube-like structures that transport food made in the leaves to all parts of the plant.
Respiration in plants
The process by which plants break down glucose using oxygen to release carbon dioxide, water, and energy.
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