Let us organize the functions of the leaves, stems, and roots that we have studied as a series of connections within one whole plant.
Basic Knowledge
The division of labor among plant organs can be summarized as one process:
① Roots: Absorb water and inorganic nutrients from the soil. Root hairs increase the surface area.
② Stems: Transport water through the xylem and sugars through the phloem. Grow thicker through the cambium (in dicots).
③ Leaves: Produce starch (sugar) through photosynthesis. Exchange gases and transpire through stomata.
Working together, these functions enable plants to live as autotrophs (autotroph). Unlike animals, plants do not need to obtain food from outside; they can obtain energy by themselves as long as they have light, water, CO₂, and inorganic nutrients.
The “three major functions of plants” are photosynthesis, respiration, and transpiration. These are independent phenomena, but they are also related to one another.
Autotroph (autotroph)（An organism that can produce organic matter by itself. Plants and some bacteria）
Heterotroph (heterotroph)（An organism that obtains organic matter from other organisms. Animals and fungi）
Water cycle（The cycle in which water on Earth repeatedly evaporates, falls as precipitation, and flows away）
Carbon cycle（The cycle of CO₂ and organic matter through photosynthesis and respiration）
Food chain (food chain)（The feeding relationship of producers → consumers → decomposers）
Producers, consumers, and decomposers（Those that carry out photosynthesis, those that eat, and those that decompose）
Further Study (Background and Significance)
Plants are producers (producer) in ecosystems. Through photosynthesis, they convert atmospheric CO₂ into organic matter, which nourishes animals and fungi. They are the starting point of food chains and the foundation of Earth’s biosphere.
Carbon (CO₂) taken in by plants from the atmosphere becomes organic matter in the leaves and forms the bodies of the plants themselves and the animals that eat them. When animals respire or die and decompose, the carbon returns to the atmosphere as CO₂. This is the carbon cycle.
Similarly, water absorbed by roots returns to the atmosphere through transpiration, forming the water cycle in which clouds form and rain falls on the land. Forests transpire very large amounts of water, affecting rainfall in inland areas.
In recent years, human consumption of fossil fuels has caused atmospheric CO₂ concentrations to rise rapidly, contributing to global warming. Afforestation and forest conservation are important measures against climate change because they fix carbon as organic matter. Understanding plant functions also provides a foundation for considering the global environment.
- Leaves = photosynthesis, gas exchange, and transpiration
- Stems = transport and support for water and nutrients
- Roots = absorption and anchoring
- Plants = autotrophs (producers)
- Three major plant functions: photosynthesis, respiration, and transpiration
- Plants support the carbon cycle and water cycle
- Forests fix CO₂ and stabilize the climate
Points to Note (Easily Confused)
① Distinguish between autotrophs (plants and photosynthetic bacteria) and heterotrophs (animals and fungi). ② Plants always respire, not only at night. During the day, they also carry out photosynthesis, so they absorb CO₂ overall. ③ Decomposers include mushrooms, molds, and bacteria. They are mainly fungi and bacteria, not plants. ④ Transpiration is closely related to stomata; without stomata, almost no transpiration would occur.
Practice
- Name all three major functions of plants.
- Choose the role of plants in an ecosystem from “producer,” “consumer,” and “decomposer.”
- Briefly explain why forests help combat global warming.