Plant Processes: Respiration, Photosynthesis, and Nutrition
Key Functions of Plant Parts
Leaves
Leaves exchange gases with the environment through the stomata. Both respiration gases and photosynthesis gases, including water vapor, are expelled through perspiration. The leaves perform photosynthesis. Leaf cells have many chloroplasts, which are the organelles where the transformation of inorganic into organic substances takes place.
Stem
The stem carries crude sap through the xylem tubes and the elaborated sap through the phloem. It also performs other functions related to nutrition and photosynthesis in green stems or the storage of reserves.
Root
The root absorbs water and mineral salts. If it is an aquatic plant, it takes water directly, and if it is terrestrial, it takes water trapped in soil pores. The root also performs functions of sap transport, both raw and processed, and storage of reserves, as in the root of the carrot or the beet.
Common Functions
Respiration
All plant cells, regardless of their location and time of day, need energy to live. This energy is provided by respiration. Organic substances contain energy. Organisms obtain energy from the combustion of some organic substances obtained with food or produced by photosynthesis. Oxygen is needed for combustion, which produces carbon dioxide and is only possible if there is oxygen in the mitochondria. In the air that surrounds all cells, a similar process occurs called cellular respiration, in which organic substances are burned.
In cellular respiration, organic matter degrades and becomes inorganic substances such as carbon dioxide and water. Oxygen is consumed, and the energy contained in organic substances is released. A part of this energy is released as heat. Respiration is a cellular process that needs oxygen and produces carbon dioxide. The energy released is used by a living being to grow, reproduce, maintain its temperature, or move.
Gas Exchange
During respiration, plants take in oxygen and expel carbon dioxide, but this is not the only exchange that occurs. With photosynthesis, plants incorporate carbon dioxide and expel oxygen. Gas exchange with the environment is contrary to what occurs during respiration.
During the day, the amount of carbon dioxide entering the plant for photosynthesis is so high that it exceeds the output of this gas from respiration. Something similar happens with oxygen. The amount of oxygen produced in photosynthesis is much greater than the oxygen consumed by respiration. To assess respiratory exchange, it is necessary to place the plant in the dark or use parts of the plant that do not perform photosynthesis, like seeds or roots. In conclusion, plants breathe both in light and darkness.
The Movement of Respiratory Gases
Oxygen in the air or oxygen dissolved in water can penetrate all parts of plants, but it does so fundamentally through the stomata of leaves. It runs inside the air spaces between cells and directly exchanges gases with them, yielding oxygen and taking carbon dioxide.
Food Processing
Animal food includes inorganic substances such as water and mineral salts and organic substances from other living beings. Plants only take inorganic substances from the environment. Organic matter is made in plants in their green organelles, mainly in the leaves, and only if they are exposed to light. The manufacture of organic matter, which is rich in carbon, is called photosynthesis, and the first substances that the plant produces are carbohydrates such as starch.
Inorganic Substances
The raw materials needed are carbon dioxide, water, and mineral salts. Photosynthetic organisms, such as leaves exposed to light, have cells equipped with abundant chloroplasts that contain a pigment called chlorophyll, which gives the green color to plants.