Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.
In this lesson, we'll be exploring the relationship between major systems and processes in plants. We'll look at the ascending cellular structure of plants from organelles to organism and how these relate to molecular functions.
What Are Plants?
Take a deep breath in. Now, release your breath. This calming activity not only slows down your nervous system but it also gives life to your body. All of our cells require oxygen to make energy and thus stay alive. But where do we get oxygen? We breathe in oxygen from the atmosphere, but the ultimate source of oxygen is from plants.
Plants are multicellular organisms that are non-motile, meaning they do not move. But the most defining characteristic of plants is their ability to make their own food from sunlight and carbon dioxide in a process called photosynthesis. Photosynthesis also produces oxygen, which humans, as well as plants, use to make energy. Today, we're going to look at the internal structure of plants, and how their cells are arranged into major organ systems to carry out important processes.
Cells are the basic units of life. But cells aren't just brick-like building blocks. They are dynamic, constantly moving and changing to adjust to their environment. Inside cells are tiny compartments called organelles that do specific jobs.
Plant cells have several unique organelles that work together to allow them to carry out their function. First, all plant cells have a thick cell wall, which surrounds their cell membrane. This helps to give plants their rigid structure, particularly in tissues like bark which need to be rigid and strong.
Vacuoles look like a large swimming pool inside a plant cell. Vacuoles are used to store water. When there is more water in the environment, such as when we water our house plants, water flows into plant cells and the plant stores it in the vacuole. This also increases plant turgidity and allows the plant to stand up straight.
Chloroplasts are the structures inside plant cells that contain chlorophyll, the chemical needed to conduct photosynthesis. Chloroplasts are found in green parts of the plant that participate in photosynthesis, such as the shoots and leaves.
Cells & Tissues
Organelles make up cells, the basic units of life. Although we typically might draw a plant cell as a generic green square, there are many types of cells inside plants. Parenchyma cells form the soft tissues of plants and the cells that do photosynthesis, as well as cells involved in plant cell structure. Collenchyma cells provide support for plants. They harden as they mature and are often part of vascular tissue or stems. Sclerenchyma cells are even more sturdy and often form parts of woody stems as they are dead at maturity.
Xylem cells also help with support of the plant, but they are also uniquely adapted to carry water for the plant. Phloem cells similarly transport sugar, nutrients and hormones around the plant, similarly to how our blood vessels transport oxygen and nutrients to our tissues.
Cells come together to form tissues in living things. There are three main types of tissues in plants: dermal, vascular tissue, and ground tissue. The epidermis in plants is similar to our dermis, or our skin. The epidermis in plants functions to protect the plant from drying out and from invaders like fungi and other pathogens. Cells in the epidermis are tightly packed together and usually are coated with a waxy substance to prevent water loss.
Vascular tissue serves the purpose of transporting water and nutrients around the plant. There are two main types of vascular tissue: xylem and phloem. Xylem transports water around the plant, and phloem transports products of photosynthesis, like sugar, nutrients, and hormones. Ground tissue is like the meat of the plant. All tissue that is not dermal or vascular is ground tissue. Cells that function in supporting the plant and performing photosynthesis are all part of the ground tissue.
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Different tissue types assemble to form organs. We might be more familiar with organs inside our own body, such as our heart or our lungs. Plants don't have a beating heart, nor do they breathe, but they do have their own important set of organs.
Leaves are factories for photosynthesis in the plant. They're packed with parenchyma cells that contain chloroplasts to absorb light and perform photosynthesis. Since leaves exchange gases, absorbing carbon dioxide and releasing oxygen, they are similar to our lungs. Stems are the structure of the plant. Stems allow plants to grow up and towards a light source in a process called phototropism. Growing towards light allows plants to make the most of photosynthesis, producing ample food for the rest of the plant. Roots are organs that extend into the soil for plants. They are specialized to absorb water and nutrients from the soil that plants need to perform their functions, including photosynthesis. These materials are transported from the roots to other organs in the plant through the xylem and phloem tissue.
There are two main organ systems in plants: the shoots and the roots. The shoots are any organs that exist above ground. This includes stems, leaves, fruits, and flowers, if the plant has any. This organ system is responsible for reproduction, growth, and performing photosynthesis. The root system includes parts of the plant that exist below ground. This system anchors the plant in the soil and allows it to absorb water and nutrients. The root system also includes tubers in some plants, structures that store food, such as potatoes and carrots.
The organ systems in a plant come together to make the entire organism. Although plants all have many features in common that we discussed here, there are also hundreds of thousands of unique plant species. Some plants grow low to the ground, specialized for windy, arid conditions, while others grow tall with enormous, sprawling leaves. Others have even evolved carnivorous habits. Regardless, however, all plants share the common structures and organizations explained here to carry out their major life processes.
Let's review. Plants are non-motile multicellular organisms that make their own food from sunlight using photosynthesis. Plant organelles include the cell wall, vacuole, and chloroplasts, the site of photosynthesis. Plant cells are varied, and some are used for photosynthesis, whereas others are used for structure and support or transport. Cells form tissues like the epidermis, or outer covering of the plant; the vascular tissue, which transports water and nutrients; and the ground tissue, which makes up the bulk of the plant. The tissues come together to form organs like leaves, stems, and roots. Organs form the two main organ systems in a plant: the roots and shoots. Organ systems come together to form an entire organism.
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