🗻 Big Picture: Every living thing is made up of cells. Plants and animals have pretty similar cells, save for a few key differences. Plants have three main structures that animals do not–a cell wall, a large central vacuole, and four specialized plastids called chloroplasts, chromoplasts, gerontoplasts, and leucoplasts.
🌱 What do we have in common with plants? It’s probably hard to say. But there are a few pretty cool things we share between us. For example, plants ‘sweat’ like we do through a process called transpiration. Even cooler is the fact that new studies show that plants can actually talk to one another through their root systems and fungal connections called mycorrhizal networks! Even with these similarities, it’s still likely a lot easier to list the ways that we’re different from one another. These differences go all the way down to the cellular level, where we still share some things in common, but there are a few pretty major differences. Let’s talk about them below.
There are two kinds of eukaryotic cells: plants and animals. Both of these types of cells share many similar features within them, like a nucleus, a nucleolus, cell membrane, mitochondria, rough ER, smooth ER, golgi apparatus (golgi bodies), lysosomes, peroxisomes, and the list goes on. Even so, plant cells contain some specialized structures that animal cells do not. Features unique to a plant cell include a cell wall, large central vacuole, chloroplasts, and specialized plastids–all of which we’re going to talk about today! Let’s get started.
Both plants and animals have a soft and flexible cell membrane called the plasma membrane that separates their interior from the environment and regulates the transport of molecules into and out of the cell. Unlike animal cells, however, plant cells also have a rigid structure attached to the exterior of their membrane called the Cell Wall.
The cell wall, composed of cellulose, proteins, and other polysaccharides, contains tiny pores that allow for the exchange of water, minerals, and nutrients between the cell and its environment. This structure’s primary function is to provide structure, support, and protection for the cell.
A vacuole is an organelle that stores and disposes of various substances, and both plants and animals have them. However, instead of the tiny vacuoles found in animal cells, plant cells have one large Central Vacuole filled with a fluid called Cell Sap.
The primary purpose of the central vacuole is to store water and maintain turgor pressure, the force exerted by stored water against the cell wall. Turgor pressure changes as water moves into or out of a plant cell via diffusion during osmosis. The more water inside the central vacuole, the more turgid the cell, and the happier the plant. There is such a thing as too much water too though, which is where the rigid structure of the cell wall comes in to keep the cell from bursting.
Plastids are a group of organelles found in every plant cell that are involved in the synthesis and storage of food. The most well known plant plastids are chloroplasts, which we’ll talk about first. Following that, we’ll go over some of the other specialized plastids found in a plant cell: chromoplasts, gerontoplasts, and leucoplasts.
Chloroplasts convert solar energy to chemical energy in a process called photosynthesis, during which plants convert solar energy, carbon dioxide, and water into glucose and oxygen. They contain an outer membrane, intermembrane space, inner membrane, stroma, and a thylakoid system, which is pretty similar to the structure of mitochondria. Both mitochondria and chloroplasts are thought to have evolved through the endosymbiosis theory, which is probably why they look so alike.
The Outer Membrane contains Porins that allow small molecules to pass freely through to the Intermembrane Space to reach the inner membrane.
The Inner Membrane is slightly more selective, with ions and metabolites only able to reach the stroma via specialized transport proteins.
The Stroma is an aqueous fluid that contains the chloroplast’s DNA, ribosomes, and thylakoid system.
The Thylakoid System itself has a third membrane which contains flattened disks stacked on top of each other called Thylakoids. Each stack is called a Granum. Chlorophyll has a green pigment and is stored in the thylakoids, which are the site at where photosynthesis begins.
Chromoplasts- are plastids that produce and store pigments other than chlorophyll. They develop from chloroplasts during things like the turning of leaves in the fall, and are generally found in fruits, flowers, and roots.
As chloroplasts deteriorate with age, they become Gerontoplasts. This generally occurs when plants stop photosynthesizing during the fall and the chloroplasts are no longer needed. Instead of letting them go to waste, gerontoplasts repurpose them by converting the chloroplasts into different organelles to be used within the cell (you heard the gerontoplasts, reuse reduce recycle! ♻️).
Leucoplasts are the non-pigmented plastids found in the non-photosynthetic parts of a plant, like the roots. They serve several purposes, including the synthesis of amino and fatty acids and storage for starch, lipids, and proteins.
The structures that set plant cells apart from animal cells are their cell wall, central vacuole, and specialized plastids.
The cell wall is attached to the exterior of the cell membrane and is composed of cellulose, proteins, and polysaccharides with pores that allow for water, mineral, and nutrient exchange. It’s primary purpose is to provide structure, support, and protection to the cell.
The central vacuole is an organelle that’s primary purpose is to store water and maintain turgor pressure –the force exerted by stored water against the cell wall.
Plastids are a group of organelles that are involved with the synthesis and storage of food. Plant cells have four main types: chloroplasts, chromoplasts, gerontoplasts, and leucoplasts.
Chloroplasts convert solar energy into chemical energy during photosynthesis. They are composed of an outer membrane, inner membrane, intermembrane space, stroma, and thylakoid system.
The thylakoid system contains flattened disks called thylakoids where chlorophyll is stored.
Chromoplasts produce and store pigments other than chlorophyll, and they tend to be found in fruits, flowers, roots, and leaves as they turn in the fall.
When chloroplasts begin to deteriorate, they transition into gerontoplasts, which recycle the chloroplast into different organelles to be used in the cell.
Leucoplasts are non-pigmented plastids that help synthesize amino and fatty acids and store starch, fat, and proteins.
1. What cell structures do plant cells have that animal cells do not?
A cell wall, a central vacuole, and specialized plastids.
2. What are the three types of plastids found within plant cells?
Chromoplasts, gerontoplasts, and leucoplasts.
3. What five structures compose a chloroplast?
An outer membrane, intermembrane space, inner membrane, stroma, and thylakoid system.
4. What is turgor pressure?
The force exerted on the cell wall by water stored in the central vacuole.
5. Where is chlorophyll located in a plant cell?
In the thylakoids of the thylakoid system in a chloroplast.
7. What is the purpose of the cell wall?
To provide structure, support, and protection for the cell, and to keep it from bursting when water fills the central vacuole and increases turgor pressure.
8. What happens when a chloroplast gets old?
It transitions into a gerontoplast which repurposes the organelle to be used elsewhere in the cell.
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