Plant Cell Structures and Functions
Tilia stem cross-section (claudio9divizia, iStockphoto)
Tilia stem cross-section (claudio9divizia, iStockphoto)
Learn about the many different structures that make up plant cells as well as what differentiates plant cells from animal cells.
People have known about cells for about 350 years. The cell was first discovered in 1665 by an English scientist named Robert Hooke. While looking through a microscope, he observed tiny box-like objects in a slice of cork. Cork is the bark from an oak tree. He named these little boxes cells. Cells are the basic units of life and they make up all living things. This idea forms the basis of the Cell Theory.
Cell Theory
The three main parts of the cell theory are:
- All living things are made of cells.
- The cell is the basic unit of structure and function in all living things.
- Cells only come from other pre-existing cells by cell division.
Image - Text Version
Shown is a colour photograph of a thinly sliced plant stem, through a microscope.
The stem is sliced to show all the cells inside its thickness. The result is a large, intricately patterned circle that stretches across a white background. The border of the circle is made up of neatly stacked rings of small green and clear ovals. Small nubs extend out from the left and right sides of this, where the cells are darker green and brown.
The largest cells are in the centre of the image. They are round and clear or pale blue. They become smaller and green or teal as they move out from the centre. At one point, the cells are arranged into rays that radiate outwards. These are small and green at first, then, then larger and red. Then the rays form a pattern of teal interspersed with dark green stripes.
In the bottom left corner is a short red line a bit longer than the border of the stem. It indicates scale and is labelled 200 micrometres.
Some organisms are made up of only a single cell. Others are made up of many cells. Organisms made of many cells are called multicellular. Cells do not all look the same. They come in many shapes and sizes. They also have different functions.
Prokaryotes are organisms which are made up of small and simple cells. Eukaryotes are organisms which are made up of large and complex cells. Animals and plants are eukaryotes. Bacteria are prokaryotes.
Plant Cell Structure and Function
Even though cells differ in size and complexity, they contain many of the same substances and they carry out similar life functions. These include growth, metabolism and reproduction.
Cells are made up of different structures that are responsible for specific functions. These structures are known as organelles. A number of these organelles are found in both animal and plant cells. This section will focus on the organelles found in plants.
Cell Structures (Cell Organelles)
Image - Text Version
Shown is a colour illustration of the structures inside a plant cell.
Each structure is labelled with a white number in a blue circle. The cell and all its parts are sliced in half, so the top is removed and the inside is visible.
The cell is surrounded by a layer of green material shaped like a shallow, five-sided bowl. The outside is dotted with small brown circles. This is labelled with the number one. A thinner, brown layer lines the green one. This is labelled two.
Most of the cell is filled with a pale yellow substance with thin blue lines and tiny dots. This surrounds all the internal structures. This is labelled three. One of the dots is labelled six.
The largest structure in the cell is a sphere on the left side. A quarter of it has been cut away to show the layers inside. The outside is purple with darker dots. This is labelled four. The centre is a small, dark blue sphere. The rest is a thick, pale blue layer. This is labelled five.
The sphere is surrounded by flattened beige bubbles that curve around, following the shape of the sphere. These are labelled seven. The outside layer of one of these structures is labelled eight.
In the bottom right corner of the cell is a blue structure that looks like a pile of long, soft, curved sacks. This is labelled nine.
In the bottom left corner is a small, red, oval structure. It is sliced in half so the inside is visible. The wall of the structure is pink with thin fingers that reach out into the centre from each side. like the teeth in a zipper. This is labelled ten.
In the centre of the cell, near the top, is half a hollow purple sphere. This is labelled eleven.
The top right side of the cell is taken up by a pale blue, teardrop-shaped structure, filled with a darker blue substance. This is labelled twelve.
Two small green, oval shapes float in between the larger structures. These are filled with towers of small green circles that look like stacks of coins. One of these is labelled thirteen.
What Makes Plant Cells Unique
- Plant cells have a cell wall.
Plant cells are different from animal cells in a number of ways. Perhaps the most obvious one is that plant cells have a cell wall. The cell wall provides strength and support to the plant, much like the of an insect or spider. Our skeletons are inside our bodies, rather than on the outside like insects or spiders.
The plant cell wall is mainly made up of the molecules cellulose and lignin. People use cellulose a lot for making paper. Cellulose can also be converted into cellulosic ethanol, which is a type of .
Image - Text Version
Shown is a close-up colour photograph of a cow's face, with grass in its mouth.
The cow is looking straight ahead, into the camera. It has dark brown eyes and nose. Its fur is soft and brown, fading to beige. The fur on its snout and ears is almost white. There is a yellow plastic tag in its right ear, and a handful of green grass sticking out of its mouth.
Humans cannot digest cellulose. It just passes through our bodies. Cellulose is better known as dietary fiber. Even though we cannot digest it, cellulose is important because it keeps waste moving through the digestive system as it should!
Lignin fills in the spaces between cellulose and other molecules in the cell wall. Lignin also helps water molecules move from one side of the cell wall to the other. This is a very important function in plants.
- Plant cells contain vacuoles.
Most adult plant cells have one large vacuole that takes up more than 30% of the cell's volume. At certain times and conditions the vacuole takes up as much as 80% of the cell’s volume! In addition to storing wastes and water, the vacuole also helps to support the cell. This is because the liquid inside the vacuole exerts an outward on the cell, much like the water inside a water balloon. It helps keep cells from collapsing inward. We call this pressure turgor pressure.
- Plant cells contain chloroplasts.
Unlike animal cells, plant cells can harness the energy of the Sun, store it in the chemical bonds of sugar and use it later. The organelle which is responsible for this is the chloroplast. Chloroplasts contain chlorophyll, the green that gives leaves their colour and absorbs light energy. , a type of prokaryote capable of photosynthesis, are considered to be the ancestors of chloroplasts!
Did you know?
Red algae (multicellular marine algae) have chloroplasts that contain the pigment phycobilin rather than chlorophyll. This gives them a reddish, rather than green, colour.
Image - Text Version
Shown is a colour photograph of transparent hexagonal bubbles filled with green circles.
The bubbles are fitted together, edge to edge, like tiles. The walls and sides are transparent. Each one is filled with a pile of translucent green circles. They are layered so that some appear dark green, and some are bright. The background is a bright, sky blue.
Plant and animal cells also have many common organelles, including the nucleus, cell membrane (called the plasma membrane in animals), endoplasmic reticulum, mitochondria and cytoplasm, as well as several others.
Learn More
Virtual Plant Cell
This interactive 360° video by Plant Energy Biology explores the internal world of the plant cell.
Cell Anatomy Game
Identify organelles in plant and animal cells in this game from Ask a Biologist.
References
Baily, R. (2020, January 24). Cell theory: A core principle of biology. ThoughtCo.
Baily, R. (2019, May 8). All about photosynthetic organisms. ThoughtCo.
BiologyWise. (n.d.). Plant cell structure and function.
Davidson, M. W. (n.d.). Plant cell structure. Florida State University.