Structure of a Plant Cell: A Visual Guide
What Are the Organelles of a Plant Cell?
One of the first things I teach my students at A-level Biology (16-18yrs) is the structure of the cell. After going over the structure of the animal cell, we turn our attention to the plant cell. These cells contain many more 'parts' than an animal cell, and a classic exam question is to compare animal and plant cells.
All plants are eukaryotic - they have a nucleus and other membrane bound organelles. Plant cells contain almost all of the organelles found in animal cells but have several new ones to help them survive. Compared to drawings of cells from earlier in education, the diagrams below look very crowded!
To learn all this complexity use the same tricks as when learning the animal cell. Start by matching cut out keywords to different parts, then try naming parts from memory. Once you have mastered this try drawing your own diagrams. To show understanding of the functions, start off using one or two sentences and then try to use metaphors to describe the job of each organelle.
Diagram of a Plant Cell
Plant Cell Definitions
- Chlorophyll - a green pigment that captures the Sun's energy for photosynthesis
- Eukaryotic - a cell that contains a nucleus and other membrane-bound organelles (e.g. mitochondria)
- Osmotic Pressure - outward pressure exerted by water (think filling a water balloon)
Function of a Plant Cell
There are lots of different types of plant cell that must all work together to keep the plant alive. Unlike animals, however, plants are usually rooted to one place - they cannot move around if things get tough. This is why plants have all the extra 'bits' when compared to animal cells.
Remember, each plant cell will actually do everything that we do:
Always remember - plants are living things!
Parts of a Plant Cell
Eukaryotic Plant Organelles
Plants have almost all of the same parts as an animal cell, namely:
- Cell Membrane
- Nucleus (separated into nucleolus, nuclear membrane and nuclear pores)
- Endoplasmic Reticulum (rough and smooth)
- Golgi Body
- Lysosomes and Peroxisomes
All of these organelles perform the same tasks in plant cells as they do in animal cells. However, because animals do not make their own food, and have a skeleton to help them move, plant cells need a few extra organelles to help them survive
Photograph of a Chloroplast
Chloroplasts are probably the most important organelle on Earth. Not only do they help plants make food (and so put plants at the base of almost all food chains) but they also release most of the oxygen we breathe.
Chloroplasts are the engines for photosynthesis. They contain a green pigment called chlorophyll that uses sunlight to combine carbon dioxide and water into sugar. The oxygen from the water isn't needed to make this sugar and so the plant releases it through pores in the leaf called stomata.
Chloroplasts are easy to identify in electron micrographs. They are cylindrical in shape and appear to have stacks of coins inside them. Evidence suggests that, like mitochondria, chloroplasts were originally a type of ancient prokaryote was eaten by another, larger prokaryote. Instead of being digested, the smaller prokaryote survived and struck up a symbiotic relationship with its would-be killer. The rest is history.
A simple storage organelle, these are numerous in the cells of tubers like potatoes! They store glucose in the form of starch for when times are tougher.
Cell Wall Diagram
Without a skeleton, plants need a different strategy to allow themselves to reach for the sky: the cell wall.
The cell wall is made of cellulose - perhaps the most common natural polymer on Earth . There are many forms of cellulose, each with a different function. The cell wall is made of layers of different celluloses - along with other molecules (e.g peptidoglycans and pectins) - to increase the strength of the cell wall.
The main function of the cell wall is to allow turgor pressure to be built up. Turgor pressure is caused by the contents of the cell pressing firmly against the solid cell wall. Without this pressure, plants could not stand up. When plants lose water, there are less contents to push against the cell wall, turgor pressure drops, and the plant starts to wilt.
Vacuoles are large storage organelles. This is where the 'sap' of the plant is stored. There is a membrane that surrounds the vacuole called the tonoplast that controls what enters and leaves the vacuole.
It is important to keep many molecules in a cell out of the way in case they affect other vital chemical reactions of the cell. But this is not the vacuole's only job; the vacuole also contains lots of water that helps keep the plant cell turgid and upright. It acts like the air bladder in a football - as you add more air the football gets firmer; as you add more water to the vacuole, the cell gets firmer. When plants wilt, they have lost water from their vacuole. There is no longer enough pressure to keep the cell rigid.
These are easily identified as large white 'gaps' in the cell - often one of the largest organelles on view.
We already know that cells must co-operate and co-ordinate. To do this they must communicate! This is made difficult for plant cells thanks to the thick cell wall that surrounds every plant cell.
Think how difficult it is to text whilst wearing gloves...
An easy solution is fingerless gloves! They allow you to communicate more easily. Plasmodesmata are gaps in the cellulose cell wall that allow neighboring cells to talk to each other. This is called the 'Symplastic Pathway' and allows molecules like proteins, RNA and hormones to pass from cell to cell.
Plant Cell Model
A Giant magnetic poster! Great for learning about the plant and used in my Biology lessons. Comes with some basic background information and an activity guide. A useful plenary resource
Functions of Plant Organelles
Provides structural support to the plant cell
The Walls of a castle
Contains chlorophyll and is the site of photosynthesis
Starch Granule (amyloplast)
Stores excess sugar as starch
Storage for dissolved solutes. Also provides structural support
The bladder in a football
Gaps in the cell wall to allow cells to communicate with each other
Secret tunnels in a prison
Nutrient Deficiency in Plants
Plants and Plant Food
Plants are producers - they make their own food by combining carbon dioxide and water (and energy from the sun) to make glucose. We call this reaction 'Photosynthesis'. Photosynthesis happens entirely in the Chloroplast - a specialised organelle that gives plants their green colour.
So why do plants need Plant food? We already know that plants make their own food (by photosynthesis, which happens in the chloroplast), so why are we feeding them? Plant food contains lots of essential nutrients that the plants need to grow properly. If the plant doesn't have these, lots of problems can occur.
Plant food is basically vitamin tablets for plants.
- Nitrogen - the main ingredient of nucleic acids (e.g. DNA), amino acids and chlorophyll. Without enough Nitrogen the leaves turn yellow because of a lack of chlorophyll.
- Phosphorus - makes up the backbone of RNA and DNA; also used in production of ATP (energy molecule in eukaryotes). Without Phosphorus, the plant cannot grow well (cells can't make DNA so can't divide their cells so can't grow) and leaves will turn purple
- Potassium - used in proton pumps and vital for protein synthesis. Leaf veins and edges becomes yellowed because the cells become damaged.
Eukaryotic Plant Cell Resources
- Molecular Expressions Cell Biology: Plant Cell Structure
An in depth exploration of all aspects of Plant Cell Structure. A simply amazing resource. Highly Recommended
- Cell Models: An Interactive Animation
An interactive flash animation comparing animal and plant cell organelles.
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