Cells
The building blocks of life! This is the fundamental starting point of all of Biology. A good understanding of cells and the processes that go on within them will enable you to answer many of the questions that come up in your GCSEs. You will often see a small sub-section of an exam question that tests your knowledge of this topic so it's worthwhile making sure you are comfortable with the similarities and differences between plant and animal cells, the jobs of all of the parts of the cell, and how specialised cells are adapted for their job.
Animal cells
There are 5 basic parts of the animal cell that you need to know about. See the diagram below for a labelled cell, and in the key word section and description of what each part is responsible for. |
Plant cells
Plant cells are usually much more regularly shaped than animal cells. In addition to the 5 parts of an animal cells, plant cells contain 3 (sometimes 2 if you are a root cell) additional structures. What are they? |
Key words
Organelle - specialised structure within a cell (eg, mitochondrion, nucleus, ribosome) Nucleus - the control centre of the cell, where the DNA is stored Mitochondria - the site of aerobic respiration Ribosomes - where protein production takes place Cell membrane - controls what goes into and out of the cell Cytoplasm - the liquid gel in which most chemical reactions take place Cell wall (plants only) - made of cellulose and gives plant strength Sap vacuole (plants only) - filled with cell sap. Keeps the cell rigid Chloroplasts (green plant cells only - not roots) - site of photosynthesis. Harvests light energy as they contain chlorophyll |
Remember: Plant root cells DO NOT contain chlorophyll or chloroplasts. This is because they are found underground and so do not have the ability to harvest light. Photosynthesis does not occur in these cells This is an amazing resource to find out more about cells
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Bacteria and yeast cells
These are special types of cells that you need to know about. They are both microorganisms and can be useful or pathogenic (cause disease). Make sure you can label each of these. The most striking thing that you will notice about bacteria is that they don't contain a nucleus! Instead they have their circular genetic material floating free in the cytoplasm. Bacteria also do not contain other organelles such as mitochondria and ribosomes
These are special types of cells that you need to know about. They are both microorganisms and can be useful or pathogenic (cause disease). Make sure you can label each of these. The most striking thing that you will notice about bacteria is that they don't contain a nucleus! Instead they have their circular genetic material floating free in the cytoplasm. Bacteria also do not contain other organelles such as mitochondria and ribosomes
Yeast are really useful to us. When given lots of oxygen, yeast undergo aerobic respiration, resulting in the production of carbon dioxide and water. This is why we use yeast to make bread - the carbon dioxide makes the bread rise. When yeast undergo anaerobic respiration in the absence of oxygen, they produce ethanol (alcohol) as a waste product. This is fermentation, and is useful to us in the process of brewing.
For more about respiration, see here
For more about respiration, see here
Specialised cells
Above I have given you examples of general animal and plant cells showing the features that they share and that are unique to plant cells. However, not all plant and animal cells look like this. Many cells are specialised to do a particular job. Here are some examples of specialised cells:
Sperm cells - tail for swimming; midpiece full of mitochondria for energy; nucleus with genetic material to fertilise egg; acrosome with enzymes to digest into the egg
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Root hair cells - these are found in the roots of the plant (not in your hair!). They do NOT have chloroplasts but do have a very large extension like a long nose. This gives the hair a large surface area, to maximise the uptake of water
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Organisation
Cells - these are the building blocks of life. During development, cells differentiate (specialise) to take on specific functions. You have muscle cells, nerve cells, epithelial cells (these cover your organs and the outside of your body), and secretory cells (those that secrete enzymes and hormones), amongst others
Tissues - this is a group of cells with similar structure and function. For example, muscle cells come together to form muscle, nerve cells come together to form nerves, etc
Organs - are made up of different tissues which all work together. For example, in the diagram above, different types of tissue come together to form a functioning kidney
Organ system - lots of different organs working together to form an organ system. The urinary system is made of the kidneys, bladder, urethra and ureter
The functioning body is made up of all of the different organ systems, tissues and cells working together
Tissues - this is a group of cells with similar structure and function. For example, muscle cells come together to form muscle, nerve cells come together to form nerves, etc
Organs - are made up of different tissues which all work together. For example, in the diagram above, different types of tissue come together to form a functioning kidney
Organ system - lots of different organs working together to form an organ system. The urinary system is made of the kidneys, bladder, urethra and ureter
The functioning body is made up of all of the different organ systems, tissues and cells working together
In the plant
Plants also have specialised cells (see above), tissues and organs.
Plant tissues include: epidermal tissue (covers surfaces), mesophyll tissue (contains chloroplasts), xylem (carries water and dissolved minerals) and phloem (carries dissolved food from leaf to rest of the plant).
Plant organs include the leaves, stems, roots and flowers - each does a specific job exactly as the organs within an animal do.
Plants also have specialised cells (see above), tissues and organs.
Plant tissues include: epidermal tissue (covers surfaces), mesophyll tissue (contains chloroplasts), xylem (carries water and dissolved minerals) and phloem (carries dissolved food from leaf to rest of the plant).
Plant organs include the leaves, stems, roots and flowers - each does a specific job exactly as the organs within an animal do.