Mitosis vs. meiosis for GCSE Biology: cell division made easy

Cell division is an essential process that is required for reproduction, growth and development. Mitosis and meiosis are two types that are both similar and different. In my experience as a teacher, I often found that students got aspects of these two processes muddled with each other and questions on this topic were often poorly answered. In this article I am to dispel some of that confusion by explaining these two processes and comparing the differences between the two. 

Mitosis explained

Mitosis is a type of cell division that creates new cells for the purpose of growth, repair and replacement of old cells. The purpose is to create new cells (daughter cells) that are identical to the original cell (parent cell). 

Cells that undergo division must first duplicate their DNA and subcellular structures e.g. mitochondria and chloroplasts. This is done in a phase before mitosis called interphase. The cell spends most of the cell cycle in this phase. 

When the chromosomes replicate, the quantity of DNA increases from 2n to 4n. Each chromosome is made up of two identical strands of DNA coiled up and held together into an X shape. This will split during mitosis, with one copy of each chromosome going into each of the two new cells. 

The rest of the cell cycle, including the phases of mitosis, are as follows:

• Prophase: during this phase the DNA coils up tightly into the X-shaped chromosomes and the nucleus breaks down leaving the DNA floating in the cytoplasm

• Metaphase: the chromosomes line up along the middle (equator) of the cell

• Anaphase: the chromosomes are pulled to either side of the cell, with each half of the cell gaining a full set of chromosomes

• Telophase: two new nuclei form around the chromosomes on each side of the cell and the rest of the cell divides 

After the cell has finished dividing, each of the new cells each contains the diploid number of chromosomes (2n). In humans this number is 46 chromosomes, made up of 23 pairs. 

Meiosis explained

Meiosis is the type of cell division used in the creation of gametes (in humans this is the sperm and egg cells). Gametes are cells required in reproduction to pass on the genetic information to the offspring. An important feature of this type of division is that each of the daughter cells has half of the number of chromosomes than the parent cell, going from diploid (2n) to haploid (n). Also each of the four daughter cells are genetically unique from each other. 

These features are important for the process of reproduction because during fertilisation two gametes with half the number of chromosomes (n) combine to form a zygote (first cell of the new embryo) with the correct number of chromosomes (2n). Also it is important that the new cells are genetically different to each other in order to create variation between offspring. 

The process of meiosis can be broken down as follows:

• Meiosis 1: This is the first cell division. Firstly the quantity of DNA in the parent cell doubles from 2n to 4n. Then the nucleus breaks down and the chromosomes line up in pairs along the centre (equator) of the cell. Here the homologous chromosomes exchange equivalent sections of DNA with each other, mixing up the combination of alleles in the new chromosomes. This is an important process for creating genetic variation in the offspring. The pairs of chromosomes are pulled to each side of the cell and the first division completes. The cells produced from this division are 2n. 

• Meiosis 2: This second division has a very similar process to mitosis and splits the two cells produced from meiosis 1 into four daughter cells. Each of the two diploid (2n) cells divides and produces two (four total) haploid (n) daughter cells, with half the number of chromosomes compared to the original parent cells. These daughter cells are gametes. 

Make sure not to get either mitosis or meiosis confused with binary fission, which is how bacteria divide to carry out asexual reproduction. This is a different process due to the fact bacteria do not have a nucleus and have very different chromosome structure (circular) compared to eukaryotic cells. 

Key similarities and differences

The key similarities between these two types of cell division are:

• They are both required for reproduction (mitosis allows the embryo to grow after fertilisation has taken place)

• The both require DNA to be replicated before they can take place

• They both require replication and division of the other cell structures 

It is common to be asked to compare the differences between the two in exam questions. In this scenario try to remember the following facts: 

Tips to help your exam prep

Mitosis and meiosis are both very visual processes, so in order to revise these topics effectively I’d recommend using visual techniques, such as:

• Watching videos with animations showing the movement of the chromosomes and how the cell changes during the cell cycle (such as those found on the Save My Exams site - link to a mitosis video, and a meiosis video)

• Replicate the changes in the chromosomes yourself using props such as coloured modeling clay / playdough / pipe cleaners

  • You could even take pictures of this and build it into a stop motion animation of your own! 

• Draw labeled diagrams / make posters or mindmaps showing the process of mitosis and meiosis and highlighting their differences

Make sure to complete plenty of practise exam questions (such as those found on the Save My Exams site) and also practise comparing the two processes as much as possible because it is really easy to get the two confused! 

I hope this information about mitosis and meiosis helps you to ace your GCSE Biology exams! 

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