Cell Division and Chromosomes

This page introduces the fundamental concepts of cell division and chromosomes in GCSE Biology Unit 2 WJEC. Chromosomes are defined as linear DNA molecules tightly coiled around proteins, carrying genetic information in the form of genes. They are found in pairs, with one chromosome from each parent.

Vocabulary: Chromosomes are linear DNA molecules tightly coiled around proteins, carrying genetic information in genes.

Human body cells contain 23 pairs of chromosomes, totaling 46. These pairs are not identical, as they contain different alleles, which are versions of a gene. The concept of sex chromosomes is also introduced, explaining that males have an X and Y chromosome, while females have two X chromosomes.

Definition: Alleles are different versions of the same gene.

The page then delves into two types of cell division: meiosis and mitosis. Meiosis is described as a reduction division that creates four genetically different daughter cells called gametes. This process involves two divisions and produces cells with half the number of chromosomes.

Highlight: Meiosis is crucial for creating genetic variation and ensuring the resultant zygote has a full set of chromosomes.

Mitosis, on the other hand, is defined as the division of a cell to produce two genetically identical daughter cells with a full set of chromosomes.

Example: Mitosis is important for an organism's growth, replacement of old cells, and repair of damaged tissues.

Comparing Mitosis and Meiosis

This page provides a detailed comparison between mitosis and meiosis, two fundamental processes in cell division GCSE WJEC unit 2b. The information is presented in a clear, comparative format to highlight the key differences between these two types of cell division.

Mitosis produces two daughter cells that are genetically identical to the parent cell. These daughter cells are diploid, meaning they have 46 chromosomes (23 pairs). Mitosis is crucial for growth, repair, and replacement of damaged cells in an organism.

Highlight: Mitosis is essential for an organism's growth and maintenance of tissues.

In contrast, meiosis produces four daughter cells that are genetically different from the parent cell and each other. These daughter cells are haploid, containing only 23 chromosomes (unpaired). Meiosis is vital for the formation of gametes during sexual reproduction.

Definition: Haploid cells have half the number of chromosomes compared to the parent cell.

The page also introduces the concept of uncontrolled cell division, which is linked to cancer. Cancer is described as a non-communicable disease where uncontrolled mitosis leads to the formation of a tumor. If cancer cells enter the bloodstream, they can spread to other organs and form new tumors.

Vocabulary: A tumor is an abnormal mass of tissue resulting from uncontrolled cell division.

Lastly, the page touches on cell differentiation, which is the process that produces specialized cells carrying out specific functions. Once a cell differentiates, it cannot divide to make an unspecialized cell.

Example: Nerve cells and muscle cells are examples of differentiated cells with specific functions.