Cell Proliferation in Organisms
- Plants and animals originate from a zygote which will divide repeatedly to form an embryo
- During this stage of development, there is a rapid increase in the number of cells which allows the embryo to grow
- This rapid increase in cell number is known as proliferation
- Proliferation for growth occur within early-stage animal embryos, as well as growth regions in plants known as meristems
- During this stage of development, there is a rapid increase in the number of cells which allows the embryo to grow
Plant meristems
- Plant growth occurs in regions known as meristems
- The cells in these regions are known as meristem cells
- Meristem cells are undifferentiated; they actively divide by mitosis to produce new plant tissue
- Meristems can be found in the growing tips of plant roots and shoots
- A meristem at the tip of a shoot is a shoot apical meristem
- A meristem at the tip of a root is a root apical meristem
- Meristem tissue with the potential to form new side branches from the main plant stem can be found in regions known as axillary buds
- Meristems can also be found parallel to the sides of a stem e.g. within the vascular bundles that contain the xylem vessels and the phloem
- These are known as lateral meristems and enable plant stems to grow in diameter
- Lateral means ‘from the side’
- The regions of meristem tissue in the vascular bundles are known as cambium
Diagram to show the location of plant meristems
The growing parts of plants are known as meristems, and can be found in the shoot apex (shoot apical meristem), the root apex (root apical meristem), and the sides of the stem (lateral meristem)
Diagram to show the location of the cambium meristem tissue
Lateral meristem tissue is known as cambium. It can be found between the xylem and phloem in stems and roots.
Early-stage animal embryos
- Following human fertilisation, the newly fertilised ovum divides by mitosis to form two diploid nuclei (i.e. each nucleus contains two sets of chromosomes) and the cytoplasm divides equally to form a two-cell embryo
- Mitosis continues to form a four-cell embryo and this process continues until eventually, the embryo takes the shape of a hollow ball called a blastocyst (with an internal group of cells called blastomeres)
- Blastomeres will eventually develop into the foetus
- These cells are undifferentiated and could develop into any type of specialised cell at this point
Cell proliferation for cell replacement and tissue repair
- Cells, such as those that form part of skin and blood, need to be constantly replaced
- This is achieved by the process of cell proliferation whereby cells divide by mitosis
- Skin cells that form part of the epidermis (outer layer of the skin) are lost on a daily basis and will be replaced multiple times during a lifetime
- This is achieved by the proliferation of the stem cells found in the basal (bottom) layer of the epidermis
- These newly formed daughter cells will form new layers in the epidermis to replace the top layers lost through wear and tear
- Tissue repair during wound healing is another example of the importance of cell proliferation
- Once the wound is sealed by a blood clot, the blood vessels will dilate to increase blood flow to the damaged area
- This enables fibroblasts and white blood cells called macrophages to reach the wound
- Macrophages will engulf any pathogen that entered through the broken skin while the fibroblasts will proliferate to facilitate the closure of the wound
- The fibroblasts achieve this by breaking down the fibrin in the blood clot while producing a new matrix of collagen fibres to help close the wound and support new skin cells
Wound healing diagram
The proliferation of fibroblasts will speed up the process of wound healing