Growth and Development Growth = Cell multiplication + Cell enlargement Cell enlargement

Plant and Animal Cells  Plants and animals are made up of cells.  Robert Hook was the first person to use a microscope in  He discovered that plants were made up of things that looked like tiny rooms. He called these cells.

Animal Cell

Plant Cell

Bacteria Cell

Bacteria Cells  Bacteria are usually made from 1 cell.  Bacteria cells are much smaller and simpler than animal and plant cells.  They still have DNA but no nucleus.  The DNA is found in the cytoplasm. Mitochondria and chloroplasts are also missing from bacterial cells.

Growth  When plants and animals grow, cells need to divide and change into specialised cells. For example, nerve cells and bone cells.  The specialised cells can carry out different jobs.  When a cell changes to become specialised the process is called cell differentiation.

Stem Cells  A fertilised egg cell contains a group of undifferentiated cells called stem cells.  Stem cells have the same simple cell structure. They divide and then differentiate (change) to form all the different specialised cells in the body.  As the embryo grows all the specialised cells form tissues and organs.  A few stem cells are found in the adult body. Bone marrow contains stem cells that turn into different types of blood cells.

Stem Cell Research  Scientists have found ways to make stem cells develop into other specialised cells. They can be taken from embryos and used to treat medical conditions.  Many people object to stem cell research because it can involve human embryos. Scientists use embryo stem cells because they are easier to grow than adult stem cells.

Chicken, Nerve and Human Stem Cells  If a person damages their nerve cells their body cannot make new ones. However, scientists have found a way to grow human nerve cells in chickens.  They have taken stem cells from human bone marrow and put them into chicken embryos.  Stem cells are special cells that have the ability to form all the different cells.  Normally stem cells from the bone marrow turn into blood cells. Scientists have found that these stem cells can be turned into nerve cells in chicken embryos.  However scientists are still a long way off using this to replace damaged nerve cells in a human today.