AQA Combined Science Biology Chapter Two

* In body cells, chromosones are found in pairs.

* Body cells divide in a series of stages called the cell cycle.

*During the cell cycle the genetic material is doubled. It then divides, forming two identical nuclei in a process called mitosis.

*Before a cell can divide it needs to grow, replicate the DNA to form two copies of each chromosone, and increase the number of sub cellular structures.

*In mitosis one set of chromosones is pulled to each end of the cell membranes divide to form two identical cells.

*Mitotic cell division is important in the growth, repair and development of multicellular organisims.

* In plant cells mitosis takes place throughout life in the shoot and root tips.

* Many types of plants cell retain the ability to differentiate throughout life.

* Most types of animal cell differentiate at an early stage of development.

Embryonic stem cells (from human embryos) and adult stem cells can be cloned and made to differentiate into many different types of cell.

Treatment with stem cells may be able to help conditions such as paralysis and diabetes.

*Stem cells from plant meristems are used to produce new plant clones quickly and economically for research, horticulture, and agriculture.

* Treatment with stem cells, from embryos or adult cloning may be able to help with conditions such as diabeties.

* In theraoutic cloning, an embryo is produced with the same gnes and the patient, so the stem cells produced are not rejected and may be used for medical treatment.

* The use of stem cells has some potentail risks, and some people have ethical or religous objections.