A minimal level of intra-tumour heterogeneity is a simple consequence of the imperfection of DNA replication: whenever a cell (normal or cancerous) divides, a few mutations are acquired - leading to a diverse population of cancer cells.
There are two main sources of vitamin A, animal sources and plant sources. Known as retinol, animal sources of this essential vitamin contain preformed vitamin A. Vegetable sources contain carotenoids, such as beta-carotene, which is converted to retinol by the body.lant sources of vitamin A include many fruits and vegetables that have rich, deep, intense color. The more intense the color of the vegetable or fruit, the more beta-carotene it contains. Plant sources of carotenes include: 1  Sweet potatoes. 2  Carrots. 3  Pumpkin. 4  Winter squash. 5  Cantaloupe. 6  Pink Grapefruit.
â The vitamin A from animal sources is retinoids, also called retinol, while plant source vitamin A is carotenoids, such as beta carotene. Animal sources of retinol is bio-available, which means the body can utilize it.