Why do cells need to divide?
So that organisms can grow and replace worn out or damaged cells
What are the two types of cell division?
Mitosis and Meiosis
What happens in Mitosis?
- Two cells are formed
- They both have the same number & type of chromasomes as the original cell
- Mitosis forms all cells in the body except the sexy cells
Descibe the stages in Mitosis...
What happens in meiosis?
- When cells divide by meiosis, four cells are formed.
- These only have half the number of chromosomes of the original cells
- Meiosis forms sex cells
Describe the stages of meiosis...
Why do cells need to be replaced?
- Skin lose thousands of cells everything we touch something....= millions cells every day
- Cells are scraped off lining of the gut as food passes along
- Cells in our spleen destroy worn out red blood cells at a rate of 100,000,000,000 a day...dats a lot.
What is genetic variation?
Cells formed by meiosis dont all have the same combination of alleles...there is genetic variation in the cells.
Describe the similarities and differences btn Mitosis and Meiosis...
Why do the offspring from sexual reproduction vary genetically?
- Because of the huge variation in the sex cells (a 'low' estimate of c8.5m different type of sex cells
- Because of the random way in which fertilisation takes place
What's the difference between:
Identical twins or Monosyygotic twins and
Identical twins or Monosyygotic twins: genetically identical...formed from the same zygote
Fraternal twins: non-identical twosm form from different zygote
Asexual reproduction or cloning
...where there is no fusion in the cells
offspring that are genetically identical to parent and each other
asexual reproduction common in plants and some animals
What role do environmental factors play?
they can significantly influence the growth and development of plants and animals
plants: level of light, water, minerals; carbon dioxide all influence growth
for humans, different physical, social environments can influence the physical and mental development of people...see identical twins who for some reasons grow apart