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1

What can 'Unspecialised' stem cells develop into ?

'Unspecialised' stem cells can develop into any other type of cell. Stem cells are found in animal zygotes (very young embryos), and in plants of all ages

2

Where are Stem cells found?

Stem cells are found in animal zygotes (very young embryos), and in plants of all ages

3

What is A zygote?

A zygote is a structure that forms when a sperm fertilises an egg.

4

The zygote then divides many times by .................. to form an embryo.

The zygote then divides many times by mitosis to form an embryo.

5

The first division of the zygote forms (how many?) cells, the next (how many?), the next (how many?) and so on.

The first division of the zygote forms two cells, the next four, the next eight, and so on.

6

Up what stage are all of the cells are identical? What are they called?

Up to the eight-cell stage, all of the cells are identical.They are called embryonic stem cells.

7

It is possible for embryonic stem cells to develop into what?

It is possible for embryonic stem cells to develop into any other specialised type of cell that the growing embryo needs - for example, nerve cells, blood cells and muscle cells.

8

Once the embryonic stem cells become specialised, can they change into any other type of cell.

However, once the embryonic stem cells become specialised, they can't change into any other type of cell.

9

What does the specialised cells form ?

The specialised cells can form all the different types of tissue that the embryo needs.

10

How are organs formed?

Groups of different types of tissues are arranged together to form organs.

11

Switching genes on and off
Cells become specialised because the genes that are not required are switched off. Only the genes needed to make a particular type of cell work are switched on. So muscle cells only have the genes needed to make muscle cell proteins switched on. All the other genes, such as those needed to make blood cell proteins and nerve cell proteins, are switched off.

Switching genes on and off
Cells become specialised because the genes that are not required are switched off. Only the genes needed to make a particular type of cell work are switched on. So muscle cells only have the genes needed to make muscle cell proteins switched on. All the other genes, such as those needed to make blood cell proteins and nerve cell proteins, are switched off.