Topic 3: Cell organisation and control of development

Question 1

How are cells organised in multicellular organisms? (2 point)

Answer 1

1. In multicellular organisms, some stem cells first become specialised to carry out a particular function (by gene expression – certain genes switched on/off)

Examples of specialised cells: Muscle cells, neurones, epithelial cells

2. Then similar cells are grouped to form tissues

Examples of tissues: Muscle tissue, nervous tissue, epithelial tissue

Question 2

Define tissue. (3 points)

Give 4 examples

Answer 2

1. A group of cells working together for {the same/one} function,
2. that contains one type of specialised cell.
3. Often. the cells have the same origin.

Examples: Muscle tissue, nervous tissue, elastic tissue, connective tissue

Question 3

Key Summary: Explain how the cells of a multicellular organism can be organised into a tissue
(4 steps)

Answer 3

1. Similar specialised cells recognise each other and join together
2. Using adhesion molecules/recognition proteins (proteins or glycoproteins) found on the cell surface membrane which have complementary shapes
3. The part of the protein which projects from the cell membrane on one cell, binds to the part of the protein which projects from the cell membrane on another cell
4. Tissue fluid is present between the two cells

Question 4

Define organ. (2 points)

Give 2 examples

Answer 4

1. Group/collection of different tissues, working together to carry out one or more functions.
2. Made of many different cell types;

eg. human heart, liver, pancreas, brain or plant leaf, root

Question 5

Define organ system. (2 points)

Give 2 examples

Answer 5

1. Group of many different organs (each made of cells/tissues) working together for the same function.
2. Made of many different cell types.

eg. digestive system, muscular system, skeletal system, respiratory system, nervous system, endocrine system, circulatory system

Question 6

What are master genes? (1 point)

Answer 6

1. Master genes are genes that are responsible for development in the early embryo.

Question 7

What do master genes control? (1 point)

How? (3 steps)

Answer 7

1. They control the development of segments of an organism, i.e. legs, arms etc.

How:

1. A master gene is a single gene whose expression is necessary to produce a signal protein,
2. which triggers switching on or switching off of many other genes in a specific order,
3. leading to the development of a specific tissue or organ.