1: Unicellular and Multicellular Organisms

Question 1

How many cells in a unicellular organism?

Answer 1

1. one

Question 2

What do unicellular organisms carry out inside them?

Answer 2

1. all the functions of life

Question 3

Give two examples of unicellular organisms.

Answer 3

1. Paramecium

2. Chlamydomonas

Question 4

Where does a Paramecium live? How long is a Paramecium?

Answer 4

1. lives in ponds

2. 0.05mm - 0.33mm long

Question 5

Where does a Chlamydomonas live? How long is a Chlamydomonas?

Answer 5

1. freshwater habitats

2. 0.002mm - 0.010mm

Question 6

Draw a Paramecium. (see p2)

Answer 6

1. cilia
2. contractile vacuole
3. plasma membrane
4. nucleus
5. cytoplasm
6. food in vesicles

Question 7

Draw a Chlamydomonas. (see p2)

Answer 7

In common with Paramecium:

2. contractile vacuole
3. plasma membrane
4. nucleus
5. cytoplasm

Different to Paramecium:

1. flagellum
2. eye spot
3. cell wall
4. chloroplast

Question 8

We are going to compare similarities and differences between Paramecium and Chlamydomonas. What functions of life are we going to compare?

Answer 8

Differences:

1. Nutrition
2. Excretion
3. Growth
4. Response

Similarities:

1. Metabolism
2. Homeostasis
3. Reproduction

Question 9

Compare ‘Nutrition’ of Paramecium and Chlamydomonas.

Answer 9

1. Paramecium feeds on smaller organisms by ingesting and digesting them in vesicles
2. whereas Chlamydomonas produces its own food by photosynthesis using a chloroplast

Question 10

Compare ‘Growth’ of Paramecium and Chlamydomonas.

Answer 10

1. Paramecium increasing in size and dry mass by accumulating organic matter and minerals from its food
2. whereas Chlamydomonas increases in size and dry mass due to photosynthesis and absorption of minerals

Question 11

Compare ‘Response’ of Paramecium and Chlamydomonas.

Answer 11

1. Paramecium reacts to stimuli, e.g. reverses its direction of movement when it touches a solid object
2. whereas Chlamydomonas reacts to stimuli, e.g. senses where the brightest light is with its eyespot and swims towards it

Question 12

Compare ‘Excretion’ of Paramecium and Chlamydomonas.

Answer 12

1. Paramecium expels waste products of metabolism, e.g. CO2 from respiration diffuses out of the cell
2. whereas Chlamydomonas expels waste products of metabolism, e.g. oxygen from photosynthesis diffuses out of the cell

Question 13

Compare ‘Metabolism’ of Paramecium and Chlamydomonas.

Answer 13

1. Both produce enzymes which catalyse many different chemical reactions in the cytoplasm

Question 14

Compare ‘Homeostasis’ of Paramecium and Chlamydomonas.

Answer 14

1. Both keep internal conditions within limits, e.g. expels excess water using contractile vacuoles

Question 15

Compare ‘Reproduction’ of Paramecium and Chlamydomonas.

Answer 15

1. Both reproduce asexually using mitosis or sexually using meiosis and gametes

Question 16

What happens to a cells surface area to volume ratio as it grows larger?

Answer 16

1. the SA:V decreases

Question 17

What does the rate at which materials enter/leave (a cell) depend on?

Answer 17

1. the surface area of the cell

Question 18

What does the surface area of a cell determine?

Answer 18

1. the rate at which materials enter/leave the cell

Question 19

What does the rate at which materials are used or produced (in a cell) depend on?

Answer 19

1. the volume of the cell

Question 20

What does the volume of a cell determine?

Answer 20

1. the rate at which materials are used or produced

Question 21

What happens if a cell becomes too large?

Answer 21

1. it may not be able to take in essential materials or excrete waste substances quickly enough

Question 22

Why are large organisms multicellular?

Answer 22

Don’t try and learn this. Understand why.

1. SA:V decreases as a cell increases
2. if a cell becomes too large, it may not be able to take in essential materials or excrete waste substances quickly enough
3. the cell can no longer survive at this size, so it divides
4. large organisms therefore consist of many cells (multicellular)

Question 23

Name two advantages of being a multicellular organism.

Answer 23

1. cells can take in/excrete essential materials/ waste substances fast enough
2. multicellular allows division of labour, which means different groups of cells can become specialised for different processes

Question 24

Through what process does a cell become specialised?

Answer 24

1. the process of differentiation

Question 25

What do emergent properties arise from?

Answer 25

1. the interaction of the component parts of a complex structure

Question 26

There is a helpful idiom that can summarise 'emergent properties'. What is it?

Answer 26

1. 'the whole is greater than the sum of the parts'

Question 27

What sort of organisms have properties that emerge from the interaction of their cellular components?

Answer 27

1. multicellular organisms

Question 28

Give an example of emergent properties in an organism.

Answer 28

1. a tiger 2. each cell is a unit of life with distinctive properties e.g. sensitivity to light in retina cells 3. individually, the cells can barely do anything 4. together, they comprise an organism that can have a profound ecological impact on its environment

Question 29

Define genome.

Answer 29

1. an organisms entire set of genes

Question 30

What percentage of an multicellular organisms genome is in each cell?

Answer 30

1. 100%

Question 31

In multicellular organisms, 100% of the genome is in each cell. Why is this significant?

Answer 31

1. each cell has the instructions to develop into any type of cell

Question 32

Which genes does a cell use in differentiation?

Answer 32

1. only the genes it needs to follow its pathway of development 2. other genes are unused

Question 33

What is a cell doing when it uses only the genes it needs to follow its pathway of development ?

Answer 33

1. differentiating

Question 34

Give an example of gene expression when a cell is differentiating.

Answer 34

1. the genes for making hemoglobin are only expressed in developing red blood cells

Question 35

What can a cell do/not do once it has begun a pathway of development?

Answer 35

1. it is fixed and cannot change to a different path

Question 36

Once a cell has begun a pathway of development it is said to be...?

Answer 36

1. 'committed' - it cannot change to a different path