1: Unicellular and Multicellular Organisms Flashcards
How many cells in a unicellular organism?
- one
What do unicellular organisms carry out inside them?
- all the functions of life
Give two examples of unicellular organisms.
- Paramecium
2. Chlamydomonas
Where does a Paramecium live? How long is a Paramecium?
- lives in ponds
2. 0.05mm - 0.33mm long
Where does a Chlamydomonas live? How long is a Chlamydomonas?
- freshwater habitats
2. 0.002mm - 0.010mm
Draw a Paramecium. (see p2)
- cilia
- contractile vacuole
- plasma membrane
- nucleus
- cytoplasm
- food in vesicles
Draw a Chlamydomonas. (see p2)
In common with Paramecium:
- contractile vacuole
- plasma membrane
- nucleus
- cytoplasm
Different to Paramecium:
- flagellum
- eye spot
- cell wall
- chloroplast
We are going to compare similarities and differences between Paramecium and Chlamydomonas. What functions of life are we going to compare?
Differences:
- Nutrition
- Excretion
- Growth
- Response
Similarities:
- Metabolism
- Homeostasis
- Reproduction
Compare ‘Nutrition’ of Paramecium and Chlamydomonas.
- Paramecium feeds on smaller organisms by ingesting and digesting them in vesicles
- whereas Chlamydomonas produces its own food by photosynthesis using a chloroplast
Compare ‘Growth’ of Paramecium and Chlamydomonas.
- Paramecium increasing in size and dry mass by accumulating organic matter and minerals from its food
- whereas Chlamydomonas increases in size and dry mass due to photosynthesis and absorption of minerals
Compare ‘Response’ of Paramecium and Chlamydomonas.
- Paramecium reacts to stimuli, e.g. reverses its direction of movement when it touches a solid object
- whereas Chlamydomonas reacts to stimuli, e.g. senses where the brightest light is with its eyespot and swims towards it
Compare ‘Excretion’ of Paramecium and Chlamydomonas.
- Paramecium expels waste products of metabolism, e.g. CO2 from respiration diffuses out of the cell
- whereas Chlamydomonas expels waste products of metabolism, e.g. oxygen from photosynthesis diffuses out of the cell
Compare ‘Metabolism’ of Paramecium and Chlamydomonas.
- Both produce enzymes which catalyse many different chemical reactions in the cytoplasm
Compare ‘Homeostasis’ of Paramecium and Chlamydomonas.
- Both keep internal conditions within limits, e.g. expels excess water using contractile vacuoles
Compare ‘Reproduction’ of Paramecium and Chlamydomonas.
- Both reproduce asexually using mitosis or sexually using meiosis and gametes
What happens to a cells surface area to volume ratio as it grows larger?
- the SA:V decreases
What does the rate at which materials enter/leave (a cell) depend on?
- the surface area of the cell
What does the surface area of a cell determine?
- the rate at which materials enter/leave the cell
What does the rate at which materials are used or produced (in a cell) depend on?
- the volume of the cell
What does the volume of a cell determine?
- the rate at which materials are used or produced
What happens if a cell becomes too large?
- it may not be able to take in essential materials or excrete waste substances quickly enough
Why are large organisms multicellular?
Don’t try and learn this. Understand why.
- SA:V decreases as a cell increases
- if a cell becomes too large, it may not be able to take in essential materials or excrete waste substances quickly enough
- the cell can no longer survive at this size, so it divides
- large organisms therefore consist of many cells (multicellular)
Name two advantages of being a multicellular organism.
- cells can take in/excrete essential materials/ waste substances fast enough
- multicellular allows division of labour, which means different groups of cells can become specialised for different processes
Through what process does a cell become specialised?
- the process of differentiation
What do emergent properties arise from?
- the interaction of the component parts of a complex structure
There is a helpful idiom that can summarise ‘emergent properties’. What is it?
- ‘the whole is greater than the sum of the parts’
What sort of organisms have properties that emerge from the interaction of their cellular components?
- multicellular organisms
Give an example of emergent properties in an organism.
- a tiger
- each cell is a unit of life with distinctive properties e.g. sensitivity to light in retina cells
- individually, the cells can barely do anything
- together, they comprise an organism that can have a profound ecological impact on its environment
Define genome.
- an organisms entire set of genes
What percentage of an multicellular organisms genome is in each cell?
- 100%
In multicellular organisms, 100% of the genome is in each cell. Why is this significant?
- each cell has the instructions to develop into any type of cell
Which genes does a cell use in differentiation?
- only the genes it needs to follow its pathway of development
- other genes are unused
What is a cell doing when it uses only the genes it needs to follow its pathway of development ?
- differentiating
Give an example of gene expression when a cell is differentiating.
- the genes for making hemoglobin are only expressed in developing red blood cells
What can a cell do/not do once it has begun a pathway of development?
- it is fixed and cannot change to a different path
Once a cell has begun a pathway of development it is said to be…?
- ‘committed’ - it cannot change to a different path
