1.1 Introduction to cells Flashcards
When was the cell theory established?
1838
What are the rules of the cell theory?
- Living organisms are composed of cells (one or more) – that is, cells are the building blocks of organisms.
- Cells are the smallest units of life – that is, a cell is a basic unit capable of carrying out all the functions of a living organism.
- Cells come from pre-existing cells (omni cellulae e cellula) – that is, cells do not show spontaneous generation.
Examples of atypical cells
- Striated muscle cell
- Giant algae: Acetabularia
- Aseptate fungal hyphae
Striated muscle cell
- Striated muscle tissue is composed of repeated units called sarcomeres.
- These show a characteristic striped (striated) pattern when viewed under the microscope.
- This challenges the idea that a cell has one nucleus, as the muscle cell (fiber) has more than one nucleus per cell.
- That is, each cell is multinucleated.
- Additionally, the average muscle fiber cell is about 30 mm long, which is much larger than a typical cell.
Diagram of a striated muscle cell
Giant algae: Acetabularia
- Acetabularia* is a genus of single-celled green algae of gigantic size, ranging from 0.5 to 10 cm in length.
- Acetabularia* consists of three easily distinguishable parts, namely: the rhizoid (which looks like small roots), the stalk, and a top umbrella made of branches that may fuse into a cap.
- As a single-celled organism, Acetabularia challenges two widely accepted notions about cells: that they must be simple in structure and small in size.
Diagram of Giant algae: Acetabularia
Aseptate fungal hyphae
- Aseptate fungal hyphae are long threads (hyphae) with many nuclei.
- They have no dividing cell walls, called septa (singular: septum).
- The result of this is shared cytoplasm and multiple nuclei (singular: nucleus).
- This challenges the idea that a cell is a single unit as the fungal hyphae have many nuclei, are very large and possess a continuous, shared cytoplasm.
Diagram of aseptate fungal hyphae
Muscle cells do not fit the cell theory because ___
They are multinucleated and are much larger than typical cells.
Why does Acetabularia challenge ideas about cells?
It is a large and complex cell.
What are aseptate fungal hyphae?
Aseptate fungal hyphae are long threads (hyphae) with many nuclei, but no dividing cell walls.
When was the electron microscope introduced?
In the early 1940s
1 nm (nanometre) = ___
10 ^-9 m
1 μm (micrometre) = ___
10 ^-6 m
1 mm (millimetre) = ___
10 ^-3 m
Diagram showing the relative size of various cells and cellular components to better understand how they compare with each other with regards to dimension.
Formula to calculate magnification
Magnification = size of drawing / actual size (scale bar)
The scale bar represents ___
The actual size of the sample in the image.
Diagram showing the triangle used to remember how to solve for different parts of the magnification formula.
The actual size of the sample in the image.
Required practical: Using microscopes to investigate stomata
All living things can be classified as ___
Unicellular (single-celled) or multicellular (many-celled) based on the number of cells that they possess.
The whole body of unicellular organisms is made up of ___
Only one cell and hence they should be able to carry out all the life processes within this cell.
Examples of unicellular organisms
Bacteria, archaea, protozoa, unicellular algae, and unicellular fungi.