HL 1 Biology

2.2-3: Prokaryotic & Eukaryotic Cells

Prokaryotic cells are mostly small in size, unicellular, and found everywhere (in soil, water, our intestines + skin, and hot water in volcanic areas). They divide in two by a process called binary fission. Example: Escherichia coli, a bacterium found in the human intestines.


  • Cell wall: protective outer layer composed of peptidoglycan.
    • Maintains shape + prevents cell from bursting
  • Plasma membrane: thin layer, mainly composed of phospholipids.
    • Controls entry and exit of substances, pumping them in or out by active transport.
    • produces ATP by aerobic cell respiration
  • Cytoplasm: fluid (with many dissolved substances, enzymes and ribosomes) filling the space inside the plasma membrane.
    • Carries out chemical reactions of metabolism.
  • Pili: hair-like structures/protein filaments sticking out from cell wall.
    • used when two cells are exchanging DNA during conjugation
    • used to pull cells together, when connected to another bacterial cell
  • Flagella: solid protein structures, corkscrew shape, projecting from cell wall
    • can rotate and propel cell to places by using energy
    • solid and inflexible (unlike eukaryote flagella)
  • Ribosomes: small grainy structures.
    • Synthesizes proteins by translating messengerRNA.
  • Nucleoid: region of cytoplasm containing the genetic material (naked DNA)
    • total amount of DNA is much smaller than in eukaryotes
    • less densely than rest of cytoplasm since there are fewer ribosomes and protein

Eukaryotic cells have a complex internal structure consisting of a nucleus and organelles in the cytoplasm with single/double membranes.


  • Nucleus:where DNA is replicated and transcribed + mRNA is modified before released to cytoplasm.
    • Stores most genetic materials of cell and contains uncoiled chromosomes, chromatin. 
  • Rough Endoplasmic Reticulum (rER): synthesizes protein for secretion from the cell.
    • proteins synthesized by ribosomes are passed into cisternae, then carried by vesicles to Golgi apparatus.
  • Golgi apparatus: processes proteins brought in from rER. Later sent to plasma membrane for secretion.
  • Lysosomes: formed from Golgi vesicles. Consists much protein and digestive enzymes.
  • Mitochondria: produce ATP for cell by aerobic cell respiration.
    • Fat used in here for cell’s energy.
  • Free ribosomes:synthesize protein, release it in cytoplasm to work as an enzyme or in other ways.


Prokaryotic cells                                                            Eukaryotic cells

Genetic Material: Naked loop of  DNA                      – Genetic Material: chromosomes with DNA
in cytoplasm/nucleoid                                       strands in nucleus/nuclear envelop
– no mitochondria                                                              – has mitochondria
– few/none internal membranes                                    – many internal membranes (ER, Golgi ap.)
– small ribosomes                                                               – large ribosomes                                              


Plant                                                                                        Animal 

– Cell wall + plasma membrane                                      – No cell wall, only plasma membrane
– Chloroplast present in cells for photosynthesis      – No chloroplasts
– Starch is the storage compound                                   – Glycogen is the storage compound
– Large vacuoles often present                                         – Vacuole not usually present
– Fixed shape/usually rectangular                                  – Able to change shape/ usually rounded


1 a) Identify with reason:

  • i)  It is a eukaryotic cell because it consists of a nucleus, seen in the center of the cell.
  • ii) The cell is part of a root tip because it has a distinct cell wall and the shape is more rectangular than rounded, which are some features presented in plant cells.
  • iii) The cell is in interphase because the chromosomes are not in sight (still coiled up), concluding that the stages of cell division has not started yet.

  b) Magnification of drawing is 2500x

  • i) Actual size of cell:
    • Magnification (2500x) = Image size (40mm)/ Actual Size
    • Actual size = Image size (40)/Magnification (2500)
    • Actual size = 0.016mm = 16µm 
  • ii) 5µm scale bar length if added to drawing
    • Magnification (2500x) = Image size/ Actual Size (5µm)
    • Image Size= Magnification (2500x) x Actual Size (5µm)
    • Scale bar length = 12500µm = 12.5mm

c) Predict what would happen to the cell if placed in concentrated salt solution for an hour: 

  • The cell will decrease in size because the water in the cell would transport to the salt solution, as it is more concentrated, reducing the cytoplasm. This process is also called osmosis, in which the water in the cell would would shift from a less concentrated solution to a solution with more concentration.
  • Since the water is decreasing from the cell, the cell shrinks and causes the plasma membrane to become more separated from the cell wall.

2 Electron micrograph of an animal cell. 

  • a) I = Mitochondria  II= Nucleus  III= Lysosomes
  • b) Magnification of micrograph
    • First convert actual size 1.5µm to 0.0015mm.
    • Magnification = Image size (5mm)/ Actual size (0.0015)
    • Magnification≈3333.3x
  • c) Length of 10µm scale bar on micrograph
    • Magnification (3333.3x) = Image size/ Actual size (10µm)
    • Image Size = Magnification (3333.3x) x Actual size (10µm)
    • Image Size  = 33333µm ≈ 33.3mm
  • d) Length of structure III
    • Magnification (3333.3x) = Image size (3mm)/ Actual Size
    • Actual Size = Image Size (3mm)/Magnification (3333.3x)
    • Actual Size = 0.0009mm = 0.9µm

3 Siphonous Green Algae

  • a) Length of the smallest branch of the siphon (µm)
    • Length of 0.6mm scale bar = 21mm
    • Magnification = Image size (21mm)/ Actual Size (0.6mm)
    • Magnification = 35x
    • Next, length of smallest branch is 4mm
    • Magnification (35)= Image size (4mm)/ Actual Size
    • Actual Size = Image Size (4mm)/ Magnification (35)
    • Actual Size = 0.1143mm = 114.3µm
  • b) The actual diameter of the siphon
    • Magnification (180x)= Image Size (28mm)/ Actual Size
    • Actual Size = Image Size (28mm)/Magnification (180x)
    • Actual Size-Diameter = 0.1556mm = 155.6µm
  • c) Looking at the structure, the Bryopsis pennata is not an animal but a plant. It is constructed with all the features a typical plant cell would have like: a cell wall, chloroplasts and a large vacuole.
  • d) Since there are no divisions visible between the nuclei, it is not multicellular. It may be either unicellular (if these single cells can have multiple nuclei) or acellular (if cell is stated to be small and has a single nucleus.)
  • e) An advantage of having interconnected, pressurized vacuoles is that all the energy and food consumed can be sent throughout the whole structure equally. A disadvantage of this branched siphons is when each of the vacuoles consume too much energy, they could burst. 
  • f) By transferring Bryopsis pennata from sea water to fresh water may cause the cells to expand in size because of osmosis. Since the water would shift to a solution with more concentration, the cells will be charged with more water. If this species containing water with salt dissolved in take too large of an amount, it is likely that the species could burst with the high pressure and decrease in materials (such as mineral).


*AA-CC: 22-4; DBQ p24 • AA-SG: 6-7

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