Cell biology flashcards

Cell biology underpins all of IB Biology. Students must understand that cells are the basic structural and functional units of life, and that all cells arise from pre-existing cells. The distinction between prokaryotic and eukaryotic cells is fundamental, as are the structures and functions of organelles found in animal, plant, and fungal cells. Students must grasp how the fluid mosaic model describes membrane structure and how substances cross membranes by diffusion, osmosis, active transport, endocytosis, and exocytosis. Cell division through mitosis maintains genetic consistency during growth and repair, while an understanding of the cell cycle, including interphase, is essential. The origin of eukaryotic cells through endosymbiosis links cell biology to evolutionary theory. Surface area to volume ratio explains key limitations on cell size.

1. Card 1

   What is the cell theory?

   Cell theory states that all living organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

2. Card 2

   What are the key differences between prokaryotic and eukaryotic cells?

   Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles, while eukaryotic cells have both, and are generally larger and more complex.

3. Card 3

   What is the fluid mosaic model of membrane structure?

   The fluid mosaic model describes the membrane as a flexible phospholipid bilayer with proteins, cholesterol, and glycoproteins embedded or attached, able to move laterally.

4. Card 4

   How does osmosis differ from simple diffusion?

   Osmosis is the passive movement of water across a selectively permeable membrane from a region of lower solute concentration to higher, whereas diffusion applies to other molecules down a concentration gradient.

5. Card 5

   What is the role of mitochondria in a cell?

   Mitochondria are the sites of aerobic cellular respiration, producing ATP through oxidative phosphorylation; they have a double membrane with a folded inner membrane called cristae.

6. Card 6

   What happens during the S phase of the cell cycle?

   During S phase (synthesis phase), the cell replicates all of its DNA so that each chromosome consists of two identical sister chromatids joined at the centromere.

7. Card 7

   What is the endosymbiotic theory?

   Endosymbiotic theory proposes that mitochondria and chloroplasts evolved from free-living prokaryotes engulfed by a host cell, supported by their double membranes and own circular DNA.

8. Card 8

   Why does surface area to volume ratio limit cell size?

   As a cell grows, its volume increases faster than its surface area, reducing the ratio and making it harder to exchange materials and remove waste quickly enough to sustain metabolism.

9. Card 9

   What distinguishes active transport from passive transport?

   Active transport moves substances against their concentration gradient and requires ATP energy, whereas passive transport moves substances down the gradient without energy input.

10. Card 10

    What are the four stages of mitosis in order?

    The four stages are prophase, metaphase, anaphase, and telophase; chromosomes condense, align, separate, and are enclosed in new nuclei respectively, followed by cytokinesis.

11. Card 11

    What structural feature of the rough endoplasmic reticulum distinguishes it from smooth ER?

    The rough endoplasmic reticulum is studded with ribosomes on its outer surface, enabling it to synthesise and process proteins destined for secretion or membrane insertion.

12. Card 12

    What is the difference between endocytosis and exocytosis?

    Endocytosis brings materials into the cell by engulfing them in a vesicle formed from the membrane, while exocytosis releases materials outside the cell by fusing vesicles with the membrane.

• Many students confuse osmosis with active transport, forgetting that osmosis is entirely passive and requires no ATP, relying solely on the water potential gradient across the membrane.
• Students often incorrectly state that plant cells burst when placed in pure water, when in fact the rigid cell wall creates turgor pressure that prevents lysis, unlike animal cells which can lyse.
• A frequent error is describing mitosis as producing genetically different daughter cells, when mitosis produces two cells that are genetically identical to each other and to the parent cell; it is meiosis that generates genetic variation.

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