IB Biology SL — Topic 1 • Cell Biology with Complete Solutions

IB Biology SL — Topic 1 • Cell Biology with Complete Solutions Cell theory 1. All living things are composed of cells 2. Cells are the smallest unit of life 3. Cells only arise from pre-existing cells Striated muscle cell Exception to cell theory! → Muscle cells fuse to form fibres that may be very long (>300mm) → Consequently, they have multiple nuclei despite being surrounded by a single, continuous plasma membrane → Challenges the idea that cells always function as autonomous units Aseptate fungal hyphae Exception to cell theory! → Fungi may have filamentous structures called hyphae, which are separated into cells by internal walls called septa → Some fungi are not partitioned by septa and hence have a continuous cytoplasm along the length of the hyphae → Challenges the idea that living structures are composed of discrete cells Giant Algae Exception to cell theory! → Certain species of unicellular algae may grow to very large sizes (e.g. Acetabularia may exceed 7 cm in length) → Challenges the idea that larger organisms are always made of many microscopic cells 7 basic functions integral to survival 1. Metabolism - Living things undertake essential chemical reactions 2. Reproduction - Living things produce offspring, either sexually or asexually 3. Sensitivity - Living things are responsive to internal and external stimuli 4. Homeostasis - Living things maintain a stable internal environment 5. Excretion - Living things exhibit the removal of waste products 6. Nutrition - Living things exchange materials and gases with the environment 7. Growth - Living things can move and change shape or size Surface area to Volume ratio It is important in the limitation of cell size! → the smaller the cell is, the more quickly and easily materials can be exchanged between its cytoplasm and environment → One consequence of this is that cells cannot grow larger indefinitely → When a maximum size is reached, cell growth stops (the cell may then divide) Calculation of actual size of a call Actual Size