B2.3.5

• Sperm cells: very long but extremely narrow. This reduces resistance and allows it to swim to the egg more easily.
• Egg cells: are spherical and have the largest volume of any human cell. This allows large quantities of food reserves to be stored in the cytoplasm.
• Red blood cells: are small and indented on both sides (thin in the middle). The small size and shape allows the to pass through narrow capillaries and gives a large surface area-to-volume ratio which makes loading and unloading oxygen faster.
• White blood cells: are small but they enlarge if they are activated and become antibody-secreting plasma cells.
• Cerebellar Granule cells: small but twin axons extend for 3mm in the cerebellar cortex. The very small volume makes it possible for the brain to accommodate 50 billion of them.
• Motor neurons: large which allows enough proteins to be synthesised to maintain the immensely long axon. It can extend for a metre of more and can carry signals from the central nervous system to the muscles.
• Striated Muscle Fibres: are larger than normal cells with a large diameter and lengths that can exceed 100mm. These dimensions allow the fibre to exert greater force and contract by a greater length than smaller muscle cells.