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First teaching 2023

First exams 2025

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Specialised Cells (HL) (HL IB Biology)

Revision Note

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Increasing Surface Area : Volume

  • It is crucial to maximise surface area to volume ratio in cells which require movement of substances across the membrane
  • The larger the surface area compared to the volume of the cell, the faster the rate of substance movement

Red blood cells

  • The function of a red blood cell (also known as an erythrocyte) is to deliver oxygen from the lungs to respiring cells
  • They are flattened and biconcave shaped in order to maximise the surface area and minimise volume
  • This means that oxygen can diffuse into the red blood cell more quickly in the lungs and out again at the respiring tissues

Adaptations of a Red Blood Cell Diagram

Red Blood Cell, downloadable AS & A Level Biology revision notes

The biconcave shape and flattening of erythrocytes increases the surface area available for oxygen absorption

Proximal convoluted tubule cells

  • The proximal convoluted tubules are tiny tubes found in the outer region of the kidney
  • The tubules are responsible for reabsorption of vital substances e.g. glucose and mineral ions from the glomerular filtrate
  • There are several adaptations to maximise surface area in the proximal convoluted tubule cells to ensure that the body reabsorb all the necessary substances
    • Microvilli - in the apical membrane
    • Invaginations - infoldings found in the basal membrane

Proximal Convoluted Tubule Cell Adaptations Diagram

proximal-convoluted-tubule-cell-adaptations

The cells of the proximal convoluted tubule cells have invaginations and microvilli to increase surface area

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.