UWCSEA - IB Biology 2025 - Topic B2.3 Cell specialisation

B2.3.1—What cell is produced by fertilisation? How does this cell turn into different cell types in the body?

a zygote is formed;

it is an unspecialized cell, known as a stem cell;

this cell divides and some cells undergo differentiation;

where certain genes are expressed;

in particular cells types;

leading to different cell;

B2.3.2—What are the unique properties of stem cells?

Stem cells have the capacity to divide indefinitely;

and can differentiate into various cell types, following different pathways;

B2.3.3—What is the location and function of stem cell niches in adult humans? 2 examples only

Bone marrow stem cells;

Maintains and promotes the proliferation and differentiation of blood cells;

Hair follicles;

support the growth and regeneration of hair by maintaining and differentiating stem cells;

B2.3.4—What are the differences between totipotent, pluripotent and multipotent stem cells?

Totipotent cells (early-stage embryos) can form any cell type, including extraembryonic tissues like the umbilical cord and placenta;

Pluripotent cells can form almost any cell type but not extraembryonic tissues;

Multipotent cells (like in bone marrow) can form a limited range of cells related to a specific tissue; e.g. only blood cells in the bone marrow;

B2.3.5—How is cell size an aspect of specialization?

The size of a cell is intricately linked to its function;

For instance, small red blood cells are optimally sized for efficient oxygen transport;

while large neurons can transmit signals over long distances;

Similarly, striated muscle fibers are large to allow contraction over a long distance;

B2.3.6—How does surface area-to-volume ratio limit cell size?

The surface area-to-volume ratio is crucial in determining a cell's efficiency in exchanging materials with its surroundings;

A higher surface are to volume ratio, found in smaller cells, allows for faster nutrient uptake and waste removal relative to the cell's volume;

This ratio limits cell size, as larger cells cannot exchange materials fast enough;

B2.3.7—What are the adaptations that increase surface area-to-volume ratios of cells?

Cells adapt to increase their surface area through structures like microvilli or flattening;

For example, erythrocytes are flattened and biconcave to maximize surface area for gas exchange;

while cells in the proximal convoluted tubule have microvilli for efficient reabsorption;

B2.3.8—What are the adaptations of type I and type II pneumocytes in alveoli?

Type I pneumocytes are extremely thin, maximizing their surface area for gas exchange;

and reducing diffusion distance;

increasing the rate of exchange;

Type II pneumocytes are specialized for producing and secreting surfactant, which reduces surface tension in the lungs and prevents alveolar collapse.

B2.3.9—What are the adaptations of cardiac muscle cells and striated muscle fibres?

Cardiac muscle cells are branched and interconnected for synchronized contraction;

with a Y shaped structure;

Striated muscle fibers are long and multinucleated, allowing for powerful, coordinated contractions;

Both contain densely packed myofibrils for efficient muscle contraction;

striated muscle could be considered acellular, as it has multiple nuclei without a specific cell membrane separating it from other cells;

B2.3.10—What are the adaptations of sperm and egg cells?

Sperm Cells

Long, streamlined, with a flagellum for mobility;

have an acrosome which contains enzymes that help penetrate the egg.

have mitochondria in the midpiece provide energy for movement

Egg Cells

Largest cell in the human body, providing ample nutrients for the embryo;

Zona pellucida and corona radiata protect and regulate sperm entry;

Cortical Granules prevent polyspermy by altering the zona pellucida after the first sperm enters;