B2.3 Cell specialisation

Stem cell

A cell that can divide by mitosis an unlimited number of times. Each stem cell has the potential to remain a stem cell or develop into a specialised cell by differentiation

Stem cell niche

A specific location which stem cells remain in, allowing tissues to regenerate and repair

Examples of tissues which retain stem cells within a niche - Bone marrow

Provides a niche for stem cells to replace red blood cells, white blood cells, and platelets

Examples of tissues which retain stem cells within a niche - Hair follicle

Located in the root of the hair, stem cells promote continual hair growth

Potency

The ability of stem cells to differentiate into more specialised cell types

Totipotency

Stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (placenta)

Pluripotency

Embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells

Multipotency

Adult stem cells that can differentiate into closely related cell types

Unipotency

Adult cells that can only differentiate into their own lineage

Structural adaptations of specialised cells

Shape, organelles it contains, size

SA:V ratio

As cells increase in size their SA:V ratio decreases

Rate of metabolism

As cell volume increases metabolic requirements are higher

Adaptations of a red blood cell

Flattened and biconcave shaped to maximise SA. Oxygen can diffuse into the RBC quickly

Adaptations of proximal convoluted tubule cells

Microvilli and invaginations which increase SA and reabsorption

Type I pneumocytes

Extremely thin alveolar cells, allowing a short diffusion distance which maximises the rate of diffusion

Type II pneumocytes

Rounded cells with secretory vesicles that release pulmonary surfactant. The surfactant reduces surface tension, maintaining alveolar shape and preventing sticking together. It also allows oxygen to dissolve

Striated muscle fibres

Striated as it has a stripy appearance. They are bundled up into fibres surrounded by sarcolemma. The fibres have many nuclei and a sarcoplasmic reticulum which stores calcium. The sarcoplasm contains mitochondria and myofibrils (actin and myosin)

3 types of muscles

Skeletal muscles, cardiac muscle, and smooth muscle

Cardiac muscle

Myogenic (can contract without external stimulation), does not tire or fatigue, lots of mitochondria, contractile myofibrils

Adaptations of sperm cells

Acrosome containing enzymes to digest the zona pellucida, mitochondria in the body for movement, flagellum for movement

Adaptations of egg cells

Zona pellucida that hardens to prevent polyspermy, follicle cells (corona radiata) which nourish and protect the ova, cortical granules to harden the zona pellucida, cytoplasm with nutrients