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IB Biology SL/Notes/B2.3 Cell specialization

IB Biology SLB2.3 Cell specializationNotes

From Zygote To Stem Cell Potential

A zygote divides to produce unspecialized cells that later differentiate. The key exam mechanism is differential gene expression: cells usually keep the same genome, but different genes are activated or suppressed, so different proteins are made. Morphogen gradients can control gene expression and body pattern formation during development. Stem cells self-renew by repeated division while remaining undifferentiated, so they can supply new cells before some descendants specialize.

Differentiation is caused by selective gene expression, not by cells getting different chromosomes.
Protein analysis can show biochemical evidence of differentiation because expressed genes produce different proteins.
Stem cells self-renew by repeated division while remaining undifferentiated and can later differentiate.

Which explanation best describes differentiation after fertilization?

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Compare Niches And Potency Levels

Stem cells are useful because they self-renew by repeated division while remaining undifferentiated, and they have potency: the capacity to differentiate into mature cell types. Adult stem cell niches provide signals that maintain, activate, or differentiate stem cells, such as bone marrow niches for blood cells or hair follicle bulge niches for hair regeneration.

Totipotent cells can form all body cells plus placental cells.
Pluripotent cells form all body cell types but not placenta or totipotent cells.
Multipotent adult stem cells repair and maintain a limited range of tissues.

The visual separates potency classes from the adult microenvironments that control stem cells.

Sort the stem-cell terms by their differentiation potential.

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Unsorted
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broadest potential
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body cell potential
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control environment
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limited tissue repair
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Sort the stem-cell terms by their differentiation potential.

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Size Fits The Cell Job

Specialized cells vary widely in size because their structure fits their function. Egg cells are large because they store nutrients; sperm are small and streamlined with a long flagellum; neurons can be very long for communication; striated muscle fibres are extended multinucleate cells for contraction.

Cell size is not random; it is part of specialization.
Large cells often need adaptations or stored resources to support their job.
Long cells, such as neurons and muscle fibres, solve communication or contraction problems.

Different cell sizes are useful because they solve different biological problems.

Match each specialized cell size/shape to its advantage.

Match
Reasons
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Match each specialized cell size/shape to its advantage.

Choose
large egg cell
small sperm with flagellum
long neuron
long multinucleate muscle fibre

Why Surface Area Limits Size

Practice

Surface area-to-volume ratio explains why cell size is limited. Surface area controls the rate of exchange across the membrane, while volume controls metabolic demand. As a cell grows, volume increases faster than surface area, so exchange cannot keep up unless the cell divides or develops exchange adaptations.

Surface area is linked to exchange of materials and heat.
Volume is linked to metabolic demand and waste production.
A larger cell has a lower SA:V ratio, so diffusion becomes limiting.

A roughly spherical cell doubles in diameter. What happens to its surface area-to-volume ratio?

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SL Transfer: Explain Specialization And Size Limits

Exam Practice

Cell specialization comes from differential gene expression after a zygote divides, stem cells provide self-renewing cells with different potencies, and cell size is constrained by surface area-to-volume ratio because exchange depends on surface area while demand depends on volume.

Differentiation: same genome, different active genes, different proteins.
Stem cells: self-renewal plus potency; specify totipotent, pluripotent, or multipotent when needed.
SA:V: as cells grow, exchange becomes less efficient because volume increases faster than surface area.
Fill Blanks
Complete the exam skeleton: Differentiation happens because differentare expressed; stem cells can self-renew and; as cells grow,increases faster than surface area.
Word bank
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Use this for core questions on differentiation, stem-cell properties/types/niches, cell size, and surface area-to-volume ratio.

A zygote divides to produce unspecialized cells that later differentiate.
Differentiation occurs when different genes are activated or suppressed in different cells.
Stem cells self-renew and have potency, the capacity to differentiate into mature cell types.
Totipotent, pluripotent, and multipotent stem cells differ by the range of cell types they can form.
Surface area controls exchange while volume controls metabolic demand; as cells grow, SA:V decreases and diffusion can limit size.

Use this for core questions on differentiation, stem-cell properties/types/niches, cell size, and surface area-to-volume ratio.

Do not list definitions without the cause-effect link, especially gene expression -> protein -> specialized function.