Stem cells and differentiation Biology AS cellular organisation

What are stem cells?

Where are stem cells found in humans?

Stem cells [blank_start]divide[blank_end] to become new cells, which then become [blank_start]specialised[blank_end]. The process by which a cell becomes specialised for its job is called [blank_start]differentiation[blank_end]. Stem cells are able to divide to produce more [blank_start]undifferentiated[blank_end] cells, i.e. they can [blank_start]renew[blank_end] themselves. In animals, stem cells are used to [blank_start]replace[blank_end] damaged cells.

Bones are living [blank_start]organs[blank_end], containing [blank_start]nerves[blank_end] and [blank_start]blood vessels[blank_end]. The main bones in the body have [blank_start]marrows[blank_end] in their centres. Here, adult stem cells [blank_start]divide[blank_end] and [blank_start]differentiate[blank_end] to replace worn out blood cells – [blank_start]erythrocytes[blank_end] (red blood cells) and [blank_start]neutrophils[blank_end] (white blood cells to fight infection).

Plants are always [blank_start]growing[blank_end] so they need new [blank_start]shoots[blank_end] and roots throughout their lives. Stem cells in plants can [blank_start]differentiate[blank_end] into various plant tissues. In plants, stem cells are found in [blank_start]meristems[blank_end] (place where [blank_start]growth[blank_end] can take place). In the root and the stem, stem cells of the [blank_start]vascular cambium[blank_end] divide and differentiate to become [blank_start]xylem[blank_end] vessels and [blank_start]phloem[blank_end] sieve tubes.

What are the uses of stem cells in medicine?

Heart disease means the [blank_start]heart[blank_end] tissue is [blank_start]damaged[blank_end] so the body can’t replace damaged heart cells. Researchers are trying to develop ways of using stem cells to make [blank_start]replacement[blank_end] heart cells to repair the damaged tissue. Alzheimer’s  nerve cells in brain [blank_start]die[blank_end] in increasing numbers causing severe [blank_start]memory[blank_end] loss. Researchers hope to use stem cells to regrow healthy [blank_start]nerve[blank_end] cells in people with Alzheimer’s. Parkinson’s disease causes uncontrollable tremors. Loss of [blank_start]nerve[blank_end] cells in the brain that produce dopamine, which is needed to [blank_start]control[blank_end] movement. Transplanted stem cells may help to [blank_start]regenerate[blank_end] the dopamine-producing cells.

Red blood cells have the following functions and adaptations:

What is the function of a neutrophil?

What are the adaptations of a neutrophil?

[blank_start]Epithelium[blank_end] cells cover the surfaces of organs. Cells joined by [blank_start]interlinking[blank_end] membranes and membranes at base. Ciliated epithelia (airways) have [blank_start]cilia[blank_end] that beat to remove particles away. Other ones (in [blank_start]small[blank_end] intestine) have [blank_start]microvilli[blank_end] to increase their surface area. [blank_start]Squamous[blank_end] epithelia (in lungs) are very thin to allow efficient diffusion of [blank_start]gases[blank_end]

[blank_start]Sperm[blank_end] cells have a flagellum so they can [blank_start]swim[blank_end] to the egg. Have lots of [blank_start]mitochondria[blank_end] to provide [blank_start]energy[blank_end] to swim. [blank_start]Acrosome[blank_end] in head contains [blank_start]digestive[blank_end] enzymes to enable sperm to penetrate the surface of the egg.

Palisade mesophyll cells are in the roots.

[blank_start]Palisade[blank_end] mesophyll cells do most of [blank_start]photosynthesis[blank_end]. They contain many [blank_start]chloroplasts[blank_end] so absorb lots of sunlight. They have [blank_start]thin[blank_end] walls – so CO2 can easily diffuse into the cell.

[blank_start]Root hair[blank_end] cells: absorb water + [blank_start]mineral ions[blank_end] from soil. have a [blank_start]large[blank_end] surface area for absorption. Have thin, [blank_start]permeable[blank_end] wall for entry of water and ions. Have extra [blank_start]mitochondria[blank_end] (energy for active transport) in their [blank_start]cytoplasm[blank_end].

[blank_start]Guard[blank_end] cells are found in [blank_start]pairs[blank_end] with gap between them to form [blank_start]stoma[blank_end]. These are tiny pores in surface of leaf for [blank_start]gas[blank_end] exchange. In light, guard cells take up water and become [blank_start]turgid[blank_end] (swollen). Thin outer walls and thickened inner walls force them to bend outwards, [blank_start]opening[blank_end] stomata. Allows gas exchange for [blank_start]photosynthesis[blank_end].