specialization bio hl

Why are multicellular organisms more efficient than unicellular organisms?

because cells develop differently carrying out different specialized functions.

The development of specialized cells occurs at very early stages of life due to the expression of some genes and not others, so the cell synthesizes specific proteins to perform its specific function.

This might be triggered due to changes in environment.

what is specialization

Specialization enables the cells in a tissue to function more efficiently as they develop specific adaptations for that role. The development of these distinct specialized cells occurs by differentiation.

structural adaptations include

Change in the The shape of the cell.

Change in the The organelles the cell contains.

and Change in the The chemical composition of the cytoplasm.

3 different examples on different specialized differentiated cells

RBCs: biconcave shape to move inside blood capillary, it has no nucleus to allow more hemoglobin to be present, binding more oxygen.

neurons: nerve cells with a long axon to transmit impulses away from the cell body. they have dendrites to receive electrical impulses and a myelin sheath to speed up transmission.

muscle cell: elongated, multinucleated, with actin and myosin contractile protein involved in muscle contraction.

evolution of multicellularity

Multicellularity have evolved many times independently in eukaryotes and in some prokaryotes. It includes a longer lifespan as the death of the cell does not affect the survival of an organism. multicellular organisms are larger so they exploit niches better, and it also shows complexity as there can be differentiation within cell types in a organism

Fertilization

when the male and female gamete fuse together forming a zygote, the zygote divides repeatedly forming an embryo with many undifferentiated unspecialized cells. Different gene expression mechanisms determine the way embryo cells differentiate and specialize. this is directed by morphogens.

Morphogens (important)

signaling molecules that are released from particular areas of tissues called the source. these chemicals diffuse to nearby cells and bind to surface receptors to activate intracellular signaling pathway that promote or represses gene expression allowing the cells to start differentiation

the differentiation of cells depend on

the concentration gradient of morphogens that the near by cells receive and the position of cells with respect to the source of the morphogens

Stem cells

Stem cells are cells that are unspecialized and undifferentiated. they can self-renew by dividing repeatedly, and they can differentiate into many different types of specialized cells in the body. they are found in different niches in the human body (liver, skin, and bone marrow) so they have great power of regeneration and repair.

characteristics of the niche for stem cells

to remain in active undifferentiated for a long period of time and to proliferate (divide) and differentiate rapidly when required

2 examples of stem cell niches

bone marrow: contains hematopoietic stem cells that can differentiate and specialize into different blood cells (WBC, RBC, platelets).

muscle fiber/cell: contains stem cells that are able to differentiate into mew muscle fibers once the muscle is injured to replace the damaged cells.

difference between totipotent, pluripotent, and multipotent stem cells

totipotent happens in early stage embryos composed entirely of stem cells, they can differentiate into any cell type and extra embryonic tissue (placenta). useful in growth of whole replacement hearts, kidneys, placenta.

pluripotent is taken at late stages (blastocyst) gradually, they change from being totipotent to pluripotent. it differentiates into a range of cell types but not every cell.

multipotent are from fetal tissue, adult stem fells and cord blood. they are limited but can differentiate into several types of mature cells. ex: stem cells in bone marrow are multipotent as they can generate different types of blood cells but not other cell types.

cell size and adaptation examples

male gamete: sperm: smallest cell in the body with length of 50-70 micro m and width of 2 to 3 micro m. and it has a streamlined head to overcome viscosity of fluids and flagella to move and reach ovum.

RBC: bi concave to fit inside small capillaries

WBC: gets larger when activating a pathogen (release antibodies from plasma cells)

Neuron: elongated cell to transmit nerve impulses throughout the body.

female gamete: ova: the cell with the largest volume it is rich in stored nutrients in cytoplasm for developing embryo.

striated muscle fiber: atypical multinucleated cell involved in muscle contractions to cause movement

surface area to volume ratio (important)

1. cells are small in size and they tend to divide to maintain high SA: V ratio

2. as the cell grows its SA:V ratio gets smaller

3. this means that the volume of the cell is increasing faster than its surface area.

4. if the volume of the cell increases then its need for nutrients and gas exchange increases, which the small surface area cannot handle so it will divide or die.

5. the larger the SA the faster diffusion rate

Importance of having large SA/V ratio (important)

As the cell increases in size its SA/V ratio decreases. cells tend to divide all the time to keep the ratio large.

it helps:

1. faster rate of diffusion of gas and nutrients

2. Nucleus has more control over the activities of the cell

3. excessive heat will radiate faster to keep the temperature of the cell constant

4. Materials and resources in the cell will be enough for all the activities of the cytoplasm

5. Smaller cells can move faster (sperm)

6. The energy generated by the mitochondria would be enough for the cell

How do cells increase SA/V ratio (important)

Flattening: Makes cells wider and thinner, increasing surface area for faster exchange. ex: RBCs are flattened discs for faster gas exchange.

Microvilli: Finger-like projections on epithelial cells that increase surface area and speed up nutrient absorption.

Invagination: Increases membrane surface area, allowing faster reactions. ex: folds of the inner mitochondria membrane increase the rate of respiration.