B.2.3 SL Flashcards
Explain differentiation and gene expression in the early stages of the embryo.
Differentiation is the development of specialized structures and functions in cells. Differentiation through gene expression occurs when different cell types express different genes. Differentiation during embryonic development depends on the position of a cell within the embryo.
Gradients of signaling chemicals called morphogens impact gene expression and as a result the differentiation of a cell
The process of differentiation during embryonic development starts with morphogens signaling molecules which direct cell fate. Retinoid acid is a morphogen that plays important roles in cell growth, differentiation and organ development. Control proliferation, differentiation and patterning during embryonic development are used to orchestrate the formation of tissues and organs. It diffuses throughout the embryo switching genes on and off imparting different cell fates depending on its concentration.
State the properties of stem cells.
Stem cells are undifferentiated cells which can have two different possible outcomes:
- Divide indefinitely to create more stem cells
- Differentiate to become a specialized cell type
State the location and function of stem cell niches. Give two examples.
Adult stem cells can be found in a wide variety of tissues. They live in specific areas of each tissue called stem cell niches which revive chemical signals that interact and integrate to influence the fate of stem cell. The conditions of a niche can allow stem cells to remain undifferentiated and dormant for years. In diseases or injury the conditions of the tissue can allow the stem cells to begin differentiating if needed. Two examples are:
- Bone marrow: red blood cells, immune cells and platelets all originate from the same type of stem cell. Called hematopoietic located in the hematopoietic stem cell niche. Provides protection to the stem cells and provides the physical and chemical signals necessary for differentiation.
- Hair follicle: melanocytes and keratinocytes all originate from the same type of multipoint adult stem cell called the hair follicle stem cell. They are located in the hair follicle stem cell niche found in a bulge region of a hair follicle. Provides protection and physical and chemical signals necessary for the cells to differentiate.
State the differences between totipotent, pluripotent and multipotent stem cells.
Cells are categorized by how much potential for additional differentiation they have. They can be totipotent meaning they are entirely potential, and can become any body cell including placenta (zygote). A zygote is totipotent and the embryo is pluripotent. They can be pluripotent meaning they have many potentials, and can become any body cell but placenta (inner cell mass of a blastocyst). Pluripotent stem cells are in the shoot apical meristem (SAM) and root apical meristem (RAM). They are responsible for plant longitudinal growth Lastly they can become multipotent meaning they have multiple potentials, and have partially differentiated but can still become multiple, related cell types (adult stem cells). Fetuses have adult multipotent stem cells in niches. Adult cells aren’t only found in adult bodies. iPSC are induced pluripotent stem cells which are used to reprogram cells.
How is cell size an aspect of specialization (with examples)?
Cell specialization allows cells to perform a function with increased efficiency. Differentiation allows cells to develop into specific shapes and sizes which maximize their ability to perform their specialized function. Some examples are:
- Sperm cell: Long and narrow cells with strong flagellum. Function is to deliver DNA to an egg cell during sexual reproduction. sperm cells are adapted to reduce resistance as the cell moves towards the egg.
- Egg cell: large spherical cells (largest cell we have). Eggs store all of the materials and nutritional reserves needed for initial development of the embryo.
- Red blood cells: biconcave disk shaped cells with small width. Fit through narrow capillary vessels and maximizes their surface area to volume ratio. Don’t have a nucleus.
- White blood cells: small when inactive but increase in size during active infection. Increase in cell RER and Golgi apparatus are used to make and secrete antibody proteins.
- Cerebellum neuron cell: cell body is very small with long narrow axons. Function in the integrations of sensory information and motor activity. Very small volume of these neurons allows the brain to densely pack.
- Motor neuron cell: large cell body with long narrow axon. Allow for rapid transmission of information along the distance. Large cell body contains many organelles for the syntheses of proteins needed to transmit electrical impulses.
- Striated muscle fibre cell: long narrow cylindrical shaped cells. Long narrow dimensions of the cells allow for a greater length of contraction. The heart is a muscle we cant control directly.
Explain surface area to volume ration.
Surface area refers to the lipid bilayer of the cell membrane or the total of all faces that make up a 3D shape. Volume refers to the internal regions of the cell or the amount of space a 3D shape takes up. For the SA : V ratio we must divide the surface area by the volume. Volume increases faster than surface area in cells causing the ratio to decrease.
- This causes a problem because there stop being enough gates to manage everything coming in and out of the cell
- Smaller cells have a larger SA:V ratio -> fewer metabolic nutrients
- Large cells have a smaller SA:V ratio -> more metabolic nutrients
- As cells grow, they stop being able to sustain themselves
- Size of the cell is reduces and kept within SA:V limits
- More cells not bigger.
- Cells grow and divide
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Discuss the strengths and weaknesses of the cube model.
Cubes are used as a model to explore the SA : V ratio. This facilitates the understanding of SA : V ratio since cubes are easier to manipulate, understand and are more tangible. However, this model may have some inaccuracies such as the fact that most cells are not cubes and tend to be more spherical.
