1.1 Introduction to cells Flashcards
(97 cards)
1
Q
When was the cell theory established?
A
1838
2
Q
What are the rules of the cell theory?
A
- Living organisms are composed of cells (one or more) – that is, cells are the building blocks of organisms.
- Cells are the smallest units of life – that is, a cell is a basic unit capable of carrying out all the functions of a living organism.
- Cells come from pre-existing cells (omni cellulae e cellula) – that is, cells do not show spontaneous generation.
3
Q
Examples of atypical cells
A
- Striated muscle cell
- Giant algae: Acetabularia
- Aseptate fungal hyphae
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Q
Striated muscle cell
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- Striated muscle tissue is composed of repeated units called sarcomeres.
- These show a characteristic striped (striated) pattern when viewed under the microscope.
- This challenges the idea that a cell has one nucleus, as the muscle cell (fiber) has more than one nucleus per cell.
- That is, each cell is multinucleated.
- Additionally, the average muscle fiber cell is about 30 mm long, which is much larger than a typical cell.
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Q
Diagram of a striated muscle cell
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6
Q
Giant algae: Acetabularia
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- Acetabularia* is a genus of single-celled green algae of gigantic size, ranging from 0.5 to 10 cm in length.
- Acetabularia* consists of three easily distinguishable parts, namely: the rhizoid (which looks like small roots), the stalk, and a top umbrella made of branches that may fuse into a cap.
- As a single-celled organism, Acetabularia challenges two widely accepted notions about cells: that they must be simple in structure and small in size.
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Q
Diagram of Giant algae: Acetabularia
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Q
Aseptate fungal hyphae
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- Aseptate fungal hyphae are long threads (hyphae) with many nuclei.
- They have no dividing cell walls, called septa (singular: septum).
- The result of this is shared cytoplasm and multiple nuclei (singular: nucleus).
- This challenges the idea that a cell is a single unit as the fungal hyphae have many nuclei, are very large and possess a continuous, shared cytoplasm.
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Q
Diagram of aseptate fungal hyphae
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10
Q
Muscle cells do not fit the cell theory because ___
A
They are multinucleated and are much larger than typical cells.
11
Q
Why does Acetabularia challenge ideas about cells?
A
It is a large and complex cell.
12
Q
What are aseptate fungal hyphae?
A
Aseptate fungal hyphae are long threads (hyphae) with many nuclei, but no dividing cell walls.
13
Q
When was the electron microscope introduced?
A
In the early 1940s
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Q
1 nm (nanometre) = ___
A
10 ^-9 m
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Q
1 μm (micrometre) = ___
A
10 ^-6 m
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Q
1 mm (millimetre) = ___
A
10 ^-3 m
17
Q
Diagram showing the relative size of various cells and cellular components to better understand how they compare with each other with regards to dimension.
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18
Q
Formula to calculate magnification
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Magnification = size of drawing / actual size (scale bar)
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Q
The scale bar represents ___
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The actual size of the sample in the image.
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Q
Diagram showing the triangle used to remember how to solve for different parts of the magnification formula.
A
The actual size of the sample in the image.
21
Q
Required practical: Using microscopes to investigate stomata
A
22
Q
All living things can be classified as ___
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Unicellular (single-celled) or multicellular (many-celled) based on the number of cells that they possess.
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Q
The whole body of unicellular organisms is made up of ___
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Only one cell and hence they should be able to carry out all the life processes within this cell.
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Q
Examples of unicellular organisms
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Bacteria, archaea, protozoa, unicellular algae, and unicellular fungi.
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What are the seven life functions?
1. Metabolism
2. Growth
3. Response (to a stimulus)
4. Homeostasis
5. Nutrition
6. Reproduction
7. Excretion
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What is metabolism?
The regular set of life-supporting chemical reactions that take place within the cells of living organisms.
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What is growth?
An increase in size or shape that occurs over a period of time.
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What is response (to a stimulus)?
A reaction by the living organism to changes in the external environment.
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What is homeostasis?
The maintenance of a constant internal environment by regulating internal cell conditions.
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What is nutrition?
- The intake of nutrients, which may take different forms in different organisms.
- Nutrition in plants involves making organic molecules (during photosynthesis), while nutrition in animals and fungi involves the absorption of organic matter.
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What is reproduction?
The production of offspring, either sexually or asexually, to pass on genetic information to the next generation.
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What is excretion?
The removal of waste products of metabolism and other unimportant materials from an organism.
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Viruses
- A single living cell is capable of carrying out all life functions.
- In contrast, a virus is a non-living example because it cannot carry out all the processes of life.
- A virus has a protein coat and, like living organisms, has genetic material (DNA or RNA).
- However, viruses do not metabolize or reproduce – this function is carried out by the infected host cell.
- Because they exhibit no properties of life outside the host cell and do not have a cellular structure, viruses are not regarded as living entities.
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Paramecium
***-Paramecium*** is a genus (group) of unicellular protozoa.
- Paramecia are usually less than 0.25 mm in size and are widespread in aquatic environments, particularly in stagnant ponds.
- They are **heterotrophs**, feeding on food particles they encounter in their environment.
- They can move in all directions using their **cilia**, small hair-like structures, that cover the whole body and beat rhythmically to propel the cell in a given direction.
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Diagram of a paramecium
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Chlamydomonas
- A genus of unicellular green algae (Chlorophyta) distributed all over the world, in soil, freshwater, oceans, and even in the snow on mountaintops.
- The algae in this genus range in size from 10 to 30 µm in diameter and have a cell wall, a chloroplast, an 'eye' that detects light, as well as two **flagella** (whip-like structures), which they use to swim using a breaststroke-type motion.
* -Chlamydomonas* are autotrophs; they can manufacture their own food using their large chloroplast to photosynthesise.
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Diagram of chlamydomonas
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What do *Paramecium* and *Chlamydomonas* exemplify?
How unicellular organisms carry out all the life processes within the one cell that makes up their whole body.
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Metabolism in a Paramecium
Most metabolic reactions are catalysed by enzymes and take place in the cytoplasm.
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Growth in a paramecium
As it consumes food, the *Paramecium* enlarges. Once it reaches a certain size it will divide into two daughter cells.
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Response in a paramecium
The wave action of the beating cilia helps to propel *Paramecium* in response to changes in the environment, e.g. towards warmer water and away from cool temperatures.
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Homeostasis in a paramecium
- A constant internal environment is maintained by collecting excess water in the contractile vacuoles and then expelling it through the plasma membrane.
- This process is called **osmoregulation** and helps *Paramecium* and *Chlamydomonas* to maintain their water balance.
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Nutrition in a paramecium
* -Paramecium* is a heterotroph.
- It engulfs food particles in vacuoles where digestion takes place.
- The soluble products are then absorbed into the cytoplasm of the cell. It feeds on microorganisms, such as bacteria, algae, and yeasts.
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Reproduction in a paramecium
- It can carry out both sexual and asexual reproduction, though the latter is more common.
- The cell divides into two daughter cells in a process called **binary fission** (asexual reproduction).
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Excretion in a paramecium
- Digested nutrients from the food vacuoles pass into the cytoplasm, and the vacuole shrinks.
- When the vacuole, with its fully digested contents, reaches the Paramecium's **anal pore**, it ruptures, expelling its waste contents to the environment.
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Metabolism in a Chlamydomonas
Most metabolic reactions are catalyzed by enzymes and take place in the cytoplasm.
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Growth in a Chlamydomonas
- Production of organic molecules during photosynthesis and absorption of minerals causes the organism to increase in size.
- Once it reaches a certain size it will divide into two daughter cells.
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Response in a chlamydomonas
*Chlamydomonas* senses light changes in its environment using its eye spot and then uses its flagella to move towards a brighter region to increase the rate of photosynthesis.
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Homeostasis in a Chlamydomonas
- A constant internal environment is maintained by collecting excess water in the contractile vacuoles and then expelling it through the plasma membrane.
- This process is called **osmoregulation** and helps *Paramecium* and *Chlamydomonas* to maintain their water balance.
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Nutrition in a Chlamydomonas
*Chlamydomonas* is an autotroph; it uses its large chloroplast to carry out photosynthesis to produce its own food.
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Reproduction in a Chlamydomonas
- It can carry out both sexual and asexual reproduction.
- When *Chlamydomonas* reaches a certain size, each cell reproduces, either by binary fission or sexual reproduction.
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Excretion in a Chlamydomonas
It uses the whole surface of its plasma membrane to excrete its waste products.
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What is a heterotroph?
An organism that feeds by taking in organic substances (usually other living things).
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What is an autotroph?
An organism that can produce its own food from inorganic sources.
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What characteristic of life is carried out by III?
Homeostasis
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Why does surface area to volume ratio matter in a cell?
- To survive, a cell needs to import molecules and expel waste products through its plasma membrane.
- If a cell's surface area is too small compared to its volume, not enough of the necessary molecules can get in, and not enough waste (including heat) can get out.
- By dividing into two smaller cells, a larger surface area to volume (SA:V) ratio is restored.
- Therefore, the surface area to volume ratio limits the overall size of a cell.
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Example of an adaptation of a cell or organism to increase surface area for exchange of materials
- In the digestive system, the small intestine has small folds that increase the surface area exposed to the digested food.
- These folds are called *villi* and are where nutrients are absorbed in the body.
- The villi increase the surface area and allow more absorption to take place.
- Additionally, the cells making up the villi have *microvilli*, which are small folds on their cell membranes that increase the surface area even more.
- This allows nutrients to be absorbed more efficiently.
- Celiac disease is a disorder where the body’s immune system destroys the villi in the small intestine, part of a complicated response to gluten (a type of protein found in wheat) in the diet.
- The result is fewer villi and reduced surface area, and the person can suffer from malnutrition as a result of the small intestine not having enough surface area to absorb sufficient nutrients.
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Diagram showing how increased surface area relates to volume
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Table showing how surface area and volume correlate
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As a cell grows, its volume increases by \_\_\_
The power of 3 (cubed), whereas the surface area increases by the power of 2 (squared). Therefore, its surface area to volume ratio decreases.
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What is the effect of a large surface area to volume ratio in a cell for the speed of heat loss?
Heat loss occurs more quickly.
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As a cell increases in size, its small surface area to volume ratio limits the rate of exchange of materials with its surroundings. A potential solution to this problem is \_\_\_
Developing projections from the cell membrane (microvilli) to increase its surface area.
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What evolutionary steps occurred that led to the evolution of simple multicellular organisms?
1. Organisms grew larger because they were no longer limited by the size of one cell.
2. Cells in such an organism were able to specialize through **differentiation**. Differentiation is a process in which unspecialized cells develop into cells with a more distinct structure and function.
3. Multicellular organisms displayed **emergent properties**. This means that the whole organism can do more things than individual cells are capable of, because of the interaction between the different parts.
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Emergent properties in the liver
- In an organ, such as the liver, many specialized cells work together.
- The cells in the liver have many functions.
- For example, Kupffer cells break down blood cells, and hepatocytes are involved in protein synthesis, carbohydrate synthesis, and lipid synthesis.
- These functions could not efficiently be done by one type of cell.
- Cells having different functions results in emergent properties appearing, and more complex functions may be performed compared to individual cells.
- In this case, the liver has many more functions than the individual cells would have had.
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What is the genome?
The complete set of genes, chromosomes, or genetic material present in a cell or organism.
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What is cellular differentiation?
- When an unspecialized stem cell changes and carries out a specific function in the body, the process is called **cellular differentiation**.
- Cells differentiate to form different cell types due to the expression of different genes.
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What are emergent properties?
According to **emergent properties**, a complex system possesses properties that its constituent parts do not have – the whole is more than the sum of its parts.
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?
Although each cell has the same genome, only certain genes are switched on in certain cells and not in others. This gives rise to the synthesis of certain proteins, which can trigger the specialised development of that specific cell and its descendants. Hence, groups of cells differentiate along different pathways to form the different specialised tissues of the embryo. Once a cell starts to differentiate, this process cannot be reversed under normal conditions.
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The whole process of differentiation, which leads to the development of the organism, involves \_\_\_
The expression of some genes and not others in a cell’s genome.
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How do cells differentiate in multicellular organisms?
They express some of their genes some of the time, but not others.
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What is a stem cell?
An undifferentiated cell of a multicellular organism that can form more cells of the same type indefinitely, and from which certain other kinds of cells arise by differentiation.
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Characteristics of stem cells
- Stem cells are unspecialized cells that can give rise to a wide range of body cells by differentiating along different pathways.
- They retain the capacity to divide indefinitely and have the potential to differentiate into specialized cell types when given the right stimulus.
- However, not all stem cells can give rise to all body cells.
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What are the four types of stem cells?
- Totipotent
- Pluripotent
- Multipotent
- Unipotent
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Example of totipotent stem cell
The eight cells of the morula (the first cells formed following fertilisation of an egg cell)
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Example of pluripotent stem cell
Embryonic stem cells of the blastocyst
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Example of multipotent stem cell
Umbilical cord stem cells
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What are the differentiated cells produced from a totipotent stem cell?
- Can differentiate into any type of cell including placental cells.
- Can give rise to a complete organism.
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What are the differentiated cells produced from a pluripotent stem cell?
Can differentiate into all body cells, but cannot give rise to a whole organism.
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What are the differentiated cells produced from a multipotent stem cell?
Can differentiate into a few closely related types of body cells.
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What are the differentiated cells produced from a unipotent stem cell?
- Can only differentiate into their associated cell type.
- For example, liver stem cells can only make liver cells.
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What is the significance of embryos?
- These are important sources of stem cells.
- Once an egg has been fertilized, it starts to divide and forms totipotent cells during the early stages, up until the eight-cell stage of the morula.
- Theoretically, each cell can still develop into a full and normal organism.
- These cells continue to divide and develop to form the pluripotent cells of the blastocyst from which all the specialised tissues of the developing embryo are generated.
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Diagram showing how pluripotent embryonic cells differentiate to form variously specialized
tissues of various organ systems.
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Given that stem cells can divide indefinitely and can potentially give rise to various specialized cells, except for unipotent stem cells that can give rise to only one type of cell, \_\_\_
Modern medicine has identified enormous therapeutic potential for these cells. Treatment for Parkinson's disease, the growth of new transplant organs, and treatment of leukemia are a few potential uses for stem cells.
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Diagram showing the possible uses of human stem cells
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Stem cells are suitable for therapeutic use because \_\_\_
They are unspecialized cells that can give rise to a wide range of body cells by differentiating along different pathways.
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What is Stargardt's disease?
- A disease of the eye.
- It is an inherited form of juvenile macular degeneration (affects a small area near the center of the retina) that causes progressive loss of central vision.
- It is caused by a recessive genetic mutation in gene ABCA4, which causes an active transport protein on photoreceptor cells to malfunction.
- This ultimately causes the photoreceptor cells to degenerate.
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Use of stem cells in the treatment of Stargardt’s disease
- Stem-cell therapy has been shown to be effective in treating Stargardt's disease.
- Patients are given retinal cells derived from human embryonic stem cells, which are injected into the retina.
- The results obtained have been quite positive as the inserted cells attach to the retina and become functional, suggesting that it may be possible to restore sight to affected individuals using stem cells.
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What is leukemia?
- A type of cancer of the blood or bone marrow is caused by high levels of abnormal white blood cells.
- People with leukemia have a higher risk of developing infections, anemia, and bleeding.
- Leukemia is among the first diseases to have been successfully treated by using stem cells – such treatment is common nowadays.
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Use of stem cells to treat leukemia
- Treatment, in this case, involves harvesting **hematopoietic stem cells (HSCs)**, which are multipotent stem cells.
- HSCs can be taken from bone marrow, peripheral blood, or umbilical cord blood.
- The HSCs may come from either the patient or from a suitable donor.
- The patient then undergoes chemotherapy and radiotherapy to get rid of the diseased white blood cells.
- The next step involves transplanting HSCs back into the bone marrow, where they differentiate to form new healthy white blood cells.
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Arguments supporting the use of embryos for the harvest of stem cells
- Cells may be used in cell therapy (replacing bad cells with good ones) to eliminate serious diseases or disabilities in the human population.
- Transplants can be easily obtained without requiring the death of another human or inflicting any kind of pressure on normal body functioning which happens when someone donates an organ.
- The stem cells are harvested from the embryo at an early stage when the embryo has not yet developed a nervous system and thus it is not likely to feel any pain.
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Of the different sources of stem cells, ___ is the most controversial.
Harvesting from embryos
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Diagram showing how embryos are created to produce stem cells that correspond to a patient and are ultimately used to generate specialized tissues that can be transplanted into the patient.
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Ethical issues of stem cells
- Using multipotent adult tissue may be effective for certain conditions, but is limited in its scope of application
- Stem cells derived from umbilical cord blood need to be stored and preserved at cost, raising issues of availability and access
- The greatest yield of pluripotent stem cells comes from embryos but requires the destruction of a *potential* living organism
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Magnification = eyepiece lens x \_\_\_
Objective lens
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What is an advantage of electron microscopes over light microscopes?
- Electron microscopes can see details of organelles as they have much better resolution than light microscopes.
- They magnify objects more than 500,000x, whereas light microscopes can only magnify objects up to 1,000x
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What are the two main types of electron microscopes?
- Transmission electron microscope (TEM) (2D)
- Scanning electron microscope (SEM) (3D)
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What is tissue?
Groups of similar cells from the same origin with the same function.
