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24 Cards in this Set

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outline cell theory

• All living organisms are composed of cells, and the products of cells (e.g. hair and scales)
• Cells are the smallest units of life
• Cells only come from pre-existing cells
discuss the evidence for cell theory
1590- The Dutch optician Zacharias Jansen invents the compound microscope. A compound microscope has 2 lenses which provide greater magnification
1665- The Englishman Robert Hooke studies cork with a compound microscope and names the structures ‘cells’
1675- Antonie van Leewenhoek another Dutchman discovers unicellular organisms
1838- Mathias Schleiden from Germany suggests that all plants were made of cells
1839- Theodor Schwann, also from Germany, suggests that all animals were also made of cells
unicellular organisms carry out all functions of life, what are they?
• metabolism which includes respiration and excretion
• response to stimuli: this is also known as sensitivity
• growth includes both in cell size and number
• reproduction, whether sexual or asexual
• homeostasis which means maintaining relatively stable conditions inside the body
• nutrition which means the source of food
what is the approximate size of a Eukaryotic cell?
10 - 100µm
what is the approximate size of a Prokaryotic cell?
1 - 5µm

what is the approximate size of a Nucleus?

10 - 20µm
what is the approximate size of a Chloroplast?
2 - 10µm
what is the approximate size of a Mitochondrion?
0.5 - 5µm
what is the approximate size of
Bacteria?
1 - 4µm
what is the approximate size of a large virus? (HIV)
100nm
what is the approximate size of a Ribosome?
25nm
what is the approximate size of a cell membrane?
7.5nm thick
what is the approximate size of a DNA Double Helix?
2.5nm diamater
what is the approximate size of a Hydrogen Atom?
0.1nm
what is the equation used to calculate the real size of an image?
magnified size ÷ magnification
explain the importance of the surface area to volume ratio as a factor limiting cell size
The size of a cell is limited by its need to exchange materials with its environment. If a cell becomes too large, its diffusion distances becomes too long to be efficient and its surface to volume ration becomes too small to allow for the necessary exchange.
how can organisms deal with the problem of the surface area to volume ratio?
By protruding extensions, or by flattening the cell. (e.g. a circulatory system - blood carries materials round the body, reducing the diffusion distance).
multicellular organisms show emergent properties, but what does this mean?
Emergent properties are those where the whole is more than the sum of their parts. This is caused by the fact that cells interact, allowing them to perform tasks together that they would not achieve, even in part, if they were alone
Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.
Cells differentiate by expression of some of their genes but not others. The genes which are not expressed by the cell, remain present in the nucleus but are packed away so tightly that they cannot be accessed.
Euchromatin is light grey when viewed with an EM and often represents the genes that are used (transcribed), Heterochromatin is dark grey and tends to contain the inactive genes.
Cells affect each other. The differentiation of any one cell is determined by the cell's position relative to others and by chemical gradients.
How are stem cells different from normal cells?
1. Stem cells are undifferentiated. This means that they have not yet specialised into a certain type of cell, as a result all (or most) of their genes can still be expressed.
2. Stem cells are self-sustaining. They can divide and replicate for long periods of time.
What are totipotent stem sells?
Cells that can become any type of cell (e.g. embryo)
What are pluripotent stem cells?
Cells that can become almost any type of tissue (e.g. blastocyst)

What are multipotent stem cells?

Cells that can become a limited number of other particular types of cells (e.g. bone marrow)
Outline a therapeutic use of stem cells.
1. Also known as cell therapy, the most common example is a bone marrow transplant, which has been used for more than 40 years. Cells in the bone marrow produce blood cells, and people with leukemia can receive a transplant of healthy, functioning bone marrow which may cure their disease.
2. Cell therapy is also used in experiments to graft new skin cells for people who have been severely burned.
3. Used to grow new corneas for people whose eyesight is failing.