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all the information for the ib biology topic 1: cells
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Rocío Fernández 1º F IBDPBiology
1.1 cell theory
• All living things are composed of cells (or cell products)
Þ Viruses need to live inside a cell to make the vital functions (so they are not living
things)
Some cells question the cell
• The cell is the smallest unit of life theory, like the striated
Þ Organelles can’t survive alone muscle cell –which has
• Cells only arise from pre-existing cells multiple nucleus–, the
Þ Cells multiplied from division Acetabularia (giant algae) –
which is too big for a single
Þ All life evolved from simpler ancestors
cell–, or the Aseptate fungal
Þ Mitosis: genetically identical hyphae –which also has more
Þ Meiosis: haploid gametes à sex cells than one nucleus–.
Microscope practical
The size of a typical animal cell ranges from 10 to 20 µm in diameter, which is about one-fifth
of the size of the smallest particle visible to the naked eye. It was not until light microscopes
of sufficiently high magnification power became available that tissues were discovered to be
made up of individual cells.
Calculating magnification
When observing a drawing it is important to know how many times it has been magnified to
have a better idea of the actual size of the specimen. This is achieved by providing the
magnification or scale bar.
1000 nm (nanometres) = 1 µm (micrometre)
1000 µm (micrometres) = 1 mm (millimetre)
,Rocío Fernández 1º F IBDP
The formula used to calculate magnification is:
Magnification = size of drawing / actual size
The scale bar represents the actual size of the sample in the image. It can be used to work
out the magnification factor or to simply specify the actual length of any component within
the image.
Measurement
Scale bar: µm à convert ruler to µm
Example: A sperm cell has a tail 50 µm long. A student draws it 75 mm long. What
is the magnification?
Functions of life
• Metabolism: The regular set of life-supporting chemical reactions that
Mnemonic rule:
take place within the cells of living organisms. F. ex.: respiration. Mr. H. Gren
• Response: Living things can respond and interact with the environment.
F. ex.: movement
• Homeostasis: The maintenance and regulation of internal cell conditions. F. ex.: water and
pH.
• Growth: An increase in size or shape that occurs over a period of time.
• Excretion: The removal of waste products of metabolism and other unimportant materials
from an organism.
, Rocío Fernández 1º F IBDP
• Reproduction: The production of offspring, either sexually or asexually, to pass on genetic
information to the next generation.
• Nutrition: feeding by either the synthesis of organic molecules (f. ex.: photosynthesis) or
the absorption of organic matter (more common in animals).
Surface area to volume ratio
The plasma membrane is responsible for the imports and exports of the cell. Also, metabolic
reactions occur on the plasma membrane.
Surface and volume affect how the cell behaves:
A larger SA:Vol ratio means that the cell can act more efficiently, for every unit of volume that
requires nutrients or produces waste, there is more membrane to serve it (and carry out these
actions more efficiently).
• Diffusion pathways are shorter, so it takes less time and, if it is active transport, energy.
• Concentration gradients are easier to generate, which makes diffusion more efficient (it
takes less solute to represent a bigger part of the dissolution).
• To absorb more nutrients (e.g. microvilli in our intestine)
A smaller SA:Vol ratio can be better in some cases.
• To lose less heat and therefore make meals more efficient (for warm-blooded animals)
• To lose less water through flat leaves (for dessert plants)
When a cell grows, its SA:Vol ratio decreases, so at some point, the cell will divide itself to
assure a high and more efficient SA:Vol ratio.
Multicellular organisms: differentiation of cells
atoms molecules cells tissues organs sytstems organism
The different parts separately don’t mean anything, but together they are very useful
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