IB Biology SL CELLS TOPIC 2 Revision Notes

Revision notes to syllabus framework  for Topic 2 (Cells) of IB Biology SL syllabus. 

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  • Created on: 29-03-13 23:02
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2.1.1 Outline the cell theory (2).
Outline: To give a brief account or summary.
All living things are made of cells.
Cells are the smallest unit of life.
Existing cells have come from other cells.
Stated in this way Cell Theory might be attributed to Schleiden and Schwann (1838).
Robert Hooke first coined the term 'cell' after observing the structure of cork in 1655.
The first observation of living cells was by Anton van Leeuwenhoek in 1674.
2.1.2 Discuss the evidence for the cell theory (3).
The cell theory has amassed tremendous credibility through the use of the microscope in the following:
Robert Hooke studied cork and found little tiny compartments that he called cells
Antonie van Leeuwenhoek observed the first living cells, called them 'animalcules' meaning little
Schleiden stated that plants are made of 'independent, separate beings' called cells
Schwann made a similar statement to Schleiden about animals
2.1.3 State that unicellular organisms carry out all of the functions of life
Metabolism; chemical reactions inside the cell, including cell respiration to release energy
Response; perceiving and responding to changes in the environment
Homeostasis; keeping conditions inside the organism within tolerable limits
Growth; an irreversible increase in size
Reproduction; producing offspring either sexually or asexually
Nutrition; obtaining food, to provide energy and the materials needed for growth
Defense; protection against enemies
2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells,
using the appropriate SI unit
nm = nanometer µm = micrometer
Molecules 1 nm
Thickness of membrane 10 nm
Viruses 100 nm
Bacteria 1 µm

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Organelles up to 10 µm
Most cells up to 100 µm (three dimensional nature/shape)
2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known
Magnification = measured size of object/ actual size of object
2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size.
A cell needs a large surface area in order to carry out metabolic functions (as chemical reactions
require a surface).…read more

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2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of
a prokaryote
Note the absence of membrane bound organelles
There is no true nucleus with a nuclear membrane
The ribosome's are smaller than eukaryotic cells
The slime capsule is used as a means of attachment to a surface
Only flagellate bacteria have the flagellum
Plasmids are very small circular pieces of DNA that maybe
transferred from one bacteria to another.
2.2.…read more

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The process starts with DNA replication, then separation of the two circular strands to either side of
the cell. Then cytokenesis occurs: division into two.
Each new cell has about half of the cytoplasm.
Growth restores the original size.…read more

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State three differences between plant and animal cells
No cell wall, just a plasma membrane Cell wall and plasma membrane present
No chloroplasts present Chloroplasts present in photosynthesizing cells
Vacuole not usually present Large fluid filled vacuole often present
Able to change shape, usually rounded Fixed shape. Usually quite regular.
2.3.6 Outline two roles of extracellular components
The plant wall maintains shape, prevents excess water uptake, and holds the whole plant up against the
force of gravity.…read more

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2.4.1 Draw and label a diagram to show the
structure of membranes.
2.4.2 Explain how the hydrophobic and hydrophilic
properties of phospholipids help to maintain the
structure of cell membranes.
The 'head's have large phosphate groups, thus they are hydrophilic (attract water) or polar. These
section are suited to the large water content of the tissue fluid and cytoplasm on opposite sides of
the membrane.
The fatty acid tails are noncharged, hydrophobic meaning they repel water.…read more

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Define diffusion and osmosis.
Diffusion: is the passive movement of particles from a region of higher concentration to a region of lower
concentration, as a result of the random motion of particles.
Osmosis: the passive movement of water molecules, across a partially permeable membrane, from
a region of lower solute concentration to a region of higher solute concentration.
2.4.…read more

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In exocytosis vesicles fuse with the plasma membrane. The contents of the vesicles are then expelled.
The membrane flattens out again.
2.5.…read more

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State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.
Growth, embryonic development, tissue repair and asexual reproduction involve mitosis.…read more



This is amazing! Is it for exams 2013?

Luisa Heyerdahl

You're a life saver!

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