This document is the complete summary required to pass the IB Biology Standard Level exams. It includes a detailed and comprehensive (yet concise) summary of Chapters 1-6 of the new textbook by Andrew Allott, as well as case studies you can mention during the exam, drawings and diagrams of relevant...
Cell biology
The cell theory:
1. Cells are the smallest units of life.
2. All living organisms are made of 1 or more cells
3. All cells come from pre-existing cells
Common cell features:
Membrane
Genetic information
Chemical reactions
Energy production
It was previously thought that cells spontaneously generate.
Nature of science:
Biological and generally scientific discoveries go hand in hand with technological
advancements
Looking for trends and discrepancies:
o Although most organisms conform to cell theory, there are exceptions:
1. Skeletal / striated muscles are multinucleated and too big, therefore
atypical.
2. Aseptate hypha (fungus) is a type of fungus that does not have a
septum separating its cells. That makes it multinucleated, which makes
it atypical.
3. Giant algae are abnormal in size. One cell can be up to 100mm long.
Limitation on cell size:
Cells with more surface area per unit of volume are able to move materials in and out
of the cell more efficiently. That is why it is crucial for cells to have a high surface
area to volume ratio.
The functions of life:
1. Nutrition – obtaining food to make energy (ATP) (cellular respiration)
2. Metabolism – chemical reactions inside the cell (enzymes!)
3. Growth – irreversible increase in size (cells multiply) (SA:V)
4. Response – the ability to respond to changes in the environment
5. Excretion – getting rid of metabolic waste
6. Homeostasis – keeping internal conditions within reasonable limits
7. Reproduction – producing offspring either sexually or asexually
,Identifying functions of life in unicellular organisms:
Paramecium: Chlamydomonas:
There are changes happening inside the These cells move when they come in
cell. The cell moves when coming in contact with each other (response). There
contact with another (response). Materials are multiple chlamydomonas, therefore
are moving in and out of the cell they can reproduce. Some are larger and
(excretion). some are smaller, which is evidence of
growth
Multicellular organisms:
Multicellular organisms have properties that emerge from the interaction of their
multiple components. They are called emergent properties.
o Emergent properties arise from the interaction of the component parts of a
complex structure.
Stem cells:
All cells have the same DNA as the stem cells. Cell differentiation is the reason
specialized tissues can develop. Unrequired parts of the DNA are switched off.
Types of stem cells:
o Embryonic stem cells (totipotent / omnipotent) +++
o Adult stem cells (pluripotent, though more tissue-specific) +
o Umbilical cord stem cells ++
Key properties of stem cells:
1. Stem cells can divide again and again to produce copious amounts of new
stem and tissue specific cells. They are therefore useful for the growth of
tissues or the replacement of cells that have been lost or damaged.
2. Stem cells are not fully differentiated. They can differentiate in different ways
to produce cell types.
,Two examples of diseases that can be treated by stem cell therapy:
1. Stargardt’s disease is a form of juvenile macular degeneration. Stem cells are injected into
the retina, which makes them specialise into retina cells.
2. Leukemia begins in the stem cells in the bone marrow. It is the most common cancer in
children. Stem cells can be transplanted into the patient’s bone marrow, which produces
various blood cells.
Cell size and scale
Conversion between units of length
mm μm nm
*10^3 *10^3
Viruses can infect bacteria, therefore they are smaller
I
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A M
1.2 – Cell ultrastructure
Nature of science – developments in scientific research follow improvements of apparatus.
The invention of electron microscopes led to a greater understanding of cell structure
Electron microscopes were invented at the same time around the world, in the 1930s
o Scanning electron microscopes (SEM) scan the surface of the sample and
show us its shape
o Transition electron microscopes (TEM) beam electrons through the sample,
showing us its interior.
Prokaryotic Eukaryotic
More primitive More advanced
Single circular DNA Many linear DNA molecules
Nucleus with a nuclear membrane (double
No nucleus (DNA is in nucleoid region)
layer) encloses the DNA
Small (less than 1µm ) in diameter Bigger in size
No membrane bound organelles Membrane bound organelles
70S ribosomes 80S ribosomes (bigger)
Carry functions of life
Have DNA, cell membrane, cytoplasm
, Prokaryotic cell structure
Cell wall – made up of peptidoglycan. To
protect and maintain the structure of the cell
Cell membrane – controls what comes in and
out of the cell. Plays a role in binary fission
(method in which bacteria divide)
Capsule – a polysaccharide structure,
helps prokaryotes cling to each other and to
various surfaces in their environment. Also
helps the cell survive.
Cytoplasm – jelly-like, water based – where
the chemical reactions take place
Pili (fimbriae) – hair-like structures on the outside of the cell wall. Used for attachment,
sexual reproduction
Flagella – hair-like structures that are longer than the pili that enable movement
Ribosomes – sites of protein synthesis
Nucleoid – region that contains single circular DNA. This region is involved with cell control
and reproduction
Plasmids – extra circular loops of DNA. Not required by the cell under normal circumstances
Cell division in prokaryotes
Binary fission
Simple process of asexual cell division
DNA is replicated into 2 daughter chromosomes that
move to opposite ends of the cell
The cytoplasm of the cell divides
Each of the daughter cells contains 1 copy of the
chromosome giving 2 genetically identical daughter
cells
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