Pearson Baccalaureate Biology Standard Level 2nd Edition Print and Ebook Bundle for the IB Diploma
Complete summaries and study guides on the chapters of Pearson Baccalaureate's Biology Standard Level IB book. Detailed summaries of up to 10 pages with illustrations. These documents helped me get a good 6 in the IB exams of May 2019 :)
--> This document is on Chapter 1: Cells
Cell theory:
1. All organisms are composed of one or more cells
2. Cells are the smallest units of life
3. All cells come from pre-existing cells
Functions of life carried out by all organisms (unicellular or multicellular):
→ metabolism, reproduction, homeostasis, excretion, growth, response, nutrition
Paramecium (no chloroplasts, heterotroph = uses vacuoles for nutrition) and Chlorella (autotroph,
chloroplasts = different approach to nutrition) → different methods to fulfil functions.
Viruses, prions and viroids are not considered living organisms as they cannot carry out al
functions of life!
Light microscope: Inexpensive, simple and easy use, 200 magnification, living or dead specimen
Electron microscope: expensive, complex and lengthy use, magnification of 500’000, dead specimen
𝒔𝒊𝒛𝒆 𝒐𝒇 𝒊𝒎𝒂𝒈𝒆
Magnification: 𝒔𝒊𝒛𝒆 𝒐𝒇 𝒔𝒑𝒆𝒄𝒊𝒎𝒆𝒏
Surface area to volume ratio:
The surface of the cell controls what materials move in and out and the rate of chemical reactions is
dependent on its ratio to the surface. = limits size of cell
= More surface area = more resources in and out for each unit volume of the cell.
→ volume grows faster than surface area. (power of 3/power of 2)
→ larger cells = modifications (changes in shape = long and thin, infoldings, outfoldings)
Cell reproduction and differentiation:
Single cell → rapid reproduction → differentiation. = production of all required cell types.
= result of the expression of certain genes but not others.
Stem cells:
Some stem cells do not differentiate and thus retain their ability to transform into any type of cell. When
stem cells divide, they produce daughter stem cells. = possibility to treat human diseases
• Growing large numbers of embryonic stem cells (= pluripotent stem cells = can differentiate
into all cell types) to replace differentiated cells which have been lost due to diseases or injuries.
(Parkinson’s, Alzheimer, Diabetes) → only carried out with mice. = ethics: death of embryos
• Tissue-specific stem cells: (e.g. blood stem cells replacing damaged bone marrow of leukaemia)
Stargardt’s disease: Inherited disease; gene coding for a defect in the processing of vitamin A. → loss of
central vision. 2010: experiments to regenerate photoreceptors in the retina
1.2 The ultrastructure of cells
Prokaryotic cells: smaller and simpler (most less then 1𝜇𝑚), appeared on earth first.
→ Bacteria and Archaea
Contain: cell wall, ribosomes, plasma membrane, nucleoid (free DNA), pili and flagella
Eukaryotic cells: bigger and more complex, have transformed from prokaryotic cells, 5𝜇𝑚 − 100𝜇𝑚,
contain organelles, compertalisation. → Plants, fungi, algae, animals, protozoa, humans…
, Cell wall: Maintains shape of the cell,
composed of peptidoglycan
Plasma membrane: Controls movement of
materials into and out of cell, binary fission.
No other internal membranes.
Cytoplasm: occupies interior of cell; all
cellular processes occur within cytoplasm.
Pili and flagella: attachment + sexual
reproduction. Flagella enable movement
Ribosomes: protein synthesis, small but
numerous.
The nucleoid region: Non-compartmentalised, contains single circular thread of DNA = bacterial
chromosome. → reproduction and cell control. Some bacteria additionally contain plasmids which are not
connected to the main bacterial chromosome and replicate independently (help to adapt to unusual
circumstances).
Binary fission: DNA is copied and the two daughter chromosomes are attached to two different regions
on the plasma membrane, the cells thus divides into two genetically identical daughter cells. The decision
includes an elongation of the cell and partitioning of the newly produced DNA by microtubule-like fibres
called FtsZ.
= DNA not enclosed, free, not attached to proteins, form one circular chromosome; no
membrane-bound organelles, no membranes except plasma membrane, cell wall, division by
binary fission, small in size.
Organelles: non-cellular structures
carrying out specific functions.
→ Compartmentalization: chemical
reactions are separated (important when
chemical reactions are incompatible) =
increased efficiency; internal membranes.
Cytoplasm: Contains organelles, fluid
portion = cytosol
ER: network of tubules which is present
almost everywhere in the cell. Allows
transportation of materials. Smooth ER
does not have ribosomes on its surface.
Smooth ER: Enzymes embedded on its surface: production of membrane phospholipids and
cellular lipids, production of sex hormones, detoxification of drugs in liver, storage of calcium, release of
glucose...
Rough ER: ribosomes involved in protein synthesis, development and
transports; RER closer to nuclear membrane.
Ribosomes: No exterior membranes, carry out protein synthesis, either
free in the cytoplasm or attached to RER; composed of RNA and
protein; composed of two subunits (80S) → Ribosomes in prokaryotic
cells only amount to 70S.
Lysosomes: → mostly in animals Intracellular digestive centres arising
from Golgi apparatus; Lysosomes are sacs bound by a membrane that
contain up to 40 different enzymes. These are involved in the catalysis of
the breakdown of nutrients. Lysosomes also fuse with of organelles to
break them down and recycle their components. + breakdown of
materials brought by phagocytosis; acidic environment.
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