quick notes for IB Biology revisions

2. Cell – the building blocks
The cell is the basic unit of life; living cells are made of
cells.
Cells  Tissue  Organ System  Organism
They are viewed using a microscope.

3. The Cell Theory
Concept Evidence
1. Living cells are made of cells Observations by microscopists
2. Cells are the smallest unit of life Discovery of viruses
Biochemical investigations of
organelles
3. Cells come from pre-existing cells Pasteur’s observation
Observation on the behaviour of cells at
division
4. Cells contain a blueprint for growth,
development and behaviour
Observations on the behaviour of
chromosomes
5. Cells are the site of the chemical
reactions of life
Discovery of enzymes
Discovery of biochemical events
Discovery of cell ultrastructure

4. The Discovery of Cell
1590
Hans and Zacharias Jansen constructed the first crude compound
microscope
1665
Robert Hooke looked at a slice of cork under a compound microscope and
discovered the cork was made up of small “boxes” that he named cells
1680
Anton von Leeuwenhoek looked at blood and pond water under a
microscope. He saw moving microscopic creatures that he named
“Animalcules.”
1824
Henri Dutrochet came to the conclusion that all living things are made of
cells. In other words, cells are the “building blocks” of life

5. The Discovery of Cell continued…
1826
Pierre Turpin observed cell division
1838
Matthias Schleiden studied plant tissue under a microscope and
discovered all plants were composed of “cells”
1839
Theodor Schwann studied animal tissue under a microscope and
found that animals were also composed of cells
Hugo von Mohl described the process of mitosis in plant cells
1855
Rudolph Virchow stated that all living cells come from other living
cells
1873
Anton Schneider observed chromosomes inside of a cell during cell
division

6. Relative Sizes of Molecules vis-à-vis Cell
Biological
Entity
Size
Molecules 1 nm
Cell
Membrane
thickness
10nm
Virus 100nm
Bacteria 1 um
Cell
Organelles
Up to 10um
Cells Up to 100 um

7. Microscopy and Magnification
Microscope – an instrument used to see objects that are too small for
the naked eye.
Compound Microscopes - are designed with a compound lens system.
Electron Microscope (EM)– use a beam of highly energetic electrons
to examine objects on a very fine scale.
Transmission EM – yields the size, shape and arrangement of the
particles which make up the specimen as well as their relationship
to each other on the scale of atomic diameters.
Scanning EM – yields the surface features of an object or "how it
looks", its texture; detectable features limited to a few manometers
Magnification - the process of enlarging the size of something, as an
optical image.
Magnification = size of image___
size of specimen

8. Cell Surface Area: Volume Ratio
Surface area - units squared (m2)
Volume – units cubed (m3)
General Principle:
As the cell gets bigger in size, the surface area:volume
ratio becomes lesser.
The rate of metabolism of a cell is a function of its mass,
whereas the rate of exchange of materials and heat energy
that metabolism generates is a function of the cell’s surface
area.
rate of metabolism : cell mass
rate of exchange of materials and heat : cell’s surface

9. Types of Cells

10. Types of Cells
Prokaryote – unicellular organisms whose cell lacks
membrane bound nucleus and organelles
ex. Bacterial cell
Eukaryote – unicellular to unicellular organisms whose cell
contain a membrane bound nucleus and organelles
ex. Animal and plant cell
N.B.
Both unicellular and multicellular organisms can do the basic
life processes.

11. Prokaryote

12. Prokaryotic Cell Structure
Prokaryotic cells are not as complex as eukaryotic cells. They have no true nucleus as the
DNA is not contained within a membrane or separated from the rest of the cell, but is
coiled up in a region of the cytoplasm called the nucleoid.
Capsule - Found in some bacterial cells, this additional outer covering protects the cell
when it is engulfed by other organisms, assists in retaining moisture, and helps the cell
adhere to surfaces and nutrients.
Cell Wall - Outer covering of most cells that protects the bacterial cell and gives it shape.
Cytoplasm - A gel-like substance composed mainly of water that also contains enzymes,
salts, cell components, and various organic molecules.
Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm and regulates
the flow of substances in and out of the cell.
Pili - Hair-like structures on the surface of the cell that attach to other bacterial cells.
Shorter pili called fimbriae help bacteria attach to surfaces.
Flagella - Long, whip-like protrusion that aids in cellular locomotion.
Ribosomes - Cell structures responsible for protein production.
Plasmids - Gene carrying, circular DNA structures that are not involved in reproduction.
Nucleiod Region - Area of the cytoplasm that contains the single bacterial DNA
molecule.

13. Eukaryote

14. Eukaryotic Cell Structure
Organelle Function
Nucleus
The “brains” of the cell, the nucleus directs cell
activities and contains genetic material called
chromosomes made of DNA.
Mitochondria Make energy out of food
Ribosomes Make protein
Golgi Apparatus Make, process and package proteins
Lysosome Contains digestive enzymes to help break food down
Endoplasmic Reticulum
Called the "intracellular highway" because it is for
transporting all sorts of items around the cell.
Vacuole
Used for storage, vacuoles usually contain water or
food. (Are you are thirsty? Perhaps your vacuoles
need some water!)
Plant cells also have:
Chloroplasts Use sunlight to create food by photosynthesis
Cell Wall For support

15. Characteristic Prokaryotes Eukaryotes
Size of cell Typically 0.2-2.0 m m in diameter Typically 10-100 m m in diameter
Nucleus No nuclear membrane or nucleoli (nucleoid) True nucleus, consisting of nuclear membrane &
nucleoli
Membrane-enclosed
organelles
Absent Present; examples include lysosomes, Golgi
complex, endoplasmic reticulum, mitochondria &
chloroplasts
Flagella Consist of two protein building blocks Complex; consist of multiple microtubules
Glycocalyx Present as a capsule or slime layer Present in some cells that lack a cell wall
Cell wall Usually present; chemically complex
(typical bacterial cell wall includes
peptidoglycan)
When present, chemically simple
Plasma membrane No carbohydrates and generally lacks
sterols
Sterols and carbohydrates that serve as
receptors present
Cytoplasm No cytosketeton or cytoplasmic streaming Cytoskeleton; cytoplasmic streaming
Ribosomes Smaller size (70S) Larger size (80S); smaller size (70S) in organelles
Chromosome (DNA)
arrangement
Single circular chromosome; lacks histones Multiple linear chromosomes with histones
Cell division Binary fission Mitosis
Sexual reproduction No meiosis; transfer of DNA fragments only
(conjugation)
Involves meiosis

16. Eukaryotic and Prokaryotic Cell Structure
Cell Structure Prokaryotic Cell Typical Animal
Eukaryotic Cell
Cell Membrane Yes Yes
Cell Wall Yes No
Centrioles No Yes
Chromosomes One long DNA
strand
Many
Cilia or Flagella Yes, simple Yes, complex
Endoplasmic Reticulum No Yes (some
exceptions)
Golgi Complex No Yes
Lysosomes No Common
Mitochondria No Yes
Nucleus No Yes
Peroxisomes No Common
Ribosomes Yes Yes