Topic 1: Cell Biology

1.1 - Introduction to cells

The evolution of multicellular organisms allowed cell specialization and cell replacement.
1.5 - The origin of cells
There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today.
1.2 - Ultrastructure

Lesson 1 - Cell Theory

❏ Write out: the four points of Cell Theory until you have them memorized
According to the cell theory:
1) All living organisms are composed of cells (one or more) / Cells are the building blocks of
organisms

2) Cells are the smallest units of life / A cell is the basic unit capable of carrying out all the functions
of life

3) Cells come from pre-existing cells / Cells do not show spontaneous generation

4) All cells contain hereditary information (DNA) / Genetic information is passed on from cell to cell
during cell division

Exceptions to Cell Theory

❏ Complete: the following table of atypical cells
Describe Exceptions to Cell Theory Image
Striated muscle cells
challenges the idea that a cell has one nucleus AND is much larger
than a typical cell
● made up of contractile filaments that slide past each other
● composed of repeated units called sarcomeres
● show a characteristic striped (striated) pattern when viewed
under the microscope
● have a single surrounding membrane, but can contain
possibly 100’s of nuclei (multinucleated)
● the average muscle fibre cell is about 30 mm long

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Giant algae (Acetabularia)
challenges the idea that cells must be simple in structure AND
small in size
● Single-celled green algae of gigantic size
● Can actually grow up to approximately 1 cm
● consists of three easily distinguishable parts - the rhizoid
(which looks like small roots), the stalk and a top umbrella
made of branches that may fuse into a cap
● One would expect a cell of this size would consist of many
cells, as it would have difficulty getting rid of metabolic
waste
Fungal Cells (Aseptate hyphae)
challenges the ideas that cells have a single nuclei, have their own
cytoplasm AND are very small
● Long threads (hyphae) with many nuclei (multi-nucleated)
● Have no dividing cell walls, called septa (singular: septum)
● Result is shared cytoplasm and multiple nuclei (singular:
nucleus)
● Fungi have cell walls made out of chitin surrounding
threadlike structures called hyphae
Red Blood Cells
challenges the ideas that cells have a nuclei, reproduce themselves
to create daughter cells (mitosis)
● RBC lack a cell nucleus, cellular organelles and cannot
synthesize protein
● Created by stem cells in bone marrow
● Specialized cells shaped like biconcave disks that carry
oxygen to different tissues

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Lesson 2 - Origins of Cell Theory
❏ Outline: the general steps of the swan-neck experiment

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 ❏ Explain: the significance of swan-neck flasks under different conditions
Flask Condition Microbial Growth Significance to disprove spontaneous generation of
present/absent cells

Shape of swan neck n/a - Allowed “air” to enter & leave system
- Larger particles like dust & microbes collected in the
bend of the neck

Unboiled broth in YES - Positive Control

sealed flask - Microbes already present in broth grew/multiplied
- Broth went cloudy
* microbes must already be present

Boiled broth in NO - Negative Control

sealed flask - Microbes were killed by heat (pasteurization)
- No microbes were formed
- Any microbes from the air were trapped in curve of swan
neck
- Broth remained clear
* no spontaneous generation of microbes

Boiled broth in flask YES - Initial microbes were killed by heat (pasteurization)
with neck broken - New microbes carried to flask in air grew and multiplied
- Broth in the broken-necked flask became cloudy
* microbes come from air, not spontaneous generation

Flask of boiled broth YES - Initial microbes were killed by heat (pasteurization)
tipped after many - Any microbes from the air were trapped in curve of swan
years neck
- Broth remained clear for a long time
- Tilted flask exposed broth to microbes in curve of swan
neck
- AFTER tipping broth became cloudy
* microbes come from dust, not spontaneous generation

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Lesson 3 - Endosymbiotic Theory
❏ Outline: the four proposed stages for forming life on Earth

1. Production of simple organic molecules, such - Miller & Urey produced amino acids & other
as amino acids, fatty acids and carbohydrates, carbon compounds by passing electric charges
must be formed through a mixture of methane, hydrogen &
ammonia

2. Assembly of larger organic molecules, such as - Deep sea vents provide energy supply for carbon
phospholipids, RNA and DNA, must be compounds to form polymers
assembled from simpler molecules

3. Replication of nucleic acids must be possible - Organisms need to pass on genes & form
for reproduction enzymes

4. Development of self-contained structures - Amphipathic carbon compounds would naturally

(surrounded by membranes) have formed bilayers separating the internal &
external chemistry

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❏ Draw & Explain: how current plant cells could have evolved from ancient bacteria (using the
endosymbiotic theory)

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 - Original primitive cells were similar to current prokaryotes with free DNA & no organelles
- As cell membranes accidentally folded during endocytosis the DNA was surrounded by a nuclear
membrane
- Organelles such as vacuoles, Golgi complex & endoplasmic reticulum also formed
- Early mitochondria were probably smaller prokaryotes that were taken in by larger prokaryotes by
endocytosis
- Instead of being digested and broken down, these cells remained inside the host cells
- Cells that could carry out aerobic respiration could provide energy to their host cell
- Over time these evolved into mitochondria
- Other small prokaryotic cells that could convert light energy to chemical energy were engulfed in
a similar way and became chloroplasts and passed on sugars produced during photosynthesis to
the host cell

❏ Evidence: for the endosymbiont theory includes that both mitochondria & chloroplasts have (list
the evidence until you have it memorized)
● Have a double membrane

● Have their own genes on circular DNA (like prokaryotes)

● Have their own 70S ribosomes

● Transcribe their own DNA; use the mRNA to synthesize their own proteins

● Can only be produced by division of pre-existing chloroplast or mitochondria

Lesson 4 - Unicellular Organisms

Unicellular organisms carry out all the functions necessary for life. These can be remembered with the
pneumonic:
Mr H Gren

Metabolism all the chemical reactions (anabolic and catabolic) that occur in organisms in order for
them to maintain life
Photosynthesis & cellular respiration are examples of these

Response organisms respond to their environment

Homeostasis maintaining a stable internal environment within the cell

Growth increase in size (volume and surface area) until the cell is too large to function efficiently

Reproduction production of offspring; asexually through binary fission or mitosis produces clones,
sexually through meiosis and then mitosis produces genetic variation

Excretion elimination of waste products

Nutrition creating or synthesizing their own organic molecules or consuming organic molecules

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 Complete: the following table of how a Paramecium and Chlamydomonas carry out all seven
functions of life

Paramecium
Metabolism - Metabolic reactions catalysed by enzymes take place in the cytoplasm
- Cellular respiration in mitochondria

Response - Have cilia used for movement

Homeostasis - Contractile vacuole responsible for expelling water and waste

- The outside is composed of a stiff but elastic membrane called a pellicle, which
controls what enters and exits the cell

Growth - grows as it consumes food; when large it divides into two daughter cells

Reproduction - Cell division through binary fission

- Have a macronucleus and one or more micronuclei
- The macronucleus expresses the genes needed to carry out cell activities.
- The micronuclei contain the genetic material that is passed on asexually to the next
generation

Excretion - Excretion of waste through diffusion out the anal pore

Nutrition - Heterotrophic = Consume food through an oral groove into the mouth opening ending
up in vacuoles
- Vacuoles digest the food using enzymes, passing on the nutrients back into the
cytoplasm to be used for energy

Chlamydomonas
● Single-celled green algae

Metabolism - Metabolic reactions catalysed by enzymes take place in the

cytoplasm

Reproduction - Have a nucleus containing genetic material

- Cell division through binary fission

Homeostasis - osmoregulation maintained by cell membrane

Growth - grows as it photosynthesizes; when large it divides into two daughter cells

Response - flagella

Nutrition - Autotrophic = Produces it own food through photosynthesis

- Contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplast

Excretion - Excretion of waste through cell membrane

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Lesson 5 & 6 - Differentiation & Stem Cells
❏ Draw: a flow chart of how single cells can form specialized tissues and organ systems

❏ Brainstorm: the component parts (tissues) of each body system that allow it to have a greater
function than each part
Digestive system Mouth (teeth, tongue), esophagus, stomach, small intestine, large intestine, rectum

Respiratory system mouth/nose, trachea, bronchi, bronchioles, alveoli (lungs)

Immune system Spleen, thymus, bone marrow, lymphatic system, white blood cells (macrophages,
t-cells, b-cells)

Nervous system Brain, spinal column, vertebrae (protect/support), nerve cells

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Draw: the progression from a fertilized egg to embryonic stem cells

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 ❏ Compare: the three types of stem cells
Embryonic stem cells Umbilical Cord Stem Adult Stem Cells
Cells

Location - embryo (first 8-16 dividing - umbilical cord (saved/used - adult tissues like bone
cells) after birth marrow, liver, skin

When an egg is fertilized with Stem cells obtained from the Obtained from some adult
sperm, a zygote is formed umbilical cord, can be frozen tissue such as bone marrow
The cell divides by mitosis till and used later on in life
it is about 8-16 cells. These
are all embryonic stem cells

“potent”-cy Totipotent (first 8) can Multipotent - can Unipotent - can differentiate

differentiate into ANY cell & differentiate into closely into their associated cell type
create a complete organism related body cells

Pluripotent (blastocyst) can

differentiate into ANY type of
body cell

Advantages - almost unlimited potential to - easily obtained & stored at - less chance of malignant
become different cells birth tumours forming
- differentiate into any cell - commercial storage facilities - fully compatible with adult
type already exist host, no rejection
- less chance of genetic - genetically matched/ - does not kill donor
damage; don’t have time to compatible because cells are
accumulate mutations from adult’s own umbilical Successfully used for bone
- less chance of rejection cord marrow transplants in
- does not kill donor Leukemia patients
Can be used to regenerate
skin tissue for bad burns

Can heal diseases like Type

1 diabetes by replacing the
damaged insulin producing
beta cells

Disadvantages - Can differentiate into any - limited capacity to - difficult to obtain

cell type; have a higher risk of differentiate - less growth potential than
becoming tumour cells (naturally develop into blood embryonic cells
- genetically different from cells) - limited ability to differentiate
adult host - limited quantity of cells in compared to embryonic stem
- kills the embryo source cells

Ethical - kills the embryo - cost of long term storage - requires consent of both
Concerns - embryos can’t give consent - longevity of stem cells adults donating & receive
Biggest ethical - questions about whether stored over time stem cells
concerns involve they are alive - could be ethical concerns if
- could lead to stem cell parents grant consent on
the use of human
embryo farms behalf of their children
embryonic stem - could lead to DNA
cells manipulation, designer
organs, designer humans

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1.2 - Ultrastructure
Eukaryotes have a much more complex cell structure than prokaryotes.

Lesson 7 & 8 - Cell Ultrastructure

❏ Draw: the ultrastructure of prokaryotic and eukaryotic cells based on electron micrographs.
Prokaryotic Cells
Bacteria & Archaea (cyanobacteria)

Cell Structure Function

Cell Wall Encloses the cell, protecting it and helping to maintain its shape; prevents the cell
from bursting in hypotonic (dilute) media.

Plasma Membrane Surrounds the cell, controlling the movement of substances in and out of the cell.

Cytoplasm Medium that fills the cell and is the site of all metabolic reactions.

Pili Protein filaments on the cell wall that help in cell adhesion and in transferring of
DNA between two cells.

Flagella Much longer than pili, these are responsible for the locomotion of the organism.
Their whip-like movement propels the cell along.

70S ribosomes Are the sites of protein synthesis.

Nucleoid region Controls all the activities of the cell, as well as the reproduction of the organism.

Plasmids Small circles of DNA that carry a few genes; often these genes give the cell
antibiotic resistance and are used in creating genetically modified bacteria.

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❏ Draw: the ultrastructure of prokaryotic and eukaryotic cells based on electron micrographs.
Eukaryotic Cells
Fungi, Protists, Plant, and Animal cells

❏ Compare & Contrast: prokaryotic & eukaryotic cells

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 ❏ Recognize & Describe: the structure and function of cells from electron microscope images

Cell Structure Description & Function Ultrastructure drawing & labels

Controls the movement of substances in

and out of the cell

Plasma
Membrane

Fills the cell and holds all organelles

Contains enzymes that catalyze various

reactions

Cytoplasm

A site of cellular respiration

ATP is generated

Mitochondria

The sites of protein synthesis

Free ribosomes produce proteins used

inside the cell itself
80S
Ribosomes Ribosomes on ER produce proteins that
leave the cell

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 Controls all the activities of the cell

Regulations cell division/reproduction of

unicellular organisms
Nucleus
Surrounded by a double membrane
(nuclear membrane)

Produces ribosomes

Part of the nucleus

Nucleolus

Responsible for producing and storing

lipids, including steroids

Smooth
Endoplasmic
Reticulum

Transports the proteins produced by the

ribosomes to the Golgi apparatus
Rough
Endoplasmic These proteins are usually used outside
Reticulum of the cell

Processes and packages proteins and

lipids released in Golgi vesicles

Golgi
Apparatus

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 Vacuoles:
Helps in the osmotic balance of the cell
Vacuoles
and in the storage of substances
*plant cells
May also have functions similar to
only
lysosomes
&
Vesicles:
Vesicles
Small sacs that transport and release
substances produced by the cell
Can join/fuse with the cell membrane
Contain hydrolytic enzymes

Lysosome Play important roles in the destruction of

*animal cells microbes engulfed by white blood cells
only
Destroys old cell organelles
Protects the cell

Maintains cell shape and prevents it from

Cell Wall bursting
*plant cells
only

Contain pigments (mainly chlorophyll)

responsible for photosynthesis
Chloroplast
*plant cells Produces glucose sugar
only

Play an important role in nuclear division

by helping to establish the microtubules

Move cell organelles around cytoplasm

Microtubules &
Centrioles
*animal cells
only

Cell movement/locomotion
May have 1-2 long whip-like flagella

Cilia & Flagella May have short waving/spinning cilia all

over cell surface

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 ❏ Compare & Contrast: plant & animal cells

❏ Explain: three advantages of using an electron microscope over a light microscope (use the term
resolution in your answer)
- Electron microscopes have a much higher resolution than light microscopes
- The resolution of a light microscope is 200 nm compared to 0.1 nm for an electron
microscope (note: The higher the value, the lower the resolution)

- Two points may not be well-defined and unclear when viewed using a light microscope, but will
appear much clearer under an electron microscope
- Note: microscope resolution is the shortest distance between two separate points that can
still be distinguished as distinct objects

- An electron microscope can magnify very small objects by about 500,000 times which makes
them suitable for studying:
- small cellular structures
- disease-causing particles, such as prions (abnormally folded proteins can cause diseases)
- Viruses

Light microscope with a magnification of about 2,000 times are a useful way to study:
- Tissues in colour
- living cells and organisms in colour

Disadvantage - Electron microscopes view dead/non-living cells/objects ONLY in black & white

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❏ Draw & Annotate: each cell from the electron micrograph
Prokaryote

Pancreatic Cell

Liver cell

Leaf cell
(palisade
mesophyll)

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1.1-1.2 & 1.5 Practice Questions
BioKnowledgy Quick Quiz on Introduction to cells (1.1)
[16 marks]

1. C
[1]
2. C
[1]
3. D
[1]
4.
stem cells are undifferentiated cells;
embryo cells are stem cells;
stem cells can differentiate in many/all ways / are pluripotent/totipotent;
differentiation involves expressing some genes but not others;
stem cells can be used to repair/replace tissues/heal wounds; 3 max

5.
differentiation is development in different / specific ways;
cells carry out specialized functions / become specialized;
example of a differentiated cell in a multicellular organism;
cells have all genes / could develop in any way;
some genes are switched on / expressed but not others;
position / hormones / cell to cell signals / chemicals determine how a cell develops;
a group of differentiated cells is a tissue; 4 max

6.
Metabolism - cytoplasm contains enzymes that carry out metabolism;
Response – cilia help the paramecium move in response to a change in the environment, e.g. temperature;
Homeostasis – water content controlled by the contractile vacuole;
Growth – consumed biomass not used in other functions of life is used to increase the mass of the paramecium
(e.g. increase the number of mitochondria) until the nucleus triggers cell division;
Reproduction – cell division initiated by the nucleus/nucleus undergoes mitosis;
Excretion - plasma membrane controls (entry and) exit of substances;
Nutrition – endocytosis/enfolding of the plasma membrane is used to consume smaller organisms;
6 max

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 BioKnowledgy Quick Quiz on Cell Ultrastructure (1.2)
[17 marks]

1. C
[1]
2. C
[1]
3. D
[1]
4. D
[1]
5. D
[1]
6. (a) Both name and function required to achieve [1].
A: name: flagella/flagellum
function: used for locomotion / beats in whip-like action to propel cell;
B: name: pili/pilus
function: used for adhesion (to another cell/surface) / transfer
of genetic material (between cells);
ECF, for one mark, can be applied if both parts of the pair are reversed. 2
(b) bacterium / bacteria / prokaryote;
reason: [1 max]
as no nuclear membrane / no nucleus;
as pili present;
as no mitochondria / membrane bound organelles;
as mesosomes / small size / circular DNA;
(Do not accept naked DNA or no histone.) 2 max
Reject reasons if cell type is incorrectly identified.

7. (a) Award [1] for each structure clearly drawn and correctly labelled. Whole cells not necessary.
(plasma) membrane—single line surrounding cytoplasm;
nucleus — with a double membrane and pore(s) shown;
mitochondria(ion) — with a double membrane, the inner one folded into internal projections,
shown no larger than half the nucleus;
rough endoplasmic reticulum—multi-folded membrane with dots / small circles on surface;
Golgi apparatus—shown as a series of enclosed sacs with evidence of vesicle formation;
ribosomes — dots/small circles in cytoplasm/ribosomes on rER;
lysosome;
Award [0] if plant cell is drawn. Award [3 max] if any plant cell structure (e.g. cell wall) is present.
5 max
(b) Award [1 max] for each organelle. Mark first answer only.
(i) translation / produces polypeptides / proteins / protein synthesis;
(ii) support of ribosomes / site of protein synthesis / synthesis of
proteins for secretion / folding of polypeptides;
(iii) produces glycoproteins / processing of proteins / forms lysosomes
/ formation of vesicles (for exocytosis); 3 max

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 BioKnowledgy Quick Quiz on The origin of cells (1.5)
[17 marks]

1. D
[1]
2. C
[1]
3. A
[1]
4. (a) simple molecules must polymerize/assemble/join together into polymers/larger molecules
origin of self-replicating molecules / formation of self-replicating molecules/genetic material/hereditary
material/RNA/DNA
simple molecules must become isolated from the surroundings/enclosed in membranes/cell
membranes form
2 max

(b) Pasteur’s experiments;

Sterilised/Boiled broth;
The container was designed to not allow contamination/created a swan neck flask;
No growth occurred in the uncontaminated container
OR growth only occurred in the open container/container that allowed contamination
This proved the microbes have to come from outside the container 3 max

5. (b) simulated conditions of pre-biotic earth (in closed container);

water vapour;
mixture of ammonia, methane, hydrogen / reducing atmosphere;
sparks/electric (discharge to simulate lightning);
condenser / cooling of mixture;
obtained amino acids; 3 max

6. eukaryotes evolved from prokaryotes;

mitochondria/chloroplasts evolved from (independent) prokaryotic cells;
taken in by larger (heterotrophic) cell by endocytosis;
theory supported by characteristics of chloroplasts/mitochondria;
[2 max] for mitochondria/chloroplast characteristics:
mitochondria/chloroplasts have naked DNA;
mitochondria/chloroplasts divide/carry out fission;
mitochondria/chloroplasts have 70S ribosomes / synthezise own proteins;
mitochondria/chloroplasts have double membranes;
cristae similar to mesosomes / thylakoid have similar structures in prokaryotes;
but theory cannot be falsified as it predicts something occurring in the past;
theory does not explain the origins of cilia/flagella/linear chromosomes/meiosis;
weaker evidence that cilia/flagella evolved from attached bacteria/spirochetes; 6 max

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