Chapter 1: Cell Biology
Section 1 : Introduction to Cells
1.1.U1: According to cell theory, living organisms are
composed of cells
1. State the three core ideas of cell theory:
I.
All living things are composed of cells (or cell products)
II. The cell is the smallest unit of life
III. Cells may only arise from pre-existing cells
2. What evidence supports the idea that living organisms are composed of
cells?
I.
Living organisms are an individual form of life
II. Organelles are a differentiated structures within a cell, that carry out
different functions
III. Cells multiply by mitosis or meiosis
1.1.A1: Questioning the cell theory using atypical examples,
including striated muscle, giant algae and aseptate fungal
hyphae
1. For each atypical example outline how it challenges conventional cell
theory
a. Striated muscle:
 Have more than one nucleus per cell (sometimes more than 100)
 Muscle cell fibres can be very long (30mm)
 The muscle fibres are surrounded by a single plasma membrane
but they are many-nucleated
⇒ The size of the cell and the fact that it has many nuclei
doesn’t conform to the idea of cell theory that a cell has to
be small and be single-nucleated
b. Giant algae:
 Extraordinarily big
 Very simple in structure especially compared to other plant cells
 Most algae are made up of a single huge cell
⇒ Algae are gigantic in size with a simple structure, opposing
the idea that cells (the most basic unit of life) has to be
microscopic and relatively complex in structure
c. Aseptate fungal hyphae:
 A fungi is composed of thread-like structures called hyphae
 Each hypha is an uninterrupted tube-like structure with many
nuclei spread along it
⇒ In fungal hyphae the cells seem to be merged rather than
divided, thus producing a bigger single-cell, which
contradicts the parameters of a cell according to cell
theory
1.1.U2 Organisms consisting of only one cell carry out all
functions of life in that cell
1. State the functions of life as demonstrated by all living organisms
The web of all enzyme-catalysed reactions in a cell or
organism (e.g. respiration)
Metabolism
Responses
Homeostasis
Growth
Reproduction
Excretion
Nutrition
Respond to and interact with the environment
Maintenance and regulation of internal cell conditions (e.g.
water and pH levels)
Living things can grow or change size/shape
Removal of metabolic waste
Produce offspring, either sexually or asexually
Feed by either synthesis of organic molecules (e.g.
photosynthesis) or absorption of organic matter
1.1.A2 Investigation of functions of life in a Paramecium and
one named photosynthetic unicellular organism
Paramecium
 A small unicellular living organism
 Belong to the kingdom of Protista
 About 0.5mm long (unless someone has super eyesight, microscope needed to
study and view them)
 Famous for their predator-prey relationship with Didinium
 Known for their avoidance behaviour
- If given an obstacle or negative stimulus, it is capable of rotating up to
360 degrees in order to “escape
 Has an oval – slipper shape
- Rounded at the front/top
- Pointed in the back/bottom
Chlorella




A type of single-celled algae
Spherical in shape
About 2-10μm in diameter
Famous for its rapid, photosynthetic reproduction
Paramecium
Chlorella
Nutrition:
 Eats small bacteria by driving them into
the gullet though the oral groove, which
acts as a mouth (phagocytosis)
 Doesn’t make own food so has to move
around and find it
Metabolism:
 Eat to stay alive, to keep sugar and
food levels up, thus energy levels up
Response:
 Respond to food since they move
towards their prey (algae, bacteria,
etc.) and then engulf it
 Respond to negative stimuli and
obstacles by rotation up to 180 degrees
and “escaping”
 They can communicate by weak
electromagnetic radiation
 Use cilia to move
Homeostasis:
 Contractive vacuole controls water
levels and is filled with it (storing it up
for when necessary)
Growth:
 They grow and maintain different sizes
Reproduction:
 They can divide both sexually and
asexually, however they prefer asexual
reproduction, yet under stressful
conditions they can sexually
Excretion:
 Release waste through cytoplasm and
cell membrane
Nutrition:
 They are green in colour thus it can be
inferred that they use chlorophyll to
break down glucose through
photosynthesis
Metabolism:
 The food goes into the cytoplasm when
released from the chloroplast to be
broken down
Response:
 They react to light since they need light
for food, thus they move towards what
they think will give them food (sunlight)
Homeostasis:
 Water is stored in the small vacuole(s)
that look like bubbles
Growth:
 They grow and maintain different sizes
Reproduction:
 They reproduce asexually
Excretion:
 Release waste through cytoplasm and
cell membrane
1.1.U4 Multicellular organisms have properties that emerge
from the interaction of their cellular components
Emergent properties: tungsten, metal cup, wires,
glass container, etc.
Final Product: Light bulb
1. Unicellular organisms carry out the functions of life, multi-cellular
organisms differentiate and show emergent properties
a. Outline, giving two specific examples of advantages of cells
differentiating to carry out a specific function
Example 1: Rod Cell
 A rod cell is located in the retina of the eye
 It absorbs light and transmits the impulses that that light gives to
the brain (coded colour waves) thus allowing humans to see in
certain colours
Example 2: Red Blood Cells
 A red blood cell is located in the blood
 Its main job is to transport oxygen to different parts of the body
for respiration
⇒ Cell differentiation is crucial since it allows cells in a tissue to carry
out their function more efficiently since they can develop the ideal
structure, with the enzymes needed to carry out all of the chemical
reactions associated with the function.
1.1.U5 Specialized tissues can develop by cell differentiation
in multicellular organisms
1.1.U6 Differentiation involves the expression of some genes
and not others in a cell’s genome
8. All cells in an organism share the same, identical genome (i.e. they all
posses the same genetic material). In which type of cells is the entire
genome active and why?
Stem cells have the entire genome activated due to the fact that when an
animal egg is fertilized, it is very simple and has few cells, but in order to
develop into a full grown fetus the few cells must have the possibility of
differentiation in order to carry out different functions such as breathing,
moving, etc.
1.1.U7 The capacity of stem cells to divide and differentiate
along different pathways is necessary in embryonic
development and also makes stem cells suitable for
therapeutic uses
9. Describe what is ment by the term stem cells
The name stem cell was given to the zygote (a fertilized ovum) and the
cells of an early embryo, thus wanting to say that all the tissues of the adult
stem from those cells.
10. Describe how newly formed cells become specialized.
When a cell specializes, it acts out to perform a specific function with
specific genes. The genes not used are switched off, and once they are
switched off they will remain like that unless triggered by a catalyst.