1.1 Introduction to cells

Question 1

Cell theory

Cell theory

Answer 1

1. Living organisms are composed of cells (or cell products)
2. The cell is the smallest unit of independent life
3. Cells can only arise from pre-existing cells

Question 2

Cell theory

Exceptions to cell theory

Answer 2

• Striated muscle – composed of fused cells that are multinucleated
• Giant algae – unicellular organisms that are very large in size (~7 cm)
• Aseptate hyphae – lack partitioning and have a continuous cytoplasm

Question 3

Functions of life

Functions of life

Answer 3

Organisms consisting of only one cell carry
out all the life functions in that single cell.
* Metabolism
* Reproduction
* Sensitivity
* Homeostasis
* Excretion
* Nutrition
* Growth

Question 4

Cell size

Cell size

Answer 4

Cells need to exchange materials with the environment in order to produce the chemical energy required for survival (via metabolism)
The rate of metabolism is a function of a cell’s mass / volume
* The rate of material exchange is a function of a cell’s surface area
As a cell grows, volume increases faster than surface area
* If metabolic requirements exceed material exchange, a cell will die
* Hence, cells must stay small or increase their SA:Vol ratio to survive

Question 5

Cell size

Small SA:Vol Ratio

Answer 5

⇧ metabolic rate
⇩ material exchange
Low survival chances

Question 6

Ccell size

Large SA:Vol Ratio

Answer 6

⇩ metabolic rate
⇧ material exchange
High survival chances

Question 7

Magnification

Calculating Magnification (MIA)

Answer 7

Magnification = Image Size ÷ Actual Size

Question 8

Magnification

Calculating Actual Size (AIM)

Answer 8

Actual Size = Image Size ÷ Magnification

Question 9

Microscopes

Light microscopes

Answer 9

Use lenses to bend light
* Can view living specimens in natural colour
* Have lower magnification and resolution

Question 10

Microscopes

Electron microscopes

Answer 10

Use electromagnets to focus electrons
* Can only view dead specimens in monochrome
* Have higher magnification and resolution
* Can show cross-sections (TEM) or surface renderings (SEM)

Question 11

Cellular Organization

In multicellular organisms

Answer 11

• Cells may be grouped together to form tissues
• Tissues may interact to form functional organs
• Organs may combine to form body systems

Question 12

Emergent Properties

What are emergent properties?

Answer 12

A function that is present in multicellular organisms, but is not present in its individual component cells.
Emergent properties arise from synergistic interactions between
the individual cells to produce entirely new aggregate functions
An example of an emergent property is the increased levels of
antibiotic resistance that can be seen in bacterial biofilms

Question 13

Stem cells

What are stem cells and what qualtites do they have?

Answer 13

Stem cells are unspecialised cells that have two key qualities:
1. Self-Renewal – They can continuously divide and replicate
2. Potency – They have the capacity to differentiate

Question 14

Stem cells

Main types of stem cells

Answer 14

Totipotent
Pluripotent
Multipotent
Unipotent

Question 15

Stem cells

Totipotent

Answer 15

Can form any cell type, as well as extra-embryonic tissue

Question 16

Stem cells

Pluripotent

Answer 16

Can form any cell type (e.g. embryonic stem cells)

Question 17

Stem cells

Multipotent

Answer 17

Can differentiate into closely related cell types

Question 18

Stem cells

Unipotent

Answer 18

Cannot differentiate, but are capable of self-renewal

Question 19

Stem cells

Stem Cell Therapy

Answer 19

Stem cells can replace damaged or diseased cells with healthy ones

Question 20

Stem cells

Therapeutic use of stem cells

Answer 20

Harvesting stem cells from appropriate sources
* Using biochemical solutions to trigger cell differentiation
* Surgically implanting new cells into patient’s own tissue
* Suppressing the host immune system to prevent rejection
* Monitoring new cells to ensure they do not become cancerous

Question 21

Stem cells

Therapeutic use of stem cells examples

Answer 21

Example → Condition → Treatment
Stargardt’s disease → Macular degeneration → Replace defective retinal cells
Parkinson’s disease → Death of nevre tissue → Replace damaged nerve cells
Lukemia → Cancer of blood →Replacement of bone marrow

Question 22

Ethics of stem cell use

Embryo

Answer 22

High growth potential (pluripotent)
Higher tumor risk
Can be generated artificially by SCNT
Requires destruction of the embryo
(results in the loss of a potential life)

Question 23

Ethics of stem cell use

Umbilical Cord Blood

Answer 23

Low growth potential Low (multipotent)
Lower tumor risk
Easily obtained and stored / preserved
Cells must be stored from birth at cost
(raises issues of financial accessibility)

Question 24

Ethics of stem cell use

Adult Tissue

Answer 24

Low growth potential(multipotent)
Lower tumor risk
Invasive to extract
May be restrictions in scope / availability

Question 25

Differentiation

Differentiation

Answer 25

All cells of an organism contain an identical genome – each cell
contains the entire set of genetic instructions for that organism

Differentiation involves the expression of some genes and not
others in the cell’s genome (i.e. selective gene expression)

The activation of different genes within a given cell will cause it
to develop differently from other cells

Question 26

Gene Packaging

Gene Packaging

Answer 26

Within the nuclei of eukaryotic cells, gene instructions
(DNA) are packaged with proteins as chromatin
* Active genes are loosely packed as euchromatin
* Inactive genes are packed tight as heterochromatin