Topic 1.1 Introduction to Cells

Question 1

What are the three main components of the Cell Theory

Answer 1

1. cells are the building blocks of life i.e. all things are composed of cells (e.g. cell -> tissue -> organ -> organ system -> organism)
2. cells are the smallest unit of life (like unicellular organisms)
3. all cells come from pre-existing cells (zygote: from sperm and egg)

Question 2

What are the Caveats to the Cell Theory

Answer 2

1. striated muscles
2. aseptate fungal hyphae
3. giant algae

Question 3

How does the striated muscle fiber contradict the cell theory

Answer 3

The striated muscle is multi-nucleated, and consists of very long fibers (muscle cells) that are surrounded by a single membrane. It contradicts the standard view of a small single nuclei within a cell and that cells function as autonomous units

Question 4

How does the fungal aseptate hyphae contradict the cell theory

Answer 4

Fungi can contain filamentous structures called hyphae that are partitioned by septa, but some fungi are not partitioned by septa and thus have a long continuous cytoplasm. This contradicts the idea that living structures are composed of discrete cells.

Question 5

How does the giant algae contradict the cell theory

Answer 5

Some unicellular species of algae can grow to be very very large, contradicting the idea that larger organisms are made of many microscopic cells.

Question 6

What must all living things be able to do?

Answer 6

M: metabolism; undertake essential reactions
R: responsive to internal and external stimuli
H: homeostasis; maintain internal conditions
G: growth/development; living things can move and change size/shape
E: excretion; removal of waste
R: reproduction; cells can produce offspring asexually or sexually
N: nutrition; living things can exchange materials and gases with the environment

Question 7

Describe how a paramecium exhibits the functions of life:

Answer 7

Paramecium remove solid waste through and anal cavity and liquids are pumped out via a contractile vacuole (excretion), they have cilia to move around (responsiveness), feeding groove called cytostome (nutrition), asexually divide through fission or by horizontal gene transfer via conjugation, essential gases and materials enter via diffusion (homeostasis), food particles are contained in vesicles w enzymes for digestion (metabolism)

Question 8

How does a Scenedesmus exhibit the functions of life?

Answer 8

exchanges gases and other important materials via diffusion (excretion/nutrition), chlorophyll pigments enable photosynthesis (metabolism), can exist unicellularly or in a colony for protection (responsiveness), daughter cell is produced asexually

Question 9

Why must cells be so small

Answer 9

As cells grow larger, the volume (unit^3) grows faster than the surface area (unit^2), so the SA:V ratio is maximized when the cell is so small. The rate of metabolism of a cell is a function of its mass/volume, so larger cells require more energy.

Question 10

What is the importance of a large SA:V ratio

Answer 10

A large SA:V ratio is crucial for the exchange of materials across the cell membrane, and if the metabolic rate exceeds the exchange rate of materials, the cell will die. The diffusion pathways are shorter and more efficient because the cell does not need to travel so far to get out, concentration gradients are easier to generate.

Question 11

How might a large SA:V be a disadvantage for an organism

Answer 11

1. small warm-blooded mammals lose heat quickly, so we have to keep eating everyday because of our high SA:V ratio.
2. desert plants lose water quickly with flat leaves, so they minimize their SA:V ratio to conserve water.

Question 12

How are cells adapted to have larger SA:V ratios

Answer 12

1. cells divide (2 cells more efficient than 1) enabling cell differentiation and specialized functions
2. cells compartmentalize (e.g. mitochondria have a double membrane) to carryout metabolic processes
3. organs can fold up to maximize absorption e.g. small intestine absorbs food molecules (fingerlike projections), and alveoli in lungs are thin membranes to maximize surface for gas exchange or villi containing microvilli and an epithelial layer

Question 13

formula for calculating magnification

Answer 13

I (image size by ruler measured) = A (actual size) x M (magnification)

Question 14

What are emergent properties

Answer 14

• arise from the interaction of component parts (e.g. cells working together allows for so many functions to be performed)

Question 15

What is cell differentiation

Answer 15

• involves the expression of some genes but not others determined by chemical signals
• unspecialized cells mature to take on individual characteristics and become more distinct from one another (changes in shape to suit function)

Question 16

What is a stem cell

Answer 16

unspecialized cell that can divide and replicate continuously whilst maintaining the ability to differentiate into specialized cell types

Question 17

Types of stem cells

Answer 17

1. totipotent - can differentiate into any type of cell
2. pluripotent - can differentiate into most types of cells
3. multipotent - can differentiate into a few closely-related cells
4. unipotent - can regenerate but only can differentiate into the associated cell type (e.g. liver stem cells regenerate more liver cells)

Question 18

Outline the therapeutic uses of embryonic stem cells

Answer 18

Embryonic stem cells are generally extracted in the early stages after fertilization and are undifferentiated and pluripotent. The ability of ESCs to retain the ability to transform and proliferate into virtually any type of cell makes its regenerative properties very useful in repairing damaged tissues or organs in the body. These make up the bulk of an embryo as it commences development.

Question 19

Outline the therapeutic uses of adult stem cells and where they are found

Answer 19

ASCs are undifferentiated cells capable of cell division that gives rise to a limited range of cells within a tissue. These include cells in the bone marrow, brain, and liver and are naturally activated by damage in these organs where they occur.

Question 20

Ethical Implications of ASCs vs ESCs

Answer 20

ESCs are controversial because the extraction of stem cells results in the death of the embryo. There is also a chance that the patient’s body could reject the ESCs which could turn cancerous or result in tumor formation. The ASCs on the other hand would come directly from the patient’s own body eliminating the risk of tumor formation. In addition there is full consent from for cells to be extracted by the patient.

Question 21

Arguments for Therapeutic Cloning

Answer 21

• may cure serious diseases or disabilities with cell therapy
• cells are genetically identical to the parent, so the so it won’t be rejected by the body
• stem cells can be taken from embryos that would have died anyway
• stem cells can be created without need to fertilize or destroy a ‘natural’ human embryo

Question 22

Arguments Against Therapeutic Cloning

Answer 22

• creation and destruction of human embryo (‘playing God’)
• more embryos are generated, so there are excess that have to be killed
• ESCs are capable of continued division and could become tumorous

Question 23

What is an induced pluripotent cell

Answer 23

iPS cells are pluripotent stem cells that can be generated from adult cells

Question 24

How do embryonic stem cells treat Stargardt’s disease

Answer 24

Stargardt’s is the most common inherited form of juvenile macular degeneration; it is due to a mutation in the ABCA4 gene that should produce proteins to clean waste left behind, which results in macular degeneration as the photoreceptor cells die due to the buildup of a waste product (lipofuscin) causing loss of central vision and limited color perception; person will eventually be blind; bone-marrow derived or other stem cells could become specialized retinal cells to replace the missing photoreceptor cells in the macula, reversing the effected of macular degeneration.

Question 25

Therapeutic use of stem cells in treating leukemia

Answer 25

Leukemia is a type of cancer relating to the blood in which too many white blood cells are produced and cannot properly mature. The proliferation of unmatured WBC prevents the body from properly fighting off infections. Chemotherapy is used to target quickly dividing cancerous cells, but it kills other quickly dividing cells such as hair and blood cells (red and platelets). The introduction of stem cells into the bone marrow can increase the chances of curing leukemia because patients can undergo more chemotherapy to kill rapidly proliferating cells whilst being able to kill blood cells killed as collateral damage of it.