UNIT 1.1

Question 1

What 3 things does the cell theory state?

Answer 1

All living things are composed of cells (or cell products)
The cell is the smallest unit of life
Cells can only arise from pre-existing cells

Question 2

Name 3 common caveats to the cell theory

Answer 2

Striated Muscle Fibres
Aseptate Fungal Hyphae
Giant Algae

Question 3

How is striated muscle fibre a caveat to the cell theory?

Answer 3

Muscle cells fuse to form very long fibres (>300mm).
Consequently, they have multiple nuclei despite being surrounded by a single, continuous plasma membrane.
This challenges the idea that cells always function as autonomous units.

Question 4

How is Aseptate Fungal Hyphae a caveat to the cell theory?

Answer 4

Fungi may have filamentous structures called hyphae, separated into cells by internal walls called septa.
Some fungi are not partitioned by septa & hence have a continuous cytoplasm along the length of the hyphae.
This challenges the idea that living structures are composed of discrete cells.

Question 5

How is Giant Algae a caveat to the cell theory?

Answer 5

Certain species of unicellular algae may grow to very large sizes (Acetabularia - 70mm)
Challenges the idea that larger organisms always consist of many microscopic cells.

Question 6

What are the functions of life ?

Answer 6

Metabolism – Living things undertake essential chemical reactions
Reproduction – Living things produce offspring, either sexually or asexually
Sensitivity(Response) – Living things are responsive to internal and external stimuli
Homeostasis – Living things maintain a stable internal environment
Excretion – Living things exhibit the removal of waste products
Nutrition – Living things exchange materials and gases with the environment
Growth – Living things can move and change shape or size
MR SHENG

Question 7

How does the unicellular organism Paramecium (Heterotroph) carry out the functions of life ?

Answer 7

• Surrounded by small hairs called cillia which allow it to move (Responsiveness / Growth).
• Engulf nutrients via specialised feeding groove called a cytostome (Nutrition).
• Nutrient particles are enclosed within small vacuoles containing enzymes for digestion (Metabolism).
• Solid Wastes are pumped out via contractile vacuoles (Excretion).
• Essential gases enter (e.g. O2) & exit (CO2) the cell via diffusion (Homeostasis).
• Paramecia divide asexually (fission) although horizontal gene transfer can occur via conjugation (reproduction).

Question 8

How does the unicellular organism Scenedesmus (Autotroph) carry out the functions of life ?

Answer 8

• Scenedesmus exchange gases & other essential materials via diffusion (Nutrition/Excretion/Homeostasis)
• Chlorophyll pigments allow organic molecules to be produced via photosynthesis (Metabolism).
• Daughter cells form as non-motile autospores via the internal asexual division of the parent cell (Reproduction)
• Scenedesmus may exist as unicells or form colonies for protection (Responsiveness).

Question 9

Explain how SA:VOL ratio limits cell size

Answer 9

• Metabolism requires exchange of materials with the environment.
• The rate of metabolism of a cell is a function of it’s mass/volume (larger cells need more energy).
• The rate of material exchange is a function of it’s surface area (larger membrane surface = more material movement).
• As a cell grows, volume increases faster than cell surface area, leading to decrease in SA:VOL ratio.
• If the rate of metabolism exceeds the rate of exchange of vital materials/waste, the cell will eventually die.
• Hence growing cells tend to divide in order to remain small (In order to maintain higher SA:VOL ratio.

Question 10

Provide 3 examples of how SA:VOL ratio is increased within organisms.

Answer 10

• Cells & tissues that are specialised for gas or material exchange will increase their surface area to optimise material transfer.
• Intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the SA of the inner lining.
• Alveoli within the lungs have membranous extensions called micro villi, which function to increase the total membrane surface.

Question 11

What is the formula used to calculate magnification?

Answer 11

Magnification = Image size (With Ruler) / Actual size (according to scale bar)

Question 12

What is the formula used to calculate actual size ?

Answer 12

Actual Size = Image size (With Ruler ) / Magnification

Question 13

Compare the use (Pros and Cons) O=of using light/electron microscopes

Answer 13

Light;
-Living specimens can be observed in their natural colour
-Dyes and fluorescent markers can be used to resolve specific structures.
-Far cheaper and far more accessible.
Electron Microscopes;
-Have much higher resolution and magnification than light microscopes.
-Transmission electron microscopes (TEM) can be used to create a cross section.
-Scanning Electron Microscopes (SEM) can be used to differentiate depth and form a 3D image.

Question 14

What is meant by ‘Emergent Properties’?

Answer 14

Multicellullar organisms are capable of completing functions that unicellular organisms could not undertake – this is due to the collective actions of individual cells combining to create new synergistic effects

Question 15

Explain (The process of) Cell differentiation

Answer 15

Differentiation is the process in development whereby newly formed cells become more specialised, and distinct from other cells; expressing characteristics that aid the cells purpose.
Since all cells contain an identical genome, differentiation occurs as the result of specific genes being activated by chemical signals.

Question 16

What is the difference between Heterochromatin and Euchromatin ?

Answer 16

Heterochromatin - Inactive genes: condensed form of chromatin in order to save space.
Euchromatin - Active Genes: expanded form of chromatin that is available to transcription machinery.

Question 17

What 2 characteristics make Stem Cells unique and useful ?

Answer 17

Stem cells are unspecialised, therefore;

• Capable of Self Renewal; Can continuously divide and replicate.
• Potency; Have the capability to differentiate into specialised cell types.

Question 18

What are the 4 main types of stem cell ?

Answer 18

• Totipotent; can form any cell type + extra embryonic cells (Placental) tissues. E.G. Zygote/Morula.
• Pluripotent; can form any cell type. E.G. Blastocyst.
• Multipotent; closely related cells. E.G. Haematopoeitic adult stem cells. E.G. Bone Marrow.
• Unipotent; Can not differenciate, although still capable of self renewal. E.G. Muscle stem cell.

Question 19

Explain the process of stem cell therapy

Answer 19

• Stem cells extracted from either; Blastocyst, Umbilical cord blood or Adult cell location (E.G. Bone marrow).
• Biochemical solutions used to trigger the differentiation of stem cells into desired types.
• Surgical Implantation of cells into the patient’s own tissue.
• Suppression of host immune system to prevent rejection of cells (If stem cells are from a foreign source).
• Careful monitoring of new cells to ensure they don’t become cancerous.

Question 20

Explain what Stargardt’s disease is and how stem cells are used to treat it .

Answer 20

NOTE FOR EXAM QUESTIONS THE STEM CELL TREATMENT PROCESS IS ALSO REQUIRED.
- Inherited form of juvenile macular degeneration (Vision loss to point of blindless)
-Caused by gene mutation that results in the malfunction of the retinal photoreceptor’s membrane protein (responsible for ATP), cannot receive adequate energy and thus cells degenerate.
TREATMENT
-Stem cells are injected into the eye -> Accepted -> attach to retina (replacing the dead malfunctioning cells with new functioning ones derived from blastocystic stem cells.

Question 21

Explain how Stem Cells are used to treat Leukaemia

Answer 21

Bone marrow transplants for patients who are immunocompromised as a result of chemotherapy.

• Bone marrow stem cells obtained from patient.
• Large dose of chemotherapy given to kill cancer, this also prevents bone marrow from being able to create blood cells.
• Harvested Stem cells injected into bone marrow, stem cells re-establish themselves and begin to create red and white blood cells.

Question 22

Explain the Ethical Considerations of stem cell therapy

Answer 22

• Multipotent adult tissue may be effective for certain conditions but has a limited scope of application.
• Stem Cells derived from umbilical cord blood need to be stored & preserved at a cost, raising issues of availability and access.
• Greatest Yield of pluripotent stem cells comes from embryos, and requires the destruction of a potential living organism.

Question 23

Outline Somatic Cell Nuclear Transfer (SCNT) and it’s pros and cons

Answer 23

SOMATIC CELL NUCLEAR TRANSFER (SCNT)
-Creation of embryonic clones via fusing a diploid nucleus with an enucleated egg (Therapeutic Cloning).
PRO: Indistinguishable from embryo derived cells.
CON: Involves ex vivo creation of embryos - excess embryos are created raising issues about exigency of said embryos.

Question 24

Outline Nuclear Reprogramming and it’s pros and cons.

Answer 24

NUCLEAR REPROGRAMMING
- A change is induced in the gene expression of a cell in order to transform it into a different cell type (Transdifferentiation).
PROS: The stem cells are autologous to the adult donor.
CONS: The technique uses oncogenic retroviruses & transgenes, increasing the risk of health consequences, I.E. Cancer.