1.1 Introduction to cells

Question 1

What does the cell theory state?

Answer 1

1. All living organisms are made up of cells.
2. The cell is the smallest unit of life.
3. Cells only arise from pre-existing cells.

Question 2

What are the three cell exceptions to ‘cell theory’?

Answer 2

Striated muscle tissue
Aseptate fungi
Giant algae

Question 3

Exception of ‘striated muscle tissue’

Answer 3

Much larger than most animal cells
Average length of 30mm, other human cells are less than 0.3mm in length
Can have one or many nucleus

Question 4

Exception of ‘aseptate fungi’

Answer 4

Challenges “living organisms are made of discrete cells”
Not divided up into sub-units containing a single nucleus
Fungi may have filamentous structures called hyphae, which are separated into cells by internal walls called septa
Have a continuous cytoplasm along the length of the hyphae

Question 5

Exception of ‘Giant algae’

Answer 5

Can grow to a length of as much as 10mm

Contain a single nucleus = not multicellular

Question 6

What are the functions of life that all cells carry out?

Answer 6

Metabolism
Response 
Reproduction
Growth 
Excretion
Homeostasis 
Nutrition

Question 7

Functions of life carried out by ‘Paramecium’

Answer 7

M: Produces enzymes which catalyse many different chemical reactions in cytoplasm
R: Reacts to stimuli
Reproduction: Reproduces asexually using mitosis or sexually using meiosis & gametes
G: Accumulates organic matter from its food
E: Expels waste products of metabolism (carbon dioxide)
H: Keeps internal conditions within limits (eg. expels excess water using vacuoles)
N: Ingesting & digesting organisms in vesicles

Question 8

Functions of life carried out by Chlamydomonas (photosynthetic organism)

Answer 8

M: Produces enzymes which catalyse many different chemical reactions in cytoplasm
R: Reacts to stimuli
Reproduction: Reproduces asexually using mitosis or sexually using meiosis & gametes
G: Increase in size by photosynthesis & absorption of minerals
E: Expels waste products of metabolism (oxygen)
H: Keeps internal conditions within limits (eg. expels excess water using vacuoles)
N: Produces its own food by photosynthesis

Question 9

Why is the surface area to volume ratio important in the limitation of cell size?

Answer 9

As a cell grows larger, surface area to volume ratio decreases.

• Not able to take in essential materials or excrete waste substances quickly enough
• Waste products will accumulate because they are produced (formed) more rapidly than they can be excreted
• Cells may overheat because the metabolism produces heat faster than it is lost over the cell’s surface

Question 10

Multicellular organisms

Answer 10

Multicellular organisms have emergent properties because they show properties that can only result from the interaction of many cells

Question 11

What are ‘specialised tissues/cells’?

Answer 11

cells in a tissue that can carry out their role more efficiently and can develop the ideal structure with the enzymes needed to carry out all of the chemical reactions associated with the function

Question 12

What is ‘differentiation’?

Answer 12

development of cells in different ways to carry out specific functions

• Happens because a different sequence of genes is expressed in different cell types
• Different genes are expressed in different cells in the body even though they contain same gene

Question 13

How does ‘differentiation’ work?

Answer 13

a cell uses only the genes that it needs to follow its pathway of development and other genes are unused.

Question 14

What are ‘stem cells’?

Answer 14

cells that have capacity to divide and to differentiate along different pathways into any cell types; versatile

Question 15

What are some important properties in biology and medicine?

Answer 15

can divide again and again

not fully differentiated

Question 16

What are the uses of stem cells?

Answer 16

• produce regenerated tissue
• grow whole replacement organs (therapeutic uses)
• non-therapeutic uses

Question 17

Therapeutic use of stem cells - Stargardt’s disease

Answer 17

Genetic disease of vision becoming worse that develops in children in age 6-12
Trials in humans:
1. A woman in 50 with Stargardt’s disease was treated by having 50,000 retina cells derived from embryonic stem cells injected into her eyes.
2. The cells attached to her eyes (retina) and remained for 4 months.
3. Improvement in woman’s vision and no harmful side effects.

Question 18

Therapeutic use of stem cells - Leukemia

Answer 18

Type of cancer in which abnormally large numbers of white blood cells are produced in the bone marrow
To cure leukemia: cancer cells in the bone marrow that are producing excessive numbers of white blood cells must be destroyed
1. A large needle is inserted into a large bone, usually the pelvis, and fluid is removed from the bone marrow.
2. Stem cells are extracted from the fluid and are stored by freezing them; only have the potential for producing blood cells.
3. A high dose of chemotherapy (treating the patient with chemicals that kills dividing cells) drugs is given to the patient to kill all cancer cells in the bone marrow
4. The bone marrow loses its ability to produce blood cells.
5. The stem cells are returned to the patient’s body.
6. They re-establish themselves in the bone marrow, multiply and produce red & white blood cells.

Question 19

Ethics of Therapeutic Use of Stem Cells (for)

Answer 19

embryonic stem cells:
Almost unlimited growth potential
Can differentiate into any type of cells in the body

Cord blood stem cells:
Easily obtained and stored
No rejections occur; fully compatible with the tissues of the adult that grows from the baby

adult stem cells:
No rejections occur; fully compatible with the adult’s tissue
Removal of stem cells doesn’t kill the adult from which the cells are taken

Question 20

Ethics of Therapeutic Use of Stem Cells (against)

Answer 20

embryonic stem cells:
Embryo is a human, and it’s immoral if the embryo dies as a result
More risk of becoming tumour cells than with adult stem cells

Cord blood stem cells:
Limited capacity to differentiate into different cell types
Limited quantities of stem cells from one baby’s cord

Adult stem cells
Difficult to obtain as there are very few of them and are buried in tissues
Less growth potential than embryonic stem cells