1.1: Introduction to Cells

Question 1

1.1.U1 State the three parts of the cell theory

Answer 1

1. The cell is the basic unit of life (parts of cells are not themselves alive).
2. All living things are composed of cells.
3. Cells come from pre-existing cells.

Question 2

1.1.U1 Outline evidence that supports the cell theory

Answer 2

Repeated observations and experiments support the cell theory. Never observed the cell theory not to be true.
- cell parts = not alive
full cells = alive
- everything ever determined to be alive has been observed to be made of cells.
- we’ve observed cells coming from other cells but never seen spontaneous generation.

Question 3

1.1.U1 Compare the use of the term theory in daily language and scientific language

Answer 3

In daily use: it is a guess; there is doubt.
In scientific use: its been shown through repeated observations and experiments. There is little/no doubt. Nothing has been shown to not support the idea.

Question 4

1.1.U2 Outline eight functions of life

Answer 4

1. Life is made of cells. All life has a cellular structure.
2. Life maintains homeostasis. All life maintains an internal environment that is different from the external environment.
3. Life responds to stimuli. An environmental factor causes life to change behaviour or physiology.
4. Life grows and/or develops. Over time an organism will change and/or enlarge.
5. Life reproduces. Cells and/or organisms make more of themselves.
6. Life requires nutrition. Energy is needed to fuel life processes.
7. Life performs metabolism, chemical reactions of life.
8. Life excretes waste products of metabolism.

Question 5

1.1.U3 Outline the activities occurring in the volume and the surface of a cell

Answer 5

Volume: the cell volume is primarily composed of cytoplasm. Many metabolic reactions are occurring in the cytoplasm - the metabolic reactions require nutrients and may produce waste.
Surface area: the cell surface area is the cell membrane, through which nutrients and gases move into the cell and metabolic wastes leave the cell.

Question 6

1.1.U3 Calculate the volume, surface area and SA:Vol ratio of a cube

Answer 6

Volume = length*length*length
SA = length*length*6
SA:Vol = SA/Vol

Question 7

1.1.U3 Explain the benefits and limitations of using cubes to model the surface area and volume of a cell.

Answer 7

Cubes are often used to model limitations of cell size. Cubes can be manipulated, visualised and easily measured. However, cells are not cubic in shape. Cells are more difficult to manipulate and measure because of their microscopic size. Luckily the relationship between SA and volume is the same in both cubes and cells

Question 8

1.1.U3 Describe the relationship between cell size and SA:Vol ratio in the cell.

Answer 8

If cell size increases, the surface area:volume ratio decreases. This means that with larger cells, there is less surface area relative to the amount of volume.

Question 9

1.1.U3 Explain why cells are often limited in size by the SA:Vol ratio

Answer 9

Since the amount of surface area (membrane) relative to the amount of volume (cytoplasm) decreases in larger cells, the cell will not have a large enough surface area (membrane) to move nutrients into or waste out of the cell. Additionally, larger cells would require more nutrients and create more waste in the metabolic reactions occurring in the cytoplasm.

Question 10

1.1.U3 List three adaptations of cells that maximise the SA:Vol ratio

Answer 10

1. Long extensions, as in neurons
2. Thin, flattened shape, as in red blood cells
3. Microvilli, as on small intestine epithelial cells

Question 11

1.1.U4 Define and provide an example of unicellular and multicellular organisms

Answer 11

Unicellular organism: an organism composed of a single cell. For example: paramecium, amoeba and chlamydomonas
Multicellular organism: an organism composed of multiple cells. For example: a turtle, and oak tree and an eagle

Question 12

1.1.U4 Define and give examples of emergent properties

Answer 12

Emergent properties are properties/characteristics/abilities that only arise from the interaction of the component parts of a structure. For example:
heart cell - characteristics of life
heart tissue - can synchronize contractions
heart organ - can pump blood
cardiovascular system - can deliver blood throughout the body
organism - can use blood for interconnected functions

Question 13

1.1.U5 Define tissue

Answer 13

A tissue is a group of cells that specialise in the same way to perform the same function.

Question 14

1.1.U5 Outline the benefits of cell specialisation in a multicellular organism

Answer 14

By becoming specialised, cells can be more efficient in their role. They can have a specialised structure and metabolism.

Question 15

1.1.U5 Define differentiation

Answer 15

Differentiation is the development of specialised structures and functions in cells.

Question 16

1.1.U6 Describe the relationship between cell differentiation and gene expression

Answer 16

Differentiation in cells is due to different gene expression in different cell types. All cells in a multicellular organism contain the same genes, but different cells will express different genes. To express a gene means to “switch it on” so that the protein (or other gene product) is made.

Question 17

1.1.U7 Define zygote and embryo

Answer 17

Zygote: the cell that results from the sperm fertilising an egg cell.
Embryo: early stages of development after the zygote divides.

Question 18

1.1.U7 List two key properties of stem cells

Answer 18

Stem cells can divide repeatedly: useful for treatment of tissues that need to replace cells that have been killed or damaged.
Stem cells are not differentiated: they haven’t “turned off” genes so they can still differentiate to produce different cell types.

Question 19

1.1.U7 Explain why stem cells are most prevalent in early embryonic development

Answer 19

The cells of the early embryo are the most versatile. As the embryo develops, the cells gradually become more differentiated.

Question 20

1.1.U7 Contrast the characteristics of embryonic, umbilical and adult somatic stem cells

Answer 20

Embryonic Stem Cells: can differentiate into any body cell (pluripotent)
Umbilical Stem Cell: can only differentiate into blood cells (multipotent)
Adult Somatic Stem Cells: found bone marrow, skin, liver and most other body tissues; limited differentiation ability (multipotent).

Question 21

1.1.U7 Define totipotent, multipotent and pluripotent

Answer 21

Totipotent: can become any body cell, plus placenta. Zygote is totipotent.
Pluripotent: can become any body cell (but not placenta). Blastocyst is pluripotent.
Multipotent: have partially differentiated but can still become multiple, related cell types (umbilical cord stem cells and adult stem cells).

Question 22

1.1.A1 Describe features of atypical cells

Answer 22

Striated muscle fiber: long, skinny cells with many nuclei.
Giant algae: very large cells, sometimes with a single nucleus or multiple nuclei.
Fungal hyphae: long, branching single cell structures.

Question 23

1.1.A2 Describe characteristics of Paramecium that allow it to perform the functions of life

Answer 23

• made of a single cell
• contractile vacuole keeps water within homeostasis levels
• cilia move the cell in response to change in environment
• nutrients in food vacuole are used for cell growth
• nucleus can divide for cell reproduction
• heterotroph that gains nutrition by eating others
• metabolism such as cell respiration and digestion
• excretion of waste through cell membrane

Question 24

1.1.A2 Describe characteristics of Chlamydomonas that allow it to perform the functions of life

Answer 24

• made of a single cell
• contractile vacuole keeps water within homeostasis levels
• flagella move the cell in response to environment
• the cell will grow and change over time
• the nucleus can divide prior to cell reproduction
• Autotroph gains nutrition by making its own food via photosynthesis
• Photosynthesis and respiration are example metabolism of the cell
• waste products (oxygen from photosynthesis) are excreted from the cell via the cell membrane

Question 25

1.1.A3 Outline the cause and symptoms of Stargardt’s disease

Answer 25

Stargardt’s disease is a recessive genetic disease. Light detection cells of the retina degenerate so vision becomes progressively worse.

Question 26

1.1.A3 Explain how stem cells are used in the treatment of Stargardt’s disease

Answer 26

Retina cells derived from embryonic stem cells are injected into the eyes. The cells attach to the retina and improve vision without harmful side effects.

Question 27

1.1.A3 Outline the cause and symptoms of leukemia

Answer 27

Leukemia is a cancer that results from an accumulation of mutations leading to uncontrolled division of the cells that create white blood cells.

Question 28

1.1.A3 Explain how stem cells are used in the treatment of leukemia

Answer 28

The person with leukemia is given chemotherapy, which kills the cancer cells. Then, bone marrow (with its adult stem cells) is transplanted from a donor* to the person with leukemia. The stem cells establish themselves, divide and start to produce blood cells.
*ideally, the stem cells from the person with cancer can be harvested before chemotherapy and then returned to their body.

Question 29

1.1.A4 List the source and mechanism of obtaining stem cells

Answer 29

Embryonic: removed from a blastocyst inner cell mass.
Cord blood: easily obtained from the umbilical cord.
Adult: buried deep in tissues, difficult to obtain.

Question 30

1.1.A4 Discuss the benefits and drawbacks of using stem cells from different sources

Answer 30

Embryonic:
+ unlimited growth and differentiation potential
+ cells won’t have genetic mutations that accumulate with age
- risk of becoming tumourous
- kills embryos
Cord Blood:
+ easy to obtain and store
+ compatible with the adult that grows from the baby (no immune rejection)
- multipotent, so limited cell types can be created
Adult:
+ fully compatible with adult donor, so no risk of immune rejection
+ don’t have to kill embryo
- hard to obtain in the body
- multipotent, so limited cell types can be created

Question 31

1.1.NOS1 Define trend and discrepancy

Answer 31

Trend: a generalisation
Discrepancy: does not fit the general trend

Question 32

1.1.NOS1 Explain why trends and discrepancies are useful in scientific study

Answer 32

Trends: lead to the development of theories and allow for predictions of what we expect to observe.
Discrepancies: might lead to new discoveries and a deeper understanding of how the world works.

Question 33

1.1.NOS1 List features of cells that would be considered a trend

Answer 33

• All cells have a cell membrane
• All cells have genetic material
• All cells have ribosomes
• All cells have cytoplasm
• All cells have energy release system

Question 34

1.1.NOS1 List examples of cell types or organisms that are “discrepancies” to typical cells

Answer 34

Giant algae can be huge, single celled organisms with:
-single nucleus (like Acetabularia)
-multiple nuclei (like in Caulerpa)
multinucleate muscle cell
extracellular parts of organisms
-vitreous humour
-plant cell wall

Question 35

1.1.NOS2 Explain why biological research must take ethical issues into consideration

Answer 35

Biological research is a human endeavour and as such will lead to people having different opinions about what is ethical and should be permitted. The opinions must be considered while deciding what is best for the collective good.