Cell Introduction (1.1)

Question 1

Spontaneous Generation

Answer 1

The idea that certain animals, like fleas could arise (spontaneously generate) from dust or that maggots could arise from dead flesh. This theory was proposed by Aristotle and held true for 2000 years until the invention of microscopes and the work of Louis Pasteur.

Question 2

Basic Cell Theory

Answer 2

The initial theory of cells;- All organisms are made up of one or more cells. - The cell is the most basic unit of life. - All cells arise only from pre-existing cells by division.

Question 3

Modern Cell Theory

Answer 3

The updated theory of cells;- The activity of an organism depends on the total activity of its independent cells. - Energy flow (metabolism and biochemistry) occurs within cells. - Cells contain DNA in the chromosomes and RNA in the cell nucleus and cytoplasm. - All cells have basically the same chemical composition in organisms of the same species.

Question 4

Exceptions to the Cell Theory:

Answer 4

• Striated muscle which challenges the idea that a cell has one nucleus that controls its function.- Aseptate fungal hyphae which challenges the idea that a cell is a single unit.- Acetabularia, giant algae, which challenges the ideas that a cell must be simple in structure and small in size.

Question 5

MR H GREN

Answer 5

Metabolism:A web of all enzyme-catalysed reactions in a cell or organism eg. respiration.Response:Living things can respond to and interact with the environment. Homeostatis:The maintenance and regulation of internal cell conditions eg. water and pHGrowth:Living things can grow and change in size/shape.Reproduction:Organisms can produce offspring, either sexually or asexually.Excretion:The removal of metabolic waste.Nutrition:Feeding by either the synthesis of organic molecules eg. photosynthesis, or the absorption of organic matter.

Question 6

Under what microscope can a typical protist cell be observed?

Answer 6

A light microscope (magnification 400x).

Question 7

Paramecium

Answer 7

Unicellular, heterotrophic organisms. Live in marine and freshwater habitats, especially stagnant ponds/basins. 100μm in size (1mm)

Question 8

Paramecium (MR H GREN functions)

Answer 8

Metabolism: CytoplasmMost metabolic activities occur in the cytoplasm eg. respiration.Response: CiliaThe wave action of the cilia moves the paramecium in response to changes in the environment eg. towards food.Homeostasis: Contractile VacuolesFill up with water and expel this water through the plasma membrane to regulate/maintain water content in the cell.GrowthAfter consuming and assimilating biomass from food the paramecium will grow larger in size until it divides.Reproduction: Cell NucleusThe nucleus can divide. Reproduction is often asexual.Excretion: Plasma MembraneControls the entry/exit of substances, including the expulsion of metabolic waste.Nutrition: Food VacuoleStores the organisms the paramecium has consumed.

Question 9

Chlorella

Answer 9

Unicellular, autotrophic organisms. Diameter of 2-10μm in size.

Question 10

Chlorella (MR H GREN functions)

Answer 10

Metabolism: CytoplasmMost metabolic activities occur in the cytoplasm eg. respiration.Response: CiliaThe wave action of the cilia moves the paramecium in response to changes in the environment eg. towards light.Homeostasis: Contractile VacuolesFill up with water and expel this through the plasma membrane to regulate water content in the cell.GrowthAfter consuming and assimilating biomass from food the algae will grow larger in size until it divides. Reproduction: Cell NucleusThe nucleus can divide to support cell division (by mitosis).Excretion: Plasma MembraneControls the entry/exit of substances, including the expulsion of waste oxygen. Nutrition: ChloroplastPhotosynthesis occurs in the chloroplasts to provide Chlorella with nutrients/food.

Question 11

Mass/Volume (SA:Vol ratio)

Answer 11

The rate of metabolism in a cell is a function of its mass/volume. Larger cells need more energy to sustain essential functions.

Question 12

Surface Area (SA:Vol ratio)

Answer 12

The rate of material exchange in/out of a cell is a function of its surface area. A large membrane surface equates to more material movement.

Question 13

What happens when a cell grows? (SA:Vol ratio)

Answer 13

When a cell grows, its volume increases faster than its surface area, leading to a decreased SA:Vol ratio. If metabolic rate exceeds the rate of exchange of vital materials and waste (low SA:Vol ratio) the cell will eventually die. So, the cell must divide in order to maintain a viable SA:Vol ratio for survival.However, cells and tissues specialised for gas or material exchange will increase their surface area to optimise the transfer of materials. Eg. microvilli on alveoli, bioncave disc shape of red blood cells.

Question 14

Emergent Property

Answer 14

Emergent properties arise when the interaction of individual components produces new functions.

Question 15

Emergent Properties in multicellular organisms

Answer 15

• Groups of cells form tissues- Organs can then be formed from a group of multiple tissues- Organs can interact to form an organ system which carries out a specific function- Organ systems collectively carry out life functions for the entire organismEg. Muscle cells -> Cardiac tissue -> Heart -> Vascular system -> A Human

Question 16

Reductionism

Answer 16

Breaking down complex systems by isolating and studying particular aspects. Looking at the chemical reactions that occur within.

Question 17

What is Cell Differentiation?

Answer 17

Cell differentiation is the process during development where newly formed cells become more specialised. This happens because parts of their genome are activated and others inactivated to give them a specific function.

Question 18

What are active and inactive genes packaged in?

Answer 18

Active genes are packaged in an expanded form called euchromatin. Inactive genes are packaged in a condensed form called heteromatin.

Question 19

Stem Cells (Properties and Definition)

Answer 19

• The ability to self renew, to continuously divide and replicate.- Potency (The capacity to differentiate into specialised cell types)Stem cells are undifferentiated biological cells that can differentiate into specialised cells and can divide (through mitosis) to produce more stem cells.

Question 20

What are the two broad types of stem cells found in mammals?

Answer 20

• Embryonic Stem Cells (Pluripotent)- Adult Stem Cells (Multipotent)

Question 21

Totipotent Stem Cells

Answer 21

Totipotent stem cells can differentiate into any type of cell, including extra-embryonic tissue (placenta) i.e the entire genome is active.

Question 22

Pluripotent Stem Cells

Answer 22

Pluripotent stem cells are found in the blastocyst (200-300 cells). They can differentiate into many types of cells i.e some parts of their genome are inactivated.

Question 23

Multipotent Stem Cells

Answer 23

Multipotent stem cells are found in the gastrula and are already committed to the ectoderm, mesoderm or endoderm, so can only differentiate into a few closely related cell types.

Question 24

Unipotent Stem Cells

Answer 24

Unipotent stem cells can self-renew and can only differentiate into one specific cell. Eg. Liver stem cells can only make liver cells.

Question 25

Stem Cell Therapy

Answer 25

Stem cell therapy aims to replace cells damaged or destroyed by disease with healthy, functioning cells. It is used to treat diseases such as cancer, diabetes, Parkinson’s etc.

Question 26

Stargardt’s Disease

Answer 26

A recessive genetic (inherited) condition that causes progressive vision loss to the point of blindness. A genetic mutation causes active transport protein in the retinal photoreceptor cells to malfunction causing the photoreceptor cells to degenerate.Embryonic stem cells (pluripotent) are treated to differentiate into retinal cells. These retinal cells are injected into the retina and become functional, improving central vision. This stem cell therapy is still in the stage of clinical trials but is looking promising for the future.

Question 27

Leukemia

Answer 27

Cancer of the blood or bone marrow leading to high levels of poorly functioning white blood cells. Hematopoetic stem cells (multipotent) are harvested from bone marrow, peripheral blood and umbilical cord blood. Chemotherapy and radiotherapy are used to kill/destroy the diseased white blood cells. HSC’s are then transplanted into the bone marrow and differentiate into healthy white blood cells. The use of a patient’s own HSC’s means there is far less risk of immune rejection.