Biology IB - Cell Biology

The cell theory

1. Cells are the basic unit of life

2. All living organisms are composed of cells

3. All cells come from other cells

What are the common characteristics of cells

1. Every living cell has a membrane that seperates the inside components of the cell from the outside environment

2. Cells contain DNA or genetic material which stores all of the instructions for cell activities

3. Cell activities are often controlled using enzymes (they are chemical reactions)

4. Cells have their own energy supply

What is the smallest living creature

Cells!

How are theories developed?

Starts as trends noticed by scientists, when there is enough repition of these trends, scientists create theories. Sometimes theories are disproven, other times there are discrepancies to theories however they are not enough to disprove it.

What are 3 exceptions to cell theory?

Giant algae: unicellular but gigantic (100mm)

Aseptate fungal hyphae: no septa, contains many divisions but still operates as one cell

Striated muscle: also really big and long (30 mm)

Magnification equation

Size of image/ Actual size of specimen

What is magnification

Magnification of the optical and objective lens

Common magnifications

40x, 100x, 400x

Unicellular organisms

• One cell must do everything

• Can be more complex than the cell in unicellular organisms

• Must perform the 7 functions of lie

7 functions of life

Nutrition – obtaining food, to provide energy and the materials needed for growth.

Metabolism – chemical reactions inside the cell, including cell respiration to release energy.

Growth – an irreversible increase in size.

Response – the ability to react to changes in the environment.

Excretion – getting rid of the waste products of metabolism.

Homeostasis – keeping conditions inside the organism within tolerable limits.

Reproduction – producing offspring either sexually or asexually

They also can move (not a function of life but important)

Why is cell size limited?

• Due to the SA to V ration

• SA must be big

• As the cell gets bigger SA to V ration decreases

Why does SA to V ration need to be large?

• Metabolism occurs through the absorption of substances into cell (reactions)

• Excretion of materials from cell (removal of waste products)

• Rate of stuff depends on surface area

• Cells can only be so big before the surface area decreases too much

Why are unicellular organisms so small

To maintain a large SA to V ratio

Volvox Aureus (Orange)

• example of a unicellular organism that lives together in colonies

• resembles a multicellular organism

• consists of a ball of protein gel and many cells are attached to its surface

• cells cooperate, but are not operating together, each carry out own functions

• not a single mass, therefore not a single organism

Caenorhabditis elgans (Orange)

• a worm, multicellular

• made of exactly 959 cells

• due to this exactness, heavily studied for things about multicellular organisms

• hermaphrodite (both male and female organs)

• 1/3 of cells are neurons

• cooperative groups of cells (no leader of supervisor, such as the human brain)

What are Emergent properties?

• characteristic

What is good about cell differentiation?

• allows for a division of labour

• specialized cells emerge

• allows for efficiency

• humans have 220 different types of cells

What is the order of structures in organisms?

Cell —> tissues —> organ —> system

How does gene expression occur through cell diffrentiation?

• All cells in the body have the same 46 genes

• they express different aspects of different genes to take on different roles

• if a gene is used, it is expressed

What are stem cells?

• have special properties that make them cool

• they can divide over and over again to produce a lot of new cells

• useful for growth and replacement of damaged cells

How do stem cells relate to cell differentiation?

• they are not fully differentiated

• this is what allowed them to take on the roles that are needed

Types of stem cells and examples

• Totipotent: can support an entire new organism (embryonic chord fluid)

• Pluripotent: can form any type of cell but not a whole new organism (blastocyst, bone marrow)

• Multipotent: limited in what it can differentiate into, typically only one group of cells (chord blood, adult cells)

Stargard’s disease (orange)

• recessive mutation to the ABCA4 gene

• affects the membrane protein which is used for active transport of retina, it malfunctions

• results in degenerative vision loss

• stem cells from embryonic fluid develop into retina cells

• trials started on mouse and then after success they started with humans

Leukaemia (orange)

• many specific mutations occur resulting in cancer of the white blood cells (an abnormally large number of them)

• Chemotherapy is used to destroy the cancer,

• results in long term health effects occur as white blood cells are now destroyed

• Cue the stem cells:

  • a large needle is inserted into a large bone (pelvis) and fluid is removed from the bone marrow (before chemo)

  • stems cells are extracted from the fluid and are stored by freezing them

  • adult stem cells so they can only produce other blood cells

  • stem cells are returned to body after and re-establish themselves in the bone marrow. they multiply and start produced red and white blood cells

• this procedure often fully cures the individual of the cancer

Paramecium (orange)