Osmosis in Plant Cells

Quite a long time ago, we did an experiment on osmosis in plant cells. I forgot to update my BIN!

First, we prepared a slide of a wet hydrilla leaf and observed it under a microscope.

Hydrilla leaf at 40x magnification

After that, we placed the leaf in a saline solution and waited for 15 minutes. We then put it on a slide and observed it under a microscope.

Hydrilla leaf at 40x magnification

I could tell that when the hydrilla leaf was submerged in a saline solution, its cytoplasm appeared to have shrunk away from the cell wall slightly. I learnt that this is because the water potential of the saline solution was lower compared to the cytoplasm of the cells. Thus osmosis occured and there was a nett movement of molecules from the cytoplasm across the partially permeable cell membrane into the saline solution, causing the cell to decrease in water content and volume, therefore the cytoplasm shrunk in volume, away from the rigid cell wall.

How Big Can a Cell Get? Practical Discussion

Questions on How Big Can a Cell Get? Practical:

From the data, what can you conclude about the relationship between surface area:volume ratio and the rate of diffusion of the liquid?
As the surface area:volume ratio decreases (surface area-volume fraction), the rate of diffusion of the liquid decreases.

What is the size of the largest single cell organism? Explain why there is a cap on the maximum size of a living cell.
The largest single cell organism is a type of xenophyophore (a type of protozoa related to amoebas) measure 10cm across. They were discovered at depths of 10.6km deep in the Mariana Trench.
The ratio of cell volume to cell surface affects the maximum size of a cell. If the cell is too big, it will take too long for diffusion to take place and for necessary molecules to be transported from the cytoplasm through the cellulose cell membrane to the environment and vice versa. This can be proved by the results of the experiment. As the surface area:volume ratio of the agar block decreases, the rate of diffusion of the liquid decreases.

How does the concept of surface area to volume ratio be applied to the multi cellular organism and the specialisation of cells? Name some examples in our body that support your reasoning.
If a multi cellular organism is made up of solely cells clumped together, the cells in the middle would not be able to gain access to necessary molecules and diffusion would not take place, so they would die. The surface area would not be enough for the organism to survive. For it to survive, it would need to have a channel cutting through the mass of cells, like a tube, for necessary molecules and nutrients to reach the cells in the middle, allowing diffusion of these molecules to take place. The surface area of the cells mass exposed to the molecules would increase, increasing the rate of diffusion. Another way would be to develop a circulatory system, where specialised cells could pass the necessary molecules to other cells.
An example of this would be red blood cells. Red blood cells have a large surface area to volume ratio to allow rapid diffusion of oxygen, so that they can supply oxygen to other parts of our body, forming part of the circulatory system. Another example would be lung cells which are flatter, so they have a larger surface area:volume ratio. The rate of diffusion of oxygen as we breathe in would be faster so more oxygen can be taken in by the cells.

How Big Can a Cell Get? Practical

Today we did an experiment on the rate of diffusion of cells and the pH of some common liquids.
We used red cabbage juice agar because it changes to a variety of colours when mixed with different bases and acids. My group's liquids were white vinegar, baking powder solution and 100 plus.

PART 1

The agar block was cut into 3 pieces of each size: 5 x 5 x 5mm, 5 x 5 x 20mm and 10 x 10 x 10mm.
They were then placed into 3 petri dishes containing the 3 different liquids. We took down the amount of time taken for the agar blocks to change colour completely (to the core).

Table 1

Paper towel/ Agar block	5 x 5 x 5mm	5 x 5 x 20mm	10 x 10 x 10mm
Surface area (S)	150mm^2	450mm^2	600mm^2
Volume (V)	125mm^3	500mm^3	1000mm^3
S:V ratio	6:5	9:10	3:5
Time for agar block to change colour (vinegar)	3:38 min	4:15 min	7:59 min
Time for agar block to change colour (baking powder)	11:23 min	16:30 min	27:00 min
Time for agar block to change colour (100+)	2:35 min	3:23 min	5:38 min

PART 2

We also soaked 30 x 20mm paper towel strips in the cabbage juice, left them to dry, and then introduced a few drops of each liquid onto each paper strip. Finally we poured an equal amount of each liquid into 3 test tubes and added equal volumes of cabbage juice to each of them The colour changes of the agar blocks in part 1, the paper strips and the cabbage juice were recorded.

Table 2

Materials	Colour Change	Vinegar	Baking Powder	100+
Agar	Initial Colour	Dark purple
	Final Colour	Red	Green	Light purple
Paper towel	Initial Colour	Light purple-blue
	Final Colour	Darker purple	Green	Light purple
Cabbage juice	Initial Colour	Dark purple
	Final Colour	Red	Green	Pink-purple

Taxonomy and Ecology

Basically this is what I need to know about taxonomy:

Taxonomy is the naming and classifying of organisms. A taxon is a group of organisms in a classification system.
 
Key concept:
The current tree of life has three domains (Bacteria, Archaea, Eukarya)
 
- All living things bear scientific names that use the binomial signature (two parts, reflecting its genus and species)
- Linnaeus Classification System: Seven levels (need to remember all seven: Kingdom, Phylum, Class, Order, Family, Genus, Species)
- Linnaeus taxonomy does not account for molecular evidence
- Interpret data given from this classification system
- There are six kingdoms (Animalia, Plantae, Protista, Archaea, Bacteria, Fungi) and preceding that, 3 domains
- Domain Bacteria branches into the Bacteria kingdom
- Domain Archaea branches into the Archaeal kingdom
- Domain Eukarya (all eukaryotes) branches into the Protista, Animalia, Plantae and Fungi kingdoms
- Classification of living things is a work in progress.
 
And a little bit on ecology:

- Living things cannot exist alone, there must be a relationship between them.

- Living things are adapted to the environment where they live.
- Ecology is the study of how living things interact with each other and with their environment.
- Abiotic factors (light, temperature, water) & biotic factors (organisms)

Microscopy Notes

Today we learnt about microscopes.

Parts of a microscope:
Arm: Supports the body tube and is the part that you can grasp to carry the microscope. Pick up your microscope by its arm, keeping it upright, and supporting it underneath with your free hand. Set it gently on your lab desk.
Base: Gives the microscope a firm, steady support.
Ocular lens (Eye piece): Magnifies ten times (l0x). This lens is often unattached, and thus it may fall out unless the microscope is kept upright.
Objective Lens: Magnifies the object by the factor marked on the particular lens. Low power (l0x) gives the smallest image, high power gives a large image (40x), and oil immersion gives the largest image (l00x). Sometimes a very low power scan objective (4x) replaces the oil immersion lens. *Objective lenses are always used in order: low, high, oil immersion.
Nosepiece: The revolving part to which objectives are attached. It must be firmly clicked into position when the objective is changed. Rough treatment can cause it to snap off.
Body tube: Joins the nosepiece to the ocular lens.
Stage: Supports the slide that is held onto it by stage clip, and has a hole so that light can shine up through the specimen. Always centre the specimen over this hole.
Coarse adjustment: Moves the body tube or stage up and down, depending on the design of the microscope, to approximately the right position so that the specimen is in focus. This knob is used only with the low power.
Fine adjustment: Moves the body tube (or stage) up and down to precisely the right position so that the specimen is perfectly in focus. Use it to achieve fine focus with the low power objective and for all focusing with the high power and oil immersion objectives.
Light source: Usually a small electric light beneath the stage that is controlled by a push-button light switch. Sometimes a mirror is used to reflect light from another source into the microscope.
Iris diaphragm: Regulates how much light goes through the specimen. It is controlled by a lever that is moved back and forth.
Condenser: A lens located above the diaphragm which concentrates the light before it passes through the specimen. Its position is controlled by a knob on microscopes in which it is adjustable
Letter 'e' magnified:

 

http://www.fossweb.com/delegate/ssi-foss-ucm/Contribution%20Folders/FOSS/multimedia_ms_1E/DiversityofLife/media/microscope.htm

http://www.udel.edu/biology/ketcham/microscope/scope.html

Is It Alive Practical Part 2

(continued from Is It Alive Practical Part 1)

PART 2

Criteria of living things tested: Requires water & nutrition (food)

Procedure:

• Label each separate sector of the petri dish A, B, C, D and E.
• Fold the facial cotton and line each sector with cotton.
• Pour the content of each tube in the respective sector that you have labeled. (You may need to rinse off all the substance with another 3ml of water.)
• Add more water to make sure that the cotton is thoroughly wet.
• Tape the sides of the petri dish and bring back to your class to continue with the observations.
• Write your observation every day for the next 3 days using the same table format.

Table 3

Substance	Changes Observed			Inference/ Evidence of Life
	After 10 min	After 24h	After 36h
A	Looks wet (from water)	Unchanged.	Unchanged.	Unaffected by water --> not alive
B	Has mixed with the water to form sludge. Bad odour.	Unchanged. Many small droplets found above it.	More condensation found above it.	Many small droplets + water vapour --> signs of respiration. --> alive
C	Grew larger. Appears to have absorbed water.	Grew larger.	Unchanged.	Can grow. But may just be absorbent. --> alive?

Information gathered from groupmates:

D: Grew green shoots and leaves.
E: Unchanged.
EXTRA: When E was soaked in a saline solution for 48h, it hatched into sea monkeys!

Reflection 2: What is Life?

Here are my reflections about "What is Life?" after the "Is it Alive?" experiment and reading 3 articles on What is Life.

What are some of the definitions of life used by scientists?
Trifonov said that life is self-reproduction with variables.
In his paper one of the possibilities he put forth to combine all the key terms he found was: Life is metabolizing material informational system with ability of self-reproduction with changes (evolution), which requires energy and suitable environment.
Koonin suggested that life requires replications with an error rate below the sustainability threshold.
Foong May Yeong suggested that life is an entity or property that is amenable to (natural) selection without a purpose (direction).
Some definitions by various scientists studied by Radu Popa include life is something capable of metabolism, and life has the capacity to evolve.

Why do multiple definitions of life exist?
Different scientists express the definition of life in different ways, and each definition is partially correct or has a point. It is very difficult to come up with a universally accepted definition of life, because life comes in various forms and people have different perspectives on this issue.

How difficult is it, in your opinion, to define life? What makes it so difficult?
I think it is extremely difficult to define life. As I said earlier, people have different definitions of life so it is difficult to come up with a universally accepted definition of life. In addition, there is always the possibility that somewhere in our universe, not on Earth, there are life forms that do not fit our typical descriptions of life. Therefore we will never really know if our definitions of life fit all life forms or not.

How were “living things” defined for you in Primary 3? What is good about that definition? Is it inadequate in any way? How so?

In Primary 3, "living things" were defined as things that needed air, water and food to survive. This definition is simple and easy to remember, and it is also true and relevant enough for Primary 3s. However, it is inadequate in the sense that it has exceptions and may be ambiguous. For example, the term "air" actually refers to oxygen. Furthermore not all creatures require oxygen to respire, for example yeast which uses anaerobic respiration.

 

What is your definition of life now?

After reading the articles, my definition of life is: Life is an entity that can evolve and reproduce, and requires energy to survive. (It may also require certain things to fuel the life processes that allow it to produce energy, like water).