Diffusion

Learning Outcomes

• Define the process of diffusion as the net movement of molecules from a region of high concentration to a region of low concentration.
• Define the process of osmosis as the net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
• Explain that osmosis is a subset of diffusion, and that osmosis is restricted to the net movement of water molecules, whilst diffusion involves the movement of any type of molecules. (Note: a partially permeable membrane does not necessarily have to be present for diffusion.)
• Explain how animal and plant cells behave differently in solutions of varying water potential.
• Appreciate the importance of diffusion and osmosis to living systems, and list examples of both processes.

Diffusion is the net movement of particles from a region of higher concentration to a region of concentration.
                         
Concentration =  amount of  a substance           --> amount -> mass (g/kg)
                           volume of a fluid (water)        volume -> cm3/ml

High concentration--> amount of substance UP
                                    volume of fluid DOWN

Low concentration--> amount of substance DOWN
                                    volume of fluid UP

WRONG example: Mom is cooking in the kitchen and you can smell the food ( NOT diffusion)

1. Is diffusion a spontaneous process (no energy required)?
 
    No, diffusion does not need energy to occur.

•  Substances tend to spread from an area where they are more concentrate to an area where they are less concentrated.
• Two or more substances can become evenly distributed (reach equilibrium) even without external interventions  

2. Why does diffusion not occur instantaneously in the living world?

    There is air in the living world, slowing down the rate of diffusion.

3. What are the factors affecting the diffusion rate?

• Temperature
• Presence of air 
• Size

Concentration Gradient

Concentration

• A measure of the amount of a substance in a specific volume 

Concentration Gradient

• The concentrating gradient between points A and B is the difference in concentration between points A and B.

Sugar molecules diffuses from point A to point B

We can say: Sugar molecules diffuses down the concentration gradient from point A to B.

• Particles diffuses down the concentration gradient
• The larger the concentration gradient, the faster the rate of diffusion.

Two types of membranes:

• Permeable membrane - Allow all substances to pass through (much large gates/holes)
• Partially permeable membrane - Allows some substances to pass through. (small gate/holes)

Application of diffusion in biology

The visking tubing encloses a solution of starch while the beaker contains iodine solution. Starch reacts with iodine to form a dark blue complex. Only the starch in the visking tubing will turn blue. 
What type of membrane is the visking tubing?

Explain.

partially permeable. Only the iodine managed to pass through the visking tubing. Starch, which has big particles, could not pass through the visking tubing.

Conclusion 

• Diffusion is an important process where substances are moved without use of energy.
• It is the net movement of particles (or molecules; or ions) from a region of higher concentration to a region of lower concentration.
• Thus the movement is down a concentration gradient.
• It is important to bear in mind that

          -The movement is random

          -The greater the concentration gradient, the faster the rate of diffusion.

Biomes

Biomes
A major ecological community of organisms adapted to a particular climatic or environmental condition on a large geographic area in which they occur.  
Biomes may be classified into:

1. Terrestrial biomes or land biomes - e.g. tundra, taiga, grasslands, savannas, deserts, tropical forests, etc. 
2. Freshwater biomes - e.g. large lakes, polar freshwaters, tropical coastal rivers, river deltas, etc. 
3. Marine biomes - e.g. continental shelf, tropical coral, kelp forest, benthic zone, pelagic zone, etc. 

 Word origin: bi: variant of bio-, esp. before a vowel + -ome: New Latin -ōma, -ōmat.

PT
Tundra Biome 
Located at latitudes 55° to 70° North, the tundra is a vast and treeless land which covers about 20% of the Earth's surface, circumnavigating the North pole. It is usually very cold, and the land is pretty stark. Almost all tundras are located in the Northern Hemisphere. Small tundra-likeareas do exist in Antarctica in the Southern Hemisphere, but because it is much colder than the Arctic, the ground is always covered with snow and ice. Conditions are not right for a true tundra to form. Average annual temperatures are -70°F (-56°C).

Ecology

Factors

oxygen salinity light

pH

-may be influenced by photosynthetic activity of aquatic plants

The more acidic a substance, the sourer it is. 

The higher the acidic, the lower the pH

7pH is neutral. 

acids --> pH1-6.9

alkali pH --> 7.1-14

Water

(neutral) --> pH7.0

Biotic Factors

Symbiosis

1.Mutualism +/+ positive! (Hermit crab)

2. Commensalism (one benefits;the other unaffected) +/0

3. Parasitism (parasite benefits and host harmed) +/- dog and fleas. worms in human body

1. competition -/- (Interspecific- a form of symbiosis) (Intraspecific-same species)

2. Predation (one feeds on the other) +/-

Producer-Primary consumer->secondary consumer->tertiary consumer-> quaternary consumer

Lab Practical 4

We had to scrub our cheek cells with a toothpick, rub it on a glass slide and place it under a microscope! After that, we placed a tiny leaf of a hydrilla plant under the microscope and here are the pictures(: It wasn't easy to take photographs, putting the camera in front of the eyepiece:0

Leaf of a hydrilla plant

Leaf of a hydrilla plant

Lab Practical 3

Lab Practical 3. First lesson learning how to use a light microscope.

Our class learnt the different types of microscopes: light microscopes(the one we used), Electron Microscope and more! We learnt how to calculate the magnification (eyepiece 10X multiplied by various objective lenses) and there were three objective lenses: scanning objective lens, low objective lens and high-power objective lens.(ascending order) Next, we learnt how to prepare a slide(which was to be put on the stage of the microscope later on).

Here are the steps:

1. Wash the glass slide thoroughly under running water. (You don't want to see thumbprints on the glass slide under the microscope!!) **You must must hold it by its sides, not the wide glass surface**

2. After you have dried all the water off the glass slide, put the substance you want to observe under the microscope.

3. For me, it was newspaper. So I had to put some water because newspaper is a solid substance. (If it is not coloured, [like cheek cells] you will have to put a drop of iodine solution or a colored liquid!)

(If it is in liquid form already, you do not need to put any any thing.)

4. Next, carefully slide the cover slip down onto the glass slide! (you don't want to see any huge air bubbles under the microscope! You will see a black line) (I had experienced this before; I saw some black dots under the microscope and mistook it for the substance.__.) To prevent any air bubbles, you will have to use a sharp object (I have been using toothpicks) to drag the cover slip along the glass slide. 

5. We have finally prepared the slide!:D

So after so many adjustments of the stage....

I came up with this wonderfully huge picture of the newspaper and the three fibered strings! (the newspaper was [] <--this size)

A tiny piece of newspaper with the letter 'S' under a microscope
The letter 'S' is upside-down and laterally inverted!

3 different coloured strings under a light microscope.
If you focus on one string, the other strings will look blur!

Drawing of Human Cheek Cells and Plant Cells

Title: Drawing of Human Cheek Cells 

Title: Drawing of Hydrilla Leaf Cells 

Complex Drawing of an Animal Cell

A Complex Drawing of an Animal Cell