PROCESS OF LIFE: DIFFUSION & OSMOSIS

Diffusion:

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration.

High Concentration: amount of substance (higher), volume of fluid (low)----many particles

Low Concentration: amount of substance (low), volume of fluid (higher)-----little/few particles

Factors:

-Temperature
-Size of Particles

- Is a spontaneous process ( no input of energy requires)
- Substances tend to spread from an area where they are more concentrated to an area where they are less concentrated
- 2 or more substance can become evenly distributed (reach equilibrium)

Concentration = amount of substance (solute) / volume of fluid (solvent)

Concentration Gradient:

The concentration gradient between points A and B is change in concentration between points A and B.

Example:
Sugar molecules diffuses down the concentration gradient from point A to point B


- Particles diffuses down the concentration gradient

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

Applications of diffusion in Biology

Chemical substances must be able to move from one place to another in order to keep the living organisms alive and growing.

For example, food substances that were absorbed need to: 

• move from one cell to another

• move in & out of the cell

• move from one part of the cell to another

Permeable Membrane	Partially Permeable Membrane
Allows all substances to pass through	Allows some substnaces to pass through

Other examples of diffusion in Biology include:
 • Movement of carbon dioxide during photosynthesis
 • Movement of oxygen and carbon dioxide in animals



Key Points:
- Diffusion is an important process where substances are moved without use of energy
- It is net movement of particles from a region of higher concentration to a region of lower concentration.
- Thus the movement is down a concentration gradient. 
- The movement is random
- The greater the concentration gradient, the faster the rate of diffusion

Osmosis:

Osmosis is the net movement of water molecules down the concentration gradient through a partially permeable membrane.

Water moves freely through pores in the partially permeable membrane.

• Solute (green) too large to move across the membrane

Differences of Diffusion & Osmosis

- Diffusion: Movement of particles in general

- Can occur both in the presence and absence of a membrane

- Osmosis: Movement of water molecules only

- Water molecules move across a partially permeable membrane

Water Potential

Water Potential is a measure of the tendency of water molecules to move from one area to another.

	Concentration	Water Potential
Surrounding Area	WATER (LOW) SUGAR (LOW)	HIGH
Within Visking Tubing	WATER (LOW) SUGAR (HIGH)	LOW

Since Water Potential is a measure of the tendency of water molecules to move from one area to another, we can also define osmosis as:

The net movement of water through a selectively permeable membrane from a region of high water potential to a region of low water potential

Animal Cell:

Animal cells

• Structure is simple

• Cytoplasm is surrounded by a partially

permeable cell membrane.

- If placed in a hypertonic solution (solution has a higher concentration of solutes than the cytoplasm).

- If cell has Lower solute concentration (high water potential) while the surroundings is Higher solute concentration (low water potential), Water leaves the cell by osmosis. The cell loses volume and shrinks (crenates)<----ANIMAL ONLY! 

- Water loss only ceases if the concentration of the cytoplasm rises to that of the surrounding solution. Water molecules leaving the cells is the same as water molecules going inside the cell. 

- If placed in a hypotonic solution (solution has a lower concentration of solutes than the cytoplasm).

- If cell has Higher solute concentration (low water potential) while the surroundings is Lower solute concentration (high water potential), Water enters the cell by osmosis. Since the cell membrane cannot reist expansion, the cell eventually bursts (crtolysis)<----ANIMAL ONLY!

Plant Cell:

- Plant cells are structurally more complex.

• They are surrounded by a cellulose cell wall

which is…

– Freely permeable to water

– Not elastic

– Able to resist cell expansion

Each plant cell contain a large central vacuole which…

– contains a solution of salt, sugars and ions

– is bound by a partially permeable membrane

- Water enters the vacuole by osmosis. If placed in a hypotonic solution (solution has a lower concentration of solutes than the cytoplasm) Vacuole swells, pushing the cytoplasm against the cell wall. The inelastic cell resists expansion and the cell become turgid. It can be described in the state of turgor. Young plants (have little woody tissue), rely on turgor for support against wind and gravity. 

- Water leaves the cytoplasm and vacuole by osmosis.

If placed in a hypertonic solution (solution has a higher concentration of solutes than the cytoplasm). The cytoplasm and vacuole shrinks, pulling the cell membrane away from the cell wall. The cell is now plasmolysed or is in a state of plasmolysis. The tissue becomes flaccid.

PLASMOLYSIS VS CRENATION:

Plasmolysis: 

- shrinking of plant cell cytoplasm, and the cell membrane moves away from cell wall.

Crenation:

- shrinking of animal cell

Isotonic Solution
An isotonic solution has the same concentration of solutes as the cytoplasm.
--> No net movement of water molecules into or out of the cell ( animal & plant)
Therefore, cells neither shrinks nor expands when placed in an isotonic solution.

Water Potential:

• A measure of the tendency of water to move from one place to another.
• A dilute solution has more water molecules per unit volume than a concentrated solution, so it has a higher water potential than a concentrated solution.
• Water always moves from a solution with a higher water potential to a solution with a with a lower one, that is, down a water potential gradient.

It should be noted that the cell wall of plant cells is permeable and allows most substances to pass through. A plant cell behaves differently from an animal cell when placed in solutions with differing water potentials. This difference is due to the presence of a cell wall in plant cells.

What happens to a plant cell when placed in a solution with higher water potential?

1. When a plant cell is placed in a solution of higher water potential, the cell sap has a lower water potential than that of the solution outside the living cell.
2. By osmosis, water enters the cell through the partially permeable cell surface membrane.
3. The cell expands and becomes turgid.
4. As water enters the cell, the vacuole increases in size and pushes the protoplasm against the cell wall. The cell does not burst because it is protected by the inelastic cell wall. The turgidity of the cell with water is called turgor. The pressure exerted by the water in the vacuole on the cell wall is the turgor pressure.

What happens to a animal cell when placed in a solution with higher water potential?

1. An animal cell will swell and may even burst in a solution of higher water potential than the cytoplasm. This is because unlike plant cells, animal cells do not have a cell wall to protect it.

Turgor plays an important role in maintaining the shape of soft tissues in plants. Most leaves and young stems, especially those of herbaceous and non-woody plants, are able to remain firm and erect because of the turgor pressure within their cells. When there is a high rate of evaporation of water from the cells, they lose their turgidity and the plant wilts.

What happens to a plant cell when placed in a solution with lower water potential?

1. When a plant cell is immersed in a solution with lower water potential, the water potential of its cell sap is higher than that of the solution outside the cell.
2. By osmosis, water from the vacuole and cytoplasm leave the cell through the partially permeable cell surface membrane.
3. The cell decreases in size and becomes flaccid or limp.
4. As the cell loses water, the vacuole decreases in size. The cytoplasm shrinks away from the cell wall. The shrinkage of cytoplasm and cell membrane away from the cell wall is called plasmolysis. The cell is said to be plamolysed. A plasmolysed cell can be restored to its original state by placing it in water or in a solution with higher water potential.

What happens to a animal cell when placed in a solution with lower water potential?

1. Placing an animal cell in a solution of low water potential will cause it to lose water. The cell shrinks. This process is called crenation. An animal cell will become dehydrated and eventually die when placed in a solution of lower water potential.

Plasmolysis causes tissues to become limp or flaccid. Cells will be killed if they remain plasmolysed for too long. 

Soil solution is a thin film of water that surrounds individual soil particles. It usually contains dissolved mineral salts or ions.

1. What is diffusion?


Diffusion is the net movement of molecules moving from a region of higher concentration to a region of lower concentration.
It is one of the transport phenomena that occur in nature, and it results in mixing or mass transport without requiring bulk motion.

More info

2. When will this process stop?

When there is no concentration gradient. The concentration of substances is equal inside and outside. It's called dynamic equilibrium.

Static equilibrium occurs when there is no action taking place.
Dynamic equilibrium occurs when two opposing actions occur at the same rate.

More on dynamic equilibrium


3. Do molecules even stop moving?

In theory, molecules never stop moving as long as the temperature is above an absolute zero. There they reach their minimum motion. When diffusion stops, the concentration of molecules are in equilibrium, but they are still moving.

Full answer

An equilibrium is said to be "dynamic". The reactions going in each direction still take place, they just take place at the same rate, so that the relative amounts of reactants and products do not change.


4. What are the factors that determine the rate of diffusion?

The rate of diffusion is directly proportional to the concentration gradient. The greater the difference in concentration between two areas, the greater the rate of diffusion. Thus, when the gradient is zero, there will be no net diffusion, as diffusion will only occur so long as a concentration gradient exists.

The rate of diffusion is indirectly proportional to resistance. In other words, the greater the resistance to diffusion, the lower the rate of diffusion. Resistance refers to anything that reduces the rate of diffusion. The width of the partitions is a resistance; the wider the partitions, the lower the resistance. And, the membrane is a resistance to the movement of ions and other charged substances in or out of cells.

The rate of diffusion is inversely proportional to distance traveled (also a function of resistance). For example, some typical diffusion rates for water are 10 µm - 0.1 sec; 100 µm -1 sec; and 1 mm - 100 sec. Diffusion is effective over short distances, but is pathetically slow over long distances.

The rate of diffusion is directly proportional to temperature. Temperature increases the rate of molecular movement, therefore, increases the rate of diffusion.

The rate of diffusion is indirectly related to molecular weight (heavier particles move more slowly than lighter, smaller ones). At room temperature, the average velocity of a molecule is fast - about 2 km/sec (=3997 mph!).

Pressure increases the speed of molecules, therefore, increase the rate of diffusion.

Solute particles decrease the free energy of a solvent. Essentially solvent molecules, such as water in a biological system, move from a region of greater mole fraction to a region where it has a lower mole fraction.

In a nutshell: 

1. Concentration gradient
2. Resistance
3. Distance travelled
4. Temperature
5. Molecular weight
6. Pressure

Journal:
Write down the key points from today's lesson.

Biomes (PT)

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).

Tundras are among Earth's coldest, harshest biomes. Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy and rainfall is scant. Tundra lands are snow-covered for much of the year, until summer brings a burst of wildflowers.

Mountain goats, sheep, marmots, and birds live in mountain, or alpine, tundra and feed on the low-lying plants and insects. Hardy flora like cushion plants survive on these mountain plains by growing in rock depressions where it is warmer and they are sheltered from the wind.
The Arctic tundra, where the average temperature is 10 to 20 degrees Fahrenheit (-12 to -6 degrees Celsius), supports a variety of animal species, including Arctic foxes, polar bears, gray wolves, caribou, snow geese and musk-oxen. The summer growing season is just 50 to 60 days, when the sun shines 24 hours a day.
The few plants and animals that live in the harsh conditions of the tundra are essentially clinging to life. They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming.
The Arctic tundra is changing dramatically due to global warming. Already, more southern animals like the red fox have moved onto the tundra. The red fox is now competing with the Arctic fox for food and territory, and the long-term impact on the sensitive Arctic fox is unknown.
It is the Arctic's permafrost that is the foundation for much of the region's unique ecosystem, and it is the permafrost that is deteriorating with the warmer global climate. Permafrost is a layer of frozen soil and dead plants that extends some 1,476 feet (450 meters) under the surface. In much of the Arctic it is frozen year round. In the southern regions of the Arctic, the surface layer above the permafrost melts during the summer and this forms bogs and shallow lakes that invite an explosion of animal life. Insects swarm around the bogs, and millions of migrating birds come to feed on them.
With global warming, the fall freeze comes later and more of the permafrost is melting in the southern Arctic. Shrubs and spruce that previously couldn't take root on the permafrost now dot the landscape, potentially altering the habitat of the native animals.
Another major concern is that the melting of the permafrost is contributing to global warming. Estimates suggest that about 14 percent of the Earth’s carbon is tied up in the permafrost. Until recently, the tundra acted as a carbon sink and captured huge amounts of carbon dioxide from the atmosphere as part of photosynthesis. This process helped keep the amount of this greenhouse gas from accumulating in the atmosphere.
Today, however, as the permafrost melts and dead plant material decomposes and releases CO2, the tundra has flipped from a carbon sink to a carbon contributor.

READ UP MORE ON CARBON CYCLE & NITROGEN CYCLE

(from: http://environment.nationalgeographic.com/environment/habitats/tundra-profile/)

Interaction among Organisms

Interactions among organisms

Types of area(Biosphere)

Lithosphere

Hydrosphere

Atmosphere

Abiotic- non living thing

Biotic- living thing

Biotic interacts with Abotic

Biotic interacts with Abotic + environment = system(dynamic)

Habitat- place where animals live

population- Small number of animals, most probably the same species

Community- Small number of animals, different species

Niche - is the role and position of a organism(species) in the community. No two species can occupy exactly the same niche.  e.g the niche of a fish is to eat plants and to provide food for its predators.

Ecosystem-habitat +biotic interacting

Abiotic factors

• Light- how much?

• Temperature- how high? (affects physiological activities of living things)

• Water- Essential for life!!!!!!!!(water needed for chemical reactions)

• Oxygen-most oxygen are aerobes(need oxygen) Unaerobes(organisms that do not need oxygen)

• Salinity- important factor for aquatic organisms

• pH- acids pH 1-6.9, water(neutral) 7.0, alkali pH 7.1-14.0  

1. competition -/- (Interspecific- a form of symbiosis) (Intraspecific-same species)
Producer-Primary consumer->secondary consumer->tertiary consumer
Producer-Primary consumer->secondary consumer->tertiary consumer
Flow of Energy:

• Only about 10% of the energy is stored as new tissues and is available for transfer to next feeding level. 90% of the energy is lost because some food may not be eaten, or passes through the body without being digested and a lot of the energy is used in respiration

Decomposers are detritivores that recycle organic matter back to inorganic nutrients (carbon, nitrates) in ecosystems. E.g. fungi, bacteria
Detritus feeder acquire nutrients from dead animals/ plants or animal waste products. E.g. certain beetles, earthworm, termites, bacteria, fungi

Biotic Factors

1.Symbiosis

-Mutualism +/+

-Commensalism +/o (one benefits, no damage to the other)

-Parasitism +/- ( host is harmed, population is benefiting)

2. Competition -/- ( both compete with each other for limited resources such as food, territory, mating.

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

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

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

Food consumed = growth + respiration + heat + egesta+ excreta

• The shorter the food chain, the greater 
  is the available food energy.

(break down food into SMALLER SUBSTANCES)

(break down food into SIMPLER SUBSTANCES)

Practical #3 & 4

Some interesting pictures from the microscope:) -

Practical #3:

From Practical #4: 

Cheek Cells

Plant Cell #1

Plant Cell #2

Cell Discussion (In Class)

Extra Information & Discussion:

http://tinyurl.com/ckrtvhp

• Function: The red blood cell delivers oxygen to body tissues via blood flow through the circulation. They take up oxygen in the lungs or gills and release it while squeezing through the  body’s capillaries.

• Structure:
• Biconcave discs, having a depressed center on both sides. (These depressed centers allow the cells to have more cell membrane surface we tend to use the phrase “higher surface area to volume ratio” which can be exposed to diffusing oxygen while transiting the lungs. This structure also allows them to be more flexible when negotiating tight passages.)
• 7.8 micrometers in diameter

• Does not have nucleus and most organelles such as mitochondria to accommodate maximum space for haemoglobin.(the compound that carries oxygen through the body.)
• check this website: http://www.wisc-online.com/objects/ViewObject.aspx?ID=ap14604
• Red blood cells are red only because they contain a (protein chemical ← wrong term.  Haemoglobin is a protein, we don’t call it a protein chemical) called hemoglobin which is bright red in colour
• The main function of the red blood cell is to transport oxygen from the lungs, to the other tissues and cells of the body. The other function of the red blood cell is to partly carry carbon dioxide, which is a waste product of metabolic activities in the body.

Consist of dead hollow cells because the walls are lignified and the cell contents disintegrate. The lignin makes the cell wall impermeable so they are in effect waterproof. It also makes the vessels extremely strong and prevents them from collapsing. They have a wide lumen and are linked end to end to create a long, hollow tube since the end cell walls have one or many perforations in them. This allows the transport of large volumes of water. The sidewalls have bordered pits (unlignified areas) to allow lateral movement of water. Xylem vessels are found in angiosperms.

Source:http://au.answers.yahoo.com/question/index?qid=20100710023937AAM9Akd

Location: the small intestines

Structure and characteristics:

- Contain many membrane-bound vacuoles

- Aglycocalyx surface coat contains digestive enzymes. ← no need to know this for now, it is beyond your syllabus

- Microvilli on the apical surface increase surface area ← once again, the portion that is underlined should be re-written as “increase surface area to volume ratio” for the digestion and transport of molecules from the intestinal lumen

The points stated below refers to the functions of the intestine, which are facilitated by the intestinal epithelial cells

• Ion uptake
• Water uptake
• Sugar uptake
• The main function of intestinal cells is associated with secreting digestive juices into the lumen (the inner cavity of an intestine or blood vessel).

1. Elongated structure that protrudes out to the soil

- This is to increase the surface area to volume ratio; thereby increasing the rate of uptake of water from the soil to the cell.

2. Large vacuole

- The root hair cell has a large central vacuole to maximize the amount of water capacity of the cell; thus, the cell is able to absorb and store more water.

3. Cell sap

- The cell sap of the root hair cell has a lower water potential than the water in the soil ← Good. We will learn what is water potential in the later lessons after ecology. Thus, the water from the soil moves into the cell via osmosis.

Read more: http://wiki.answers.com/Q/What_is_the_structure_of_root_hair_cells#ixzz21S1j6XeB

For the points below, it is more of how the various structures in the cell contributes to the function of a cell.  May be said for plant cells in general, and is not specific to only the root hair cell.

4. Nucleus

-Contains contains chromatin material, consisting of the DNA if the cell which is important (inherited by the daughter cells)

5. Plasma membrane

-Controls the movement of substance into and out of the cell and is used for cell identification.

6. Cell Wall

-The cell wall is a strong surface, surrounding the plasma membrane, which protects the cell and give it its shape. It also prevents expansion when too much water enter the cell.

7. Cytosol

-The cytosol is made up of water, salts and organic molecules and many enzymes that speed up reactions. It is important as it suspends the cell organelles within it.

Read more: http://sst-health-science-class-107.blogspot.sg/2010/01/root-hair-cell.html