Homostasis - Nutrition part 2 (The digestive system) - 23 August 2012

The Digestive System 

The alimentary canal

It is a series of connected tubes which functions to carry out digestion

It consists of the mouth, esophagus (previously known as gullet in primary school), stomach, small intestine, large intestine, rectum and anus. 

The accessory organs 

It consists of salivary glands, gall bladder, liver and pancreas.

Digestion 

There are two types of digestion - mechanical digestion and chemical digestion.

Mechanical digestion

In simple terms, it means moving parts breaking down food substances.

Example: Mouth and stomach from the alimentary canal.

Chemical digestion 

Chemical digestion refers to the breaking down of food substances chemically. Note that chemical digestion requires enzymes. 

Example: Mouth, stomach and small intestine from the alimentary canal.

Enzymes = chemical substances that break things down. Therefore, they are involved in chemical digestion. 

The different digestion and where it takes place in our human body

We learn 3 different digestion in sec 1, namely Carbohydrate digestion, Protein digestion and Fat digestion.

Mouth: Only carbohydrate digestion takes place here, where polysaccharides are broken down into smaller polysaccharides and/or maltose)

Stomach: No carbohydrate digestion and fat digestion take place in the stomach; only protein digestion takes place. It is also where protein digestion starts. Proteins are broken down into small polypeptides here.

Lumen of small intestine: Carbohydrate digestion takes place. Polysaccharides are broken down into maltose and other disaccharides by an enzyme from the pancreas. Protein digestion also takes place; polypeptides are broken down into amino acids. Fat digestion takes place here too. Fat droplets are broken down into glycerol and fatty acids by an enzyme from pancreas.

Epithelium of small intestine: Carbohydrate digestion takes place. Disaccharides are broken down into monosaccharides by an enzyme which comes from the small intestine. Protein digestion takes place; polypeptides are broken down into amino acids. Fat digestion also takes place, fat droplets are broken down into glycerol and fatty acids by an enzyme from pancreas.

Note that the enzymes from the pancreas take part in carbohydrate digestion and lipid digestion (fat digestion). Bile is produced in the gall bladder and salivary amylase is produced in the salivary glands. 

The small intestine 

The small intestine is approximately 6 meters long. 

Duodenum: Where the fat globules are broken up into fat droplets by bile salts.

Ileum: More digestion, less absorption as most of the food substances are not simple substances.

Jojenum: Less digestion, more absorption as most of the food substances have been digested already.

Villi 

Villus is a single protrusion.

 

Epithelial cells in the small intestine

- Has microvilli

 

(taken from cellfunctioning.wikispaces.com, edited by me)

Homostasis - Nutrition Part 1 - 22 August 2012

There are 5 main food groups, Carbohydrates, Proteins, Lipids, Inorganic substances and Dietary fibre.

Carbohydrates

Carbohydrates consist of monosaccharides, disaccharides and polysaccharides.

Monosaccharides

There are 3 types of monosaccharides that we have learnt - Glucose, Fructose and Galactose.

Formulas:

Glucose + Glucose = Maltose
Fructose + Glucose = Sucrose
Galactose + Glucose = Lactose

Disaccharides

Disaccharides are when 2 monosaccharides. 

Polysaccharides

Polysaccharides are when multiple monosaccharides are combined.

Proteins

Proteins are broken down into polypeptides and polypeptides can then be further broken down into amino acids. The reverse can also occur (ie Amino acids combine to form polypeptides and polypeptides can then combine to form proteins.)

Deficiency: Kwashiokor (characterised as a bloated stomach)

Lipids/Fats       

Lipids, also known as fats, is broken down into glycerol and fatty acids. Glycerol can combine with fatty acids to form lipids.

Inorganic substances comprises vitamins and and minerals.

Vitamins 

We have learnt 5 types of vitamins, namely Vitamin A, C, D, E and K.

Vitamin A

Deficiency results in night blindness.
Source: Carrot, dark-green leafy vegetables, eggs

Vitamin C

Deficiency results in scurvy.
Source: Fresh citrus foods, green vegetables

Vitamin D

Deficiency results in rickets.
Source: Sunlight, fortified milk and margarine, eggs and butter, cod liver oil.

Vitamin E

Deficiency results in anemla.
Source: Vegetable oils like soyabean oil and corn oil.

Vitamin K

Deficiency results in excessive bleeding.
Source: Sunlight, fortified milk and margarine, eggs and butter, produced by the micro-flauna found in the large intestine.

Minerals consists of calcium and iron.

Calcium 

Deficiency results in rickets.
Source: Cereals, green vegetables, eggs and fruits.

Iron

Deficiency results in anemla.
Source: Liver, meat, eggs and green vegetables.

Dietary fibre

Deficiency results in constipation. 

Osmosis - 14 and 21 August 2012

Osmosis - What is 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. Some solutes are too large to move across the membrane.

Diffusion and Osmosis... what is the relationship?

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. 

Water molecules move from a region of high water potential to a region of low water potential.

Relating Water Potential to Osmosis...

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. 

Osmosis in animal cells

Animal cells

• Structure is simple
• Cytoplasm is surrounded by a partially permeable cell membrane. 

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

Water will leave the cell by osmosis as the cell has a higher water potential than its surroundings. The cell will lose volume and shrink (crenate). Water loss only ceases if the concentration of the cytoplasm rises to that of the surrounding solution.

Note that 'cenate' can only be used for animal cells!

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

Water enters the cell by osmosis as the surrounding solution has a higher water potential than the cell. Hence, the cell gains volume and expands. Since the cell membrane cannot resist expansion, the cell eventually bursts (cytolysis)

Note that the term 'cytolysis' is only to be used for animal cells! Find out why later! 

The plant cell 

• Plant cells are structurally more complex.
• They are surrounded by a cellulose cell wall which is freely permeable to water, not elastic and is able to resist cell expansion.
• Each plant cell contains a large central vacuole which contains a solution of salt, sugars and ions and is  bound by a partially permeable membrane. 

Osmosis in plant cell 

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

Water enters the vacuole by osmosis. The vacuole swells, pushing the cytoplasm against the cell wall. The inelastic cell wall resists expansion and the cell becomes rigid, also known as turgid. It can be described as in a state of turgor.

Young plants, which have little woody tissue, rely on turgor for support against wind and gravity.

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

Water leaves the cytoplasm and vacuole by osmosis. 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.

A non-woody plant which loses lots of water has many plasmolysed cells, and as a result, the plant wilts. No longer fully filled with water, the tissue loses support and becomes floppy or flaccid.

Plasmolysis vs Crenation       

Plasmolysis is the shrinking of a plant cell cytoplasm (due to loss of water), and the cell membrane moves away from cell wall.

However, crenation is the shrinking of animal cell.

Isotonic solution

An isotonic solution has the same concentration of solutes as the cytoplasm. It also has the same water potential as the cytoplasm.


In both animal and plant cells, there is no net movement of water molecules into or out of the cell.


Therefore, the cells neither shrinks nor expands when placed in an isotonic solution.

Diffusion part 2 - 2 August 2012

Applications of diffusion in Biology

Example 1

To stay alive, the amoeba which is a unicellular organism needs to obtain nutrients and remove waste efficiently by the process called diffusion.

Example 2

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 need to move from one cell to another, move in & out of the cell and move from one part of the cell to another.



One way through these processes can occur is by diffusion across membranes.

Example 3

There are 2 types of membranes - The partially permeable membrane and the permeable membrane



Partially permeable membrane

A partially permeable membrane allows some substances to pass through.

Permeable membrane


A permeable membrane allows all substances to pass through.

Diffusion across a permeable membrane

An example of a partially permeable membrane is the visking tubing.

Other examples

• Movement of carbon dioxide during photosynthesis.

• Movement of oxygen and carbon dioxide in animals.

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.

Diffusion part 1 - 2 August 2012

So what is DIFFUSION?

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

Diffusion is a spontaneous process (no input of energy required). It can also be called as a passive process.

Substances tend to spread from an area where they are more concentrated to an area where they are less concentrated.

Two or more substances can become evenly distributed (reach equilibrium) even without external
interventions.

Concentration Gradient

Firstly, what is a concentration?

Concentration is the amount of substance (in mass) divided by it's volume (in litres). In other words, a measure of the amount of a substance in a specific volume.

So, what is concentration gradient?

The concentration gradient is the change in concentration between two regions.

Here is an example of the concentration gradient:

From the graph, we can also say that difference in the concentration between points A and B is the concentration gradient between points A and B.

If the above graph shows the concentration of sugar at points A and B, sugar molecules will diffuse down the concentration gradient from point A to point B.

Things to note about concentration gradient and diffusion:

Firstly, particles diffuse down the concentration gradient.
The larger the concentration gradient, the faster the rate of diffusion.

Ecology - Ecology interactions among organisms part 4 - 2 August 2012

Cycling of Nutrients in an Ecosystem

 

Read up about Carbon cycle and Nitrogen cycle!

Ecological Pyramids

An example of an ecological pyramid is:

 (image taken from: http://mrskingsbioweb.com/ecology.html)

 3 types of pyramids learnt:

1. Pyramids of numbers
2. Pyramids of biomass
3. Pyramids of energy

Pyramids of numbers

The pyramid of numbers indicate the relative numbers of individuals at each trophic level

An example of a pyramid of numbers

(image taken from: http://www.learner.org/workshops/sheddinglight/VideoConnection/highlights/highlights6.html)

Pyramids of biomass

It is the relationship between biomass and trophic level by quantifying the amount of biomass present at each trophic level of an ecological community at a particular moment in time. The dry mass of all the organisms at each trophic level may be estimated.

(definition of pyramid of biomass is taken from http://en.wikipedia.org/wiki/Ecological_pyramid#Pyramid_of_biomass)


An example of the pyramid of biomass

(Image taken from: http://studydroid.com/?page=studyPack&packId=29966&begin=0)

Pyramid of energy

It shows the total energy utilized at each trophic level.

And example of the pyramid of energy

(image taken from: http://www.tutorvista.com/biology/salient-features-of-ecological-pyramids#)