Sunday, November 9, 2008

CONCEPT 8.2) The Light Reactions Convert Light Energy to Chemical Energy


wavelength: distance between adjacent waves.
electromagnetic spectrum: range of types of electromagnetic energy from gamma waves to radio waves.
pigment: chemical compound that determines a substance's color paper.
chromatography: laboratory technique used to observe the different pigments in a material
photosystem: cluster of chlorophyll and other molecules in a thylakoid.


  • Sunlight is a form of electromagnetic energy that travels in waves.
  • Visible light: 400 nm (nanometers) violet ~ 700 nm, red.
  • Shorter wavelengths energy > Longer wave lengths energy
  • Energy wavelengths shorter than the visible light can cause damage on organic molecules (proteins, nucleic acids). //eg. Ultraviolent radiation
  • A substance's color is due to chemical compounds: pigments.
  • When light shines on a material containing pigments: ----> 1. absorbed 2. transmitted 3. reflected
  • Chloroplasts absorb well: blue-violet, red-orange light
  • Chloroplasts do NOT absorb well: green light (transmit, reflect) -> why plants are GREEN!!!

- Paper chromatography is used to observe the different pigments in a green leaf:

  • Pigments travel at different rates depending on how easily they dissolve, how strongly they are attracted to the paper.
  • This laboratory technique can be used to separate and analyze the pigments in a leaf.

Harvesting Light Energy

  • Within the thylakoid membranes is the chlorophyll, other molecules all together: photosystems.
  • Each photosystem contains a few hundred pigment molecules (+ chlorophyll a, b & carotenoids).
  • A pigment molecule absorbs light energy --> One of the pigment's electrons gains energy ("ground state" to "excited state"-unstable) --> excited electron falls back to ground state --> exits an electron in the next pigment molecule --> so on...."jumping" --> arrives at the reaction center --> primary electron acceptor (traps the excited electron from the chlorophyll a molecule) //
  • -----> Now energy is able to make ATP and NADPH in the rest of the thylakoid membrane.

Chemical Products of the Light Reactions

-light strikes photosystem and transfer excited electrons to the primary electron acceptor.
-electrons split water and releases oxygen
-excited electron goes through electron transport chain and pumps H+ions across the membrane to thylakoid.
-light excited electrons get ransferred to NADP.

"Water-splitting photosystem"- releases oxygen (waste product), hydrogen ions:
  • First photosystem traps light energy --(light-excited electrons)--> electron transport system//
  • --> release of energy --> chloroplast use to make ATP

"NADPH-producing photosystem":
  • Photosystem transfer excited electrons & hydrogen ions --> NADP+ --> light reactions (light energy --> chemical energy of ATP & NADPH) --> produces NADPH
  • Sugar is to be produced in the Calvin Cycle process.

1. Explain why a leaf appears green.
A leaf appears green because chloroplasts doesn't absorb green light well. Unlike other colors such as blue-violet and red-orange lights that are well absorbed, green light is rather transmitted or reflected because of the particular wave-length that is not able to get absorbed in the chloroplast pigments.

2. Describe what happens when a molecule of chlorophyll a absorbs light.
When chlorophyll a absorbes light, it makes the molecule get excited and makes it transfer the energy to another near molecule.

3. Besides oxygen, what two molecules are produced by the light reactions?
Hydrogen ions and NADPH is produced by the light reactions, besides oxygen.

4. Where in the chloroplast do the light reactions take place?
It takes place in the chloroplast's thylakiod membrane.

Saturday, November 8, 2008

CONCEPT 8.1) Photosynthesis Uses Light Energy to make food.



Chloroplast: organelle found in some plant cells and certain unicellular organisms where photosynthesis takes place. These contain chemical compounds called chlorophylls.
Chlorophyll: pigment that gives a chloroplast its green color; uses light energy to split water molecules during photosynthesis.
Stroma: thick fluid contained in the inner membrane of a chloroplast
Thylakoid: disk-shaped sac in the stroma of a chloroplast; site of the light reactions of photosynthesis.
Light reactions: chemical reactions that convert the sun's energy to chemical energy; take place in the membranes of thylakoids in the chloroplast.
Calvin cycle: cycle in plants that makes sugar from carbon dioxide, H+ ions, and high-energy electrons carried by NADPH.


Looking at the structure of a plant leaf.....
- Leafs in a plant contain the most chloroplasts and are the major sites for photosynthesis to take place.
- Chloroplasts are concentrated in the cells of the mesophyll (inner layer of tissure).
- On the surface of the leaf, there are pores called stomata, where CO2 enters and O2 exits through.
-Veins carry water and nutrients, and also other organic molecules produced in the leaves, through stomatas and to other parts of the plant.

Looking inside the chloroplasts' structure...
~ inner& outer membrane
~ inner: thick fluid - stroma

~ stroma: Many disk-shaped sacs: thylakoids
~ Thylakoids:
+ each has a membrane surrounding the interior space.
Thylakoids arranged in stacks are called grana.

- Photosynthesis is a process of plants and other producers, or autotrophs, converting the energy of sunlight into useful energy that is stored in organic molecules.
- Photosynthesis is the opposite of cellular respiration.
- The chloroplast uses "excited" electrons, along with CO2 and hydrogen ions, to produce sugar molecules.
-Photosynthesis occurs in 2 main stages: theLight Reactions & the Calvin Cycle.
The Light Reaction
1. Sun light energy>> chemical energy
2. Chlorophyll molecules in the membrane captures energy.
3. Chloroplasts use these energy to remove electrons from water. ---> Splits H2O --> Oxygen ("waste product" go out through stomata) & Hydrogen ions
4. Electron & Hydrogen ions in chloroplast ---> NADPH (energy carrier)
5. Chloroplast use the stored energy to make ATP too.
+++ Overall: Light energy stored ---> chemical energy ---> NADPH & ATP
The Calvin Cycle
- NADPH & ATP made by light reactions provides energy to make sugar from the atoms in:
CO2 + Hydrogen ions + high-energy electrons carried by NADPH
- Enzymes for the process located outside the thylakoids, dissolved in stroma.

1. Draw and label a simple diagram of a chloroplast that includes the following structures: outer and inner membranes, stroma, thylakoids.
2. What are the reactants for photosynthesis? What are the products?
Reactants: CO2, H2O

Products: Glucose, Oxygen
6 O2 + 6 H2O ->->-> C6H12O6 + 6 O2

3. Name the two main stages of photosynthesis. How are the two stages related?
Two main stages: the light reactions, the Calvin Cycle
They are related in that the light reactions recieve is the process of storing the sun light energy and converting them into chemical energy, making NADPH and ATP rich in energy. Then the Calvin Cycle uses these NADPH and ATP to make sugar for the chloroplast.

Tuesday, September 9, 2008


Multiple Choice
Choose the letter of the best answer.

1. Which of the following is not an organic molecule?
c. water

2. Which of the following terms includes all the other terms on this list?
b. carbohydrate

3. Which term is most appropriate to describe a molecule that dissolves easily in water?
c. hydrophilic

4. Cholesterol is an example of what kind of molecule?
b. lipid

5. The 20 amino acids very only in their:
c. amino groups

6. A specific reactant an enzyme acts upon is called the:
d. substrate

7. An enzyme does which of the following?
b. lowers the activation energy of a reaction

8. Besides satisfying your hunger, why else might you consume a big bowl of pasta the night before a race?
Pasta contains carbohydrates, which is an organic compound made up of sugar molecules. We need sugar for energy, and therefore I might consume a big bowl of pasta, so I would be ready to use up a lot of energy at the race.

9. How are glucose, sucrose, and starch related?
Glucose is a monosaccharide, sucrose is a disaccharide, and starch is a polysaccharide, which are all carbohydrates, linked and related to each other. Sucrose consists of a glucose molecule linked to a fructose molecule. When sucrose, a major carbohydrate in plant, is consumed, it is broken down into glucose and fructose. Starch consists entirely of glucose monomers linked in a long polymer chain.

10. What are steroids? Describe two functions they have in cells.
Steroids are lipid molecules with four fused carbon rings each. They circulate in your body as chemical signals, such as hormones, and also has a hydrophobic characteristic.

11. How are polypeptides related to proteins?
Amino acids are linked together into a polypeptide chain, by the cells, trying to create proteins.

12. How does denaturation affect the ability of a protein to function?
Denaturation unravels and loses the normal shape of the protein. It affects the polypeptide chains to become tangled up with one another, and since the protein’s function varies depending on its shape, it would also lose its ability to work properly.

14. The reaction below shows two amino acids joining together.

a. One product of this reaction is represented by a question mark. Which molecule is it?
When the two amino acids joined together, it went through a dehydration reaction, releasing a water molecule, which should be filled in as H20 in the question mark.

b. What is this kind of reaction called? Explain.
The process of a water molecule released when a monomer is added to a chain, or when two monomers join together, is called a dehydration reaction.

c. If an amino acid were added to this chain, at what two places could it attach?
It would attach on the OH (Hydrogen Oxygen) atom or the H (Hydrogen) atom on the other side.

15. Use the graph to answer the questions below.

a. At which temperature does enzyme A perform best? Enzyme B?
Enzyme A performs best in about 37 degrees, and enzyme B performs best in about 77 degrees.

b. Knowing that one of these enzymes is found in humans and the other in thermopilic (heat-loving) bacteria, hypothesize which enzyme came from which organism.
Enzyme A should be the enzymes found in humans, because its best performing temperature is the average human body temperature. Enzyme B would be the enzyme found in thermophilic bacteria, because the bacteria is heat-loving, and 77 degrees is pretty high.

c. Propose a hypothesis that explains why the rate of the reaction catalyzed by enzyme A slows down at temperatures above 40˚C.
Enzyme A is the enzyme found in humans. If the human body temperature rises above 40˚C, the person is close to death. The human body cannot perform its abilities when it reaches to that certain amount of temperature. That could be why this enzyme slows down at this point, since it is not able to perform anymore at that stage.

Tuesday, September 2, 2008

Concept 5.3) Lipids include fats and steroids



Lipid: is one of a class of water-avoiding compounds.
Hydrophobic: avoids water molecules.
Fat: is an organic compound consisting of a three-carbon back-bone (glycerol) attached to three fatty acids (: contains long hydrocarbon chains).
Saturated fat: is fat in which all three fatty acid chains contain he maximum possible number of hydrogen atoms.
Unsaturated fat: is fat with less than the maximum number of hydrogen in one or more of its fatty acid chains. This is because some of its carbon atoms are double-bonded to each other.
Steroid: is a lipid molecule with four fused carbon rings.
Cholesterol: is a steroid molecule present in the plasma membranes of animal and human cells. It can be the starting point from which your body produces other steroids.

Lipids and Fats

  • Compounds, that have characteristic of being unable to mix with the class of water, like oil, all called lipids, and they are said to be hydrophobic.
  • Lipids have functions of acting as a boundary that surrounds and contains the aqueous, or watery, contents of your cells.
  • Other types of lipid circulate in your body as chemical signals to cells.
  • The other type of lipids is – fat, which stores energy in your body, as well as cushions your organs and provides your body with insulation.
  • All the carbon atoms in the fatty acid chains form single bonds with each other, and the rest of their bonds are with hydrogen atoms.
  • Saturated fat- most animal fats, such as butter.
  • Unsaturated fat- generally fats in fruits, vegetables, and fish, such as corn oil, olive oil, and other vegetable oils.
  • Having diets of consuming much rich saturated fats can be unhealthy, building up lipid-containing deposits within the walls of blood vessels, called plaques. Plaques can reduce blood flow, and may lead to heart diseases.
  • It has hydrophillic head and hydrophobic tails.


  • Are classified as lipids because of its hydrophobic characteristics, but they are different from fats in structure and function.
  • They circulate in your body as chemical signals, such as hormones.
  • Cholesterol is best-known for an example of a steroid. But substances with high levels of cholesterol in the blood can link to the risk for cardiovascular (heart and blood vessel) disease.
Concept Check
1. What is the difference between saturated and unsaturated fat?
2. What are lipids, and what are its characteristics?
3. What are steroids?

Sunday, August 31, 2008

5.2) All About Carbohydrates

CONCEPT 5.2 Summary
Carbohydrates provide fuel and building material

Carbohydrates can be used as an energy source just after a meal, or can be stored up for later use. They are a very important source of energy.

Q. What is 'carbohydrate'?
A. A carbohydrate is an organic compound made up of sugar molecules, which contains carbon, hydrogen, and oxygen elements. The molecular formula for it is always a multiple of CH2O, which is the basic formula. Most sugar molecules found in nature have cores that are ring-shaped carbon skeletons.

Q. What are 'monosaccharides'?
Monosaccharides are simple sugars that contains only one sugar unit.
E.g.) glucose, fructors, galactose ...etc
(-ose: full of sugar)

Q. What is glucose and what are the functions of sugars in our body?
A. Glucose can be in both straight-chain and ring-shaped forms. They are the particular molecules that mainly fuels supply for cellualar work, by breaking down the glucose molecules and extracting their stored energy inside it.

The carbon skeletons of monosaccharides can also be used as raw material, by the cells, for producing other types of organic molecules. The glucose molecules that haven't been used by the cells are left to get larger, or be made as fat molecules.

Disaccharides, in the other hand, are molecules that have been formed by two monosaccharides together, going through the dehydration reaction, by the cells. It means "double sugar", and the most common is sucrose.

Q. What is a sucrose?
A. Sucrose is a disaccharide consisting of two monosaccharides linked together. The major carbohydrate is in plant sap, that consists of linked glucose and fuctose molecules. It nourishes all the plant parts, by being taken in from the stems or roots of plants, and the sucrose then breaking down into glucose and fructose molecules for use.

Q. What are 'polysaccharides'?
Polysaccharides are long polymer chains made up of simple sugar monomers, or complex carbohydrates.
E.g.) Starch - a polysaccharide that consists entrirely of glucose monomers, found in plant cells.
└ (rich: potatoes, rice, corns)
*How it works
Inside a plant: starch chains branch and coil up → plant cells need sugar for energy → plants break down starch molecules → stored glucose is now obtained

Some polysaccharides:
+ Starch stores energy in potato cells.
+ Glycogen stores energy in turkey muscle cells :
In animals. Chain of many glucose monomers. Energy → breaks down the cell → glucose
+ Cellulose makes broccoli stem fibers rigid:
In plants. Serves as building materials - protect cells, stiffen. Made of glucose monomers.
Multiple cellulose chains are linked together with hydrogen bonds → forms cable-like 'fibers' in the tough walls of plant cells.
Cellulose keeps our digestive system healthy, by passing unchanged throughout our digestive system, due to the strong bonds, but does not serve as a nutrient. But some animals, this might make their digestive system worse, so they have microorganisms that inhabits them and breaks down the molecule, thus giving glucose.

'Almost all carbohydrates are hydrophilic.' and this is because many of hydroxyl groups are in their sugar units. This leads to the monosaccharides and disaccharides forming sugary solutions, while dissolving readily in water.

*Cellulose, some starch does not dissolve in water, still hydrophilic.



Q. What is 'carbohydrate'?

Q. What are 'monosaccharides'?

Q. What is glucose and what are the functions of sugars in our body?

Q. What is a sucrose?

Q. What are 'polysaccharides'?
____ _____ _____
*Note: Please, if you find any errors or suggestions on this piece of work, tell me so that I can correct any mistakes and get to improve on it. :)

Book: BIOLOGY, Exploring Life (N. Campbell, B. Williamson, R. J. Heyden)
Picture & diagram source:

Friday, August 29, 2008

5.1) The main ingredient of organic molecules - Carbon!

  • Organic molecule - Carbon-based molecule. (Bonds with hydrogen, oxygen, nitrogen ...etc)
  • Inorganic molecule - Non-carbon-based molecule (Water, oxygen, amonia ...etc)
  • Hydrocarbon - Organic molecule composed of only carbon and hydrogen atoms. Many of these are important fuels. (Methane) Our body's energy storing fat molecules contain long chains of these.
  • Functional Group - Group of atoms within a molecule that interacts in predictable ways with other molecules.
  • Hydrophilic - Attracts water molecules.
  • Monomer - Small molecular unit that is the building block of a larger molecule.
  • Polymer - Long chain of small molecular units (monomers).

    (Partly from the book, "BIOLOGY, Exploring Life" Glossary)


Carbon Skeletons, Functional Groups, Monomers, and Polymers..

  • Most molecules of a cell are carbon-based, other than water.
  • Backbone of carbon atoms bonds to one another, and may brach off with atoms of other elements. This basic structure is the foundation of a wide range of molecules in life.
  • The reason why the carbon atoms are so common in living things is because carbon's highest energy level are just 4 electrons. To satisfy it by holding 8 electrons in the outer energy level, carbon can form up to 4 bonds with other atoms, branching off in up to four directions.
  • The carbon skeleton and the attached functional groups determine the properties of an organic molecule.

  • Thousands of different kinds of polymers exist in every living cell, and they are all formed by only as fewer than 50 kinds of monomers.
  • Life's large molecules are grouped as four main categories, which are carbohydrates, lipids, proteins, and nucleic acids.

Building and Breaking Polymers

  • Every time a water molecule is released when two monomers bond to each other, making a polymer chain longer. This reaction is called dehydration, which basically means removing water.
  • When cells break a polymer chain, either to obtain energy, or use them to build new polymers, they add water between the bonds of monomers. This process is called a hydrolysis reaction, which means that water is used to break down.

  • Building polymer - water released.
  • Breaking polymer - water added.

Concept Check

Q. How many bonds in the most, can a carbon have, and why?
Q. What is the difference between organic and inorganic molecules?
Q. What are the four main categories of large molecules in life?
Q. Give one common functional group.
Q. Waht is the difference between a dehydration reaction and a hydrolysis reaction?


Picture taken from:

Thursday, August 28, 2008

Blog Start! About Myself...

My name is Angela Lee. I am a grade 9 student and this is my first year at AISG in Guangzhou, China. I have been living in Dongguan city of Guangdong Province in China for five and a half years, although my home country is Suwon, Republic of Korea.
I like drawing, listening to music and sometimes just resting.

This is a blog for our science class, and our teacher is Mr Jacobson. This is my first year studying biology and I find it quite interesting except for when there are so much to remember!! Biology is quite a big subject, and there are so much more things to learn about it. I look forward to spending a great year, doing my best in biology... and everything else :) (...I HOPE :P).