THE STRUCTURE OF THE EYE

Today, we will discuss the basic structure of the human eye.

•          Lens: For focusing of objects onto the retina.

•          Iris: Controls the amount of light entering the eye by changing the size of the pupil.

•          Pupil: This is the aperture (hole) bounded by the iris.

•          Retina: The back of the eye where the image is formed. Contains the light sensitive structures rods and cones.

•          Rods: Needed for night vision since they are very sensitive to light. Helps to distinguish between black and white objects.

•          Cones: Needed for day time vision and for distinguishing between colors.

•          Optic nerve: Transmits the image from the retina to the brain.

•  The lens divides the eye into anterior and posterior chambers. The anterior chamber contains the fluid called aqueous humor and the posterior chamber contains the gel-like substance called the vitreous body.
• The ciliary muscles control the thickness of the lens. That is, it stretches the lens.
• The Canals of Schlemm drain the aqueous humor.

ANSWERS TO QUESTIONS FOR THE DAY

1.      If the hydrogen ion concentration of a solution is 1 x 10^-5. What is the pH of the solution?

       A.      1

       B.      10

       C.      5 (pH = -log [hydrogen concentration]; so pH =  -log [1 x 10^-5]; pH =5). Hint: Just take the opposite of the exponent when you have the concentration in the form 1 x 10^-5

       D.     2

2.      If the hydrogen ion concentration of a solution is 1 x 10^-3. What can you say about the solution?

A.      I t is a weak acid

B.      It is a strong acid (pH=3)

C.      It is a weak base

D.     It is a strong base

3.      If the hydroxyl ion concentration of a solution is 1 x 10^-5. What is the pH of the solution?

A.      6

B.      7

C.      8

D.     9 (The pOH= 5 from pOH = -log [hydroxyl concentration] ; since pH+pOH=14; pH=14-5=9)

4.      If the hydroxyl ion concentration of a solution is 1 x 10^-3. What can you say about the solution?

A.      I t is a weak acid

B.      It is a strong acid

C.      It is a weak base

D.     It is a strong base (pOH=3; so pH=14-3=11)

QUESTIONS FOR THE DAY

1.      If the hydrogen ion concentration of a solution is 1 x 10^-5. What is the pH of the solution?

          A.      1

          B.      10

          C.      5

          D.     2

2.      If the hydrogen ion concentration of a solution is 1 x 10^-3. What can you say about the solution?

A.      I t is a weak acid

B.      It is a strong acid

C.      It is a weak base

D.     It is a strong base

3.      If the hydroxyl ion concentration of a solution is 1 x 10^-5. What is the pH of the solution?

A.      6

B.      7

C.      8

D.     9

4.      If the hydroxyl ion concentration of a solution is 1 x 10^-3. What can you say about the solution?

A.      I t is a weak acid

B.      It is a strong acid

C.      It is a weak base

D.     It is a strong base

ACIDS AND BASES

What are acids?
Acids are substances that produce hydrogen ions (H+) or hydronium ions (H₃O⁺ ) in solution.
For example: HCl +H₂O -----> Cl^- + H₃O⁺   

                 HCl -----> Cl^- + H⁺  

This is known as the Arrhenius concept for acids.

What is a base?

A base is a substance that can produce hydroxyl ions (OH^-) in solution.

For example: NaOH -----> OH^- + Na⁺  

This is known as the Arrhenius concept for bases.

There are other definitions for acids and bases. These include Bronsted-Lowry and Lewis concepts.

I will just discuss Bronsted-Lowry concept since it will help you identify some common acids/bases.

Bronsted-Lowry definition for acids: Acids are proton donors (H⁺ ) 
For example: Ammonium ion is an acid because it can donate a proton.  NH₄⁺ -----> NH₃ + H⁺

Bronsted-Lowry definition for bases: Bases are proton acceptors.

For example: Ammonia is a base because it can accept a proton. NH₃ + H⁺ -----> NH₄⁺

Exam tip: You should be able to identify common acids and bases.

Test for acids

Acids will turn blue litmus paper red.

Test for bases

Bases will turn red litmus paper blue.

pH scale 

The pH scale is used to indicate the strength of acids and bases. It is the negative log of the hydrogen ion concentration. The values range from 0 to 14 with 7 as the neutral point. pH of normal water is 7. From 0-7 is acidic and 8-14 is the the basic zone. The acidity increases from right to left and basicity increases from left to right. That is, a pH of 2 is more acidic than pH of 5, and pH of 13 is more basic than pH of 9.

Neutralization reactions

An acid will always react with a base to produce a salt and water. This is know as the neutralization reaction.

Example: HCl + NaOH ---------> NaCl + H₂O

Exam tip: You should be able to identify neutralization reactions.

NUCLEIC ACIDS

Today, we want to look at the structure of DNA and RNA.

STRUCTURE OF DNA

DNA stands for deoxyribonucleic acid. This is the basic unit of our genes. DNA consist of a sugar molecule called deoxyribose, a phosphate, and nitrogen bases. These three things make up the nucleotide. So we can say that the basic unit of the DNA is the nucleotide. The sugar and the phosphate together make up the nucleoside.

The nitrogen bases are adenine (A), guanine (G), cytosine (C), and thiamine (T).

Adenine (A) always binds to thiamine (T)

Guanine (G) always binds to cytosine (C)

DNA is located in the nucleus of the cell and it has a double helix structure.

STRUCTURE OF RNA

RNA stands for ribonucleic acid. This is involved with the synthesis of protein. RNA consist of a sugar molecule called ribose, a phosphate, and nitrogen bases. These three things make up the nucleotide. So we can say that the basic unit of the RNA is the nucleotide. The sugar and the phosphate together make up the nucleoside.

The nitrogen bases are adenine (A), guanine (G), cytosine (C), and Uracil (U).

Adenine (A) always binds to Uracil (U)

 Guanine (G) always binds to cytosine (C)

RNA is located in the cytoplasm of the cell and it is a single strand.

Types of RNA:
1. mRNA--- Messenger RNA: This is code for protein synthesis. 
2. tRNA ---- Tranfer RNA: This carries the amino acids.
3. rRNA ---- Ribosomal RNA: This reads the code on the mRNA.

Note the difference between DNA and RNA. DNA has thiamine but no uracil. RNA has uracil but no thiamine.

ANSWERS TO THE QUESTIONS FOR THE DAY

1. A car is traveling at the speed of 20 mph. How far will it travel in 5 hrs?
A. 4 mi
B. 100 mi  (distance = speed x time; 20 mph x 5 hrs= 100)
C. 20 mi
D. 25 mi

2. A car is traveling at the speed of 20 mph. How far will it travel in 30 minutes?
A. 600 mi
B. 50 mi
C. 10 mi (distance = speed x time; change 30 minutes to hours first, then 20 mph x 0.5 hrs= 100)
D. 15 mi

3. What is the distance traveled in 5 seconds by the car whose graph is shown below?

A. 10 m
B. 50 m (The distance is the area under the graph from 0-5 s, this is a triangle so Area=1/2 x 5 x 20 = 50)
C. 100 m
D. 20 m

Use the graph below to answer the following questions.



4. During which time interval is the object decelerating?
A. 12-16 s
B. 4-10 s
C. 0-2 s
D. 10-12 s

5. During which time interval is the object accelerating?
A. 12-16 s
B. 4-10 s
C. 0-2 s
D. 10-12 s

6. During which time interval is the object moving with a constant speed?
A. 2-10 s
B. 4-10 s
C. 0-2 s
D. 10-12 s

7. During which time interval did the object travel the greatest distance?
A. 2-10 s (The distance is the area under the graph. You can estimate this using the number of boxes)
B. 4-10 s
C. 0-2 s
D. 10-12 s

7. During which time interval did the object travel the shortest distance?
A. 2-10 s
B. 12-16 s
C. 0-2 s The distance is the area under the graph. You can estimate this using the number of boxes)
D. 10-12 s

8. An object travels a distance of 15 meters when an force of 4 N  act on it. What is the work done?
A. 30 J
B. 19 J
C. 60 J (Work = force x distance)
D. 11 J

QUESTIONS FOR THE DAY

1. A car is traveling at the speed of 20 mph. How far will it travel in 5 hrs?
A. 4 mi
B. 100 mi
C. 20 mi
D. 25 mi

2. A car is traveling at the speed of 20 mph. How far will it travel in 30 minutes?
A. 600 mi
B. 50 mi
C. 10 mi
D. 15 mi

3. What is the distance traveled in 5 seconds by the car whose graph is shown below?

A. 10 m
B. 50 m
C. 100 m
D. 20 m

Use the graph below to answer the following questions.



4. During which time interval is the object decelerating?
A. 12-16 s
B. 4-10 s
C. 0-2 s
D. 10-12 s

5. During which time interval is the object accelerating?
A. 12-16 s
B. 4-10 s
C. 0-2 s
D. 10-12 s

6. During which time interval is the object moving with a constant speed?
A. 2-10 s
B. 4-10 s
C. 0-2 s
D. 10-12 s

7. During which time interval did the object travel the greatest distance?
A. 2-10 s
B. 4-10 s
C. 0-2 s
D. 10-12 s

7. During which time interval did the object travel the shortest distance?
A. 2-10 s
B. 12-16 s
C. 0-2 s
D. 10-12 s

8. An object travels a distance of 15 meters when an force of 4 N  act on it. What is the work done?
A. 30 J
B. 19 J
C. 60 J
D. 11 J

IMPORTANT MOTION FORMULAS

There are some few motion formulas that you should know for the test.

1. Distance = speed x time 

2. Work = Force x distance

3. acceleration = change in velocity  =  Final velocity - Initial velocity  

                            change in time              Final time - Initial time

                            

Positive slope means the car is accelerating, that is the velocity is increasing with time. Zero slope means the velocity is constant (that is, not changing with time), and negative slope means the car is slowing down (that is, the velocity is decreasing with time)

Also, you must know the standard international (SI) units of the following:

1. Work -------------Joules (J)

2. Force ------------- Newtons (N)

3. Velocity ---------- meters per second (m/s)

4. Time ------------ seconds

A 12-STEP APPROACH TO STUDY FOR THE SCIENCE TEST

SCIENCE REVIEW-Overview

SCIENCE REVIEWThe topics that are generally covered in the test have been grouped into twelve instructional modules below. You will be tested only on the basic concepts of physics, chemistry and biology. Click on science topics and select any of the topics listed in the module to review.

Lesson 1:	Basic structure of atom Cell structure and function Functions of cell organelles Types of tissues
Lesson 2:	Movement of substances across the cell membrane Acids and bases, pH scale Carbohydrates, proteins, lipids and nucleic acids
Lesson 3:	Basic structure of the eye Basic structure of the ear Nervous system
Lesson 4:	Circulatory system Introduction to mechanics (motion/forces) Electrical circuits
Lesson 5:	Balancing chemical equations and writing formulas Essentials of photosynthesis and respiration Classifying organic compounds Magnetism Electromagnetism
Lesson 6:	Interpretation of graphs and pictograms Analyzing and making conclusions from experiments Data analysis
Lesson 7:	Endocrine system Digestive system Genitourinary system
Lesson 8:	Reproduction in mammals Basic parts of a flower Reproduction in plants (the process of pollination Genetics
Lesson 9:	Modes of heat transfer Calculating heat energies and phase diagrams Temperature conversions (Kelvin, Celsius, Fahrenheit)
Lesson 10:	Gas laws (Boyle, Charles, Gay-Lussac) Types of energy (Potential, kinetic, etc…..) Chemical bonds, equilibrium and equilibrium constants Mixtures, types of solutions, solubility
Lesson 11:	Concepts of the food pyramid, food web and food chain Light (diffraction, refraction, reflection, dispersion) Basic concepts on waves Sound waves Catalyst and enzymes
Lesson 12:	Symbiosis Ecology The Electroscope Radioactivity and half-life Tropism Tropism

PHYSICS - LAWS OF MOTION

We will study some physics today. Horray! You need to know some basic physics for the test. We will consider some of the laws of motion and their applications.

NEWTOW'S LAWS OF MOTION

1. A body at rest will remain at rest or if it is in motion, it will continue to move unless an opposing force acts on it. This law explains why if you leave a book on a table, it will be there forever unless somebody moves it. It also explains why somebody is thrown out of a moving car or bus live a projectile when the vehicle comes to a sudden stop. You move at the same speed of the vehicle you continue to move with this speed until the windshield stops you (opposing force)

2. The force on an object is directly proportional to its acceleration and the mass. The acceleration is inversely proportional to the mass. In others words, as the acceleration and the mass increase, the force increases. As the mass increases, the acceleration decreases and vice versa.

Force = Mass x Acceleration 

3. Action and reaction forces are equal but in opposite directions. What does this mean? If you push a wall, you exert an act force on it. The wall pushes you back with the same force (reaction force) which is in the opposite direction. The same thing happens with you standing on the ground.

QUANTITIES

There are two types of quantities used in science.

1. Scalar quantity: This quantity has only magnitude. Example: mass, time, density, volume, distance, speed, etc. Only the magnitude or size matters! For example, traveling 2 miles is distance or traveling at the speed of 2 mph or 2 km/hr.

2. Vector quantity: This quantity has both magnitude and direction. For example, displacement, velocity, weight, force, etc. The direction has to be specified.  For example, traveling 2 miles north is displacement or traveling at the velocity of 2 mph or 2 km/hr west.

STRUCTURE OF THE ATOM AND ELECTRON CONFIGURATION

ANSWERS TO REVIEW QUESTIONS FOR THE DAY

1. Which structure includes all of the others?
1. nucleolus
2. nucleus
3. chromosomes
4. genes

2. Most cell membranes are composed principally of
1. DNA and ATP
2. proteins and lipids
3. chitin and starch
4. nucleotides and amino acids

3. Which structure is usually present only in animal cells?
1. vacuole
2. cell wall
3. nucleus
4. centriole

4. Normally, in the process of osmosis, the net flow of water molecules into or out of the cell depends upon differences in the
1. concentration of water molecules inside and outside the cell
2. concentration of enzymes on either side of the cell membrane
3. rate of molecular motion on either side of the cell membrane
4. rate of movement of insoluble molecules inside the cell

5. Sodium ions are "pumped" from a region of lower concentration to a region of higher             concentration in the nerve cells of humans. This process is an example of
              A. diffusion

              B. passive transport

              C. osmosis

               D. active transport

6. An organelle differs from an organ in that an organelle

          A. is a substructure of a cell

          B. contains one specific type of tissue

          C. is larger than an organ

          D. cannot be stained

REVIEW QUESTIONS FOR THE DAY

1. Which structure includes all of the others?
1. nucleolus
2. nucleus
3. chromosomes
4. genes

2. Most cell membranes are composed principally of
1. DNA and ATP
2. proteins and lipids
3. chitin and starch
4. nucleotides and amino acids

3. Which structure is usually present only in animal cells?
1. vacuole
2. cell wall
3. nucleus
4. centriole

4. Normally, in the process of osmosis, the net flow of water molecules into or out of the cell depends upon differences in the
1. concentration of water molecules inside and outside the cell
2. concentration of enzymes on either side of the cell membrane
3. rate of molecular motion on either side of the cell membrane
4. rate of movement of insoluble molecules inside the cell

5. Sodium ions are "pumped" from a region of lower concentration to a region of higher             concentration in the nerve cells of humans. This process is an example of
              A. diffusion

              B. passive transport

              C. osmosis

               D. active transport

6. An organelle differs from an organ in that an organelle

          A. is a substructure of a cell

          B. contains one specific type of tissue

          C. is larger than an organ

          D. cannot be stained

ANSWERS TO QUESTIONS FOR THE DAY

1. How would cream crackers taste if it is chewed slowly?

A. Sweet     B. Bitter     C. Sour      D. Tasteless

2. What will be the end-product of maltose digestion?

A. glucose     B. glucose and galactose    C. galactose     D. glucose and fructose

3. What will be the end-product of sucrose digestion?

A. glucose     B. glucose and galactose    C. galactose and fructose     D. glucose and fructose

4. What will be the end-product of lactose digestion?

A. glucose     B. glucose and galactose    C. galactose and fructose     D. glucose and fructose

5. Which of the following will turn blue-black when test with Lugol's solution?

A. protein     B. starch    C. glucose     D.  fructose

Another name for iodine/alcohol solution is Lugol's solution.

QUESTIONS FOR THE DAY

1. How would cream crackers taste if it is chewed slowly?

A. Sweet     B. Bitter     C. Sour      D. Tasteless

2. What will be the end-product of maltose digestion?

A. glucose     B. glucose and galactose    C. galactose     D. glucose and fructose

3. What will be the end-product of sucrose digestion?

A. glucose     B. glucose and galactose    C. galactose and fructose     D. glucose and fructose

4. What will be the end-product of lactose digestion?

A. glucose     B. glucose and galactose    C. galactose and fructose     D. glucose and fructose

5. Which of the following will turn blue-black when test with Lugol's solution?

A. protein     B. starch    C. glucose     D.  fructose

CELL CHEMISTRY

There are three types of substances that life is dependent on. These are carbohydrates, proteins, and lipids (fats).                                                                                                                                                        

C  

1. Carbohydrates: These are used to produce energy for cellular activities.                                          

Types of carbohydrates:                                                                                                                            (a) simple sugars (monosaccharides): One sugar molecule–  Examples: Glucose, fructose and galactose.            

                               

(b) disaccharides: Two monosaccharide joined together.                  

Examples: Lactose = glucose + galactose; Sucrose = glucose + fructose; Maltose = glucose + glucose 

   

Exam hints: Memorize what the disaccharides are composed of.  In order words, what are the end products if you break down or digest a disaccharide.

                                                                                

(c) Complex sugars: Starch, cellulose and glycogen are made up of so many glucose joined together.

Exam hints: Glycogen is the storage form of carbohydrate in animals only . Cellulose is only found in plant cells.

2. Proteins are made up of amino acids. Proteins are the structural building blocks of the organism.

3. Lipids (Fats and oil) are made up of fatty acids and glycerol.

Test for some food substances:

Type of food substance	Test
Starch	Iodine test: Turns blue-black
Simple sugar (Glucose)	(a) Benedicts test: Brick-red coloration (b) Fehlings test: brick red coloration
Protein	Biuret test: light-blue color becomes purple
Lipid	Paper test: Oil stains paper

Exam hints: Memorize the test for the food substances.

ANSWERS TO THE QUESTIONS FOR THE DAY

1. A student placed a blue ink drop in a jar of water. After some time, the whole water turned blue. Which of the following processes occurred?
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

2. Water enters the roots of plants by which of the following process?
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

3. Oxygen from the atmosphere enters the blood from the lung by ____________________ .
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

4. The Na+/K+ ATPase pumps sodium and potassium in  and out of the cell by ____________ .
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

5. When a red blood cell (RBC) is placed in a hypertonic solution, it will ____________________ .
A. Increase in size
B. Shrink
C. Rupture
D. Remain the same

6. When a red blood cell (RBC) is placed in a hypotonic solution, it will ____________________ .
A. Increase in size and rupture
B. Shrink
C. Crenate
D. Remain the same

QUESTIONS FOR THE DAY!

1. A student placed a blue ink drop in a jar of water. After some time, the whole water turned blue. Which of the following processes occurred?
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

2. Water enters the roots of plants by which of the following process?
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

3. Oxygen from the atmosphere enters the blood from the lung by ____________________ .
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

4. The Na+/K+ ATPase pumps sodium and potassium in  and out of the cell by ____________ .
A. Osmosis
B. Simple Diffusion
C. Active Diffusion
D. Facilitated diffusion

5. When a red blood cell (RBC) is placed in a hypertonic solution, it will ____________________ .
A. Increase in size
B. Shrink
C. Rupture
D. Remain the same

6. When a red blood cell (RBC) is placed in a hypotonic solution, it will ____________________ .
A. Increase in size and rupture
B. Shrink
C. Crenate
D. Remain the same

MOVEMENTS ACROSS THE CELL MEMBRANE

Today, we will discuss the various types of movements across the cell membrane. This is a very important topic that you should know very well for the test. Don't just memorize the definitions but know different applications of the concepts. It is important to know some of the examples of hand!

Movement of substances across the cell membrane

1. Diffusion or passive transport: It is the movement of materials from a region of higher to a region of lower substance concentration.                                                                                                                                                                                                                                         Examples: When a bottle of perfume is opened, the scent spreads throughout the room. A drop of ink placed in a cup of water spreads throughout the water by diffusion.                                                
2. Active transport: It is the movement of molecules from a region of lower concentration to a region of higher concentration in which energy is needed in the form of ATP. The movement of the substance is against a concentration gradient.                                                                                                                                                                                                                                                          Examples: Sodium is pumped out of the cell by active diffusion. Potassium is pumped into the cell by active diffusion.                                                                                                                                       
3. Osmosis: It is the flow of water molecules from a less concentrated solution (hypotonic solution) to a higher concentrated solution (hypertonic solution) through a semi-permeable membrane.                                                                                                                                                                Example: When a red blood cell is placed into water, the water flows across the cell membrane into the cell because of the dissolved salts in the cytoplasm.                                                              Water flows from the soil into the roots of plants by osmosis.                                                                   
4. Facilitated diffusion: As certain substances move into the cell by simple or passive diffusion, they create the opportunity for other substances to go into the cell freely.                                                                                                                                                                                              Example: Glucose follows sodium as it enters the cell by facilitated diffusion.                                               
5. Endocytosis: This is the process by which the cell engulfs or captures substances into the cytoplasm. It consist of pinocytosis (Cell-drinking) and phagocytosis (Cell-eating)                                                            
6. Exocytosis: This the process by which the cell extrudes or gets rid of substances  from within the cell to the outside.