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_ BiologyFolio.Dec09.

Active transport

Sodium ion approach the carrier protein. The carrier protein has a site for the sodium

ions and another site to bind the ATP molecules.

The carrier protein binds the sodium ions. The ATP molecules is split into ADP and

phosphate. The splitting of ATP releases energy to the carrier protein.

Energy from the ATP changes the shape of the carrier protein to release the sodium ions

outside the cells.

The carrier protein turn to original shape.

Plasma membrane1


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Plasma membrane is made up ofprotein and phospholipid.

A phospholipid is an amphipathic molecule. This means that it has both a

hydrophilic region and a hydrophobic region.

The polar head region is hydrophilic (attracted towater) while the non-polar tail is hydrophobic

(repelled by water).

The interaction of the tails of the phospholipid

bilayer prevents adjacent phospolipid from packing

too tightly together. This makes the membrane

more fluid.

The characteristic of the phospholipid bilayer is semi-permeable. It only allow

some substances to cross the plasma membrane.

2

Structure of

plasma membrane

Examples of substances that move across the

plasma protein

Phospholipid

bilayer

i. Lipid-soluble molecules : fatty acid, glycerol and

vitamin A,D,E,K.

ii. Non-polar molecules : O2,CO2iii. Small molecules : H2O

Pore protein i. Small water-soluble molecules & ions : K+,Na+,Ca+.

Carrier protein i. Large water-soluble molecules : glucose and amino

acid.


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Facilitated diffusion Facilitated diffusion is the movement of molecules from region of high

concentration to region of low concentration with the help of transport protein.

Facilitated diffusion that occurs with the help ofcarrier protein only allows

molecules insoluble in fats such as glucose and amino acids to cross the plasmamembrane.

The mechanism of carrier proteins in facilitated diffusion is as follows :

(a) The solute moves to the binding site of the specific carrier protein.

(b) The solute binds to the carrier

protein at the binding site and

triggers the carrier protein to

change its shape.

(c) The carrier protein changes its

shape and moves the solute across

the membrane.

(d) The carrier protein returns back to

its original shape.

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Facilitated diffusion that occurs through pore protein only allows small charged

molecules such as mineral ions to pass through the pore in the protein molecules.

Effects of different concentration

of solution on red blood cell

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5

Concentra

tion of

solution

Environment of cell Explanation

Hypotonic When red blood cell are placed in a

hypotonic solution (distilled water),

water molecules diffuse into the red

blood cells by osmosis.

The red blood cells gain water and

swell and finally burst because they

have no cell walls.

The red blood cells are said toundergo haemolysis.

Isotonic If red blood cells are immersed in an

isotonic solution (0.85% sodium

chloride solution), water molecules

flow across the membrane at the

same rate in both directions.

There is no net movement of water

molecules across the membrane.

The red blood cells maintain their

shape. The concentration in the red blood

cells is the same as the

concentration in the environment,

that is 0.85% sodium chloride

solution.

Hypertoni

c

When red blood cells are placed in a

hypertonic solution such as 4%

sodium chloride solution (salt

solution), water molecules diffuse

out of the cells by osmosis. Water is rapidly lost.

The red blood cells will shrivel and

probably die.

This process is called crenation of

red blood cells.


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Effects of different concentration

of solution on plant cellConcentra

tion of

solution

Environment of cell Explanation

Hypotonic When a plant cell is immersed in a

hypotonic solution such as water,

water molecules diffuse into the

cell by osmosis.

The vacuole gains water, expandsand exerts pressure outwards on the

cell wall.

This pressure is called turgor

pressure. It caused the plant cell

become turgid.

The turgidity of the cells give the

plant mechanical support.

Isotonic If the plant cell is immersed in an

isotonic solution such as 5% sucrose

solution, there is no net movementof water across the plasma

membrane.

Water flows across the membrane

at the same rate in both directions.

The cells volume and shape remain

constant.

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_ BiologyFolio.Dec09.Hypertoni

c

When a plant cell is placed in a

hypertonic solution such as 30%

sucrose solution, water molecules

diffuses out of the cell by osmosis.

Water is lost from the vacuole and

cytoplasm.

The vacuole shrinks and becomessmaller. The cytoplasm, together

with the plasma membrane,

shrinks and is pulled away from the

cell wall.

The plant cell loses water and

shrivels. The cell becomes flaccid,

causing the plant to wilt.

This process is called plasmolysis.

If the plasmolysed plant cell is

immersed in a hypotonic solution,

there is a net movement of water

into the cell.The cell will expand and

become turgid again.

The plant cell is said to undergo

deplasmolysis.

Lock and key hypothesis

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An enzyme is a molecule with an active site that has a specific shape.

The active site of the enzyme (the lock) is a place where its substrate

molecule (the key) fits in exactly.

The substrate molecule fits into the active site to form an enzyme-substrate

complex.

The enzyme speeds up the change of the substrate into its product. The product

then leaves the active site.

The enzyme remains unchanged and can be used again to act on more

substrates.

Production of extracellular enzyme

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1. The instruction for producing the extracellular enzyme comes from the DNA in the

nucleus. The information in the DNA is copied into messenger RNA (mRNA).

2. mRNA goes out of the nuclear pore and attaches itself to ribosome on the Rough

Endoplasmic Reticulum (ER).

3. The protein that synthesized in the ribosome transported through rough ER.

4. Proteins wrapped in vesicles (transport vesicles) bud offfrom the side of rough ER.

5. These transport vesicles will fuse with the membrane of the Golgi Apparatus.

6. These protein are then modified along the golgi apparatus and form enzymes.

7. Modified proteins finally buds off as a secretory vesicles at the other end of the golg

apparatus.

8. Secretory vesicle contain modified protein fuse with plasma membrane to secrete the

enzyme.

Effects of temperature on the rate

of enzyme reaction

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Effects of pH on the rate of

enzyme reaction

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Enzymes are denatured by changes in the pH level of the reaction medium. An enzyme that functions at pH7, the optimum pH, will be inactive when its reaction

medium becomes too acidic or too alkali.

A change in pH results in a change in the concentration ofhydroxide ions (OH-) and

hydrogen ions (H+). The excess of hydroxide ions or hydrogen ions destabilize the

enzyme by changing the shape of the active site and the enzyme stops functioning.

The effects of changes in pH on the rate of enzyme reaction are reversible. An enzyme

that is inactive in a low pH will be active again when it is at optimum pH.

Each enzyme function actively at its optimum pH.

Technique of plant tissue culture

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_ BiologyFolio.Dec09. Tissue culture is a technique in reproduction which involves the transfer of tissues o

cells from an organism into a suitable culture medium to produce a whole new organism

that is identical to the existing organism.

New individuals that are produced are generally identical to the original parent and

called clones.

The culture medium must be sterile to kill microorganisms that would contaminate the

culture. The culture medium contains nutrients for the growth and differentiation of cellsThe cultures are incubated at an optimal temperature of 37oC and at an optimal pH level

Figure below shows the tissue culture technique used in the production of orchids in

Malaysia.

Technique of cloning

Cloning is a highly artificial form of asexual reproduction based on mitosis to form new

individuals.

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_ BiologyFolio.Dec09. The new individuals have the same genetic material as the parent and are called

clones.

The cells actively divide by mitosis, differentiate and develop to form whole new

individuals which are identical to the parent.

In animals, cloning is carried out by replacing the nucleus of an unfertilized egg cell with

the nucleus from a diploid cell.

The offspring is produced by mitosis from a diploid cell and not by fusion ogametes.

Steps in the cloning process are as follows :

(a) A somatic cell (from the skin) is taken from an adult animal A.

(b) An ovum from another female animal B is taken and its nucleus is removed.

(c) The nucleus from the cell of animal A is then placed inside the ovum.

(d) The ovum is then placed in a petri dish containing nutrients solution where i

divides repeatedly to form an embryo.

(e) The embryo is then transferred into the uterus of another female animal.

(f) The young animal born is a replica of animal A.

Comparison between mitosis &

meiosis

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15

Mitosis Aspect Meiosis

In somatic cells Place

occur

In reproductive organs

(testis and ovary)

Parent cell divides once Number of

divisions

Parent cell divides twice

Produces two diploid daughter

cells

Number of

daughter

cells

Produces four haploid daughter

cells

(gametes)

Synapsis does not occur Synapsis

of

homologou

s

chromoso

mes

Synapsis occurs during prophase

I

Cytokinesis occurs once Number of

cytokinesis

Cytokinesis occurs twice

Crossing over does not occur Crossing

over of

chromatids

of

homologou

s

chromosomes

Crossing over occurs during

prophase I

Each daughter cell has the

same number of

chromosomes as the parent

cell

Number of

chromoso

mes in

daughter

cells

Each daughter cell has half the

number of chromosomes of the

parent cell

Daughter cells are genetically

identical to the parent cell

Genetic

compositio

n of

daughter

cells

Daughter cells are genetically

non-identical to the parent cell

and to each other

Occur during interphase

before mitosis begins

DNA

replication

Occurs once during interphase

before meiosis I

Produces cells for growth,

maintenance and repair of

body tissues

Role in the

animal

body

Produces gametes, results in

genetic variation among the

gametes, reduces chromosomes


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Human digestive system

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18

Part of the

system and

related

organs

Secretion

(pH)

Enzymes/activ

e substance

Enzyme action/other actions

Mouth

Teeth

Salivary glands

Tongue

---

Saliva

(alkaline)

---

---

Amylase

---

Mechanical digestion and mixing of foodwith saliva.

Hydrolysis of starch:

Starch + water amylase maltose

Rolling food into a bolus for easy

swallowing.

Oesophagus --- --- Peristalsis (a series of wave like muscular

contractions of the oesophagus) to move

food down to the stomach.

Stomach

-a muscular

sac that mixes

food with

gastric juice

into a paste

called chyme.

Gastric

juice

(acidic,pH

1.5-2.0)

Mucus

Hydrochloric

acid

Pepsin

Rennin

---

i. Stops the action of enzyme amylase

ii. Provides an acidic medium

iii. Kills bacteria in the food

Hydrolyses proteins:

Protein + water pepsin peptone +

polypeptides

Converts the soluble milk protein

caseinogens into insoluble casein.

Caseinogenrennin

casein

Protects the stomach wall from the acid

and enzymes.

Duodenum

Liver Bile Bile salts Emulsifies fats into smaller droplets to


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Comparison between ruminants

and rodents

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Ruminants Aspects Rodents

Digest cellulose in the stomach Digestion of

cellulose

Digest cellulose in the caecum

Bacteria and protozoa in the

stomach secrete the enzyme

cellulase

Presence of

cellulose

enzyme

Bacteria and protozoa in the

caecum secrete the enzyme

cellulase

Stomach has four chambers The structure

of the stomach

Stomach has one chamber

Caecum is short Length of the

caecum

Caecum is long and large

The food first goes into the

rumen and reticulum.It is then

returned to the mouth to be

chewed again. The food is then

swallowed into the omasum and

lastly abomasum.

The time for

the food to go

through the

alimentary

canal

The food goes through the

alimentary canal twice. The

rodents eat back the partially

digested food after it has

passed the alimentary canal the

first time.


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Absorption of nutrient in the villus

Glucose, amino acids, minerals, vitamin B and C are absorbed by simple

diffusion into the bloodcapillaries. These substances are carried by the hepatic

portal vein to the liver and then distributed to the body cells by the circulatory system.

Glycerol, fatty acids and vitamin A, D, E, Kare absorbed into the lacteal of the

villus. The fatty acids and glycerol diffuse across the epithelium and recombine to form

fat droplets. The fat droplets and vitamins A, D, E, K in the lacteals are carried out of theileum by a larger lymphatic vessel called thoracic duct. From the ileum, the thoracic

duct carries the content of the lacteal into the blood stream via the left shoulder vein

(left subclavian vein) and then distributed to the body cells by the circulatory system.

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Structural adaptations of the leaf

for photosynthesis

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E

X

T

E

R

N

A

L

F

E

A

T

U

R

E

S

Structure Adaptation Explanation

Lamina of

the leaf

Broad, flat and

thin

The broad and flat shape provides a

large surface area for the maximumabsorption of sunlight and carbon

dioxide

Thin leaf allows light to penetrate and

reach the cells. It also allows carbon

dioxide to diffuse rapidly to the cells in

the leaf

Position of

the leaf

Leaf is positioned

at right angle to

rays of sunlight

To absorb maximum sunlight

Arrangeme

nt of the

leaf

Leaves are

arranged in a

mosaic pattern so

that they do not

overlap

To absorb maximum sunlight

Upper

epidermis

Translucent Allows sunlight to pass

I

N

T

E

Palisade

mesophyll

cells

Contain the

greatest number

of chloroplasts Closely packed

For maximum absorption of sunlight for

photosynthesis

Spongy

mesophyll

cells

Loosely arranged

with large air

spaces between

the cells

Provides large air pockets to facilitate

the diffusion of carbon dioxide and

oxygen

Carries out photosynthesis

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_ BiologyFolio.Dec09.R

N

A

L

F

E

A

T

U

R

E

S

Contain

chloroplasts

Stoma Many Allows the exchange of gases between

the cells in the leaf and the atmosphere

Vascular

bundles in

the vein

(xylem and

phloem)

Branch out to

form a network

Both xylem and

phloem are long

and continuous

tubes

Transport water, minerals and products

of photosynthesis efficiently and quickly

Equations of mechanism of

photosynthesis

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Light reaction of photosynthesis

1. Light reaction occurs in the granum of the chloroplast only in the presence of light

and involves the trapping oflight energy and the formation of materials required

for the dark reaction.

2. Energy from sunlight is absorbed by the chlorophyll to split the water molecules into

hydroxyl ions and hydrogen ions. This process is called photolysis of water.

4H2Osunlight 4H+ + 4(OH)-

chlorophyll

3. Each hydroxyl ion is neutralized by releasing its electrons to the chlorophyll. A neutral

hydroxyl group is formed. Four hydroxyl groups combined together to form water and

oxygen.

4(OH)- - 4 electrons 4(OH)

4(OH) 2H2O + O2

4. Each hydrogen ion receives an electron from the chlorophyll and is neutralized. A neutral

hydrogen atom is formed. The hydrogen atoms are used in dark reaction to reduce carbon

dioxide.

4(H)+ + 4 electrons 4(H)

Dark reaction of photosynthesis

1. Dark reaction occurs in the stroma with or without light and involves using the products

from the light reaction to form glucose.

2. Hydrogen atoms produced during light reaction are used in dark reaction to reduce carbon

dioxide to basic units of glucose (CH2O). This reduction of carbon dioxide process

involves a series of complex chemical reactions which require enzymes.

CO2 + 4(H) (CH2O) + H2O

3. Six units of (CH2O) combine together to form a molecule of glucose.

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6(CH2O) C6H12O6 (glucose)

4. Glucose is converted into starch, cellulose, other sugars (sucrose) and lipids. When

combined with nitrogen, glucose is converted to protein.

5. The overall process of photosynthesis can be represented in the following equation:

12H2O + 6CO2sunlight C6H12O6 + 6O2 + 6H2O

chlorophyll

Gaseous exchange between

alveolus and blood capillary

1. Inhaled air in the alveolus contains more oxygen and less carbon dioxide compared to

the quantities in the blood capillaries of the lungs.

2. Hence the partial pressureofoxygen is higher in the air of alveolus compared to

the partial pressure of oxygen in the blood capillaries.

3. The higher partial pressure of oxygen in the alveolus causes the oxygen to dissolve in

the layer of moisture on the wall of the alveolus and diffuse out of the alveolus into the

blood capillaries.

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4. During respiration, carbon dioxide is produced. The blood capillaries in the body

transport the carbon dioxide to the alveolus.

5. Hence the partial pressure of carbon dioxide in the blood capillaries is higher

than the partial pressure of carbon dioxide in the alveolus.

6. As a result, the carbon dioxide in the blood capillaries diffuses out of the blood

capillaries into the alveolus and expelled during exhalation.

Gase

ous

27

Respirat

ory gas

Partial

pressureEffect

Air of

alveol

us

Blood

capillar

ies

Oxygen High Low Oxygen in the

alveolus diffuses

into the blood

capillaries

Carbon

dioxide

Low High Carbon dioxide in

the blood

capillaries diffuses

into the alveolus


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exchange between blood capillary

and body cells

1. In the body cells which lack oxygen, the high partial pressure of oxygen in the

blood caused the oxygen to diffuse out of the capillary into the body cells.

2. The body cells contain a high concentration of carbon dioxide, a product of cellular

respiration.

3. Hence the partial pressure of carbon dioxide in the body cells is higher than the

partial pressure of carbon dioxide in the blood capillaries.

4. Carbon dioxide diffuses out of the body cells into the blood capillary.

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