Year 2 Life Science Notes

Topic Page
Chapter 1: Enzymes 2
Chapter 2: Cellular Transport 5
Chapter 3: Nutrition in Plants 6
Chapter 4: Seed Structure and Germination 9
Chapter 5: Hydroponics 12
Chapter 6: Plant Transport 14
Chapter 7: Human Transport 18
Chapter 8: Nutrition in Man 22
Chapter 9: Human Digestive System 27
Chapter 10: Human Reproductive System 30
Life Science Important Terms 35
End of Year Practice Essay Questions 40

By: Oscar Chiang

 Chapter 1: Enzymes

- What are Enzymes?

Enzymes are proteins which act as biological catalysts (speed up biochemical reactions) that
remain unchanged at the end of the reaction.

- Characteristics of Enzymes
1. Being proteins, they are sensitive to temperature and pH changes. They work efficiently
within an optimal temperature and pH. High temperature and different pH values will
denature and inactivate enzymes. Enzymes are more sensitive to pH changes than to
temperature changes.

2. Enzymes are not affected by the reactions they catalyse (they return to their original
shape at the end of the reaction).

3. Enzymes is not required in large quantities as they are not used

up/denatured/inactivated in a reaction. The same enzyme molecule can process a large
number of substrate concentration. (Enzymes are reusable).

4. Enzymes are highly specific. Enzyme molecule has specific shape and special site (the
active site) on the molecule can bind only to specific substrate.

- Lock-and-key hypothesis

Legend
Substrate = ‘Key’ Substrate
Enzyme = ‘Lock’ has binded
to the active
site

The enzyme has a specific

A chemical reaction occurs. The enzyme remains unchanged and
active site and can only bind to
a specific active substrate. is ready for another reaction.

The substrate, which is the ‘key’ will bind to the active site of the enzyme, which is the ‘lock’.
Then, the enzyme will catalyse the reaction and the products would move away from the
active site, The enzyme is now able to take another substrate molecule into its active site.

By: Oscar Chiang Page 2

 - Factors that affect enzyme activity
1. Temperature
2. pH
3. Substrate concentration
4. Enzyme concentration

1. Temperature
rate of reaction ① Low temperature à Lesser kinetic energy the enzymes and
② substrates à Lower rate of reaction

1-1
optimum temperature For every 10℃ rise in temperature up to 37℃, the enzyme activity
doubles.
denatur
② Theoptimum temperature, 37℃, is the temperature at which
mes

① ③
nzy

enzymes catalyse a reaction at the maximum rate. Most enzymes in

e
e

d enzym
ive

human have an optimum temperature of about 37℃.

t
inac

③ Enzymes denature (irreversible) à the active site will change

es

shape à substrate is unable to bind to enzyme’s active site à rate

37 temperature 1°C of reaction decreases.

2. pH
rate of reaction

1-
①② Extreme pH (on both ends) à enzymes are denatured.
Enzymes are highly sensitive to pH changes. A slight change in pH
most human cells can affect the rate of enzyme-catalysed reactions as each enzyme
trypsin functions optimally at a particular pH.
pepsin ① ②
At very high or very low pH values, ionic bonds within the enzymes
① ②
① ② are disrupted and this changes the active site.

2 7 9 pH
3. Substrate Concentration
rate of reaction ① Increasing substrate concentration increases rate of reaction as

Let
② there are available enzymes for the substrate to bind to.
② Increasing substrate concentration after all enzymes are unavailable
enzyme is
①
limiting factor! will not increase rate of reaction as the rate is already at its maximum
as all enzymes are forming enzyme-substrate complex.

Example:
If an enzyme can bind with 5 substrates per second, and there is one
enzyme and 5 substrates, it will be at the maximum rate of reaction. If
there are 5 more substrates added, the rate of reaction will remain the
substrate concentration same.

4. Enzyme concentration
As enzyme levels increase, reaction rate will increase till substrate concentration < enzyme
rate is concentration and substrate is the limiting factor.
g factor rate of reaction

It
substrate is
limiting factor!

concentration

enzyme concentration

By: Oscar Chiang Page 3

 - Commercial applications of enzymes
1. Food processing industry
2. Textile industry
3. Detergents

1. Food processing industry

• Protease tenderises meat
• Lactase catalyses the hydrolysis of lactose in making lactose free milk or ice cream.
• Cellulase catalyses the breakdown of cellulose and the removal of seed coats from
cereal grains.

2. Textile industry
• Amylase helps remove starch that is used as stiffeners from fabrics.

3. Detergents
• Protease and amylase help dissolve protein and starch in clothes respectively.

By: Oscar Chiang Page 4

 Chapter 2: Cellular Transport

1. Diffusion
Diffusion is the net movement of particles from a region of higher concentration to a lower
concentration. (No need for partially permeable membrane)

It is a passive process.
Cannot occur in solids.

2. Osmosis
Osmosis is the net movement of water molecules from a region of higher water potential to
a region of lower water potential across a partially permeable membrane.

What is water potential?

Water potential is the measure of tendency of water.

The higher the water potential is, the steeper the concentration gradient is, and osmosis will
occur faster.

It is a passive process.

When placed in… Animal Cells Plant Cells

Hypotonic solution (lower solute Burst / Lyse Expand and
concentration than cell) becomes turgid
Hypertonic solution (higher solute Shrink and crenate Flaccid /
concentration than cell) Plasmolysed
Isotonic solution (equal solute No change No change
concentration)

3. Active Transport
Active transport is the movement of water from a region of lower solute concentration to a
region of higher concentration which requires energy, in the form of ATP molecules.
Example: Occurs in the root hair cells of the plant – will be elaborated in Chapter 6.

It is an active process (so it requires energy).

Recall: Year 1
ATP molecules are produced in the mitochondria in the nucleus of the cell, through
respiration.
A saturated solution is a solution that maximum amount of solute is dissolved in a volume of
solvent.

By: Oscar Chiang Page 5

 Chapter 3: Nutrition in Plants

- What is growth?
Growth is the gradual increase of size or number, often leading to an increase in biomass of
an organism.

- Ways to measure growth

1. Height of plant
The increase in the height of plant is measured by a measuring tape or ruler. Need to
specify the range of measurement.

2. Size of leaf
The surface area of the leaf is estimated by using graph paper or measuring the length
and breadth of the leaves.

3. Number of leaves
The number of leaves is counted over a period of time.

4. Length of roots
The length of the roots is measured, sometimes using a string. The range needs to be
specified.

5. Biomass
Fresh Mass Dry Mass
• Mass of plant when it is alive. • Mass of plant when it is
• Includes the mass of water completed devoid of water,
content within the plant. measuring only the mass of
• May fluctuate depending on the biological matter.
amount of water it contains. (As • More reliable.
water content can change
depending on conditions and a
plant may contain less water if
the weather is hot) as such it is
less reliable.

- Measuring dry mass

Firstly, remove and clean the plant to make sure it does not contain any other material.
Press the plant in between two pieces of absorbent paper to squeeze out as much liquid as
possible. Then, place the plant in the oven at low temperature (about 40°𝐶) for a day.
Remove the plant from the oven and obtain its mass. Place the mass back into the oven for a
few more hours. Obtain the mass of the plant again. If the mass is consistent for at least 3
readings, the reading is the dry mass of the plant. If it is not consistent, repeat the heating
process till a consistent mass is achieved.

By: Oscar Chiang Page 6

 - Factors affecting plant growth
1. Light
a. Quality (Wavelength)
• Sunlight is a natural source of light, hence, it cannot be changed or
manipulated.
• Quality of light from light bulbs, an artificial source of light, can be changed
or manipulated and hence they are usually used in experiments in the
laboratories.
• Plants also reflect all green light and absorb blue and red light the most.

b. Intensity (Brightness)
• As light intensity increases at first, the stomata of plants will open, allowing
the rate of photosynthesis to increase. This continues till the high light
intensity results in a high temperature and the stomata will close to prevent
excessive loss of water by transpiration.

c. Duration (Photoperiod)
• The number of hours of light and darkness that a plant receives in a day.
• Affects whether the plant will flower or not.
• E.g., Soybean plants only flower when day length is shorter than crucial
period.

2. Temperature
Directly affects
a. Photosynthesis
• Rate of photosynthesis is optimum when temperature is between (18°𝐶 –
27°𝐶)

b. Respiration
• Respiration is the oxidation of food substances with the release energy in
living cells. Primary source of energy for plants is from the sun. During
photosynthesis, the energy is captured as chemical energy which is stored in
the form of starch in plants. Therefore, as temperature affects
photosynthesis, it would indirectly affect respiration.

By: Oscar Chiang Page 7

 3. Mineral nutrients
• Macronutrients – Plants require them in large amounts.
e.g., Nitrogen (N), Phosphorus (P) and Potassium (K) are macronutrients.

• Micronutrients – Plants require them in small amounts.

e.g., Copper (Cu), Zinc (Zn) and Iron (Fe) are micronutrients.

- Role of mineral elements in plant functions

Nutrients Function Deficiency Symptoms
Nitrogen (N) Needed to form proteins and Stunted growth
chlorophyll. Required for growth of Light green older leaves
plants especially young plants. Older leaves turn yellow and
die
Phosphorus (P) Components of nucleic acids, Stunted growth
phospholipids and ATP. Required for Purplish veins in older leaves
flowering plants. Fewer seeds and fruits
Potassium (K) To activate enzymes and maintain Reduced growth
water-soluble balance and will affect Curled, mottled or spotted
photosynthesis. Required for root older leaves
and sustaining fruit growth in plants. Burned leaf margins
Weakened roots and stems.

- Other sources of Nitrogen for Leguminous Plants

Leguminous plants (e.g., string beans, soybeans, peas, alfalfa, clover) are to form a symbiotic
relationship with Rhizobium Bacteria.

A symbiotic relationship is a relationship that both parties from each other; the leguminous
plants obtain nitrogen while the bacteria obtain food and shelter from the relationship.

The Rhizobium Bacteria live in the nodules and convert atmospheric nitrogen to ammonia,
and the plant will make use of ammonia to make amino acids.

By: Oscar Chiang Page 8

 Chapter 4: Seed Structure & Germination

- What is a seed?
A seed in a plant is the part that develops from ovule after fertilisation. Seeds are enclosed
in the fruit which develops from the ovary after fertilisation.

- Structure of a dicotyledonous seed

Embryo – consists of a radicle (the root), the plumule, epicotyl (upper stem) and hypocotyl
(lower stem).
Cotyledons – contains food reserves, mainly starch, for the embryo when grows.
Testa (seed coat) – Encloses the embryo and cotyledons; protects the embryo from injury
and drying out.
Micropyle: a tiny opening in the testa for water to enter the seed before germination.

- Dormancy of seeds
Dormancy is a mechanism to prevent germination of the seed during unsuitable
environment conditions, when the probability of seedling survival is low.

By: Oscar Chiang Page 9

 - Stages of Germination
1. The seed absorbs water and swells. When conditions are suitable, the seed will
germinate.
2. The radicle will grow first and burst through the testa. The radicle will grow downwards.

Hypogeal Germination
3. Epicotyl will start to grow and elongate rapidly that it pulls the plumule out from
between cotyledons.
4. The epicotyl will then straighten once the plumule leaves are above the soil.

In hypogeal germination, the cotyledons will stay below the soil.

Epigeal Germination
3. The cotyledons are then raised out of the soil due to rapid growth of the
hypocotyl before the epicotyl growth.
4. The epicotyl growth later brings out the plumule from the cotyledons.

In epigeal germination, the cotyledons are raised out of the soil.

- External Conditions for Germination

1. Water
• Water is entered through the micropyle.
Function:
• Water softens the testa and make it permeable to gases for better gaseous
exchange.
• Food materials in the cotyledons will become soluble for the embryo’s use.
• Enzymes are activated.

2. Oxygen
Oxygen is required for the cells to undergo aerobic respiration (the breakdown of
glucose in the presence of oxygen), to release energy for germination and growth.

3. Temperature
Seeds germinate within certain range of temperatures that can differ for different
species. A suitable temperature is essential to activate the enzymes involved in
germination and growth.

By: Oscar Chiang Page 10

 4. Light
The effect on light on germination differs for different plants.

Many seeds are not influenced in the germination by the presence or absence of light.

However, there are some seeds affected by light, either require light for germination or
cannot germinate in the presence of light.
e.g.,
Need light - geranium, petunia
Do not need light – delphinium, calendula

- How does a seed grow into a plant?

By: Oscar Chiang Page 11

 Chapter 5: Hydroponics System

Types of Systems Open System Closed System

Advantages No need to incur the cost of pump There is no contamination of the
system which is used in the closed environment as the solution is re-
circuit to re-circulate the nutrient circulated within the system.
solution.
The system recycles nutrient
The concentration of nutrients and pH solutions as effectively as possible.
of the solution does not need to be
checked if a fresh solution is always
used. This saves manpower.

Disadvantages The cost of regular replacing of The nutrient solution has to be

nutrient solution is high. sampled and analysed at least once
a week to ensure that the nutrient
The run-off contaminates the balance is maintained > this is
environment as the used nutrient labour intensive.
solution can cause eutrophication > to
remove eutrophication, it will cost A pump system is needed to
more. recirculate and oxygenate the
nutrient solution.

Factors Quality that it measures Optimum range for

hydroponic nutrient solution
pH Acidity or alkalinity of the 5.8 – 6.5
nutrient solution
Electrical Conductivity (EC) The strength of nutrient 1.5 – 2.5
solution

Nutrient Film Technique Deep Flow Technique Aeroponics

It is cost-efficient as the nutrient It is cost-efficient as the nutrient It is cost-efficient as the nutrient
solution is being reused. solution is being reused. solution is being reused.

There is a lower consumption of Small changes of nutrient levels, pH, The roots are well aerated > faster plant
nutrient solution as there is only a thin temperature, and dissolved oxygen growth.
film of nutrient solution flowing. concentration would not affect the
plants. It uses 65% less water and only 25% of
the nutrient input compared with
hydroponics.

By: Oscar Chiang Page 12

 The pump must not fail or else it can The pump must not fail or else it can If any of the high-pressure pumps,
cause plants to wither. cause plants to wither. sprinklers and timers break down, it can
damage or kill the plant easily.
It is not suitable for plants with large
tap-root systems > it will clog up the The root chamber must be disinfected,
trough and impede (hinder) the flow of or diseases may affect the roots.
nutrients.

Advantages of Hydroponics Disadvantages of Hydroponics

It is easier to sow and harvest crops compared to soil farming. Without soil as a buffer, any failure to the hydroponic system
Although hydroponics is still labour intensive, the work is not leads to rapid plant death.
so heavy and technology can be put to good use in parts of Failures include breakdown of pumps and sprinklers. This will
the operation. lead to rapid plant death as they will not be receiving enough
nutrient solution.
In closed systems, water stays in the system and can be re-
circulated, this is useful in drier areas. pH and EC values need to be checked regularly in closed
systems. This requires manpower.
More efficient use of space. Therefore, maximum crop yield.
Plants are susceptible to pathogens without the protection
There is a high degree of control over the nutrients used, and provided by soil microorganisms.
this reduces cost.
Aeration can be a problem and plants can become water-
No nutrient is released into environment in closed systems. logged. (Aeroponics solves this problem)
This minimises eutrophication.

There is no limitation in terms of fertility of soil as the growing

locations can be extended to areas not suitable for soil
farming.

In a controlled environment, crops can be grown out of

season or in unsuitable climates.
Template By: Mdm Krystal Lee

By: Oscar Chiang Page 13

 Chapter 6: Plant Transport

- Plants are multicellular organisms.

Division of Labour: each cell has a specific function.

- Plant Transport System

• The plant transport system lies in the vascular bundle.
The vascular bundle includes xylem and phloem.

• Drawing of dicotyledons stem

Walls of xylem are thicker than the walls of phloem because it is heavily lignified.
Vascular bundle of the dicotyledons stem is neatly arranged around the epidermis.

• Drawing of dicotyledons root

The vascular bundle of dicotyledons root is in the endodermis.

• Drawing of leaf

By: Oscar Chiang Page 14

 - Phloem
Function: Transport carbohydrates (such as sucrose and amino acids) from the leaves to
other parts of the plant.
It is a bi-directional flow.

Structure:
• Made of sieve tube cells which form together to form sieve tubes.
• Sieve tube cells does not have cell organelles such as nucleus and vacuoles, hence,
they are unable to maintain itself.
• Therefore, there are companion cells accompanied next to sieve tube cells which
help to maintain the sieve tube cells.

• Companion cells are living cells with functional plasma membrane, mitochondria and
nucleus.

Capable of respiration (aerobic respiration; the breakdown of glucose and oxygen)

to release energy in the form of ATP molecules for active transport of sucrose from
leaves to phloem.

- Xylem
Function: Transport water and mineral salts from the roots to other parts of the plant.
Provides mechanical support to the plant as the walls are heavily lignified.
It is a unidirectional flow.

Structure:
• Made of tracheids and vessels.
• Dead cell walls with no protoplasm – nucleus, cell membrane and cytoplasm.
• Adjacent cell walls broken down to form a long, continuous thin hollow tube.
• Walls are heavily lignified.

- Root hair cells

Function: To absorb water and mineral salts from the surroundings.

Adaptations:
• Long and thin
This increases surface area to volume ratio, increasing rate of absorption.

• High concentration of cell sap

This maintains the low water potential in the cell to facilitate the intake of water via
osmosis.

• Living cells
Living cells contains mitochondria. With mitochondria, the cell is able to undergo
aerobic respiration to release energy in the form of ATP molecules for the active
transport of mineral salts from the surroundings into the cell.

By: Oscar Chiang Page 15

 - Movement of water
• Root Pressure

Root pressure is caused by the low water potential of xylem sap which is created by
dissolved minerals and sugars.

• Capillary Action

Capillary Action occurs when the forces binding a liquid together (cohesion and
surface tension) and the attracting forces that bind water molecules to another
surface (adhesion) are greater than the force of gravity.

Cohesion is the attractive forces that attract water molecules together. (Water
molecules have strong cohesion forces between the molecules)

Adhesion is the attractive forces that attract water molecules to other molecules.
(Water molecules ‘stick’ to the surface of its surrounding)

By: Oscar Chiang Page 16

 • Transpiration Pull
What is transpiration?
Transpiration is the loss of water vapour through aerial parts of the plant.

Water evaporates from leaf cells to water vapour and moves to the air spaces in the leaf. Water
vapour will then diffuse out of the leaf through the stomata. When water evaporates from the leaf
cells, the leaf cells’ water potential decreases. The water in the xylem will diffuse into the leaf cell via
osmosis through the partially permeable cell membranes.

- Rate of Transpiration
• Humidity
Higher humidity (more water vapour in the surrounding air) à reduces
concentration gradient of water vapour between intercellular air spaces and outside
air à reduces the rate of diffusion of water vapour out of the stomata à reducing
rate of transpiration.

• Temperature
Higher temperature à increase the rate of evaporation of water in the leaf cells à
increase the rate of diffusion of water vapour out of the cell à increase the rate of
transpiration.

• Light
Presence of light triggers the opening of the stomata, therefore leading to an
increase rate of transpiration.

• Wind speed
Higher wind speed à increase rate of removal of water vapour from the leaves
surface à steepening the concentration gradient à increase rate of transpiration.

By: Oscar Chiang Page 17

 Chapter 7: Human Transport

- Double Circulation
In double circulation, the blood passes through the heart twice for every complete circuit of
the body.
• Pulmonary Circulation
The pulmonary (heart and lungs) circulation carries deoxygenated blood from the
heart to the lungs and returns oxygenated blood to the heart.
• Systemic Circulation
The systemic circulation transports oxygenated blood from the heart around the
body and returns to the heart with deoxygenated blood.

Advantages of Double Circulation:

• Pressure in the systemic circulation is high to serve the body efficiently while
pressure in the pulmonary circulation is lower to ensure slower blood flow, allowing
more time for exchange of gases, for the diffusion of oxygen and carbon dioxide
between the capillaries and the air sacs of the lungs to be efficient.
• Oxygenated blood is separated from deoxygenated blood.

Artery Vein
Oxygenated blood (exception of pulmonary Deoxygenated blood (exception of
artery) pulmonary vein)
Always on the left side of the heart Always on the right side of the heart

- Heart
Consists of…
4 Chambers
• Right Atrium
• Right Ventricle
• Left Atrium
• Left Ventricle

4 Blood Vessels
• Vena Cava (deoxygenated blood into the heart)
• Pulmonary Artery (deoxygenated blood into the lungs)
• Pulmonary Vein (oxygenated blood from the lungs)
• Aorta (oxygenated blood to the lungs)

4 Valves
• Tricuspid Valve & Bicuspid Valve (Atrioventricular Valves)
• Semi-lunar Valves (2 valves)

By: Oscar Chiang Page 18

 Interior View (simplified) Exterior View
pulmonary Lungs pulmonary aortic arch
artery
pulmonary arch
""
"""
Atrium ↑\aor+a vein superior pulmonary artery
cava Right '_

Left Atrium vena pulmonary

cava veins
↑
↓
inferior
vena
valve cava
valve

valve
semilunar
Ventricle Left Ventricle
Right

- Valves
• Atrioventricular valves
Chordae tendineae is attached to the valve flaps to the respective ventricle walls.
The Tricuspid Valve is located on the right side of the heart while the bicuspid Valve
is located on the left side of the heart.
Both valves are to prevent backflow of blood from ventricle to atrium.

• Semi-lunar valves
They are found in the aorta and pulmonary artery, both valves are to prevent
backflow of blood into the ventricles.

Side Note: Valves are forced open from the bottom of the valve / \ when the blood
pressure from the bottom is greater than the top.

- Blood Vessels
• Artery
Structure Function
Thick, muscular, and elastic wall Withstand the high blood pressure
from the heart.
Muscular layer Control diameter of artery. Constricts
to narrow artery dilates to widen
artery lumen.
Elastic walls Maintain blood pressure.
Small lumen Maintain high blood pressure of blood.

• Vein
Structure: Thin wall and thin muscular layer.
Function: To carry blood at low pressure.
Structure Function
Large lumen To reduce resistance to blood flow
which is at low pressure (so that blood
flows more easily)
Valves To prevent backflow of blood (since
there is low pressure)

By: Oscar Chiang Page 19

 • Capillary

Structure Function
Thin wall – only one-cell thick Allow diffusion of water and other
dissolved substances through the wall
easily.
Branched and small lumen To slow down blood flow for effective
diffusion of materials.
Leaky Allow white blood cells to squeeze
through the endothelial cells into the
tissues.

- Blood
Blood is a tissue made up of plasma (55% of blood), red blood cells, white blood cells and
Platelets.

• Plasma
Plasma is a pale-yellowish liquid, 90% made up of water.

The plasma transports dissolved substances such as

1. Proteins (fibrinogens, antibodies)
2. Mineral salts
3. Food substances (glucose, amino acids, fats)
4. Waste products (carbon dioxide in the form of hydrogen carbonate ions HCO-3)
5. Hormones (insulin)

• Red Blood Cell

Structure Function
Contains haemoglobin (a protein) To carry oxygen to all parts of the body.
No nucleus To carry more haemoglobins, therefore,
more oxygen.
Circular Biconcave Disc Increases surface area to volume ratio
for faster diffusion of oxygen in and out
of the cell.

By: Oscar Chiang Page 20

 • White Blood Cell
There are two types of white blood cells:
1. Lymphocytes
They have large, rounded nucleus.
Produce antibodies to protect against pathogens.

2. Phagocytes
Lobed nucleus.
Able to engulf and ingest foreign particles.

• Platelets
Irregular shape and helps in blood clotting.

By: Oscar Chiang Page 21

 Chapter 8: Nutrition in Man

- Types of nutrients
1. Carbohydrates (Macronutrient)
2. Proteins (Macronutrient)
3. Fats/Lipids (Macronutrient)
4. Vitamins & Mineral Salts (Micronutrient)

1. Carbohydrates
Made up of Carbon (C), Hydrogen (H) and Oxygen (O) elements.

Excess carbohydrates are converted to glycogen and fats for storage.

• Source of carbohydrates
Potato, Rice, Noodles, Bread

• Function of carbohydrates
Provide energy for cell activities.
Needed to form nucleic acids such as DNA.
Synthesize lubricants (e.g., in the throat) such as mucus.

• Monosaccharides
Glucose
Fructose
Galactose

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

• Polysaccharides
Glycogen
Starch (Enzyme: Amylase, Product: Maltose)
Cellulose
Similarity: Made up of many glucose molecule
Difference: Different arrangement

By: Oscar Chiang Page 22

 2. Proteins
Proteins are made up of Carbon (C), Hydrogen (H), Oxygen (O) and Nitrogen (N). Sulfur (S)
may also be present in the ‘R’ group. The following shows an amino acid, a building block of
proteins.

• Source of Proteins
Fish, Lean Meat, Cheese, Milk (alternatives for vegans include tofu)

• Function of Proteins
Repair and replace worn-out body cells.
Make enzymes and some hormones such as insulin.
Form antibodies to fight diseases.

3. Fats and Lipids

Made up of Carbon (C), Hydrogen (H), Oxygen (O) but it contains much less oxygen in
proportion to hydrogen.

• Source of Fats
Butter, Fatty Meat, Nuts

• Function of Fats
Source of energy and storage of energy.
Form parts of cell membrane.
Insulate against excessive heat loss.
Prevent water loss from the skin surface.
Act as solvent for fat soluble vitamins (Vitamin A and D) and hormones.

By: Oscar Chiang Page 23

 4. Vitamins and Minerals
Vitamins and Minerals are required in small amounts in the body but play important roles in
metabolic activities in our body.

Vitamin C
• Food rich in Vitamin C
Citrus fruits such as oranges and lemons, fresh green vegetable such as broccoli.

• Dietary importance of Vitamin C

Needed to form intercellular substances.
Needed to maintain healthy epithelial tissues (a sheet of cell at the surface of the
body exposed to external environment and lining internal body cavities)

• Deficiency of Vitamin C
Scurvy (e.g., swollen gums, loosening teeth)

Vitamin D
• Food rich in Vitamin D
Egg yolk, Milk, Fish liver oil

• Dietary importance of Vitamin D

Promotes absorption of Calcium and Phosphorus compounds.
Enables body to form bones and teeth with the Calcium and Phosphorus
compounds.

• Deficiency of Vitamin D
Poor bone and teeth formation which leads to rickets.

Calcium
• Food rich is Calcium
Milk, cheese, eggs, dark green vegetables (e.g., spinach)

• Dietary importance of Calcium

Required for building of bones and teeth.
Needed for the clotting of blood.
Needed for normal functioning of muscles.

• Deficiency of Calcium
Rickets

By: Oscar Chiang Page 24

 Iron
• Food rich in Iron
Liver, red meat, egg yolk, bread

• Dietary importance of Iron

To form haemoglobin (found inside red blood cell which transports oxygen).
To form myoglobin (a protein in muscles that store oxygen).
To make certain enzymes involved in cellular respiration.

• Deficiency of Iron
Nutritional Anaemia (Tiredness and breathless as there are fewer haemoglobin
formed)

Dietary fibre
• Food rich in Dietary fibre
Fresh fruits and vegetables, wholemeal bread

• Dietary importance of Dietary fibre

Provides bulk to the intestinal contents.
Help peristalsis (wavelike, muscular contractions of the wall of the digestive tract)
which enables food to be mixed and churned properly with digestive juices and
moves the food along the alimentary canal.

• Deficiency of Dietary fibre

Constipation (lack of dietary fibre cause indigestible matter to move slower in the
digestive track, causing too much water to be absorbed and the faeces will be hard
and dry)

Water
Water is important to life as it is an essential constituent of protoplasm where
biochemical reactions take place.

• Dietary importance of Water

Major constituent of digestive juices
Solvent for both salts and many organic compounds in the body
Transports materials such as digested food substances, excretory products,
hormones, around the body.

• Testing for Starch

We can test for starch by adding iodine solution (original colour is brown) to the
food sample. If starch is present, the iodine solution turns blue-black. If not, it will
remain brown.

Steps:
For 2cm3 sample, add 1-2 drops of iodine solution.

By: Oscar Chiang Page 25

 • Testing for Reducing Sugars
Reducing sugars: Glucose, Fructose, Galactose, Maltose, Lactose.
Non-reducing sugars: Sucrose

We can test for reducing sugars by using Benedict’s solution (original colour is blue).
If large amount of reducing sugar is present, orange-red precipitate is observed. If
moderate amount of reducing sugar is present, yellow precipitate is formed. If small
amounts of reducing sugar is present, green precipitate is formed. Else, it will remain
blue.

Steps:
To 2cm3 of sample solution, add an equal volume of Benedict’s solution.
Shake the mixture.
Place in boiling water bath for 2-3 minutes.
Observe formation of precipitate.

• Test for Fats

We can test for fats by doing the Emulsion test. If lipids are present, a white
emulsion (white cloud mixture) will be present. If not, a homogenous clear solution
is formed when water is added.

Steps:
Add a drop of sample to the test tube.
Add 2cm3 of ethanol to the test tube. Shake the mixture thoroughly.
Add 2cm3 of water to the mixture.

• Test for Proteins

We can test for proteins by doing the biuret test using copper(II) sulfate (original
colour is blue) solution. If proteins are present, a lilac colouration is observed. If not,
the solution will remain blue.

Steps
Add 2cm3 of sample solution to a test tube.
Add half the amount (in this case 1cm3) of sodium hydroxide solution.
Shake the mixture.
Add 1% copper(II) sulfate drop by drop, shaking it after each drop.

By: Oscar Chiang Page 26

 Chapter 9: Human Digestive System

- Why do we digest food? Human Digestive System

We digest food as food cannot be absorbed by our
bloodstream into the cells through the partially permeable
membrane immediately. Large molecule such as starch,
proteins and fats must be broken down into smaller substances
like monosaccharides, amino acids, fatty acids and glycerol
before they can be absorbed.

- Digestion
1. Physical Digestion
Breaking up of food into small particles mechanically so that
surface area to volume ratio increases to enable enzymes to
act on it more efficiently.
2. Chemical Digestion
Breaking down of large molecules to smaller soluble
substances, involving hydrolytic reactions catalysed by
digestive enzymes.

- Mouth
pH ≈7
Physical Digestion: The teeth cut and grind the food into smaller pieces.
Chemical Digestion: Salivary amylase in the saliva digests starch to maltose.

The food is rolled into boli (singular – bolus) to go to the oesophagus.

- Oesophagus
pH ≈7
Physical Digestion: X
Chemical Digestion: Salivary amylase from the mouth is still taking place in the oesophagus
so the process of breaking down starch to maltose is still taking place.

Peristalsis - The oesophagus works antagonistically (when one contracts, the other relaxes)
to pass the food down the oesophagus.

By: Oscar Chiang Page 27

 - Stomach
pH ≈2
Physical Digestion: The stomach churns food to smaller pieces.
Chemical Digestion: The pepsin (protease) in the gastric juice breaks down protein into
polypeptide.

Gastric juice in the stomach contains hydrochloric acid, pepsin and rennin.

• Function of hydrochloric acid (HCl)

Changes pepsinogen (inactive) to pepsin (active)
Provides a slightly acidic medium which is suitable for rennin and pepsin.
Kills germs and bacteria.

The stomach is a muscle (made up of protein) but the pepsin does not break it down as
there is a thick layer of mucus on the stomach.
The hydrochloric acid will only change pepsinogen (inactive) to pepsin (active) when there is
food which is another mechanism to prevent pepsin from breaking down the stomach.

- Small intestine
ph ≈8

There are 3 parts of the small intestine – duodenum, jejunum and ileum.

Physical Digestion: Emulsification – break down fats into smaller fats globules by bile so that
surface area to volume ratio is increased for faster digestion by lipase.
Chemical Digestion:
Pancreatic juice – pancreatic amylase, trypsinogen (protease) and pancreatic lipase (bind to
fats).
Intestinal juice – maltase1, sucrase1, lactase1, enterokinase, erepsin (protein) and intestinal
lipase.

Absorption:
Amino acids and glucose are absorbed by the blood capillary via diffusion and active
transport.
Fatty acids and glycerol are absorbed by the lacteal bigger than amino acids and glucose
which can clog up the blood vessels.

There are villi (singular – villus) on the walls to increase surface area to volume ratio so that
rate of absorption of nutrients is faster.
The villi walls of the small intestine are one-cell thick so that there is a shorter diffusion
distance.

1
enzymes which break down the respective disaccharides into monosaccharides

By: Oscar Chiang Page 28

 - Large intestine
pH ≈8

The large intestine is made up of the caecum, appendix, ascending colon, transverse colon,
descending colon and rectum.

The large intestine is mainly to absorb water and mineral salts from undigested food
material (although most are absorbed by the small intestine already).
Physical Digestion: X
Chemical Digestion: X

Absorption of water and mineral salts from undigested food takes place here although most
has been absorbed in the small intestine.

- Nutrients and Gastrointestinal Tract Disorders

Constipation
Diarrhoea

By: Oscar Chiang Page 29

 Chapter 10: Human Reproductive System

- What is sexual reproduction?

Sexual reproduction involves a male and a female. The male produces reproductive cells
called gametes or sperms. The female produces reproductive cells called eggs or ova (plural).
In sexual reproduction, a sperm fuses with an egg to give rise to an offspring.

- Puberty
Puberty is the rapid growth and development during which a person becomes sexually
mature and capable of reproducing.
Puberty is brought about by increased secretion of certain hormones in the body.
Puberty occurs in girls at about 10 years of age while 12 years of age for boys.
During puberty, the reproductive organs mature and develop to produce sperms or mature
eggs.

Physical Changes
Boys Girls
Facial hair grows and hair starts to grow in Hair starts to grow in the pubic region and
the pubic region and armpits. armpits.
Voice-box enlarges, and voice deepens.
The penis and testes size increases. The breasts and uterus enlarge, and hips
broaden.
Production of sperms begins, and Menstruation and ovulation begin.
ejaculation occurs.

By: Oscar Chiang Page 30

 - Male Reproductive System

1. Testes (singular – testis)

• Produces male gametes (sperms)
• Produces male sex hormones (testosterone – responsible for development and
maintenance of secondary sexual characteristics in males)

2. Scrotum
• Encloses the testes to protect the testes
• Keep the testes at a slightly lower temperature than the body which is the optimum
temperature for sperm production

3. Coiled tubes (epididymis)

• Site for sperm maturation

4. Sperm duct (vas deferens)

• Transport sperms from the coiled tubes to urethra during sexual intercourse.

5. Prostate gland
• Produces seminal fluid (sperm + seminal fluid à semen, to keep sperms alive)

6. Urethra
• Carries urine and semen at different times through the penis.

7. Penis
• Carries urine and semen out of the body.
• Becomes stiff and erect as sexual intercourse and releases sperms into the vagina

By: Oscar Chiang Page 31

 - Female Reproductive System

1. Ovaries (singular – ovary)

• Releases an egg (or ovum) every 28 days into the
oviduct (fallopian tube).
• Produces female sex hormones

2. Oviducts (fallopian tubes)

• Connects ovaries and the uterus, muscular wall contractions help move ovum to the
uterus.
• Egg fertilisation occurs here.

3. Uterus (plural – uterine, womb)

• Embryo is implanted in the uterus lining.
• Embryo is protected and developed into a foetus.

4. Cervix
• Help keep the baby in the uterus until it is ready to be born.

5. Vagina
• Opening for the entry of penis during sexual intercourse.
• Site for sperms to be deposited.
• Outlet for the birth of baby.

- Differences between a sperm and an ovum

Sperm Ovum
Extremely small Large
Several millions per ejaculation One ovum per 28 days during ovulation
Able to swim with the aid of tail Unable to move on its own
Differentiated into head, neck and tail Round
when matured.
Carries an X-chromosome or Y- Carries an X-chromosome
chromosome

By: Oscar Chiang Page 32

 - Menstrual cycle
Lasts for about 28 days.

The cycle starts with menstruation, bloody discharge from the vagina. The bleeding is caused
by the breaking down of the uterine lining, together with blood.

Menstruation lasts from 1st to the 5th day and occurs after two weeks of ovulation (from
previous menstrual cycle).

Once the uterus wall has recovered, it begins to rebuild its lining under the influence of a
hormone from the ovary. Meanwhile, the ovary is maturing a new ovum.

On the 14th day of the menstrual cycle, ovulation occurs. The mature ovum is released into
the fallopian tube (oviduct). The ovum will move along the fallopian tube towards the
uterus.

If the ovum is not fertilised (fusion with sperm), it eventually disintegrates, and the lining of
the uterus wall will break down.

The uterus and blood flow out through the vagina 14 days after ovulation, signalling the start
of the next menstrual cycle.

- Fertilisation and development of zygote

A zygote is a fertilised egg where cell division has not taken place yet.
An embryo is the egg after cell division.

When semen is ejaculated into the vagina, the sperms will swim up through the uterus into
the oviducts. If they meet an ovum, only one sperm will be able to fuse with the ovum to
form a zygote. After a zygote is formed, cell division occurs to form an embryo which then
attaches itself on the uterine lining and develops.

By: Oscar Chiang Page 33

 - Placenta

Placenta allows oxygen and dissolved oxygen and dissolved food substances to diffuse into
the foetal blood system and waste products such as carbon dioxide to diffuse from the
foetus into the maternal blood system for removal.

The placenta is made up of the uterine lining and fetal blood capillaries.

The amniotic fluid inside the amniotic sac will allow the baby to ‘float’.

- Umbilical Cord
There are two umbilical arteries (away) to transport deoxygenated blood and metabolic
waste such as carbon dioxide and urea from the foetus to the placenta.

There is one umbilical vein to transport oxygenated blood and nutrients such as glucose
(required for respiration) and amino acids from the placenta to the foe

By: Oscar Chiang Page 34

 Life Science Important Terms

- Factors that affect enzyme activity

Temperature (optimum - 37 °C), pH and substrate concentration

- When placed in hypotonic solution (low solute concentration à high WP)

Animal cell: burst/lyse
Plant cell: expand/turgid

- When placed in hypertonic solution (high solute concentration à low WP)

Animal cell: crenate
Plant cell: plasmolysed

- Macronutrients functions and deficiency

Nutrients Function Deficiency Symptoms
Nitrogen (N) Needed to form proteins and Stunted growth
chlorophyll. Required for growth of Light green older leaves
affects leaves plants especially young plants. Older leaves turn yellow and
die
Phosphorus (P) Components of nucleic acids, Stunted growth
phospholipids, and ATP. Required for Purplish veins in older leaves
affects veins and flowering plants. Fewer seeds and fruits
flowers
Potassium (K) To activate enzymes and maintain Reduced growth
water-soluble balance and will affect Curled, mottled or spotted
affects roots and photosynthesis. Required for root older leaves
stems and sustaining fruit growth in plants. Burned leaf margins
Weakened roots and stems.

- Rhizobium Bacteria
Only affects leguminous plants (e.g., soybeans). Rhizobium bacteria live in nodules and
convert atmospheric nitrogen to ammonia for the plants to make amino acids.

- Dicotyledonous seed
Embryo – consists of a radicle (the root), the plumule, epicotyl (upper stem) and hypocotyl
(lower stem).
Cotyledons – contains food reserves, mainly starch, for the embryo when grows.
Testa (seed coat) – Encloses the embryo and cotyledons; protects the embryo from injury
and drying out.
Micropyle – a tiny opening in the testa for water to enter the seed before germination.

- Types of Germination
Hypogeal Germination (cotyledons are stay below the soil)
Epigeal Germination (cotyledons are raised above the soil)

- External Conditions for Germination

Water (soften testa to make it permeable to gases),
Oxygen (for aerobic respiration),
Temperature (activate the enzymes in germination and growth),
Light (some plants need light while some don’t)

By: Oscar Chiang Page 35

 - Optimum pH and EC for hydroponics
pH: 5.8 – 6.5
EC: 1.5 – 2.5

- Cross sections of root, stem and leaf

Cross sections of root

Cross section of stem

Cross section of leaf

- Structure of phloem and xylem

Phloem: sieve tube cells to form sieve tubes (no cell organelles) – requires companion cells
which are capable of respiration.
Xylem: Dead adjacent cell walls with no protoplasm, heavily lignified (provide mechanical
support), thicker than phloem.

- Root hair cell adaptations

Long and thin – increase surface area to volume ratio to increase rate of absorption.
High concentration of cell sap – maintains a lower water potential so that water can diffuse
into the root hair cell via osmosis.
Living cells – so that it contains mitochondria for aerobic respiration to release energy for
the active transport of mineral salts from the surroundings into the cell.

- Hydroponics
Factors Quality that it measures Optimum range for hydroponic
nutrient solution
pH Acidity or alkalinity of the nutrient 5.8 – 6.5
solution
Electrical The strength of nutrient solution 1.5 – 2.5
conductivity (EC)

By: Oscar Chiang Page 36

 - Movement of water up a plant
Transpiration Pull
Transpiration occurs when water evaporates out of the leaf through the stomata. Water
evaporates from leaf cells to water vapour and moves to the air spaces in the leaf. Water
vapour will then diffuse out of the leaf through the stomata. When water evaporates from
the leaf cells, the leaf cells’ water potential decreases. The water in the xylem will diffuse
into the leaf cell via osmosis through the partially permeable cell membranes.

Root Pressure
Root pressure is caused by the low water potential of xylem sap which is created by
dissolved minerals and sugars.

Capillary Action
Capillary Action occurs when the forces binding a liquid together, cohesion, and the
attracting forces that bind water molecules to the xylem walls, adhesion, are greater than
the force of gravity.

- Blood vessels
Artery Vein
Structure Function Structure Function
Thick, muscular, Withstand the high Thin wall, thin Due to lower venous
and elastic wall blood pressure from the muscular layer blood pressure.
heart.
Muscular layer Control diameter of Valves To prevent backflow of
artery. Constricts to blood (since there is low
narrow artery dilates to pressure)
widen artery lumen.
Small lumen Maintain high blood Large lumen To reduce resistance to
pressure of blood blood flow which is at
low pressure (so that
blood flows more easily)

- Components of Blood
Plasma, White Blood Cell, Platelets,
Red Blood Cell (1. contains haemoglobin à carry oxygen. 2. no nucleus à carry more
haemoglobin. 3. circular biconcave disc à increase surface area to volume ratio)

- Blood flow in the heart

pulmonary Lungs

""
"""
cava Right Atrium ↑\aor+a '_
vein

Left Atrium

↑
↓

valve
valve

valve
semilunar
Ventricle Left Ventricle
Right

By: Oscar Chiang Page 37

 - Testing for Starch
For 2cm3 of sample solution, add 1-2cm of iodine solution. If blue-black coloration is seen,
starch is present.

- Testing for Reducing Sugar

Add an equal amount of Benedict’s solution as the sample solution and place it in a boiling
water both for 2-3 minutes. If brick-red precipitate is seen, reducing sugar is present in large
amounts. If yellow precipitate is seen, reducing sugar is present in moderate amounts. If
green precipitate is seen, reducing sugar is present in small else amounts. Else, if it remains
blue, reducing sugar is absent.

- Testing for Protein

For 2cm3 of sample solution, add 1cm3 of sodium hydroxide. Then add copper(II) sulfate
drop by drop, shaking it after each drop. If the mixture changes to lilac, proteins are present.
Else, if it remains blue, proteins are absent.

- Testing for Fats

Add one drop of sample to a clean test tube. Add 2cm3 of ethanol to the test tube. Then, add
2cm3 of water to the mixture and shake the mixture. If the mixture is milky, fats are present.
Else, if it remains clear, fats are absent.

- Vitamins and Minerals

Vitamins / Food rich in Dietary importance Deficiency
Minerals
Vitamin C Citrus fruits For the formation of intercellular Scurvy
substances.
Vitamin D Egg yolk Absorption of phosphorus and Rickets
calcium.
Calcium Milk Clotting of blood. Rickets
Iron Liver To form haemoglobin. Nutritional Anaemia

- Mouth
Physical Digestion: Chewing
Chemical Digestion: Starch à Maltose

- Oesophagus
Peristalsis – muscles work antagonistically to pass the food bolus down the oesophagus. No
physical digestion involved.

- Stomach
Physical Digestion: Churning (caused by peristalsis)
Chemical Digestion: Protein à Polypeptide
• Hydrochloric Acid
Provide acidic medium for the action of enzymes, kills germs and bacteria and
changes inactive forms of enzymes in gastric juice to active forms.

By: Oscar Chiang Page 38

 - Small intestines
Duodenum
Physical Digestion: Emulsification is when big fat globules are broken down by bile into
smaller fats globules to increase surface area to volume ratio for faster digestion by lipase.
Pancreatic juice (secreted from pancreas) contains pancreatic amylase, protease -
trypsinogen and pancreatic lipase.
Intestinal juice (secreted from intestinal glands) contains maltase, sucrase, lactase, protease
(erepsin) and intestinal lipase.
Chemical Digestion:
Protein à Polypeptide Note:
Polypeptide à Amino Acids Absorption of food occurs in
Starch à Maltose the jejunum and ileum.
Maltose à Glucose
Sucrose à Glucose + Fructose
Lactose à Glucose + Galactose
Fats à Fatty Acids + Glycerol

Structure Function
Villi and microvilli (finger-like projections) To increase surface area to volume ratio for
faster rate of absorption.
One-cell thick To reduce diffusion distance for faster rate
of absorption.
Lacteal Absorbs only fatty acids and glycerol.
Blood capillary Absorbs only amino acids and
monosaccharides.

- Menstrual cycle
1st to 5th day: Breaking down of uterine lining, bloody discharge from the vagina.
11th to 17th day: Fertile period
14th day: Ovulation

- Placenta
Allows dissolved oxygen and dissolved food substances to diffuse into the foetal blood
system. Allows waste products to diffuse into the maternal (mother’s) blood system for
removal.

- Umbilical Cord
Two umbilical arteries to transport deoxygenated blood away from the baby.
One umbilical vein to transport oxygenated blood and nutrients such as glucose to the baby.

- Differences between a sperm and an ovum

Sperm Ovum
Extremely small Large
Several millions per ejaculation One ovum per 28 days during ovulation
Able to swim with the aid of tail Unable to move on its own
Differentiated into head, neck and tail Round
when matured.
Carries an X-chromosome or Y- Carries an X-chromosome
chromosome

By: Oscar Chiang Page 39

 End of Year Practice Essay Questions

Describe how oxygen from the alveoli (air sacs) of the lungs reaches the muscle cells of the
leg. [6m]
A: Oxygen from the alveoli of the lungs diffuses through the blood capillaries and is carried
by the red blood cells to the pulmonary vein and flowing into the left atrium. The left atrium
contracts, pushing blood into the left ventricle. When the left ventricle contracts again,
oxygenated blood is pumped into the aorta and flows down the body. The arteries branch
out into arterioles into blood capillaries. Lastly, oxygen diffuses out of the blood capillaries
into the tissue fluid and into the muscle cells of the leg.

Describe double circulation in man and explain its advantages beneficial? [5m]
A: The double circulation in man comprises of systemic and pulmonary circulation.
The pulmonary circulation refers to the transport of deoxygenated blood from the heart to
the lungs and oxygenated blood from the lungs to the heart.
The systemic circulation refers to the transport of oxygenated blood from the heart to the
rest of the body and return of deoxygenated blood from the rest of the body.
① Blood pressure in pulmonary circulation is lower than the systemic to slow down blood
flow to allow more time for exchange of substances.
② Blood pressure in the systemic circulation is higher than the pulmonary as more pressure
is required to pump blood to the rest of the body.
③ Separation of oxygenated and deoxygenated blood creates a steeper concentration
gradient of oxygen between blood capillaries and tissue cells.

A regular menstrual cycle has a duration of 28 days. State and describe the different stages
that occur in one cycle. [6m]
From Day 1 to Day 5, menstruation occurs. Menstruation is the breaking down of the uterine
lining, causing bloody discharge through the vagina. After Day 5, the uterine lining is being
repaired. On Day 14, ovulation occurs, where an ovum is released from the ovary into the
oviduct. The fertile period is between Day 11 and Day 17. After Day 17, the uterine lining
continues to thicken and maintain to prepare the implantation of the embryo. If the ovum is
not fertilised, it is disintegrated and the uterine lining will be broken down again, repeating
the cycle.

Outline the differences between the umbilical artery and umbilical vein. [3m]
①There are two umbilical arteries but one umbilical vein in the umbilical cord.
② The umbilical artery transports deoxygenated blood and wastes substances while the
umbilical vein transports oxygenated blood and nutrients such as glucose.
③ The umbilical artery flows away from the foetus to the placenta while the umbilical vein
flows towards the foetus from the placenta.

Explain how the structure of the vein and artery supports its function. [4m]
① The vein has valves. The valves prevent the backflow of blood as there is a low blood
pressure flowing in the vein.
② The vein has a large lumen. This helps to reduce resistance of the blood, which is flowing
at a low pressure, to allow deoxygenated blood to flow back easily to the heart.
③ The artery has a small lumen. This helps to maintain the high blood pressure of the artery.
④ The thick, muscular, elastic wall. This helps to withstand the high blood pressure in the
artery.

By: Oscar Chiang Page 40

 Explain how the structure of the capillary supports its function. [4m]
① It is one cell thick. This reduces the diffusion distance and allow dissolved substances in
the blood diffuse through the wall of the capillary easily.
② It is leaky. This allows white blood cells to squeeze through the holes between the cells,
but not the red blood cells.
③ It is highly branched. This increases surface area to volume ratio to increase the rate of
exchange of substances.
④ Microscopically small lumen. This helps to slow down blood flow and allow more time for
diffusion of substances between the blood capillaries and tissue cells.

Describe the journey of a sperm upon ejaculation, and eventually leading to the
development of foetus. [6m]
During ejaculation, sperm is released into the vagina. The sperm swims up the uterus into
the oviduct where fertilisation will occur. Fertilisation occurs when the nucleus of the sperm
fuses with the nucleus of the ovum, forming a zygote. The zygote is swept in the oviduct
towards the uterus. Cell division occurs and forms a ball of cells. The ball of cells implants
itself into the walls of the uterus and develops as an embryo. The embryo continues to
develop in the uterus, forming the foetus.

By: Oscar Chiang Page 41