Chapter 1: Characteristics of Life – MRS GREN

Videos:
https://www.youtube.com/watch?v=jpO52VTHecQ

Kognity link for more details & examples: https://sia.kognity.com/schoolstaff/app/cambridge-igcse-

biology-2019/book/characteristics-classification-of-living-organisms/characteristics-of-living-organisms/the-big-picture/?
source=Table%20of%20contents

1) Define Movement: as an action by an organism or part of an organism causing a

change of position or place.

2) Define Respiration: as the chemical reactions in cells that break down nutrient
molecules and release energy for metabolism.

3) Define Sensitivity: as the ability to detect or sense stimuli in the internal or

external environment and to make appropriate responses.

4) Define Growth: as a permanent increase in size and dry mass by an increase in

cell number or cell size or both.

5) Define Reproduction: as the processes that make more of the same kind of
organism by passing on the genetic material.

6) Define Excretion: as removal from organisms of the waste products of

metabolism (chemical reactions in cells including respiration), toxic materials,
and substances in excess of requirements.

7) Define Nutrition: as taking in of materials for energy, growth and

development; plants require light, carbon dioxide, water and ions; animals need
organic compounds and ions and usually need water.
 Chapter 2: Cell Structure & Levels of Organisation
Videos:
https://www.youtube.com/watch?v=LdKcTtabr6Y
https://www.youtube.com/watch?v=kGd-5HSDo6g

3D Model on Kognity: (CHECK IT OUT, IT’S SO COOL!!)

https://sia.kognity.com/schoolstaff/app/cambridge-igcse-biology-2019/book/organisation-of-the-organism/cell-
structure-and-organisation/the-big-picture/?source=Table%20of%20contents

Animal Cell:

Plant Cell:

Features found in only plant cells:

 Cell Wall: This is a rigid layer surrounding the cell made of cellulose, it gives
the plant its shape and prevents it from bursting.
 Chloroplasts: They are sacs which contain chlorophyll which is a green pigment
that traps sunlight for photosynthesis.
 Vacuole: This is a large room in the center of the cell, it stores sugars and
salts and controls movement of water in and out of the cell.

N.B.

** Aerobic respiration occurs in the Mitochondria.

** Cells with high metabolic rate require large numbers of mitochondria to provide
sufficient energy.
** Magnification = Image size/Actual size

Levels of Organization in an Organism:

Cells  Tissue  Organ  System  Organism

Definitions:

 Tissue as a group of cells with similar structures, working together to perform

a shared function.

 Organ as a structure made up of a group of tissues, working together to

perform specific functions.
 Organ system as a group of organs with related functions, working together to
perform body functions.

**Specialized cells are cells with modifications to suit their functions.

Examples: Ciliated cells, Nerve cells, Sperm Cells, Root hair cells, Red blood cells, White blood
cells, etc.
The structure and function of each has been explained in their respective chapters.

Chapter 3: Movement in and out of cells

(Diffusion, Osmosis & Active Transport)

Videos:
https://www.youtube.com/watch?v=PRi6uHDKeW4
https://www.youtube.com/watch?v=eDeCgTRFCbA

Diffusion:

It’s the net movement of particles from a region

of their higher concentration to a region of their
lower concentration down a concentration
gradient, as a result of their random movement
and kinetic energy.

Factors affecting the rate of diffusion:

1) The steepness of the concentration

gradient:
The steeper the gradient the faster the
particles diffuse.

2) The surface area of the exchange

membrane:
 The larger the surface area of the exchange membrane the faster particles
diffuse.

3) Thickness of the exchange membrane:

The thinner it is, the easier it will be for particles to go through it, the
faster the diffusion rate.

4) Temperature:
Increasing the temperature  particles have more kinetic energy  faster
movement, thus increasing the rate of diffusion.

5) Particle size:
Large particles diffuse slower than smaller ones. Also, depending on the pore
size, large particles could be trapped in case of small pores.

** Gases & liquids can diffuse as long as it’s from higher conc. to lower conc.

Osmosis:
It’s the net movement of water molecules
from a region of higher water potential
(dilute solution) to a region of lower water
potential (concentrated solution), through a
partially permeable membrane.

For example, movement of water through

the cell membrane.

Key definitions:

 Turgor pressure: It’s the pressure of the water pushing against the cell
wall. Turgor pressure helps plants to maintain their structure.
**When placed in a dilute solution, water moves in the cell. The cell swells
and it’s said to be turgid.
  Flaccid: When water moves out of the plant cell, turgor pressure is lost, and
the cell is said to be flaccid. This causes leaves to welt.
 Plasmolysis: In a very concentrated solution, the cytoplasm may shrink to
the point that the cell membrane is pulled away from the cell wall.

The effect of immersing plant/animal tissues in solutions of different

concentrations:
 Animal Cell Plant Cell

Dilute Water moves in the cell and the Water moves in the cell and
Solution animal cell swells. the plant cell becomes turgid.

If placed in pure water, it’s The strong cell wall prevents

considered very dilute compared the plant cell from bursting.
to the animal cell and a large
amount of water moves in the
cell causing the animal cell to
burst.

Concentrate Water moves out of the cell and Water moves out of the cell
d Solution the animal cell shrinks. and the plant cell shrinks.

If the solution is too If the solution is too

concentrated, the animal cell will concentrated, the plant cell
shrivel beyond repair. will be plasmolyzed.

Importance of water potential and osmosis in plants and animals:

 In plants: Water in the soil is often part of a solution that is more dilute than
the solution inside the root hair cells. As a result, water enters the root hair
cells by osmosis. The water is then pulled through the plant by transpiration.

 In animals: Animal cells and tissues must be able to control osmosis in order to
function properly. For example, a red blood cell that gains too much water could
swell and burst, because it is not protected by a cell wall (unlike plant cells).
Body cells can be damaged if they lose or gain too much water by osmosis. To
prevent this type of damage, the water concentration of the blood and of the
cytoplasm in cells is very closely controlled by the kidneys.

Active transport:
It’s the movement of particles through a cell membrane from a region of lower
concentration to a region of higher concentration using energy from respiration.
** Active transport involves the use of carrier molecules made of protein =
Protein carriers. (molecules that help transport particles across the membrane)

Example of substances that move by active transport:

- Ion uptake by root hairs.
- Uptake of glucose by epithelial cells of villi and kidney tubules
 Chapter 4: Biological Molecules (Chemicals of life)
Elements
Biologica Monomers
it’s
l &/or Uses Test
made up
Molecule Polymers
of
- Glucose: Fast source of
energy. It makes up - Starch:
Monomers polymers such as Iodine + Starch 
(Single unit starch, glycogen & Blue color
sugars): Main cellulose.
Carbohydrates

one is - Starch: stored in plant - Glucose:

Glucose. cells to be used later. Benedict’s test:
C, H & O
- Glycogen: stored in Benedict solution +
Polymers: animal cells (liver & Glucose  Green –
Starch, muscles) to be used Yellow – Orange > Red
glycogen, later when glucose
cellulose… levels drop in blood. If no glucose is
- Cellulose: Cell wall present – Blue
structure.
- Enzymes
Amino acids Biuret test:
Proteins

C, H, O & - Antibodies
(monomer)  Biuret solution +
N - Muscles
Polypeptides Protein  Purple
- Protein carriers

Fatty acids + Ethanol + fat 

Lipids C, H & O - Energy
Glycerol solution turns cloudy.
DCPIP:
Vitamin DCPIP solution +
C Vitamin C  Blue
changes to colourless

Videos:
https://www.youtube.com/watch?v=FgfknBZaVTI

https://www.youtube.com/watch?v=YO244P1e9QM&t=33s

https://www.youtube.com/watch?v=JGZj6DsUZhE
Important of water in body functions:
Chapter 5: Enzymes
Video: https://www.youtube.com/watch?v=rlH1ym916Fo

Chapter 6: Plant Nutrition

The structure of a leaf
The leaves are the organ for photosynthesis. It is where photosynthesis takes place. The
structures of leaves are adapted for efficient photosynthesis as shown in the table below.

Adaptation Function

Most leaves are broad and so have a large surface area

Large surface area
allowing them to absorb more light.

A thin shape means a short distance for carbon dioxide

A thin shape
to diffuse in and oxygen to diffuse out easily.

This chemical gives the leaves their green colour and

Chlorophyll
transfers light energy to chemical energy.

Networks of veins support the structure of the leaf and

Veins
transport substances to and from the cells in the leaf.

These are small holes on the underside of the leaf that

Stomata
allow gases to diffuse in and out.
**Features & adaptations of a leaf (cellular structure):

1) Waxy cuticle: waterproof  reduces the amount of water lost from the leaf.
2) Upper epidermis: Thin and transparent to let light through for photosynthesis. [Notice
that it has no chlorophyll and therefore doesn’t photosynthesize]
3) Palisade mesophyll: Tightly packed and arranged very close together to absorb as much
light as possible and allow less light to scatter. It has many chloroplasts with chlorophyll
to absorb light for photosynthesis.
4) Spongy mesophyll: Has spaces to allow for faster diffusion of CO2 for photosynthesis.
5) Stomata & guard cells: Allow CO2 to diffuse into the leaf. [Notice that the stomata are the
gap between the guard cells – not the guard cells themselves] (Guard cells have few chloroplasts
as well so they can photosynthesize)
6) Xylem: Transport of water
7) Phloem: Transport products of photosynthesis.

(Palisade cells, spongy cells and guard cells are the only cells that photosynthesize)

Videos:
https://www.youtube.com/watch?v=co0JdqUlycg https://www.youtube.com/watch?v=Kv_0udatlh8&t=108s
https://www.youtube.com/watch?v=jtuX7H05tmQ https://www.youtube.com/watch?v=QXdujo4PZ7c
https://www.youtube.com/watch?v=HxVD4i7NSw8 https://www.youtube.com/watch?v=LEQqd91uWsY

Chapter 7: Animal Nutrition

 Part 1: Nutrition & Balanced Diet
Videos:
https://www.youtube.com/watch?v=kFx9a3TSvXg

https://www.youtube.com/watch?v=aQX8AkbuzjY&t=200s

https://www.youtube.com/watch?v=0lr-82ey1_I

https://www.youtube.com/watch?v=VsihqvxpqOc

Nutrition – Study of food and related process

Plants are autotrophic – they produce their own food and come at the bottom of the food chain.
Humans and other animals are heterotrophic (also known as holozoic) – they eat other plants
and animals and cannot produce their own food.

Humans require a balanced diet.

Definition: This is one which supplies the different types of food in adequate
amounts and the correct proportions, and proⅵdes the body with sufficient energy for its
needs.

Humans use food for:

• Energy for body processes.
• Building materials, to build the cells of the body.
• Chemical reactions in the body.

There are seven chemical components of a balanced diet:

1) Carbohydrates: To proⅵde energy.
2) Fats: To proⅵde energy, insulation, and to construct parts of cells.
3) Proteins: To build muscle, make enzymes and hormones, and construct parts of cells. It is
normally obtained from the muscles of animals. The disease caused by protein deficiency
is called kwashiorkor.
4) Minerals are ions of certain elements (i.e. inorganic), which are needed for particular
purposes within the body. For example:
a. Calcium is needed for bone formation. Without calcium, bones are soft. Calcium
deficiency is called rickets.
b. Iron is required for haemoglobin, in blood. Oxygen is transported around the body
by binding to haemoglobin. Iron is plentiful in liver and kidneys. Iron deficiency
results in anaemia.
5) Vitamins Various biological compounds required by the body. Some examples:
a) Vitamin A is needed by the eyes. Vitamin A deficiency is called xerophthalmia and
leads to blindness.
b) Vitamin C keeps the lining of the mouth and gums healthy. It is found in green
vegetables. Lack of it causes scurvy.
 c) Vitamin D is needed to enable calcium to harden bones. Lack of it causes rickets.
6) Water Makes of 60-80% of the body. The body’s chemical reactions take place in it.
7) Fibre: Stimulates the smooth passage of food through the gut. Mainly made of cellulose,
it aids faeces formation.

 Malnutrition is the result of not having a properly balanced diet.

Part 2: Digestion

Key concepts & definitions:

- Ingestion: Food is taken into the mouth.

- Digestion: The breakdown of complex organic foods into small, soluble
molecules.
- Absorption: The uptake of soluble food substances into the body across cell
membranes.
- Assimilation: The use of soluble food substances by cells in the body.
- Egestion: The removal of undigested food om the body (not to be confused
with excretion or secretion).
- Mechanical Digestion: The action of the teeth biting a small piece of food
from a large one is considered mechanical digestion, the teeth also tears and
grinds the food into a bolus to give it larger surface area for faster chemical
digestion.
- Chemical Digestion: The action of enzymes on food molecules to break them
down into absorbable
particles.
- Food is moved along the
alimentary canal through
peristalsis

Chemical Digestion:
(We’re going step-by-step according to what’s being
digested and where.)
1) Mouth:
Salivary glands release saliva into the mouth. Saliva contains water and mucus to
lubricate the food bolus, it also contains amylase enzyme.

Enzyme released: Amylase.

Food digested: Starch.

Starch (polysaccharide) ------- > Maltose (disaccharide)

2) Stomach: Stomach cells secrete juice to aid digestion.

Juice secreted contains:

1. Pepsin enzyme: breaks down proteins  Shorter polypeptides
Works best at pH 2 (acidic environment)
2. Hydrochloric acid: kills bacteria and provides an optimum pH for pepsin to
work.
3. Mucus: It lines the wall of the stomach to protect it from the acid and to
prevent digestion of the stomach itself by enzymes. It also lubricates food
and makes it easier to churn in the stomach.

Enzyme released: Pepsin.

Food digested: Protein.

Protein (long chain of amino acids) ------- > Polypeptides (shorter chain)

3) Small intestine:

A couple of organs release digestive juices that pour into the small intestine to
help digest carbohydrates, fats & proteins.

a) Liver: releases bile. This bile is poured into the small intestine through the
bile duct. Excess bile is stored in the gall bladder.
What does bile do?
Bile emulsifies fats.
 Emulsification is the breaking down of fat into smaller droplets. (Mechanical
digestion)

b) Pancreas: releases pancreatic juice –

Pancreatic juice contains:
- Sodium hydrogen carbonate neutralizes the hydrochloric acid coming
from the stomach.
- Amylase: Starch ---- > Maltose
- Lipase: Lipids --- > Fatty acids + glycerol
- Trypsin: Proteins --- > Polypeptides

c) Small intestine: release a mixture of enzymes:

- Lipase: Lipids --- > Fatty acids + glycerol
- Protease: Polypeptides (short chain proteins) --- > Amino acids
- Maltase: Maltose (disaccharide) --- > Glucose (monosaccharide)

Part 3: Absorption & Egestion

After digesting all types of food, it’s absorbed into the blood stream to be
transported to all cells.

Absorption happens in the

small intestine (the ileum,
to be specific). The interior
wall of the ileum is covered
with a layer of villi; each
villus is covered with
another layer of microvilli.

Adaptations of the villi:

◦ Large surface area  Faster diffusion

◦ Blood capillaries  Faster diffusion

◦ Each villus contains a lacteal  Absorbs fat

◦ Lined with microvilli  Large surface area  Faster diffusion

** Most water is reabsorbed in the small intestine to avoid water loss in faeces.

All digested food is absorbed in the small intestine as explained above. The
remaining undigested parts, such as cellulose from the plant cell walls, move to the
large intestine.

In the large intestine, bacteria act on those parts to produce useful substances
such as Vitamin K.

Then, the rest of the unwanted substances are egested out of the digestive
system as faeces.

Diseases associated with the digestive system:

Diarrhea caused by cholera –

a) Cholera is a disease caused by bacteria present in contaminated food and water.
b) They pass to the small intestine where they stick to the intestinal walls.
c) Here they release toxic proteins that causes a secretion of chloride ions into the small
intestine.
d) This lowers the water potential in the gut thus water moves into the gut via osmosis, leading
to diarrhea, which is the loss of watery faeces. (This is causes water loss & dehydration)

This can be avoided using oral rehydration therapy, where patients drink a mixture of
water, glucose and salts to rehydrate themselves.

Summary of Enzymes & substances digested

Carbohydrates
Where digestion Where Broken down
Enzyme Substrate
happens produced into

Mouth Salivary amylase Salivary glands Starch Maltose

Small intestine - Pancreatic

Pancreas Starch Maltose
Duodenum amylase
 Where digestion Where Broken down
Enzyme Substrate
happens produced into

Small intestine - Ileum Amylase SI Maltose Glucose

Proteins
Where digestion
Enzyme Substrate Broken down into
happens

Stomach Protease - pepsin Proteins Begins the breakdown into Polypeptides

Small intestine - Protease - trypsin Proteins Continues the breakdown into Polypeptides

Small intestine Protease - peptidase Peptides Completes the breakdown into amino acids

Lipids
Where digestion Where
Enzyme Substrate Broken down into
happens produced

Small intestine - Fatty acids and

Lipase Pancreas Lipids
Duodenum glycerol

Part 4: Teeth
Structure:
Tooth decay:
a) If we do not keep our teeth clean,
plaque (a sticky film of bacteria) will
start to build up on them.
b) The bacteria in the plaque will use the
sugar as food for respiration.
c) The bacteria release acid as a waste
product, and this acid begins to
dissolve the calcium salts in tooth
enamel.
d) Once the hard enamel has been
dissolved, the much softer dentine and
pulp will be exposed to the acid and a
painful cavity can form.
 Chapter 8: Transport in plants
Videos:
Leaf Structure: https://www.youtube.com/watch?v=co0JdqUlycg&t=6s

Transport 1: https://www.youtube.com/watch?v=jtuX7H05tmQ&t=1s

Transport 2: https://www.youtube.com/watch?v=Kv_0udatlh8

Transport 3: https://www.youtube.com/watch?v=QXdujo4PZ7c&t=2s

#
 Chapter 9: Transport in Animals
Videos:
https://www.youtube.com/watch?v=y1DsaAzYamQ&t=2s
https://www.youtube.com/watch?v=co6iuDpaQTM&t=3s
https://www.youtube.com/watch?v=gExUCrpAKyQ&t=1s
https://www.youtube.com/watch?v=qWSWWPZYGHU&t=2s
https://www.youtube.com/watch?v=o0-1OknbO3M&t=111s
https://www.youtube.com/watch?v=o0-1OknbO3M

Mammals have a double circulatory system, meaning that blood passes through the heart twice
each circuit of the body.

The Double Circulatory system helps:

- Separate oxygenated from deoxygenated blood.

- Ensure efficient blood transport and maintains blood pressure.

The heart ♥

Semilunar valve

Semilunar valve

Atrioventricular valve

Atrioventricular valve
Key points about the structure of the ♥:
- The septum separates Oxygenated blood from deoxygenated blood.
- Valves prevent the backflow of blood. They open and close to keep blood
flowing in the same direction. (Make sure you know names of the valves)
- The ♥ is a muscle that contracts and relaxes to pump blood to the whole
body.

Compare between the left ventricle & right ventricle:

- The wall of the left ventricle is more muscular than the right ventricle and
is also thicker. This is because the left ventricle pumps blood:
o At higher pressure
o Through longer distance (to the whole body).

Use the ♥ diagram on page 1 to track the direction of blood flow:

Note that blood vessels entering the heart are veins, and the ones leaving the
heart are arteries. The left side of the heart always contains oxygenated blood
because it receives blood fresh from the lungs and pumps it to the body, the right
side always contains deoxygenated blood because it receives is from the body.
You can memorise this by the word LORD: Left Oxygenated – Right Deoxygenated

Coronary Heart Disease

What is CHD?

Coronary artery disease develops when the major blood vessels that supply your heart with
blood, oxygen and nutrients (coronary arteries) become damaged or diseased. Cholesterol-
containing deposits (plaque) in your arteries and inflammation are usually to blame for coronary
artery disease.

When plaque builds up, it narrows your coronary arteries, decreasing blood flow to your
heart. Eventually, the decreased blood flow may cause chest pain (angina), shortness of breath,
or other coronary artery disease signs and symptoms. A complete blockage can cause a heart
attack.
Risk factors
Risk factors for coronary artery disease include:

 Age. Simply getting older increases your risk of damaged and narrowed arteries.

 Sex. Men are generally at greater risk of coronary artery disease. However, the risk for
women increases after menopause.

 Family history. A family history of heart disease is associated with a higher risk of
coronary artery disease, especially if a close relative developed heart disease at an early
age. Your risk is highest if your father or a brother was diagnosed with heart disease
before age 55 or if your mother or a sister developed it before age 65.

 Smoking. People who smoke have a significantly increased risk of heart disease. Exposing
others to your secondhand smoke also increases their risk of coronary artery disease.

 High blood pressure. Uncontrolled high blood pressure can result in hardening and
thickening of your arteries, narrowing the channel through which blood can flow.

 High blood cholesterol levels. High levels of cholesterol in your blood can increase the
risk of formation of plaque and atherosclerosis. High cholesterol can be caused by a high
level of low-density lipoprotein (LDL) cholesterol, known as the "bad" cholesterol. A low
level of high-density lipoprotein (HDL) cholesterol, known as the "good" cholesterol, can
also contribute to the development of atherosclerosis.

 Diabetes. Diabetes is associated with an increased risk of coronary artery disease. Type 2
diabetes and coronary artery disease share similar risk factors, such as obesity and high
blood pressure.

 Overweight or obesity. Excess weight typically worsens other risk factors.

 Physical inactivity. Lack of exercise also is associated with coronary artery disease and
some of its risk factors, as well.

 High stress. Unrelieved stress in your life may damage your arteries as well as worsen
other risk factors for coronary artery disease.

 Unhealthy diet. Eating too much food that has high amounts of saturated fat, trans fat,
salt and sugar can increase your risk of coronary artery disease.
Prevention
The same lifestyle habits that can help treat coronary artery disease can also help prevent it
from developing in the first place. Leading a healthy lifestyle can help keep your arteries strong
and clear of plaque. To improve your heart health, you can:

 Quit smoking

 Control conditions such as high blood pressure, high cholesterol and diabetes

 Stay physically active

 Eat a low-fat, low-salt diet that's rich in fruits, vegetables and whole grains

 Maintain a healthy weight

 Reduce and manage stress

Angioplasty and stent placement (percutaneous coronary revascularization)

Your doctor inserts a long, thin tube (catheter) into the

narrowed part of your artery. A wire with a deflated
balloon is passed through the catheter to the narrowed
area. The balloon is then inflated, compressing the fat
deposits against your artery walls.

A stent is often left in the artery to help keep the

artery open.

Coronary artery bypass surgery

A surgeon creates a graft to bypass blocked coronary

arteries using a vessel from another part of your
body. This allows blood to flow around the blocked or
narrowed coronary artery. Because this requires open-
heart surgery, it's most often reserved for cases of
multiple narrowed coronary arteries.
Blood Vessels

Blood Components:

1) Red Blood Cells – Transport Oxygen.

Adaptations:

a. Biconcave disc with no nucleus – Large surface area

- transport more Oxygen.
b. Small & flexible – can squeeze through narrow
capillaries
c. Contain Hemoglobin – Binds with Oxygen to be
transported around.

2) White Blood Cells – Defense system.

1. Lymphocytes: Secrete antibodies

which kill pathogens.
The antibodies produced are specific and can only
recognize the antigen of a certain type of pathogens. (Ab’s are specific
just like enzymes!)
 2. Phagocytes: They kill bacteria by engulfing them, taking them in the cell
then kill them by digesting them using enzymes, this process is called
phagocytosis.

Sometimes, WBCs are the reason for tissue rejection in transplants.

1. WBCs detect the antigens and recognize the tissue is foreign.

2. Lymphocytes release antibodies.
3. Lymphocytes and phagocytes eventually cause tissue destruction.

3) Platelets: Blood clotting

a. Platelets stick together at the site of injury and form a plug.
b. Fibrinogen (soluble protein) -----(Thrombin) ----> Fibrin (insoluble protein)
c. Fibrin fibers form a mesh that hold platelets together  Stronger clot.
d. The clot hardens and forms a scab.

Importance of blood clotting:

- To prevent blood loss & entry of pathogens.

4) Plasma: Transports substances to tissues & cells.

This makes up most of the blood. It is mostly water with some substances
dissolved in it, these include carbon dioxide, hormones, food nutrients, urea and
other waste products.

Plasma squeezes out of the capillaries to transport nutrients and oxygen to

tissues. Once it’s squeezed out, it becomes something called Tissue Fluid.
Summary of Blood Components – their structure & function:

Tissue Fluid & The Lymphatic System:

Tissue fluid bathes the cells and allows nutrients to diffuse into cells, and waste
substances to diffuse out into the tissue fluid. Most of the tissue fluid is
reabsorbed into the capillary at the venous end. (where capillaries join to form
veins)

Some larger molecules, such as lipids and large proteins, cannot re-enter the
capillary, thus must be carried away by the lymph system. These molecules enter
the lymph vessels and travel as a fluid called lymph. Lymph passes through lymph
vessels and drains into the blood system in the chest cavity.

Lymph nodes are present along the lymph vessels. Their function is to filter the
lymph fluid, removing bacteria and foreign particles from it. They therefore help
protect the body from infection.

The lymphatic system plays a big role in the protection against disease as they
produce Lymphocytes. (Where are lymphocytes produced?)
**Just like veins, lymph vessels have valves to prevent backflow of the fluid.
Brief Summary Of the Functions Of The Lymphatic System:

- Production of lymphocytes.
- Transport of digested fats from villi
to blood stream (lacteal – in the villi).
- Transport of lymph from the tissue
fluids to the blood stream.
 Chapter 10: Breathing & Gas Exchange
Part 1: Breathing System

A bit about the trachea:

The trachea is a tube that connects the nasal cavity to the lungs.

It’s lined with C-shaped cartilage.

Function of the cartilage – Keeps the trachea open to let the air in the lungs. It
allows flexibility in the trachea (to open and close when breathing in and out).

The trachea is lined with two types of specialized cells:

 Goblet cells: secrete mucus to trap dust and pathogens and prevent them
from going into the lungs.
 Ciliated cells: waft the mucus out of the airway.
Goblet cells

Airflow: Trachea  Bronchus  Lt & Rt Bronchi  Bronchioles  Alveoli

 Mechanism of breathing: Inhalation & Exhalation
Feature Inhaling Exhaling

diaphragm Contracts and flattens Relaxes and returns to its domed

shape

Intercosta External muscles – Contract External – Relax

l muscles
Internal – Relax Internal – Contract

ribs Move up & outwards Move back down and inwards

Volume Increases Decreases

Pressure Less than atmospheric pressure. Higher than atm. pressure.

Air flow Air flows in (due to difference in Air flows out

pressure)

Composition of inspired and expired air:

 Gas Inspired Expired

Oxygen 21% 16%

CO2 0.04% 4%

Nitrogen 79% 79%

Water Vapour Variable High

Oxygen’s used up by cells for respiration and it releases Carbon dioxide. This is
why the % of Oxygen is less in the expired air than the inspired air while Carbon
dioxide is more in expired air as it was produced during respiration.

Nitrogen is unchanged as it isn’t used by cells.

Part 2: Gas Exchange

Gas exchange is the diffusion of
Oxygen in and Carbon dioxide out. It
happens in the alveoli.

The alveoli are adapted for their

function in the following ways:

1. Very thin wall – one cell thick

 Shorter distance  Faster
diffusion.

2. Moist surface – alveoli are lined

by a thin film of water in which gases dissolve in during diffusion.

3. Large surface area  faster diffusion.

4. The difference in concentration of gases between the alveolus and the

capillary is very large, increasing the diffusion rate of gases.

5. Rich blood supply – alveoli are surrounded by capillaries  faster diffusion.

Breathing rate and depth during exercise:

 1. During exercise, muscles need to contract faster.

2. Muscle contraction needs energy  Energy from (aerobic) respiration.

3. As a result of aerobic respiration, CO2 concentration increases in blood and

this increase is detected by the brain.

4. The brain signals the heart to beat faster with increased rate and depth of

breathing in order to supply oxygen faster to muscles.

5. Faster heart rate and deeper breathing prevents/delays anaerobic

respiration and hence the accumulation of lactic acid.

Effects of smoking:
Short Term Effects:

Cilia can’t vibrate anymore.

Goblet cells release more mucus which makes the trachea narrower.

Nicotine increases heart beat rate and blood pressure.

Carbon monoxide combines with haemoglobin instead of oxygen  Less oxygen

transported to cells.

Diseases Caused By Tar:

Chronic Bronchitis:

Tar makes goblet cells in trachea produce excess mucus  Mucus falls into lungs

Bacteria in mucus breed causing infections like bronchitis

The layer of excess mucus lining the walls of the alveoli increase the diffusion
distance of gases making gas exchange slower

Emphysema:
The excess mucus lining the alveoli irritates it, causing strong coughs which
damage the alveoli.

The alveoli lose its shape and the surface area for gas exchange decreases.

Lung Cancer:

When tar reaches the lungs, it is absorbed by cells of the bronchi, bronchioles
and the lungs.

The tar causes excessive division and reproduction of these cells which develops
into cancer.

Diseases Caused By Nicotine:

Coronary Heart Disease:

Nicotine helps cholesterol deposition on walls of coronary arteries. This causes

atheroma.

Carbon monoxide binds with haemoglobin making carboxyhaemoglobin and

decreases the oxygen carrying capacity of red blood cells.

Less oxygen is delivered to the heart, a heart attack or failure can take place
leading to death.

Videos:
https://www.youtube.com/watch?v=XYLi9zCghd8&t=101s

https://www.youtube.com/watch?v=LXGG-HgtJoI

https://www.youtube.com/watch?v=fQsgZloXNPY&t=26s

https://www.youtube.com/watch?v=LXGG-HgtJoI&t=7s
 Chapter 11: Respiration

Aerobic respiration Anaerobic respiration

Chemical reactions which use Chemical reactions which break down
Definition Oxygen to break down nutrient nutrient molecules to release energy in
molecules to release energy. the absence of Oxygen.
Animals (in muscles): Glucose  Lactic acid
Glucose + Oxygen  Carbon
Word Equation Plants & Yeast: Glucose  Alcohol +
dioxide + Water
Carbon dioxide
Animals: C6H12O6  2C3H6O3
Chemical Equation C6H12O6 + 6O2  6CO2 + 6H2O Plants & Yeast: C6H12O6  2C2H5OH +
2CO2
Animals: Lactic acid
Products Carbon dioxide & Water
Plants & Yeast: Alcohol & Carbon dioxide
More energy produced for each Less energy produced for each glucose
Energy produced
glucose molecule. molecule.

Duration Lasts longer For a short period of time

How energy is used around the body:

 Muscle contraction  Cell division

 Maintenance of body temp.  Protein synthesis

 Transmission of nerve impulse

During anaerobic respiration, lactic acid builds up in muscles. Lactic acid is a toxic product
that needs to be removed from our blood.

This is why we breathe faster even after finishing exercising – to pay the oxygen debt.

 Oxygen debt – the amount of oxygen needed to oxidize lactic acid produced.

 Lactic acid is converted to Carbon dioxide and water.

How’s the Oxygen debt paid off? (How’s lactic acid removed from the blood?)
 Through increased rate and depth of breathing, leading to – aerobic respiration

 Faster heart rate – transports lactic acid faster from muscles to the liver. (The liver is where lactic acid is

oxidized to be removed)

 Deeper breathing – increases oxygen supply for aerobic respiration and to convert lactic acid to CO2

and water.

Videos:
https://www.youtube.com/watch?v=ZkqEno1r2jk&t=1s
https://www.youtube.com/watch?v=HZtXLhm7ISA
https://www.youtube.com/watch?v=ZkqEno1r2jk&t=1s
https://www.youtube.com/watch?v=40Wp3-ntNis&t=3s
Chapter 12: Coordination & response
Nervous system
Structure & function of the eye
 The Pupil Reflex

 This is a reflex action carried out to protect the retina from damage in bright light and protect
us from not seeing objects in dim light.
 In dim light the pupil dilates (widens) in order to allow as much light into the eye as possible.
 In bright light the pupil constricts (narrows) in order to prevent too much light entering the eye
and damaging the retina.
 Lens Accommodation
(Viewing Near & Distant Objects)

 The way the lens brings about fine focusing is called accommodation.
 The lens is elastic and its shape can be changed when the suspensory
ligaments attached to it become tight or loose.
 The changes are brought about by the contraction or relaxation of the
ciliary muscles.
 Rods & Cones
 There are two types of receptor cells in the retina:
o Rods which are sensitive to dim light
o Cones which distinguish between different colours in bright light
 There are 3 types of cone cells which are sensitive to different colours of light (red,
blue and green)
 The fovea is an area on the retina where almost all of the cone cells are found
 Rod cells are found all over the retina, other than the area where the optic nerve
attaches to the retina – there are no light-sensitive cells at all in this area, and so it is
known as the blind spot.

The Endocrine System

 Plant Tropisms
 Plants can respond to changes in environment (stimuli) for survival, e.g. light, water,
gravity
 Their responses are usually much slower than animals
 They grow either towards a stimulus (known as a positive response) or away from a
stimulus (known as a negative response)
 The responses are known as tropisms.
  It is very important to a plant that its roots and shoots grow in the right directions
 Shoots must grow upwards, away from gravity and towards light, so that leaves are able to absorb sunlight.
 This means that shoots have a positive phototropic response and a negative gravitropic response.
 Roots need to grow downwards into the soil, away from light and towards gravity, in order to anchor the plant
and absorb water and minerals from the soil particles.
 This means that roots have a negative phototropic response and a positive gravitropic response.

The Role of Auxin

Plants respond to stimuli by producing a growth hormone called auxin which controls the direction of growth of roots
or stems. Therefore we say plants control their growth chemically.

Auxin is mostly made in the tips of the growing stems and roots and can diffuse to other parts of the stems or
roots.

Auxin makes the cells behind the tip get longer; the more auxin there is, the faster they will grow

If light shines all around the tip, auxin is distributed evenly, and the cells all grow at the same rate – this is what
normally happens with plants growing outside

When light shines on the shoot from one side though, the auxin in the tip concentrates on the shady side, making
the cells on that side grow faster than the cells on the sunny side

This unequal growth on either side of the shoot causes the shoot to bend and grow in the direction of the light.
Plant Hormones & Weedkillers

 Most weedkillers contain synthetic hormones like auxin – known as 2,4D

 They are selective so they are sprayed onto an area such as a lawn or farm crops and the synthetic auxin affects
the weeds but not the grass / crop plants
 The weeds respond by growing very fast, exhausting their energy reserves due to respiration and then dying,
leaving more space, nutrients and water for the grass or crop plants to grow.

Videos:
https://www.youtube.com/watch?v=n0Zc01e1Frw https://www.youtube.com/watch?v=Nn2RHLWST-k
https://www.youtube.com/watch?v=quQr6X1Q58I https://www.youtube.com/watch?v=vJhsyS4lTW0
https://www.youtube.com/watch?v=y9Bdi4dnSlg&t=1s https://www.youtube.com/watch?v=EZ5tU45Ti_g
https://www.youtube.com/watch?v=PxSkuyjZ3MM https://www.youtube.com/watch?v=05ITJlgPcR0

Chapter 13: Drugs

Videos:
https://www.youtube.com/watch?v=XYLi9zCghd8 https://www.youtube.com/watch?v=jYaZyZ_Bmkc&t=1s
https://www.youtube.com/watch?v=EXBW00yEgUU&t=1s

A drug is a chemical substance that modifies and affects chemical reactions of the body when taken in. Many drugs are useful to us
like medicinal drugs: antibiotics, painkillers, etc. All medicines contain drugs but not all drugs are medicines.

Some drugs, however, are abused or misused by users to feel relaxed, or reach euphoria. Alcohol and heroin are examples of such
drugs.

Medicinal Drugs:

They’re drugs used to help our bodies fight illness or disease.

 Antibiotics: https://www.youtube.com/watch?v=jYaZyZ_Bmkc
o They’re substances which kill bacteria but don’t harm other
living cells (don’t kill viruses). Most antibiotics are made by
fungi. Example: Penicillin.
o Antibiotics attack bacteria in a variety of ways, for example,
antibiotics can: ***
 Disrupt the bacterial cell wall.
 Prevent bacteria from reproducing.
 Cause the bacteria to burst open.
  Interfere with protein synthesis in bacteria  Stop bacterial growth.
o Development of resistant bacteria:
 Bacteria have the ability to evolve through DNA mutations and divide rapidly to produce strains that are resistant
to existing antibiotics.
 This is due to people not completing their antibiotics course (for a short period of time) or overusing
antibiotics for the wrong conditions (viral diseases, for example).
 When patients stop taking their antibiotics before completing the course, some of the bacteria will be
remaining. The remaining bacteria can mutate and develop resistance to the antibiotics used. The drug-
resistant bacteria can continue to reproduce to make more drug-resistant bacteria.
 On the long run, the antibiotics we have will fail to kill the bacteria and we have to make new effective antibiotics
which the bacteria haven’t gained resistance to.
 MRSA (Methicillin-resistant Staphylococcus aureus) are an example of bacteria which developed resistance to
many antibiotics. This makes it difficult to treat such infections.

o How to minimize the development of bacterial resistance?

 Doctors are more cautious about prescribing antibiotics.
 Patients should complete the course of their antibiotics.
 Antibiotics are used only when they’re really needed.
o Antibiotics and viral diseases – why don’t they work? ***
 Antibiotics aren’t effective against viral infections because..:
 Viruses have different structures & characteristics to bacteria, and they don’t have cell walls.

Misused Drugs **Smoking – Gas exchange chapter

Alcohol:

Effects of alcohol consumption:

 Alcohol lengthens reaction time:

Alcohol is a depressant** – it slows down our reflexes and causes the time taken to respond to stimuli to be longer.
 Liver cirrhosis (liver damage):
Alcohol is broken down into fats by the liver. High doses of alcohol can cause fat deposition in the liver leading to a disease
called Liver cirrhosis.
 Negative social implications:
Alcohol increases aggression and violence which leads to an increase in crimes.
 Death: Large doses of alcohol can result in unconsciousness, coma and death.
 Alcoholism: Alcohol abuse and dependence. It’s when a person can’t manage without alcohol and needs to consume large
quantities regularly.

Heroin: Narcotic/addictive drug. It’s also a powerful depressant**.

Effects of heroin use:

 It slows down many of the brain functions.

 Reduces pain and slows down breathing.
 Produces a feeling of euphoria – intense happiness.
 It’s addictive – users become dependent.
o Users can quit, however, withdrawal symptoms include anxiety, diarrhea, nausea, vomiting, etc..
  Heroin is usually injected through the veins. Needles used are usually unsterile and can be a major method by which hepatitis
virus and HIV spread from one person to another.

How does heroin affect the nervous system?

- There’s a group of neurotransmitters in the nervous system

called endorphins.
- Endorphins reduce pain and enhance the mood. They’re
also produced when we exercise.
- What happens when heroin enters the brain?
Heroin enters the brain  Heroin is converted to Morphine
 Morphine fit in place of endorphins (hence enhancing the mood)  Production of natural endorphins is reduced.

PED – performance enhancing drugs

 Testosterone - It is one of a group of hormones known as steroids which stimulate anabolic reactions to occur in the
body (meaning the synthesis of large molecules from smaller ones), so it is known as an anabolic steroid

 One of the effects of testosterone is to cause more proteins to be made in muscles so that muscles become larger
and stronger

 Taking anabolic steroids therefore increases muscle mass, helps athletes train harder and for longer periods of
time, and can increase aggression which can give an edge when competing

 The use of anabolic steroids in sports is banned as it gives an unfair advantage and also has serious side effects,
including:

o increases risk of heart disease o increases risk of kidney damage

o increases risk of liver damage o affect the menstrual cycle in women

Chapter 14: Reproduction
Types of asexual reproduction
Plant reproduction
Human Reproduction
Male reproductive system
Videos:
https://www.youtube.com/watch?v=-ekRRuSa_UQ https://www.youtube.com/watch?v=X1m4Dyr1N18
https://www.youtube.com/watch?v=CuxaXghfyeE https://www.youtube.com/watch?v=wcVC3TFI7fQ
https://www.youtube.com/watch?v=ZDP_ewMDxCo https://www.youtube.com/watch?v=xyN48VnRYUY
https://www.youtube.com/watch?v=_5OvgQW6FG4&t=196s https://www.youtube.com/watch?v=R8_ScKzLAfE
https://www.youtube.com/watch?v=i9zj9V8OWRk&t=17s
 Chapter 15: Organisms & their environment
Food chains and food webs

Definitions:

● Food chain - a diagram which shows the order of energy transfer through feeding in an
ecosystem.
● Trophic level - the trophic level of an organism refers to its position in the food chain,
food web, pyramid of numbers or pyramid of biomass.
● Pyramid of numbers - shows the number of organisms in each trophic level of a food
chain.
● Pyramid of biomass - shows the total mass of organisms in each trophic level of a food
chain.
● Biomass - the total mass of living material.

The source of all energy in a food chain is light energy from the Sun.
 Food Webs
 A food web is a network of interconnected food chains
 Food webs are more realistic ways of showing connections between
organisms within an ecosystem as animals rarely exist on just one type
of food source
 Food webs give us a lot more information about the transfer of energy in
an ecosystem
 They also show interdependence – how the change in one population
can affect others within the food web
 For example, in the food web shown here, if the population of insects decreased:
o The population of grass plants would increase as there are now less species feeding off them
o The populations of frogs and voles would decrease significantly as insects are their only food source
o The population of thrushes would decrease slightly as they eat insects but also have another food source to rely
on (slugs)
 Most of the changes in populations of animals and plants happen as a result of human impact – either by overharvesting
of food species or by introduction of foreign species to a habitat
 Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or web

Trophic Levels
 Trophic levels describe the position of an organism in a food chain, web or pyramid
 Animals (known as consumers) can be at different trophic levels within the same food web as they may eat both
primary, secondary and / or tertiary consumers
 Energy flows from the sun to the first trophic level (producers) in the form of light
 Producers convert light energy into chemical energy and it flows in this form from one consumer to the next

 Eventually all energy is transferred to the environment – energy is passed on from one level to the next with some
being used and lost at each stage
 Energy flow is a non-cyclical process – once the energy gets to the top of the food chain or web, it is not recycled but
‘lost’ to the environment
 This is in direct contrast to the chemical elements that organisms are made out of, which are repeatedly recycled

Transfer of Energy
 At each stage in a food chain only about 10% of the energy received by an organism gets passed on to the next trophic
level:

Why is this?

 In order for the energy to be passed on, it has to be consumed (eaten)

 However not all of the energy grass plants receive goes into making new cells that can be eaten
 The same goes for the energy the vole gets from the grass, and the energy the barn owl gets from the vole

 Only the energy that is made into new cells remains with the organism to be passed on
 Even then, some of this energy does not get consumed – for example few organisms eat an entire organism, including
roots of plants or bones of animals – but energy is still stored in these parts and so it does not get passed on
 The majority of the energy an organism receives gets ‘lost’ (or ‘used’) through:
o making waste products eg (urine) that get removed from the organism
o as movement
o as heat (in mammals and birds that maintain a constant body temperature)
o as undigested waste (faeces) that is removed from the body and provides food for decomposers

 This inefficient loss of energy at each trophic level explains why food chains are rarely more than 5 organisms long
  In the example above, something that preyed regularly on the barn owl would only get 0.1J of energy from each barn owl
it ate
 In order to survive, it would have to:
o eat a huge number of them every day to get the amount of energy it needed to survive (are there that many barn
owls close together?)
o not expend much energy itself hunting them (is this likely?)

Energy Transfer in Human Food Chains

 Humans are omnivores, obtaining energy from both plants and animals, and this gives us a choice of what we eat
 These choices, however, have an impact on what we grow and how we use ecosystems
 Think of the following food chains, both involving humans

wheat → cow → human

wheat → human

 Given what we know about energy transfer in food chains, it is clear that if humans eat the wheat there is much more
energy available to them than if they eat the cows that eat the wheat
 This is because energy is lost from the cows, so there is less available to pass on to humans
 Therefore, it is more energy efficient within a crop food chain for humans to be the herbivores rather than the
carnivores
 In reality, we often feed animals on plants that we cannot eat (eg grass) or that are too widely distributed for us to collect
(eg algae in the ocean which form the food of the fish we eat)

Pyramids of Number
 A pyramid of numbers shows how many organisms we are talking
about at each level of a food chain.
 The width of the box indicates the number of organisms at that trophic
level
 For example, consider the following food chain:

 Despite the name (and the example above), a pyramid of numbers

doesn’t always have to be pyramid-shaped, for example:
  This is because the size of the organism is also important – one large organism, like the oak tree in the pyramid above,
contains enough energy to support many smaller organisms (the insects)

Rules to remember when drawing a pyramid of numbers:

 You cannot change the trophic level of the organisms – they must stay in the same order as in the food chain with
producers on the bottom, followed by primary consumers, then secondary consumers, then tertiary consumers
 Generally, the larger an individual organism is, the less of them there are

Pyramids of Biomass
A pyramid of biomass shows how much mass the creatures at each level would have
without including all the water that is in the organisms (their ‘dry mass’).

Pyramids of biomass are ALWAYS pyramid-shaped, regardless of what the pyramid of

numbers for that food chain looks like

This is because the mass of organisms has to decrease as you go up a food chain – if we
take our first food chain as an example, it’s impossible to have 10kg of grass feeding 50kg
of voles feeding 100kg of barn owls.

Carbon Cycle
Nitrogen Cycle

Water Cycle
 Population
A population is defined as a group of organisms of one species, living in the same area at
the same time.

A community is defined as all the populations of different species in an ecosystem.

An ecosystem is defined as a unit containing the community of organisms and their

environment, interacting together (e.g. a decomposing log, a lake).
Videos:
https://www.youtube.com/watch?v=eGG7hyx_HlA https://www.youtube.com/watch?v=E6WAQpRulhA
https://www.youtube.com/watch?v=wGfOoRrICto https://www.youtube.com/watch?v=nADXMU7mrUk
https://www.youtube.com/watch?v=UMbrxi_DsXc https://www.youtube.com/watch?v=2lqhJNgn_Wg
https://www.youtube.com/watch?v=bvqN9H3QtTQ https://www.youtube.com/watch?v=mCHdhXMFhcU
https://www.youtube.com/watch?v=-oVavgmveyY https://www.youtube.com/watch?v=vZ9b5c8BOT4
https://www.youtube.com/watch?v=MfCLqCGqe6E https://www.youtube.com/watch?v=zrD3tMNPjXU
https://www.youtube.com/watch?v=oe2kPpmhLuc

Chapter 16: Humans and their influence on ecosystems

Improving Food Production

 Modern technology has increased food supply substantially in the following ways:
o Agricultural machinery has replaced humans and improved efficiency due to the ability to
farm much larger areas of land
o Chemical fertilisers improve yields – fertilisers increase the amount of nutrients in the soil
for plants, meaning that they can grow larger and produce more fruit
o Insecticides and herbicides – these chemicals kill off unwanted insects and weed species,
meaning that there is less damage done to plants and fruit lost to insects (insecticides), as
well as reducing competition from other plant species (herbicides)
o Selective breeding – animals and crop plants which produce a large yield are selectively bred
to produce breeds that reliably produce high yields
Monocultures

 Monoculture farming means that on a given area of agricultural land only one type of crop is
grown (eg trees for palm oil grown in Indonesian rainforest)
 This large-scale growth of a single variety of plant does not happen naturally in ecosystems, where
there are usually many different species of plants growing which, in turn, support many species
of animals (high biodiversity)
 In monocultures, biodiversity is much lower
 Another issue with monocultures is the increase in pest populations – if a particular pest feeds on
a crop, farming it in large areas repeatedly means there is an ample supply of food for the pest,
causing the population to increase
 Often farmers will spray insecticides onto crops in order to control the pests. This leads to:

o harmless insects being killed as well

o pollution by pesticides (which are often persistent chemicals which accumulate in food
chains)
o pests potentially becoming resistant to them, reducing their effectiveness

Intensive Livestock Farming

 In developed countries, large numbers of livestock are often kept in an area that would not
normally be able to support more than a very small number
 They are often fed high energy foods, regularly given medication such as antibiotics as a
preventative measure against disease and kept in artificially warm temperatures and small spaces
that do not allow for much movement
 Ecological issues with intensive farming include:
o reduction in biodiversity in areas where large amounts of land are used to graze cattle (as
only grass is grown so in effect it becomes a monoculture)
o overgrazing can lead to soil erosion
o large numbers of cattle produce large amounts of methane, a greenhouse gas

Global Food Supply

 When people do not receive enough food, famine occurs

 This can be caused by a variety of factors, including natural disasters, such as drought and
flooding, increasing population, poverty, and unequal food distribution

 As the global human population increases, food production must also be increased to support the
increasing population
 This is a problem as more land is required to grow crops and animals, meaning
that deforestation is happening at an increasing rate, and there is also an increasing amount
of greenhouse gases emitted from animal production
 Greenhouse gases cause global warming, which is a worldwide issue that leads to increased natural
disasters, such as tropical storms and drought, as well as rising sea levels, which floods homes and
reduces the amount of habitable land.
 Reasons for Habitat Destruction

 The increasing human population of the planet is causing destruction of many habitats from
rainforest to woodland to marine
 Many habitats are destroyed by humans to make space for other economic activities, or
by pollution from these activities, and this reduces the biodiversity of these areas
 This interrupts food chains and webs, meaning that more species may die because their prey is
gone

 The main reasons for habitat destruction include:

 Deforestation

 Deforestation is the clearing of trees (usually on a large scale)

 If trees are replaced by replanting it can be a sustainable practice
 Generally the trees are being cleared for the land to be used in a different way (for building, grazing
for cattle, planting of monocultures such as palm oil plantations etc) and therefore it is not sustainable.
 As the amount of the Earth’s surface covered by trees decreases, it causes increasingly negative
effects on the environment and is a particularly severe example of habitat destruction

 Undesirable effects of deforestation include:

o Extinction of species
o Loss of soil
o Flooding
o Increase of carbon dioxide in the atmosphere
Causes & Effects of Pollution
 Plastic Pollution
 Plastics have a large negative impact on both land and water habitats due to their non-
biodegradability

 In marine habitats:

o Animals often try to eat plastic or become caught in it, leading to injuries and death

o As the plastic breaks down it can release toxins that affect marine organisms

o Once it has broken down into very small particles, it is commonly ingested by animals
and enters the food chain

 On land:

o Plastic is generally disposed of by burying in landfills

o As it breaks down, it releases toxins into the surrounding soil and as such the land is no
good for growing crops or grazing animals and can only be used for building on several
decades after burial

Female Hormones
 Female contraceptive hormones are excreted from the body in urine and then make their way into
the water supply, as they are not filtered out by sewage treatment plants

 If they reach male aquatic organisms, such as fish and frogs, which are very sensitive to the
hormones, it causes feminization.

 This is where male organisms begin to produce eggs and lose the ability to reproduce

 Consequently, a smaller amount of offspring is produced which can harm the species survival and
also disrupts food chains for animals that usually feed off these organisms

 In addition, these hormones can reduce the sperm count in human males, which causes fertility
problems

Eutrophication
 Runoff of fertiliser from farmland enters the water and causes increased growth of algae and
water plants

 The resulting ‘algal bloom’ blocks sunlight so water plants on the bottom start to die, as does the
algae when competition for nutrients becomes too intense

 As water plants and algae die in greater numbers, decomposing bacteria increase in
number and use up the dissolved oxygen whilst respiring aerobically

 As a result there is less oxygen dissolved in water, so aquatic organisms such as fish and insects
may be unable to survive.
Acid Rain
 Combustion of fossil fuels that contain sulfur impurities creates sulfur dioxide.

 This is released into the atmosphere where it combines with oxygen to form sulfur trioxide.

 Sulfur trioxide dissolves in water droplets in clouds and forms acid rain.

Climate Change
 A greenhouse gas is a gas that absorbs infrared radiation from the Sun so it remains trapped in
the Earth’s atmosphere

 This is important to ensure Earth is warm enough for life, however if levels of these gases in the
atmosphere increase it leads to an increase in the greenhouse effect which causes the Earth’s
average temperature to rise

 There are many greenhouse gases, the most important are:

o Water vapour o Nitrous oxides

o Carbon dioxide o CFCs

o Methane
  The greenhouse effect works in the following way:
o The Sun emits rays that enter the Earth’s atmosphere

o The heat bounces back from the Earth’s surface

o Some heat is reflected back out into space

o Some heat is absorbed by greenhouse gases and is trapped within the Earth’s atmosphere –
this is normal

o However, as the levels of greenhouse gases in the atmosphere rise due to human activities
the Earth’s average temperature rises beyond normal (an enhanced greenhouse effect),
causing global warming or climate change

Consequences of global warming due to an enhanced greenhouse effect:

 Ocean temperatures increase which causes melting of polar ice caps / rising sea levels / flooding /
coral bleaching

 Increasing temperatures can cause extreme weather like super storms, flooding, droughts

 These extreme weather events can lead to changes in or loss of habitats

 This means that there will be a decrease in biodiversity as food chains are disrupted and
extinction rates increase

 There could also be increases in migration of species to new places, increased spread of pests
and disease

Sustainable Resources
 We use many resources from the Earth; some, such as food, water and wood, are sustainable resources
 A sustainable resource is one which is produced as rapidly as it is removed from the environment so that it does not
run out
 Some resources, such as fossil fuels (coal, oil and natural gas), are non renewable because what we use cannot be
replaced
 These resources, once used, cannot be produced any more and so they need to be conserved by reducing the amount we
use and finding other, sustainable resources to replace them

 Fossil fuels are being used as an energy source in increasing amounts

 In addition, they are the raw materials for many other products we make – eg almost all plastics that are made start
with oil as a raw material
 Some products, especially those made from paper, plastic, glass or metal, can be reused and recycled – this reduces
waste in the environment and reduces the amounts of raw materials and energy needed to make new products
 Some resources, such as forests and fish stocks, can be maintained – enabling us to harvest them sustainably so that
they will not run out in the future

Sustainable Development
 Sustainable development is defined as development providing for the needs of an increasing human population
without harming the environment
 When developing the way in which we use resources to manage them sustainably, we have to balance conflicting
demands – eg:
o the need for local people to be able to utilise the resources they have in their immediate environment with the
needs of large companies to make money from resources such as forests and fish
o the need for balancing the needs of humans for resources with the needs of the animals and plants that live in
the areas the resources are taken from (preventing loss of habitat and extinction)
o the need to balance what current populations need with what future populations might need – for example if
we harvest all the fish we need to feed people now, this might lead to overfishing which would deplete stocks for
future generations
 For development to occur sustainably, people need to cooperate at local, national and international levels in the
planning and management of resources

Sustaining Forests
 Forests are needed to produce paper products and provide wood for timber
 Much of the world’s paper is now produced from forests which replant similar trees when mature trees are cut,
ensuring that there will be adequate supply in the future
 Tropical hardwoods such as teak and mahogany take many years to regrow but are highly desirable for furniture

 Using these types of wood has now been made more sustainable due to the introduction of several schemes designed
to monitor logging companies and track the wood produced (eg the Forestry Stewardship Council)
 Education helps to ensure logging companies are aware of sustainable practices and consumers are aware of the
importance of buying products made from sustainable sources
 Sustaining Fish Stocks
 Managing fish stocks sustainably includes:
o Controlling the number of fish caught each year (quotas)
o Controlling the size of fish caught (to ensure there are enough fish of a suitable age for breeding remaining)
o Controlling the time of year that certain fish can be caught (to prevent large scale depletion of stocks when fish
come together in large numbers in certain areas to breed)


o Restocking (breeding and keeping offspring until they are large enough to survive in their natural habitat then
releasing)
o Educating fishermen as to local and international laws and consumers so they are aware of types of fish which
are not produced sustainably and can avoid them when buying fish

Sewage Treatment
 As human population grows, the need for freshwater increases
 A significant amount of water we consume is used to flush away human waste (sewage) into pipes
 The pipes carry the sewage and water to treatment plants where the organic waste is removed and the water
cleaned so it can be returned to natural water sources without causing eutrophication

 Crude sewage flows through a screen in which large materials like paper and sticks are trapped so they can be
removed and burned
 The sewage is passed slowly through channels where grit and other heavy particles picked up along the way settle to
the bottom – the grit is later washed and returned to the land
 The channels lead into sedimentation tanks where the solid material settles on the bottom as sludge and the liquid
part, called effluent, remains on top

 The sludge is removed by pumping it into tanks where anaerobic bacteria decompose it – often the bacteria
produce methane which can be collected and used as an energy source for the plant
 The effluent (liquid) is treated with aerobic bacteria to remove any organic waste in it, before being treated
with chlorine to kill the bacteria
 At this point it is clean enough to return to natural water systems or be passed on to a second treatment plant where it
is processed further to make it pure enough to reuse as drinking water

Endangered Species
 An endangered species is at risk of becoming extinct
  There are several reasons why a species can become endangered – the population of the species may fall below a
critical level due to
o hunting
o climate change
o pollution
o loss of habitat
o introduction of non-native species that outcompete native species

 Endangered species can be helped by conservation measures such as:

o education programmes
o captive breeding programmes
o monitoring and legal protection of the species and of their habitats
o seed banks as a conservation measure for plants – seeds of endangered plant species are carefully stored so that
new plants may be grown in the future

 A species may be at risk of becoming extinct if there is not enough genetic variation in the population as random
changes in the environment may quickly cause extinction because the remaining organisms are all very similar and
may not have the adaptations to survive such changes
 There are moral, cultural and scientific reasons for conservation programmes, including:
o reducing extinction rates of both plant and animal species
o keeping damage to food chains and food webs to a minimum and protecting vulnerable ecosystems (eg the
rainforests)
o protecting our future food supply and maintaining nutrient cycles and possible sources of future medical
drugs and fuels

Videos:
https://www.youtube.com/watch?v=8PQiucc268c https://www.youtube.com/watch?v=wXJiHr8jWBs
https://www.youtube.com/watch?v=_bk2nnDI68g https://www.youtube.com/watch?v=wXJiHr8jWBs
https://www.youtube.com/watch?v=6LAT1gLMPu4 https://www.youtube.com/watch?v=Nf8cuvl62Vc
https://www.youtube.com/watch?v=VILCk2CpUCw https://www.youtube.com/watch?v=nvVp0BqT82M
https://www.youtube.com/watch?v=k9NLmD-cPgc https://www.youtube.com/watch?v=Zk1J2EW-nmQ
https://www.youtube.com/watch?v=gBLQUplzZZo https://www.youtube.com/watch?v=N3m_NtQTnfc
https://www.youtube.com/watch?v=BS-gN6jiXw4 https://www.youtube.com/watch?v=jphrpR9ffKA