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IGCSE BIOLOGY
SECTION 2 LESSON 3
Content
Section 2
Structures
and
functions
in living
organisms
a) Levels of organisation
b) Cell structure
c) Biological molecules
d) Movement of substances
into and out of cells
e) Nutrition
f) Respiration
g) Gas exchange
h) Transport
i) Excretion
j) Coordination and response
Content
Lesson 2
e) Nutrition
Flowering plants
2.15 describe the process of photosynthesis and
understand its importance in the conversion of
light energy to chemical energy
2.16 write the word equation and the balanced
chemical symbol equation for photosynthesis
2.17 understand how varying carbon dioxide
concentration, light intensity and temperature
affect the rate of photosynthesis
2.18 describe the structure of a leaf and explain
how it is adapted for photosynthesis
2.19 understand that plants require mineral ions
for growth and that magnesium ions are needed
for chlorophyll and nitrate ions are needed for
amino acids
2.20 describe experiments to investigate
photosynthesis, showing the evolution of
oxygen from a water plant, the production of
starch and the requirements of light, carbon
dioxide and chlorophyll
Content
Lesson 3
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
Types of nutrition
AUTOTROPHS –organisms that can
produce complex organic compounds
from simple inorganic molecules.
They are the PRODUCERS in a food
chain.
HETEROTROPHS – organisms that
cannot produce their own food, but
acquire complex organic molecules by
consuming plants or other animals.
Biological molecules
Our diet needs
to contain
sufficient and
balanced
quantities of
carbohydrates,
proteins and
lipids.
Biological molecules
carbohydrates
Sugar
Starch
Cellulose
Different foods contain
different kinds of sugar.
Eg fruit contains fructose
or glucose. Lactose is in
milk. Table sugar is
sucrose.
Sugar gives us
energy, so we call
it an energy food.
Biological molecules
carbohydrates
Sugar
Starch
Cellulose
Different foods contain
different kinds of sugar.
Eg fruit contains fructose
or glucose. Lactose is in
milk. Table sugar is
sucrose.
Sugar gives us
energy, so we call
it an energy food.
Starch is found
particularly in
bread, potatoes
and cereals.
Starch is a storage
molecule, but it does
provide us with
energy.
Biological molecules
carbohydrates
Sugar
Starch
Cellulose
Different foods contain
different kinds of sugar.
Eg fruit contains fructose
or glucose. Lactose is in
milk. Table sugar is
sucrose.
Sugar gives us
energy, so we call
it an energy food.
Starch is found
particularly in
bread, potatoes
and cereals.
Starch is a storage
molecule, but it does
provide us with
energy.
Cellulose is found
in plant cell walls
It is a structural
molecule, and
supports the plant
cell.
Biological molecules
Fats
Fats also contain C, H and O, but relatively less
O. Fats occur in both plant and animal foods.
Fats – solid at room temperatures.
Oils - liquid at room temperatures.
Biological molecules
Fats
Fats also contain C, H and O, but relatively less
O. Fats occur in both plant and animal foods.
Fats – solid at room temperatures.
Oils - liquid at room temperatures.
Fats also give us energy. They also provide
insulation in humans and other mammals, and are
energy stores.
Biological molecules
Proteins
Proteins contain C, H and O, and also some
nitrogen (N) and a little suplhur (S).
Proteins are found in milk, eggs, meat and fish.
Biological molecules
Proteins
Proteins contain C, H and O, and also some
nitrogen (N) and a little suplhur (S).
Proteins are found in milk, eggs, meat and fish.
Proteins are needed for
growth and bodybuilding (muscles and
skin), and they are also
used to make enzymes.
Components of our diet
Minerals: contain certain elements essential for
the proper functioning of our bodies.
Components of our diet
Minerals: contain certain elements essential for
the proper functioning of our bodies.
Calcium
Needed for
hardening
our bones
and teeth.
Occurs in
Deficiency
foods such as results in
milk, cheese rickets
and fish
Rickets
Rickets is a softening of bones
in children due to deficiency or
impaired metabolism of vitamin
D, magnesium, phosphorus or
calcium, potentially leading to
fractures and deformity.
Rickets is among the most
frequent childhood diseases in
many developing countries.
Components of our diet
Minerals: contain certain elements essential for
the proper functioning of our bodies.
Calcium
Iron
Needed for
hardening
our bones
and teeth.
Occurs in
Deficiency
foods such as results in
milk, cheese rickets
and fish
Present in
haemoglobin,
the red
pigment in
blood used to
carry oxygen
Occurs in a
number of
foods,
especially
liver and
kidneys
Deficiency
results in
anaemia
Anaemia
Anaemia is a decrease in
the number of red blood
cells in the blood, meaning
that less oxygen can be
carried by the blood to
various organs and
tissues,. The main
symptoms are tiredness
and lethargy.
Components of our diet
Vitamins: a collection of organic substances
needed in small quantities in the body. Their
overall function is to help control the chemical
reactions taking place in the body.
Components of our diet
Vitamins: a collection of organic substances
needed in small quantities in the body. Their
overall function is to help control the chemical
reactions taking place in the body.
Vitamin A
Important for
our eyes –
helps protect
their surfaces
Found in fish
liver oil, and
carrots.
Deficiency
makes it
difficult to
see in dim light
Components of our diet
Vitamins: a collection of organic substances
needed in small quantities in the body. Their
overall function is to help control the chemical
reactions taking place in the body.
Vitamin A
Vitamin C
Important for
our eyes –
helps protect
their surfaces
Found in fish
liver oil, and
carrots.
Deficiency
makes it
difficult to
see in dim light
Needed for
strong gums
Found in citrus Deficiency
fruits, green
results in
vegetables and scurvy
blackcurrants
Scurvy
Scurvy can result in
swollen gums, severe pain
in joints, shortness of
breath, and blurred
vision.
Components of our diet
Vitamins: a collection of organic substances
needed in small quantities in the body. Their
overall function is to help control the chemical
reactions taking place in the body.
Vitamin D
Necessary for
bones to take
up calcium
salts
Occurs in fish
liver oil, and
can be made in
the skin
provided
sunlight is
present.
Deficiency
results in
rickets.
Components of our diet
Fibre is necessary for a healthy balanced diet,
but the body can’t absorb it. It helps our
digestive system to process food and absorb
nutrients. It helps your bowel to pass food by
making stools soft and bulky. It helps prevent
constipation.
Fibre is found in foods such as brown rice, oats,
wholegrain breads and cereals.
Components of our diet
Water makes up more
than two-thirds of the
weight of the human
body. It serves as a
lubricant, helps
regulate body
temperature, prevents
and relieves
constipation. Without
enough water we can
become dehydrated.
The human digestive system
(also known as the alimentary canal)
From mouth to anus
The human digestive system
The human digestive system
In digestion, large
insoluble molecules
are broken down
into smaller
soluble particles
that can be
absorbed into the
bloodstream.
The human digestive system
Mouth – mechanical
chewing of the food.
Salivary glands
produce the enzyme
amylase which begins
breaking down
polysaccharides into
simpler sugars.
The human digestive system
Oesophagus (also
known as the gullet).
Passes food down
from the mouth to the
stomach by a process
known as peristalsis.
Peristalsis
Rings of muscle
around the
oesophagus
effectively ‘squeeze’
food towards the
stomach, as you
would with
toothpaste in a
tube.
The human digestive system
Stomach – more
mechanical digestion
happens here. The
stomach produces the
enzyme protease, and
also hydrochloric acid
which kills bacteria,
and this acid also
provides the ideal
conditions for
protease.
The human digestive system
Pancreas – produces
many enzymes,
including amylase,
protease and lipase.
The human digestive system
Small intestine – can
be over six metres
long. Digested food is
absorbed here into
the blood stream.
The surface area of
the small intestine is
greatly increased by
the presence of small,
finger-like projections
called villi (villus).
Villi
The human digestive system
Large intestine – as
the fibre and other
undigested material
passes along the large
intestine, water is
absorbed from it, so it
becomes more solid.
This solid matter then
passes on to the
rectum where it is
stored as faeces.
The human digestive system
The Liver – produces a
substance known as
bile, which is stored in
the gall bladder
before it is released
into the small
intestine.
Bile has 2 functions:
The human digestive system
The Liver – produces a
substance known as
bile, which is stored in
the gall bladder
before it is released
into the small
intestine.
Bile has 2 functions:
1. It neutralises the acid
from the stomach, producing
more alkaline conditions.
The human digestive system
The Liver – produces a
substance known as
bile, which is stored in
the gall bladder
before it is released
into the small
intestine.
Bile has 2 functions:
2. It emulsifies fats – i.e. it
breaks large drops of fat
into small droplets to
increase their surface
area, so enzymes can
work faster.
Pause time!
Definitions
Ingestion
Digestion
Absorption
Assimilation
Egestion
Definitions
Ingestion
Digestion
Absorption
Assimilation
Egestion
This is the process of taking in food
substances through the mouth.
Definitions
Ingestion
This is the process of taking in food
substances through the mouth.
Digestion
This is the mechanical and chemical
breakdown of food into smaller, more
soluble, components.
Absorption
Assimilation
Egestion
Definitions
Ingestion
This is the process of taking in food
substances through the mouth.
Digestion
This is the mechanical and chemical
breakdown of food into smaller, more
soluble, components.
Absorption
Assimilation
Egestion
This is the process of taking soluble food
through the wall of the small intestine by
diffusion into the blood stream.
Definitions
Ingestion
This is the process of taking in food
substances through the mouth.
Digestion
This is the mechanical and chemical
breakdown of food into smaller, more
soluble, components.
Absorption
This is the process of taking soluble food
through the wall of the small intestine by
diffusion into the blood stream.
Assimilation
This is the process whereby absorbed
food is altered chemically by the liver or
chemical substances before being utilised
by the cells of the body.
Egestion
Definitions
Ingestion
This is the process of taking in food
substances through the mouth.
Digestion
This is the mechanical and chemical
breakdown of food into smaller, more
soluble, components.
Absorption
This is the process of taking soluble food
through the wall of the small intestine by
diffusion into the blood stream.
Assimilation
This is the process whereby absorbed
food is altered chemically by the liver or
chemical substances before being utilised
by the cells of the body.
Egestion
This is the process where solid undigested
food material is removed from the
digestive system via the anus.
Biological molecules
Simple sugars
Starch / glycogen
Biological molecules
Fatty acids, glycerol
Fats, oils (lipids)
Biological molecules
Amino acids
Proteins
ENZYMES
ENZYMES
Enzymes are biological catalysts – they speed up
the rate of chemical reactions going on inside
living things.
ENZYMES
Enzymes are biological catalysts – they speed up
the rate of chemical reactions going on inside
living things.
What are the features of enzymes?
ENZYMES
Enzymes are biological catalysts – they speed up
the rate of chemical reactions going on inside
living things.
What are the features of enzymes?
• Enzymes are globular proteins
• Every enzyme has an area called its active site
• Enzymes are specific
• Enzymes are affected by temperature and pH
ENZYMES
• Commonly named by adding the ending
“-ase” to the substrate molecule being
acted upon.
• Eg. sucrase works on sucrose, lipase
works on lipose.
• A few enzymes are known by common
names, eg. pepsin, trypsin
ENZYME ACTION
Substrate
Product
Enzyme
e.g. Sucrose
Glucose + Fructose
Sucrase
Enzyme summary
Salivary Gland produces amylase which
breaks down
carbohydrates (such as
starch) into simple
sugars (eg. glucose)
Enzyme summary
Stomach – produces
protease which breaks
down proteins into
amino acids
Enzyme summary
Pancreas – produces
amylase (carbohydrates
 sugars), protease
(proteins  amino
acids), lipase (fats 
fatty acids + glycerol)
Enzyme summary
Small intestine – produces
amylase (carbohydrates 
sugars), protease (proteins
 amino acids), lipase (fats
 fatty acids + glycerol)
Enzyme summary
One more thing ………….
Maltase, thought to be
produced by the walls
of the small intestine,
converts the
disaccharide maltose
(formed by the action
of amylase on starch)
into the simple sugar
glucose.
Content
Lesson 1
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
Content
Lesson 1
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
Content
Lesson 1
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
Content
Lesson 1
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
Content
Lesson 1
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
Content
Lesson 1
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
Content
Lesson 1
e) Nutrition
Humans
2.21 identify sources and describe functions of
carbohydrate, protein, lipid (fats and oils), vitamins A,
C and D, the mineral ions calcium and iron, water and
dietary fibre as components of the diet
2.22 describe the structures of the human alimentary
canal and describe the functions of the mouth,
oesophagus, stomach, small intestine, large intestine
and pancreas
2.23 understand the processes of ingestion, digestion,
absorption, assimilation and egestion
2.24 explain how and why food is moved through the
gut by peristalsis
2.25 understand the role of digestive enzymes, to
include the digestion of starch to glucose by amylase
and maltase, the digestion of proteins to amino acids
by proteases and the digestion of lipids to fatty acids
and glycerol by lipases
2.26 understand that bile is produced by the liver and
stored in the gall bladder, and understand the role of
bile in neutralising stomach acid and emulsifying
lipids
End of Section 2 Lesson 3
In this lesson we have covered:
Nutrition – human