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Unit 3
Chemistry and Life
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the title.
• Photosynthesis and Respiration
• The Effect of Chemicals on the
Growth of Plants
• Food & Diet
• Drugs
• End
Photosynthesis
and
Respiration
Photosynthesis
• Plants make their own food by
taking in substances from their
surroundings (the environment).
• Plants use light energy to produce
glucose from carbon dioxide and
water.
• Oxygen is also produced.
• This process is photosynthesis.
• The equation for the
photosynthesis is:
• carbon dioxide + water  glucose + oxygen
• During photosynthesis carbon dioxide is
absorbed through the leaves of plants.
• Water is drawn up through the roots
and oxygen gas is released into the air
through the leaves.
• The light energy required for
photosynthesis is absorbed by the
chlorophyll in the leaves.
Respiration
• Animals need sources of energy.
• They use this energy for a lot of things,
including warmth and movement.
• Animals can obtain energy from the
reaction of glucose with oxygen to
produce water and carbon dioxide.
• This process is called respiration.
• Respiration is the reverse of
photosynthesis.
glucose + oxygen  carbon dioxide + water + energy
• Since photosynthesis and respiration
are going on at the same time the
amounts of oxygen and carbon dioxide
in the air stay the same.
The Greenhouse Effect
• Carbon dioxide in the
atmosphere causes
the greenhouse
effect.
• The clearing of
forests means that
less carbon dioxide is
removed from the
atmosphere by
photosynthesis.
• Increased levels of
carbon dioxide in the
air may also be due
to greater use of
fuels.
• More carbon dioxide
in the atmosphere
could cause it to
keep more of the
Sun's energy as heat,
a process known as
global warming.
Photosynthesis and
Respiration
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and Respiration.
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The Effects of
Chemicals on the
Growth of Plants
Using chemicals to save
plants
• The amounts of healthy crops can be
reduced in the following ways:
• crops are eaten by pests, e.g. insects
and slugs
• bacteria and fungi can cause plants to
become diseased
• weeds use up essential substances in
the soil, so there is less food for the
plants.
• Pesticides are used to control pests
• Fungicides prevent diseases
• Herbicides kill weeds.
• Pesticides are toxic and so must be
used with care.
• Natural predators can also be used
to safely control pests.
Fertilisers
• For healthy plant growth the
following elements are needed:
• Nitrogen
• Phosphorous
• Potassium.
• These elements are taken in
through the roots of plants as
compounds dissolved in water.
• In areas of natural vegetation,
decay of vegetable and animal
remains returns all essential
elements to the soil.
• Harvesting of crops prevents the
natural return of these essential
elements to the soil.
• Fertilisers are added to the soil to
restore essential elements.
• Examples of natural fertilisers
include compost and manure.
• Increased demand for food has resulted
in the use of artificial fertilisers.
• Artificial fertilisers are made by the
chemical industry
• The major artificial fertilisers are
compounds containing ammonium,
nitrate, phosphate or potassium.
• To be effective, fertilisers must be
soluble in water.
• The extensive use of nitrate
fertilisers may have increased the
amount of nitrates in rivers, lochs
and the public water supply.
• The presence of large quantities of
nitrates can leave the water
lifeless.
• Some plants, such as clover, beans
and peas have root nodules which
change nitrogen from the air into
nitrates.
The Effects of
Chemicals on the
Growth of Plants
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Chemicals on the Growth of Plants
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Food and Diet
Elements in the Body
• A balanced diet provides the body with
all the elements and compounds you
need.
•
•
•
•
•
The main elements in your body are
Oxygen
Carbon
Hydrogen
Nitrogen.
• Elements are present in the diet
and in the body as chemical
compounds and not as the free
elements.
• Essential compounds include
carbohydrates, fats and proteins.
• More than 60% of body weight is
made up of water.
• Minerals supply the body with
small quantities of
• calcium for bones and teeth
• iron for the blood
• trace elements
• Some trace elements are toxic, if
you take too much of them.
Carbohydrates
• Carbohydrates
form an important
class of food
made by plants.
• Carbohydrates
are used by the
body to produce
energy.
• Carbohydrates
are compounds
which contain
carbon, hydrogen
and oxygen.
• Carbohydrates
can be divided
into sugars and
starches.
Sugars
• Glucose, fructose,
maltose and
sucrose (table
sugar) are
sugars.
• Sugars are sweet
and very soluble
in water.
• Most sugars can
be detected by
Benedict's test.
• Sucrose cannot be
detected by
Benedict’s test.
• Sugars are
carbohydrates
with small
molecules.
Starch
• Starch can be distinguished from
other carbohydrates by the iodine
test.
• Starch is not sweet and does not
dissolve in water.
Reactions of
carbohydrates
• Starch is a
polymer made of
many glucose
molecules linked
together.
• Plants convert the
glucose into
starch for storing
energy.
• During digestion starch is broken
down to glucose.
• Digestion takes place so that the
carbohydrate can dissolve in blood.
• The glucose is carried by the blood
stream to body cells where
respiration occurs.
• In digestion the starch is broken
down by acid and by enzymes.
• Body enzymes function best at
body temperature.
• Enzymes are destroyed at high
temperatures.
Fats and Oils
• Fats and oils are
important types
of food obtained
from both plants
and animals.
• Fats and oils are
much more
concentrated
sources of energy
than
carbohydrates.
• Fats and oils can be detected by a
filter paper test.
• Put some oil or fat on a piece of
filter paper and a transparent spot
appears.
• Animal fats are called saturates.
• Saturates are believed to increase
the level of a substance called
cholesterol in the bloodstream.
• A high cholesterol level may cause
heart disease.
• Vegetable oils are called
polyunsaturates.
• Polyunsaturates are less likely cause
heart disease.
• Medical opinion suggests that it is
better for your heart if you eat less
fat.
• Where possible foods containing
polyunsaturates should be eaten.
Proteins
• Proteins form an
important class of
food obtained
from both plants
and animals.
• Proteins provide
material for body
growth and
repair.
Testing for proteins
• If proteins are heated with soda
lime an alkaline gas is released
(turns pH paper blue).
Proteins
• Proteins are chemicals made from
carbon, hydrogen, oxygen and
nitrogen.
• Proteins are polymers made up of
many amino acid molecules linked
together.
• The amino acids required to make
animal proteins are obtained from
animal and vegetable foods.
• In the body, animals make up
particular proteins from those amino
acids, as they are required for
certain jobs.
• During digestion proteins in foods
are broken down to amino acids.
• A vegetarian diet must include a
wide variety of vegetables to supply
all the necessary amino acids.
Fibre
• Fibre keeps the
gut working well,
preventing
constipation.
• Fibre absorbs
water and swells
• This swollen fibre
is bulky so the gut
muscles work on
as food is
squeezed along.
Vitamins
• Vitamins are
complicated
carbon
compounds.
• They are needed
to keep the body
healthy.
• If our diet lacks
important
vitamins we will
suffer from poor
health.
Food additives
• Food additives are substances which
are added to the food we eat.
• Food additives can be used only if
they have been tested and
approved.
• Food additives can be used to
increase the nutritional value of
food.
• Sometimes extra materials are
added.
• Sometimes missing materials are
supplied, for example vitamins and
minerals
• Food additives can be used to
improve the keeping qualities of
food.
• Adding food preservatives means
that the food will not go off as
quickly.
• Food additives can
also be used to:
• alter the appearance
of food by adding
colour.
• alter the taste of food
by adding flavour.
Food and Diet
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Drugs
Drugs
• A drug is a substance, which alters
the way the body works.
• Drugs can damage health because of
the way they can affect the body
and lifestyle.
Alcohol
• Alcohol is a drug.
• If we take too
much alcohol it
can have many
harmful effects on
our bodies,
particularly the
liver and the
brain.
• Alcohol is measured in units.
• A bottle of alcopop or a pint of beer
contains about 2 units.
• A pub measure of spirit or a glass of
wine contains about 1 unit.
• Alcohol is broken down by the body
at about 1 unit per hour.
• Alcoholic drinks
can be made by
the fermentation
of starch and
sugars present in
fruit and
vegetables.
• The type of
alcoholic drink
varies with the
plant from which
the starch or
sugar comes.
Fermentation
• During fermentation glucose is
broken down to form alcohol;
carbon dioxide is also produced.
• Fermentation is brought about by
enzymes present in yeast.
• The chemical name for the alcohol
produced by fermentation is called
ethanol.
Distillation
• Distillation is used to increase the
concentration of alcohol in the liquid
produced by fermentation.
• Water and alcohols are separated by
distillation because they boil at
different temperatures.
• This separation is not complete.
Other drugs
• Some drugs, including medicines,
alcohol, nicotine and caffeine are
legal.
• Other drugs, including cannabis, LSD
and ecstasy are illegal.
• Being unable to manage without a
drug is called addiction.
• Methanol, another alcohol, is very
poisonous, causing blindness and
death.
• Methylated spirits (meths) contains
methanol.
• It has both a colour and a bad
tasting substance added to it to
prevent people from drinking it.
Medicines
• Chemical reactions are going on all
the time to keep the body working
properly.
• Medicines contain drugs which help
the body when it is not working
correctly.
• Some drugs, including antibiotics, can
fight micro-organisms which interfere
with the chemical reactions.
• Medicines are usually made up of many
chemicals.
• Only some of these chemicals (the active
ingredients) work on the body.
Drugs
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The End
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