science world 1 – chapter 13
food for life
THE NEED FOR FOOD
You need food for three reasons:
*
for energy.
*
for growth.
*
to keep your body healthy and functioning correctly.
Plants are able to make their own food via photosynthesis, but
animals have to obtain their food from other organisms.
The process of obtaining energy from food in your body is
called respiration. The chemical energy stored inside the food
molecules is changed into energy that helps you send messages
around your body, move your muscles and keep your body
warm. The energy in food is measured in units called kilojoules
(kJ).
FOOD TYPES
There are various substances in the food you eat, but they all
contain some water. The dry matter in food is made of four
main food types:
Carbohydrates – found in fruit, vegetables, cereal, rice,
potatoes, bread and pasta.
Proteins – found in meat, fish, chicken, nuts, eggs and cheese.
Fats – found in margarine, butter and oil.
Vitamins and minerals – found in fruit, vegetables, nuts and
meat.
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PLANT FOOD
Plants and algae make all the materials needed for the growth
and repair of their cells. To do this they must absorb simple
materials from the air, water or soil. The whole process is
summarised as follows:
1.
Chlorophyll molecules in the plant absorb sunlight.
2.
This energy from the sun is used to make carbohydrates
from water and carbon dioxide (i.e. photosynthesis).
H2O + CO2 + sunlight  carbohydrates + O2
3.
These carbohydrates (i.e. food) are transported to all cells
in the plants.
4.
The carbohydrates are broken down to supply energy for
plant growth (i.e. respiration).
carbohydrates + O2  H2O + CO2 + energy
DIGESTING FOOD
The job of the digestive system is to break down the food you
eat into smaller molecules that are able to pass into your
bloodstream. Digestion is both the physical breakdown of
large lumps of food into smaller ones, and the chemical
breakdown of food.
The chemical breakdown of food occurs with the help of
substances called enzymes. These substances speed up
chemical reactions that break down large insoluble food
molecules into small soluble ones. There are different enzymes
used to break down carbohydrates, proteins and fats.
FOOD TRANSPORT IN HUMANS
Once food has been broken down by your digestive system it
enters the bloodstream. Blood carries food to all the cells in
your body and carries wastes away from them.
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The blood is pumped around the body by your heart. Your
heart is only slightly larger than your fist, but it pumps blood
around your body about 70 times a minute for your whole life.
The heart pumps blood through three types of blood vessels:
Arteries – are very muscular and carry blood containing oxygen
away from the heart.
Veins – are thinner than arteries and carry blood containing no
oxygen back to the heart.
Capillaries – are extremely thin and allow food, oxygen and
water to pass into the cells, and wastes to pass
back out.
SPELLING WORDS
No.
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2
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8
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15
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20
EASY
food
energy
healthy
water
minerals
sugar
fruit
starch
mouth
liver
anus
vein
heart
blood
plasma
waste
contract
stem
root
leaves
HARD
functioning
respiration
process
muscles
carbohydrates
proteins
vitamins
vegetables
glucose
nutrients
fertiliser
digestion
oesophagus
stomach
intestine
contraction
enzyme
arteries
capillaries
vessels
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