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8/13/2019 9D Plants for Food
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KS3 Biology
9D Plants for Food
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9D Plants for Food
Contents
Plants as food
Fertilizers and competition
Summary activities
Pests and pesticides
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Humans in food chains
Humans eat many different foods and so
are at the top of many food chains.
What are the food chains for the
ingredients in this slice of pizza?
wheat(bread) human
grasscows milk(cheese) human
tomato human
pepper human
What do these and all food chains have in common?
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All food chains start with a producer.
Plants as producers
glucose
light energy
chlorophyll
carbondioxide
water oxygen
Plants are called producers because they produce the foodthat humans and all other consumers depend on.
How do plants make their food?
Plants use light energy to carry out photosynthesis:
The glucose produced by plants is converted into starch for
storage or used to make proteins, fats and other substances.
Which parts of plants can be eaten?
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Plants provide food in many different formssome foods are
from the leaf, the stemor the rootof a plant,others are the
seedor the fruitof a plant.
Food from plants
Which parts of plants are these foods from?
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Which part of a plant?
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9D Plants for Food
Contents
Plants as food
Fertilizers and competition
Summary activities
Pests and pesticides
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Healthy plant growth
Plants need carbon dioxide and water
for photosynthesis but they also need
small amounts of mineral saltsforhealthy growth.
Mineral salts are dissolved in water in the soil and so plantsabsorb these nutrients in the water they take in from the soil.
Where do plants get mineral salts from?
The three main elements in mineral salts are:
nitrogen (N)needed for healthy leaves;
phosphorus (P)needed for healthy roots;
potassium (K)needed for healthy flowers and fruit.
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Fertilizers and plant growth
Farmers add chemicals called
fertilizersto soil to make sure
that their crops get enough
mineral salts.
Manufactured fertilizers can
be expensive. So why do
farmers choose to use them?
Plants take in mineral salts from the soil and in time there
are less nutrients available in the soil.
Fertilizers help crops to grow well and so increase the
farmers crop yield.
What other types of fertilizer are there?
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Competition between plants
Organisms that share a
habitat have to compete
with each other for limitedliving resources.
A weed is any plant that
is growing in the wrong place.
Weeds are a problem for
farmers as they compete
with the crops for resources
such as light, water, living
space and mineral salts.
How does competition
affect the growth of crops?
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Controlling weeds
Weeds compete with crops
for living resources and this
can reduce crop yield.
What can farmers do to
control weeds?
One way farmers can controlweeds is to use chemicals
called herbicides(or
weedkillers).
Weeds are part of the foodweb. How might using
herbicides affect other
organisms in the food web?
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9D Plants for Food
Contents
Plants as food
Fertilizers and competition
Summary activities
Pests and pesticides
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Pests and plant growth
Pestsare animals that eat and damage crops and so can
be a problem for farmers.
Pests reduce crop yield and compete with humans for food.
What animals might be considered as pests by farmers?
Caterpillars are pests specific to
a type of plant such as cabbages.
Snailsand slugs are pests that
eat the leaves of many plants.
Other common pests includeinsects, birds and mice.
If the number of pests is reduced, what happens to crop yield?
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Controlling pests
What can farmers do to control pests?
One method of pest control is theuse of pesticidesthat kill pests.
Pesticides contain poisonous
chemicals called toxins.
What are the advantages and disadvantages of pesticides?
Pesticides can kill useful animals as well as the pests that
they were meant to kill.
Pests are part of the food web and the toxins in pesticidescan affect other organisms in a food chain or food web.
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Introducing a pesticide at the bottom of a food chain can
have huge effects on the organisms above.
Consider the following food chain from a lake:
Pesticide in a food chain
A pesticide called DDTwas sprayedon the lake to control mosquito larvae.
DDT is a toxin that does not break
down in the environment and so stays
in animals bodies if it is eaten.
plantplankton zooplankton
smallfish
largefish
grebe(bird)
The plant plankton at the bottom of the food chain
absorbed some of the DDT from the water.
How did this affect the rest of the food chain?
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Each zooplankton ate lots of plant plankton and got several
doses of DDT. Each zooplankton contained5 ppmof DDT.
Each small fish ate many zooplankton and so consumed
even more DDT.
How much DDT do you think each small fish contained?
Each small fish contained10 ppmof DDT.
Pesticide in a food chain
plantplankton zooplankton
smallfish
largefish
grebe(bird)
DDTabsorbed
5ppm 10ppm
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Pesticide in a food chain
Each large fish ate several small fish and so consumed
even more DDT.
How much DDT do you think each large fish contained?
Each large fish had 250 ppmof DDT in it.
Each grebe ate several large fish therefore getting more
than one dose of DDT.
How much DDT do you think each grebe contained?
plantplankton zooplankton
smallfish
largefish
grebe(bird)
DDTabsorbed
5ppm 10ppm 250ppm
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Each grebe had the amazing amount of1600 ppmof DDT
in its tissue which could kill the bird.
In most cases, this amount of toxin made the birds eggs
have very thin shells. These eggs broke very easily and so
not many chicks were born alive.
This example is actually based on real events that took placein the USA in the 1950s. It shows how a toxin can be passed
on in a food chain and gets more concentrated at each step.
Pesticide in a food chain
plantplankton zooplankton
smallfish
largefish
grebe(bird)
DDTabsorbed
5ppm 10ppm 250ppm 1600ppm
This is called bioaccumulation.
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DDT lead to the decline many species of birds.
What do these pyramids of numbers show about the effectof spraying the lake with the toxin DDT on the numbers of
organism in a food chain?
Pesticide in a food chain
grebe (bird)
large fish
small fish
zooplankton
plankton
before spraying after spraying
f
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DDT was considered as a safe pesticide
when it was first used to kill insect pests.
The problem was that DDT does not
break down in the environment and the
levels of this toxin that built up in top
carnivores proved to be a major hazard.
Pesticide in a food chain
Alternative chemicals are now used as pesticides instead of
DDT. These new pesticides break down quickly in theenvironment .
Why arent these new pesticides hazardous to wildlife?
Today, many countries, including the UK, have banned the
use of DDT to protect the environment.
C
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9D Plants for Food
Contents
Plants as food
Fertilizers and competition
Summary activities
Pests and pesticides
Gl
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Glossary
competitionThe demand by two or more organisms forlimited shared resources, such as nutrients, space or light.
cropA plant that is grown to be of use to humans.
fertilizerA chemical that is added to soil to provide plantswith the mineral salts needed for healthy growth.
herbicideA chemical used to kill weeds.
pestAn animal that damages crops and competes withhumans for food.
pesticideA chemical used to kill pests.
toxinA poisonous chemical. weedA plant growing in the wrong place that competes
with a crop.
A
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Anagrams
M lti l h i i
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Multiple-choice quiz