9d plants for food

8/13/2019 9D Plants for Food

1/24

Boardworks Ltd 20041 of 20


KS3 Biology

9D Plants for Food


2/24



9D Plants for Food

Contents

Plants as food

Fertilizers and competition

Summary activities

Pests and pesticides


3/24



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?


4/24



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?


5/24



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?


6/24



Which part of a plant?


7/24

Boardworks Ltd 20041 of 20 Boardworks Ltd 20057 of 24

9D Plants for Food

Contents

Plants as food


Summary activities



8/24


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.


9/24


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?


10/24 Boardworks Ltd 20041 of 20 Boardworks Ltd 200510 of 24

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?



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?



9D Plants for Food

Contents

Plants as food


Summary activities




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?



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.



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?



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.



smallfish

largefish

grebe(bird)

DDTabsorbed

5ppm 10ppm




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?


smallfish

largefish

grebe(bird)

DDTabsorbed

5ppm 10ppm 250ppm



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.



smallfish

largefish

grebe(bird)

DDTabsorbed

5ppm 10ppm 250ppm 1600ppm

This is called bioaccumulation.



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?


grebe (bird)

large fish

small fish

zooplankton

plankton

before spraying after spraying

f



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.


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



9D Plants for Food

Contents

Plants as food


Summary activities


Gl



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



Anagrams

M lti l h i i


24/24

Multiple-choice quiz

9d plants for food

Documents