MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 9csumm
9C Summary Sheets
Plants and photosynthesis
Photosynthesis
This is a chemical reaction and so can be written as a word equation:
water + carbon dioxide (+ light energy) ¾¾¾¾→ glucose + oxygen
reactants (light is not a substance products
and so is not a reactant)
Light energy and chlorophyll are needed for photosynthesis to happen. The light energy is changed into chemical energy which is stored in the glucose that is made.
Getting the water
Water is taken out of the soil by the roots. Roots are branched and spread out to help them absorb water from a large volume of soil. They also have root hair cells which are adapted to their function - they have a large surface area to help them absorb water quickly. The water flows up xylem tubes (made of hollow cells) to the leaf.
Water is also needed because mineral salts are dissolved in it, which are needed to keep plants healthy. Water also stops plants wilting and can keep their leaves cool.
Getting the carbon dioxide
Air, containing carbon dioxide, diffuses into leaves through small holes called stomata. Leaves are thin so that the carbon dioxide does not need to go very far before reaching the cells that need it. Photosynthesis can often be speeded up by increasing the amount of carbon dioxide around a plant.
Getting the light
Many leaves are wide so that they have a big surface area to trap as much sunlight as possible. Most photosynthesis happens in the palisade cells which are found near the upper surface of leaves. Palisade cells are packed with chloroplasts. Chloroplasts contain chlorophyll which absorbs light energy. Photosynthesis can often be speeded up by increasing the amount of light.
Respiration
Plant cells release the energy stored in glucose using aerobic respiration (another
chemical reaction):
glucose + oxygen ¾→ carbon dioxide + water (+ energy)
All living cells need energy and so all living cells respire. Respiration happens all the time but photosynthesis can only happen when there is light.
Uses of glucose
Glucose is a type of sugar. It is used for three things:
- respiration
- making other substances that act as stores of energy (eg starch)
- making new materials for growth.
Glucose is turned into cellulose (for cell walls), fats and proteins. To make proteins, mineral salts called nitrates are needed.
New substances made by a plant are carried around the plant in phloem tubes. New substances help to build up a plant's biomass (the mass of all the materials in the plant except water).
9C Target Sheet
Name _____________________________ Class ____________
Topic
Targets
Before the unit
I have learned this
I have revised this
9Ca
1
Know where photosynthesis occurs.
2
Know how plants store the food they make.
3
Know the word equation for photosynthesis.
4
Know what aerobic respiration is and where it occurs
9Cb
Know how leaves are adapted to the job they do.
Know how gases get into and out of leaves.
Know what the products of photosynthesis are used to make.
Know why plants need the different substances they make from glucose.
9Cc
Know how roots are adapted to the job they do.
Know why plants need water.
Know some of the mineral salts needed by plants.
Know how substances are transported around a plant.
9Cd
Know which gases form the atmosphere.
Know which processes add carbon dioxide to the atmosphere.
Know why plants are important in keeping the atmosphere in balance.
Understand some consequences of clearing forests.
9C Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
9Ca - A light reaction/Plants respire too
Word
Pronunciation
Meaning
aerobic respiration
air-O-bick
Chemical reaction that releases energy from glucose. It uses up oxygen and produces
res-per-ay-shun
carbon dioxide and water.
biomass
The mass of material (except water) that makes up an organism.
chlorophyll
klor-O-fill
Green substance found inside chloroplasts. It absorbs light.
glucose
Type of sugar made during photosynthesis.
photosynthesis
foto-sinth-e-sis
Chemical reaction that plants use to make their own food. It needs light to work. Carbon dioxide and water are the reactants and glucose and oxygen are the products.
raw material
Something used up in a chemical reaction. Also called a reactant.
reactant
Something used up in a chemical reaction. Also called a raw material.
phloem tube
flow-em
Tube made from chains of living phloem cells. Carries glucose and other soluble substances up and down the plant.
product
Something made in a chemical reaction.
starch
Insoluble carbohydrate made from glucose and used as a storage material in plants.
word equation
Simple way of showing what happens in a chemical reaction.
9Cb - Leafy adaptations/Sugary food
adapted
When something has a particular shape to help it do a function (job). A root hair cell has a shape that helps it absorb water and is said to be 'adapted to its function'.
amino acids
am-mee-no ass-ids
The building blocks of proteins.
cellulose
A substance used to make cell walls.
chloroplast
klor-O-plast
Green disc containing chlorophyll. Found in plant cells. Where glucose is made by photosynthesis.
diffusion
dif-few-shun
The random movement of particles from where there are a lot of them to where there are fewer of them.
fat
Substance needed by living things to make cell membranes. Our bodies also use fats as a store of energy and to keep warm.
function
Something's job.
guard cells
Cells which open and close the stomata.
mineral salt
Chemical found in soil that plants need to grow healthily.
nitrate
night-rate
Mineral salt that plants need to make proteins.
oil
Liquid fat, often found in nuts and seeds.
palisade cells
pall-iss-aid
Cells found in leaves, containing many chloroplasts.
protein
A substance made from amino acids. Proteins are needed for growth and repair.
stoma
stO-ma
Singular of stomata.
stomata
stom-mart-a
Small holes on the underside of leaves which let gases into and out of the leaf.
9Cc - The root of the matter
absorb
Soak up.
Chemical found in soil that plants need for healthy growth.
root hair cell
Cell found in roots. The root hair has a large surface area to help the cell absorb water quickly.
wilting
When a plant does not have enough water and droops.
xylem tubes
zy-lem
Tube made from chains of dead, hollow xylem cells. Carries water and dissolved mineral salts up a plant.
9Cd - A changing atmosphere
global warming
The process of the Earth's atmosphere warming up. It is partly caused by an increase in carbon dioxide in the air.
methane
The gas that is 'natural gas'. Also formed in large amounts in the digestive systems of cows. Methane absorbs heat and so helps global warming.
9Da1 Starch in plants 1
Apparatus
- Food samples - Pipette
- Water - Iodine solution
- Spotting tile
Iodine will stain your skin.
Method
1 You will be provided with a range of human foods that come from plants.
For each food, write down the part of the plant that it has come from in the results table below.
2 Use a pipette to add two drops of iodine solution to each food.
3 Look for a blue-black colour. If it appears after testing, then starch is present.
4 Enter your results in the table below.
Recording your results
Name of food
Part of plant
Does it contain starch?
Considering your results/conclusions
Do all the parts of the plants that you tested contain starch? ______________________________
_______________________________________________________________________________
Do any of the food samples contain more starch than others?
Starch is a store of energy for the plant. For each food tested that contained starch, suggest a reason why a store of energy might be needed in that part of a plant.
Suggest some reasons why humans might eat the foods that do not contain starch.
[ observing, considering ]
9Da2 Water in fruit
How can you find out how much water is in fruit?
Some fruits are juicier than others. Even different varieties of the same kind of fruit can have different amounts of juice.
Planning
1 What are you going to investigate? You could:
- find out how much of an apple is water
- find out which varieties of apple have the most water in them
- find out whether apples or pears have the most juice, or compare other fruits
- find out if all fruits of the same variety have the same amount of water.
2 You could remove the water from the apple by heating. How will you know when all the water has been lost?
3 What apparatus will you need? Write down how you will use it and draw a diagram to help your explanation
4 a What are you going to measure?
b How many measurements will you take?
c How will you take this measurements?
5 How will you make sure your test is fair?
6 How will you stay safe while doing this experiment?
7 Show your plan to your teacher before starting any practical work.
Prediction
8 Write down what you think will happen. Try to explain why you think this will happen.
[ Planning ]
9Da3 Starch in plants 2
You will be provided with a range of human foods that come from plants. For each food, write down which part of a plant it has come from. Some of these foods contain starch and you are going to test the foods for this substance.
1 Think about the parts of a plant where starch (an energy source) might be stored. Try to predict which foods might contain starch.
1 Use a pipette to add two drops of iodine solution to each food.
2 Look for a blue-black colour. If it appears after testing, then starch is present.
2 Make a table to record your results. Include in your table which part of a plant each food is.
3 a Did all the parts of the plants that you tested contain starch?
b Did any of the food samples contain more starch than others?
c How could you tell this from your results?
4 For each food that tested positive for starch, suggest a reason why a store of energy might be needed in that part of a plant.
5 Suggest some reasons why humans might eat the foods that did not contain starch.
[ observing, presenting, considering ]
9Da4 The plants we eat
1 The drawings below show plants that we eat. For each one, write down the name of the plant and which part of it we eat. Use the words in the box to help you.
apple broccoli carrot celery flower fruit hazel nut
leaf lettuce potato root runner bean stem tomato
Name _________________
Part of plant ___________
2 All the materials in all the foods are made using glucose. What process do plants use to make
glucose? ___________________________________________________________________
3 Some glucose is turned into proteins and fats. These are often stored in seeds. Choose one food from question 1 which you would expect to contain a lot of protein and fat.
__________________________________________________________________________
4 Glucose is often turned into starch. Choose one food from question 1 which contains a lot of starch.
[ knowledge ]
9Da5 Uses of glucose
1 Copy this drawing of a cell in a leaf. It is called a palisade cell and it makes lots of glucose by photosynthesis.
2 What process happens in the cell to make glucose?
3 Most of the glucose is changed into starch as soon as it is made. Label your palisade cell drawing to show where you would expect to find starch.
4 Some plants can store starch in special parts. Which one of these stores a lot of starch?
orange apple flower potato tomato pear
5 People eat food with starch in it to give them energy. Why do plants store up starch?
6 Glucose molecules are shaped like this:
Many glucose molecules join in a line to form a starch molecule. Make a drawing of what you think a starch molecule looks like. The links between each glucose molecule can be shown by a straight line.
7 Some of the glucose is used to make cellulose. Label your palisade cell drawing to show where you would expect to find cellulose.
8 Some of the glucose is used to make fats and oils. These are needed to make cell membranes. Label your palisade cell drawing to show where you would expect to find oils and fats.
9 Glucose is used for aerobic respiration in plants. Copy and complete the word equation for aerobic respiration.
______________ + ______________ → carbon dioxide + water (+energy)
10 Aerobic respiration happens in the cytoplasm of every cell. Label your palisade cell drawing to show where you would expect to find respiration happening.
9Da6 Energy from plants
Only a small amount of the light energy that strikes a leaf is actually converted into chemical energy stored in starch. The diagram shows why this happens.
This diagram shows what happens to the energy in leaves eaten by a cow.
1 Why are plants sometimes referred to as 'producers'?
2 Suggest a reason why a cow eating the grass leaves would not gain all the energy that the leaves had absorbed from the Sun.
3 What percentage of the energy eaten by a cow is used to make new tissues?
4 A cow has an input of 3000 units of energy from eating one square metre of grassland per year.
a How many units of energy are used in respiration?
b How many units of energy are actually lost in the waste products?
5 Suggest a reason why a human eating beef from the cow would not gain all the energy that was stored in the leaves.
6 In densely populated countries there is a shortage of land for producing food. Suggest a reason why people in such countries use their farmland to grow crops rather than farming animals.
[ knowledge, numeracy ]
9Da7 Human food chains
Very little of the light energy that strikes a leaf is actually used to make glucose. Some of the glucose that is produced is converted into starch as a store of energy. If an animal (a consumer) eats the starch it gains some of that stored energy. At each stage in a food chain, some energy is passed onto the next consumer. Each consumer carries out respiration and so some of the energy is lost. Humans usually eat food from short food chains. This means that there are fewer links in the chain and so less energy is lost between the plant and the human food.
In developing countries people may get only 2 or 3% of their energy from eating meat. Their diets are often largely made up of plant products such as rice and maize. These mainly vegetarian diets provide most of the energy needs and mean that humans gain more of the original energy stored by plants. In densely populated countries there is a shortage of land for producing food. Growing crops is a more effective use of land than farming animals.
Some human food chains are much longer. These often involve the eating of animals caught in the wild. One of the longest involves the Inuit people of northern America and Greenland. Their diet consists chiefly of meat. Many of the animals they eat store a lot of energy as fat.
1 Why are plants referred to as 'producers'?
2 Suggest a reason why animals lose more energy through respiration than plants.
3 A cow uses 34% of the energy it eats in respiration and uses 6% to build new tissues. A cow consumes 3000 units of energy from eating one square metre of grassland per year.
a How many of these units are used by the cow to release energy through respiration?
b How many of these units are available to a human eating beef from a cow?
4 Explain why the mainly vegetarian diets of developing countries provide a cheaper source of energy than meat-rich diets.
5 Suggest a reason why it is more efficient to grow crops than to rear animals in densely populated countries.
6 Suggest a reason why the Inuit food chain is longer than a farmed food chain.
7 Explain whether you think the energy lost as the Inuit food chain progresses is important to the Inuit diet.
[ knowledge, literacy, numeracy ]
9Db1 Which fertiliser is best?
Which fertiliser is best for growing duckweed?
- Three large beakers - Two different liquid fertiliser samples
- Distilled water - Duckweed
- Measuring cylinder - Labels
1 Take three large beakers and fill them half full with distilled water.
2 Add 1 cm3 of one of the fertilisers to one of the beakers. Label this beaker 'A'.
3 Add 1 cm3 of the other fertiliser to another beaker. Label this beaker 'B'.
4 Do not add anything to the third beaker. Label this beaker 'C'.
5 Add about 20 duckweed plants to each beaker.
6 Place all the beakers in a warm, light place. Look at them again in three weeks' time.
7 Label the drawings below to show what you have done.
Which fertiliser do you think will work best? Why?
Describe in your own words what happened. Did the fertilisers make any difference? Look carefully at the lengths of the roots, the number of roots, and the colour and size of the leaves.
Beaker A _______________________________________________________________________
Beaker B _______________________________________________________________________
Beaker C _______________________________________________________________________
Why did you need Beaker C? _______________________________________________________
Would you recommend people to use fertilisers? ________________________________________
Explain why or why not. ___________________________________________________________
Which fertiliser would you recommend to a gardener? ___________________________________
Why would you recommend it? _____________________________________________________
9Db2 Comparing a lawn and wasteland
- Worksheets 9Db/3 and 8Dd/3
- One small square of transparent plastic sheet (1 cm by 1 cm)
1 Read all the information below before you start.
2 Hold the plastic square 30 cm above the lawn on Worksheet 8Dd/3. With your eyes shut, drop the square. The area where it lands is a sample. The plastic square is acting as a quadrat.
3 Count the number of plants inside the square. Any plant that is more than half-way into the square is counted; any plant that is less than half-way into the square is not counted. Write down the number of each type of plant that you have counted. Take 10 samples.
4 Repeat this method using the wasteland on Worksheet 9Db/3.
1 For the lawn, draw a table to show how many of each plant you counted in each quadrat. Write down the total number of each plant you counted.
2 Estimate the total number of each plant in the lawn by doing this calculation:
total number of plants counted
total area sampled (in m2) = number of plants per m2
number of plants per m2 × total area of lawn (in m2) = total number of plants on lawn
3 Do the same with the results you gained from the wasteland.
4 What are the differences between the lawn and wasteland populations?
5 Are there any weed species which grow in the wasteland that are not present in the lawn?
6 Compare the grass cover of the lawn and the wasteland.
7 Suggest reasons for the differences in results between the lawn and the wasteland. Think about how the plants compete for nutrients and water and how a lawn is cared for.
8 What advice might you give in order to clear the weed plants form the lawn without damaging the grass?
9 When a farmer ploughs a field, bare earth is left exposed. Use your results from the wasteland to suggest what might happen if this soil is left too long before sowing crop seeds.
[ knowledge, presenting, considering ]
9Db3 The wasteland
9Db4 Plant biomass
The mass of the material that an organism is made from (apart from water) is called its biomass. Plants make new biomass from the glucose they produce. The glucose can be used for respiration or turned into other more complicated molecules. Other elements are sometimes needed to help make these molecules. These elements are contained in mineral salts. Elements which a plant needs a lot of are called major elements and elements which a plant needs only a little of are called trace elements.
1 a What is biomass?
b Why do you think water is not included when measuring a plant's biomass?
2 Gardeners often put fertiliser on their soil. The label below shows what is contained in a brand of fertiliser.
a What element needed to make protein do nitrates contain?
b What is the name of the chemical that contains nitrates in this fertilser?
c What element do you think phosphates contain?
d Phosphates are needed to make DNA. In which part of a cell do you think phosphates are most needed?
e Magnesium is needed to make chlorophyll. What do you think would happen if a plant did not get enough magnesium?
f Which of the mineral salts in the fertiliser do you think are major elements and which do you think are trace elements? Explain your reasoning.
g Write a list of all the elements you would expect to find in the compounds that make up a plant's biomass.
[ literacy, knowledge ]
9Db5 The problem with fertilisers
Fertilisers are spread on fields by farmers to help their crops grow. Using fertilisers can be difficult and expensive. Fertilisers can also cause problems if they are washed off fields into lakes and rivers by the rain. This causes algae to grow very quickly. The algae soon become overcrowded, which means that they cannot get enough light for photosynthesis and they die. Bacteria feed on the dead algae and as their numbers grow they use up all the oxygen in the water. This lack of oxygen kills other organisms living in the water.
1 Some fertilisers are sprayed over crops by helicopters.
a Give one advantage of this means of spraying.
b Give one disadvantage of this means of spraying.
2 On some very large farms, the fertiliser spreaders are controlled by computer. The computer is loaded with a satellite picture showing how the plants grew in each part of the field in the previous year. The computer then automatically adds extra fertiliser to the parts of the field where the plants grew poorly when the spreader gets to that part of the field. Less fertiliser will be added to the parts of the field where the plants grew well.
a Give one advantage of the system for the farmer.
b Give one disadvantage of the system for the farmer.
c Give one advantage of the system for the surrounding habitats.
3 a Most fertilisers contain potassium mineral salts. What are the other two main mineral salts in fertilisers?
b Some plants need more of one type of mineral salt than others. Fertilisers are now made with different amounts of mineral salts for different types of plants. What are the advantages of this?
4 Penmark Fertiliser costs £5/kg. It is recommended that a farmer uses 1g/m2. How much would it cost the farmer to use this fertiliser on a field measuring 100 m by 150 m? Show your working.
5 a Explain why fertilisers can often be found in rivers and lakes.
b Explain how fertilisers affect the growth of algae.
c Suggest a reason for the increase in bacteria in water containing fertilisers.
d Suggest some organisms that might die from lack of oxygen in the water.
9Db6 Using herbicides
Herbicides are used by farmers to kill weed plants. Weeds compete with crop plants for mineral salts. Farmers gain higher yields from crops grown without weeds. Some herbicides, such as Paraquat, kill all plants. Other herbicides, such as 2,4 D, only kill plants with broad leaves so crop plants with narrow leaves are unaffected. These are called selective herbicides. Herbicides are sprayed over fields and often affect organisms living in hedges, too. The food web below shows some organisms that might live in a hedge.
1 Explain why farmers spray herbicides on fields.
2 Why do farmers prefer to use herbicides rather than pull weeds out of the ground?
3 Why are the plants important in this food web?
4 Which plants in the hedge would be damaged by spraying:
a Paraquat
b 2,4 D?
5 Why do farmers prefer to use selective herbicides?
6 What might happen to the number of blackbirds living in this hedge if a herbicide is used?
7 Suggest what the effect would be of spraying 2,4 D on a lawn containing grass, dandelions and thistles. Explain your answer.
[ knowledge, literacy ]
9Dc1 Pesticides and birds
The cards below give some information about the effect of pesticides on the wild bird population. Cut out the cards and put together the evidence in the correct order to explain what happened to the birds.
---------------------------------------------------------------------------------------------------------
DDT can alter the behaviour of birds, sometimes preventing them building proper nests.
Some of the pesticide is washed into lakes and rivers.
concentration of DDT: 0.00005%.
The populations of many wild birds have decreased over the last 30 years.
DDT is absorbed by tiny organisms in the water called plankton.
In large amounts DDT can be poisonous to birds.
DDT may cause wild birds to become infertile.
Any pesticide in the plankton gets
into the fish.
A pesticide (DDT) is sprayed over fields of crops to kill insect pests.
Fish eat many plankton organisms.
concentration of DDT: 1.2%
DDT can cause birds to lay eggs with thinner shells. As a result more eggs are likely to be broken.
Many wild birds, such as osprey and heron, eat fish.
concentration of DDT: heron 3.5%, osprey 14%
DDT builds up inside fish.
9Dc2 Pesticides 1
The picture shows the back of a packet of pesticide. A pesticide is a chemical that kills pests. Pests are organisms that harm plants that we want to grow.
ZYMAC
For use on flowers, fruit and vegetables. Kills ants, aphids, blackfly, whitefly, caterpillars and mites. Kills the insects when they are sprayed directly with Zymac or when they eat plants sprayed with Zymac.
How to use:
Add 14 cm3 of Zymac to 1 litre of water.
Spray on the solution using a garden sprayer.
Warnings:
Do not get on skin. Do not breathe in spray. Wash hands after use. Dangerous to fish. Extremely dangerous to bees.
1 Why do farmers and gardeners use pesticides?
2 What does Zymac kill?
3 Using pesticides can harm other organisms that people do not want to harm. What other organisms may Zymac kill?
4 Look at the following food chains. For each organism in each food chain say how it is affected by spraying Zymac.
a lettuce → rabbit → fox
b rose bush → aphid → ladybird
c pondweed → tadpole → stickleback
5 What precautions should a gardener take while using Zymac?
6 Some plants that we eat are grown 'organically'. Find out what this means.
[ knowledge, literacy, research ]
9Dc3 Toxic chemicals and food chains 1
This is a food chain from a British lake.
algae → water flea → stickleback → kingfisher → peregrine falcon
In the 1940s and 1950s a pesticide called DDT was used. At about this time it was noticed that the number of peregrine falcons had fallen dramatically. In the early 1960s this was found to be due to DDT. The DDT in the bodies of female peregrine falcons caused them to lay eggs with very thin shells. When the birds tried to sit on their eggs (to incubate them) the eggs smashed.
DDT was sprayed onto fields, but even if pesticides are more carefully applied they can still get into food chains. Dieldrin is a pesticide that was used to coat wheat seeds to kill beetles that might otherwise eat all the grain in a store. However, wood pigeons ate the grain. Eventually the pigeons had eaten so much that they died. And even the dead birds passed on the dieldrin. Foxes are sometimes scavengers. By eating the dead pigeons they also died.
Neither DDT nor dieldrin break down easily and they are described as being persistent. They can be spread in fish all around the world. Even penguins in Antarctica have been found with DDT in their bodies. Newer pesticides are designed to be biodegradable.
1 What is a pesticide?
2 Using the food chain at the top of the page, explain how peregrine falcons came to be so badly affected.
3 Explain how foxes came to be poisoned by dieldrin. Draw a food chain to illustrate your answer.
4 What is meant by the word persistent?
5 What does the word 'scavenger' mean?
6 How do you think DDT got into penguins in the Antarctic?
7 If you were developing a new pesticide, what features would you make sure it had? Write down three features.
8 What does biodegradable mean?
9Dc4 Pesticides 2
A pest is an organism that destroys crops. Pesticides are chemicals that are sprayed onto crops to kill the pests. Insecticides kill insect pests. Some pesticides will kill other organisms that live in hedges surrounding a field. The food web below shows some organisms that may be found in a hedge.
1 Explain why farmers spray insecticides on fields.
2 Name three organisms that might be killed if the farmer sprayed insecticide.
3 What might happen to the number of wrens in the hedge if insecticide was sprayed?
4 What might happen to the number of nettles in the hedge if insecticide was sprayed?
5 Some farmers do not spray next to hedges. They leave a three-metre-wide strip around their fields where chemicals are not sprayed.
a Write down one advantage of this.
b Write down one disadvantage for the farmer.
9Dc5 Toxic chemicals and food chains 2
1 Look at this graph. It shows the amounts of pesticide found in the muscles of three different birds in a particular area. The further along a food chain an animal is, the more likely it is to have higher amounts of pesticide in its muscles.
a Of the three birds shown on the graph, which do you think is:
i a top predator
ii a primary consumer?
b The numbers on the vertical axis are in ppm (parts per million). What do you think this means?
c DDT is a pesticide that has never been used in Antarctica. However, the chemical is found in the muscles of penguins. Explain why you think this is.
d Here is a food chain ending with a heron. Draw a pyramid of numbers for this food chain.
algae ¾→ water flea ¾→ stickleback ¾→ trout ¾→ heron
e Using your pyramid of numbers to help you, explain why herons used to die from the effects of DDT, but trout did not.
2 Pesticides are not the only chemicals to affect animals. Oil spills also cause serious damage to environments. Find out about the Exxon Valdez oil spill in Alaska in 1989.
a Describe how the oil killed animals in and around the sea.
b Describe how the clean-up operation on the shore killed even more animals.
[ knowledge, research ]
9Dc6 Pesticide articles
Here are some extracts from various publications about pesticides and birds.
This is part of an advertisement for DDT from 1954.
The great expectations held for DDT have been realized. During 1946, exhaustive scientific tests have shown that, when properly used, DDT kill s ahost of destructive insect pests, and is a benefactor of all humanity.
Pennsalt produces DDT and its products in all standard forms and is now one of the country's largest producerts of this amazing insecticide.
Today, everyone can enjoy added comfort, health and safety through added comfort, health and safety through the insect-killing
powers of Pennsalt DDT products … and DDT is only one of Pennsalt's many chemical products which benefit industry, farm and home.
Here is a table from a scientific paper, called Owls as Biomonitors of Environmental Contamination, by Steven R. Sheffield who works in The Department of Environmental Toxicology in a university in the USA. The table shows the results of some experiments and studies into owls and pesticides.
Species of owl
Pesticide
Findings
barn owl
aldrin/dieldrin
627 dead owls examined. Poisoning found in 8.8% of owls on average (40% in some agricultural areas).
eagle owl
dieldrin
Dieldrin-treated wood used for shavings in the cages of rats fed to owls linked to at least 20 owl deaths.
eastern screech owl
DDE
13% eggshell thinning when fed a diet containing 10 ppm DDE.
endrin
Owls fed 0.75 ppm endrin produced 43% fewer fledged owlets than those fed diet with no endrin. No eggshell thinning.
great horned owl
aldrin
One owl found dead in an aldrin-treated rice field.
This is an extract from an A-level text book.
It is known that DDT can alter the behaviour of birds sometimes preventing them building proper nests. It may cause them to become infertile and can result in the egg shells being so thin that they break when the parent bird sits on them during incubation. In Britain these effects led to a marked decline in the 1950s and 1960s of populations of peregrine falcons, sparrowhawks, golden eagles and other predatory birds.
This is from a website run by a company who make genetically modified plants.
We have developed genetically improved corn. The corn is protected against the European and southwestern corn borer. We have also developed genetically engineered cotton that is resistant to the bollworm.
These new plants will allow farmers to increase crop yields and use fewer insecticides.
This is part of a letter written to a newspaper.
29 March 2002
Dear Sir/Madam,
In a recent letter someone stated that an association set the standards for organic foods. The truth is that standards are arrived at through consultation with consumers, farmers, retailers, processors, government and other policy bodies.
500 pesticides are routinely used in conventional farming - only six are allowed if food is to be 'organic' and permission must be granted before four of these can be applied. Organic farmers do need to use pesticides very occassionally to control fungal diseases such as potato blight which is endemic in the UK. Organic standards prohibit the use of carcinogenic chemicals such as Lindane or organophosphates…
Yours faithfully,
Dennis Avery is the director of the Center for Global Food Issues in the USA. He said this in a television interview:
'The biggest threat to human food supply today, to human cancer, and to wildlife maintenance would be organic farming. It couldn't give us the food supply we need today, it couldn't give us attractive fruits and vegetables, and it couldn't give us the yield to protect wildlife habitats from what would otherwise be ever-expanding cropland.'
1 Why are pesticides used on crops?
2 a Name one pesticide and state what its effects are on birds that prey on other animals.
b How do pesticides get into the bodies of these birds of prey in nature?
3 Name two alternatives to using pesticides.
4 List two advantages and two disadvantages of using pesticides.
5 When DDT was first marketed, some scientists claimed that the fact that it was persistent was a good thing. Why do you think they thought this?
(Hint: Think about how long a crop grows for and what would happen to a pesticide that breaks down easily.)
6 For each of the extracts, say whether you think the author is for or against using pesticides.
7 If you wanted to express your opinion about pesticides, which of the ways used in the extracts above would you use? Why?
8 Do you think that pesticides should be used for human food even if they harm other animals?
9 Find out how pests are controlled on organic farms.
[ literacy, research ]
9Dc7 Controlling mosquitoes
Malaria is transmitted to humans when they are bitten by an infected mosquito. Malaria is a disease that kills millions of people every year, particularly in the developing world.
Death rates from malaria, per 100 000 people
Countries in Asia and Africa have used the pesticide DDT to kill mosquitoes that spread malaria to humans.
Below are some extracts arguing for and against the use of DDT in controlling the mosquitoes.
DDT saves lives
Last year, malaria deaths in Africa reached an all-time high. Yet despite this crisis, political pressure from governments and environmental groups is building at the United Nations Environment Program to pass a treaty that will 'reduce and/or eliminate' one of the world's best anti-malarial tools. That tool is, of course, DDT. The arguments against using DDT in controlling this disease are stunningly naive. Yes, it is a serious pollutant which causes bird populations to suffer - but it also saves human populations from the plague of malaria.
In the 1950s, a global campaign against malaria used DDT spraying to eradicate the disease from the USA and Europe. Elsewhere it diminished greatly. Unfortunately overuse of DDT in agriculture bred DDT-resistant mosquitoes.
The benefits of DDT are gained at almost no environmental risk. Contrast DDT's use in malaria control, where a few grams are sprayed, on the interior walls only, of a home, with the use of DDT in the 1960s when tonnes were sprayed directly into the environment and onto every farmer's fields. DDT house-spraying is among the cheapest, most effective interventions against the disease. If precaution matters, Africa should use more DDT against malaria, not less.
So, if DDT can be this successful, why ban or make it more difficult and expensive for the world's poorest, most disease-ridden countries to obtain? The World Wildlife Fund claims DDT has direct harmful effects on the human body and is 'campaigning for a global phase-out by 2007.'
What are absent from such claims are scientific studies to demonstrate these alleged health effects. For all the research into the effects of DDT, neither scientists nor the WWF can name one negative health effect which has been independently confirmed as being related to exposure to DDT.
DDT protest by scientists is wrong, says WWF
A letter of protest against plans to ban DDT, being circulated among many of the world's leading scientists, is misleading and inaccurate, WWF said today. If DDT were banned throughout the world, says the letter, millions more people in the developing world could die form malaria. WWF believes the more relevant question is whether the same public health benefits of reducing malaria could be achieved at even lower risk to health and wildlife by other control methods. 'We have called for a phase-out of the use of DDT by 2007' said a spokesperson. 'A much more concerted effort must be made to develop new alternatives to DDT. In response to this challenge, WWF is attempting to find a constructive, effective and affordable way forward.'
1 Why is DDT used to kill mosquitoes?
2 One way of controlling mosquitoes is to drain the wetlands that they use for breeding. Suggest a reason why the author of extract 1 thinks that using DDT is a better alternative.
3 What was the effect of overusing DDT in the 1960s?
4 Describe the difference in the amounts of DDT used to protect crops in the past and the amount used in killing mosquitoes today.
5 Suggest reasons why the author of extract 2 would like to see the use of DDT banned.
6 In your opinion, should DDT be used to control the spread of malaria at the expense of other organisms such as wild birds? Give reasons for your answer.
7 Find out about the other 'constructive, effective and affordable' methods of pest control the author of extract 2 might be referring to.
9Dc8 Biological control
Biological control involves using natural predators rather than chemical pesticides to reduce the numbers of pests. The predator is called a biological control agent.
Farmers in Australia grow sugar cane plants as a crop. This food web shows some of the information needed if they are to decide on using biological control to reduce the number of pests. The cane toad is not native to Australia, but some farmers think that it might be a useful biological control agent.
1 What reason might a farmer have for using biological control instead of chemical pesticides?
2 From the food web name two pests that the farmers might want to kill.
3 Suggest a reason why the cane toad might be an effective way of controlling pests.
4 Explain why using the cane toad as a biological control agent might be a disaster for the wider environment.
5 Imagine that you are responsible for suggesting to farmers a suitable biological control agent in their fight to reduce the number of pests.
Outline the research you would need to carry out before you could make a sensible suggestion.
9Dd1 The farmer's year
1 A farmer grows wheat, potatoes and sugar beet. The table shows the jobs that need to be done during the year.
Month
Jobs to do on the farm
September
harvest potatoes, plough fields
October
harvest sugar beet, plough fields, plant wheat
November
spread fertiliser on sugar beet fields
December
spray wheat
January
spread manure on fields
February
March
spray wheat, plant sugar beet, spread fertiliser on potato fields
April
plant potatoes
May
spray potatoes, sugar beet and wheat
June
keep potatoes well watered
July
harvest wheat
August
continue to harvest wheat
a In which month are potatoes planted?
b How long do potatoes take to grow?
c What food substance do potatoes contain a lot of?
d The potatoes are sprayed in May. What do you think they are sprayed with?
e Why do you think the potatoes are sprayed?
f The potatoes, sugar beet and wheat are sprayed with different chemicals. Why do you think this is?
g Why does the farmer spread fertiliser on the fields?
2 Another farmer wants to chop down a wood and turn it into fields.
a Why do you think the farmer wants to do this?
b Why do you think some people would not want the farmer to do this?
9Dd2 Greenhouse design 1
Below is a diagram of an empty greenhouse. It is going to be used to grow an important crop plant. Use the following advice to help you draw in features that would result in a high yield of crops. For each feature, explain why it has been included and how it helps the plants to grow. Write these explanations in your book.
- The temperature must not get too hot or too cold.
- The light must not be too bright or too dark.
- The plants need a supply of water, carbon dioxide and mineral salts.
- The running costs must be as low as possible.
9Dd3 Greenhouse design 2
Below is a drawing of a greenhouse that is to be used to grow an important crop plant.
1 a Why are the lamps included in the greenhouse design?
b At what time of year might the lamps be used regularly?
2 Explain how the heater and the ventilation flaps can be used to set a particular temperature for photosynthesis.
3 Why is a sprinkler system used to water the plants?
4 Explain how the fertiliser would be used to help the plants to grow.
5 In some greenhouses charcoal is burnt to produce carbon dioxide. Explain why this is done.
6 Some plants are grown in greenhouses to produce fruit. For plants to produce fruit their flowers must be pollinated. What problems might there be in pollinating flowers inside a greenhouse?
7 Suggest one type of plant that might be grown successfully in a greenhouse like this.
9Dd4 Growing lettuces
Lettuces are often grown in long tunnels made from clear plastic, with doors at the ends.
An experiment was carried out, growing lettuces in different tunnels in six different places around the UK. The tunnels were all like the one shown in the picture and had no additional heating or lighting. A sample of 200 lettuces was taken from each tunnel and dried to work out the biomass.
1 Give one advantage and one disadvantage of using plastic tunnels to grow lettuces.
2 a What is meant by biomass?
b Why do you think the lettuces were dried in order to measure the biomass?
c List four substances you would expect to find in a dried sample of lettuce.
3 What was the mean biomass of one lettuce in
a sample B b sample C?
4 a Extra carbon dioxide was pumped into one of the tunnels. Which one?
b How do you know this?
c Explain why this extra carbon dioxide has caused this effect on the plants.
5 This was not a fair test since some of the factors (variables) could not be controlled. Which factors could not be controlled?
6 Explain why the biomass of the lettuces grown in the tunnels without extra carbon dioxide was not the same.
7 To get as much biomass as possible, a lettuce grower will keep the plants well watered and some lettuce growers will add extra carbon dioxide. What other things could be done?
[ knowledge, considering ]
9Dd5 Organic farming
Farmers have been very successful in using their knowledge of how plants grow to improve the yields of their crops. This has involved the use of fertilisers, weedkillers and pesticides. Over the years, farmers have become more aware of many of the problems linked to the large-scale use of chemicals. Many are now trying to reduce the damage that can be done to the environment as a result of their farming.
Some farmers try to avoid using manufactured chemicals to help their crops grow. This is called organic farming. Food from organically grown plants is becoming more popular with the public.
1 A farmer wants to grow his crops without damaging the surrounding environment. Explain why he might:
a use selective weedkillers (or herbicides)
b not spray the weedkiller too close to the edge of his fields
c use a biological control agent to prevent pests from damaging his crops
d preserve hedges on his land.
2 a Organic farmers do not use artificial fertilisers to help their crops to grow. Suggest a reason why they might keep some animals such as cows on their farms.
b Suggest a reason why organically grown fruit and vegetables are more expensive than those grown using manufactured chemicals.
9D Summary Sheets
Plants as food
When green plants carry out photosynthesis they use carbon dioxide and water to produce glucose and oxygen. Some of the glucose is used by the plants to release energy through respiration. Plants can also convert glucose into starch to act as a store of energy. Humans can eat these stores of starch to gain energy. Plants also use glucose to make other substances such as protein and cellulose. Human food chains are short so that more of the energy originally stored by plants is available as food.
→
grass
cow
beefburger
potato
chips
Improving plant growth
When growing crop plants for food, farmers want to produce the largest amount of useful material (yield) possible. They use fertilisers to add important mineral salts to the soil so that the crops have a constant supply of these important nutrients. This is necessary because the plants are removed from the soil taking the mineral salts with them. The crop plants do not decompose in the field, which would allow the mineral salts to get back into the soil. Farmers can use manufactured or natural, organic fertilisers to improve the quality of the soil.
Manufactured fertiliser.
Manure is an organic fertiliser.
A problem can arise when other plants start growing in the fields as well as the crops. These are called weeds and compete with the crop plants for the resources needed for healthy growth. Weeds reduce the growth of crops so farmers use chemicals called weedkillers or herbicides to remove them from fields. Some weedkillers are selective, and only kill weeds, not crops.
Pests and pesticides
Animals which eat crops to gain the stored energy are called pests. Farmers use chemicals called pesticides to kill them. One problem with using pesticides is that they might kill harmless wild animals as well or disrupt food webs in the environment. Specific pesticides can be used that are only harmful to particular types of pests. Another problem with pesticides is that the poison can build up in food chains and have unexpected and unwanted effects on larger predators. Modern farming techniques now often take into account the possible harmful effects on the surrounding environment.
Controlling environments to increase crop yields
The growth of crops in open fields is often affected by changes in the weather or season. Sometimes crops are grown in carefully controlled conditions inside greenhouses. Here the plants can be provided with the optimum temperature, light intensity, carbon dioxide concentration and supply of water and mineral salts to ensure the best possible growth despite the changing conditions outside.
9D Target Sheet
9Da
Know the products of photosynthesis.
Know what plants use starch for.
Know the importance of plants in human food chains.
Know the importance of starch in a balanced diet.
9Db
Know some examples of mineral salts contained in fertilisers.
Know why fertilisers are added to soil.
Know what weeds are.
Know how the growth of weeds can be controlled.
9Dc
Know what a pest is.
Know some examples of pests.
Know why farmers use pesticides.
Know some problems with using pesticides.
9Dd
Know the environmental conditions that best suit photosynthesis.
Know why photosynthesis is important for plant growth.
Know how the conditions inside a greenhouse are changed.
Know how greenhouses can be used to improve crop yields.
9D Word Sheets
9Da - Eat your greens
A type of sugar made during photosynthesis.
Process that plants use to make their own food. It needs light to work. Carbon dioxide and water are used up. Glucose and oxygen are produced.
respiration
ress-per-ay-shun
Process that releases energy from food. Carbon dioxide is produced as a waste gas.
Substance that plants use as a store of food.
9Db - Helping crops to grow
compete
All organisms need some of the same things and so each organism tries to get these things before other organisms. For example, plants compete for light.
decompose
To break down into smaller pieces.
decomposers
Microbes and other smaller organisms which break down dead plants and animals, and animal waste, e.g. bacteria and fungi.
decomposition
The process of something decomposing.
fertilisers
Something that can be added to soil to increase the amount of nutrients available in the soil.
herbicide
A chemical that kills weeds. Also called a weedkiller.
mineral salts
Chemicals found in the soil which plants need for good growth. Can also mean chemicals found in our food which are needed in small quantities for health.
selective breeding
When humans choose certain animals and plants that have useful features and breed more of these organisms.
weedkiller
A chemical that kills weeds. Also called a herbicide.
yield
How much useful material a crop plant or farm animal produces.
9Dc - Problems with pests/Toxic chains
insecticide
A chemical that kills insects.
persistent
If something does not get broken down easily in nature very quickly and stays around for a long time, it is said to be persistent.
pesticide
pest-iss-ide
Chemical that kills pests.
pest
An organism that damages crops that humans grow.
specific pesticide
A pesticide that is harmful to only a few pests.
toxic
Another word for poisonous.
9Dd - Better growth/Greenhouse crops
optimum temperature
The best temperature for a plant to grow in.