Energy Flow and Living Things
Summary Sheet
Photosynthesis
Green plants make their own food in a process called photosynthesis. The plant takes in carbon dioxide, from the air, through its leaves and water, from the soil, through its roots. The food made in photosynthesis is a sugar called glucose. Oxygen is also produced and is released into the air. Photosynthesis is a chemical reaction and can be written as a word equation.
sunlight
carbon dioxide + waterglucose + oxygen
chlorophyll
Light energy and chlorophyll are needed for photosynthesis to happen. Chlorophyll is a green chemical found in chloroplasts in the leaves of plants. Chlorophyll absorbs sunlight. The plants use the light energy to combine carbon dioxide and water together to make glucose and oxygen.
How fast photosynthesis happens (the rate of photosynthesis) is affected by four factors:
1. Light– if there is more light photosynthesis happens faster.
2. Water– if there is not enough water photosynthesis slows down.
3. Temperature – the best temperature is about 300C – anything above 400C will slow photosynthesis right down
4. Carbon dioxide – if there is more carbon dioxide photosynthesis will happen quicker
To measure the rate of photosynthesis we can use Elodea, a pondweed. When photosynthesis is taking place the Elodea releases oxygen. The time taken for the oxygen to fill up the funnel down to the mark is measured. The faster photosynthesis happens the more oxygen is released.
The glucose produced in photosynthesis can be used by the plant for energy or converted to starch and stored.
To show that a leaf contains starch:
1. Boil the leaf in water for 2 minutes.
2. Turn off the Bunsen burner.
3. Put the leaf into a test tube of ethanol and put the test tube into the hot water.
4. Wait until the green chlorophyll comes out of the leaf.
5. Use tweezers to take the leaf out of the ethanol and dip it into the hot water.
6. Place the leaf on a white tile and add a few drops of iodine solution.
Chemicals in Agriculture
Modernfarmingmethods can cause environmentalproblems.
Whatisdone / Whyitisdone / ProblemsthiscausesLand is cleared of hedges and trees and trees / tocreatemorelandfor cropsand makeit easierformachineryto movearound / Destroys habitats
Pesticides are used / tokill peststhat competewithor harmthe crops / Can kill useful organisms as well as pests. Damages food webs
Fertilisers are used / theycontainmineralsthat help plantstogrowand increasethe yield / Can wash into streams and rivers and cause pollution so that the organisms inthewaterdie.
Biological control / tocontrol pestswithout using chemicals / The biological control agents (predators) may become pests themselves.
Habitats
A habitat is the place where an organism lives, for example, garden soil is an earthworm’s habitat. The surroundings of an organism are called itsenvironment.Theconditionsinanenvironment are caused by physicalenvironmental factors. Examplesincludehowlightitisandwhatthe temperatureis.
All the animals and plants that live in a habitat make up a community. A group of the same species of animals or plants living in the same habitat is called a population. For example when we talk about the population of Linwood, we mean the number of human beings living in Linwood.
An ecosystem is made up of a community of living things and their habitats.
Tosurviveinahabitat,organismsneedvariousresources.An animal needs food,water, oxygenand shelter,and itneedstofindamate toreproduce.Plantsneedlight, waterandcarbon dioxide inorder tomakefood. Theyalsoneedminerals,oxygenand spacetogrow.
Biotic and Abiotic Factors
Biotic factors are living factors that can affect an ecosystem. Biotic factors include the number of predators, competition between organisms, availability of food and disease.
Abiotic factors are non-living (physical) factors that can affect an ecosystem. Abiotic factors include temperature, light intensity, rainfall, concentration of oxygen and carbon dioxide, pH of the soil.
Biotic and abiotic factors affect the resources available in a habitat, for example the number of predators can affect how much food is available.
Food Chains and Food Webs
Animals can be placed into three groups based on what they eat:
- A carnivore is an animal that eats only animals
- A herbivore is an animal that eats only plants
- An omnivore is an animal that eats both plants and animals
A predator is an animal that hunts and eats another animal. The prey is the animal it eats. For example, if a fox eats a rabbit the fox is the predator and the rabbit is the prey. The feeding relationships between organisms can be shown in a food chain e.g.....
Cabbage Rabbit Stoat Fox
The arrows show where the energy goes in a food chain, in other words, “what gets eaten by what”.
All food chains begin with a green plant. Green plants use the sun’s energy to make their own food; they are producers. The other organisms in the food chain must eat to get food; they are consumers. The animal that eats the green plant is known as the primary consumer. This is then eaten by the secondary consumer. The last animal in the food chain is known as the top carnivore.
CabbageRabbit Stoat Fox
ProducerPrimarySecondaryTop
ConsumerConsumerCarnivore
All the food chains in an ecosystem can be shown in a food web. A food web contains many interlinking food chains.
Investigating an Ecosystem
Ecologists are scientists who study habitats and ecosystems. Ecologistsoftenneedtoknowthesizeofapopulation in a ecosystem.Itwouldbeimpossibletocount allthe organismsinan ecosystem, sotheytakesamples and then estimatethetotalpopulation.
Ecologists use a number of techniques that allow us to sample an ecosystem and use this as a representation of the whole ecosystem. All sampling is carried out randomly so as to not bias the results (keep the test fair).
Aquadrat isasamplingsquareusedtoestimateplantpopulations.Itisplaced randomlyonthe ground andthenumber ofplantsinsideitiscounted eachtime. Themoresamplesthataretaken, themorereliableanestimatewillbe.
Energy Flow and Living Things
Summary Sheet