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Grade 7 Unit A Notes
Interactions and Ecosystems
1.0 Relationships exist between living things and their environment.
1.1 Defining an Ecosystem and Learning about Basic Needs
-
An ecosystem is an area where living things ___________ with other living
things and non-living things.
___________ Factors – living things within an ecosystem. [bio = life]
___________ Factors – non-living things in an ecosystem.
Example : Your Backyard
Biotic
Abiotic
Plants
Soil
Insects
Water
Animals
Air
- Ecosystems may be as large as an ocean or desert or as small as a puddle or
rotting log.
- Earth contains many ecosystems.
- Each ecosystem contains a variety of different species.
___________ – living things that can reproduce young that resemble their parents.
________________ – a number of members of the same species living together in
the same area.
________________ – all the populations of different species living and
interacting in the same area.
________________ – an area where all living things and non-living things within
a community interact.
-
The needs of living things within an ecosystem include:
o ____________
o __________ to provide nutrients (carbohydrates, fats, proteins,
vitamins, & minerals)
o ____________ to sustain activity
o ____________ for cellular respiration
o Suitable living conditions (eg. Range of temperature and shelter)
_______________ Respiration – the breaking down of food for cells.
1.2 Interactions among Living Things
Symbiotic Relationships
______________ – is whenever different living things live closely together where
the relationship may benefit one or both living things.
- unlike a predator/prey relationship, a symbiotic relationship rarely
ends in the death of one or the two organisms.
Types of symbiotic relationships include:
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_______________ – is when one of the species in the relationship benefits while
the other one neither benefits nor is harmed.
Example: barnacles growing on a whale
________________ – is when both species in the relationship benefit.
Example: a snapping shrimp and a goby fish
________________ – is when one of the species in the relationship benefits whil
the other is harmed but not typically to the point of death.
Examples: you and a mosquito, or a dog and fleas
- All of these relationships involve a behavioural adaptation.
________________ - in general, are ways in which an organism responds to its
environment.
Example of a physical adaptation: The bills and legs of the Great Blue
Heron allow them to fish in shallow water.
- Successful adaptations typically allow a parent to survive and pass on the
characteristics to the next generation.
1.3 Human Impacts of Ecosystems
Garbage and Waste Management
-
Human invention and technology has affected the amount and type of
____________ we produce.
- Prior to the advance of modern technologies, most waste was biodegradable.
________________ – waste that can broken down by the environment.
-
1)
2)
3)
4)
Originally waster was handled by dropping garbage into open pits called
dumps.
These dumps were not managed to prevent fires nor did they provide
protection against dangerous chemicals and disease causing bacteria from
getting into the water system by rainwater runoff or leaching.
Improvements over the years:
Recycling – management of items such as paper, glass, plastics, etc…
Composting – management of biodegradable waste.
_____________ – burning of waste products where toxic fumes are not likely.
Hazardous waste operations – management of waste poisonous to the
environment.
5) Sanitary Landfills – open pits that are lined with clay and a system of pipes to
prevent leaking and compacted in 0.5m layers.
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2.0 The Flow of Energy and Cycling of Matter can be Trace and Interpreted in
Ecosystems.
2.1 Ecosystems have Interactions among Producers, Consumers, and Decomposers.
Consumers
______________ – is an organism that has to seek out and eat, or consume, other
living things for food. Can be organized into three basic groups.
1) _______________ – are organisms that consume animals (eg. Cats & preying
mantis)
2) Herbivores – are organisms that consume plants (eg. Deer & grasshoppers)
3) _______________ – are organisms that consume both animals and plant
matter (eg. Humans and bears)
Producers
____________ – an organism that can nourish themselves, typically green plants.
____________________ – the processing of water taken in by the roots and
carbon dioxide taken in by the leaves using the sun’s energy to produce food.
- products are food, in the form of sugars and starches, and oxygen.
- important to life on Earth for two reasons:
1) Plants, through photosynthesis, create stored chemical energy that consumers
can process as food.
2) Photosynthesis provides the oxygen in the air needed for cellular respiration.
-
In order for most organisms to release the energy stored in their food, plants
and animals included, they need oxygen.
____________ _________ – is a process in which oxygen combines with food in
the cell of an organism to break it down in to carbon dioxide, water, and energy.
Summary:
Photosynthesis (Fig. 2.5, pg 30)
Water + Carbon Dioxide + __________ PRODUCES Food + _____________
Cellular Respiration (Fig. 2.6, pg 31)
Food + Oxygen PRODUCES Water +Carbon Dioxide + _____________
Scavenger and Decomposers
___________ – are consumers that don’t usually kill their food. Instead, they feed
off of the remains of living things killed by other organisms.(eg. Crows, ravens, maggots)
________________ – are consumers that break down (decompose) dead plants
and animals as well as animal waste (eg. Fungus)
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-
But more than just a “clean-up crew,” decomposers provide nutrients to plants
through their actions.
Decomposers can be Helpful and Harmful
Helpful Examples:
(i) Baker’s Yeast (single celled decomposer) feed on sugars in food
producing carbon dioxide that causes bread to rise.
(ii) E. Coli (bacteria) help breakdown food in your large intestine
producing vitamins your body needs to be healthy.
Harmful Examples:
(i) Candida albican (a yeast) usually suppressed by your immune system,
can cause a disease called thrush.
(ii) E. Coli (bacteria) commonly found in foods such as ground beef, milk,
and apple juice, can produce highly toxic chemicals as they breakdown food leading to
food poisoning.
2.2 Food Chains Demonstrate the Flow of Energy in Ecosystems.
-
A food chain is a convenient way to show how energy moves among living
things in an ecosystem. (eg. Fig. 2.10, pg 35)
o First in the food chain is the producer.
o Followed in turn by a primary consumer
o Followed then possibly by a secondary consumer.
o Followed finally by a potential tertiary consumer.
_____________ Consumer – a herbivore such as a mouse or an elephant (only
eat plants).
_____________ Consumer – a carnivore eating a herbivore such as a fox.
_____________ Consumer – a carnivore eating a carnivore such as a human.
- Producers far out-number consumers within an ecosystem.
- In turn, primary consumers out-number the secondary consumers, who, in
turn, out-number tertiary consumers…forming a ______________.
Flow of Energy
-
Plants use as much as 90% of the energy they get from their food to sustain
their life leaving only about 10% in stored supplies to pass on to a herbivore.
Herbivores, in turn, use 90% of the energy they obtain from plants to sustain
their life leaving only 10% in stored supplies to pass on to a carnivore.
The 90% of energy “consumed” by plants and herbivores is not used up,
merely converted into energy not accessible to other living things (eg. Heat).
Energy is, therefore, not recycled in an ecosystem, it flows in a one-way path.
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Food Webs
Food Webs – represents ____________________ food chains in a more realistic
representation of an ecosystem’s complex network.
- all begins with a _____________ creating the energy for the web.
- that energy flows in a multitude of directions through various
herbivores than onto either carnivores or onto decomposers.
- as well, the energy from the plants may go directly to decomposers
by-passing all consumers.
- following each pathway in a food web will break it down into
various food chains. (Fig. 2.16, pg 42)
-
A change in the number of any given species can negatively affect some parts
of the web while creating a boom for other parts of the same system.
Example : an increase in grasshoppers in a grassland food web would negatively
impact other herbivores while causing an increase in the frog population.
2.4 Matter Cycles in Ecosystems
-
Matter continually moves from the abiotic environment (non-living things) to
the biotic environment (living things) and back again. This sort of movement
of matter is called a _____________.
The Water Cycle
Water Cycle – is created by the main processes of _______________,
___________________, and ___________________.
- Plants and animals absorb or take-in some of the water and give off water
vapours through transpiration in the case of plants and exhaling or
perspiration in the case of animals. (Fig. 2.19, pg 45)
The Carbon Cycle
Carbon Cycle – follows the flow of carbon ____________ through an ecosystem.
- Typically, carbon dioxide is released to the environment by animals when
food is broken down.
- Plants, in turn, take carbon dioxide from the atmosphere and combine it with
water to create food.
- Decomposers also release forms of carbon to the soil and water as they break
down food (Fig. 2.20, pg 46)
3.0 Changes can be Observed and Monitored in Ecosystems
- Ecosystems are always ______________.
- Sometimes these changes are natural (eg. Droughts and floods), while other
changes come as a result of human activity (eg. Forest clear-cutting and dams).
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3.1 Investigating the Distribution of Living Things in an Environment.
Distribution of Living Things
________________ – of living things refers to the population of any given
species of plant and animal in a specific area.
- Plant and animal populations are ________ evenly distributed throughout a
physical space in the ecosystem.
3.2 Interactions and Changes Occur in Ecosystems
-
An imbalance within an ecosystem of either biotic or abiotic factors or both
can cause problems. (eg. Drained wetlands used as farmland destroyed many
organisms in the ecosystem).
All Things Change
-
Factors that can cause ecosystems to change:
________________ – is when a non-native species is introduced, either
intentionally or accidentally, into an ecosystem.
- A lack of predators, or a naturally stronger species, can result in the successful
introduction of that species.
Example: 100 starlings intentionally introduced to Central Park in New York in
1890 now number more than 200 million species.
- 25% of all plant species in Canada are NOT native (eg. Zebra mussels).
_________________ – involves living things competing with other living things
in their community for limited resources such as food, water, and space to live.
_________________ – occurs when an animal hunts other animals for food.
- Large numbers of predators will mean a decrease in the population of prey.
- A decrease in the population of prey will then mean a decrease in the
population in predators.
- Finally, a decrease in the population of predators means an increase in the
population of prey.
- This relationship is cyclical and is typically sustained indefinitely unless
human represent the predators, the result could lead to the extinction of the
prey. (Fig. 3.6, pg 60)
Weather conditions can also affect the ecosystem. Poor conditions (eg. Draught)
can slow or stop plant growth. Natural disasters such as floods or fires caused by
lightning can also kill plants and animals.
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3.3 Succession: How Ecosystems Change over Time
- The predictable pattern of change in ecosystems is called succession.
- There are two forms of succession: primary & secondary succession
1) Primary Succession – occurs in areas where no life exists due to absence of
soil (eg. Volcanic islands). The succession begins with a pioneer species: lichen.
______________ Species – typically the first organism to arrive to an area,
helping to break down rocks into soil.
- Mosses, fungi, grasses, and herbs are next to establish themselves in the
developing soil, followed by shallow rooted trees, until finally larger trees
establish themselves creating a climax community.
______________ Community – is when diverse species develop into a stable,
though still changing, ecosystem. (Fig. 3.9, pg 63).
2) Secondary Succession – occurs when a community has been destroyed or
disturbed by natural occurrences or human activity (eg. A newly forested area or
fire stricken area).
- The first species to appear in secondary succession are the wild grasses and
weeds. The succession that follows mirrors that of primary succession.
4.0 Maintaining Sustainable Environments Requires Knowledge, Decisions, and Actions.
4.1 Intended and Unintended Consequences of human Activities within Ecosystems.
Human Impact on Ecosystems: Chemical Use
-
The use of pesticides by people, in addition to the immediate solution they are
intended to produce, typically enter the food chain and produce some very
undesired results.
- The imbalance created by the impairment or death of a species by these
chemicals, affects the entire ecosystem leading to impairment or death of its
predators and their predators.
- Migratory species are very vulnerable to the use of pesticides as they visit so
many localities.
Example: The devastating affect the pesticide DDT had on the people of Borneo. (pg 67).
Human Impact on Ecosystems: too Little too Late?
-
Human activity such as hunting, bioinvasion, farming, urban development,
and foresting have affected species to varying degrees.
________________ – when a species has dramatically declined in numbers.
Ex. The wood bison and burrowing owl.
________________ – when a species is in danger of extinction.
Ex. The Beluga whale and Whooping crane.
________________ – when a species has been entirely eliminate.
Ex. Dinosaurs
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-
Though extinction of a species is a natural phenomenon, human activity has
increased the rate or altered the natural course of succession entirely.
4.2 Information from Scientific Investigation can Assist Environmental DecisionMaking.
The Saving of the Peregrine Falcon
-
-
-
Scientists, such as ecologists and environmentalists, have assisted in curbing
the declining numbers of the endangered peregrine falcon. Scientists observed
a dramatic decrease in peregrine populations.
Studies revealed the peregrine was originally threatened by a _____________
the bird carried in its body that weakened the shells not permitting the young
inside to fully mature.
______________ breeding programs were established to assist with the bird’s
reintroduction to its natural environment.
A release and monitoring program have observed the success of the program.
As a result of the scientific plan for the peregrine’s return, the bird’s status has
been downgraded from endangered to threatened.
4.3 There are Limitations to Scientific and Technological Knowledge.
-
In dealing with environmental issues, science cannot always provide answers
due to a lack of evidence or studies.
Example: The Golden Toad in Costa Rica has vanished without a clue as to why.
-
In addition to the apparent die-offs, deformities in other species of amphibians
have no clear explanation due to a lack of evidence or obvious alteration to the
environment thought to be at fault.
-
Scientists believe many amphibians are at risk due to one of the following
theories.
(i)
climate changes
(ii)
pollution
(iii)
disease
(iv)
ultraviolet radiation
4. 4 Using Evidence from Many Sources can help Analyze a Local Environmental
Problem.
Ecological Footprint
Ecological ____________ – is the amount of land needed to sustain our food,
transportation, entertainment, shelter, and sanitation needs.
- The average Canadian requires 7.7 hectares (77 000m²).
- 1.7 ha actually available per person on Earth.
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-
Average ecological footprint worldwide is ______ ha.
Humans use more of the Earth’s resources than the environment can safely
support, but there are ways of reducing our ecological footprint.
o Reduction in the amount of water used.
o Reduction in the use of energy.
o Reducing consumable materials.
o Reusing products where possible.
o Recycling waste materials.
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Unit B – Plants for Food and Fibre
1.0 Understanding structures and life processes of plants helps us to interpret their needs.
- All seed plants have the same basic structures.
Ex) cactus and pine tree.
1.1 The Body of Seed Plants
Seed Plants – those plants that make seeds.
- come in all shapes and sizes.
- have the same structures, which do the same job in all plants.
- structures:
Flowers – each flower usually has both male and female parts for reproduction.
Stems – provide a pathway for movement of water and food.
- support the leaves and reproductive structures.
Seeds – contain an embryo that will form a new plant.
- contain a food supply for the embryo.
Leaves – produce food for the plant.
- take in and release oxygen and carbon dioxide.
- allow water to exit the plant.
Cones – there are separate male and female cones for reproduction.
Roots – absorb water and dissolved nutrients.
- anchor the plant in the soil.
1.2 Plant Processes
A Process for Moving Water Up from the Roots
- Plants move water from the roots up to the leaves through several processes.
Transpiration – the plant process that pulls the water up from the roots.
1st - evaporation of water from the surface of the leaves.
2nd – evaporated water pulls water inside stem up to the leaves.
3rd – water is continuously pulled which brings water into the roots.
Capillary Action - movement of liquid up a narrow tube.
Two processes help move the water up the narrow tube.
Cohesion – water is attracted to other water particles.
Adhesion – water is attracted to the walls of the narrow tube in stem.
In a very narrow tube the force of adhesion and cohesion is more attractive than
the force of gravity, which allows the water to move up through the stem.
Osmosis – in cells, the movement of water across the cell membrane.
- moves water into roots from the soil.
- water naturally moves:
High Water
Low Water
Concentration
→
Concentration
(in the soil)
(in the roots)
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A Process to Make Food
Photosynthesis – process by which plants use light energy, carbon dioxide, and
water to make their own food.
Chloroplasts – the structure in plants cells that carry out photosynthesis.
Equation
Solar + Carbon
Energy
Dioxide
→
+ Water
Food
+ Oxygen + Water
A Process to Use Food
Cellular Respiration – the process in which cells break down sugar particles into
carbon dioxide, water, and energy.
Mitochondria – the structure in plant & animal cells that carry out cellular
respiration.
Equation
Food
+ Oxygen
+
Water
→
Energy +
Carbon + Water
Dioxide
Processes to Move Substances In and Out of Plant Cells
- After making the food, the plants must transport it to the other cells.
Pores – tiny openings in the cell membrane of plant cells.
- acts like a filter, allow certain substances to move in and out of the cell.
- 2 important processes to move substances.
1) Diffusion – the movement of particles from an area of high concentration to an
area with a low concentration.
Concentration – the number of particles of one substance in a certain volume of
another substance.
2) Active Transport – the process in which large particles cross the cell
membrane; active transport requires energy.
Diffusion
- Can be seen in all substances.
- Substances move from HIGH → LOW concentrations
Osmosis
- Is basically the diffusion of water
- Very common in cells because water is small enough to move through pores.
A Process to Exchange Gases
Gas Exchange – the process by which carbon dioxide and oxygen move in and
out of the plant.
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1.3 Reproduction of Seed Plants
Life Cycle – the stages that an organism passes through in going from one
generation to the next.
Seed → starts → Seedling → grows & develops → Adult → pollination → Seed
to
reproductive
grow
structures
The Seed Stage
- A seed has 3 main parts
(i)
embryo
(ii)
stored food – used to nourish embryo until able to survive on own.
(iii) seed coat
The Seedling Stage
- Grows very fast.
- Produces own food through photosynthesis and nutrients from soil.
The Adult Stage
- Produces reproductive structures
Ex) flower or cone
Reproduction of Seed Plants
Pollination – process in which male and female parts of a plant join to produce a seed.
- Male part is called the pollen.
Pollen – small, sticky cells
- a plant produces millions of pollen grains
- Female part is called ovary.
Ovary – usually in the centre of the blossom.
- contains an ovule
st
1 Occurs after a pollen gain lands on the stigma of a flower, above the ovary.
2nd Pollen grain produces a pollen tube that grows down to the ovule.
3rd Pollen grains then transfer to the ovule and grow into a seed.
- Cone-bearing plants (conifers) usually have separate male and female cones
Male – produce pollen
Female – produce ovules (once pollinated seed develops on female cones)
- Many plants such as conifers & wheat fields, are pollinated by wind.
Pollinators – organisms that carry pollen from one flower to another.
1st the organism lands on a flower in search of nectar.
2nd pollen gets stuck to the body of the organism.
3rd then the organism transports the pollen to the next flower.
- Although it is done naturally, farmers develop ways to ensure it happens.
Ex) beehives near their plants
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Reproduction without Seeds
Vegetative Reproduction – reproduction of seed plants that does not involve the
production of seeds.
- these reproduced plants are genetically identical.
Examples
(i)
Some plants reproduce from stems
(ii)
Runners – long stems that grow along the soil of the surface and produce
new plants.
(iii) Rhizomes – stems that form underground stems and produce new plants.
(iv)
Bulbs, tubers, & corms – underground stems produced close to the plants.
(v)
Suckers – new plants that are produced from the roots of the parent plant.
- Common in the horticultural industry; new plants are produced in nurseries.
Technology to Reproduce Plants
Cuttings – a cut piece of a plant that is used to reproduce that plant.
- cuttings usually have a part of the stem and a few leaves.
Grafting – a technology to reproduce plants that involves attaching part of one
plant to a second plant.
1.4 Plant Structures are Adapted to Their Environment
-
Orange trees can not grow in Alberta, but white pine trees can.
Plants have structures and adaptations that match their environment?
Examples
(i)
(ii)
(iii)
(iv)
(v)
(vi)
(vii)
Cacti in Dry environments
- have think stems to conserve water
- have tiny spines for protection
Grass
- thin leaves so many can fir in a small place for easy pollination.
- depth of roots help find water in drought conditions.
Sunflower
- have large, wide leaves to capture lots of sun.
Pretty Flowers
- have bright colours and sweet nectar to attract insects.
White Spruce Trees
- have thin needle-like leaves with thick resin coating to protect from
drying out.
Some plants
- have fibrous thick mat of roots to gather water near upper layers of soil.
- have long taproot that collect water that is deep in the soil.
Wild Mustard
- have adapted to produce seeds in a short growing season.
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1.5 Plant Needs and Growing Conditions
-
Plants need the right amount of:
- Light
- Water
- Nutrients
- Space
Plants need different amounts of Light
Ex) A fern needs less light than a marigold does.
Plants need different amounts of Water
Ex) A cactus needs very little water.
A rice plant needs to grow in water.
Plants need different Nutrients
Nutrients – are substances that provide the energy and materials that plants need
to grow. The main nutrients are:
- nitrogen
- phosphorous
- potassium
- calcium
- magnesium
- Plants need sufficient amounts of each nutrient to grow and develop properly.
Ex) Lack of nitrogen leads to yellow leaves
Plants need different amounts of Space
Ex) Buttercup plants need very little space compared to redwoods.
** Understanding a plants needs is an important tool to maximise a plants growth.
2.0 Plants play an essential role in the environment and in meeting human needs.
- Plants are important for human life on earth.
2.1 The Role of Plants in the Environment
- Plants have an important effect on the environment.
Examples
(i)
Plants provide Oxygen
Ex) produced by photosynthesis
(ii)
Plants provide Shelter
Ex) birds nest
(iii) Plants provide Food
Ex) produced by photosynthesis
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(iv)
(v)
Plants build and protect soil
Ex) decomposition builds soil
Prevents erosion – process that moves soil.
Plants are crucial for the Food Chain
Ex) Most common consumers are herbivores
2.2 We use Plants in Many Ways
-
Plants have an unlimited number of uses such as:
- Medicine (Ex) Paintbrush plant heals rheumatism
- Food (Ex) fruits & vegetables help keep us healthy
- Fibre (Ex) Shelter, Clothing, & Paper
- Other useful products (Ex) glue & rubber
2.3 Managing Living Resources
Living Resources – those living things that can be used to meet human needs.
- It is important to manage living resources to maintain healthy populations of
all the living things that make up those resources.
Changes Caused by Human Activity
1st Aboriginals used living resources for medicine, food, and fibre and so they
developed a close relationship with the living resources.
2nd Introduction of European tools allowed Aboriginals to be more efficient and
started to have a greater affect on the environment.
3rd European settlers started using living resources for themselves and others.
Which has led to great impacts, and a serious need to manage these resources.
Managing Living Resources for Now and the Future
Non- sustainable resources - In many places in the world humans are using living
resources more quickly than they are being replaced. This means they will not have
enough available in the future.
This has led to managing plans such as:
- Established methods and regulations.
Ex) What species can be harvested?
How they are to be removed?
How the forest is restored and replanted after harvesting?
This allows both industry and the living resources to co-exist.
3.0 Soil is an important resource that human activity can protect or degrade.
- Soil is a natural resource that is important to provide a healthy place for plants to
grow and many organisms to live.
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3.1 What is Soil?
- Soil is not just dirt. Soil has:
Minerals – pure, natural solid materials that are the building blocks of rock.
Organic Particles – particles that come from plants and animals that have died.
Humus – partly decomposed material from plants and animals that once lived.
Sandy Soil
- Is light brown
- Does not form clumps
- Mostly minerals, very little humus
- Dries quickly because water runs through it very fast.
Clay Soil
-
Feels slippery when moist.
Sticks together and can form a tight ball.
Dry clay is very had.
Colour can vary.
Lots of very small minerals, and little humus.
Fine texture.
Can hold lots of water, but little space for air.
Loam Soil
-
Crumbly, like a moist cake.
Dark brown or black.
Balance between organic particles and minerals.
Absorbs lots of water, and can stay moist for a long time.
Lots of nutrients, and is great for plants to grow.
** Each plant is adapted and grows the best in different types of soil.
3.2 Our Practices Can Improve or Degrade Soil
- Human harvesting techniques over time can remove the important nutrients from
the soil so future plants would not be able to grow well.
- Soil is an important natural resources.
Ex) animal food and shelter & human food and fibre
Fertilizer Use
- The lost nutrients in the soil can be replenished by fertilizers.
- 2 types of fertilizers.
1) Organic – made from sources such as animal or plant waste.
Ex) Animal manure or urea
2) Chemical – mixtures of types of chemicals that promote plant growth.
Ex) Potash (for potassium)
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-
The amount of fertilizer is important because too much and too little can be
harmful to either the plant or the environment.
Irrigation
- Is used to grow plants in dry areas.
- Ensures plants get the right amount of water at the right time.
- Must be carefully managed to promote optimal growth conditions.
Clearing the Land
- Before plants can be grown the land must be cleared:
- To prevent competition from other plants.
- Making it easier to plant seeds.
- Forest harvesters remove the desirable species and leave the rest, and then
replant young trees to keep the forest sustainable.
- Too much clearing can cause problems:
- Soil can be blown away by the wind.
- Pounding rain can compact the soil making it hard for new plants to
lay down roots.
- Clearing plants could take away shade, which keeps it cool and moist.
Plowing Changes Soil
- Plowing is the process of cutting into the soil and turning the top layer over,
which creates more air spaces and makes it less compact helping plants grow.
- Overtime plowing can damage the soil.
- Alberta farmers found that a top layer of stubble (trash cover) helps protect
the soil.
- An Albertan created the Noble Blade in the 1930s which allowed farmers
to plough under the surface thereby killing the weeds, but leaving stubble
on the surface. Today it is used around the world.
Crop Rotation Helps to Keep Soil Healthy
- Planting the same crop on the same soil year after year could lead to the soil
running out of important nutrients.
- Fertilizer can be expensive and hazardous to the environment.
Crop Rotation-practice of planting a different crop in a particular field each year.
- the crops that are rotated should be chosen based on their nutrient needs.
Ex) 1st plant should use lots of phosphorous, but little nitrogen.
2nd plant should use lots of nitrogen, but little phosphorous.
4.0 The ways that plants are gown and used are related to human needs, technology, and
the environment.
-
Human activities must focus on using sustainable practices to ensure the
environment does not collapse.
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4.1 Modifying Environments to Increase Yields
-
The human population is increasing every year, which means humans need
more plants to produce food and fibre to meet their needs.
Yield – the amount of useful plant material produced per plant, or per area
planted in a particular crop.
- Humans have developed many technologies to provide the best growing
conditions for plants, thereby increasing yields.
Ex) fertilizers
Shelter
Artificial Environments
(i)
Greenhouses – plants grown in controlled settings, with the appropriate
light, temperature, and nutrients to meet their needs.
(ii)
Hydroponic systems – plants grown in gravel or course sand, with a
continuous flow of nutrient-rich water pumped through.
4.2 New Plant Varieties are Developed by Selective Breeding
-
As time has gone by more and more types of certain vegetables have been
created to meet specific demands.
Ex) Carrots have been grown to:
- stay fresh in the store during the winter.
- develop in the short growing season of Alberta.
Species – living things of the same kind that are able to reproduce.
Variety – a group of organisms of the same species that has specific
characteristics that can distinguish it from other varieties of that species.
Traits – a characteristic of an organism.
- Humans produce plants with specific traits that we need or want.
Ex) Plants that can tolerate salty soil or colder climates.
Selective Breeding
Selective Breeding – a technology for producing new varieties of an organism
that involves choosing parents with desired traits in order to produce offspring with these
traits.
Ex) Farmers might notice certain plants grow taller, so they use their seeds
to grow their next years crop.
Genetic Engineering – process in which single genes are added to a plant’s
genetic material.
- the genes can come from other plants or totally different
living things.
Gene – tiny piece of material in a cell’s nucleus.
- each gene in a cell is responsible for the inheritance of certain traits or
characteristics.
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-
New varieties of plants can cause other problems like be more attractive to
insects, which could lead to the use of more herbicides (economic &
environmental costs)
Ex) Genetically engineered canola plants
4.3 Controlling Weeds and Pests
-
On Earth, some plants are considered useful and some harmful.
Plants that interfere with the growth of these crops are called weeds.
Ex) quack grass & smartweed
- Animals that eat or affect the growth of crops are called pests.
Ex) army cutworm larva
- Farmers must find a way to maximize crop yield.
I. Herbicides – a chemical that kills unwanted plants.
II. Pesticides – chemicals that are poisonous to insects.
- Possible Complications:
- Certain species of plants and insects could become immune.
- Certain useful plants and insects could be harmed.
- Could have environmental consequences.
III. Biological Control – a technology for controlling pest in which natural
predators of the pest are introduced to reduce their population size.
- Usually takes a long time.
- Not useful for large outbreaks.
4.4 Consequences of Environmental Management
Unintended Consequences – results of an action, not predicted or planned.
Environmental Management – the process of balancing the needs of humans
with the needs of the environment.
- Important to look at all possible consequences of human actions.
Monoculture – the practice of growing only one type of crop in a large area.
- Useful to cut down on cost and ferilizer use.
- Problems:
- Insect population explosion (large supply of food)
- Reduce biodiversity
Biodiversity – the number of different species in an environment.
- Our goal should be creating a sustainable environment.
Sustained – can be maintained or continued indefinitely.
- In any decision, economic and social effects should also be considered.
Economic – Crop rotation increases yields and consistency of poduction.
Social – Farm stability could ensure jobs for families.
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Grade 7 Unit C Notes
Heat and Temperature
1.0 Early Theories of Heat
- Until about 1600, heat was thought of as a combination of fire and air.
- Scientists came up with the CALORIC theory
Caloric Theory – heat was an invisible fluid (caloric) because it flowed from a
hotter object to a colder one.
Heat Is Energy
-
Heat is a form of energy.
Energy comes from the movement of the tiny particles that make up all
matter.
Franklin Stove – invented by Benjamin Franklin. When the front is open it works
as a fireplace, and when it is closed it works as a cook top.
Pg 184 – timeline for heat.
1.2 Heat Technologies in Everyday Life
Standard of Living – a measure of how well we live. In North America = high.
Making Sustainable Choices
Sustainable – something that can be maintained or continued indefinitely. Using
our resources wisely and do as little damage as possible to the environments when we use
them.
2.0 States of Matter & The Particle Model of Matter
-
Everything in the universe is made up of matter and this matter can exist in
three states: solid, liquid, and gas.
These states result from adding or taking away heat energy.
Fact File: ice is water in a solid state.
o Freezing point = 0ºC – liquid to solid
o Melting point = 0ºC – solid to liquid
o Boiling Point = 0ºC – liquid to gas
o Condensation = 100ºC – gas to liquid (cooling process)
Particle Model of Matter
-
All matter is made up of extremely small particles and these particles are
always moving.
Each particle has energy of movement (KINETIC).
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-
Adding heat to matter makes the particles move faster.
There are spaces between the particles.
Heat & the Particle Model of Matter
Solid State – particles are attached to each other in all directions.
- Definite shape and volume.
- Particles very limited in movement
- Move back and forth around a fixed position.
- Less Kinetic energy than a liquid or gas.
Liquid State – particles loosely attached, easily slip past each other.
- Liquids take the shape of the container and has a definite volume.
- More spaces between the particles of solids.
- More movement of particles than of solids.
- More Kinetic energy than a solid.
Gas State – particles are not connected to one another.
- Gas fills the empty space of a container,
- No definite shape or volume.
- More spaces between the particles than solids or liquids.
- More movement of particles than solids and liquids.
- More Kinetic energy than solids or liquids.
- Adding Heat to the particles increases the Kinetic energy while taking heat away
decreases the kinetic energy.
2.2 Heat & Temperature
Temperature – a measure of how hot or cold matter is. Measure in degrees
Celsius.
Thermal Energy – total kinetic energy of all the particles the substance contains.
Ex. A pot and bowl of soup could have the same temperature, but the
larger container (pot), would have the larger thermal energy.
Heat – the energy that transfers from one substance to another because of
differences in kinetic energy.
Measuring Temperature with Thermometers
-
300 years ago John Locke, an English scientist, proved that our sense of touch
was not a good way to measure temperature.
Galileo Galilei, an Italian scientist, produced the first device to measure
temperature in 1590.
Gabriel Daniel Fahrenheit, a German physicist, developed a more accurate
means of measuring temperature in the 1700s.
Anders Celsius, a Swedish astronomer, came up with a different scale in 1742.
* Conversion of Fahrenheit to Celsius:
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ºC = (5/9)(ºF – 32)
2.3 Heat Affects the Volume of Solids, Liquids, and Gases
Expansion & Contraction of Solids
Expansion – as the thermal energy of a solid increase the volume increases.
Contraction - as the thermal energy of a solid decrease the volume decreases.
Thermal Expansion – expansion of a substance caused by an increase of thermal
energy.
- Expansion joints were invented to deal with this and are used on bridges,
highways, and between railroad tracks.
2.4 Heat Transfers by Conduction
Conduction – transfer of heat energy between substances that are in contact with
each other.
- A chain reaction – particles do not move from one end to another but rather
stay in the same position and transfer heat by bumping into each other.
Conductors – a material that allows transfer of heat.
- Heat travels in one direction:
HIGH Thermal Energy
TO
LOW Thermal Energy
- Conduction most common in solids, less in liquids, and rare in gases.
- Metals are good examples of conductors.
Insulators – materials that do not allow easy transfer of heat.
- Plastic, Cork, and wood are good examples of insulators.
- In household products, we usually combine insulators and conductors to make
safe tools.
2.5 Heat Transfers by Convection and Radiation
Convection – heat is transferred when particles in a liquid or gas move from one
area to another.
Convection Current - when these particles move in a circular motion.
- heat transfers in only one direction:
HIGH Thermal Energy
-
TO
LOW Thermal Energy
Convection can result in heat loss.
Ex. Storm windows on an old house.
Radiation – transfer of energy of invisible waves that can travel great distances.
Radiant Energy - energy transferred from its source by radiation.
- Materials that ABSORB heat energy = dull or dark.
- Materials that REFLECT heat energy = shiny and light coloured.
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3.0 Understanding heat & temperature helps explain natural phenomena & technological
devices.
3.1 Natural Sources of Thermal Energy
Solar – energy from the sun.
Geothermal – energy from deep inside the Earth.
Focus on Solar Energy
-
Energy from the sun that is produced by nuclear reactions that occur inside the
sun.
Every 40 minutes, the level of energy that come to Earth = energy used by
humans for one full year.
Using the Sun’s Energy for Solar Heating
- Solar heating can be either PASSIVE or ACTIVE.
1) PASSIVE
- Basic approach for passive solar heating is to reduce heat loss and
increase heat gain from the sun by doing the following.
- Insulating the building as much as possible.
- Place most windows on the south side.
- Large overhangs above the windows to provide shade from the
summer sun, and in winter, the sun rays are lower and can enter
the building.
- Warmth carried to other rooms by convection currents.
- Use of special materials can increase thermal efficiency.
- Extra panels of glass and special coatings on windows allow
radiant energy in and prevent it from reflecting out.
- A stone or brick wall inside with the sun shining on it can act as a
storage area for thermal energy, which can be transferred to the
room when the sun sets.
2) ACTIVE
- Has three components:
1) Collector
2) Heat storage unit
3) Heat distribution system
- System works the following way:
(i) Water used in the collector to trap solar energy.
(ii) Copper tubing on a black surface is placed under a glass pane.
(iii) Sun’s rays pass through glass and area becomes heated.
(iv) Insulation assists in containing thermal energy.
(v) Water running through copper tubing becomes heated.
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-
-
(vi) Heated water is pumped to the heat storage unit by distribution
unit.
In a prairie climate the combination of active and passive solar heat can
usually meet 75% of a family’s heating needs. In warmer climates, the
percentage is higher.
The use of trees can also be applied to the outdoors. Trees block cold winter,
wind, and provide shade in the summer.
A back up system is usually required for both systems and is only used when
sunlight is not available or when not enough heat was collected during the
day.
Solar Energy and Electricity
- Solar energy can be converted to electricity.
Solar Array - Solar cells arranged in panels and connected.
- Series of arrays placed to capture and store the sun’s energy in low voltage
batteries.
Costs and Benefits of Solar Energy
Benefits
- Sun’s energy not limited.
- Available to everyone.
- Does not create pollution.
- Does not carry radiation risks.
Costs
- Setting up a solar system is usually more expensive than electrical or fossil
fuel systems.
- A back up system is required.
- Solar cells are expensive.
- Disposal of used solar cells is an environmental concern.
-
Passage systems continued to be a lower cost option although maximizing
solar energy this way can be expensive because of the special design and
materials needed.
3.2 Heating System Technologies
THERMOSTATS
- Device used to control the air temperature in indoor environments.
- Most rooms kept at “room temperature” = 20C.
- Also useful in adjusting the temperature of electrical appliances (oven).
- The switch is a BIMETALLIC STRIP that consists of two different metals
joined together. When heated one expands faster than the other causing the
strip to bend. As the strip bends and unbends it opens and closes an electrical
circuit that controls a heat regulating device such as a furnace.
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Heating Systems
LOCAL
- Provide heat for only one room or a small area of a building.
Ex. Fireplaces, space heaters.
CENTRAL
- Provides heat from a single, central source such as a furnace.
- Heat transfers through ducts, pipes, and vents.
- Most homes use FORCED AIR heating, while older homes used HOT
WATER heating.
-
Both systems use convection currents to warm areas.
Keeping Cool
-
Basic parts of a cooling system are:
1) A storage tank
2) Compressor
3) A Freezer unit
4) Condenser coils
5) Refrigerant
Refrigerant – a liquid that evaporates at a very low temperature.
Fig 3.13 – how a typical fridge works.
(i)
Refrigerant in the storage tank is pumped to the freezer unit
(ii)
Where it evaporates as it goes through it.
(iii)
Cools as it evaporates so heat is transferred from warm air inside
by the food to the refrigerant.
(iv)
Food becomes cooler as the refrigerant becomes warmer.
(v)
As a vapor the refrigerant flows through the compressor to the
condenser coils.
(vi)
Condenser coils on the back of the fridge release heat to
environment, which cools down the refrigerant.
(vii) Refrigerant then re-enters the storage tank.
Heat Loss and Insulation
INSULATION
- Used in buildings to limit heat loss to the colder environment or to limit the
amount of heat that is able to enter a cooler building on a hot day.
Thermal Conductivity – ability of a material to transfer heat by conduction.
- Building a house – want good insulators, not conductors.
Ex. Stone or brick outside, Styrofoam paneling, fiberglass insulation
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Heat Loss
Thermogram – an infrared photo that uses different colors to diagnose areas of
greatest heat loss.
- Areas of greatest heat loss in a house:
o Walls
35%
o Ceiling and Roof
25%
o Floor
15%
o Gaps & poorly sealed areas
15%
o Windows
10%
- Every insulator is given a R-value.
R-value – rating system to inform consumers of the insulators effectiveness.
- The higher the R-value the better the product is at providing insulation.
4.0 Technologies that use heat have benefits and costs to society and to the environment.
- 72% of our energy needs are met by using fossil fuels such as coal, oil, and
natural gas. What happens when these resources run out?
4.1 Looking at Different Sources of Heat
- There are two types of natural resources:
1) Renewable – natural resources that can be replaced.
Ex. Sun, wind, and trees
2) Non-renewable – natural resources that cannot be replaced. Once used, it is
no longer available.
Ex. Coal, oil, and natural gas
Focus on Fossil Fuels
-
Fossil fuels formed from the remains of plants and animals that lived millions
of years ago.
Oil and natural gas are extracted from the ground by pumping.
Coal is mined.
Used world wide because they are fairly easy to obtain and transport.
Have been available in large quantities and have a variety of purposes.
Cheaper than other energy sources because of its availability.
Alternatives for Thermal Energy
Wind Energy
- Energy of moving air is captured by windmills.
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- Used on large wind farms which consists of dozens and sometimes
hundreds of windmills constructed in windy areas to capture energy from
the wind.
Nuclear Energy
- Nuclear fission is a process that uses small amounts of radioactive
uranium to produce vast amounts of heat.
- Canadian scientists developed CANDU (Canada Deuterium Uranium)
reactor to provide nuclear energy. The best safety record in the world.
- Produce large quantities of electricity but eh fuel used requires special
handling because it is harmful to living things.
Hydro-electric Power
- Energy generated by moving water through a dam.
Reservoirs - dams built across rivers to create large artificial lakes.
- Very clean and renewable.
- No Air pollution
- Not expensive to generate but expensive to build.
- Upset or destroy local ecosystem.
- Long distance transmission lines needed and must be built.
4.2 Energy Consumption
-
3 main users of energy are homes, transportation, and industry.
Transportation uses 66% of oil used.
o In Canada, 75% of this oil is used by cars and trucks.
Cogeneration – production of 2 forms of energy, usually heat and electricity,
from one energy source.
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Science in Action 7
Unit D – Structures and Forces
5.0 Structures are found in natural and human-made environments
Structure – any object that provides support.
- Can be made of one or more parts.
- Can be large or small.
Structural Strength – the capacity of a structure to support both the load of its
own material plus any additional load applied to it.
Structural Stability – the ability of a structure to maintain its position even when
it is being acted on by forces.
- being balanced, difficult to topple over.
Force – a push or pull, tends to cause an object to change its movement or shape.
- force measured in newtons.
1.1 Classifying Structural Forms
- There are 3 basic structural forms.
1) Solid structure - structure made of a solid piece of strong material.
- Has little to no space inside it.
- Relies on its own mass to resist the forces that act on it.
- Usually stronger, but harder to move.
2) Frame structure – structure consisting of a rigid arrangement of parts
joined together.
- Strength of a frame comes from how the components are joined.
- No one component is as strong as the components combined.
- Usually lighter than solid structures.
3) Shell structure – structure with a solid outer surface and a hollow inner
area.
- Surface may be rounded or flat in shape (rounded is stronger).
- Is lighter than solid structures.
- Is stronger than frame structures.
- Commonly used for protection.
1.2 The Function of Structures
Function – the use or purpose of a structure.
Ex) The function of a park bench is to provide comfort and invite seating.
- Many structures have multiple functions.
- Should be taken into account when designing a structure.
- For ideas, many inventors look at the natural world
Common Function, Different Design
- Structures can have very different designs, but the same function.
- Structural design is always developing, many times through trial and error.
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Ex) Roofs
- Structures can be classified by ways other than function and design.
- Type of material they are made of.
- How they work.
- Aesthetics
Aesthetics – the pleasing appearance or effect an object has because of its design.
- Not every structure has to be aesthetic.
- Humans have always shared a need for beauty in their
surroundings.
Ex) First Nation People – buffalo drawings.
1.3 Human-Built Structures around the World
- There are many reasons for the huge variation in structures around the world.
- Climate
- Culture
- Tradition
- Technology
- Economics
Ex) The Human Home
- All have 2 things in common.
(i)
Basically stable
(ii)
Provide shelter for people to live in
6.0 External and Internal Forces act on Structures
- When designing a structure the internal and external forces that will act on it
must be taken into account.
2.1 Measuring Forces
Force – is a push or a pull that tends to cause an object to change its movement or
shape.
- There are 3 factors that effect the force on a structure.
1) Magnitude, or size, of the force.
2) The direction of the force.
3) The location where the force is applied.
Newton - the standard unit for measuring force
- named after Sir Isaac Newton (discovered the law of gravitation).
2.2 External Forces Acting on Structures
External Force – force applied to an object by something else.
Ex) Gravity – a downward pull on everything on Earth.
Mass – amount of matter in an object.
- usually measured in grams or kilograms.
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- the larger the mass the greater the gravitational force.
Centre of Gravity
Centre of Gravity – imaginary point in an object where the downward force of
gravity acts.
- When a structure is balanced at its centre of gravity, it will stay balanced.
- The location of the centre of gravity of a structure determines its stability.
- To increase a structure stability one should increase the width of the base, add
more mass to the part of the structure close to the ground.
Symmetry
Symmetry – balanced arrangement of mass on opposite sides of a line or plane,
or around a centre of axis.
- If both sides have the same mass, the force of gravity on both sides is equal, and
the structure would be stable.
- If one sides has more mass is would also have a greater gravitational force, and
the structure would be unstable.
Load
- When a structure is designed, the load the structure will have to resist must be
taken into account.
Load – external force acting on an object.
- load can be measured as weight.
- 2 types
(i) Static Load – weight of a structure, and the non-moving load it supports
[dead load] (Ex. Weight of a bridge, including nails and beams)
(ii) Dynamic Load – moving or changing force acting on an object
[live load]
(Ex. Downward force of a car on a bridge)
- There are 2 conditions to decide which type of bridge should be built.
(I)
What the bridge is crossing.
(II)
What kind of loads the bridge will be supporting.
- There are 4 main types of Bridges
1) Beam bridge – bridge supported by a beam or several beams.
- most common bridge.
- bridge is flat and supported at it 2 ends, might have additional
vertical piers.
2) Truss bridge – bridge supported by trusses.
- Lightweight, but strong bridge.
Truss – framework of beams that form triangles.
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3) Suspension bridge – bridge having its roadway hung from large
cables supported between tall towers.
- Modern ones have strong concrete towers on both ends to support the
main cable, and then smaller cables are connected to the main one.
4) Arch bridge – bridge supported by an arch or a series of arches.
- Designed to withstand heavy loads.
- Each part is supported by the next, and eventually the ground.
Performance Requirements – conditions that a structure, once it is built and in
operation, must meet to show it is performing to certain standards.
- Includes:
- Safety
- Cost
- Efficiency
- Bridges are usually evaluated based upon the amount of mass it can support in
comparison to its own mass.
2.3 Internal Forces within Structures
Internal Force – force that one part of a structure exerts on other parts within
the same structure (Ex. Tension in an elastic).
- There are 3 types of internal forces.
1) Compression – force that acts to squeeze an object or push parts
within an object together.
- Solid structures are best at resisting due to strong materials wtihin.
2) Tension – force that stretches and pulls apart an object.
- A structure with parts that must resist are running shoes.
- Can be advantageous such as cables on a suspension bridge.
3) Shear – force that acts to push parts that are in contact with each other
in opposite directions.
- Structures with parts that resist shear include doors and scissors.
Complimentary Forces – two or more forces acting on an object at the same
time. Ex) Bending
2.4 Designing Structures to Resist Forces and Maintain Stability
- The strongest two-dimensional structure is the triangle.
Structural Components
Arches – curved structures used in bridges and gateways.
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- Can support a large load because the force of the load is carried down through
the arch to the foundation.
Beams – flat surfaces supported at both ends.
- If the beam is too weak it will bend into a U-shape.
- Changing the shape of a beam can increase its strength.
I-beam – beam that has a cross-section in the shape of a ‘I’.
Girders – long structure in the form of a hollow rectangular prism.
Truss – framework of beams that form triangles.
Cantilever – structure that is supported at only one end or point.
- when it bends it forms a N-shape.
Columns – solid, upright support structure in the shape of a cylinder.
- There are always limits to a structure.
Structural Stress – effect of all the forces acting on a structure at one time.
Structural Fatigue – weakening of a structure due to the external and internal
forces acting on it.
- Usually caused by abnormal use of the structure.
- Results in a permanent change in the structure.
Structural Failure – breakdown of a structure due to the external and internal
forces acting on it.
- Failure takes the form of:
- Buckling
- Shearing
- Separating of Components
- Deformation
- To avoid failure a structure needs:
Strength – defined by the load at which it fails.
Stiffness – ability to withstand changing shape under a load.
Building for Structural Stability
- Designing a structure that is symmetrical distributes the load evenly and helps
reduce internal forces such as tension, compression, and shear.
- Selecting the best material for each part of a structure increases its strength.
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7.0 Structural strength and stability depend on the properties of different materials and
how they are joined together.
3.1 Materials and their Properties
- Materials properties should be taken into account when designing a structure.
- Some properties of materials.
- Brittleness – ease at which it breaks.
- Ductility – ability to be made into a wire.
- Hardness
- Plasticity – ability to be shaped.
- Resistance to heat
- Resistance to water
- Compression
- Tensile strength
- Other considerations.
- Aesthetics
- Consume demand
- Availability
- Cost
- Effect on the Environment
- Disposal of Waste
Testing Deformation and Flexibility of Materials in Structures
Deformation – a change of shape in any structural component, or in the structure
itself, because the material is unable to resist the force acting on it.
Flexibility – ability of a material to be bent under force repeatedly and not fail.
3.2 Joining Structural Components
- The joints of a structure are another limiting factor.
Joint – place at which 2 or more components of a structure are joined together.
- may be fixed or movable.
Joints that Rely on Friction
Friction – the force that results when the surface of one object moves against the
surface of another object.
- depends on the roughness and smoothness of the 2 surfaces.
- can be used to prevent the individual components from slipping apart.
3 examples:
(i) Nails, screws, rivets, tacks, and staples
- Works by friction between two components.
34
(ii) Interlocking Pieces
- Works by increasing friction by increasing the area in contact
(iii) Mass
- As mass increases the friction increases.
Joints that Rely on Bonding
- Structures can also be joined by changing 2 surfaces into one common material.
Ex) Glue, Tape, Cement, Welds
Fixed or Movable?
Fixed joints – are rigid and prevent any movement.
Movable joints – are flexible or mobile so that parts of the structure can move as
required.
- Choosing the appropriate joint depends on:
- material of the components.
- how the structure is to be used.
- where it is located.
- When designing a joint for a structure it is important to build one that lasts.
3.3 Properties of Materials in Plant and Animal Structures
Materials in the Human Structure
- Each part of the human body has special properties and unique material that
matches its function.
Bones, Ligaments, and Cartilage of the Fame Structure
Bones – are hard and rigid.
- form a structural frame that supports and protects.
Ligaments – strong, flexible connective tissue that connects bones.
Cartilage – found on ends of bones.
- smooth surface that reduces friction from movement.
Muscle and Tendons
Muscle – made of semi-solid fibrous tissue that contracts and relaxes.
- 656 in human body.
- located throughout the body (Ex. heart, digestive system, legs)
Tendon – connect muscles to bones.
- strong and flexible.
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- can hold even when the bone breaks.
Joints
- Specialized for various functions.
Ex)
Ball and socket joints – hips and shoulders
Hinge joints – elbows and knees
Pivot joints – spinal column and wrists
- There are some joints that are immovable
Ex)
Bones in the skull
Skin, the Human Shell
- Forms a shell and frame structure.
- Is a tough, flexible material:
- Waterproof
- Protection against bacteria
- Regulates body temperature
Material in a Tree’s Structure
- Wood is made up of several layers.
Bark – protects inner layers
Woody layer – contains phloem (transports sugars within tree)
Vascular Cambium – contains dividing cells
Sapwood – conducts water and minerals within the tree
Heartwood – provides main support
8.0 Structures are designed, evaluated, and improved in order to meet human needs.
4.1 Building Safe Structures in All Environments
- All structures are created to satisfy human needs.
- The most significant factor taken into account in design is safety.
Margin of Safety – the limits within which the safety aspects of a structure are
considered to be acceptable.
Ex) Steel beams must be able to withstand 4 times their maximum intended load.
- To ensure safety all aspects of a structure are tested and monitored.
Test - Driving cars into brick walls
Monitor - Experts keep track of how well a structure performs
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Accounting for Environmental Factors
- Every designer has to deal with each individual local condition.
(i) Climatic Conditions
(ii) Terrain Conditions
(iii) Earthquake Risk
4.2 Strengthening Materials to Improve Function and Safety
- Sometimes structural problems can be solved by combining materials and
components in new arrangements.
1) Corrugation – forming a material into wave-like ridges or folds.
Ex) Corrugated cardboard
2) Lamination – process of gluing layers of material together to create a strong
bond.
3) Strengthening Component Arrangements
- If stronger material is not available the components can sometimes
by arranged in a stronger arrangement.
Ex) trusses & arches
4) Changing Methods of Fastening
Ex) changing nails to screws
5) New Materials
Ex) using Kevlar for tires
4.3 Evaluating Designs from an Overall Perspective
- When evaluating a design one must take into account:
- Cost
- Benefits
- Safety
- Impact on the Environment