Chapter 6 Essential plants: Where do plants fit into our living system?
6.1 Could our living system exist without plants?
1 Toxic chemicals are used by conventional cotton farmers to kill insects, caterpillars or other organisms, such as fungi or bacteria, that might attack the plant and destroy it.
2 Organic farming methods might include natural predators to kill or deter the organisms that attack the plants, selective breeding of disease-resistant cotton, and natural substances produced by other plants to protect plants from insect activity or disease, either by extracting it and spraying it on the cotton plants, or by planting
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4 these other plants among the cotton plants. Alternatively, they may include substances that are not harmful to help protect the plants.
It costs more to produce cotton organically because it is more labour intensive to establish and run. Natural remedies may be more expensive than mass-produced insecticides and so on. However, yields of organic cotton are usually higher.
Many people are very concerned about the destruction of our environment, and are
6.2 How does the plant world grow and continue?
1 Plants produce fruit because it contains the seeds from which young plants grow. In this way plants reproduce.
2 prepared to pay extra to help preserve it. Cotton is renowned for consuming the most toxic chemicals of any crop. Organic cotton farming produces higher yields with less destruction of the environment.
Some plants reproduce by producing seeds that then grow into new plants. The seeds may be inside fruit or in seed pods. Some, like grass, ivy and strawberries, send runners, which produce new shoots, along under the ground. Some, like potatoes, have bulbs in their root system that produce new bulbs.
6.3 What’s my role in supporting the plant system?
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6.4 How do plant and animal systems interrelate?
1 The mistletoe bush supplies the mistletoe bird with almost all of its food requirements by producing berries. The mistletoe bird enables the mistletoe bush to propagate—that
2 is, to reproduce. Thus, they both depend on each other.
The fruit produced by the mistletoe bush contains very sticky seeds, which stick to the birds’ tail when it is passed out as waste. When the bird rubs its tail against a eucalypt tree, the seed transfers to the tree and sends roots into the tree to obtain nutrients from it. (It is a parasite.)
6.1 Could our living system exist without plants?
What do you know about plants as producers?
1 Plants produce simple sugars by the process of photosynthesis, which they then use as their source of energy.
2 All animals need simple sugars as a source of energy but cannot produce these sugars, so animals must eat plants and/or animals that eat plants in order to obtain the simple
3 sugars. ( Note : When our body breaks down proteins and fats it produces sugars, but not in sufficient amounts to provide all we need.) a Chlorophyll is a green pigment found in plants and some other organisms that enables them to undergo photosynthesis. b Plants and some other organisms such as algae contain chlorophyll.

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The equation for photosynthesis: carbon dioxide + water → glucose + oxygen.
‘Sunlight energy’ is usually written above the arrow and ‘chlorophyll’ is usually written below the arrow.
Most plants look green because of the presence of chlorophyll in their leaves and other parts. Chlorophyll is a green pigment.
A vacuole is used by plant cells to store substances the cell has produced, water,
7 dissolved foods and wastes.
Auto means ‘self’ or ‘by itself’; troph means ‘food’. An autotroph produces its own source of energy, so it is called a producer.
Consumers are also known as heterotrophs. 8
What do you know about plants?
1 Plants are used by animals for food and shelter and by people for food, shelter, clothing, building homes, furniture and other items, including paper, as well as a sources of medicines and essential oils. Plants are essential for maintaining healthy soils and helping prevent soil erosion and soil salinity.
Student responses might include some of the uses listed in question 1.
Cows eat grass to survive. Owls may eat berries or other plant products, as well as
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5 small animals that eat plant products, and also use trees for shelter, nesting and protecting their young. People use plants for food, building homes and furniture, fabrics for clothes, and so on. Coal-fired power stations use coal that is derived from ancient plants to produce electricity.
Student response
Rainforests are like the lungs of the Earth. During photosynthesis they take up much of the carbon dioxide in the atmosphere and produce oxygen, which is needed by most living organisms. The excessive build-up of carbon dioxide in the atmosphere causes global warming, so the forests are needed to keep this under control. Logging of old-growth forests also results in the extinction of many species that depend on the
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Big ideas
1 Plants provide glucose for energy and other essential nutrients. They also help produce the oxygen we need.
2 forests for their survival.
Most plants cannot tolerate salt, so the build-up of salt in soils causes plants to die and the land to become barren and then eroded.
Plants can also provide the fibres needed for fabrics and paper, timber for furniture and other objects, such as building frames, window frames and floors, essential oils for perfumes and soaps, and medicines.
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Plant cells contain chloroplasts in which chlorophyll is stored, a cell wall for structural strength, and large vacuoles in which many substances are stored. a Examples of food plants: apple trees, potatoes, orange trees, banana plants, strawberry plants b Examples of plants for shelter: pine trees, eucalypt trees, mahogany trees and jarrah trees c Examples of plants for clothing: cotton bush, flax, hemp d Examples of plant for medicine: the willow tree was once the source of the early version of aspirin; gum trees are a source of eucalyptus oil, which can be breathed in with steam to help alleviate congestion

5 Photosynthesis is the process by which plants and some other organisms, such as algae, convert carbon dioxide and water into simple sugars, such as glucose and oxygen, in the presence of sunlight energy and chlorophyll.
Photosynthesis takes place within the chloroplasts that are found inside leaf cells. 6
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Chlorophyll is an important chemical because, without it, photosynthesis could not take place and so plants and animals could not exist.
Student research
Student research
10 Coal is produced when ancient plant material is covered in layers of mud and silt, which prevent oxygen from reaching it. The coal is broken down by anaerobic bacteria, which do not require oxygen to produce energy. This broken down material is exposed to high pressures from the weight of the sediments above it for thousands of years and coal is eventually produced.
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12 a b c d
Oxygen and water vapour will be produced.
Photosynthesis
To produce simple sugars that plants need for energy.
Nothing e The branch was stripped of its leaves in order to show what leaves produce.
This is a form of a controlled experiment. f The experiment could be improved by testing a variety of plants, rather than one. Different conditions could be tried as well, such as having some plants out of the light and others in the presence of light, but with all other factors the same.
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6.2 How does the plant world grow and continue?
What do you know about plants as living things?
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2 a b a
Ferns are vascular plants.
Mosses are non-vascular plants. flowering plant b c d e i j k f g h flowering plant moss fern fern moss flowering plants flowering plant flowering plant conifer flowering plant
Mosses reproduce by forming spores in capsules. Ferns reproduce by producing spores on the back of their leaves. Conifers reproduce by producing seeds that are encased in woody cones. Flowering plants reproduce by producing flowers that contain eggs; when the flower is pollinated the eggs develop into seeds that are encased in fruit or seed pods.
Christmas tree—conifers
Student response will depend on the plants studied in Practivity 6.2.
Vascular plants contain tube-like structures for carrying water and food around to the different parts of the plant. Non-vascular plants do not contain these structures.

7 Student response will depend on the plants studied in Practivity 6.2.
What do you know about plant parts?
1 Three main parts of plants: leaves, stems and roots.
2 If a plant is tall, it needs a thick woody stem to give it the structural strength to stay upright so that the upper leaves and stems are supported. Smaller plants don’t need
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4 such thick woody stems to support the plant.
Stomata are usually found on the underside of leaves so that they are out of the direct sunlight. This means that the amount of water lost by the leaves is reduced so that they don’t dry out too easily.
Xylem tissue consists of a series of vessels that are like tubes. The cell wall that lines each tube is coated with lignin to help provide structural support. Phloem tissue is also tube-like and it contains companion cells, which are living cells involved in the transport of glucose.
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Root cells are not exposed to sunlight and therefore could not undergo photosynthesis; thus, they don’t need chloroplasts.
Root hairs increase the rate and efficiency of water absorption from the soil.
Student research
What do you know about plants reproducing without a partner?
1 Asexual reproduction is reproduction without a partner.
2 a In strawberries, the plant produces long thin extensions of the stem, which then spread across the ground and form roots and leaves at the other end. The runners
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5 eventually rot, leaving little plants around the parent plant. b In potatoes, the plant stores its food in starchy tubers located below ground.
Eventually these break away from the roots and form buds (tiny baby tubers) on their surface (called ‘eyes’), which then start forming shoots and leaves; hence, new potato plants form. c Garlic reproduces in a similar manner to potatoes. It forms a cluster of small bulbs that are encased together in papery ‘envelope’. This eventually forms green shoots, which come out of the cluster and grow into a new plant.
Vegetative propagation can be used artificially to make new plants by cutting out a bud and some surrounding tissue from one plant, then cutting open a stem of another plant, inserting the bud and tying it in place. The new stem growing from the bud will be of the variety the bud was taken from.
A fruit salad tree has up to eight varieties of fruit grafted onto the one tree.
Ferns have two life cycles. First, the fern reproduces asexually by producing spores in spore cases on the underside of the leaves. When there is sufficient moisture, these spores are released and they start to grow in the surrounding soil, forming many small plants around the parent plant, which are identical to the parent plant. These plants then reproduce sexually, producing eggs and sperm and hence a new generation of
6 plants that are now different from the parent plant.
Humans reproduce sexually, so our life cycle is more like the second life cycle of ferns.
A rhizoid is a structure like a root or a special kind of stem that attaches and anchors a 7 fern formed by asexual reproduction to the ground.
What do you know about plants reproducing with a partner?
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Male flowering parts Female flowering parts

Stamen
Anther
Filament
Carpel
Stigma
Ovule
Ovary
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2 Pollination occurs when a pollen grain, which contains sperm cells, lands on the stigma, which is the tip of the uppermost part of the female part of the flower.
Fertilisation occurs when a male sperm cell joins with the female egg cell (ovule).
The fertilised egg develops into a seed, from which a new plant will grow.
3 Pollen needs to be small enough to be carried by an insect or by the wind to the female part of a flower of the same species.
Big ideas
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Fruit salad trees are ideal for people who have a very small garden as they can have a variety of fruit from the one tree. runners, tubers, bulbs a petal b c d anther filament sepal
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6 f e g h receptacle ovule style stigma
Mosses and liverworts: reproduce by forming spores in capsules.
Ferns: reproduce by two cycles—first, asexually by producing spores on the back of their leaves, which then drop onto the ground and form new plants; then by sexual reproduction.
Conifers: reproduce by producing seeds that are encased in woody cones.
Flowering plants: reproduce sexually by producing flowers that contain eggs; when these are fertilised they form seeds that are encased in fruit or seed pods.
Student response
Stomata are microscopic holes in the surface of the leaf of a plant through which the plant obtains most of the oxygen and carbon dioxide it needs from the air and through
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9 which water is lost to the air.
Possible answers include: animals are able to move around their environment from place to place, whereas plants are anchored to the one spot; animals cannot produce the simple sugars they need for energy, whereas plants can; animals can only produce carbon dioxide as a waste product, whereas plants also consume it for the process of photosynthesis, helping keep carbon dioxide levels in the atmosphere in balance; the cells of animals do not contain chloroplasts and do not have cell walls, whereas the cells of plants have cell walls and much larger vacuoles and, except for the cells in the roots, also contain chloroplasts.
Pollination is the process by which a grain of pollen lands on the stigma, the tip of the uppermost part of the female part of the flower. Pollen is a substance produced by a flowering plant. It contains sperm cells.
The Venn diagram would consist of two intersecting circles—plants and animals.
The animals part could include: can move from place to place, must eat plants or animals that eat plants to obtain the sugars they need for energy, consume oxygen and produce carbon dioxide as a waste product. The plants part could include: cannot

move from place to place, produce the sugars they need for energy by photosynthesis, consume and produce both oxygen and carbon dioxide, cells have cell walls and much larger vacuoles and, except for root cells, contain chloroplasts; can reproduce asexually as well as sexually. The common part could include: built up from many cells, must obtain water and nutrients from their environment, obtain the energy they need from glucose and oxygen, depend on each other.
10 Asexual reproduction is often more successful because it does not require the presence of other plants of the same species to occur.
11 The decaying fish would have added nutrients to the soil, which the plant needed, thus making it grow better.
12 If the stomata of a leaf were covered with vaseline, oxygen and carbon dioxide would be prevented from entering the leaf and water would be prevented from leaving the leaf. Thus, the leaf would not be able to undergo photosynthesis.
13 Brightly coloured flowers help attract insects and birds, which are needed to pollinate the flower.
14 The pollen grains produced by the flower get stuck on the hairs on insect bodies. They can be transferred to the female part of that flower or another flower on either the same plant or a different plant of the same species.
15 a Pollen grains have simple shapes, mostly like balls, and most appear to have little bumps of different shapes on their surface. b c
Student research
Hay fever results when a person’s body overreacts to the pollen grains that enter their nose.
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18 The number of humans grows and continues as a result of sexual reproduction, whereas plants can grow and continue through asexual and sexual reproduction. When plants reproduce asexually, the plants that are produced are the same as the parent
6.3 What’s my role in supporting the plant system?
What do you know about alternative farming practices?
1 Organic produce is free from chemicals that could harm humans and the environment.
It is tastier and more nutritious, and growing it is more sustainable and has much less impact on the environment.
2 plant. In sexual reproduction, in both humans and plants, a male sex cell must enter a female sex cell (egg) to fertilise it. In the case of a plant, the male sex cell sends a tube down to the egg, whereas in humans it ‘swims’ in a fluid up to the egg.
Permaculture is a more sustainable farming method because:
• the soil nutrients come from the local environment; no additional nutrients need to be manufactured and added to the soil
• a variety of plants are grown together, rather than just a limited number or even just one
• natural means are used to reduce the problem of pests and diseases; no pesticides or herbicides are needed to spray onto the plants
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Less energy and materials are used because synthetic chemicals do not need to be manufactured and transported to the farm; usually the farm is located closer to the consumer, so less energy and fuel is used in transporting the produce to the consumer.
Monoculture is the production of a single crop, such as wheat, on a very large scale. 3
What do you know about producing your own food?

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Items necessary for creating a successful kitchen garden include: having a space that the Sun can reach, good soil, a variety of seeds and seedlings, gardening equipment such as a spade, a source of water such as a rainwater tank, wire or wire mesh for some plants to climb on and/or to prevent animals from eating the food, timber such as old sleepers for retaining walls, a compost heap or compost bin, old newspapers, pea straw and/or hay.
Compost is rich in plant nutrients and therefore is a natural source of the nutrients the plants need to grow.
Student response
Student response
When growing your own food, energy is saved because: the food does not need to be transported to your home; the labour in caring for the crop does not require machinery; the food can be eaten straight away so energy is not required for refrigeration and lighting where the food is stored, and transport vehicles and
6 supermarkets are not required; artificial substances such as fertilisers do not need to be manufactured and transported.
Student response. It is a scientific pursuit when experiments have been conducted to improve the yield and quality of the produce and the procedures and materials are modified as a result.
Big ideas
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Reasons people grow their own food can include: pleasure; to have fresher, more nutritious and tastier food; to save money; to help the environment. a Permaculture is a sustainable method of farming in which the farm is viewed as a living system, the food is grown in a way that minimises harm to the environment, and a variety of plants are grown together to benefit both the grower and others. b Monoculture is the production of a single crop, such as wheat, on a very large scale. It is not as sustainable, has a much greater impact on the environment and generally uses chemicals, such as artificial fertilisers and pesticides. c Organic farming refers to using sustainable practices that do not harm the
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7 environment, such as natural means to maintain soil fertility and to deal with pests and disease. d Agriculture is the cultivation of land and the rearing of animals to supply humans with their food.
A kitchen garden is a garden set up at people’s homes or at small community gardens or schools to grow some or all of the fruit and vegetables and herbs they need.
When planning a kitchen garden, the following factors need to be considered: the availability of a protected area that receives a lot of sunlight but does not get too hot; the availability of soil and water; how much shade or sunlight each plant needs; and whether the plant needs something to grow on to support its weight.
Student response
The zucchini would need to be placed in the right position so that it receives the right amount of sunlight, the soil would need to be well drained and the zucchini would need to be planted near other plants that grow well with it and help protect it.
Compost would need to be added to build up the soil each year to maintain the supply of nutrients it needs. The soil would need to be regularly watered and mulch should be added each year to help keep the soil moist. For recipes: student response.
Factors to consider for this kitchen garden plan to work include the following. Ensure enough sunlight reaches the plants—they will not grow well if in shadow nearly all

day. If neighbours have tall trees around the garden area, or the house is a two-storey house, this area may not be suitable. In addition, the roots of neighbouring trees may intrude onto the land and deprive the plants of much of the nutrients from the soil they need. If there are a lot of possums in the area, or bats or cockatoos or similar birds, the produce may be eaten by them, so the grower may need to house the plants in a greenhouse or cover the entire garden with fine netting or wire mesh. Soil drainage
8 will need to be investigated as well to ensure there are no problems.
Student response
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6.4 How do plant and animal systems interrelate?
What do you know about creating a natural balance?
1 Ladybird beetles eat aphids and mites, so plants that are being attacked by aphids will attract ladybird beetles.
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Student research
Lettuces can be grown near strawberries and parsley to help protect each other from pests.
What do you know about relationships between plants and animals?
1 Plant (a) would be pollinated by wind because it has wispy tufts that could float in the wind. Plant (b) would attract insects with its bright colour and so would be pollinated
2 by insects.
Student research
Big ideas
1 Companion planting is when one plant species is planted near another plant species to
2 help protect it from insect attack or disease and help it grow more vigorously.
Many plants rely on certain animals, such as insects and birds, to pollinate their flowers and also on animals, such as birds, bats and possums, to spread their seed. In
3 some cases, they have a relationship with a species that helps protect them from attack by insects, grubs or other pests.
Animals rely on plants as their ultimate food source. Animals cannot make the sugars they need for energy, so they must eat plants or animals that eat plants to survive.
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Plants also provide other essential nutrients. Many animals also rely on plants for shade and shelter and for materials to build nests or to line their burrows.
When a pygmy possum eats the nectar from a flower, its fur will brush against the pollen, which will stick to its fur. This enables the pollen to be transferred to the female part of the flower.
Companion plants may release chemicals that repel or kill insects or disease organisms that might otherwise attack the plant. Sometimes they may help provide extra nutrients or they may help keep the soil moist.
Avocado growers could increase the chances of cross-pollination occurring by having beekeepers put their hives in among the avocado plants.
Pitcher plants are still considered autotrophs even though they eat animals to supplement their diet because they still produce their own sugars by undergoing photosynthesis.
Student response
Student research

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14 a Plants put a lot of energy into producing flowers with vibrant colours and shapes because this helps attract insects that are needed to pollinate the flowers, increasing their survival. b Insects see blue, purple and yellow best and so are more likely to visit flowers of these colours. c If all the bees left the city, any flowering plants that rely solely on bees for pollination would die out unless other insects were able to pollinate them also. d If all the plants in the city died, most of the insects, birds and native animals would be lost also as they would lose their sources of food and shelter. Fruit and vegetables would have to be transported a long distance, which would add to their cost and decrease their tastiness. The city would be much drier without all the shade provided by the trees, the ground would become more eroded, it would be far dustier and flooding would result more easily, with mud slides being common.
Transferring ideas Amazing mangroves
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6.1 Could our living system exist without plants?
1 Mangroves are autotrophs because they produce their own sugars for energy by
2 photosynthesis.
Plants help keep our oxygen levels in the atmosphere at the level we need to survive.
If we had no plants, we would not survive because the oxygen we have consumed would not be replenished in the atmosphere. If plants and other organisms that produce oxygen had not developed, animals would never have developed on Earth. a b
Student response
Student research a Mangroves take only oxygen from the air, both through the stomata in their leaves and through their pneumatophores, whereas other plants also take oxygen from the soil through their roots. If there is a lot of pollution in the air, you would expect
6.2 How does the plant world grow and continue?
1 Favourable growing conditions for a mangrove would include: sheltered areas along the coast and on the banks of tidal rivers where the water circulates well but does not flood; places where there is little pollution in the water or the air; areas where nutrients are provided through rotting leaf litter and so on.
2 that mangroves would take up more of the pollution and thus be affected. b Student response. One response might be that mangroves can be used as an indicator of air quality; if they are starting to die, something drastic needs to be done to identify and solve the problem.
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Propagules are germinated seeds that are buoyant and able to float in the water. When they reach an appropriate place, they take root. If mangroves dropped seeds, the seeds might not reach an appropriate place to settle and so would not germinate and take root as easily.
Mangroves use asexual reproduction—the plant produces copies of itself.
Salt water would passes up narrow tube-like structures in the mangrove plant. As the cells do not absorb the salt, its concentration would increase. The concentrated salt solution would then be passed out of the stomata in the leaves. When the water

evaporates, the salt is left behind on the leaves and so the leaves taste salty when licked.
6.3 What’s my role in supporting the plant system?
1 Many eucalypt trees and acacias have been removed from rural properties so that the farmer can grow crops or grass for cattle and sheep. In many countries, huge tracts of
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3 forests and rainforests have been cleared to harvest the timber and to use the land for agriculture or housing.
Student response
Student response
6.4 How do plant and animal systems interrelate?
1 If a mangrove swamp was destroyed, many of the organisms that lived in the swamp would die because they can only survive in this environment.
2 The seven-horned mangrove spider would have the same number of legs and a segmented body like any other spider, but there would be seven horn-shaped lumps growing out of its body. These and its body might be green or brown so that is well camouflaged among the foliage of the mangrove.
3 It is only a mutual relationship if the mangrove benefits from the presence of the oysters as well. There is no information to suggest that the mangrove benefits from the oysters.