QCAA Agricultural Science Plant production B
15 sample questions with marking guides and sample answers
Legume crops require microorganisms for the development of root nodules to improve
grain fill.
nitrogen fixation.
root development.
carbon sequestration.
Reveal Answer
grain fill.
Grain fill is the phase where seeds accumulate starch and proteins; while nitrogen is essential for this, the direct function of root nodules is acquiring that nitrogen, not the filling process itself.
nitrogen fixation.
Legumes form symbiotic relationships with bacteria (such as Rhizobium) in root nodules to perform nitrogen fixation, converting atmospheric nitrogen () into ammonia () that the plant can use for growth.
root development.
While nitrogen supports overall plant growth, the specific biological purpose of the microorganisms within the nodules is to fix nitrogen, not to directly drive the physical development of the root system.
carbon sequestration.
Carbon sequestration is primarily achieved through photosynthesis and biomass accumulation, whereas the specialized function of root nodules is the fixation of atmospheric nitrogen.
Aphids are a common pest in cereal crops. The table identifies different control methods.
| Control method |
|---|
| Monitoring aphid population |
| Crop rotation |
| Preserving predators, e.g. ladybirds |
| Introducing enemies, e.g. parasitic wasps |
| Use of insecticides |
| Use of seed dressings |
Identify which control methods are biological controls.
Reveal Answer
Two biological control methods are preserving predators, e.g. ladybirds, and introducing enemies, e.g. parasitic wasps.
| Descriptor | Marks |
|---|---|
identifies preserving predators and introducing enemies | 1 |
Explain two advantages of using biological controls.
Reveal Answer
Biological organisms can be used as a biological control method to reduce the use of chemicals, which can be harmful to other useful organisms. This also reduces the expense of using costly insecticides.
| Descriptor | Marks |
|---|---|
explains an advantage of biological controls | 1 |
explains a second advantage of biological controls | 1 |
Grafting in horticulture is
growing plant tissue on a cultured medium.
planting a piece of source plant material.
cross-pollinating unrelated plants.
joining plant tissues together.
Reveal Answer
growing plant tissue on a cultured medium.
This describes plant tissue culture or micropropagation, where plant cells are grown in a sterile, nutrient-rich medium.
planting a piece of source plant material.
This refers to propagation by cuttings, where a severed plant part is planted to regenerate roots, rather than fusing two plants together.
cross-pollinating unrelated plants.
This describes hybridization or sexual breeding, whereas grafting is an asexual technique that physically combines existing plant parts.
joining plant tissues together.
Grafting is the horticultural technique of joining tissues from two different plants (the scion and rootstock) so they unite and grow as a single organism.
Explain how sowing rates and plant spacings differ between dryland and irrigated environmental conditions for a broadacre crop of your choice.
Reveal Answer
Sowing rate is often less for dryland cropping than irrigated cropping, as water is a limitation in dryland cropping and lower sowing rates have lower plant density, resulting in lower competition for water.
Plant spacing will normally be greater in dryland cropping compared to irrigated, so that plant density is less under conditions where water is limited.
For example, the sowing rate for dryland cotton is less and plant spacing greater, when compared to irrigated cotton.
| Descriptor | Marks |
|---|---|
explains a difference in sowing rate between dryland and irrigated conditions | 1 |
explains a difference in plant spacing between dryland and irrigated conditions | 1 |
identifies a relevant broadacre crop | 1 |
Use an example to identify two characteristics of a beneficial organism used in a plant production system.
Reveal Answer
Ladybirds. Ladybirds eat aphids and help keep the aphid population down. Ladybirds will eat aphids across a wide range of crops.
| Descriptor | Marks |
|---|---|
identifies a beneficial organism for plant production | 1 |
identifies one characteristic of a beneficial organism | 1 |
identifies a second characteristic of a beneficial organism | 1 |
Identify an advantage of tissue culture and explain how this can be used in an agricultural setting.
Reveal Answer
An advantage of tissue culture is that a desirable plant can be multiplied rapidly.
This can speed up the testing and evaluation time for plant breeders and decrease the time taken to reach commercial production.
| Descriptor | Marks |
|---|---|
identifies an advantage | 1 |
explains the advantage | 1 |
Describe the genetic relationship between the original plant and the new plant in the process of tissue culture.
Reveal Answer
They are clones.
| Descriptor | Marks |
|---|---|
provides clone | 1 |
What function does abscisic acid perform in plants?
inhibiting growth
stimulating root growth
decreasing internodal length
increasing rate of ripening fruit
Reveal Answer
inhibiting growth
Abscisic acid is primarily a growth-inhibiting hormone that induces dormancy in seeds and buds and helps plants tolerate stress.
stimulating root growth
Stimulating root growth is a primary function of Auxins, not abscisic acid.
decreasing internodal length
Changes in internodal length are typically associated with Gibberellins (which increase length), not abscisic acid.
increasing rate of ripening fruit
Increasing the rate of fruit ripening is the primary function of the gaseous hormone Ethylene.
Identify two plant pests or diseases that are significant for plant industries. Describe why each pest or disease is a major issue for its respective industry.
Plant pest/disease 1:
Plant pest/disease 2:
Reveal Answer
Plant pest 1: Citrus — fruit flies
Fruit flies infest citrus plants and cause significant damage to seedlings, flowers and fruit, significantly reducing crop yields.
Plant pest 2: Cotton — bollworm
Bollworms do significant economic damage to cotton crops by damaging the lint in cotton bolls. This negatively influences the yield and quality of the crop.
| Descriptor | Marks |
|---|---|
identifies a plant pest and affected industry | 1 |
describes the pest’s effect on the industry | 1 |
identifies a second plant pest and affected industry | 1 |
describes the second pest’s effect on the industry | 1 |
Use an example to explain two benefits for farmers who use genetically engineered crops.
Reveal Answer
An example of a genetically engineered crop is Bt cotton.
The benefits of Bt cotton include improved crop yields due to better pest resistance and reduced use of pesticides, which is better for the environment.
| Descriptor | Marks |
|---|---|
Identifies a genetically engineered crop AND describes 2 benefits of the identified crop | 3 |
Identifies a genetically engineered crop AND describes 1 benefit of the identified crop | 2 |
Identifies a genetically engineered crop | 1 |
Does not satisfy any of the descriptors below. | 0 |
Legume pasture species can support sustainable plant production by
increasing groundwater recharge.
improving soil structure/porosity.
removing excessive sodium from the topsoil.
improving potassium availability in soil for plant use.
Reveal Answer
increasing groundwater recharge.
Deep-rooted legume pastures are typically used to increase water usage and reduce groundwater recharge, helping to prevent rising water tables and dryland salinity.
improving soil structure/porosity.
Legumes contribute organic matter and have root systems that help bind soil particles into aggregates, improving soil structure and porosity for better water infiltration and aeration.
removing excessive sodium from the topsoil.
Most legume species are sensitive to salinity and do not actively remove sodium from the soil; high sodium levels typically inhibit their growth rather than being remediated by them.
improving potassium availability in soil for plant use.
Legumes are primarily known for increasing soil nitrogen through biological nitrogen fixation, not for improving potassium availability.
Explain the role of a beneficial organism in a plant production system. Use two examples in your response.
Reveal Answer
Beneficial organisms enhance plant production.
Pollinators are essential for the transfer of pollen from male to female flowers and plants. Farmers rely on pollinators to help their crop achieve optimal yield.
Nematodes can be beneficial in destroying and controlling larvae of crop-damaging species, leading to higher plant yields.
| Descriptor | Marks |
|---|---|
Explains the role of beneficial organisms | 1 |
Explains an example | 1 |
Explains a second example | 1 |
Identify the genetic technique used to naturally combine desirable genes found in two or more different plant varieties to produce superior pure-breeding offspring.
grafting
hybridisation
tissue culture
genetic modification
Reveal Answer
grafting
Grafting is a vegetative propagation technique that physically joins parts of two plants to grow as one, but it does not combine their genetic material to produce new offspring.
hybridisation
Hybridisation involves crossing two different plant varieties to combine their desirable genes through sexual reproduction, creating superior offspring that can be selected for pure-breeding traits.
tissue culture
Tissue culture is a method of cloning plants by growing cells or tissues in a sterile medium, primarily used for rapid propagation rather than creating new genetic combinations.
genetic modification
Genetic modification involves artificially inserting specific genes into an organism's DNA using biotechnology, rather than the natural combination of genes through breeding varieties.
The table gives the results from a trial conducted on sugarcane over five years. A fallow crop of soybeans was planted, grown and ploughed back into the soil prior to planting the sugarcane.
A control practice was to leave the soil fallowed between sugarcane harvest and the next season’s planting.
At each location the mean crop yield was measured over five years.
| Location | Legume fallow: Nitrogen fertiliser applied (kg/ha) | Legume fallow: Mean yield (t/ha) | Bare fallow: Nitrogen fertiliser applied (kg/ha) | Bare fallow: Mean yield (t/ha) |
|---|---|---|---|---|
| Site 1 | ||||
| Site 2 | ||||
| Site 3 | ||||
| Site 4 | ||||
| Site 5 | ||||
| Site 6 |
Draw a conclusion about the most suitable crop rotation system to use. Use the table to justify your conclusion.
Reveal Answer
The most suitable crop rotation system is legume fallow.
In general, sites that used legume fallow were able to produce a similar yield but use significantly less nitrogen fertiliser.
| Descriptor | Marks |
|---|---|
concludes that legume fallow is the most suitable crop rotation system | 1 |
identifies that legume fallow produces the same yield with less fertiliser | 1 |
Identify two advantages of the crop rotation system identified in 9a).
Reveal Answer
Advantages of reducing the use of fertiliser are that it would significantly reduce costs and potential run-off into waterways.
| Descriptor | Marks |
|---|---|
identifies 1 advantage of the crop rotation system | 1 |
identifies another advantage of the crop rotation system | 1 |
Provide one disadvantage of the crop rotation system identified in 9a).
Reveal Answer
A disadvantage of the legume fallow system is that the cost of planting soybeans and ploughing them back into the soil could outweigh the cost of the nitrogen fertiliser.
| Descriptor | Marks |
|---|---|
identifies a disadvantage of the crop rotation system | 1 |
A farmer has purchased a neglected overgrown orchard. Which option would be the initial strategy to use in an IPM strategy?
chemical control of pests and diseases
biological control using predators
physical removal of vegetation
physical traps for insects
Reveal Answer
chemical control of pests and diseases
Chemical control is considered the last resort in an Integrated Pest Management (IPM) hierarchy and should not be used before monitoring or attempting less invasive methods.
biological control using predators
Biological control is typically introduced after the environment is managed and pests are identified; introducing predators into an unmanaged, overgrown area is often ineffective.
physical removal of vegetation
Sanitation and habitat modification are the first steps in IPM for a neglected site; clearing overgrowth removes pest habitats, reduces disease reservoirs, and allows access for monitoring.
physical traps for insects
While traps are used for monitoring, they are not the primary initial strategy for a heavily overgrown area where habitat sanitation must occur first to reduce the overall pest load.
A beef producer in southern Queensland wants to take advantage of an unseasonal late-winter rainfall of 110 mm and plant a summer forage crop. The beef producer is unsure if the crop will be grazed off or mechanically removed as hay or bale-wrapped silage. This decision will depend on future growing conditions.
The table shows the mean rainfall usually experienced in the region. The information in the graphs describes the characteristics of three different varieties of forage sorghum suitable for the region.
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean rainfall (mm) | 129.8 | 144.0 | 104.7 | 43.0 | 45.3 | 37.4 | 31.8 | 26.8 | 24.2 | 49.5 | 66.3 | 104.3 |
Key
Rating: 1 = poor, 9 = excellent
Performance Ratings:
| Use | Sorghum A | Sorghum B | Sorghum C |
|---|---|---|---|
| Cold start | 9 | 5 | 5 |
| Beef grazing | 8 | 9 | 5 |
| Dairy grazing | 9 | 6 | 4 |
| Sheep grazing | 7 | 4 | 4 |
| Hay making | 8 | 5 | 5 |
| Fast feed | 9 | 5 | 4 |
| Late summer/carryover feed | 3 | 9 | 5 |
| Pit silage | 3 | 9 | 9 |
| Round bale silage | 9 | 6 | 6 |
Determine the best variety of forage sorghum for this producer to plant. Justify your decision with four pieces of evidence from the data.
Reveal Answer
Decision: The best variety of forage sorghum to plant is Sorghum A. This is the best option because:
• it tolerates a cold start — planting in late winter
• it is close to the best variety for beef grazing
• it can be grazed or hayed and is also suitable for bale silage
• the expected rainfall between late August and summer will ensure it will continue to grow and provide a feed source while waiting for summer rains.
The producer can expect to have more summer rain, and should have natural grass cover to continue the growth of their cattle.
| Descriptor | Marks |
|---|---|
Chooses an appropriate variety of sorghum | 1 |
Identifies a reason | 1 |
Identifies a second reason | 1 |
Identifies a third reason | 1 |
Identifies a fourth reason | 1 |