Biology Unit 4 Chapter 5 - Energy and Ecosystems

Selectively breeding cattle with a low RFI may help to limit global warming. Use the information in Figure 3 to explain how. (2) Low RFI High RFI Mean rate of methane production 142.3 190.2 / g day -1

Cattle with low RFI produce less methane; Methane linked to greenhouse effect

Other scientists investigated the release of methane from rice fields. They investigated the effect of adding organic material (straw) and inorganic substances on the release of methane from rice fields. Research findings are not always of direct use to farmers. What else would rice farmers need to know before acting on the results of this investigation? (2)

Cost of substance; Frequency of application

Two-spotted mites are pests of strawberry plants. Ecologists investigated the use of predatory mites to control two-spotted mites. They released predatory mites on strawberry plants infested with two-spotted mites. They then recorded the percentage of strawberry leaves occupied by two-spotted mites and by predatory mites over a 16-week period. Farmers who grow strawberry plants and read about this investigation might decide not to use these predatory mites. Suggest two reasons why. (2)

Cost of treatment; Takes a long time to act

The pigs were allowed to eat as much food as they wanted. How could this have decreased the reliability of any conclusions drawn from the investigation? (2)

Different growth rates; Not due to temperature

The molecular structure of some pesticides makes them non-biodegradable. Explain why. (2)

Different shaped molecules; Do not fit active sites of enzymes produced by decomposers

Apart from affecting the number of earthworms, suggest how a decrease in the pH of the soil slows down the rate of leaf decomposition. (2)

Fewer decomposers; Acid conditions denature enzymes

Give the equation that links gross productivity and net productivity. (1)

Gross productivity = net productivity + respiratory loss

Scientists measured the mean temperature in a field each month between March and October. The table shows their results. Month Mean temperature / oC March 9.0 April 11.0 May 14.0 June 17.0 July 20.0 August 18.0 September 16.0 October 14.0 The gross productivity of the plants in the field was highest in July. Use the data in the table to explain why. (2)

High temperature allows enzymes to work faster; Photosynthesis reactions are faster

Parathion is an organophosphate pesticide used to control insect pests on cotton plants. Although parathion is biodegradable, its breakdown by soil bacteria can take several weeks. An enzyme was isolated from a species of bacterium found in soil. Parathion was mixed with a solution of this enzyme. Suggest why parathion is broken down more rapidly by the isolated enzyme than by a soil bacterium containing the same enzyme. (1)

Higher enzyme concentration

Describe and explain how intensive rearing of domestic livestock would affect the amount of energy absorbed from gut of consumers. (1)

Increase because fed food with high nutritive value

Adult toads spend most of their time on land but lay their eggs in water. These eggs hatch into tadpoles, which live in water and develop into adults. The tadpoles are much smaller than adult toads. Use this information to explain why the tadpoles are affected more rapidly by pesticides in water than adult toads. (2)

Large surface area to volume ratio; shorter diffusion pathway

Keeping cattle indoors, in barns, leads to a higher efficiency of energy transfer. Explain why. (1)

Less energy lost as heat

The net productivity of the plants in the field was higher in August than in July. Use the equation in part (b)(i) and your knowledge of photosynthesis and respiration to suggest why. (2)

Less respiration; Lower energy loss

The R : A ratio is higher in mammalian primary consumers than in insect primary consumers. Suggest a reason for this higher value. (1)

Mammals have a high body temperature

Although BST increases milk yield in cattle, some dairy farmers in the USA do not use it. Suggest one explanation for this. (1)

May not be cost-effective

The horse's mean energy expenditure was higher in March than it was in August. Use information in the table to suggest why. (2)

More energy is lost in March because it is colder; Needs to maintain body temperature

Many farmers in California plant hedges around the fields in which crops are grown. They plant a large variety of plant species with a range of flowering times. These hedges are called insectary hedges because they are designed to attract insects. Explain why these insectary hedges attract a large variety of insect species. (3)

More niches; Variety of food sources; Different insects at different times of year;

Purple loosestrife is a plant which grows in Europe. It was introduced into the USA where it became a pest. Suggest why purple loosestrife became a pest when it was introduced into the USA, but is not a pest in Europe. (2)

No competition in US; Environment more favourable

Methane is produced by anaerobic microorganisms in the soil. The scientists found that rice fields that are not flooded do not produce large amounts of methane. Suggest why. (2)

Not flooded aerobic conditions; Not flooded less active anaerobic microorganisms

Fire-ants are a serious pest in parts of the USA. An investigation was carried out to find the best way to control the fire-ant population. The graph shows the results of this investigation. Describe the effect of using insecticide followed by biological control. (2)

Number of fire-ants falls rapidly; Population remains low

The scientists looked at previous studies on the effects of various pesticides on tadpoles. They found that most of these studies: 1) were carried out on tadpoles of the African clawed toad 2) measured the LC50 of each pesticide over 1 to 4 days in the absence of any biotic factor. The scientists concluded that these previous studies were of limited use when trying to assess the effects of malathion on the tadpoles of toads found in the USA. Suggest why the scientists reached this conclusion. (3)

Only carried out on one species of toad; Only tested short term; Did not look at effect of predation

The ecologists repeated the investigation but sprayed chemical pesticide on the strawberry plants after 10 weeks. After 16 weeks no predatory mites were found but the population of two-spotted mites had risen significantly. Suggest an explanation for the rise in the two-spotted mite population. (2)

Pesticide kills predatory mites; Two-spotted mite reproduces

The use of organochlorine pesticides has been severely restricted, due partly to their bioaccumulation in food webs. They have been replaced by organophosphate pesticides, which do not accumulate in food webs. Explain how bioaccumulation of some pesticides can occur in food webs. (2)

Pesticide not biodegradable; Stored in tissues

Explain how farming practices increase the productivity of agricultural crops. (5)

Pesticides prevent consumption of crop; Pesticides remove competition; Selective breeding of crops; Greenhouses enhance light; Ploughing improves drainage

Potato plants originate from the Andes mountains in South America. They are adapted for survival in a cool climate. The potatoes we eat are food storage organs, called tubers, and are produced on underground stems. The graph shows the rates of photosynthesis and respiration for one variety of potato plant. When this variety was grown in a hot climate, with a mean daytime temperature of 23.5 °C, it failed to produce tubers. Use information in the graph to explain why no tubers were produced. (2)

Photosynthesis rate only just above respiration rate; Little gain in biomass or net loss in biomass due to night-time respiration

Energy from the sun may ultimately end up in dead plant matter. Describe how. (2)

Photosynthesis; Carbon-containing substances

Give one advantage to farmers of attracting insects to their crops. (1)

Predators of pests of crop plants; Pollination of crops

The burrows produced by earthworms improve drainage and aeration of the soil. Suggest how these burrows help to increase the rate of leaf decomposition. (2)

Provides oxygen for aerobic respiration; by bacteria

Residual food intake (RFI) is the difference between the amount of food an animal actually eats and its expected food intake based on its size and growth rate. Scientists have selectively bred cattle for low RFI. Explain the advantage to farmers of having cattle with a low RFI. (2)

Reduced cost; due to more growth rate with same amount of food

Give two reasons why the percentage of energy transferred between consumers is generally low. (2)

Respiration; Excretion

In some countries, pigs are reared in intensive units in which the temperature is controlled. Agricultural scientists investigated the effect of temperature on pig growth and on the efficiency with which the pigs converted food to biomass. In the investigation, the scientists used pigs of the same breed, with similar genotypes. Explain why. (2)

Same breed so similar alleles; So only temperature affects results

The ratio of the dry biomass of animals to the dry biomass of seaweeds is always a lot less than one. Explain why. (2)

Seaweeds are producers; Loss of energy between trophic levels

The average efficiency of energy transfer between producers and primary consumers in pyramids of energy is around 10 %. Suggest why the efficiency of energy transfer from producers to primary consumers in this food web is higher than 10 %. (2)

Single-celled producers are more digestible; All of producer eaten

Describe the reasons for the low efficiency of energy transfer through ecosystems. (5)

Some light is not of appropriate wavelength; Some light misses chloroplasts; Heat loss in consumers; Energy loss via respiration in consumers; Loss via excretion

Give two reasons why all the light energy reaching the producers cannot be used in photosynthesis. (2)

Some light misses chloroplasts; Only certain wavelengths of light used

Energy is transferred through an ecosystem. Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer. (6)

Some light not of appropriate wavelength; So efficiency of photosynthesis in plants is low; Energy is lost by consumers through respiration; and heat; Efficiency lower in older animals; Carnivores use more of their food than herbivores

A horse was kept in the field from March to October. During the summer months, the horse was able to eat more than it needed to meet its minimum daily requirements. Suggest how the horse used the extra nutrients absorbed. (2)

Stored as fat; Used for growth;

Spotted knapweed is a common weed in the USA. Two methods, chemical control and biological control, have been used to reduce the numbers of spotted knapweed plants. The table shows the results of an investigation comparing the effectiveness of these two methods. Describe the pattern of plant numbers resulting from the use of (i) chemical control (ii) biological control (2)

chemical: numbers fluctuate throughout year; biological: numbers fairly constant throughout year

Use your knowledge of energy transfer to explain the difference in biomass between hares and their predators. (2)

energy loss between trophic levels; Only some of energy in hare biomass converted to predator biomass, e.g. energy used by predators to catch hares

Monoculture often involves the use of large amounts of pesticides. Some of these pesticides are toxic to species that are not pests. These animals may be killed immediately when the pesticide is applied. Explain one other way by which the use of pesticides can lead to the death of animals that are not pests (2)

food source killed by pesticide; insufficient food for survival

The graph shows the number of species of insects reported to be resistant to at least one insecticide between 1920 and 1980. (slow increase then sharp increase at 1950). Suggest one reason why there was a rapid rise in resistant species after 1950. (1)

increased use of insecticides

Describe two problems caused by the use of non-specific insecticides. (2)

kill useful insects, such as pollinators; kill predators of pest leading to later increase in pest numbers

Where monoculture takes place on a large scale, farmers often remove hedges. Explain two benefits to the farmer of removing hedges. (2)

more space for crop; easier to use machines

Suggest an explanation for the percentage of energy lost in faeces for the herbivore being larger than that for the carnivore. (2)

much of food indigestible; indigestible material contains energy

Explain why heavy metal ions may accumulate in food webs. (2)

not biodegradable; taken up by producers and thus passed up food chains

Explain how chemical control leads to the changes in the number of spotted knapweed plants from March to June. (1)

number of plants drops because of reapplication, then rises because insecticide washed away

Many hedges have been removed from arable land in recent years. Explain two advantages to farmers of removing hedges. (2)

reduced competition for light, therefore increase in crop growth; more room so ease of ploughing

Describe how the temperature of the soil around developing tubers could be measured throughout their growing period. (2)

soil thermometer; consistent depth of readings

Explain why food chains rarely have more than five trophic levels. (2)

some energy lost at each stage in the food chain; little energy left at the top of food chain

Explain why the spotted knapweed plants were never completely eliminated when using chemical control (2)

some plants are not sprayed; plant may be resistant to spray

Rather than use chemical pesticides or biological agents, farmers often use an integrated system of chemical pesticides and biological agents to control agricultural pests. Explain the advantages of using an integrated system to control agricultural pests. (5)

(Biological Agents) Only needs one application; Pests do not develop resistance; Reduces chemical residues; (Chemical pesticides) Acts quickly; Can apply to specific area

Calculate the ratio of R : A for mammalian primary consumers. (R = 12.25 A = 12.50) (1)

0.98 : 1

Calculate the value of P. (1)

3.74

It has been estimated that an area of 8100m2 of grassland is needed to keep one cow. The productivity of grass is 21 135 kJm-2 year-1. What percentage of the energy in the grass is used in the production of new tissue in one cow? Show your working. (2)

3.74 x 10^6 x 100 ------------------------- 21135 x 8100

Calculate the percentage of energy transferred from primary consumers to tertiary consumers. (Primary Consumers - 7079 Tertiary Consumers - 45) (1)

45/7079 x 100 = 0.636 %

Give the advantages and disadvantages of using biological control. (6)

Advantages: Only needs one application; Pests do not develop resistance; Does not leave chemical residues in environment; Disadvantages: Does not get rid of pest completely; May become a pest itself; Slow acting

When RFI is calculated, low values are negative. Explain why they are negative. (1)

Amount of food taken in less than expected.

Pesticides may be either biodegradable or non-biodegradable. Explain what is meant by biodegradable. (2)

Broken down; by bacteria

As a result of this investigation, the scientists concluded that more studies on pesticides should be carried out in natural habitats rather than under laboratory conditions. Suggest two advantages of carrying out such investigations in natural habitats. (2)

Can see effect of other biotic factors; Can see effect of abiotic factors

Describe and explain how intensive rearing of domestic livestock would affect the amount of energy respired. (1)

Decrease because movement restricted

Suggest what causes the rate of photosynthesis to decrease above 21°C. (2)

Enzymes denatured; Light independent reaction disrupted

Explain how light energy is used to generate ATP in plants. (3)

Excites electrons from chlorophyll; Electrons passes down carriers; Energy released during transfer

Complete the equation to show how net production is calculated from the energy in ingested food. P = (1)

F - E - R

Explain how the intensive rearing of domestic livestock increases net productivity. (4)

Fed on controlled diet so higher proportion of digested food absorbed; Movement restricted so less respiratory loss; Kept inside so less heat loss; Genetically selected for high productivity

Bovine somatotropin (BST) is a hormone used by some farmers in the USA to increase milk yield. BST has a number of effects. One of these is to increase the rate of mitosis. Explain how an increase in the rate of mitosis increases milk yield in cows. (2)

Larger udders; Cells are milk producing

The diagram shows the transfer of energy through a cow. The figures are in kJ × 106 year-1. A = energy absorbed from the gut C = energy consumed in food F = energy lost in faeces P = energy used in production of new tissue R = energy lost by respiration U = energy lost in urine Complete the following equation for the energy used in the production of new tissue. Use only the letters C, F, R and U. (1)

P = C - R - U- F

Scientists investigated the effect of a pesticide called malathion on the survival of tadpoles of species of toads found in the USA. The scientists determined the LC50 for the tadpoles of each species over a 16-day period in an aquarium. The LC50 is the concentration of malathion that killed 50 percent of a population of tadpoles. The scientists also investigated whether the presence of a predator of tadpoles changed the effect of malathion. Suggest two advantages of using the LC50 to determine the effect of a pesticide. (2)

Provides a standard/benchmark; 2. Can compare (different pesticides/chemicals); 3. Does not kill all the tadpoles/organisms/population;

Scientists have developed a standard procedure for comparing RFI in cattle. They control two factors. These are type of food and environmental temperature. Explain why each of these factors needs to be controlled. (4)

Type of food: May vary in protein; May affect digestibility; Temperature Will affect heat loss; Need to maintain body temperature

When malathion is used as a pesticide, it is often sprayed onto aquatic habitats at concentrations of 0.1 to 1.6 mg dm-3. The scientists tested the effect of malathion at concentrations of 0.001 to 10 mg dm-3. Suggest why. (2)

Using less pesticide is more cost effective; May be more concentrated due to evaporation

Explain how the use of pesticides can result in resistant strains of insect pests. (5)

Variation in pest population; Due to mutation; Allele for resistance; Pests with resistance survive and breed; Increase in frequency of allele

The efficiency of conversion of food to biomass is lower at 0 oC than it is at 20 oC. Suggest an explanation for the lower efficiency. (2)

Will lose more heat; So more food used in respiration

Explain why the spotted knapweed plants were never completely eliminated when using biological control (2)

because biological control never eats all plants; as weeds diminish so do control agents

Explain what is meant by monoculture. (1)

cultivation of single species

Insecticides are pesticides which kill insects. A low concentration of insecticide was sprayed on the leaves of rose plants to kill greenfly which were feeding on the plants. Ladybirds eat greenfly. One month after spraying, the concentration of insecticide in the tissues of ladybirds was found to be higher than the concentration sprayed on the rose plants. Explain why. (3)

greenflies take in small mass of insecticide from leaves; ladybirds eat large numbers of greenflies; insecticide cannot be broken down

Suggest suitable units for the measurement of energy transfer in pyramids of energy. (1)

kJ m-2 yr -1

Suggest suitable units to represent biomass in pyramids. (1)

kg m-²

Explain why small mammals have a higher rate of respiration than larger mammals. (2)

smaller mammals have a larger SA:V ratio; so lose more heat